Anaerobic Treatment of Industrial waste water

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Anaerobic Treatment of

Industrial Wastewater

BioE 202 Iowa State University



Anaerobic Waste Treatment : An Overview

Historical development

Mainly used for reducing mass of high solids wastes, e.g. human waste(nightsoil), animal manure, agricultural waste and sludge.

Early applications of anaerobic waste treatment include:

• Mouras automatic scavenger - cited in French journal Cosmos in 1881• Septic tank- developed by Donald Cameron in 1895 (England)• Imhoff tank: developed by Karl Imhoff in 1905 (Germany)



Popularity of anaerobic processes

Energy crisis in 70 and 80’s- a renewed interest in anaerobic process

0

200

400

600

800

1000

1200

1 9 7 8

1 9 8 1

1 9 8 4

1 9 8 7

1 9 9 0

1 9 9 3

1 9 9 6

1 9 9 9

N o . o f p l a n

t s

Anaerobic treatment plants for industrial applications (Source: Franklin, 2001)



Anaerobic treatment within wastewater processing

Domestic wastewater (100)

Preliminary treatmentBar screen, ComminutorGrit chamber etc.

Primary sedimentation

(100)

Primary sludge(35)

Aerobic treatment

(65)

e.g. Activated sludge,Trickling filter, RBC

Secondary sedimentation

Oxidized to CO2 (30)Converted to sludge (35)

Secondary sludge(25)

Effluent (10)

Anaerobic digester(60)



Anaerobic treatment of solids

How do we achieve high SRT in anaerobic treatment systems?

Anaerobic treatment of high solids such as animal manure, biologicalsludge, nightsoil, etc. is commonly known as “anaerobic digestion” andis carried out in airtight container known as an anaerobic digester (AD).

AD is usually a continuous flow stirred tank

reactor (CFSTR) for which HRT ~ SRT

Design based on volatile solids (VS) loading rate

Anaerobic treatment of wastewaters requires along SRT to achieve better treatment efficiency

The ratio of SRT/HRT ~ 10-100

The high ratio allows the slow-growing methanogens to remainin the reactor for a longer time



Anaerobic Waste Treatment

Anaerobic treatment is a biological process carried out in the absenceof O2 for the stabilization of organic materials by conversion to CH4 and inorganic end-products such as CO2 and NH3

Organic materials + Nutrients CH 4 + CO 2 +NH 3 + Biomass Anaerobic microbes

Anaerobic processes

Anaerobic fermentation Anaerobic respiration



Anaerobic fermentation

In anaerobic fermentation, there is no external electron acceptor.

The product generated during the process accepts the electronsreleased during the breakdown of organic matter. Thus, organicmatter acts as both electron donor and acceptor. The processreleases less energy and the major portion of the energy is still

contained in the fermentative product such as ethanol.

Glucose Pyruvate

Energy

Electron

Ethanol

Anaerobic fermentation of glucose to ethanol



Anaerobic respiration

Anaerobic respiration on the other hand requires external electron

acceptor. The electron acceptors in this case could be SO42-, NO3- or CO2. The energy released under such a condition is higherthan anaerobic fermentation.

Glucose Pyruvate

Energy

Electron

CO2 + H2O

SO42-

CO2NO3

-

H2S

CH4

N2

Anaerobic respiration of glucose, preference for electron acceptors

O2 > NO3-

> SO42-

> CO2



Advantage of anaerobic processes

1. Less energy requirement as no aeration is needed0.5-0.75 kWh energy is needed for every 1 kg of COD removal by aerobic processes

2. Energy generation in the form of methane gas

1.16 kWh energy is produced for every 1 kg of COD fermented in anaerobic process

3. Less biomass (sludge) generation

Anaerobic process produces only 20% of sludge compared with aerobic process

Soluble BOD1 kg

Aerobic process

CO2 + H2O

0.5 kg

New biomass

0.5 kg

Biodegradable

COD

1 kg

Anaerobic process

CH4 gas

> 0.9 kg

New biomass

< 0.1 kg



4. Less nutrients (N & P) requiredLower biomass synthesis rate also implies less nutrients requirement : 20% of aerobic

5. Application of higher organic loading rate

Organic loading rates of 5-10 times higher than that of aerobic processes are possible

6. Space saving

Higher loading rates require smaller reactor volumes thereby saving on disposal cost

7. Ability to transform several hazardous solventsincluding chloroform, trichloroethylene and trichloroethane to an easily degradable form

…Advantages of anaerobic processes



Limitations of anaerobic processes

1. Long start-up time

Because of lower biomass synthesis rate, it requires a longer start-up time to attain a biomass concentration

2. Long recovery time

If an anaerobic system is subjected to disturbances either due to biomass wash-out, toxic substances or shock loading, it may take longer time for the system to return to normal operating conditions

3. Specific nutrients/trace metal requirements

Anaerobic microorganisms, especially methanogens, have specific nutrients

e.g. Fe, Ni, and Co requirement for optimum growth

4. More susceptible to changes in environmental conditions

Anaerobic microorganisms especially methanogens are prone to changes in conditions such as temperature, pH, redox potential, etc.



5. Treatment of sulfate-rich wastewater

The presence of sulfate not only reduces the methane yield due to substrate Competition, but also inhibits the methanogens due to sulfide production

6. Effluent quality of treated wastewater

The minimum substrate concentration (S min ) from which microorganisms are able

to generate energy for their growth and maintenance is much higher for anaerobic treatment systems. Anaerobic processes may not be able to degrade organic matter to the level to meet the discharge limits for ultimate disposal.

7. Treatment of high protein & nitrogen containing wastewater

The anaerobic degradation of proteins produces amines which are no longer be degraded anaerobically. Similarly nitrogen remains unchanged during anaerobic treatment. Recently, a process called ANAMMOX ( ANaerobic AMMonium OXididation) has been developed to anaerobically oxidize NH 4

+ to N 2 in presence of nitrite.

NH 4 + + NO 2

- N 2 + 2H 2 O

…Limitations of anaerobic processes

NH4+ + 1.32 NO2

- + 0.066CO2 + 0.13H+ 1.02 N2 + 0.26NO3- + 0.066CH2O0.5N0.15



Comparison between anaerobic and aerobic processes

Anaerobic AerobicOrganic loading rate

High loading rates:10-40 kg COD/m3-day Low loading rates:0.5-1.5 kg COD/m3-day

(for high rate reactors, e.g. AF,UASB, E/FBR) (for activated sludge process)

Biomass yield

Low biomass yield:0.05-0.15 kg VSS/kg COD High biomass yield:0.35-0.45 kg VSS/kg COD

(biomass yield is not constant but dependson types of substrates metabolized)

(biomass yield is fairly constant irrespectiveof types of substrates metabolized)

Specific substrate utilization rate

High rate: 0.75-1.5 kg COD/kg VSS-day Low rate: 0.15-0.75 kg COD/kg VSS-day

Start-up time

Long start-up: 1-2 months for mesophilic

: 2-3 months for thermophilic

Short start-up: 1-2 weeks



Anaerobic AerobicSRT

Longer SRT is essential to retain the slowgrowing methanogens within the reactor

Microbiology

Anaerobic processes involve multi-stepchemical conversions and a diversegroup of microorganisms degrade theorganic matter in a sequential order

Aerobic process is mainly a one-species phenomenon, except fornutrient-removal processes

Environmental factors

The process is highly susceptible tochanges in environmental conditions

SRT of 4-10 days is enough for theactivated sludge process

The process is more robust tochanging environmental conditions

Comparison between anaerobic and aerobic processes



How much methane gas can be generated through complete anaerobic degradation of 1 kg COD at STP ?

Step 2: Conversion of CH 4 mass to equivalent volume

Based on the ideal gas law, 1 mole of any gas at STP (Standard Temperature

and Pressure) occupies a volume of 22.4 L 1 Mole CH4 ~ 22.4 L CH4 16 g CH4 ~ 22.4 L CH4 1 g CH4 ~ 22.4/16 = 1.4 L CH4 ---------- (2)

Step 1: Calculation of COD equivalence of CH 4 CH4 + 2O2 CO2 + 2H2O 16 g 64g

16 g CH4

~ 64 g O2

(COD) 1 g CH4 ~ 64/16 = 4 g COD ------------ (1)



Step 3: CH 4 generation rate per unit of COD removed

From eq. (1) and eq. (2), we have, => 1 g CH4 ~ 4 g COD ~ 1.4 L CH4 => 4 g COD ~ 1.4 L CH4 => 1 g COD ~ 1.4/4 = 0.35 LCH4

or 1 Kg COD ~ 0.35 m3 CH4 ----------- (3)

Complete anaerobic degradation of 1 kg COD produces 0.35 m 3 CH 4 at STP



MethaneCarbon dioxide

COMPLEX ORGANIC MATTER

Proteins Carbohydrates Lipids

Amino Acids, Sugars Fatty Acids, Alcohols h y d r o l y s i s

INTERMEDIARY PRODUCTS(C>2; Propionate, Butyrate etc) a

c i d o

g e n e s i s

Acetate Hydrogen, Carbon dioxide

a c e t o g e n e s i s

Organics Conversion in Anaerobic Systems

m e

t h a n o g e n e s i s

72 28



Homoacetogenes (3)

Homoacetogenesis has gained much attention in recent yearsin anaerobic processes due to its final product: acetate, whichis the important precursor to methane generation.The bacteria are, H2 and CO2 users. Clostridium aceticum and Acetobacterium woodii are the two homoacetogenic bacteria

isolated from the sewage sludge.

Homoacetogenic bacteria have a high thermodynamicefficiency; as a result there is no accumulation H2 and CO2

during growth on multi-carbon compounds.

CO2 + H2 CH3COOH + 2H2O



Methanogens (4 and 5)

Methanogens are unique domain of microbes classified as Archeae, distinguished from Bacteria by a number of characteristics, includingthe possession of membrane lipids, absence of the basic cellularcharacteristics (e. g. peptidoglycan) and distinctive ribosomal RNA.Methanogens are obligate anaerobes and considered as a rate-limiting

species in anaerobic treatment of wastewater. Moreover, methanogensco-exist or compete with sulfate-reducing bacteria for thesubstrates in anaerobic treatment of sulfate-laden wastewater.

Two classes of methanogens that metabolize acetate to methane are:

• Methanosaeta (old name Methanothrix ): Rod shape, low K s, high affinity

• Methanosarcina (also known as M. mazei ): Spherical shape, high K s,low affinity



Methanosaeta Methanosarcina

Growth kinetics of Methanosaeta andMethanosarcina



Essential conditions for efficient anaerobic treatment

• Enough nutrients (N & P) and trace metals especially, Fe, Co, Ni, etc.COD:N:P = 350:7:1 (for highly loaded system) 1000:7:1 (lightlyloaded system)

• Avoid excessive air/O2

exposure

• No toxic/inhibitory compounds present in the influent

• Maintain pH between 6.8 –7.2

• Sufficient alkalinity present (mainly bicarbonates)

• Low volatile fatty acids (VFAs)

• Temperature around mesophilic range (30-38 oC)

• SRT/HRT >>1 (use high rate anaerobic reactors)



Best industrial wastewaters for anaerobic treatment

• Alcohol production

• Brewery and Winery

• Sugar processing

• Starch (barley, corn, potato, wheat, tapioca) and desizing

waste from textile industry.

• Food processing

• Bakery plant

• Pulp and paper

• Dairy

• Slaughterhouse

• Petrochemical waste



Environmental factors

The successful operation of anaerobic reactor depends on maintainingthe environmental factors close to the comfort of the microorganismsinvolved in the process.

Temperature

Anaerobic processes like other biological processesoperate in certain temperature ranges

In anaerobic systems: three optimal temperature ranges:

Psychrophilic (5 - 15o

C) Mesophilic (35 – 40 C)

Thermophilic (50-55 oC)



Effect of temperature on anaerobic activity

Rule of thumb: Rate of a reaction doubles for every 10 oC

rise in temperature up to an optimum and then declines rapidly



pH

There exist two microbial domains in terms of pH optima namely

acidogens and methanogens. The best pH range for acidogens is 5.5 – 6.5 and for methanogens is 7.8 – 8.2. The operating pH for combinedcultures is 6.8-7.4 with neutral pH being the optimum. Since methano-genesis is considered as a rate limiting step, it is necessary to maintainthe reactor pH close to neutral.

Low pH reduces the activity of methanogens causing accumulation of VFA and H2. At higher partial pressure of H2, propionic acid degradingbacteria will be severely inhibited thereby causing excessive accumulationof higher molecular weight VFAs such as propionic and butyric acids andthe pH drops further. If the situation is left uncorrected, the process may

eventually fail. This condition is known as going “SOUR” or STUCK”. Remedial measures: Reduce the loading rates and supplementchemicals to adjust the pH: alkaline chemicals such as NaHCO3, NaOH,Na2CO3, quick lime (CaO), slaked lime [Ca(OH)2], limestone (orsoftening sludge) CaCO3, and NH3 can be used.



Cont..

Relative activity of methanogens to pH

0.0

0.3

0.5

0.8

1.0

1.3

3 4 5 6 7 8 9 10 11

pH

A c t i v i t y

pH dependence of methanogens



An anaerobic treatment system has its own buffering capacity against

pH drop because of alkalinity produced during waste treatment: e.g.the degradation of protein present in the waste releases NH3, whichreacts with CO2 forming ammonium carbonate as alkalinity.

NH 3 + H 2 O + CO 2 NH 4 HCO 3

The degradation of salt of fatty acids may produce some alkalinity.

CH 3 COONa + H 2 O CH 4 + NaHCO 3

Sulfate and sulfite reduction also generate alkalinity.

CH 3 COO - + SO 4 2- HS - + HCO 3 - + 3H 2 O When pH starts to drop due to VFA accumulation, the alkalinitypresent within the system neutralizes the acid and prevents furtherdrop in pH. If the alkalinity is not enough to buffer the system pH,

we need external additions.

Cont..Natural buffering



All microbial processes including anaerobic require macro (N, P andS) and micro (trace metals) nutrients in sufficient concentration to

support biomass synthesis. Anaerobic micro-organisms, especiallymethanogens, have specific requirements of trace metals such asNi, Co, Fe, Mo, Se etc. The nutrients and trace metals requirementsfor anaerobic process are much lower as only 4 - 10% of the CODremoved is converted to biomass.

Nutrients and trace metals

Inhibition/Toxicity The toxicity is caused by substances present in the influent wasteor byproducts of metabolic activities. Heavy metals, halogenatedcompounds, and cyanide are examples of the former type whereassulfide and VFAs belong to latter . Ammonia from either group

Cont..

COD:N:P = 350:7:1 (for highly loaded system) 1000:7:1(lightly loaded system)



Anaerobic contact process (ACP)

Influent Effluent

Waste sludgeRecycled sludge

Completely mixedreactor

Biogas

Degassifier

Biogas

Settling tank

Anaerobic contact process is essentially an anaerobic activated

sludge process. It consists of a completely mixed reactor followedby a settling tank. The settled biomass is recycled back to thereactor. Hence ACP is able to maintain high concentration of biomass in the reactor and thus high SRT irrespective of HRT.

Degasifier allows the removal of biogas bubbles (CO2, CH4)attached to sludge which may otherwise float to the surface..



ACP was initially developed for the treatment of dilutewastewater such as meat packing plant which had tendencyto form a settleable flocs. ACP is suitable for the treatmentof wastewater containing suspended solids which render

the microorganisms to attach and form settleable flocs.

The biomass concentration in the reactor ranges from 4-6 g/Lwith maximum concentration as high as 25-30 g/L depending

on settleability of sludge. The loading rate ranges from 0.5 – 10 kg COD/m3-day. The required SRT could be maintained bycontrolling the recycle rate similar to activated sludge process.

Cont..

…Anaerobic contact process (ACP)



Anaerobic filter

• Developed by Young and McCarty in the late 1960s totreat dilute soluble organic wastes

• The filter was filled with rocks similar to the trickling filter• Wastewater distributed across the bottom and the flow wasin the upward direction through a bed of rocks

• Whole filter submerged completely

• Anaerobic microorganisms accumulate within voids of media(rocks or other plastic media)

• The media retain or hold the active biomass within the filter

• The non-attached biomass within the interstices forms bigger

flocs of granular shape due to rising gas bubble/liquid

• Non-attached biomass contributes significantly to waste treatment

• Attached biomass not be a major portion of total biomass

• 64% attached and 36% non-attached



Feeding tank at 4oC

Biogas

Effluent

Peristaltic pump

Media

Perforated Al plate Sampling

port

Heater

Constant temperaturerecirculation line

Water bath

Peristaltic pump

Sludge wastage

Upflow Anaerobic Filter



Originally, rocks were employed as packing medium inanaerobic filter. But due to very low void volume (40-50%),serious clogging problems were witnessed. Now, manysynthetic packing media are made up of plastics; ceramic tilesof different configuration have been used in anaerobic filters.

The void volume in these media ranges from 85-95 %.Moreover, these media provide high specific surface area,typically 100 m2 /m3, or above, which enhances biofilm growth.

Cont..

Anaerobic Filter Packing



Downflow anaerobic filters are similar to a trickling filter inoperation. DAF is closer to fixed film reactor as loosely held

biomass/sludge within the void spaces is potentially washedout of the reactor. The specific surface area of media is moreimportant in DAF than UAF.There is less of a clogging problem and wastewater with some

SS concentration can be treated using DAF.

Downflow anaerobic filter (DAF)

Cont..

Since anaerobic filters are able to retain high biomass, a longSRT can be maintained. Typically HRT varies from 0.5 – 4 daysand the loading rates vary from 5 - 15 kg COD/m3-day. Biomasswastage is generally not needed and hydrodynamic conditionsplay an important role in biomass retention within the void space.

Anaerobic Filters



Upflow Anaerobic Sludge Blanket (UASB)

UASB was developed in 1970s by Lettinga in the Netherlands.

UASB is essentially a suspended growth system in which properhydraulic and organic loading rate is maintained in order tofacilitate the dense biomass aggregation known as granulation.The size of granules is about 1-3 mm diameter. Since granules

are bigger in size and heavier, they will settle down and beretained within the reactor. The concentration of biomass in thereactor may become as high as 50 g/L. Thus a very high SRTcan be achieved even at a very low HRT of 4 hours.

The granules consist of hydrolytic bacteria, acidogen/acetogensand methanogens. Carbohydrate degrading granules showlayered structure with a surface layer of hydrolytic/fermentativeacidogens. A mid-layer comprising of syntrophic colonies andan interior with acetogenic methanogens.

UASB R t



Effluent

Influent

biogas

UASB Reactor



When the waste contains sulfate, part of COD is diverted tosulfate reduction and thus total COD available for methaneproduction would be reduced greatly.

Effect of sulfate on methane production

Sulfide will also impose toxicity on methanogens at aconcentration of 50 to 250 mg/L as free sulfide.



8e +8H+ + SO42- S2- + 4H2O

• COD/SO42- ~ 0.67

8e +8H+ + 2O2 4H2O

2O 2 / SO 4 2- = 64/96 ~ 0.67

Theoretically, 1 g of COD is needed to reduce 1.5 g of sulfate

Stoichiometry of sulfate reduction



Example 2

A UASB reactor has been employed to treat food processing

wastewater at 20oC. The flow rate is 2 m3 /day with a mean solubleCOD of 7,000 mg/L. Calculate the maximum CH4 generation rate inm3 /day. What would be the biogas generation rate at 85% CODremoval efficiency and 10% of the removed COD is utilized for biomasssynthesis. The mean CH4 content of biogas is 80%. If the wastewater

contains 2.0 g/L sulfate, theoretically how much CH4 could begenerated?

Solution:

Maximum CH4 generation rate:

The complete degradation of organic matter in the waste couldonly lead to maximum methane generation and is also regardedas theoretical methane generation rate.



(7000 x 10-6)

Total COD removed = ----------------- x (2) kg/d (10-3)

= 14 kg/d From eq. (3) in example 1, we have

1 Kg COD produces 0.35 m3 CH4 at STP 14 Kg COD produces ~ 0.35 x 14 = 4.9 m

3

CH4/d at STP

At 20C, the CH4 gas generation = 4.9 x(293/273) = 5.3 m3/d

The maximum CH4 generation rate = 5.3 m3/d

Cont..

:



Cont..

As 10% of the removed COD has been utilized for biomass synthesisremaining 90% of the removed COD has thus been converted to CH4 gas. COD utilized for CH4 generation = 11.9 x 0.9 kg/d

= 10.71 kg/d From eq. (3) in example 1, we have:

1 Kg COD produces 0.35 m3 CH4 at STP 10.71 Kg COD produces ~ 0.35 x 10.71 = 3.75 m3 CH4/d at STP At 20C, the CH4 gas generation = 3.75 x (293/273)

= 4.02 m3/d

The bio-gas generation rate is larger as it also contains CO2 and H2S4C.02/0.80= 5.03 m3/d



When the waste contains sulfate, part of COD is diverted tosulfate reduction and thus total COD available for methaneproduction would be reduced greatly.

Sulfate-reducing bacteria Organic matter + Nutrients + SO 4

2- H 2 S + H 2 O + HCO 3 - + New biomass

Theoretically, 1 g COD is required for reduction of 1.5 g sulfate.In this problem, there is 2 g/L sulfate.

Total COD consumed in sulfate reduction = 1.33g = 1330 mg

COD available for methane production = (7000 –1330) mg/L= 5670 mg/L

Methane generation rate when sulfate is present

Cont..



Cont..(5666.67 x 10-6)

Total COD available = ----------------- x (2) kg/d for CH4 generation (10-3)

= 11.33 kg/d From eq. (3) in example 1, we have: 1 kg COD produces 0.35 m3 CH4 at STP 11.33 kg COD produces ~ 0.35 x 11.33 = 3.97m3 CH4/d at STP At 20C, the CH4 gas generation = 3.97 x(293/273) = 4.3 m3/dThe CH4 generation rate when sulfate is present = 4.3 m3/d

Presence of sulfate reduces methane yield by about 19%

However, total biogas will now contain more H 2 S, adding volume

Cont..

Expanded bed reactor (EBR)



Expanded bed reactor (EBR)

• Expanded bed reactor is an attached growthsystem with some suspended biomass.

• The biomass gets attached on bio-carriers

such as sandman, pulverized polyvinylchloride, shredded tire beads.

• The bio-carriers are expanded by the upflow

velocity of influent wastewater and recirculated effluent.

• In the expanded bed reactor, sufficient upflowvelocity is maintained to expand the bed by 15-30%.

• The expanded bed reactor has less cloggingproblems and better substrate diffusion within thebiofilm.

• The biocarriers are partly supported by fluid flowand partly by contact with adjacent biocarriers, which

retain the same relative position within the bed.



H b id t UASB/AF



Hybrid system: UASB/AF

Hybrid system incorporates both

granular sludge blanket (bottom)and anaerobic filter (top). Suchapproach prevents wash-out of biomass from the reactor. Further

additional treatment at the top beddue to the retention of sludgegranules that escaped from thebottom sludge bed.

UASB reactor facing a chronic sludgewash-out problem can be retrofittedusing this approach.

Hybrid system may be any combi-

nation of two types of reactor

Anaerobic baffled reactor



Biogas

Sludge

Anaerobic baffled reactor

In anaerobic baffled reactor, the wastewater passes overand under the baffles. The biomass accumulates inBetween the baffles which may in fact form granules withtime. The baffles present the horizontal movement of of biomass in the reactor. Hence a high concentration of biomass can be maintained within the reactor.



SETTLE DECANT FEED REACT

SETTLED

BIOMASS

SUPERNATANT

DECANTPORTS

BIOGAS RECYCLE

EFFLUENT FEED

BIOGAS

Anaerobic Sequential Bed Reactor



So and Q can be measured easily and are

known upfront

VOLR can be selected!

How do we select VOLR?

Conducting a pilot scale studies

Find out removal efficiency at different VOLRs

Select VOLR based on desired efficiency

VOLR

E f f i c i e n c y ,

%



Design based on hydraulic loading rate

V = a . Q

a . Q

A = --------

H

H : Reactor height (m)

a : Allowable hydraulic retention time (hr)

Q : Wastewater flow rate (m3/h)

A : Surface area of the reactor (m2)

Permissible superficial velocity (V a)

V a = H/ For dilute wastewater with

COD < 1,000 mg/L



Solids retention time (SRT)

An anaerobic digester is a completely mixed reactor for which solidretention time(SRT) and hydraulic retention time (HRT) is the same.

V, m3

Influent flow rate(Q), m3 /day

HRT, days =

Volume V (m3)= day

Flow rate Q (m3 /day)

For a given SRT (HRT), the size of reactor can beeasily determined since flow rate (Q) is known to us

Digester volume, V (m

3

) = Flow rate (Q) x SRT (

C )



Volatile solids loading rate

The size of an anaerobic digester can also be estimated basedon volatile solids loading rate expressed as kg VS/m3-day.

V, m3

Influent VSkg/day

Volatile solidsloading rate,

(kg VS/m3- day)

Influent VS (kg/day)

Reactor volume (m3)

=

For a given volatile solids loading rate, the size of reactor canbe easily determined since influent VS (kg/day) is known to us.

Influent VS (kg/day)

Digester volume, V (m3) =

Volatile solids loading rate,(kg VS/m3

- day)



Green cow power



What happens to the left-overs?

Common misconceptions about anaerobic digesters include that anaerobic

digestion and the resulting biogas production will reduce the quantity of manureand the amount of nutrients that remain for utilization or disposal. An anaerobicdigester DOES NOT MAKE MANURE DISAPPEAR! Often the volume of material(effluent) handled from a digester increases because of required dilution water forsatisfactory pumping or digester operation. On average, only 4% of the influentmanure is converted to biogas. None of the water! The remaining 96% leaves the

digester as an effluent that is stable, rich in nutrients, free of weed seed, reducedor free of pathogens, and nearly odorless. This means that a farm loading 1,000gallons per day into a digester can expect to have 960 gallons of material(effluent) to store and ultimately utilize. Depending on digester design andoperation, solids can also settle out in the bottom of the digester and/or form afloating scum mat. Both the scum mat and the solids will eventually need to bemechanically removed from the digester to assure desired performance. Whenevaluating the actual performance and operation of a digester, it is important todetermine and account for the amount and type of material retained in thedigester and the cost of lost digester volume and ultimate cleaning.More anaerobic digester information can be found at: www.biogas.psu.edu

http://www.biogas.psu.edu/

http://www.biogas.psu.edu/

Anaerobic Treatment of Industrial waste water

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