Biogas Book 111711

The Authors:The Authors:The Authors:The Authors:

Prof. Jaime Q. DilidiliAssociate ProfessorCollege of Engineering and Information TechnologyTechnology Development Division HeadAffiliated Renewable Energy Center for Region IVCavite State University

Dr. Camilo A. PolingaAssociate ProfessorCollege of Engineering and Information TechnologyExtension and Promotion Division HeadAffiliated Renewable Energy Center for Region IVCavite State University

Engr. Rosalie Ararao-PelleStudy LeaderAffiliated Renewable Energy Center for Region IVCavite State University

Dr. Ruperto S. SangalangUniversity ProfessorCollege of Economics, Management and Development StudiesProject LeaderAffiliated Renewable Energy Center for Region IVCavite State University

BIOGAS TECHNOLOGYIN THE PHILIPPINES

A Synthesis of Various Readings on Biogas Technology

CAVITE STATE UNIVERSITY - AFFILIATED RENEWABLEENERGY CENTER FOR REGION IV (CvSU-AREC IV)

Indang, Cavite, Philippines2011

First Printing 2011

Philippine Copyright © by CvSU-AREC, 2011

All rights reserved.No parts of this book may be reproducedin any form or by any meanswithout the written permissionof the copyright owner.

Published and exclusively distributed by theCvSU-ARECCavite State UniversityTelefax No.: (+6346) 415-0010email address: [email protected]

ISBN 978-971-9032-67-0

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ForewordThe interest in using biogas to address the problem of pollution in the countrystarted in the midsixties. This gained momentum in the midseventies as thegovernment through the Energy Development Board recognized the need tosupport programs that are aimed at complementing grid based energy.

After a series of crash programs, the Department of Energy sought to promotethe development and utilization of renewable energy sources in the country inthe late eighties by establishing a network of institutions that would specialize inspecific renewable energy programs. The Affiliated Non-conventional EnergyCenter (ANEC) of the former Don Severino Agricultural College, now Cavite StateUniversity, was organized and later tasked to specialize in biogas energy.

I have been fortunate to head this center since its inception and the nationalbiogas center that was organized under its wing in 1996.

The DSAC-ANEC National Biogas Center initiated activities to developawareness and acceptance of biogas as an energy source with the help of anon-government organization from Japan, the Department of Agriculture and theDepartment of Energy. After assessing several existing models, the centersuccessfully developed and patented a simplified biogas model which becamethe focus of several regional and national training programs on biogas. Thesetraining programs culminated in the construction of hundreds of biogasinstallations all over the country. Public and private organizations currentlycontinue to adopt biogas technology as a way of addressing ecological concernseven as the sector also reaps economic benefits from the use of biogas systems.

The many years of experience in promoting and establishing biogas systems inthe Philippines provided the men and women behind this project with data thatserved as background material for this book. While no information on topics likethis could ever be complete, our team hopes that this book would furtherencourage our various publics to continue adopting the biogas technology, andto continue looking for ways to improve the operation of biogas systems in thecountry and, perhaps, elsewhere in the region. If such information as we haveincluded in this book would be able to elicit the interest of even a few on thepotentials of using biogas as a viable energy source, our efforts would havebeen more than compensated.

RUPERTO S. SANGALANGProject Leader, CvSU-AREC

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AcknowledgmentThe Cavite State University – Affiliated Renewable Energy Center acknowledgeswith gratitude the cooperation and assistance of the following institutions andpersons in the preparation of the Biogas Technology in the Philippines: ASynthesis of Various Readings on Biogas Technology:

Dr. Divinia C. Chavez, President of Cavite State University and Project Director ofCvSU-AREC for utmost support in the preparation of this publication;

The Department of Agriculture (DA), the Department of Science and Technology(DOST) and the Department of Environment and Natural Resources (DENR)and their sub-units for their assistance in collecting and gathering the neededinformation;

The Department of Energy (DOE) for the financial support in the preparation andprinting of this publication, and the DOE’s regional offices for the provision ofvaluable information on biogas technology;

Prof. Rene Alburo and staff of San Carlos University – AREC for the assistance inthe conduct of biogas regional forum for the Visayas and Mindanao regionswhich also gave way for the CvSU-AREC staff to collect the needed data and visitbiogas projects in Cebu;

The owners and managers of the different biogas installations especially themanagement of Wellisa Farms for allowing the CvSU-AREC staff to observethe full operation of the farm and take pictures of the biogas installations;

The Philbio for providing list of their biogas projects and other needed information;

Dr. Ruperto S. Sangalang, CvSU-AREC Project Leader; Prof. Jaime Q. Dilidili,head of CvSU-AREC Technology Development Division; Dr. Camilo A. Polinga,head of CvSU-AREC Extension and Promotion Division; and Engr. Rosalie A.Pelle, CvSU-AREC Study Leader for the preparation, reviewing and editing thecontent of the manuscript; and,

The present and former staff of CvSU-AREC, namely: Mrs. Gloria L. Martonitoand Dr. Elizabeth E. Polinga for editing the manuscript; David F. Almazar forgathering information, preparing plans and estimates and providing picturesneeded for the publication; Elmer Matel, Ma. Zobel Caraan, Camille Joy Capupusand Jeffrey Cotoner for assisting in editing, layouting, cover-design, drawing/illustrations and photographic works; and Engr. Rene Marasigan and Mr. CielitoPulido for being part of CvSU biogas development projects.

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INTRODUCTION 2

CHAPTER I. Historical Development of Biogas Technology 4

Historical Development of Biogas Technology 4Trends and Advancements of Biogas Technology 13

CHAPTER II. Biogas Technological Process 18

Biogas Technological Process 19Stages in Biogas Fermentation Process 19Classification of Biogas Fermentation Process 21Factors that Influence Biogas Production 23

CHAPTER III. Comprehensive Utilization of Biogas Technology 32

Biogas Utilization 32Sludge Utilization 36Biogas Technology as Waste-Treatment Facility 38

CHAPTER IV. Design of Biogas Digester 40

Design of Biogas Digester According to Form and Structure 40Advantages and Disadvantages of Various Designs 46Digester Models in the Philippines 54

CHAPTER V. DSAC-Model Biogas Digester 56

DSAC-Model Biogas Digester 56Components of DSAC-Model Biogas Digester 57Principles of Operation 58Design Formulas 59Sizing of Biogas Digester 61Pre-Construction Consideration 62Site Consideration 64

Contents

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Page

Construction Techniques (DSAC-Model RectangularFixed-Dome Digester) 65a. Lay-outing 65b. Excavation 66c. Bottom Construction 66d. Flooring Construction 66e. Wall Masonry 67 f. Construction of Inlet 68g. Construction of Hydraulic Tank 68h.Top Beam Construction 70 i. Dome Construction 70 j. Sealing the Digester 72 k. Air and Water-tightness Tests 73

CHAPTER VI. Tubular Polyethylene Digester 78

Major Parts of TPED Biogas Digester 78Installation of TPED Biogas Digester 79Protection of Polyethylene Plastic Digester and Gas

Reservoir 80Preparation of the Polyethylene Plastic Digester 81Preparation of Gas Reservoir 82Methods of Constructing the Biogas System 82

CHAPTER VII. Covered Lagoon Digester 86

Covered Lagoon Digester 86Components of Covered Lagoon Digester 86Covered Lagoon Design Variables 87Operation and Maintenance of Covered Lagoon Digester 88The Covered In-Ground Anaerobic Reactor (CIGAR) 89

CHAPTER VIII. Operation and Maintenance of Biogas Digester 94

Initial Loading 94Regular Loading 95Stirring/Agitation of Slurry 96Condensate Removal 96Servicing Scum Problem 96Periodic Maintenance of the Digester 97

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Page

CHAPTER IX. Biogas Upgrading 100

Biogas Upgrading 100Determination of the Hydrogen Sulphide Content 101Biogas Upgrading Techniques 102Biogas Purification Process by ITDI 107

CHAPTER X. Benefits from Biogas Technology 110

Benefits from Biogas Technology 110Economic Assessment of DSAC-Model Biogas Digester 110Cost Component of the Biogas System 111Energy Value of Biogas 112

CHAPTER XI. Opportunities and Barriers of Biogas Technology 116

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Page

1 Participants of the First National Training Course on Biogas Technology 7

2 Biogas installations in the Philippines 12 3 60-seater biogas-fueled train 13 4 Synergy Biopower Containerized Control Center 14 5 XC-Series external combustion systems

25kWe-52kWe 15 6 Record-beating A4, with a maximum speed of

327.2 km/hr (203 mph), runs on biogas 15 7 Guascor 957 kW engine generator set 16 8 Biogas purification using pressure swing absorption

process 16 9 The biogas technological process 19 10 Stages of biogas fermentation 20 11 The three stages of fermentation 20 12a Mechanical stirrer 27 12b Hydraulic stirrer 27 12c Gas stirrer 28 13 Comprehensive utilization of biogas technology 31 14a Biogas stoves/burners 33 14b Biogas lamp 33 14c General motors dual-fuel generator sets designed by

Don Hardy with power output of 60 to 200 kW 34 14d Double door refrigerating machine 35 15a Sludge used as organic fertilizer 37 15b Liquid sludge is recycled to clean animal pen 37 16 Biogas technology in wastewater treatment system 38 17a Fixed-dome digester 41 17b1 Top floating gas holder digester 41 17b2 Separate floating gas holder digester 42 17c Bag digester 42 18 Construction shapes of biogas digester 43 19 Different orientations of inlet and outlet for design

flexibility 44 20 Ground digester 45 21 Semi-buried digester 45

Page

List of Figures

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Underground digester 46 23 Cylindrical fixed-dome digester 47 24 Spherical hydraulic digester 48 25 Ellipsoidal hydraulic digester 48 26 Flexible bag-type combined digester/holder 49 27 Two-chamber rectangular digester with

floating gas holder 50 28 Fixed-dome digester with separate gas holder 51 29 Deenbandhu biogas digester 52 30 Rectangular/Square fixed dome digester 53 31 DSAC-Model biogas digester 56 32 Basic components of a DSAC-Model biogas system 56 33 Design formulas 59 34 Planning/Preparation 62 35 Lay-outing 65 36 Excavation 66 37 Bottom construction 67 38 Flooring construction 67 39 Wall masonry 68 40 Construction of inlet 69 41 Construction of hydraulic tank 69 42 Top beam construction 70 43a&b Dome construction 71 44 Sealing the digester 72 45 Water-tightness test 73 46a Air-tightness test 74 46b Manometer 74 47a Lay-out 75 47b Plan 76 47c Longitudinal section 76 47d Section of inlet pipe and hydraulic chamber 76 48a Concrete trench 79 48b Trench dug in the ground 79 48c Digester on top of the ground w/o trench 80 48d The funnel type entrance of manure with screen

protection of digester 81 48e First model 83

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1 Preferable retention time and gas production atdifferent temperatures 24

2 C/N Ratio of some organic materials 25 3 Potential gas yield of selected raw materials 29 4 Toxic level of various inhibitors 30 5 Applications of one cu.m. biogas 36 6 Mineral composition of sludge 36 7 Bill of materials for a 6 cu.m. DSAC-Model biogas

plant 75 8 Materials needed for the onstruction of

Tubular Polyethylene Digester 84 9 Troubleshooting of biogas plant 98 10 Performance efficiency of ITDI scrubber system 108

48f Second model 8349 Covered lagoon digester 8650 CIGAR at Rocky Farm 9051 The CIGAR system 9052 Lagoon digester and biogas handling 9153 URC RF 12 9254 Lagoon effluent 9255a Flow diagram for chemical absorption 10555b Flow diagram for high pressure water

scrubbing 10555c Flow diagram for pressure swing

absorption 1055d Flow diagram for cryogenic separation

process 10655e Schematic representation of membrane

separation 10656 Biogas purification process by ITDI 107

Page

List of Tables

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APPENDIX A. Utilization of Biogas Sludge as Feed Substitute for Hogs 120

APPENDIX B. Wellisa Farm Waste to Energy Project 127

APPENDIX C. Biogas Expert/Contractors/Suppliers in the Philippines 137

Page

1 Monthly average weight of hogs given partly substituted with biogas digester sludge, kg 124

2 Monthly average gain in weight of hogs given diets partly substituted with biogas digester sludge,% 125

3 Mean feed conversion efficiency of hogs given diets partly substituted with biogas digester sludge, % 125

4 Summary of carcass quality evaluation of hogs given diets partly substituted with biogas digester sludge 126

5 Biogas Experts/Contractors/Suppliers in the Philippines 137

Appendices

Appendix Tables

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INTRODUCTIONThe Philippines has 13.46 million pigs and 135.64 million

chickens (BAS, 2007). Of the 13 million pigs, 9 million are foundin the smallhold raisers because livestock raising is secondary tocrop production in terms of agriculture livelihood. The averagenumber of pigs raised in the smallhold sector is about 8 headswhere households in the villages augment family income fromthe sale of pigs. With this number of heads, the total manureproduction reached to more than 30 thousand tonnes per day.This volume is quite tremendous and if not properly managed willbecome the major pollutant of air and water.

Management of animal wastes is a big problem in theanimal producing areas since very few raisers have biogasdigesters. Wastes are allowed to flow freely to open fields, thusemitting foul odors and contaminating surface and undergroundwater.

Agriculture (livestock and crop production) contributed 32%of the total greenhouse gases emmissions (1994 Philippine GHGInventory). These greenhouse gases consist of carbon dioxide(CO2), methane (CH4), nitrous oxide (N2O) and other gaseswhich came mainly from livestock wastes.

Why Biogas Technology?

n There is a need for low cost waste treatment facility due to the growing animal industry.n Waste treatment plus energy generation technologyn Waste utilizationn Environment-friendly alternative

Biogas technology provides solution to pollution problembeing a “waste-treatment facility” and at the same time an“energy-generating device”.

Biogas Technology in the Philippines 2

Interest in biogas development grew with the encouragingreports from the official mission of the Philippine CoconutAdministration after its return from a European tour in 1965.The main interest in biogas stemmed from its pollution preventionand public health aspects rather than from its fuel energygeneration potential, as firewood was abundantly available then.

In the early 70s, Dr. Felix D. Maramba, an agriculturalengineer by profession of the Araneta University Foundation,pioneered the development of biogas technology at Maya Farms,an integrated livestock farm, meat processing and canningoperation in the Antipolo Hills of Rizal Province. Demonstrationmodels of Indian, Chinese and European types were set up by thefarm in order to obtain the necessary experience and to assessthe suitability of different types of plants. The models werelater modified and used as pilot plants. Biogas produced at thefarm supplies 40% of the total power requirement of the farmand was used for domestic applications, cooking vats in thecanning plant, fuel of burners for heating and gasoline enginesrunning a feed mill, operating a 60-KVA electric generator andrunning farm vehicles.

The late President Ferdinand E. Marcos directed the EnergyDevelopment Board (now Department of Energy) in the laterpart of 1976 to embark in a crash program to use biogas assubstitute fuel.

Chapter IHISTORICAL DEVELOPMENTOF BIOGAS TECHNOLOGY

History of Biogas Technology in the Philippines


He instructed the establishment of model biogas plants in stockfarms in every province and towns where there are breedingstations. In the early 80’s, as part of the “crash programme”,the Bureau of Animal Industry and the EDB, launched a programon “Biogas ng Barangay” (Village Biogas Project). Loans weremade available to livestock owners through financial institutions.Demonstration projects at the regional and provincial levels wereestablished; 340 units of concrete biogas plant, 321 units inLuzon, 18 in Visayas and 1 in Mindanao. Available fresh pigmanure per year was estimated at 8.9 million tons, indicating abiogas production potential of 502 million cubic meters per year.The Indian design with a floating gas holder was more popular.The model did not last long because of the maintenance problem.Due to lack of government support on the technology and theseries of reorganization in the government, the continuity andprioritization of the project became less important. Otherorganizations engaged in extension of biogas technology werethe National Housing Authority, the Engineering Battalion of themilitary, and the Department of Community Development. TheDevelopment Bank of the Philippines granted loans to farmers atlow interest rates for the biogas projects.

The Philippine Rural Life Center (PRLC), a non-governmentorganization promoted a culvert model biogas system in the early80s. The PRLC trained people from the government as well asprivate sectors in the field of animal production and biogastechnology. Many units of the model were copied and installed insome selected villages but the continuity ceased because the PRLCproject was also terminated in the late 80’s.

Also in the late 80’s, the Affiliated Renewable EnergyCenters (ARECs - formerly ANEC) were established at differentstate colleges and universities nationwide to serve as extensionarm of the Department of Energy (DOE) in promoting renewableenergy in the rural areas.

5 Biogas Technology in the Philippines

The Cavite State University (CvSU), formerly Don SeverinoAgricultural College (DSAC) was very active in the developmentof the design especially for semi-commercial pig raisers.

CvSU-AREC: Revitalize Biogas Technology

Cavite State University – Affiliated Renewable EnergyCenter (CvSU-AREC) was established in 1989 by the Departmentof Energy (DOE) in its efforts to promote the use of RenewableEnergy Technologies (RETs) in Region IV. There were otherARECs established in several strategically located colleges anduniversities (both private and public)in other regions of the countryto serve as DOE’s extension arm to the rural areas.

During the first few years of the project, informationawareness campaigns were conducted to promote the use ofRenewable Energy resources such as wind, hydro, solar andbiomass. The Center was successful in arousing the interest ofthe people in the livestock sector but not so successful in convincingthem to invest in any of these technologies mainly because ofthe availability of grid electricity in their area and most clientslack needed capital and they were used to receiving dole outprojects from the government.

In the 90’s, pig production in the Philippines rapidly grew,but gained negative impact due to significant environmentalproblems brought by the industry. Being aware of these, theCvSU-AREC team reassessed its position and focused its thruston BIOGAS TECHNOLOGY, a decade old technology which offersenergy generation and environmental protection. Seminars andtrainings on biogas technology were attended by AREC staff anda number of working models were constructed to obtain an in-depth knowledge of the technology.


A major opportunity for additional knowledge came inSeptember 1991 when STET, an NGO from Japan, sponsored thethree-month hands-on training on Biogas Technology at the BiogasResearch and Training Center for Asia and the Pacific (BRTC) inChengdu, People’s Republic of China, which was participated inby Prof. Jaime Q. Dilidili, head of the Technology DevelopmentDivision of the CvSU-AREC. This was followed in November 1991by a 45-day hands-on training sponsored by the InternationalInstitute for Rural Reconstruction (IIRR) with Indian technician astrainors. Since then, the center’s capability was strengthenedand enhanced. These trainings enabled the AREC staff to fullyunderstand the principles and processes of Biogas Technology,which eventually facilitated the transfer of knowledge andexpertise to more than a hundred clienteles.

In 1993, the First National Training Course on BiogasTechnology was conducted at the then Don Severino AgriculturalCollege with the primary objectives of promoting the technologyand producing skilled biogas technician to construct and supervisethe construction of a biogas plant.

Figure 1. Participants of the First National TrainingCourse on Biogas Technology


A Chinese Biogas Digester Model was also designed andconstructed at the CvSU main campus for validation purposes. Inthe course of evaluation, its performance was subjected tonecessary adjustments to make it an effective working model.Difficulties were encountered in the replication of the same modeland the transfer of the technology in the absence of highlyspecialized skills for that purpose. It was at this point that theCenter designed a simple model which is adaptable to Filipinomasonry skills, easy to construct and readily operational. Thus,the birth of DSAC-Biogas Digester Model which was awarded bythe Intellectual Property Office (IPO) a Utility Model RegistrationNumber UM 2-1997-15098 on April 9, 2002.

The National Biogas Technology Extension Program in KeyLivestock Areas was implemented in 1996 in cooperation with theDepartment of Energy and the Department of Agriculture whereinCvSU was designated as the National Biogas Demo and TrainingCenter. Since then, a number of local, regional and nationalfora, seminars, hands-on trainings and workshops were conductedto promote the technology. Participants were from various sectorsof the society: private individuals, companies, NGOs, agro-industry,government agencies and DOE including the 20 ARECs in thecountry. In the course of promoting the technology, the followingwere developed: training module, technoguide, a number ofbrochures and printed materials. The printed materials aimed tocreate awareness among the biogas enthusiasts. Linkages wereestablished between DOE (represented by CvSU – AREC IV) andvarious government agencies such as the Department of Agriculture(DA), Department of Environment and Natural Resources (DENR),Laguna Lake Development Authority (LLDA), Department ofScience and Technology (DOST), and Provincial Government ofBatangas to name a few.

Likewise, the technical expertise of the Center was soughtby several non-government organizations (NGOs) such as Soro-soro Ibaba Development Cooperative, Inc. (SIDCI) in Batangas


City; Women’s Ecology Center of St. Scholastica’s College atMendez, Cavite during the time when Sis. Maryjohn Manansanwas the Directress; Center for Ecozoic Living and Learning (CELL)of the Columban Fathers at Silang, Cavite; Angels’ Hills RetreatCenter at Tagaytay City and others.

Hands-on trainings were conducted in Davao City, Cagayande Oro City, Butuan City and Gingoog City catering mainly to theparticipants from Mindanao. Participants from the Visayas weretrained in Cebu City, Bilar, Bohol and Dumaguete City, while thatfrom Luzon were accommodated at CvSU Main Campus at Indang,Cavite. The participants were asked to propagate and practicethe new learned technology in their respective areas of coverage.To date, a number of CvSU Biogas Digester Model in varying sizeshad been constructed nationwide, addressing the requirementsof small-medium-large livestock producers, thus, helping thegovernment in its effort to protect the environment and energyconservation.

CvSU-AREC believes that it has done its share in promotingsustainable livestock industry development of the country andcontributing to environmental protection. The Center has earnedrecognition for its expert services in Biogas System as applied toPower Generation and Livestock Waste Management.

BAI Experience in the Promotion of Biogas Technology

In 1995, the low-cost Biogas Technology using Polyethylenetube was introduced in the Philippines by the Bureau of AnimalIndustry (BAI). Modification of the plastic tube biogas digesterbeing introduced in Vietnam by Thomas R. Preston was done andapplied by the research staff of BAI. With the advent of small andaffordable unit (3 to 5 cu.m. at P6,500.00-13,000.00), BAITubular Polyethylene Digester (BAI-TPED) has gained popularity.The main breakthrough is the utilization of polyethylene plastictube for the digester that is simple and easy to maintain.


In the same year, a program on the promotion of thislow-cost biogas technology was launched to cater to the demandsof the increasing number of small household pig raisers in thecountry. The project was conceived so that affordable, easy toinstall and adaptable biogas model will be available to smallhousehold pig production units. The promotional strategy wascontinued by the different regional offices and local governmentunits under the Department of Agriculture. Some livestockcooperatives and NGOs were also tapped for the project andpromoted biogas technology to their members.

The technology gained wider acceptance and continuedto progress. There were about 254 units installed nationwide butsome of these are not functioning already due to some problemsi.e. damages caused by animals, natural calamities, falling trees,flood etc. Monitoring the units installed at different places becamea problem due to lack of funds for travels of staff.

The biogas project gained small support from the Foodand Agriculture Organizations. The farmers raising 10 to 20 pigs& feeding sugarcane juice were tapped for the project“Diversification of Sugarcane Juice.” The project included theinstallation of biogas digester to selected cooperators to managethe manure. The units installed served as demonstration orshow window for other pig raisers in the locality. Through thisproject, other interested local government officials requestedthe BAI to conduct training for farmers and technicians in theirrespective localities. The project was coordinated with otherregional offices where training was conducted. The project hastrained 300 farmers, 25 key farmers and 200 agriculturaltechnicians. Repair and maintenance of the digester becamethe major constraints due to the unavailability of materials andtechnicians to do the repair of the biogas system.


References:Avilla, HF. et.al. 2006. Biogas Technology Development in the Philippines: Status and

Propects. Country Paper presented to the ASEAN Rural Energy Forum andTechnology Exhibition.

Dilidili, J.Q. et.al. 2008. Terminal Report on Validation od Biogas Technology and ItsUtilization in the Philippines. CvSU-AREC IV.

Maramba, Felix D. 1978. Biogas and Waste Recycling. The Philippine Experience.Regal Printing Company.

www.agribusinessweek.com/philbio-the-leader-in-biogas-technologieswww.pcierd.dost.gov.ph/index2.php?option=com_docman&task=doc_view&grid=

21&Itemid...

PhilBIO and Biogas Technology

Philippine Bio-Sciences Co., Inc. or PhilBIO was establishedin 1998 with the goal of promoting biogas technology utilizationin the country. A subsidiary of AsiaBioGas Co. Ltd, withheadquarter in Thailand, PhilBIO’s first waste-to-energy projectwas constructed at the Rocky Farm in the province of Rizal. Todate, it has completed 60 Covered In-Ground Anaerobic Reactor(CIGAR) Projects. These systems treat wastewater effectivelythrough proper cultivation of microbial sludge to removesignificantly BOD and COD in wastewater, and capturing biogasfor an on-site power use.

Status of Biogas Technology in the Philippines

In 2006-2008, CvSU-AREC conducted a research entitled“Validation of Biogas Technology and Its Utilization in thePhilippines” which was funded by the Philippine Council for Industyand Energy Research and Development (PCIERD). Result of thestudy showed that there are more than 900 units of biogasdigesters installed throughout the country. The total capacity ofthese digesters is estimated at 662,457 cu.m. (Figure 2).

Through the years, the country has also developed pool ofexperts on the technology. Appendix C shows the list of experts/contractors/suppliers of the technology in the country.


Figure 2. Biogas installations in the Philippines


A remarkable advancement in biogas technology is theworld’s first biogas-fueled train in Sweden. This train makesdaily trip between Linkoping just south of Stockholm, andVastervik, 80 kilometers away from the Baltic coast. It canaccommodate 60 passengers in a single car and could run 600kilometers at a maximum speed of 130 kilometers an hour. SvenskBiogas, which developed the train for a cost of 10 million kronor(the equivalent of €1.05 million or US $1.26 million), replacedthe diesel engines of an old Fiat locomotive by two Volvo gasengines.

Replacing the engine has made the train more environmentfriendly, since the combustion of biogas, like other biofuels,helps reduce greenhouse gas emissions.

Source: AFP, October 24, 2005; Tim Franks, BBC News, October 24, 2005

World’s First Biogas-fueled Train

Trends and Advancements of Biogas Technology

Figure 3. 60-seater biogas-fueled train


Figure 4. Synergy Biopower Containerized Control Center

In August 2007, the Ontario Power Authority (OPA) hasgranted its first SOC (Standard Offer Contract) for a Biogas -Anaerobic Digester system to Fepro Farms (Klaesi Farm) locatednear Cobden, Ontario. Biogas created by the Klaesi anaerobicdigester is converted into electricity and heat by the SynergyBiopower System. Designed and manufactured in Canada byPowerbase, the Synergy System is a containerized, turnkey, state-of-the-art heat and power system for biofuel applications.

Source: http://www.powerbase.com/biopower/news.html


Figure 5. XC-Series external combustion systems25kWe-52kWe

Source: http://www.tezmanholding.com/cmpny_energy.htm#xc

Figure 6. Record-beating A4, with a maximum speed of327.2 km/h (203 mph), runs on biogas

Source: http://www.autobloggreen.com/tag/biogas/


Figure 7. Guascor 957 kW engine generator setSource: http://www.ecw.org/prod/2008BiogasCaseStudy.pdf

Figure 8. Biogas purification using pressure swing absorption process

Source: http://www.moleculargate.com/landfill-gas-purification.html


Chapter IIBIOGAS TECHNOLOGICAL

PROCESSWhat is Biogas?

Biogas is a combustible gas that all organic matters (e.g.animal manures and crop residues) produce when fermented anddecomposed by anaerobic bacteria under conditions of uniformhumidity, constant temperature and full enclosure in a tank.

Biogas is very common in nature and can easily be detectedin the marshland, rice fields and domestic sewage canal. If youput bamboo stick into the black mud at the bottom of a pond,bubbles can be observed to come out. These bubbles are biogas.This gas is produced by different kinds of bacteria under certaincondition. These bacteria eat organic substances and biogas is akind of excretion from them. The bacteria work well in theabsence of air in the environment, so that full enclosure isnecessary to enhance biogas production.

Biogas is composed of 60 to 70 percent methane (CH4), 30to 40 percent carbon dioxide (CO2) and traces of other compoundssuch as hydrogen sulfide (H2S), nitrogen gas (N2), hydrogen gas(H2), carbon monoxide (CO) and other hydrocarbon compounds.It is about 20 percent lighter than air and has ignition temperaturein the range of 650oC to 750oC. Methane itself is odorless, colorlessand tasteless, but the other gases contained in biogas give it aslight smell of rotten egg. The gas burns with clear blue flamesimilar to that of LPG. Upon complete combustion, one cubicmeter of methane can reach a temperature of 1400oC and release8,562 to 9,500 kcal heat (1kcal of heat will raise the temperatureof 1 kg of water by 1oC).


Figure 9. The biogas technological process

Stages of Biogas Fermentation

There are three important stages in biogas fermentationprocess: (1) liquefaction stage; (2) acid production stage; and(3) methane production stage (Figures 10 and 11).

One complete combustion of one cubic meter of biogas can release5,500 to 6,500 kcal of heat.

Biogas Technological Process

The biogas technological process (Figure 9) is accomplishedby means of fermentation/digestion of organic materials (suchas crop residues, human and animal wastes, distillery wastes)through the actions of a number of microorganisms underanaerobic condition to produce biogas and sludge. Anaerobiccondition is provided by a simple device known as “biogasdigester” (further discussion in Chapter IV).


Figure 10. Stages of biogas fermentation

Figure 11. The three stages of fermentation


In the first stage, liquefaction stage, a group offacultative bacteria (fermenting bacteria) acts upon the organicsubstrate. By enzymatic hydrolysis, the polymers are convertedinto soluble monomers that become the substrate for the nextstage.

In the second stage, acid-production stage, the solublesubstrate from the first stage is acted upon by acetogenic bacteriato yield hydrogen, acetic acid and others such as propanic,butyric, lactic and formic acids. These become the substratefor the last stage. Studies showed that 70% of the methaneproduced come from acetic acid, thus, making it the singlemost important substrate for methane production.

In the third stage, methane production stage, the methaneproducing (methanogenic) bacteria utilize as substrate the simplecompounds such as acetic acid, hydrogen, formic acid and CO2to form methane and carbon dioxide.

There are many processes which could be adopted for thefermentation of different wastes for various purposes. Theycan be divided according to the following:

a. Continuous Feeding

The manure is fed continuously into the digestereveryday. The digester collection system/mixing tank isdirectly connected to the wastes canal system of the livestockproject. The effluent is discharged simultaneously in thesame amount of the influent. Thus, the fermentation inthe digester goes on continuously. This process is characterizedby constant fermentation, uniform gas production and easy

1. Method of feeding


Classification of Biogas Fermentation Process

b. Semi-Continuous Feeding

2. Temperature

The temperature of mesophilic fermentation rangesfrom 30oC to 45oC. This process feature low gas production(1 m3 biogas/m3 digester/day), simple operation, low initialcost, and is suitable for low temperature industrialwastewater treatment.

Thermophilic fermentation can be accomplished witha temperature ranging from 45-60 degrees centigrade. Thisis characterized by rapid fermentation, high gas yield (2ºCgas/m3 digester/day) and short retention time. This systemis appropriate in fermenting wastes from distilleries, wineand sugar refineries where high temperature feedstock isavailable.

b. Mesophilic Process

a. Thermophilic Process

A large quantity of feedstock is put into the digester inthe first feeding. When gas yield gradually drops down, freshraw material is introduced and the same amount of effluentis being discharged regularly.

c. Batch Feeding

Digester is charged with feedstock manually by batch.When gas yield drops down to a low level after a period offermentation, the digester can be emptied and fed onceagain.

control. This method is widely used in medium and largesize digesters.


These processes indicate that fermentation occurs intwo or more digesters. Feedstock is first charged in thefirst tank and the effluent coming from the first digester isfurther digested in the second digester. Multi-stage digestersare characterized by long retention time, gooddecomposition of organic matter and high investment.

3. Fermentation Stages

There are several factors which affect or stimulate gasproduction. The operational success of the digesters depends onthe following parameters:

c. Ambient Temperature Process

Factors that Influence Biogas Production

a. Single-Stage Fermentation

b. Two-Stage and Multi-Stage Fermentation

The three stages of biogas fermentation take place inthe digester tank, e.g. fixed-dome digester and the othertype comprising of one tank. In this case, the solid retentiontime (SRT) and hydraulic retention time (HRT) are the same(SRT=HRT).

The operating temperature for this process ranges from18oC to 30oC. The fermentation of this process is muchinfluenced by earth and atmospheric temperature. Its mainfeatures include: suitable for rural areas, low cost, gasproduction is dependent on temperature (0.25 to 0.5 m3

gas/m3 digester/day), and simple construction. Below 10oC,bacterial activity ceases, thus, gas production stops.


1 . Temperature

The temperature directly affects process conditionsby microbial growth rates. The methane bacteria are verysensitive to sudden temperature changes, and for optimumprocess and stability, the temperature should be controlledcarefully within a narrow range of selected operatingtemperature. It should be remembered that highertemperature yields more gas.

2. Retention Time (RT)

Retention time is the theoretical time that the inputmaterial remains inside the digester before it is expelled.Temperature is inversely related to retention time; the higherthe temperature, the shorter is the retention time. Thevolume of slurry input should be given sufficient time for thebacteria to digest the materials before it leaves the digester.Theoretically,

Digester slurry volumeRT (Days) =

Daily input volume

or, Digester slurry volume = RT X Daily input volume

Table 1. Preferable retention time and gas production at different temperatures

Temperature Selected Retention Time(Day) Cow Pig Chicken

10 ˚C -15 ˚C 70 330 100 420 ˚C 45 600 190 625 ˚C 35 700 220 930 ˚C 30 630 260 1135 ˚C 20 1000 310 13

Gas Production

(lit/head/day)


3. pH or degree of Acidity or Alkalinity

The optimum pH value for biogas fermentation is 6.5– 7.5 although it may tolerate a pH level of 6 to 8. The pHvalue varies and adjusts automatically. Below 6 or above 8necessitates adjustment of pH level for it may inhibit or stopthe digestion process. Methane producing bacteria are verysensitive to pH condition and changes. Under acidic conditions,pH values can be improved by adding ash fertilizer, dilutedammonia water or mixture of them, fermented liquor andlime.

4. Carbon-Nitrogen (C/N) Ratio

The bacteria need both carbon and nitrogen to survive.They consume carbon about 25 to 35 times faster than theyconsume nitrogen. Thus, proper digestion proceeds at anoptimum rate when the carbon content of the slurry or inputmaterials used is about 20 to 30:1. High C/N ratio meansshort supply of nitrogen and fermentation is subjected toacidic inhibition. Low C/N ratio means excessive ammoniawhich lead to inhibition. The common sources of carbon areleaves, grasses and raw materials rich in cellulose. Sources ofnitrogen are manure and urine. C/N ratio of some organicmaterials are shown below.

Table 2. C/N Ratio of some organic materials

Source: PAES 414-2:2002.

M aterial C /N RatioCattle m anure (with straw) 25-30

Dairy m anure 10-18Horse 19

P ig m anure 5-8Poultry m anure (fresh) 6-10

R ice straw 48-115Saw dust 300-723

Sugar cane (trash) 50W ater hyacinth 20-30


Materials with high C/N ratio could be mixed with those oflow C/N ratio to bring the average ratio of the compositeinput to a desirable level.

5. Agitation

Without stirring the small digester, the fermentingslurry can be divided into three layers: scum in the upperpart, liquid in the middle, and sludge at the bottom. Themain function of stirring is to break these layers and distributethe slurry inside the digester uniformly. The procedurepromotes contact between the old and fresh slurry andbetween microbes and substrate, thus, acceleratingfermentation rate and enhancing gas yield. There are threekinds of stirrer:

a. Mechanical stirrer

Mechanical stirrer (Figure 12a) can be operated manuallyor by means of electricity. The usual construction is a pipehaving baffle placed at the middle of the digester to providethe stirring action.

b. Liquid Stirrer

In this method, a certain amount of the effluent is drawnfrom the outlet of the digester by means of pump or othermanual device and returned into the inlet to provide astrong liquid stir (Figure 12b).

c. Gas Stirrer

The biogas is drawn from the digester by means of apump and returned back to the bottom of the digester topromote stirring action (Figure 12c).


Figure 12a. Mechanical stirrer

Figure 12b. Hydraulic stirrer


6. Types of raw materialThe kind of raw material as input is one of the

major factors which influence gas production. Thecommon materials used for methane production are cropresidues, human excreta, animal wastes, distilleries andfood processing plant wastes, and others which containhigh concentration of organic waste. The potential gasyield of some raw materials is presented in Table 3.

Figure 12c. Gas stirrer

The kind of fermentation process being used hasa great influence on gas production. The most commontypes are single-phase and two-phase fermentationprocesses. Other types are: Anaerobic Filter (AF); Upflow Anaerobic Sludge Bed (UASB); Expanding Bed;Biological Cycle (AF & UASB).

7. Fermentation process


Table 3. Potential gas yield of selected raw materials

8. Toxicity

Mineral ions, heavy metals and detergents are some ofthe toxic materials that inhibit the normal growth ofpathogens in the digester. Small quantity of mineral ions(e.g. sodium, potassium, calcium, magnesium, ammoniumand sulphur) also stimulates the growth of bacteria, whilevery heavy concentration of these ions will have toxic effect.Similarly, heavy metals such as copper, nickel, chromium,zinc, lead, etc., in small quantities are essential for the growthof bacteria but their higher concentration has toxic effects.Likewise detergents including soap, antibiotics, organicsolvents, etc. inhibit the activities of methane producingbacteria and addition of these substances in the digestershould be avoided. Although, there is a long list of thesubstances that produce toxicity on bacterial growth, theinhibiting levels of some of the major ones are given inTable 4.

(Concentration: 6%)

Materials Liters of Biogasper kg Total Solids

Cow dung 110-300Horse dung 240-340

Pig dung 220-480Chicken dung 310-350

Human excreta 330-470Rice straw 320-470

Wheat straw 370-510Corn stalk 360-550

Green grass 400


Table 4. Toxic level of various inhibitors

References:

Sangalang, et.al.. 1993. Comprehensive Utilization of Biogas Technology. Proceedings of the First National Training Course on Biogas Technology. CvSU-ANEC._______. 1996. Biogas Technology: A Training Manual for Extension. FAO/TCP/ NEP/4451-T_______. Biogas Digest. Volume I. Biogas Basics. ISAT._______. 1989. The Biogas Technology in China, BRTC, China..

Source: The Biogas Technology in China, BRTC, China, 1989.

Inhibitors Inhibiting ConcentrationSulphate (SO4) 5,000 ppm

Sodium Chloride (NaCl) 40,000 ppmNitrate 0.05 mg/ml

Copper (Cu++) 100 mg/lChromium (Cr+++) 200 mg/l

Nickel (Ni+++) 200-500 mg/lSodium (Na+) 3,500 - 5,500 mg/l

Potassium (K+) 2,500 - 4,500 mg/lCalcium (Ca++) 2,500 - 4,500 mg/l

Magnesium (Mg++) 1,000 - 1,500 mg/lManganese (Mn++) above 1,500 mg/l


Chapter IIICOMPREHENSIVE UTILIZATION

OF BIOGAS TECHNOLOGY Biogas system requires a simple plant known as biogas

digester, and users have only to feed proper amount of wastematerials everyday, every two or every three days. Thiscontinuous operation can give users a constant gas volume whichcan supply the daily fuel requirement of a family or a business.Effluent from this plant could be stored in a storage tank andcould be used as liquid fertilizer. Sludge at the bottom of theplant is also pumped out and used as organic fertilizer in thefarm. A biogas plant therefore produces two resources, the gasand the effluent. It also treats waste materials and in theprocess produces biogas. The plant itself therefore, serves asanti-pollution device (Figure 13).

Biogas burners or stoves. Biogas burners or stoves (Figure14a) work satisfactorily for domestic cooking under waterpressure of 75 to 85 mm. The stoves may be single or doubleburner varying in capacity from 0.22 to 1.10 m3 of gas consumptionper hour. Generally, stoves of 0.22 and 0.44 m3 (8 and 16 cu ft)capacity are more popular. A 1.10 m3 (40 cu ft) burner isrecommended for a bigger family with larger plant size.

Biogas lamp. Biogas can be used for lighting (Figure 14b) innon-electrified rural areas. Special types of gauze mantle lampsconsuming around 0.07 to 0.14 m3 of gas per hour are used forhousehold lighting. A great variety of lamps which have single ordouble mantles are already available in the market. Generally,mantle lamp is used for indoor purposes and 2-mantle lamps foroutdoors.

Biogas Utilization


Figure 14a. Biogas stoves/burners.

Such lamps emit clear and bright light equivalent to 40 to 100 ftcandle powers. These are generally strong, well built, bright,efficient and easy to adjust. Compared to stoves, lamps aremore difficult to operate and maintain.

Figure 14b. Biogas lamp


Fuel for Engines. Biogas can be used to operate four strokespark ignition engines. Biogas engines are generally suitable forpowering vehicles like tractors and light duty trucks as has beensuccessfully experimented in China. When biogas is used to fuelsuch engines, it may be necessary to reduce the hydrogen sulphidecontent. Using biogas to fuel vehicles is not much of an attractiveproposition as it will require carrying huge gas tanks on thevehicle.

Electricity Generation. Generating electricity (Figure 14c) is amuch more efficient use of biogas than using it for gas light.From energy utilization point of view, it is more economical touse biogas to generate electricity for lighting. In this process,the gas consumption is about 0.75 m3 per kw hour with which25x40-watt lamps can be lighted for one hour, whereas thesame volume of biogas can serve only seven lamps for one hour(BRTC, 1983).

Figure 14c. General Motors dual-fuel generator setsdesigned by Don Hardy with power output of 60 to 200 kW

Source: http://home.philbio.com.ph/docs/On_Going_Projects/Beijing%20RE%20conference


Refrigerating machines. Biogas can be used for absorption typerefrigerating machines (Figure 14d) operating on ammonia andwater and equipped with automatic thermo-siphon. Since biogasis only the refrigerator’s external source of heat, just the burneritself has to be modified. Refrigerators that run with keroseneflame could be adapted to run on biogas.

Figure 14d. Double-door refrigerating machineSource: www.RefrigeratingMachines.com

What Can You Do with One Cubic Meter of Biogas ?

Table 5 shows some typical applications of one cu.m. of biogas.


Sludge can be utilized in the following ways: as fertilizer(liquid and solid form) to agricultural crops, as dipping media forseed soaking, as feeds for freshwater fish, as feed supplementfor pigs (Appendix A) and as soil conditioner, among others. Table6 shows the mineral composition of sludge.

Sludge Utilization

Table 5. Applications of one cu.m. biogas

Table 6. Mineral composition of sludge

Source: Maramba, 1978.

Ap p licatio n 1 m 3 b io g as eq u iva len tL igh ting equa l to 60-100 watt bu lb fo r 6 hoursC ook ing can cook 3 m ea ls fo r a fam ily o f 5 -6

0 .454 kg o f lpg 3 .47 kg o f f irewood 1 .40 kg o f charcoa l

F ue l rep lacem ent 0 .7 kg o f pe tro l 0 .52 kg o f d iese l 0 .24 m 3 o f p ropane

S haf t power can run a one horse power m otor fo r 2 hours

E lec tric ity genera tion can genera te 1 .25 k ilowatt hours o f e lec tric ity

Mineral Solid Sludge Liquid SludgeN, total, % 2.07 0.08P2O5, total, % 7.31 0.15P2O5, available, % 4.97 0.15K2O, total, % 0.75 0.03Ca, % 4.9 traceMg, % 0.64 -Fe, ppm 0.77 0.66Cu, ppm 0.01 0.18Zn, ppm 145 0.28Mn, ppm 0.96 0.47Organic matter, % 49.6 -


Figure 15a. Sludge used as organic fertilizer

Figure 15b. Liquid sludge is recycled to clean animal pen.


Biogas Technology as Waste-Treatment Facility

Figure 16. Biogas technology in wastewater treatment system


The biogas digester is a physical structure commonly knownas biogas plant. It is also known as bio-digester, bio-reactor oranaerobic reactor. The main function of this structure is toprovide anaerobic condition for the bacteria to survive. As achamber, it should be air and water tight. It can be made ofvarious construction materials and in different shapes and sizes.Some of the commonly used designs are discussed below.

The biogas digester design can be grouped according totheir varied forms and structures.

1 . According to Gas Storage

The design of biogas digester may vary accordingly tosuit the requirements of the owner. This can be divided intothree groups, namely: fixed-digester, floating gas holder andbag digester.

a. Fixed-Dome Digester

Fixed-dome digester (Figure 17a) is the mostcommon type of design. The four major components ofthe digester which are gas storage, fermentationchambers, hydraulic tank and inlet tanks are integratedinto one structure. Its distinct advantages over the otherdesigns are:

1. All concrete construction, hence, durable and lifelong investment. Simple structure. Least cost.

2. No moving parts and metal components, thus, easy to maintain.

Chapter IVDESIGN OF BIOGAS DIGESTER


Design of Biogas Digester According to Forms andStructure

3. Capable of generating higher gas pressure (on the average 10 times higher than floating gas holder type). 4. Can be completely constructed underground, thus save land space. Input materials flow easily into the digester by gravity, hence simplifying operation.

b. Floating Gas Holder Digester

The floating gas holder digester makes use of a floatingtank for gas storage. This can be further subdivided into:

Figure 17a. Fixed-dome digester

1 . Top Floating Gas Holder Digester

The floating tank for gas storage is directly installedon top of the digester. This is usually employed forsmall size digester (Figure 17b1).

Figure 17b1. Top floating gas holder digester


2. Separate Floating Gas Holder Digester

The application of this style is for medium to large size digester. There are two tanks involved: one is the fermentation tank and the other is the gas storage tank (Figure 17b2).

c. Bag Digester

The bag digester is a type of digester with a bag forgas storage (Fig. 17c).

Figure 17b2. Separate floating gas holder digester

Figure 17c. Bag digester


2. According to Geometrical Shapes

Biogas digester can be constructed in various geometricalshapes: vertical cylinder, spherical, rectangular, square, pipe-shaped, oval, spindle-shaped, elliptical, arch, oblate, etc.(Figure18).

Figure 18. Construction shapes of biogas digester


The arrangement of the different components of biogassystem can vary according to what is suitable to the condition ofthe area. The different orientations of inlet and outlet areshown in Figure 18 for design flexibility.

3. According to Orientations

Figure 19. Different orientations of inlet and outlet for design flexibility


4. According to Buried Position (Figures 20 to 22)

Biogas digesters can be erected either of the followingways:

a. Ground digester

b. Semi-buried digester

Figure 20. Ground digester

Figure 21. Semi-buried digester


c. Underground digester

Figure 22. Underground digester

1. Cylindrical Fixed-Dome Digester

Advantages:· Reinforced concrete construction· No steel sheets required· Generally, it runs on batch-continuous process, i.e. plant

waste maybe included· The total cost is normally less than that of floating

gasholder· Plant materials maybe used· The digester and the gasholder maybe built below ground

level, hence, it is easy to insulate them in cold regions· If built underground, the above surface area maybe used

for other purposes.

Advantages and Disadvantages of Various Designs


MOVABLE COVER

GAS STORAGE

FERMENTATION CHAMBER

GAS PIPEOUTLET P IT

OUTLET PIPE

Disdavantages:· No provision for stirring the slurry in the plant· Stirrer can be fitted through dome· The necessity of removing the sludge twice or more

often in a year· Outside China, this type is not very popular in view of

lack of construction and plastering experience· Requires highly skilled workers for construction

2. Spherical Hydraulic DigesterAdvantages:

· The same features as cylindrical fixed-dome digester

Disdavantage:· More difficult to construct than the cylindrical fixed-

dome

INLET PIPE

Figure 23. Cylindrical fixed-dome digester

INLET PIT


Figure 24. Spherical hydraulic digester

Advantages and Disadvantes are the same with SphericalDigester.

3. Ellipsoidal Hydraulic Digester

MOVABLE COVER


INLET P IT

GAS PIPE

INLET PIPE

Figure 25. Ellipsoidal hydraulic digester

HYDRAULICCHAMBER

GAS PIPE

INLET PIT

INLET PIPE


MOVABLE


HYDR AULICCHAMBER

GAS PIPE

GAS

SLURRY

LEVELLEDSURFACE

OUTLETINLET

Figure 26. Flexible bag-type combined digester/holder

4. Flexible Bag-Type Combined Digester/Gas Holder

Disadvantages:· Must be made of strong plastic resistant to ultra violet rays (Hypalon-Neoprene plastic is used)· Cost depends on local price of plastic materials (if available)· Plastic can be accidentally cut during handling and

installation· Should be provided with pressure release valve,

otherwise, the bag may explode· Rodents have been known to destroy the plastic bag· Stirring is not possible· Bends in inlet and outlet may cause blockage

Advantages: · Portable · Constant gas pressure may be obtained · Relatively quick to erect · Low capital cost


· Digester is easy to construct · Uniform gas pressure · Offers the possibility of heating the slurry by using solar

energy

5. Two Chamber Rectangular Digester with Floating Gas Holder (without water seal and with water seal)

Disadvantages: . High initial cost · Needs frequent stirring · Clogging problem have been experienced

· Susceptible to scum formation · Needs the services of a skilled welder · Gas tank is easily corroded· Leakage is a perennial problem· High rehabilitation cost• Needs annual maintenance

Advantages:

MIXING DEVICE

GAS PIPE

OUTLET

INLET

OUTLET

GASHOLDERGUIDE

FLEXIBLE HOSE

GAS VALVEMIXING DEVICE

COVERED MANHOLE

INLET

Figure 27. Two-chamber rectangular digester with floating gasholder

(without water seal) (with water seal)


6. Fixed-Dome Digester with Separate Gas Holder

Advantages:· The digester dome is subjected to little gas pressure

(determined) by the weight of the gas holder· Uniform gas pressure; hence, appliances may be

designed and used at their optimum working conditions· No steel sheets or reinforcing steel bars are needed for

the gas holders

Disadvantage:· Additional work and cost of building the water tank as

gas holder

GA S

SLURRY DISPLACEMENT TANK

LOOSECOVER

REMOVABLE MANHOLECOVER SEALED W/C LA Y

INLET

GAS PIPE

FLOATER

WATER

BAMBOO CEMENTGAS HOLDER

Figure 28. Fixed-dome digester with separate gas holder

7. Deenbandhu Biogas Digester

Advantages:· All concrete construction hence, durable· Operates on displacement principle as in Chinese digester


Figure 29. Deenbandhu biogas digester

· Low initial cost· Uses commonly available construction materials

Disadvantages:· Needs special skills and training for construction· Non-uniform gas pressure

8. Rectangular/Square Fixed Dome Digester

Advantages:· Easy to construct· Uses commonly available construction materials· Operates on displacement principle· Less susceptible to scum formation· Less foreign matters accumulation inside the digester· Can be constructed above/under ground· Can be easily adapted for floating gas holder digester

PVC PIPE

MIXINGTANK

GAS OUTLET PIPE

INITIAL SLURRY LEVEL

DIGESTER TANK

CENTER

OPENING

OUTLETTANK


OUTLET

SLURRY TANK TODECREASE PRESSURE ONGAS HOLDER TOP

GAS PIPE

INLET

Figure 30. Rectangular/Square fixed-dome digester

GAS

SLURRY

Disadvantages:· Non-uniform gas pressure· Requires special training for construction


There are several models of biogas digester already in thecountry. Most common are fixed-dome type, bag type, and forlarger applications, the covered lagoon digester. There are alsosome floating-type biogas digesters, while the drum-type is veryfew.

Depending on the size of the livestock project, the authorsare recommending the following digester models/designs for small,medium and large applications: DSAC-Model Biogas Digester,Tubular Polyethylene-Based Digester (TPED) and Covered LagoonDigester, respectively.

DSAC-Model biogas digester is a rectangular fixed-domedigester which is a combination of Chinese and Indian model.This model is durable because of its all-concrete constructionand is adaptable to small-medium-large scale applications (seedetails in Chapter V).

The TPED model is an improved bag-type digesteradaptable to small scale application. This modified technology iseasier to build and less expensive (see details in Chapter VI).However, this model is mainly used for energy-generation andnot for waste treatment.

The covered lagoon digesters are huge digesters adaptableto large scale applications. The system is generally used in powergeneration (see details in Chapter VII).

Digester Models in the Philippines


Chapter VDSAC-MODEL BIOGAS

DIGESTERThe DSAC-Model biogas digester is a rectangular fixed-

dome digester. It is a modification combining the features ofChinese and Indian models.

Among its special features are the following:n Environment-friendly, 60%-80% pollution reduction capabilityn Low costn Easy to construct and simple to operaten All concrete construction, durable and with less maintenancen Flexibility of designn Self stirringn With built-in safety mechanismn Can generate biogas from 35-60% of the digester volumen Adoptable to small-medium-large scale animal production,

slaughterhouses and food processing plant

Figure 31. DSAC-Model biogas digester (Utility Model No. 2-1997-15098)


The biogas digester is composed of an inlet, inlet pipe,gas storage, digester and the outlet chamber (Figure 32).

Figure 32. Basic components of a DSAC-Model biogas system

Components of DSAC-Model Biogas Digester

The Inlet. The inlet serves as the collection tank of themanure. It can either be circular or rectangular in shape. It isdivided into two compartments, namely: the collectioncompartment and the inlet compartment. The collectioncompartment is directly connected to the canal system of theanimal pen. It collects the manure and serves as a sedimentationtank where foreign matters which are non-biodegradable likesand, hair, etc. could be collected to avoid its entry to the digester.The inlet compartment is connected to the digester through aninlet pipe which then conveys the slurry to the digester. The inletshould be provided with cover to avoid the entrance of rainwaterand for safety purposes.

The Digester and Gas Storage. This is the fermentationtank which provide anaerobic condition needed for the bacteriato act on the organic wastes. The fermentation process is allowed


to be completed in the digester for a certain period of timeknown as the retention period. During the fermentation process,biogas is generated and stored in the gas storage which form asthe dome cover of the digester. The structure must be air- andwater-tight.

The Outlet Chamber. The outlet chamber serves as thehydraulic tank which maintain the pressure of the biogas insidethe gas storage. It can either be circular or rectangular inshape. The chamber is provided with discharge outlet wheresludge or effluent can be collected.

Manhole. Between the digester and the outlet chamberis a manhole which provide an access to the inside of the digesterif necessary.

The Gas Line. The gas line is the delivery line of gasfrom gas storage tank to the appliances being used. It is locatedat the midline of the dome cover. It is made of stainless steelpipe.

The biogas plant operates in a displacement principle.The slurry in the inlet flows into the fermentation tank (digester)through the inlet pipe. Fermentation process occurs inside thedigester due to the action of bacteria. During the fermentationprocess, biogas is generated and stored in the gas holder. Theslurry is allowed to stay inside the digester for a certain numberof days to allow the fermentation process to complete. Oncedigested, the slurry settles down as it becomes more densecompared to the fresh slurry.

The digested slurry is then pushed by the incoming freshslurry into the outlet chamber. The pressure developed by thegas generated inside the digester assists also in pushing thedigested slurry towards the outlet chamber to the discharge outlet.

Principles of Operation


Design Formulas

Consider a rectangular fixed-dome biogas digester, the designformulas are as follows (see Figure 33).

Figure 33. Design formulas

f

h

W

f

h

L

W

V

V

1

2


Let h = height of rectangle w = width of digester f = top of dome R = hydraulic radiusV1 = gas chamber volumeV2 = slurry chamber volumeVt = total volume of digesterVo = volume of outletVs = volume of slurry

The useful relationship for this type of digester are:

1. f/w = 1/3

W2 + 4f2

2. R =8f

3. Vo = 1/3 x V2, that is, Vo is one third the slurry chamber volume

4. Vs = V2, that is, the slurry volume is equal to the volume of digester below the top dome.

5. Height of inlet/outlet pipes = 1/2 h, that is, the inlet/ outlet pipes are placed 1/2 the height of the wall.

6. Mixing pit volume should be slightly larger than the daily charge.

7. Manhole dimension is standard for all volumes of digester.


There are two approaches in determining the size of abiogas digester. The decision is made by the owner/operator tofit his needs.

1. The size of the unit to produce a certain amount of gas needed

2. The size of the unit to process/treat a given amountof organic matter (pig manure, chicken manure, etc.)as a waste management system.

Generally, in case wherein the volume of organic matterto be treated is known and the need for gas is minimal, theoverriding consideration, therefore is the quantity of the rawmaterials to be treated. Other questions are: What digestervolume is needed to handle these materials? What is thequantity of gas expected? How will this gas be utilized? What isthe cost involved?

For example: Assume a medium-sized piggery with one(1) boar, fifteen (15) sow and one hundred twenty fatteners.

The average daily manure production are:1 Boar = 4.91 kg15 Sow = 3.97 kg120 Fattener = 3.84 kgManure Production = 1 boar * 4.91 kg + 15 sows * 3.97 kg

+120 fatteners * 3.97 kg = 4.91 + 59.55 + 460.8 = 525.26 li/day

Slurry Volume = 525.26 liters * 2 (1 vol. of manure: 1 vol. of water)= 1,050.52 li/day

Sizing of Biogas Digester


Planning/Preparation

It is recommended that the builder reads the entireconstruction procedures to have an idea of what is involved,the time period required and the construction materials tobe used.

Pre-Construction Consideration

Figure 34. Planning/Preparation

Digester Volume = 882 li/day *40 days retention time = 42,020.80 liters = 42.02 cu.m.

Estimated Gas Production = 42.02 cu.m. * 0.5 cu.m. biogas/ cu.m. digester volume

= 21.01 cu.m. biogas per day


Some important reminders in planning for the constructionof biogas unit:

1. Order and purchase all materials in advance.2. Prepare all tools needed in the construction.3. Building a biogas tank is not similar to building a house

or a piggery. One crack in a house or piggery structureis permissible but not in a biogas digester. Any sourceof leak for gas will render the biogas digester useless.

4. Water-proofing concrete is relatively easy, but gas-proofing is difficult. This requires materials not appliedin ordinary masonry work.

5. Costing. Ask the question whether some materialscould be suitably substituted by others which are lessexpensive but adequate for the job.

6. Available labor. Check if the required labor andtechnical skills could be easily obtained and if not,where to secure them.

7. Check water table. The water table should not exceedhalf of the height of digester wall. If necessary, thewhole structure may be elevated to compensate forthe high water table (although it may involve someproblems like more backfill needed and more effortsin lifting/handling manure into the digester). As arule, it is best to avoid high groundwater areas forbiogas units.

8. Avoid construction during rainy season for it may causeconstruction delay, thus, affecting the quality ofconcrete work.

9. Follow strictly the scientific methods for working withconcrete. The payoff is highly durable, more lastingand efficiently functioning biogas unit.


10. Other reminders. Consider the available animalwaste, amount of manure available, amount of gasproduction and potential utilization of biogas by-products.

The following guidelines are helpful in choosing an idealsite for biogas project.

1. Water table. Biogas units should be constructed ata site where water table is low. The maximum thata water table may be allowed to rise is ½ of theheight of the digester. If the water table in theselected site is too high, look for another site.

2. Site location. It should be located as much aspossible downhill or downstream with respect toa well or spring. Ideally, the minimum distanceshould be 15-20 meters to avoid watercontamination in case of leaks from the digester.

3. Accessibility. The site should be as clean as possibleto the point of gas utilization, but at the same time,close to the source of raw materials such as piggeryor poultry.

4. Soil formation. The biogas digester should beconstructed on stable soil foundation.

5. Vegetation. The digester should be away from rootsof big trees that may damage the structure.

6. Sunlight. The digester is completely underground.In the tropics, the unit should be placed in an openarea for greater exposure to sunlight. The heatprovided by the sun will promote greater gasproduction.


Site Consideration

7. In cold areas, the digester should be constructedunderneath the house/kitchen/ animal stalls to protect itfrom extremely low temperature.

8. Feeding. The feeding of raw materials to the inlet/mixingtank should be accomplished via sloping canals or throughthe action of gravity. This is advisable for increasedefficiency and less labor cost in handling the manure.

9. The site should be closed to where the effluent is to beused/stored like vegetable garden or drying bed.

a. Lay-outing

After the place has been carefully identified, the area shouldbe cleared from grasses, debris and other materials whichmight obstruct the free movement of workers doingconstruction. Minor site development is necessary for soilsurface with sloping terrain; however, this is not needed forflat surfaces.

Figure 35. Lay-outing

Construction Techniques (DSAC-Model Rectangular-Fixed Dome Digester)


b. Excavation

Earth bank should be as vertical as permissible. A 20 cm gapon both sides shall be allowed for backfill.

Figure 36. Excavation

c. Bottom Construction

For a biogas plant of not more than 10 cu.m., a 20 cm x 20cm footing shall be provided to carry the load of the digesterwall. The soil must be properly drained and compacted. Thefooting must be reinforced with 10 mm RSB properly spacedwith stirrups.

d. Flooring Construction

A 10 cm thick flooring shall be reinforced with 10 mm diameterRSB spaced at 40 cm on center both ways. The RSB shall beconnected to the footing. Use class A concrete mixture withwater proofing compound.


Figure 37. Bottom construction

e. Wall Masonry

Wall should be reinforced concrete hollow blocks. The wallshould be reinforced with 10 mm reinforcement steel barsplaced at 40 cm distance (vertical bars) and every two layersfor the horizontal bars. Use class A mortar with water proofingcompound. Provide column in excess of 3 m span. Tie wiresfor the screen must be embedded and anchored to thehorizontal bars.

Figure 38. Flooring construction


Figure 39. Wall masonry

f. Construction of Inlet

A 200 mm diameter concrete pipe is connected to the digesterat about half-way down the digester wall. The other end ofthe pipe is connected to the mixing pit where mixing ofmanure and water is done. The inlet pipes must be laid at a30 degrees angle to the digester wall.

g. Construction of Hydraulic Tank

This tank serves as the outlet tank. It must be providedwith stairs and open manhole as access into the inside of thedigester. The floor level must be on the same level with theupper part of top beam. The height of overflow must be atleast 10 cm lower than the lower surface of the dome.


Figure 40. Construction of inlet

Figure 41. Construction of hydraulic tank


h. Top Beam Construction

A 20 cm x 20 cm beam reinforced with 4 - 10 mm diameterRSB with stirrups spaced at 20 cm shall be connected tosupport the top dome. The beam shall be anchored on thevertical bars.

Figure 42. Top beam construction

i. Dome Construction

The dome should be cast-in place. The curvature of theform works is based on the design curvature of the dome(inside). The curvature of the reinforcement bars shall bebased on the curvature of the dome plus 1/2 the thicknessof the dome which should be not less than 5 cm. Thereinforcement must be 10 mm diameter RSB spaced at 15cm (both the curved and the horizontal bars) and the curvedbars shall be anchored at the top beam.


Figure 43a. Dome construction

Figure 43b. Dome construction


Figure 44. Sealing the digester

j. Sealing the Digester

The biogas digester must be water-tight and air tight. Thewalls and dome must be reinforced with screen beforeplastering with class A mortar mixed with sealing compound.Apply three layers of plaster (1/2”, 1/4”, and 1/4” ofthickness). Each layer must be applied continuously and shouldbe finished within one day. All corners must be curved-finished. The plaster should be mixed with water proofingcompound.


k. Air and Water-Tightness Tests

Figure 45. Water-tightness test

a. Water -Tightness Test

For Shallow Groundwater

1. Dry the digester and check the leakage appearing on thewall, dome, and bottom. If water drips on the innersurface of the digester, this means that the digester is notto water-tight.

2. If water level in the digester changes more than 5 mm for12 hours, the digester is water-tight by the level ofgroundwater.

3. Lower the groundwater level and follow the method fordeep groundwater.

For Deep Groundwater

1. Pour water until the digester is filled with water.2. At first, the concrete absorb some amount of water. Wait

for 3-5 hours and then mark the water level.3. If drawdown of water level is not more than 5 mm for 12

hours, the digester is water-tight enough. Cover the openarea to prevent evaporation.


Figure 46b. Manometer

b. Air-Tightness Test

Figure 46a. Air-tightness test

1. Drain water until the hydraulic pressure tank is empty.2. Set manometer (pressure meter) and valve.3. Close valve and pour water until pressure inside the digester becomes the desired value of 80-120 cm water.4. If the pressure drawdown is not more than 3% of original value, the digester passes the air-tightness test.5. The pressure inside the digester

will be affected by manyfactors such as temperature,atmospheric pressure, andsunlight. If there is notendency of pressuredrawdown, then the digesterpassed even if somefluctuation is observed.


Table 7. Bill of materials for a 6 cu.m. DSAC-Model biogas plant

Plan of a 6 cu.m. DSAC-Model biogas plant (Adequate size for 30 heads of pigs or 2,000 heads of chicken)

Figure 47a. Lay-out

Quantity Unit Item description300 pcs. CHB # 5 or 660 pcs. Portland cement30 pcs. Sahara waterproofing8 cu.m. White sand2 cu.m. Crushed gravel, 3/4"

75 pcs. RSB, 10-mm diameter4 kgs. CWN, assorted, 1,2,3

40 pcs. Coco lumber, 2" x 2" x 12'6 kgs. G.I. tie wire, #162 pcs. Plywood, 1/4" x 4' x 8'2 pcs. Plywood, 1/2" x 4' x 8'2 pcs. Lawanit, 1/8" x 4' x 8'2 pcs. Concrete pipe, 8" diameter1 pc. Stainless pipe, 8" diameter1 pc. Ball valve, 1" diameter

20 m. Screen wire, 1/2" x 1/2"1 unit burner gas stove (heavy duty)


Figure 47b. Plan

Figure 47c. Longitudinal section

Figure 47d. Section of inlet pipe and hydraulic chamber


Chapter VITUBULAR POLYETHYLENE

DIGESTER The Tubular Polyethylene Digester (TPED) developed by

the Bureau of Animal Industry of the Department of Agriculture isa biogas technology for small swine farmers. TPED is simple,cheap and easy to install. For a measly Php10,000-P15,000, afarmer can have TPED in his backyard. TPED can provide asteady supply of fuel for cooking, thus cut LPG expenses. Inaddition to this savings, foul odor of decomposing animal manurecan be eliminated.

TPED biogas system has the following six major parts:

1. Trench. This is where the digester is placed. This can beconstructed in several ways; either with hollow block sidingsdug in soil or placed on top of soil.

2. Digester. This is made of polyethylene bag where manure andurine are placed and where biogas is produced.

3. Safety valve. This is made of one liter capacity plastic bottlewhere excess gas evaporates to avoid gas reservoir fromerupting.

4. Gas Reservoir. This is a polyethylene bag where the biogasproduced is stored.

5. Heavy Wooden Object. This is placed on top of the reservoirwhen burner is used to provide pressure on the gas reservoirso that gas will flow to the burner.

6. Stove. This is where biogas is used.

Major Parts of TPED Biogas Digester(Derived from Technology Adoption and Commercialization of Low -Cost and Environment Friendly Biogas System, Quirino State College)


Preparation of Trench

A trench may be constructed in several ways. Adoptersprefer to construct a concrete trench to protect the digesterfrom soil erosion which may damage the digester (Figure 48a).

Trench can also be just dug in the soil without concretingit but the life-span of the polyethylene bag is at stake (Figure48b).

Figure 48b. Trench dug in the ground

Figure 48a. Concrete trench

Installation of TPED Biogas Digester


The polyethylene digester can be placed on top of theground but should be fully protected (Figure 48c).

When digging the trench it is important to observe the following:

n The sides and the floor should be smooth with no protrudingstones or roots which could damage the plastic film.

n The floor should have a slope of about 25% from the inlet tothe exit (this would be 25cm for a biodigester of 100cmlength).

n The soil that is excavated should be moved away from theedges of the trench so that movement around the bio-digesterduring or after installation, or subsequent heavyrains, will notcause soil to fall onto the plastic.

Figure 48c. Digester on top of the ground w/o trench

Protection of the Polyethylene Plastic Digester and GasReservoir

The polyethylene plastic digester and gas reservoir mustbe protected against astray animals as well as children and fallingtwigs. The digester and gas reservoir should be enclosed withscreen or fence made out of indigenous materials to serve asprotection to the structure (Figures 48d).


Figure 48d. The funnel type entrance of manure withscreen protection of digester

Preparation of the Polyethylene Plastic Digester

1. Cut the polyethylene bag in accordance with the length of thetrench prepared (usually from 8 to 10 meters).

2. Lay the plastic flat on a smooth surface then insert one intothe other to double the polyethylene bag. Extra care must beobserved to protect the plastic.

3. Install the gas outlet. Cut a small hole from the inlet on oneedge of the tube. Fit the plastic washer (PVC card) into asmall male PVC adapter and insert through the hole from theinlet to the outer portion of the plastic digester. Put anotherwasher and rubber piece and fit it with the female adapterfirmly. Cover the gas oulet with a piece of plastic to preventthe escape of air.

4. Insert a 4” PVC pipe at one end of the plastic tube. Fold theplastic around the PVC pipe and tie it with rubber strip. Sealthe inlet with plastic cover tied with rubber strip.

5. To fill the polyethylene tube with air, place the plastic cover atone end of the tube then grasp the other end with both handsand open the plastic in front of an electric fan in order toinflate the polyethylene tube.


6. Once the polyethylene bag is inflated, insert 1” PVC pipe coveredwith plastic and tie the folded end of the digester with rubberstrips to avoid escape of air.

7. Carry the tube carefully and place it in the ditch or trench. Putthe PVC pipe in 45 degrees inclination and fix it temporarily.

8. Fill the digester tube with 3/4 of water. For regular gasproduction, install a transparent plastic bottle of 1 to 2 literscapacity. Use a PVC Tee, 2 PVC of 1/2 diameter and about 30cm long. Fix the gas outlet using the 1/2 diameter PVC pipe,a PVC elbow, 2.5 meters plastic hose, and a safety valve. Puta hose inside the bottle with 3 - 4 cm submerged in water tomaintain the 3 psi capacity of the gas reservoir.

Preparation of Gas Reservoir

The gas reservoir is made up of polyethylene bags around3 meters long. This is connected near the safety valve and joinedby a PVC Tee. Put the gas reservoir horizontally in an elevatedplace and put a heavy object above the reservoir to give pressureon it when the gas is in use. The heavy object is removed whengas is not in use to allow the gas reservoir to resume its originalshape as the used methane gas is replaced.

Methods of Constructing the Biogas System

The method of constructing a TPED biogas system dependson the location of the pig pen and the number of householdsusing the biogas system. TPED biogas system models areillustrated in Figures 48e and 48f.

For more detailed steps in constructing the digester, youmay visit this site: http://www.wcasfmra.org/biogas_docs/5%20Vietnam%20Plastic%20Tube%20Manual%20Biodigester.pdf


Figure 48e. First model

Figure 48f. Second model


References:

Avilla, H.F. et.al. 2006. Biogas Technology Development in the Philippines: Status and Propects. Country Paper presented to the ASEAN Rural Energy Forum and Technology Exhibition.Benigno, S.O. and H.K Banciles. 2000. Technology Adoption and Commercialization of Low Cost and Environment Friendly Biogas System. Maiden Issue.Rodriguez, L. and T.R. Preston. Biogas Digester Installation Manual. University of Tropical Agriculture Foundation

Table 8. Materials needed for the construction of Tubular Polyethylene Digester


A covered lagoon digester is alarge anaerobic lagoon with longretention time and high dillutionfactor. Typically, this is beingused with flush manuremanagement systems thatdischarge manure at 0.5 to 2percent solids. The in-ground,earth or lined lagoon is coveredwith a flexible or floating gastight cover. They are not heatedand considered ambienttemperature digesters.Retention time is usually 30-45days or longer depending onlagoon size. Biogas productionin the system tends to varyseasonally due to temperaturefluctuations.

Figure 49. Covered lagoondigester

Chapter VIICOVERED LAGOON DIGESTER

Components of Covered Lagoon Digester

Solids separator. A gravity solids trap or mechanical separatorshould be provided between the manure and the lagoon.

Lagoons. Two lagoons are preferred; a primary anaerobic wastetreatment lagoon and a secondary waste storage lagoon.

Floating lagoon cover. The most effective methane recoverysystem is a floating cover over all or part of the primary lagoon.


Biogas utilization system. The recovered biogas can be usedto produce space heat, hot water, cooling or electricity.

Covered Lagoon Design Variables

Soil and foundation. Locate the lagoons on soils of slow-to-moderate permeability or on soils that can seal throughsedimentation and biological actions. Avoid gravelly and shallowsoils over fractured or cavernous rock.

Depth. The primary lagoon should be dug where soil andgeological conditions allow it to be as deep as possible. Depth isimportant in proper operation of the primary lagoon and of lesserimportance in the secondary lagoon. Deep lagoons help maintaintemperatures that promote bacterial growth. Increased depthallows a smaller surface to minimize rainfall and to cover size,which reduces floating cover cost. The minimum depth of liquidin the primary lagoon should be 12 ft.

Loading rate, hydraulic retention time and sizing of primarylagoon. The primary anaerobic lagoon is sized as the larger ofvolatile solids loading rate (VSLR) or a minimum HRT.

Volatile solid loading rate. The VSLR is a design number,based primarily on climate, used to size the lagoon to allowadequate time for bacteria in the lagoon to decompose manure.

Minimum hydraulic retention time. The VSLR procedure isappropriate in most cases, however, modern farms using largevolumes of processed water may circulate liquids through aprimary lagoon faster than bacteria can decompose it. To avoidthis washout, a minimum hydraulic retention time (MINHRT) isused to size the lagoon.

Primary lagoon inlet and outlet. The primary lagoon inlet andoutlet should be located to maximize the distance across thelagoon between them.


Rainfall. Rainfall is not a primary factor in determining thepotential success of a covered lagoon. In areas of high rainfall, alagoon cover can be used to collect clean rain falling on the coverand pump it off to a field. In areas of low rain, a lagoon coverwill limit evaporation and loss of potentially valuable nutrient richwater.

Cover materials. Many types of materials have been used tocover lagoons. Floating covers are generally not limited indimensions. A floating cover allows for some gas storage.Availability of materials, serviceability, and cost are factors to beconsidered when choosing a cover material.

Cover installation techniques. A lagoon cover can be installedin a variety of ways depending upon site condition.

Full perimeter attachment. The entire lagoon surface iscovered and the edges of the materials are all attached to theembankment.

Completely floating or partially attached cover. The covermay be secured on the embankment on one to three sides or thewhole cover can float within the lagoon. All or some of the sidesmay stop on the lagoon surface than continuing up theembankment.

Operation and Maintenance of Covered LagoonDigester

Primary Lagoon Operation. The proper design andconstruction of a primary lagoon leads to a biologically activelagoon that should perform year round for decades. Any changein operation will most likely be due to change in farm operationresulting in an altered volatile solids loading or hydraulic load tothe lagoon. The owner should make a weekly visual inspection ofthe lagoon level.


Primary lagoon maintenance. Minimal maintenance of theprimary lagoon is expected if the design volatile solids and hydraulicloading rates are not changed. Lagoon banks should be keptfree of trees and rodents that may cause embankment failure.Weeds and cover crops should be cut to reduce habitat forinsects and rodents. Occasional plugging of inlet and outlets canbe expected. Accumulated sludge should be removed every 3 to5 years. Sludge can be removed by agitating and pumping thelagoon or by draining and scraping the lagoon bottom.

Cover operation. Operating a lagoon cover requires removingthe collected biogas from below the cover regularly orcontinuously. Large bubbles should not be allowed to collect. Ifthe cover is designed to accumulate rainfall for pump off,accumulated rainwater should be pumped off.

Cover maintenance. The cover should be inspected weekly forrainwater accumulation, tearing, wear, and proper tensioning ofattachment ropes. The rainwater pumpoff system should bechecked after rainfall and maintained as needed.

The Covered In-Ground Anaerobic Reactor (CIGAR)

In the Philippines, the Covered In-Ground AnaerobicReactor (CIGAR), a type of covered lagoon digester, wasintroduced by PhilBIO in the year 2000 when it constructed itsfirst biogas project in Rocky Farm (Figure 50). The CIGAR(Figure 51) effectively breaks down organic contaminants througha multi-step biological treatment of the waste-water in theabsence of oxygen. High density polyethylene (HDPE) liners andcovers are used to provide for an air-tight system and to preventleachate from percolating through the ground and polluting localground water aquifer resources.


Figure 50. CIGAR at Rocky Farm

The wastewater, afterpassing the CIGAR system,resulted to around 95%destruction of harmfulbiochemical oxygen demand(BOD) and 80% reduction ofchemical oxygen demand(COD). Suspended solid isreduced and color is improvedin CIGAR system. The digesteris designed to maintain a 30-day retention time andtemperature of 35oC toeffectively reduce pathogenicmaterials. The effluent is thensent to a final treatmentlagoon where normalfacultative aerobic processpredominates.

Figure 51. The CIGAR systemSource: http://cdm.unfccc.int/usermanagent/FileStorage/5HHJ719OINSKCQ53PPTFPANBANH91I


Figure 52. Lagoon digester and biogas handling

Biogas is also produced in a CIGAR system. The biogasproduced is used to generate electricity for use on-site. A biogas-fueled generator is usually installed in the farm providing thepower need of the farm. Surplus biogas are flared rather thanreleased to the atmosphere until such time that structural barriersare removed to allow the export of any surplus electrical energyto the local distributing grid.

The Universal Robina Corporation (URC) RF 12 in Bulacanis the largest biogas project done by PhilBIO with 1.08 MW powerplant (Figure 53).


Figure 53. URC RF 12

Figure 54. Lagoon effluent

References:

http://cdm.unfccc.int/usermanagent/FileStorage/5HHJ719OINSKCQ53PPTFPANBANH91Ihttp://pcierd.dost.gov.ph/index2.php?option=com_docman&task=doc_view&grid=21&Itemid=41http://www.biogaspsu.edu/coveredlagoon.htmlhttp://www.calstart.org/info/publications/Biomethane_from_Dairy_Waste_Full_Report.pdfhttp://www.philbio.com.ph


Chapter VIIIOPERATION AND MAINTENANCE

OF BIOGAS DIGESTERLike any other equipment, the biogas should be properly

maintained to achieve efficient operation. A properly builtstructure and sufficiently available materials may not producethe desired results due to faulty operation and/or maintenance.

Initial Loading

1. Starter/Seeding. The initial raw materials known as“starter” should contain slurry with high bacteria population.About 5 - 10% of the total slurry volume should be addedwhen the digester is about 25% full.

2. Cattle dung is a good starter since cattle have methaneproducing bacteria in their stomachs. Starter can also bemade from any manure by adding to its 5-10% “old” slurryobtained from another digester or when cleaning thedigester. Starter can also be prepared by storing manure ina container.

3. Filling the digester. The digester should be filled as quicklyas possible. The following steps should be kept intoconsideration:

a) Be sure to open all valves to relieve any pressure build-up in the digester dome before putting any slurry intothe digester. It is advisable not to connect the pipingsystem to the digester when loading.

b) Mix manure and water thoroughly until there are nomore “lumps”. This will increase gas production sincethe bacteria will have more contact surface with themanure.


About 1 liter of water is added to every kilogram ofmanure. The slurry should be mixed thoroughly until the rightconsistency is obtained. However, in actual practice, there isno fixed water-manure proportion since this will depend on thetype of manure being used and its moisture content. Thetechnique will be developed through experience.

The loading of materials should be done regularly. Ideally,it should be daily. The amount of slurry should be in accordancewith the requirement of the particular digester volume and itsretention time. Less slurry being loaded would result to lowergas production whereas excessive slurry would result in rawmaterials wastage since slurry will not be fully digested.

Regular Loading

c) Fill the digester with slurry up to beam level. This is thesame level as the outlet chamber floor.

d) Do not load any new slurry to the digester until at least 3days after burnable gas is produced.

4. If the above conditions are not possible, just let the slurryflow into the digester until such time that the digester isfilled up to the level of the outlet chamber floor. Thenecessary bacteria will grow biologically and biogas can beproduced in 30 to 40 days.

5. The following materials should not enter the digester:a) Earth or sand;b) Straw, grasses, leaves, etc. – remove all floating materials

at the mixing pit before allowing them to enter into thedigester. These materials will float on the slurry surfaceand may cause problem.

c) Oil, soap, detergent, disinfectant, etc. – these materialswill disrupt bacteria activity and may even kill the bacteria.


The loading of new slurry materials displaces an equalvolume of effluent to the outlet chamber. This effluent must beremoved otherwise the digester would be overloaded. The correctdigester level is that at zero gas pressure, the slurry should be atthe level of the outlet chamber floor.

Stirring/Agitation of Slurry

Mechanically disturbing the slurry inside the digester withthe use of stirrer performs two vital functions: first, to stimulatebacterial activity and second, to break the “scum” layer whichforms a mat of vegetable/organic matter at the slurry surfaceand thus, restricts the gas flow. If left undisturbed, the scumwould get thick and harden, which may require opening thedigester to remove it. Stirring should be done daily – about 3 to 5minutes in the afternoon. The stirring should be 360o in onedirection and 360o in another direction. For the DSAC-Model,there is no need for stirring since the system operates ondisplacement principle (see Principles of Operation on page 58).

Condensate Removal

The condensate or water that settles in the piping systemmust be removed monthly since condensate accumulation mayobstruct gas flow. The condensate removal may be done by liftingthe gas pipe so that the water in the pipe will be drained backinto the digester. Another method is to provide the gas pipesystem with condensate trap for easy removal of water.

Servicing Scum Problem

Scum very seldoms developed in a DSAC-Model biogas plant.In other designs where this is a perennial problem, the followingare the steps that should be undertaken:


1. Release all gas in the digester. Manometer reading shouldbe zero.

2. Disconnect the gas piping closest to the digester.3. Remove manhole (if present in the structure).4. Inspect the scum layer and check its thickness.5. Remove scum manually with buckets through the manhole.

CAUTION: In removing the scum, be cautious about thepresence of fire nearby. Smoking near the digester isdangerous. The digester may still contain gas and mayexplode.

Periodic Maintenance of the Digester

Unlike the DSAC-Model biogas digester, some digester modelsneed periodic maintenance. In these cases, the digester may needto be emptied at least once a year to remove the settled sludgeand other inorganic solids, like sands and stones that accumulateat the digester bottom. The materials are removed manually throughthe manhole with the use of buckets or pumps. This is also anoccasion to check for possible leaks or structural damages.

Take precaution when entering the digester. There arepoisonous gases inside. Also, complete emptying of the digestershould be done if the following conditions occur:

a) Stirring becomes too difficult due to heavy accumulationof inorganic solids (sand, pebbles, etc.) and/or presenceof thick scum.

b) Gas production ceases completely. This may be due tothe introduction of toxins (detergents or disinfectants)into the slurry.

c) Gas production slows down despite regular daily loadingand stirring. There may be leaks in the structure.

Regular cleaning of the inlet tank should also be done, aswell as checking for leaks in the pipes and the digester.


Table 9 shows the possible remedies to most common problemsencountered by biogas plant users.

Table 9. Trouble shooting of biogas plantP rob le m C au s e R e m e d y

G a s p re s s ure do e s no t rise

V e ry fe w ba c te ria In c re a se t he n um be r of ba c te ria by s e e din g o r ad din g slu dg e fro m a n e x is tin g dige s t e r

L ac k o f t im e Fo r co ld w e at he r, w a it fo r a fe w w e ek s .

L ea k a g e a t ga s pip e or g as c o nn ec t ion

Lo ca t e th e le a k a ge a nd pu t so a p s u ds on th e pipe /c o nn ec t ion .

G a s t ap op e n Un us e d g a s t a p s h ou ld b e ch e c ke d a nd clo s e d.

T e m p era t ure is low . In c re a se t e m p er at ur e b y pro v iding c ov e r.

P re s e nc e of s c um S tir t he s lurry in t he d ige s te r.

T oo m u ch fe e d ing or t oo lit tle fe e d ing

P ut th e rig ht a m o un t o f ra w m a te ria ls .

P re s e nc e of inh ibit ors ( de t er ge nt s , c he m ic a ls , e t c.)

Av oid th e en tra n c e of t h es e m a te ria ls int o t he d ige s te r. Co nt inu e d a ily a d e qu at e lo a din g.

R a w m a t e ria ls t oo th ic k o r t oo th in.

Add m o re w a te r t o d ilut e t he raw m a t e rials .

G a s d oe s n ot bu rn P o or q ua lity In itia l g as c o nt a in s a ir, ca rb on dio x id e a nd ot he r in f la m m a b le g a se s .

P re s e nc e of a ir in t he ga s p ipe

Re le a s e a ir in t h e g a s p ipe .

Fla m e is un s ta b le ( lon g, an d w e ak , s m a ll a nd pu ls a t ing )

P o or g as q ua lit y In itia l g as c o nt a in s a ir, ca rb on dio x id e a nd ot he r in f la m m a b le g a se s .

In co rre c t g a s p re s s ure Co rre c t g as p re ss u re to ab ou t 7 5 t o 8 5 m m w a te r.

G a s je t in s to v e is b loc k e d Cle a n g a s je t

P re s e nc e of c on de n sa t e w at e r in t he g as lin e.

Re m o v e c on de ns a t e an d pro v ide w a t e r tra p ping se rv ic e .

Ra w m a te ria ls do no t flo w int o t he d ige s te r.

In le t /ou tle t pip e is c log ge d .

Cle a n t he p ipe by ins e rt ing a po le in to th e pipe s .

Dig es t e r pla n t o v erf low . O u tle t pip e is c log ge d . Cle a n t he p ipe by ins e rt ing a po le in to th e p ipe s .

S lu rry is t oo th ick . Add m o re w a te r t o im pro v e dilut ion .

O u tle t c ha m b e r to o h igh . O ut le t o f h yd ra ulic c ha m be r sh ou ld b e lo w e re d by ele v a t ing t h e in le t.


Biogas consists of methane (CH4) carbon dioxide (CO2)along with some trace gases such as water vapour, hydrogensulfide (H2S), nitrogen, hydrogen and oxygen.

Carbon dioxide and trace gases such as water vapor andH2S must be removed before the biogas can be used because:

n the hydrogen sulfide gas is corrosiven water vapour may cause corrosion when combined with H2S on metal surfaces and reduce the heating value

Energy recovery from biogas is becoming more common,but the process are hampered with the presence of hydrogensulfide (H2S). Hydrogen sulfide (H2S) is a colorless, very poisonousgas. It is flammable and forms explosive mixture with air(oxygen). H2S itself has an offensive odor of “rotten eggs” atconcentration as low as 50 parts per billion by volume (ppbv) andis toxic at concentrations above 100 parts per million by volume(ppmv). H2S is a health and safety hazard, and when combinedwith carbon dioxide (CO2) and water vapor (H2O), corrodes plantequipment such as boilers and piping, and can ruin power-generating equipment. A combustion product of H2S is SO2. Thismakes the exhaust gases very corrosive (sulphuric acid) andcontaminates environment (acid rain).

High levels of H2S can also interfere other processess suchas killing useful bacteria in an anaerobic digester. Reducing H2Soffers cost savings associated with less maintenance, increasedprocess and energy efficiency, and reduced toxic emissions.

Chapter IXBIOGAS UPGRADING


The incombustible part of biogas, CO2, lowers its calorificvalue. On the average, the calorific value of biogas is 12.5 MJ/m3. By removing the CO2 from the biogas, the calorific value isincreased. Stripping CO2 and H2S from biogas is so called upgradingof biogas. By upgrading biogas to natural gas quality, containingapproximately 88% CH4, it is suitable for more advancedapplications in which the heat is not wasted, resulting in a higherefficiency.

Determination of the Hydrogen Sulfide Content inBiogas

H2S content of the gas can be measured by the followingmethods.

Laboratory Method. H2S content of gases is usually measurediodometrically using cadmium acetate.

Lead Acetate Method. A simple way of determining the presenceof H2S in biogas is a test with lead acetate paper. A piece ofpaper soaked with lead acetate solution is held in the gas streamfor a short time. The strip of paper will turn black if H2S ispresent. The difficulty with this method is its high sensitivitywhich means that even a very small amount of H2S can bedetected. A small amount of H2S, however, is not an indication ofgreatly reduced efficiency of the desulphurization. Simpledesulphurization plants may still posses an adequate purifyingperformance.

Detection with Iodine Solution. Another simple method fordetecting H2S is with an alcoholic solution of iodine which isoften available in first aid kits. A small amount of biogas is carefullyintroduced into the iodine solution. If H2S is present the reddishbrown solution will decolour. The formation of elementary sulphurcauses a milky turbidity.


Test-tube Method. The test-tube method is a very exact andsimple method of determining the H2S concentration in biogas.Suitable tubes are available for measuring the concentration inboth raw and purified gas. The gas detector apparatus (ca. 450,-DM) and the individual test tubes (ca. 5,- DM each) are relativelyexpensive. Also, the test tubes can only be preserved for a limitedtime. This method is only expedient in the regional biogasextension service or similar advisory services. This apparatuscould then be used to provide empirical field values for individualplants. The intervals for recharging the purifying agent can thenbe laid down.

There is no simple, cheap test method available as of now.For this reason a close control of the desulphurization plant isstrongly recommended.

Biogas Upgrading Techniques

Techniques of upgrading biogas in large applications are:chemical absorption, high pressure water scrubbing, pressure swingadsorption, cryogenic separation and membrane separation.

Chemical absorption of H2S into iron-chelated solutionsoffers a highly efficient removal of H2S from a gaseous biogasstream. The iron-chelated solutions function as a pseudo-catalystwhich can be regenerated. The H2S is removed almost completelyand converted to elemental sulphur. After the absorption processa scrubber is needed to remove the CO2 (Figure 55a).

High pressure water scrubbing is based on the physicaleffect of dissolving gases in liquids. In a scrubber, CO2 as well asH2S, dissolves in the water while CH4 does not because of theirdifference in solubility. This makes it a very simple process(Figure 55b).


Pressure swing adsorption separates certain gas speciesfrom a mixture of gases under pressure, according to the species’molecular characteristics and affinity for an adsorption material.The adsorption material adsorbs H2S irresistably, and this ispoisoned by H2S. This upgrading system consists of four adsorbervessels filled with adsorption materials (Figure 55c).

In cryogenic separation, the different chemicals in biogasliquefy at different temperature-pressure domains allowing fordistillation. Typically, a temperature of -170oC and a pressure of80 bar is used. Producing pure CH4 from biogas is done by coolingand compressing the crude biogas to liquefy CO2 which then easilyseparated from the remaining gas (Figure 55d).

In membrane separation, CO2 and H2S will pass through acertain membrane while CH4 does not. This is also a very simpletechnique since only a compressor and a membrane are needed.However, this technique is expensive and results to a low methaneyield (Figure 55e).

Of the many processes available, only the ‘dry process’ issuitable for small biogas plants. The desulphurization of biogas isbased on a chemical reaction of H2S with a suitable process.

Lime Process. The oldest process is the desulphurizationof gases with quick lime, slaked lime in solid form or with slakedlime in liquid form. The process using quick or slaked lime hasnot been applied on a large scale for a long time. The largeamounts of odourous residue that are produced cannot besatisfactorily disposed of. The handling of large amounts ofdissolved or suspended slaked lime requires elaborate equipment.

Large concentrations of CO2 which are present in biogasmake the satisfactory removal of H2S difficult. The CO2 also


reacts with the quick and slaked lime and uses it up quickly. TheCa(HCO3)2 formed reacts with Ca(SH)2 which is formed by thereaction of H2S with Ca(OH)2 thus, resulting in the reoccurance ofH2S.

By Ferrous Materials. Ferrous materials in the form ofnatural soils or certain iron ores are often employed to removeH2S. The ferrous material is placed in a closed, gas tightcontainer (of steel, brickwork or concrete). The gas to bepurified flows through the ferrous absorbing agent from thebottom and leaves the container at the top, freed from H2S.

Chemistry. The absorbing material must contain iron inthe form of oxides, hydrated oxides or hydroxides. These reactas follows:

2 Fe(OH)3 + 3 H2S Fe2S3 + 6 H2O

Fe(OH)2 + H2S FeS + 2H2O

This process terminates, of course, after some time. The greaterpart of the iron is then present as a sulfide.

Regeneration. By treating the sulphidized absorbent withatmospheric oxygen, the iron can be returned to the active oxideform required for the purification of the gas:

2 Fe2S3 + 3 O2 + 6 H2O 4 Fe(OH)3 +3 S2

2 FeS + O2 + 2 H2O 2 Fe(OH)2 + S2

The used absorbent can, therefore, be “regenerated”.This regeneration cannot be repeated indefinitely. After a certaintime the absorbent becomes coated with elementary sulphur andits pores become clogged. Purifying absorbents in gasworks (cokeplants) acquire a sulphur content of up to 25% of their originalweight, i.e. 40% sulphur by dry weight.


Figure 55a. Flow diagram for chemical absorption

Figure 55b. Flow diagram for high pressure water scrubbing

Figure 55c. Flow diagram for pressure swing absorption


Figure 55e. Schematic representation of membrane separation

Figure 55d. Flow diagram for cryogenic separation process


Biogas Purification Process by ITDI

The biogas purification process developed by the IndustrialTechnology Development Institute (ITDI) consist of biogas digester,compressor, series of scrubbers, storage tank for scrubbed biogas,converted gasoline fed generator, and appliances for electricityutilization (Figure 56).

Figure 56. Biogas purification process by ITDI


References:

http://www.fao.org/docrep/T0541E/T0541E0b.htmhttp://www.scielo.br/scielo.php?script=sci_arttext&pid=s0104-66382004000300006http://www.watersanitationhygiene.org/References/EH_KEY_REFERENCES?Sanitation/ BioGas/PurificationHullu, J.D. et al. 2008. Comparing different biogas upgrading techniques. Interim Report.Silverio, C.M. Purification of methane from biogas digester and conversion for electricity generation (http://8th-astw.dost.gov.ph/alt_energy/ITDI_BIOGAS.pdf

The scrubbers consist of four units of 8 inches diameterPVC pipes each of 50 liters capacity. It is either packed withsodium hydroxide (NaOH) for the removal of CO2 and iron filingsfor the removal of H2S.

Performance efficiency of the scrubber system is shownin Table 10.

Table 10. Performance efficiency of ITDI scrubber system

CO2 CH4

Heating Value

(BTU/ft3)CO2 CH4

Heating Value

(BTU/ft3)29.1 70.9 695 1.0 99 970 96.530.5 69.5 681 1.5 98.5 965 95.129.1 70.9 695 1.0 99 970 96.540 60 588 0.4 99.6 976 9940 60 588 0.5 99.5 975 9931 69 676 0.2 99.8 978 99.429 71 696 0.1 99.9 979 99.730 70 686 0.5 99.5 975 98.333 67 657 4.5 95.5 936 86.4

Untreated Biogas Treated (Scrubbed) Biogas CO2

Removal Rate (%)


Chapter XBENEFITS FROM

BIOGAS TECHNOLOGYThere are two (2) kinds of benefits that can be derived

from using the biogas system. First are the tangible benefits inwhich we can put money value on it. These include energygeneration and production of feed materials and high qualityfertilizer for crops. In most cases, these benefits are in theform of savings because the amount allocated for the purposewas not spent because of available biogas and its by-products.However, in larger applications, the technology becomes a sourceof income especially when used in producing high quality fertilizer.

The other type of benefit is the intangible benefit whichwe cannot put money value such as promotion of the conservationof natural resources by not cutting trees for firewood, controllingpollution by proper waste disposal, thereby reducing odor, groundand surface water contamination and reduction of greenhousegas emissions. These benefits are more rewarding because manis given the right to live in a fresh, clean and beautifulenvironment.

The generated biogas is a potential energy in which theowner has the option for use. He may use all of it or just part ofit depending on his particular need. The extent of his actual useof biogas will spell out the magnitude of his savings.

The financing support for biogas generation is necessaryfor the success of the system. The investment is capital intensiveat front end but the long term benefits of the technology is

Economic Assessment of DSAC-Model BiogasDigester


worth supporting the development. Borrowed capital can beamortized from the savings enjoyed in the system. The technologylevel or skills necessary to adopt the technology is within thecompetence of the average Filipino farmers. The raw materialfor biogas is agricultural waste but the end products are vital toimproving the quality of life.

To be able to visualize what will happen to our moneyinvested on biogas works, we have to consider all the benefitsderived from the system and evaluate it against the cost ofusing the system.

For our discussion, we will use an 8 cu. m. DSAC-Modelbiogas digester to be used in a piggery project with 30 hogscapacity.

Cost Component of the Biogas System

A. Initial Investment Cost

The investment is the initial capital used in theconstruction and installation of the system, including theexcavation. Investment cost for a 8 cu.m. biogas digester issummarized below.

Item Assumptions Investment Cost

Biogas System P10,000.00/cu.m. P80,000.00 Excavation P450/cu.m. @12.5cu.m. 5,625.00

———————Total P85,625.00

B. Operating Expenses

Operating expenses refer to the amount used inoperating the biogas system which include labor,repair and maintenance, interest on investment and


depreciation. The biogas worker is required to check the systemat least two days per week. If he is paid with P279.50 per day(site basis), then the total labor cost per year is P29,068.00.Annual repair and maintenance is estimated at 3% of the initialinvestment since the digester has no moving parts. The interestrate is 37.92% which is based on the prevailing bank interestrate assuming that the money is loaned. Depreciation cost isestimated using a straight line method and a 25-year life spanof the digester with zero salvage value. Operating expenses issummarized below.

Items Cost

1. Labor P 29,068.002. Repair and Maintenance 2,568.753. Interest on Investment 16,234.504. Depreciation 3,425.00

———————-—Total P 51,296.25

Energy Value of Biogas

a) Fresh manure production = 30 hogs x 3 kgs/day= 90 kgs/day = 90 li/day= 32.85 cu.m. per year

b) Volume of digester required = 90 li/day x 2*= 180 li/day x 40 days RT= 7200 li = 7.2 cu.m.

c) Biogas production = 7.2 cu.m. x 50% (50% methane production) = 3.6 cu.m. per day

= 1,314 cu.m./yr * (1:1 manure-water ratio)


In this case, the volume of digester required is 7.2 cu.m. It isrecommended that we use an 8 cu.m. biogas digester.

d) Equivalent in conventional energy

1 cu.m. of biogas = 3.47 kgs of firewood = 0.45 kg LPG

d.1. firewood = 3.47kg/u.m. biogas x 1,314 cu.m./yr = 4,559.6 kgs/yr

Peso equivalent = P22,798.00

d.2. LPG = 0.45kg/cu.m. biogas x 1,314 cu.m./yr = 591.3 kgs/yr

Peso equivalent = P30,103.00

Since we are evaluating the economic performance of thedigester, we have to consider everything that can be generatedfrom the digester as benefits. We assumed that the family usesbiogas as substitute for either firewood or LPG, and thereforecalculated the value of firewood or LPG saved for a year. Majorityof the society are now using LPG instead of firewood, therefore,we will consider the amount saved from the use of biogas asreplacement for LPG. However, the volume of LPG equivalent ofbiogas produced is very large (equivalent to more than 53 LPGtanks). Therefore, we assumed that only 165 kgs of LPG (15tanks of LPG in a year) are consumed and counted as savings infuel. Other biogas produced are sold to three different neighborsat the rate of half of price of LPG and in assumption that theyare consuming one tank of LPG per month. In this case, thethree neighbors will be paying P280.00 per month for theirbiogas consumption.

Peso equiv =(165 kgs/yr x P50.91/kg)+(P280/mo x 12mo/yr x3 neighbors)

= P18,480.15


The economic value of recovered sludge as feed materials andorganic fertilizer follows the same format of substitution andextent of use. As much as 30% of the feed requirements can besubstituted by sludge and that sufficient organic fertilizer (asmuch as 40%) can be recovered from the digested sludge. In thisexample, we will use 15% feed requirement substitution and 20%organic fertilizer recovery.

e) feed material recoverable from sludgee.1. Total feed consumption of hogs = 18,000 kgs/yre.2. Amount of feed materials to be substituted with sludge (15%) = 2,700 kgs/yre.3. Peso Equivalent (P23/kg) = P62,100

f) Organic fertilizer from sludgef.1. Volume of digested sludge = 32.85cu.m./yrf.2. Organic fertilizer recovered (20%) = 6.57 cu.m./yr

= 6,570 kgs/yrf.3. Peso Equivalent (P5/kg) = P32,850.00f.4. Processing Cost (50%) = P16,425.00f.5. Net Savings/Income = P16,425.00

g) Total Savings/Income = Saving/Income in Energy + Feeds + Fertilizer = P18,480.15 + P62,100 + P16,425.00 = P97,005.15

h) Net Savings = P45,708.90i) Return on Investment = 53.40%j) Payback Period = 1.87 years


Today, recognition of biogas technology as a solution topollution problem is more important than energy recovery.Compliance to environmental regulations and avoidance fromcomplaints of local people are the major drivers influencing theowner to invest in the technology. The economic advantage ofrecovering and using biogas as energy source is just secondaryreason for having a digester.

The widespread acceptance and dissemination of biogastechnology has not yet materialized in the country. One mainreason, often mentioned, is the required high investment capital.But often the reason for failure is the unrealistically highexpectations of potential users. Biogas technology cannot solveevery problem of a farm, a village or a big animal productionunit.

Biogas technology is not a universally accepted technologylike transistor radio. A biogas plant has to fit into existing farming,production or waste disposal systems. Attempts to make thesystem fit to the biogas plant will result in expensive and frustratingfailures. Biogas technology has many competitors. Energy canbe produced by fuelwood plantations (with other positive side-effects), by solar systems, hydro-power and other renewableenergy technologies. Producing high quality fertilizer can bedone in other cheaper way such as composting which are evencloser to traditional techniques. What makes biogas an attractiveoption is the fact that this technology can provide solutions to avariety of problems simultaneously as “waste-treatment facility”and as an “energy-generating device”.

Chapter XIOPPORTUNITIES AND BARRIERS

OF BIOGAS TECHNOLOGY


Barriers in the promotion of biogas technology canbe categorized into three: 1) financial, 2) information, and3) technical. Barriers that fall under the financial aspectare:

- high investment cost- lack of institutional support- limited access to financing schemes- lack of incentives to technology adaptors- lack of local government policies to support

technology promotion in the countryside

Meanwhile, the barriers that fall under the informationaspect are:

- unclear delineation of roles of agency in NRE- technology gap between the users and the

technology itself- poor public image of the technology- inadequate information- absence of a databank

Finally the barriers that fall under the technical aspect are:

- lack of service standards- lack of experiences on technology adoption- lack of service technicians- lack of biogas engineers and contractors

References:______. Biogas Digest Volume 1: Biogas Basics. ISATDilidili, J.Q. et al. 1998. Technology Validation of Biogas Technology and Its Utilization in the Philippines. Terminal Report. CvSU-ANEC.www. adb.org/Clean-Energy/documents/PHI-PFS-Biogas-Swine- Waste.pdf______. 2004. The Philippine Recommends for Agricultural Waste Processing and Management. PCARRD.


Appendices


The study aimed to: utilize digester sludge as feedsubstitute for fattening hogs; determine the effects of substitutingsludge on feed intake, length of fattening period and carcassquality; and determine the optimum level of sludge susbtitutionfor better growth performance of hogs. Completely RandomizedDesign (CRD) was used, with three treatments and tworeplications. The treatments were: T1 = 15% sludge substitution;T2 = 30% sludge substitution; and T3 = control (no sludgesubstitution).

Results of the study revealed that growth and developmentof hogs fed with sludge is comparable to that fed with 100%commercial feeds. Also, the carcass yield of hogs fed withsludge is not significantly different from hogs fed 100% commercialfeeds.

IntroductionEnvironment pollution as a consequence of livestock

production is becoming a serious problem. When animal manureis treated to prevent pollution but not utilized for other purposes,production expenses can increase considerably. At the same time,manure which is considered a renewable natural resource is justwasted. Livestock farming should end up not only at marketingbut should also extend to the utilization of animal wastes.

Appendix AUtilization of Biogas Sludge as

Feed Substitute for Hogs

Abstract

The study was conducted by: C. A. Polinga, J. Q. Dilidili, R. S. Sangalang,E. E. Polinga, R. P. Ararao and R. R. Marasigan - 1996


The development of biogas digester partly solves energyproblems as well as environmental pollution in the country. As aresult of this technology, various studies have been conducted tomaximize the use of the products of biogas technology - thebiogas and the sludge.

The Biogas Research Training Center for Asia and the Pacificin Chengdu, China conducted a study on the supplementation ofanaerobic digested effluent to animal feeds. Although preliminaryfindings indicated a certain degree of acceptance, it is not enoughto easily adopt the technology since some important factors likebreed/variety of pigs, environmental conditions and kind offermentation materials are relative from each locality.

Hence, a verification trial on the use of biogas sludge asfeed supplement for hogs was conducted. It aimed to utilizedigester sludge as feed substitute for hogs; determine the effectsof substituting commercial feeds with sludge on the feed intake,length of fattening period and carcass quality of hogs; anddetermine the optimum level of sludge substitution for bettergrowth performance of hogs.

Six piglets were used in the study. These were dividedinto three test groups and grown-finished for 5 months. Thepiglets in each test group had similar initial weights. The twotest groups received the digester sludge substitute while thelast test group was the control group which received the basicration (100% commercial feeds).

Materials and Methods

A. Experimental Animals


C. Experimental Feeds and Feeding

The biogas digester sludge used in this study was obtainedfrom a 30-m3 biogas plant located at the new piggery projectof the Don Severino Agricultural College (DSAC). ContinuouspH monitoring of the biogas sludge was done everyday duringthe entire duration of the experiment.

Newly gathered sludge was filtered first before beingadded to the animal feeds to eliminate the impurities presentin the sludge.

Sludge was supplemented to the basic feed ration(commercial feed) of the hogs in the two test groups. Thedigester sludge was added to the feed according to the feedconsumption of animals. The first group was fed with highlevel of digester sludge, 30% by weight of feeds, while thesecond test group was fed with medium level of digester sludge,which was 15% by weight of feeds. The control group receivedthe basic feed ration (100 percent of commercial feeds). Thetype of commercial feed given to the two test groups wasexactly the same with that of the control group. Wet feedingmethod was followed since pigs do better on wet feed than ondry feed (Cullision, 1987). The animals were fed twice a day,in the morning and in the afternoon.

B. Biogas Digester Sludge

D. Data Gathered

The following data were gathered: monthly liveweight(kg), liveweight gain (kg), daily consumption (kg) of theanimals, feed conversion efficiency (%) of the animals, andthe pH value of the gas produced.


Gain in weight (kg) was computed using the formula:

GW = W2-W1 where:

GW = gain in weight, kg W1= weight of the animal in the previous month, kg

Feed Conversion Efficiency was computed using the formula:

GWFCE= x 100

FCwhere: FCE = feed conversion efficiency, % GW= gain in weight, kg FC = feed consumption of the animal during that

month, kg

Carcass quality was expressed in terms of slaughter weight(kg), carcass weight (kg), dressing percentage, carcass length(cm), and backfat thickness (cm).

Dressing percentage was computed using the formula:

carcass weight Dressing Percentage = x 100

slaughter weight

Carcass length was measured from the shoulder of the hogto the end of its ham. Backfat thickness was determined byusing a ruler. This was measured in three points of the hog’sback: one in the midline and the other two, each 1 1/2 to 2inches (3.8 - 5.0 cm) from the midline to front or rear.


E. Results and Discussion

Gain in Weight

The monthly average weight and gain in weight of theanimals are shown in Tables 1 and 2.

The results indicated that the growth response of the animalsfed with sludge as feed substitute is as normal as the animals fedwith basic ration of 100 percent commmercial feeds.

There were no significant differences (P>0.01) amongtreatments. The result implies that hog raisers can substitute15 to 30 percent of the feed requirements with biogas sludge.This is tantamount to 15 to 30 percent savings in feeds withoutaffecting the growth and development of the animals and willeventually result in a 15 to 30 percent additional income.

The data gathered were subjected to Analysis of Variance.Means were compared using Duncan’s Multiple Range Test (Gomezand Gomez, 1976).

Table 1. Monthly average weight of hogs given diets partly substituted with biogas digester sludge, kg

Age, months Control15% 30%

Initial weight 18.00 20.50 16.001 30.25 32.50 28.502 41.40 42.90 39.453 58.30 60.25 57.104 77.05 81.70 80.955 90.60 92.00 91.00

Treatment


Carcass Quality

The summary of carcass quality evaluation is shown inTable 4. The hogs given diets substituted with sludge gavecomparable carcass quality to that of hogs fed with the basicration of 100 percent commercial feeds.

Feed Conversion Efficiency

The feed conversion efficiency was observed in hogs fedwith 100 percent commercial feeds, although it was notsignificantly different (P>0.01) from the other treatments.This was followed by hogs fed with 15 percent sludge substituteand the least was on hogs fed with 30 percent sludgesubstitute with 24.53 and 24.16 percent, respectively.

Table 2. Monthly average gain in weight of hogs given diets partly substituted with biogas digester sludge, kg

Table 3. Mean feed conversion efficiency of hogs given diets partly substituted with biogas digester sludge, %

Age, months Contro l15% 30%

1 12.25 12.00 12.502 11.15 10.40 10.953 16.90 17.35 17.654 18.75 21.50 23.855 12.95 10.30 10.05

Treatm ent

Treatment Total Mean1 2

1 12.25 12.00 12.50 24.532 11.15 10.40 10.95 24.163 16.90 17.35 17.65 26.22

Replication


Conclusion

Based from the results obtained, it is concluded thatsusbtituting sludge to the feed ration of hogs has no adverseeffect on their growth and development. Likewise, the substitionof 30 percent sludge (by weight of feeds) to the feed ration ofhogs gives a desirable result since the amount of commercialfeeds that would be consumed by hogs would be lessened by asmuch as 30 percent. Finally, the results proved that the sludgecould substitute the necessary feed and nutrient requirement ofhogs.

Recommendations

Based from the results, the following are highlyrecommended: substitution of sludge to the feed ration of hogsat the amount of 30% by weight of feeds; further study on theutilization of sludge as feed substitute of hogs using higher levelsto test the maximum level at which the animal would gain betterperformance; and study on the utilization of sludge to thefeedstuff of other farm animals.

Table 4. Summary of carcass quality evaluation of hogs given diets partly substituted with biogas digester sludge


Appendix BWellisa Farms

Waste to Energy ProjectIt is common knowledge that majority of farms

(commercial as well as backyard) in the Philippines lack properwaste treatment facilities. This is a complex problem whenthe total number of pigs consumed per year is around 12 millionheads. This amounts contributed to severe contamination ofsurface and groundwater resources, besides air and land pollutionissues. Wellisa Farm in Tayud, Consolacion, Province of Cebu, isan exception to this situation in terms of waste managementas well as energy utilization.

The farm is owned and operated by Mr. WellingtonChanlim, a leading entrepreneur in the agro-production (hograising and poultry) industry in Cebu. Although the mainoperation is based in Bantayan Island (situated in thenorthernmost tip of Cebu Province), the Tayud Farm caters tothe small and medium retailers of the municipality and the city.

As one of the wholesale buyers of eggs in Bantayan,Wellisa Farms trades on an average of over 2 million eggs perweek which are transported from the island of Bantayan toCebu. These eggs are transported in egg-trays made of paperpulp compared to the plastic trays being used in other parts ofthe country. The project is being nominated for the category“Renewable Energy for Non-power Application” to demonstrateto the hog raising industry that tapping the waste can providethe energy revenue streams for the project. The projectdemonstrates a clear example of environmental and economicsustainability.


Biogas digester system

A settling pond is installed after the outlet portion of thedigesters to settle suspended solids regularly discharged where itis collected and dried for fertilizer use. On the last division ofthe settling pond, a water pump is installed to pump the waterback to the piggery building for cleaning and flushing the pens.

Settling Pond System

Biogas Digester System

The Biogas Digester System installed at Wellisa Farm isthe fixed-dome type Chinese model digester. This design wastaken from the Biogas Research and Training Center (BRTC), inChengdu, PROC and was introduced and popularized by Universityof San Carlos - Affiliated Nonconventional Energy Center (USC-ANEC) in the provinces of Cebu and Bohol. The system consistsof four (4) concrete digesters of 100.0 cu.m. each, batch fedwith an average retention time (RT) of 14 days per digester.


Settling pond system

Cleaning of pens using effluent


Gas Collection System

Each digester produces an average of 250-280 cu.m. ofgas per day on pig manure alone. However, when chicken dung(fresh) was added into the feed material, the digesters wereable to generate 300-350 cu.m. of gas per digester (1.0-1.5cu.m. per digester volume) for a total of 1,200 to 1,400 cu.m.daily gas production. Since gas is generated on an hourly basis,biogas coming from the digester is piped and stored in gascollectors. In the farm, four (4) 30.0 cu.m. cylindrical steel gascollectors are placed over a cylindrical concrete water tank toensure a steady supply of gas for use in the farm. As gas isbeing utilized and consumed, the tanks lower itself to the waterseal tank and rises to its maximum level and height as it is beingrefilled. This type of gas collecting increases gas pressure by asmuch as 8kpa which is the working pressure for most gas fueledequipment.

Gas collection system


Fertilizer System

Most of the manpower assigned in the facility areconcentrated in the scooping and drying of digested sludge whichin itself is an enterprise. Workers assigned in the sludge collectionget additional compensation of P4.00 for every sack of driedsludge they collect everyday. On the average 20-25 sacks (40.0kg) are collected and dried per day. Dried sludge is then mixedwith processed chicken dung to balance the potassium andphosphorus requirement (chicken dung is high in nitrogen butlow in K, P) and bagged. The organic fertilizer, under the brandname DURABLOOM, is commercially sold at an average of P200.00per sack and now getting its share of the market. At present,Wellisa Farm Tayud disposes an average of 20,000 bags permonth in the Visayas Region alone.

A worker making organic fertilizer


Egg-tray processing

The pulp molding system used a Silfurton machine thatwas procured by Wellisa Farms to support its demand for egg-trays to deliver eggs from Bantayan to Cebu. The system producesan average of 20,000 pieces of paper pulp egg-trays per day.Most of this is consumed by Wellisa Farms. However, the projecthas reduced the dependency on egg-trays bought commerciallyat a price of Php 3.00 per piece and has reduced the cost pertray by almost 50%.

Pulp Moulding System


Use of Resources (including Power and Energy)The system resource consumption is summarized as:

Biogas Digester and Farm Operations:

Electric Consumption : 30kwDigester Volume : 4x100 cubic meterFeeding material : 10 cubic meter of chicken dung

and pig manureGas Production : 1000 cubic meter per dayHeating Value : 5500 kcal/cubic meterRecycled water for washing of pigs : 20,000 liters per day

Paper Pulp Molding Machine:

Electric Consumption : 75kwThermal Consumption: 600 liters of diesel or

1000 cubic meter of biogasWaste paper consumption: 2000 kg per day

The total electric consumption of around 125kw (peak) isbeing evaluated to be generated using a biogas engine or otherappropriate technology (using biogas) to eliminate the dependencyon the grid power. Government financial intervention is beingconsidered for this project. As there is no envisioned shortageof gas from the waste stream (as supported by the operationsfor the past two years) this option is not considered. Themaintenance of the biogas digester system is done in batchesand does not affect the continuous operations of the system.

There is also no change in the supply conditions for recyclednewsprint which ensures timely delivery and stable costs.


The project aims to mitigate and enhance the followingenvironmental impacts:

Thermal Energy, the biggest environmental impact perhapsis the fuel switch from diesel to biogas. Prior to the developmentof the biogas system the thermal consumption for the paper pulpmolding machine was around 600 liters of diesel fuel each day.This has been replaced by 1000 cubic meter of biogas. This alsosaves the daily logistics problems of transporting the diesel andrefueling activities. The annual saving on diesel fuel is estimatedat 1200 barrels or 200 liters.

Water Pollution: Most pig farms as well as chicken farmsall over the world are confronted with the issue of meetingcompliance standards for waste water discharge. All over thePhilippines this problem is evidenced by the water quality withinthe river systems in major hog raising municipalities. WellisaFarms, Tayud has demostrated that operations of a piggery canmitigate and manage the water polutions concerns if appropriatewaste management systems are installed and maintained.

Air Pollution: The multi-stakeholder approach involvingthe local community and the Department of Environment andNatural Resources will attest to the improvement in the air qualityat Wellisa Farms, Tayud. The operations are free of the odorthat is common in most piggery operations.

Land Pollution: The use of settling ponds and the solidseparation for organic fertilizer has mitigated the land pollutionthat would be caused by lagoons which is the common practice inthe industry.

Environmental Impact


Also the application of organic fertilizer will replace theusage of chemical fertilizers that pollute the land and water overa period of time. An average of 600 bags (40kgs each) oforganic fertilizer is manufactured per month. Also the use ofpaper egg-trays as compared to plastic egg trays.

Water Recycling: The project recycles on an averageabout 20,000 liters of water each day. The system is almost aclosed loop with very little water being pumped from thegroundwater on a daily basis. Thus the scarce groundwaterresource at Tayud is available for other users within the area.

Paper Recycling: The project recycles on an average of2000 kgs of used newspapers, cartons and other paper materialsthat are purchased from recyclers. This amounts to an annualrecycling of 720 tons of paper.

The successful operation of the project provides livelihoodfor the 30 laborers who are also encouraged to make additionalincome through the production of organic fertilizer. Most of themanpower assigned in the sludge collection get an additionalcompensation for every sack of dried sludge they collect everyday.The success of the project has encouraged the owners to ventureinto much larger project involving paper pulp molding using biogas.This will certainly put Cebu on the global map as a manufacturerof high quality, low priced paper pulp products. The outcome ofsuch project will certainly have an economic impact not only ona local level but also on a regional level.

Source: 2006 Green-E Awards Application. Category-Renewable Energy forNon-Power Application. Nominated by Solution Using Renewable Energy Inc.(SURE).

Contribution to the Local Economy


Appendix CBiogas Experts/Contractors/Suppliers in the Philippines


Source: Technology Validation of Biogas Technology and Its Utilization in the Philippines:Terminal Report, CvSU-ANEC.


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Biogas Book 111711

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