RESOLUTION OF MINK WASTE MANAGEMENTverschurencentre.ca/images/2018/mink-report.pdf · dairy manure...

RESOLUTION OF MINK WASTE MANAGEMENTFermentation and digestion methods to resolve mink waste management issues

FALL 2017

2 Resolution of Mink Waste Management

AcknowledgementsThe Verschuren Centre would like to acknowledge the financial support of the Canada Mink Breeders Association and the Atlantic Canada Opportunities Agency (ACOA) for supporting this research. Additionally, we would like to thank the industry members for sharing information and samples in order to help work toward technology solutions in a number of areas.

A large number of researchers assisted with this project including Stephen Kelloway (lab manager), Elizabeth MacCormick (plant research assistant), Andrew Crowell (bio-products research assistant), Dr. Valentine Nkemka (Post-doctoral researcher), and Dr. Alberta Aryee (post-doctoral researcher), as well as students, Matt MacNeil and Randy Hopkins. VCSEE Administrative support from Debi Walker is key in co-ordinating multifaceted projects such as this, with project oversight provided by Dr. Beth Mason.

3Resolution of Mink Waste Management

Executive SummaryThe American mink (Neovison vison) has been primarily bred for commercial fur production, highly prized for its use in clothing and the pelt is traded on the global market as dried skin. Mink farming and processing generates a substantial volume of mink fat. Mink fat is commonly disposed or used as crab bait, organic compost, rendered and sold as low-grade oil used in livestock feed rations and other low value supplies of minimal economic benefit to the industry. It can however be utilized in high value cosmetics and lather treatments. In 2014, the mink industry accounted for $140 million of Nova Scotia’s economy. With a 60% price drop in recent years due to world-wide oversupply, weaker demand and incidence of the Aleutian disease in mink, generating alternative source of income for mink farmers from by-products is a laudable venture. In addition, in 2016 the Provincial Government of Nova Scotia enacted legislation to force removal of all mink waste off farm to specific processors of these wastes. This created additional economic burden on the industry as a whole.

The ProblemAt the time of the legislation on mink waste, there were two main outlets for manure (liquid and solid), waste food, and carcasses. These had both been provided funding through ACOA (Atlantic Canada Opportunities Agency), in anticipation of the up-coming environmental legislation, one being a composting facility and one an anaerobic digester. However, even the combination of these two facilities could not service all producers and the digester at least was not running optimally with this combination of inputs. A solution was sought that would perhaps re-distribute the wastes to better optimize these processes, while possibly adding an additional and separate processing method to manage the carcasses and fats, which are not suited to the existing systems. Additionally, to try to extract more value from mink by-products in order to enhance the economics of waste management.

The SolutionMink fat was clarified through a novel filtration method, to match the purity required for use in cosmetics. This method was relayed to the industry partners. Mink carcasses were hydrolyzed and can also then be separated into purified fats and a liquid protein. This protein could be utilized for a number of uses, such as pet feed, or put through the anaerobic digester. Removal of the carcasses would enhance the composting success, though the composted mink carcasses were able to be co-pelletized with willow, and exhibited heat (btu) potential similar to commercial wood pellets.

The anaerobic digester has not been running productively on mink manure and has been mostly taking dairy manure and dairy store returns, and some liquid mink manure. The digester has also recently changed hands and has been undergoing restructuring. A range of inputs that would be co-digested with the mink manure have been explored and are being optimized to provide a recipe that would enable better functionality and biogas production.

BenefitsSegregation of manure waste products into additional value stream processes provides opportunities to remove these less desirable products from the composting and digester facilities, enabling those to operate closer to optimal. A natural segregation of liquid manure to the digester and solids manure and feed waste to the composter would further optimize these processes, though proximity to production point does not always make this ideal. Supplementation in the digester with co-digested products can further enhance the viability, though the large digestate volumes remain an issue. As suggested below, there are up-coming options for this.


Next StepsFurther optimization of the ideal recipe for the anaerobic digester to maximize biomethane output while optimizing the uptake of mink manure will involve further experimentation on the range of other feedstuffs available locally to the digester. Some research has been conducted to reduce both digestate volume and nutrient extraction post digestion, thereby reducing the land base required for disposal and the associated transportation costs. Some novel nutrient extraction technologies available in Europe should be explored with the new ownership for the anaerobic digester, once recipe optimization has been achieved.

On both the composting and digestion side, removal of key challenging mink by-products and direction to other processes, not only will enhance the effectiveness of these two core processes, but provides other potential revenue or value addition streams for disposal. Some novel markets explored here included the use as biomass pellets, and efficacy as plant growth medium, though there may be a concern on contamination in the latter, and efficacy of AD kill would need to be checked.Further refinement of carcass hydrolysate production and market options for this product should also be explored.


Table of ContentsChapter 1: Alternative Methods for Refining Mink Oil ..................................................................6Introduction .................................................................................................................................................6Mink Oil Characteristics ...........................................................................................................................6Traditional Oil Refining Methods ..........................................................................................................6Environmental Concerns .........................................................................................................................7Project Objective........................................................................................................................................8Methods ........................................................................................................................................................8Quality Indices ............................................................................................................................................8Fatty acid profile ........................................................................................................................................9Results and Discussion......................................................................................................................... 10Conclusions .............................................................................................................................................. 16Chapter 2: Acid Hydrolysis of Mink Bodies ..................................................................................... 17Introduction .............................................................................................................................................. 18Industry Concern .................................................................................................................................... 18Opportunity .............................................................................................................................................. 18Project Objective..................................................................................................................................... 18Methods ..................................................................................................................................................... 19Formic acid hydrolysis ........................................................................................................................... 19Lactic acid hydrolysis ............................................................................................................................ 19Results and Discussion......................................................................................................................... 20Conclusions .............................................................................................................................................. 23Chapter 3: Plant Growth Trial using Mink Compost ................................................................... 24Introduction .............................................................................................................................................. 25Industry Concern .................................................................................................................................... 25Opportunity .............................................................................................................................................. 25Project Objective..................................................................................................................................... 25Methods ..................................................................................................................................................... 26Results and Discussion......................................................................................................................... 28Compost Analysis .................................................................................................................................. 28Plant Growth ............................................................................................................................................ 29Root Morphology .................................................................................................................................... 32Conclusions .............................................................................................................................................. 34


Chapter 4: Fuel Pellets from Mink Compost ................................................................................... 35Introduction .............................................................................................................................................. 36Opportunity .............................................................................................................................................. 36Project Objective..................................................................................................................................... 36Methods ..................................................................................................................................................... 37Results and Discussion......................................................................................................................... 38Conclusions .............................................................................................................................................. 40References ................................................................................................................................................ 41Chapter 5: Anaerobic Digestion .................................................................................................................Introduction .............................................................................................................................................. 46Materials and methods ......................................................................................................................... 48Analysis & design of co-digestion of substrates in batch reactors......................................... 50Results ....................................................................................................................................................... 53Anaerobic digestion in continuous stirred reactor ....................................................................... 546. Appendix ................................................................................................................................................... 57Preliminary report on nutrient extraction methods post anaerobic digestion ..................... 59


Chapter 1il

Chapter 1Alternative Methods for Refining Mink Oil


IntroductionInterest in value-added processing of by-products generated by mink farming is increasing. Finding alternative uses of mink carcasses such as rendering the thick layer of subcutaneous fat to oil following fur harvesting is more attractive than simply disposing the carcasses, landfilling, and is also economic and environmentally friendly. Mink oil, once purified, possesses desirable attributes for use in cosmetics and oil conditioning products.

Mink Oil CharacteristicsMink oil has a unique fatty acid composition and high oxidative stability among animal-derived fats and oils. Some of the physical and chemical characteristics of refined mink oil have been shown to be comparable to those of the human body oils thus making it a valuable alternative supplemental oil in skin care products, particularly as emollient in the cosmetics industry. However, the unpleasant odor of unrefined mink oil limits its use and value. Mink oil can be refined to value-added products such as cosmetic-grade oil for use in hypo-allergenic facial oils and cosmetics, and to condition and preserve leather.

Traditional Oil Refining MethodsCrude oils usually contain various impurities, products and other derivatives from breakdown of the oil during processing. These include free fatty acids, peroxides, aldehydes and ketones and related impurities. These substances must be removed during processing due to their effects on the quality e.g. appearance, odor, stability, value and other properties of the oil. Current methods for refining oil are laborious and multi-step, requiring separate unit processing steps such as washing/degumming, neutralization, bleaching, deodorization, dehydration, filtering and others, using strong acids and bases, large volumes of water for repeated washing, equipment investment, high energy consumption, waste disposal and are environmentally unfriendly.

Environmental ConcernsMink oil is rendered and refined using high temperature processes (110-115oC) and saponified to reduce free fatty acids. Oils are traditionally refined chemically using alkaline and acids and physically by steam stripping and distillation of free fatty acids (Čmolík and Pokorný, 2000; Sharma et al., 2013). Chemical refining includes degumming with water to remove the phospholipids and metals, addition of an acid (phosphoric or citric acid) to convert the remaining non-hydratable phospholipids (Ca, Mg salts) into hydratable phospholipids, neutralizing the free fatty acids with excess amount of sodium hydroxide solution, followed by repeated washing out of soaps and hydrated phospholipids. The oil is bleached with natural or acid-activated clay minerals to adsorb coloring components and to decompose hydroperoxides, and then deodorized by steam distillation (2-6 mbar and 180-220°C) to remove volatile components such as aldehydes and ketones. Additional bleaching steps may be required for some oils by crystallization of the wax esters followed by filtration or centrifugation. In physical refining, temperatures of 240-250°C are required during steam distillation (stripping) to remove the free fatty acids. Physical refining also requires that the content of phosphatides in the oil to be refined be less than 5 mg phosphorus/kg oil. In both of these commercial refining methods, the use of large volumes of chemicals and water and elevated temperatures results in fat-containing acid water effluents with attendant disposal problems, electricity cost and formation of trans-fatty acids and polymeric compounds, as well as low yields and oil losses due to the emulsification and saponification that occur during the processes and loss of quality of the oils.


Project ObjectiveIn recent years, there has been increasing demand for environmentally friendly techniques for materials production and more sustainable use of resources. The aim of this project is to demonstrate the feasibility of a one-step green process for refining crude mink oil. This present refining method is an improved, alternative, milder, cost-effective process and green technology which circumvents the above -mentioned drawbacks.

MethodsThe use of absorbents can achieve the same purpose of refining crude oils (Patterson, 2009; Taylor, 2009; Ramli et al., 2011). The conventional methods for refining oil are expensive and cumbersome. A better approach is the use of absorbents. This technology has been used in municipal drinking water, food and beverage, odor removal, industrial pollution control, as well as in homes. The absorbents are designed to intercept contaminants and allow a flow of the refined substance through the material. This is similar to permeable reactive barriers (PRB) used in waste remediation processes (Thiruvenkatachari et al., 2008; Obiri-Nyarko et al., 2014). The method is based on leveraging the attractive forces and adsorption capacity of absorbents facilitated by the large surface network of submicroscopic pores. This allows the contaminants in the oil to adhere to the absorbent media. During the physical adsorption process, as the dissolved adsorbate (the material being adsorbed) transverses the pore channels (macro-, meso- and micro-pore systems) of the absorbent, the molecules of the contaminants are attracted onto the surface structure of the absorbent where the attractive force between contaminants and the absorbent is greater than the attractive forces that keep the contaminants dissolved in the crude oil resulting in refining the oil and allowing the clean oil to be collected. The absorbent may then sometimes be used as an additive for other processes or animal feed.

Quality Indices The free fatty acid (FFA) content, peroxide value (PV), anisidine value (AV), thiobarbituric acid reactive substances (TBARS) and saponification value (SV) of unrefined mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM) were determined according to AOCS standard methods. These are all parameters specified for quality standards required for higher value use.

Fatty acid profileFatty acid methyl esters (FAMEs) were prepared using potassium hydroxide as described by International Standard method ISO-IDF (ISO, 2002). Briefly, 25 mg oil sample and 200 μL of hexane were mixed and vortexed. Then 50 μL of 2 N KOH (in methanol) was added and vortexed for 1 min. The mixture was allowed to react for 5 min in dark. After that 125 mg of sodium bisulfate monohydrate (NaHSO4.H2O) was added to stop the reaction. The sample was centrifuged for 5 min at 9,000 × g at 5 ºC. The supernatant was carefully collected and diluted with 1.25 mL hexane. 0.5 mL aliquot of the diluted supernatant is further diluted with 0.5 mL hexane. Aliquots of 1 μL were injected in a 200:1 split mode GC on a NSP-5 inert column; 30m x 0.25mm.

Attenuated total reflectance-Fourier Transform Infrared spectroscopyInfrared spectra were recorded at room temperature in the range 500-3600 cm-1 on Thermo-electron Nicolet 6700 FT-Infrared Spectrometer (Thermo Nicolet Corp., Madison, WI, USA) equipped with attenuated total reflectance (ATR) accessory. FTIR spectra were subtracted against the background of air spectrum. Background scan and mink oil samples were sequentially measured with a spectral resolution of 4 cm-1. An aliquot of the oil sample in a thin film was used for FTIR spectra recording.


Nuclear Magnetic Resonance (NMR) spectrometry NMR was used to obtain information on molecular structures of the oil. 1H and 13C NMR spectra were recorded in deuterated chloroform (CDCl3) as solvent on 400 MHz spectrometer at ambient temperature.

Results and DiscussionTable 1: Comparative quality indices of mink oil. Free fatty acid (FFA) content, anisidine value (AV), thiobarbituric acid reactive substances (TBARS), and saponification value (SV) of unrefined mink oil (UMP), mink oil refined using three absorbents (SI, ARI, and SII), and the industry purified mink oil (IPM).

Samples FFA TBARS AV SV EV % Glycerin

Unrefined Mink Oil 3.85 6.34 7.66 134.84 127.19 6.95

Industry Purified Mink Oil 2.02 4.02 136.79 132.76 7.26

Absorbent 1 (SI-M) 3.85 8.49 7.66 144.27 136.61 7.47

Absorbent 2 (AR-M) 3.85 10.89 7.66 143.71 136.05 7.44

Absorbent 3 (SII-M) 3.90 8.51 7.75 146.74 138.99 7.60

A qualitative analysis of the ATR-FTIR spectra of both crude and refined mink oils revealed no differences in their spectral features or shifts in position of the bands, but slight differences in the intensity of some absorption bands (Figure 1 a and b).

Figure 1a: Comparative ATR-FTIR spectra of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM)


Figure 1b: Comparative ATR-FTIR spectra of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM)

The main absorption bands were observed at the following regions, C-H stretching vibrations between 3050 and 2800 cm-1 (Fig. 2a), carbonyl stretching vibrations (C=O) between 1780 and 1680 cm-1 (Fig. 2b) and C-O 1200 and 1100 cm-1.


Figure. 2a: Region of hydrogen stretching vibrations of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM).

Figure 2b: Region of carbonyl stretching vibrations of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM).


Figure 3b: 1H NMR (400 MHz, CDCl3) spectra of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM).


Figure 3b: 13C NMR (CDCl3) spectra of unpurified mink oil (UPM), mink oil refined using the three absorbents (SI, ARI and SII) and the industry purified mink oil (IPM).


ConclusionsOverall, this adsorptive process was an effective way of refining crude mink oil using a properly designed system that addresses absorbent selection and bed design parameters (e.g. bed surface area, depth, and contact time). The selected absorbents can also be regenerated in situ. These absorbents are low cost and the process is green, simple and can be performed in one-step. Considering the low level of investment, capital and operating costs, and market potential for refined mink oil, the commercialization potential of this process is high.

The present refining method produces refined mink oil at low equipment investment and energy consumption, effectively removes small molecules which account for the odor in mink oil, impurities and other compounds which promote oxidation.


Chapter 2Acid Hydrolysis of Mink Bodies


IntroductionNova Scotia is home to roughly half of the mink producers within Canada (Statistics Canada, 003-0015). This industry represented over 170 million dollars in annual exports in 2014, however a decrease in profits have been noted in recent years (Statistics Canada. Table 003-0014). Methods to increase profits and decrease costs are required to improve the sustainability of the industry, in light of the imposition of new environmental costs.

Industry ConcernA large issue within the mink industry is the treatment of waste (manure, mink bodies, bedding, etc.) produced from the production of mink. Currently composting and anaerobic digesters facilities have been developed for the treatment of mink waste however these facilities are not yet running at optimal efficiency, and it is questionable whether mink carcasses are ideally suited to either processing method.

OpportunityComposting has been successfully used for the disposal of mink bodies but requires separation and long composting time periods to fully degrade to a safe product, which shows limits on market potential. The advantage of this method is the production of a saleable product from the current waste stream. However, compost is considered a low value product, and it is proposed that either separate technology or pre-treatment of the bodies prior to composting may allow for the liberation of higher value such as protein hydrolysates, and mink oil.

Project ObjectiveThis study examines two acid hydrolysate methods for the further degradation of the mink bodies for liberation of high value compounds prior to composting. Both methods of acid hydrolysis have been successfully used to produce fish hydrolysates, however their application to mink has yet to be examined

MethodsFormic acid hydrolysisFormic acid (88%) was added to portions of homogenized mink bodies at a pre-determined 2.3 gram to 100 gram ratio. The resulting slurries were mixed well and allowed to incubate at 37°C for 1, 3, 5, and 7 days. At each sampling time point the slurries were subject to centrifugation at 4000 rpm for 20 minutes. The resulting layers (oil, sludge, hydrolysate, and residue) were separated and dried by air drying in a 50°C oven. The liquid fraction was evaporated in a freeze drier. The resulting fractions were subject to automated Soxhlet extraction with petroleum ether (Gerhardt Co., Germany) and organic nitrogen determination by elemental analysis on a CHNSO 2400 (Perkin Elmer, Woodbridge ON) as described by the manufacturer.


Lactic acid hydrolysis Homogenized mink bodies were mixed with lactic acid producing bacteria (LAB) at a pre-determined inoculum to substrate (100 gram) ratio. Lactose was added as a fermentable carbon source in the range 10 -20 gram to 100 gram ratio. The resulting slurries were mixed well and allowed to incubate at 37°C for 3, 5, and 7 days. At each time point the slurries were subject to centrifugation at 4000 rpm for 20 minutes. The resulting layers (oil, sludge, hydrolysate, and residue) were separated and dried by air drying in a 50°C oven. The liquid fraction was evaporated in a freeze drier. The resulting fractions were subject to automated Soxhlet extraction with petroleum ether (Gerhardt Co., Germany) and organic nitrogen determination by elemental analysis on a CHNSO 2400 (Perkin Elmer, Woodbridge ON) as described by the manufacturer.

Results and DiscussionTwo mink waste products were provided for analysis: a byproduct obtained following mink oil recovery and the entire mink bodies. Protein and fat analysis (ether soluble material) were carried out on both products (Table I) to assess their potential for further hydrolysis. As can be seen from Table I, the oil by-product contains a significant amount of both oil/fat (~30%) and protein (~20%) that could be liberated and turned into high value product such as mink oil or protein hydrolysate. More research into methods to extract value products from this waste material is required and certainly warranted in combination with the oil clarification work in the prior chapter 1. The mink bodies have a much higher protein content (~30%) and lower fat content (~10%) on an as is basis. This suggest that a limited amount of mink oil can be liberated however there may certainly be value as a protein source. Two acid hydrolysis methods were employed to liberate protein from the mink bodies.

Table 1: Chemical analysis of oil by-product and mink body

Oil By-Product Mink Body

Water 44.1 ± 0.3 54 ± 0.3

Fat 29.9 ± 0.5 10± 1

Protein 19 30

Table 2: Mass balance (wet and dry) for LAB fermentation of mink body

Residue Sludge Oil Liquid

Day Wet Dry Wet Dry Wet Dry Wet Dry

3 66.3 66.0 25.3 27.3 0.5 1.1 8.0 5.6

5 53.4 63.5 34.3 26.2 0.3 0.9 12.0 9.4

7 52.0 54.2 36.9 37.2 0.5 1.2 10.9 7.5

Table 3: Protein and fat analysis (dry matter) for LaB fermentation of mink body

Protein Residue Protein Sludge Protein Liquid Fat Residue Fat Sludge

Day (%) (%) (%) (%) (%)

3 51 45.6 47.8 12.2 21.3

5 50.1 41.2 47.7 13.1 18.7

7 46.8 41.4 48.4 14.5 14.3

Formic acid fermentation was carried out through the addition of formic acid and allowing the slurry


to incubate for a week. This method has the advantage of producing limited odor compared to the LAB method, however a stronger acid is employed. The mass balance obtained from the fermentation can be found in Table 4. A clear decrease in residue is observed reaching a minimum at Day 5 while in increase in sludge is observed reaching a maximum at Day 5 and decreasing on Day 7. An increase in liquid hydrolysate is observed reaching a maximum at Day 5, however the dry matter continues to increase as a function of time. The oil layer reaches a maximum at Day 5.

From these observations, at least a 5-day incubation is required to maximize mink oil liberation and protein hydrolysate recovery. The incubation time can theoretically be decreased if the temperature is increased. The protein and fat content for each of the fraction can be found in Table 5. From this data, it can be calculated that this hydrolysis method can allow for the extraction of 13 grams of mink oil and 38 grams of protein isolate per 1 kg of mink body (1-1.5 bodies). The sludge layer is composed of 35% protein and 40% fat, suggesting this layer may be a further potential source of mink oil and protein isolate as it makes up of about 15-20% of the original mink body. This would potentially represent an additional 60 grams of oil and 50 grams of protein per 1 kg of mink.

Table 4: Mass balance (wet and dry) for formic acid fermentation of mink body

Residue Sludge Oil Liquid

Day Wet Dry Wet Dry Wet Dry Wet Dry

1 82±2 82±5 2.3±.02 3.4±0.3 .76±0.03 3.0±0.2 15±1 11±5

3 53±3 63±5 18±3 22±4 0.9±0.6 3±2 28±3 12±2

5 42±2 51±5 23±1 31±5 1.3±0.4 4±1 34±1 14±2

7 48±1 60±1 17±2 19.6±0.8 1.2±0.3 4±1 34±1 16.4±0.9

Table 5: Protein and fat analysis (dry matter) for formic acid fermentation of mink body

Protein Residue Protein Sludge Protein Liquid Fat Residue Fat Sludge

Day (%) (%) (%) (%) (%)

1 54.4 41.9 71.4 23±1 32±6

3 60.1 43.3 70.9 14.9±0.2 38±3

5 59.3 45.1 68.9 16.7±0.8 34±3

7 58.6 42.9 69.1 15.6±0.8 36.9±0.5

Further processing time or additional processing technologies (enzyme, ultrasound, microwave, etc.) are required to release the trapped protein and oil from the sludge layer. Overall formic acid fermentation is an excellent method of extracting protein content and oil from the mink bodies either as an alternative to composting or to selectively isolate the oils prior to composting. However, the effect of formic acid product on the composting process requires further examination to determine maximum loading ability.


ConclusionsAlthough lactic acid failed to provide efficient hydrolysis for the mink bodies, formic acid was shown to be an excellent method of hydrolysis for extraction of protein and mink oil from the bodies prior to composting. Overall 1.3% of the body can be extracted as mink oil and 3.8% as dry protein. Further processing of the sludge layer may release larger quantities of both protein and oil. Overall formic acid fermentation may be a method to recover higher value compounds prior to composting. It is important to note when looking toward a market for protein hydrolysate that there are already hydrolysates approved for use in animal feed under the Feeds Act (Schedule IV), however further testing for the destruction of the Aleutian disease vector would be required in order to be able to register this hydrolysate for use, specifically for pet food. It is unlikely in the current climate that it would be approved for use in feed produced for animals destined for human consumption, if only for perception. The hydrolysis work demonstrated that it is possible to fractionate oil for higher value uses, and possible the basal solids for plant products (bone meal), while exploring the use of the hydrolysate in feed.


Chapter 3Plant Growth Trial using Mink Compost


Introduction Mink farming has been a common practice in Nova Scotia for over 75 years, and today it continues to contribute to the provincial economy with over 100 farms located across the province.

Industry ConcernA very common concern surrounding mink farms in the Atlantic region is the treatment of waste produced during fur farming practices. If waste streams are not properly managed, wastes such as manure has the potential to pollute water systems through runoff of phosphorus (Cochrane 2002). There is also concern surrounding the containment of mink pathogens with the advent of the Aleutian disease. With increasing environmental concerns, mink producers are turning to composting as an environmentally acceptable process for converting waste biomass into a stable end-product that is odourless and pathogen-free (Cochran 2002). One such facility has set up specifically to take solids mink waste, while some liquid waste are being diverted to the anaerobic digestion unit.

OpportunityMuch of the waste (manure, mink bodies, bedding) can be composted, resulting in a soil conditioner which can be utilized in agricultural practices. This can create a value-added locally produced product which is diverted away from land application, incinerators or landfills. Mature composts are a valuable source of nitrogen for our Atlantic soils, and with proper management and applications they can provide producers with additional benefits such as organic matter, as well as nitrogen and other plant nutrients.

Project ObjectiveFor many greenhouse growers in the local region, peat moss is a popular substrate used in the propagation of seedlings, transplants, and various other greenhouse plants. This study compares the use of a mature mink compost against the more traditional peat moss many local horticulturalists and gardeners currently use.

MethodsMink bodies were mixed with wood shavings and placed in static piles which allowed natural decomposition to occur for approximately 12 months, with intermittent turning, primarily under cover and then cured outdoors. The mink compost was then sieved to remove bone fragments and any other large debris.

Pot experiments were conducted to test the effect of mink compost potting mixtures on the early growth of barley as a model species. Red solo cups were filled with approximately 355 ml of either controls (peat/sand blend) or mink compost mixtures for a total of 4 treatments, Table 1.

Figure 1: Mature compost made from mink bodies and wood shavings.


Table 1: Growth mediums for mink compost trial. Controls included a 50:50 ratio of peat and sand (A) and a 100% peat mix (C). Mink composts included a 100% mink compost mix (B) and a 50:50 ratio of mink compost and sand (D)

Code Treatment

A Peat and Sand (50:50)

B Mink Compost

C Peat

D Mink Compost and Sand (50:50)

Barley (Hordeum vulgare L.) seeds (6 seeds in each pot) were planted at ~3 cm depth. 10 replicates from each of the four treatments were transferred to a light rack where they remained for 20 days at 13 hours of light per day and a constant temperature of 23°C ± 0.5. Pots were randomly placed on the rack and rearranged seven times during the 20 day trial. At 7 days after planting, each cup was fertilized with 50 ml of a 20-20-20 NPK fertilizer mix. After 20 days, the plants were harvested and plant productivity was recorded along with differences in physical, chemical, and biological properties between treatments.

Germination was determined after one week by dividing the number of plants germinated by the number of seeds planted in each cup, and shoot length was measured for each plant by recording the length of the longest leaf. Two plants from each cup were used to measure fresh and dry weights of both shoots and roots. Plants were weighed immediately after harvest for fresh weight and then dried at 55°C for 48 hours and weighed again for dry weight.

Sugar content in the leaves was measured immediately after harvest using an Atago Digital Pocket Refractometer. To measure for sugar content, 1 shoot from each cup was rolled between hands for approximately 30 seconds. The shoot was then pushed through a rudimentary press made with a pipette tip. 3 to 4 liquid drops were placed onto the refractometer optical plate and measured for a brix reading.

To determine root morphology, WinRHIZO software was used to analyze scanned root mass from one plant from each cup. Length, root surface area, volume, and number of forks was recorded for each scanned root.

Chlorophyll was measured using methods described by Hiscox and Tsraelstam, 1979. Shoots from one plant per cup were frozen immediately after harvest. During the extraction process, 100 mg of frozen tissue was placed in a vial containing 7 ml of DMSO. This was incubated at 65°C for 30 minutes. The volume of DMSO was then increased to 10 ml. Samples were lightly mixed and allowed to settle. 1 ml of solution was then added to a cuvette to be analyzed in a spectrophotometer (CCM-200 OPTI-SCIENCES Inc.) against DMSO at both 645 and 663 nm (Arnon 1945).

Soil from each cup was set aside during harvest to be used for the measurement of electrical conductivity (EC) and pH. 20 ml of soil from each cup was mixed with 20 ml of distilled water. Samples were mixed 4 times over 30 minutes and allowed to settle for another 30 minutes before analysis. EC and pH were measured using a Thermo Scientific Orion VersStar Advanced Electrochemistry meter.


Results and DiscussionCompost AnalysisIn-house analysis showed the C:N ratio of the mink compost was 10.6, the pH was 5.8, and the moisture content on day of sampling was 77%. A sample of the mink compost was sent to Department of Agriculture’s analytical lab, Harlow Institute, located at the Dalhousie Faculty of Agriculture in Bible Hill NS for further mineral fertilizer assay analysis. Results are listed in table below.

Table 2: Parameters of mink compost. Sample was analyzed at the Harlow Institute, located in Bible Hill, NS.

Mink Compost

Parameter As Received Dry Basis

Dry Matter (%) 34.93 -

Nitrogen (%) 0.88 2.52

Calcium (%) 1.396 3.996

Potassium (%) 0.051 0.145

K2O (%) 0.061 0.176

Phosphorus (%) 0.691 1.979

P2O5 (%) 1.583 4.531

Magnesium (%) 0.071 0.202

Sodium (%) 0.05 0.144

Boron (ppm) ND < 10

Copper (ppm) 5.22 14.95

Iron (ppm) 1046.13 2994.93

Manganese (ppm) 99.04 283.55

Zinc (ppm) 105 300.59

Plant GrowthAll treatments showed similar germination rates, except for the peat moss treatment which showed very low rates of germination at only 30%. Comparatively, the other treatments were all between 75 and 83%.

Table 3: Percent germination measured 7 days after planting.

% Germination

100% Peat moss 30

50:50 Sand and peat moss 88

100% Mink Compost 83

50:50 Mink and Sand 75


A common trend observed throughout the results section is that pots receiving only peat moss substrate had very little success, resulting in lower germination rates and lower growth rates for both above and below ground biomass. The pH of peat moss is acidic and usually found in the range between 3.9 and 4.5 which is generally too low as most plants perform better in more alkaline conditions. It is possible the acidity of the peat moss was too high for the growth and establishment of barley, which has a recommended pH of 6.0.

Table 4: Average pH results from peat and mink compost substrates used in the barley growth trial.

pH

50:50 Sand and Peat 5.472

100% Mink Compost 4.533

100% Peat 3.921

50:50 Sand and Mink 5.462

The peat and mink compost pots which were mixed with 50% sand had the highest pH results at approximately 5.4. The sand used in the trial had a pH of approximately 6, and thus created conditions in the preferred soil pH range for barley which is between 5.0 and 8.3 (Valenzuela and Smith 2002). Pots receiving only peat moss had the lowest average pH at approximately 3.9 which is considered low for successful plant growth. The mink compost which had an original pH of 5.8 appears to have decreased during the growth trial. This may be a result of the addition of fertilizer which can sometimes increase the acidity of the growth medium.

Figure 2: Example pot from each treatment 20 days after planting. From left to right: A) 50:50 peat moss and sand, B) Mink compost, C) Peat moss, and D) 50:50 mink compost and sand.


Table 5: Average shoot length for barley plants grown in varying amounts of peat moss and mink compost.

Length (cm)

100% Peat 6.6

50:50 Sand and Peat 34.1

100% Mink Compost 37.0

50:50 Sand and Mink 38.0

Table 6: Fresh weights of barley shoots and roots including moisture contents. Table includes the root to shoot ratio for both fresh and dry materials.

Fresh Weight (g) Moisture Content (%) Root:Shoot

Shoot Root Shoot Root Fresh Dry

100% Peat 0.0513 0.0838 81.1 80.2 1.80 3.67

50:50 Sand and Peat 0.5080 0.1216 84.2 70.0 0.24 0.43

100% Mink Compost 0.6298 0.1726 88.1 60.5 0.29 1.12

50:50 Mink and Sand 0.8026 0.2093 85.5 67.2 0.26 0.49

The above ground biomass was minimal in the 100% peat moss cups. Early growth slowed and eventually stopped during the first 7 days of the trial. There was also minimal root growth from barley seeds planted in 100% mink. The addition of sand had a beneficial effect on both the above and below ground biomass. The 50:50 sand and peat mix showed more growth, however the pots containing mink compost had more impressive results.

The mink compost mixtures had the largest shoots and roots, with 50:50 mink compost and sand mix showing the greatest shoot mass. The mink compost showed the highest moisture content in the shoots, which is evident in Figure 1. When excluding the results of the peat treatment, the pots with sand had the highest moisture content in their roots. This may reflect the drainage capacity of growth mediums containing sand; roots may be stimulated to retain more moisture when exposed to periods of drought.

Analysis of average sugar content in the leaves showed little difference between treatments with 100% mink compost showing 6.7%, 50:50 sand and peat at 6.8%, and 50:50 sand and mink at 6.9%. The 100% peat mix, however, did show higher levels of sugar with a brix reading of 8.2%. Plants under stress reduce their sugar metabolism and this may be evident with the higher sugar concentrations found in the leaves of barley planted in 100% pleat moss. Comparatively, the lower yet similar brix readings for the remaining 3 treatments could reflect plants which are not under stress and metabolizing sugar effectively for that particular growth stage (Akincil and Lösel 2012).


Table 7: Chlorophyll analysis from barley shoots grown in mink compost and peat substrates.

Chla (g l-1) Chlb (g l-1) Tot Chl (g l-1)

50:50 Sand and Peat 0.029 0.009 0.038

100% Mink Compost 0.027 0.007 0.034

100% Peat 0.003 0.001 0.004

50:50 Sand and Mink 0.030 0.009 0.039

The results from the 100% peat mix had minimal chlorophyll amounts. By the end of the 20-day growth trial, these plants had shown signs of chlorosis (browning) which suggests a lack of chlorophyll. The lack of chlorophyll can suggest poor drainage and the absorbent qualities of peat moss may have been a factor for the poor growth quality in this treatment. The ability for peat moss to hold moisture can also lead to poor drainage, which negatively affects roots by restricting air flow and enabling root rot.

Chlorophyll results were similar between the other treatments, however the treatments which contained sand had slightly higher amounts of total chlorophyll.

Root MorphologyTable 8: Elements of root morphology from barley plants analyzed by WinRHIZO root analyzing software.

Length (cm)Surface Area

(cm2)Root Volume

(cm3) Forks

50:50 Sand and Peat 425.34 35.39 0.2351 2993

100% Mink 335.67 31.26 0.2321 1758

50:50 Mink and Sand 360.67 36.38 0.2946 2336*Results of the 100% peat moss treatment were not included

Root growth for peat treatments was minimal. The longest root systems were found in the 50:50 sand and peat treatment, which could reflect the root system “searching” for nutrients by extending the root length and number of forks. Although all treatments did receive fertilizer mid-way through the trial, these results could still reflect trends in early root growth.

The mink treatments had shorter root systems with less forks, suggesting there was adequate nutrients available. The root volume was highest in the 50:50 mink and sand treatments, possibly due to the addition of sand which allowed more airflow through the cups. The ability for a root system to hold onto water allows the plant to withstand periods of drought, suggesting these plants may be able to cope with periods of stress due to drought.


Figure 3: Scanned images representative of each of the four growth media treatments. Images show barley root development at 20 days after planting.

The long, thin roots of the sand and peat moss treatment are evident in the above image. The mink treatments show slightly shorter, yet thicker root biomass.

ConclusionsResults from the mink compost nutrient analysis shows that a mature mink compost can be considered a beneficial agricultural amendment, providing essential macro and micro nutrients to plants while providing beneficial organic matter and supporting microbial growth. It would be anticipated that the mink compost could be similar in profile to the addition of a portion of bone meal to potting mixtures, which has been considered a desirable practice. The higher calcium and phosphorus content of the mink compost may attest to this.

Trial results suggest mixing mink compost with sand creates a substrate which encourages growth of plants in excess of basic peat potting blend, while providing draining to encourage root growth and development. Plants grown in pots containing mink compost had more above ground growth and had robust root systems capable of providing relief during potential periods of drought.

The mink compost and sand mixture used in the study was an excellent medium for use in greenhouse work, however, the marketability of product may be limited due to the public perception of potential pathogen exposure. Further research is suggested to determine the fate of pathogens during the composting process and whether plant uptake or contamination is a possible risk.


Chapter 4Fuel Pellets from Mink Compost


IntroductionToday, many countries are attempting to meet climate and energy targets through reduction in CO2 emissions, consuming less energy, and generating primary energy with renewable sources (Miranda et al., 2015). Due to several factors such as the increase of oil prices, the growth of agricultural production, and the search for alternative uses for generated wastes, biomass has reappeared as an energy source to help meet those targets (Miranda et al., 2015). Biomass is defined as the biodegradable fraction of organic products and waste generated from agricultural activity, forestry, and related industries (Miranda et al., 2015).

Many agricultural industries in the Atlantic region produce organic by-products that may be utilized as a fuel source. The cost to harvest, handle, and transport agricultural residue and other biomass materials often places biomass at a competitive disadvantage to fossil fuels (Christiansen, 2008). To increase the density of biomass, it can be mechanically compressed into pellets which can result in higher energy density, lower transportation and energy costs, and allows for automatic feeding in domestic and industrial sized boilers (Stelte et al., 2011).

OpportunityAs an alternative to fossil fuels, many agricultural residues and by-products are now being pelletized for fuel. Fuel pellets are popular, and the country as a whole is a large exporter, and as such there has been increasing interest in creating a competitive heating product from underutilized materials. Agricultural residues such as composted animal carcasses from local mink farms in the Atlantic region may be utilized as a pelleted fuel source when composted and combined with other sources of biomass material.

Project ObjectiveThe objective of this research project was to examine the potential to incorporate composted mink bodies into fuel pellets by combining mink compost with a willow-hybrid, a typical purpose grown biomass. Fuel pellets were assessed for their durability and heating value.

MethodsMink bodies were mixed with wood shavings and placed in piles which allowed natural decomposition to occur for approximately 12 months. The mink compost was then sieved to remove bone fragments and any other large debris.

A further source of woody biomass was required for the pelletizing process. A commercial variety of locally grown willow hybrid (Salix variety) was used as a binding agent during the pelletizing process. Three fuel pellets were created consisting of varying amounts of mink compost and willow biomass.


Table 1: Composition of fuel pellets made from mink compost and willow.

Composition

50W:50M 50% willow, 50% mink compost



The material was mixed in a drum agitator until a consistent blend was created. The biomass was then fed through a pellet mill where inside rollers pushed the mix through a ring die, which condensed the product into pellet form. Pellets were cooled before being screened to separate residual fines. The 3 mink compost pellets were compared against 3 commercial varieties of wood pellets available in the local area; Shaw and Shaw Premium (Nova Scotia), and Canwick Hardwood (Quebec).

Moisture content was determined by placing pre-weighed samples in an oven at 60°C for 24 hours. These samples were then used to determine the ash content. Oven dried samples were place in a furnace at 600°C for 4 hours and the remaining material was weighed to determine inorganic content.

The internal energy of combustion for the pellets was determined using a constant volume Parr bomb calorimeter. For each type of pellet, a sample was weighed and placed inside the bomb with an ignition wire in place. 20 atm of oxygen was added to the closed system before being placed in a silvered bucket which contained 2 L of water. The bucket was then placed in a calorimeter jacket which included a surrounding insulating air space so that the required adiabatic conditions were satisfied reasonably well. A stirrer was inserted into the water and the initial temperature was monitored every 30 seconds for 5 minutes. The sample was then ignited and the temperature was recorded every 30 seconds until it remained constant for at least 5 minutes. This was repeated 3 times for each pellet type. The heat capacity of the pellets was calculated as Kilojoules of heat combustion per gram of material and is presented as kilojoules per kilogram as well as British Thermal Units (BTU) per pound.

Results and DiscussionThe mink compost pellets were generally uniform in size and were durable enough to withstand bagging and handling. The 50W:50M pellets did show some evidence of loss of uniformity and began to break apart after handling. Industry suggests fuel pellets should have a high-gloss sheen on the side of the pellet to minimize the amount of dust it would produce during transport to the end user (Christiansen, 2008). The below image shows a dull finish to the 50:50 mix, with increasing amounts of exterior gloss as the percentage of willow increases.


The 75W:25M and 90W:25M showed less amounts of breakdown after handling and was comparable to the amount of wasted material found in commercial fuel pellets.

Table 2: Percent moisture content and percent ashing of fuel pellets. Samples include various mink-willow mixtures as well as commercial wood pellets.

Moisture Content (%)% Ashing (dry basis)

50W:50M 7.89 10.359

75W:25M 7.38 10.132

90W:10M 6.67 5.737

Canwick Hardwood 6.73 0.657

Shaw 6.78 0.282

Shaw Premium 7.07 0.444

Moisture content between samples was fairly consistent, however the 50 and 25% mink compost pellets had slightly higher moisture contents. Percent ashing had more varied results. Ash content is the inorganic residue remaining after the water and organic matter have been removed by heating. This provides a measure of the total amount of minerals within a sample. The commercial varieties of wood pellets have low inorganic matter, showing less than 1% for all three samples. The fuel pellets made from mink bodies show much higher levels of inorganic material, with both the 25 and 50% mink pellets showing over 10% inorganic material. The 10% mink pellets showed lower amounts at just over 5%.

Burning fuel pellets made from 25 or 50% mink compost would result in more ash waste when compared to ashes left from burning commercial varieties.

Image 1: Fuel pellets made from varying mixtures of mink compost and willow. From left to right: A) 50W:50M, B) 75W:25M, and C) 90W:10M.


Table 4: Heat capacity of pellets made from varying mixtures of mink compost and willow. Samples are compared against commercially available wood pellets. Results shown in both kJ/kg and BTU/lb.

Heating Value

Pellet Type kJ/kg BTU/lb

50W:50M 16,834 7,237

75W:25M 16,680 7,171

90W:10M 18,053 7,761

Shaw Premium 19,111 8,216

Canwick Hardwood 19,167 8,240

Shaw 19,534 8,398

The heating value results between the 50W:50M blend and the 75W:25M blend were very similar, with only an approximate 1% difference between them. These were approximately 6.8% lower than the heating values observed in the 90W:10M blend.

Willow has heating value of approximately 8,240 BTU/lb (Reeb, 2009), and when blended with a 50W:50M mink compost it is estimated that the heating value decreases by 12%, while the heating value of a 90W:10M blend decreases approximately 6%.

A good quality wood pellet should have a heating value of approximately 8,250 BTU/pound (Reeb, 2009) which was observed for all 3 commercial varieties of wood pellets. Lower quality fuel pellets have lower ratings for heating capacity. For comparison, green sawdust is rated at 4,500 BTU/lb, poultry litter at 5,000 BTU/lb, and grass pellets at 6,800 BTU/lb, all of which are lower than the heating capacity of the mink compost pellets.


ConclusionsThe heating capacity of the mink compost/ willow pellets was lower than the commercial wood varieties, however they were still comparable to or greater than fuel pellets made from other agricultural residuals. The addition of willow was important for the durability and heating capacity of the pellets. Equally the mink compost brought improvement in pellet quality above the 100% willow

All biomass feedstocks will pellet differently. Optimizing pelletizing efficiency and quality is essential to produce a higher quality product. Changing the thickness of the pellet mill, the milling speed, as well as temperature and pressure are all factors that can potentially increase product quality.

Transporting pellets long distance may require a very hard pellet to minimize breakdown during shipping, however if the pellets are to be burned onsite, particularly for industrial use or have minimal travelling distance, a lower quality pellet may be a viable option.

The willow hybrid used in the study is considered a short-rotation woody crop which may represent a potential source of renewable biomass feedstock for the agro-forestry and bioproducts sectors in the local region. When combined with agricultural residues low in cellulose and lignin, it can provide the tensile and compressive strength required to produce a higher quality pellet. Additionally willow can be utilized in marginal areas as a remedial for bio-uptake of excess nutrient leachate, such as may be necessary in a composting area.

A mink compost fuel pellet which included 75% willow resulted in durable pellets with a heating capacity of approximately 7,200 BTU/lb, providing a potentially efficient fuel supply for local industries.

ReferencesAkıncı, Ş., and Lösel, D. M. (2012) “Plant Water-Stress Response Mechanisms.” Water Stress. Print.

Christiansen, R. (2008). The art of biomass pelletizing. Biomass Magazine. Retrieved from http://biomassmagazine.com/articles/2465/the-art-of-biomass-pelletizing

Čmolík, J. and Pokorný, J. (2000). Physical refining of edible oils. Eur. J. Lipid Sci. Technol. 102: 472-486.

Cochrane, L. (2002). On-farm composting of mink manure. Nova Scotia Department of Agriculture and Fisheries Fact Sheet. Retrieved from http://nsfa-fane.ca/wp-content/uploads/2011/06/On-FarmCompostingofMinkManure.pdf

Friesen, D. (2012). Biomass heating feasibility guide. Agricultural Utilization Research Institute. Retrieved from http://www.auri.org/assets/2012/08/MNRER-Biomass-Heating-Presentation-24-Jul-2012-2.pdf

Hiscox, J, and Israelstam, G. (1979). A method for the extraction of chlorophyll from leaf tissue without maceration. Canadian Journal of Botany. 57:1332-1334.

Miranda, T., Montero, I., Sepulveda, F., Arranze, J., Rojas, C., and Nogales, S. (2015). A review of pellets from different sources. Materials. 8, 1413-1427.


Obiri-Nyarko, F., Grajales-Mesa, S.J. and Malina, G. (2014). An overview of permeable reactive barriers for in situ sustainable groundwater remediation. Chemosphere, 111: 243-259

Patterson, H.B.W. Adsorption. In: Bleaching and purifying fats and oils. Theory and practice. Chapter 2, pp. 53-67 (G.R. List (ed.), AOCS Press, Urbana, IL. (2009).

Ramli, M.R., Siew, W.-L., Ibrahim, N.A., Hussein, R., Kuntom, A., Razak, R.A.A. and Nesaretnam, K. (2011). Effects of degumming and bleaching on 3-MPCD esters formation during physical refining. J. Am. Oil Chem. Soc. 88: 1839-1844.

Reeb, J. (2009). Home heating fuels. Oregon State University Extension Service. EC 1628-E.

Sharma, H., Giriprasad, R. and Goswami, M. (2013). Animal fat-processing and its quality control. J. Food Process. Technol. 4: 252. doi:10.4172/2157-7110.1000252

Stelte, W., Holm, J., Sanadi, A., Barsberg, S., Ahrenfeldt, J., and Henriksen, U. (2011). Fuel pellets from biomass: the importance of the pelletizing pressure and its dependency on the processing conditions. Fuel. Vol 90, Issue 11, Pages 3285-3290.

Taylor, D. Adsorbents. In: Bleaching and purifying fats and oils. Theory and practice. Chapter 3, pp. 69-95 (G.R. List (ed.), AOCS Press, Urbana, IL. (2009).

Thiruvenkatachari, R., Vigneswaran, S. and Naidu, R. (2008). Permeable Reactive Barrier for Groundwater Remediation. J. Ind. Eng. Chem. 14: 145-156.

Valenzuela, H., and Smith, J. (2002). “Sorghum-sudangrass hybrids.” Sustainable Agriculture 680 10. Web. 9 April 2016.


Chapter 5Addressing issues and optimization of Anaerobic Digestion of Mink Waste


1.0 IntroductionAnaerobic digestion has been used as a waste management technique and as a means of recovering renewable energy from mink manure by mink farmers in Weymouth, Nova Scotia, Canada. The plant was initially commissioned to treat mink manure and the waste feed. However, due to the fall in the demand of mink fur on the international market, the volume of mink manure going to the biogas plant for treatment has significantly reduced. As a consequent, the plant now digests other organic wastes such as fish processing wastes and grocery food waste (Table 1).

Table 1. The table shows the current and future feedstocks that could be suitable co-substrates at the Southwest Eco Energy Biogas Plant.

Feedstock Current usage Comments

Liquid mink manure Reduced digestion volumes

Suitable due to high methane potential and easy for pumping

Solid mink manure Reduced digestion volumes

Low methane potential and contains stones and gravel which results in clogging and pump failure

Fish processing waste Available Potential of high Na ions

Grocery food waste mainly milk and juices

Available Comes with the packaging material and there is need for separation

Green cart waste from Municipality/ restaurant food waste

Planned for the future High tip fee and sorting required

Dairy cow manure Planned for the future Faraway from the plant but can be accessed

Beef cattle manure Planned for the future Close to the plant

Seaweed waste Planned for the future Tip fee needed and high KOH

Sewage sludge Planned for the future Permit required

In addition, the plant hopes to expand by including additional feedstocks such as sewage sludge, seaweed processing waste and green wastes from the Municipality of Weymouth. However, the plant is now facing some operational problems such as maintaining a pH of 6.8 to 7.6 that has been reported suitable for efficient anaerobic digestion (Jha et al., 2011). The current low pH of 5.28 in the anaerobic digester have resulted in process failure as observed by the significant decrease in methane production and the shut down of the combined heat and power (CHP) generator. Initial pH adjustment of the liquid content with NaOH did not increase the pH to neutral as feeding of the digester was not suspended. Table 2 shows the pH of the different individual waste streams and processing steps during biogas production at the plant. Wood furnace for heat generation is currently operational as an alternative heat source to the waste heat from the CHP system for supplying heat to the receiving/hydrolytic reactor and the main biogas digester, maintaining temperatures of 40 °C and 35 °C, respectively. Also, the heat generated was not sufficient to operate the pasteurization units, which operates at 70 °C for 90 minutes. Currently, the hydrolyzed liquid is directly digested without pasteurization, which is against regulations.

Investigation of process failure and recovery of full-scale biogas plant

co-digesting organic wastes and mink manure


The processing of organic waste at the Southwest Eco Energy begins when the waste is tipped into a 200 m3 receiving/hydrolysis tank, which is buried below the ground and operates at 40 °C (Figure 1). The hydrolyzed liquid is mixed and then circulated into batch pasteurization tanks that sanitize the liquid at 70 °C for 90 minutes prior to feeding the main 1500 m3 biogas digester. The digestate obtained after anaerobic digestion is stored in an open 1500 m3 concrete tank before farmland application.

Figure 1. Schematic diagram showing the processes steps during the anaerobic co-digestion of grocery food waste, mink manure and fish waste at the Southwest Eco Energy Plant,

Weymouth, NS, Canada.


ObjectiveThe aim of the current project was to investigate the cause of process failure and also to evaluate different procedures and strategies for process recovery. Sub-samples of the various waste streams fed into the digester were collected from different processing steps and analyzed for their physio-chemical properties and composition. Methane potential batch test using the AMPTS II light is planned with the individual sub-samples and the mixture of one or more co-substrates. Moreover, evaluation of the process recovery time using continuous stirred reactor is also planned and shall utilize the substrate mixed feed from the hydrolysis tank and in co-digestion with dairy manure or seaweed processing waste.

2.0 Materials and Methods2.1 Substrate sourceSub-samples of the mixed waste feed from the receiving tank, main digester tank and the effluent of the digestate tanks were collected. We also collected sub-samples of fish processing waste, mink manure and the waste feed (Table 2).

Table 2. pH of the various waste streams and from different processing tanks. The sample date was 2017-07-06.

Sample collection point Substrate pHTotal solids (TS in %)

Mixed waste stream fed into the digester from the 200 m3 receiving/hydrolysis tank, operational temperature of 40 °C Mixed wastes

4.24 21.9 ± 0.2

Inoculum from main 15 00 m3 anaerobic digester, operational temperature of 35 °C Inoculum

5.28 3.7 ± 0.6

Digestate from 15 00 m3 digestate reservoir Digestate

6.30 3.4 ± 0.6

Fish waste Fish waste 3.94 37.0 ± 0.2

Liquid mink Manure Mink Manure 6.97 1.2 ± 0.4

Mink waste feed Mink waste feed 5.35 47.9 ± 1.1

2.2 pH adjustment of the digester liquid contentAs the pH of the digester was 5.28 and low, we mixed the liquid from the digester: digestate liquid: mink manure in the percentage ratio of 40:40:20 % v/v and the pH increased to 5.9. Table 3 shows the resultant pH after mixing the digester liquid; digestate liquid and mink manure in the percentage ratios of 33.3:33.3:33.3, 40:40:20 and 45: 45:10 % v/v. Mixing of the digestate liquid and the liquid of the main biogas digester can be performed industrially by recirculation and exchange of the liquid volumes with a recirculation pump.


Table 3. pH adjustment by mixing the digester content (inoculum), digestate and liquid mink manure.

Substrate types Ratio (% v/v) pH

Inoculum: digestate: mink manure 33.3: 33.3: 33.3 6.00 ± 0.01

Inoculum: digestate: mink manure 40: 40: 20 5.90 ± 0.02

Inoculum: digestate: mink manure 45: 45: 10 5.74 ± 0.02

Readily available seaweed processing waste (SIR) that has a high pH of 10.07 was used to adjust the pH of the inoculum by adding 5, 10, 20, 30 and 40% v/v of the SIR sludge. pH adjustment with 20 to 40% of the SIR resulted in an increase in the inoculum pH from 6.28 to 6.8-8.01 (Table 4), which is within the range reported to be suitable for methane production .

Table 4. pH adjustment of anaerobic inoculum with seaweed processing waste sludge.

Inoculum (% v/v) Seaweed processing waste (SIR) (% v/v)

pH

100 0 6.28

95 5 6.29 ± 0.06

90 10 6.33 ± 0.03

80 20 6.87 ± 0.02

70 30 7.45± 0.01

60 40 8.01 ± 0.09

0 100 10.07

ReferencesJha, A.K., Li, J., Nies, L., Zhang, L., 2011. Research advances in dry anaerobic digestion process of solid organic wastes 10, 14242–14253. doi:10.5897/AJB11.1277

3. Anaerobic co-digestion of mink manure, dairy manure and food waste in methane potential batch test and in continuous stirred tank reactor

3.1. Aim of the processThe aim of this project is to evaluate the optimum feedstock mixtures of which are digested at the Southwest Eco Energy (SEEL) Biogas Plant. These laboratory-scale trials shall be evaluated in batch and continuous anaerobic digesters. The methane potential batch test shall be performed using the automatic methane potential system AMPTS II light, Bioprocess Control AB, Lund, Sweden (Figure 1). While the continuous anaerobic digestion shall be performed using 5 L Eppendorf bioreactor and the operational conditions shall be set following the full-scale digester operation.

3.2. Feedstock and inoculum characterizationThe various waste streams; mink manure (MM); dairy manure (DM); food waste (FW) together with the inoculum shall be characterized. A readily available feedstock such as corn silage that has a high carbon to nitrogen ratio shall also be characterized for use as a co-substrate. Initial feedstock characteristics such as the pH, total solid (TS), volatile solids (VS), chemical oxygen demand (COD),


elemental C and N, NH4+-N, total bicarbonate alkalinity, volatile fatty acids and the macro and

micronutrient content shall be analyzed. The optimum substrate ratio of MM, DM, FW and corn silage shall be determined using the recommended optimum C:N ratio of 20 to 30 (Wang, Yang, Feng, Ren, & Han, 2012). The main waste streams (MM, DM and FW) which are digested at the Weaver Biogas Plant are expected to lead to a process with high NH4

+-N, which can in turn result in ammonia inhibition. However, other optimization parameters such as organic loading rate (OLR), hydraulic retention time (HRT), substrate pre-treatment and macro and micronutrient composition are significant.

3.2.1 Feedstock and inoculum handling and safety issuesAnaerobic digestion just like compositing (aerobic digestion) is used for organic waste decomposition and stabilization. During composting, aerobic microorganisms break down organic matter in the presence of oxygen in heat energy and CO2. The high temperature attained during this process in crucial for pathogen destruction. However, anaerobic digestion process which takes place in the absence of oxygen, produces little heat energy as the heat energy in the form of methane. Hygienization of potential infectious or pathogenic organic wastes prior or after anaerobic digestion is recommended by European Commission Regulation No 1774/2002. This should be performed by either thermophilic digester operation for 24 hours at 55°C and at a retention time of 20 days, or substrate pre-treatment at 70°C for 1 hour during mesophilic digestion, or post–treatment of the digestate at 70°C for 1 hour, or composting of the digestate (Braun, Holm-nielsen, & Seadi, 2002). This procedure is a standard practice in the Biogas Industry aimed at limiting the spread of pathogenic microbes. However, hygienization is not a requirement when digesting plant waste and energy crops prior to anaerobic digestion.

In our study, the collected organic waste streams (MM, DM and FW) shall be hygienized in 5 L sealed beaker placed in a heating water bath at 70 °C for 1 hour holding time before freezing until use. The inoculum shall not be hygienized, since the waste streams fed into the biogas digestion has already been sanitized before anaerobic digestion.

3.3. Methane potential batch test using the AMPTS II lightAMPTS II light is a piece of analytic equipment for the online determination of methane potential in which CO2 of the produced biogas (60% CH4 and 40% CO2) is absorbed in 3 M NaOH and the upgraded biomethane is then measured continuously using a flow cell. The system also has a data acquisition system to a computer where the graphs and data for the daily methane production of cumulative methane yields can be visualized.About 1600 to 2000 mL of active anaerobic sludge or inoculum shall be incubated with and without a known amount of substrate e.g. (mink manure) for a period of 30 days. The experimental period is determined by the biodegradability of the feedstock and the experiment is usually terminated when the amount of methane produced in less than 2 ml/g volatile solids (VS) added. The difference in the methane produced from the added feedstock and the inoculum is the specific methane production from the feedstock. Internal standard similar to the feedstocks’ characteristics is included in the assay for validation of the results and also for assessing the biological activity of the inoculum. In order to validate the test results, the theoretical methane yield and the experimental yields are compared. 1 g VS carbohydrate (cellulose) yields 415 ml CH4.


4.1 Experimental design of batch test using the AMPTS II lightThe experiment shall evaluate methane potential from the substrates in duplicate in 2000 mL glass reactor of the AMPTS II light system (Figure 1).1. Inoculum control (Weaver Biogas Plant) x 2 replicate 2. Avicel cellulose x 2 replicate (Internal standard)3. Mink manure (MM) x 2 replicate4. Dairy manure (DM) x 2 replicate5. Food waste (FW) x 2 replicate6. Corn silage (CS) x 2 replicate7. Co-digestion of MM/DM/FW using the annual volume ratios x 2 replicate8. Co-digestion of MM/DM/FW + maize silage to a C/N ratio of 25 x 2 replicate

4.2 Experimental procedureAt the startThe inoculum was pre-incubated to reduce the residual methane production from the inoculum for about 5 to 7 days at the experimental temperature of 40 °C.

TS and VS of the inoculum were measured after the incubation period or prior to the test together with that of the feedstock. Measurement of volatile compound was performed for feedstocks that are suspected to contain volatile compounds (e.g. ensiled crops). Under estimation of the methane potential can be the result of not measuring these volatile compounds. Oven drying at 105 °C for 24 hours shall result to the loss of volatile compound together with water. The chemical oxygen demand (COD) is preferred for liquid samples such as dilute wastewater.

Inoculum versus substrate ratio was set at 1:1 or 2:1 in terms of g VS added. inoculum characteristics TS, VS, pH, alkalinity, NH4

+-N were measured for characterising the feedstock for TS, VS or COD and elemental analysis, micronutrients and chemical composition.

All the E-flasks were filled with 1600 to 2000 mL or in g of the inoculum and an amount of substrate added and pure substrate used as control. These were mixed gently so that the substrate mixed well with the inoculum and then flushed with nitrogen for about 2 to 3 minutes. Reactors were sealed with the stoppers and connected to the tubing lines (see AMPTS II manual details).

The E-flasks were placed in pre-heated water baths set at the desired experimental temperature (40 °C in this case).

4.3 During and after the experiment Recommended water level of the gas flow measuring device were maintained to the fill mark with deionized water (DI) water. Measurements were taken of the pH of the reactor liquid, TS, VS and other parameters including head space volume in the E-Flask (the methane concentration in the head space of the feedstock is seldom higher than that of the inoculum).

Figure 1. Set-up of methane potential batch test AMPTS II light.


Methane production of feedstock was calculated by subtracting methane produced by substrate minus methane produced by inoculum and expressing the methane potential as normal L or normal mL g-1 VSadded. VFA measurements of ensiled crops and other substrates were monitored since loss of VFA has been reported during oven drying when determining TS values (Kreuger, Nges, & Björnsson, 2011). After the experiment the inoculum was autoclaved at 120 °C for 30 minutes or disinfected with bleach and disposed of as hazardous waste, since it may contain pathogens.

4.4. Results. Batch BMP values were established for all primary ingredients in use currently, though some substrates proved less than ideal for anaerobic biomethane production, requiring prolonged lag times and less than ideal biogas composition. These values were compared to literature data to then assess the carbon nitrogen and VS in the recipies currently used as these relate to BMP and the failing biomethane production. It was evident from the initial composition of ingredients and the BMP values that the calculated recipies may not provide the optimal C:N ratio or solids content for optimal VS utilization into methane, as indicated by the low BMP for specific ingredients, hence it was proposed to run the co-digestion of substrate with a more balanced ingredient of high C:N composition. Due to time limitations the experiment described below is under way at the writing of this report.

5.0 Anaerobic co-digestion in a CSTRIn this experiment, the effect of addition of an energy crop (corn silage) with a high C/N is to be evaluated at a C/N ratio of 25. Corn silage shall be used to adjust the C/N prior to anaerobic digestion. The reactors shall be inoculated 1600 mL of active anaerobic sludge or inoculum. The 5 L Eppendorf bioreactor shall be operated similar to the full-scale digester operational conditions (Figure 2).

The digester temperature shall be maintained under mesophilic (40 °C) condition with a heating element. Manual feeding of the reactor shall be performed with a 100 mL syringe or a screw pump by withdrawing appropriate liquid amounts and also pumping equal feed volume to maintain a constant active reactor volume. Using syringes or screw pumps for feeding the substrate mixture into the bioreactor is suitable for this process type as the total solid or TS content is about 10%. The hydraulic retention time (HRT) shall be set at say 25 days while the organic loading rate shall be set at 3.0 g VS Lreactor

-1. d-1. The reactors shall be operated for at least 2 hydraulic cycles, which is 2 × 25 days HRT making a total treatment period of 50 days. This is to ensure the establishment of a semi-steady state, observed as constant methane yields and volumetric methane production rates as indicators.

Below are the equation used for calculating the HRT and OLR:

and [1]

[2]

where V is the active reactor volume, F is the flow rate and C is the concentration of the feedstock.

HRT= ! !

! !!

OLR=! !"#

! ∗! !!

! !,

Figure 2. Eppendorf bioreactor that shall be used for the continuous anaerobic co-digestion of mink manure, dairy manure, food waste and corn silage.


Table 1 shows the operational parameter for operating the biogas digester.Table 1. Calculations for operation of a CSTR of the co-digestion of MM/DM/FW/CS.

Continuous stirred tank reactor for Anaerobic co-digestion of MM/DM,FW/CSReactor volume mL 5000

Active reactor volume mL 3000

Flow rate mL 120

Water for 50% dilution mL 75

Sample volume mL or g 45

VS % ww 20

g VSS added 9

HRT (days) 25

OLR (gVS /L/d) 3

Hydraulic cycles 2

Total treatment period (days) 50

Experimental design of the anaerobic co-digestion in a CSTRThe following treatments shall be included in the experiment,

1. Co-digestion of MM/DM/FW using the annual volume ratios x 2 replicate2. Co-digestion of MM/DM/FW + corn silage (adjusted C/N ratio of 25) x 2 replicate

Experimental procedureTS, VS and C/N ratio of the various wastes will be measured again and the C/N ratio adjusted with corn silage as in the experimental design. Blends will be incubated for 5 to 7 days in order to reduce background methane production. The reactors fill will be 3000 mL of inoculum and reactor flushed with nitrogen for about 2 to 3 minutes to create anaerobic condition, and temperature set at 40C.

Sample of the produced biogas are taken with a syringe and stored in evacuated vials for analysis of gas by GC following calibration of the GC each time with a standard with gas composition of approximately 60% CH4 and 40% CO2. Gas volumes are measured the with a 100 mL glass syringe that is equipped with a three way valve in a fume hood.

Feeding of the reactor daily is achieved by withdrawing and replacing equal volumes of effluent and feed. The pH, TS, VS, total alkalinity, COD and NH4

+-N are analyzed immediately from the liquid samples and liquid samples saved (-20 °C) for volatile fatty acids (acetate, propionate, n-and i-butyrate and n-and i-valerate) and soluble nutrient analyses. Temperature readings are logged automatically, which shall be used to correct the methane produced at room temperature to zero degrees or Normal volumes of methane and express the methane potential normal L or normal ml per g VSadded.


References Angelidaki, I., Alves, M., Bolzonella, D., Borzacconi, L., Campos, J. L., Guwy, A. J., … van Lier, J. B. (2009).

Defining the biomethane potential (BMP) of solid organic wastes and energy crops: a proposed protocol for batch assays. Water Science and Technology, 59(5), 927 LP-934. Retrieved from http://wst.iwaponline.com/content/59/5/927.abstract

Braun, R., Holm-nielsen, J. B., & Seadi, T. a L. (2002). Potential of Co-digestion. IEA Bioenergy, 16. https://doi.org/10.1007/s11356-015-4998-1

Kreuger, E., Nges, I., & Björnsson, L. (2011). Ensiling of crops for biogas production: effects on methane yield and total solids determination. Biotechnology for Biofuels, 4(1), 44. https://doi.org/10.1186/1754-6834-4-44

Nkemka, V. N., & Murto, M. (2013). Two-stage anaerobic dry digestion of blue mussel and reed. Renewable Energy, 50. https://doi.org/10.1016/j.renene.2012.06.041

Wang, X., Yang, G., Feng, Y., Ren, G., & Han, X. (2012). Optimizing feeding composition and carbon-nitrogen ratios for improved methane yield during anaerobic co-digestion of dairy, chicken manure and wheat straw. Bioresource Technology, 120, 78–83. https://doi.org/10.1016/j.biortech.2012.06.058


Chapter 6Black Soldier fly bioconversion of mink compost


BackgroundWith the large volumes of both food waste and organic manure being relatively low value sources of nutrients, there has been interest of late, particularly in Europe, but also now in Canada, to convert these nutrients into higher value addition products that may be of use in both animal and human food. Insect protein is of particular interest as it comprises a significant portion of the diet in many countries in Asia already. The European interest in insect protein is very much oriented toward more efficient ways to feed the anticipated population growth, due to expected limitations in animal and cereal protein yields.

A number of insects have been identified as potential candidates for this bioconversion, of which the Black Soldier Fly (BSF) has been successfully raised at commercial scale. The BSF larvae stage feeds on a variety of organic waste, and produces larvae high in proteins and oil. Both whole larvae and the protein meal (following oil extraction) provides a rich ingredient for livestock and human nutrition, and the meal has been approved for use in poultry diets here in Canada. With cereal protein meals in the range of $350-450/tonne and animal meals in the range $1000-15000/tonne, bioconversion of organics could be a profitable opportunity.

ObjectiveCurrently, only meal produced from pre-consumer organics is approved for use in animal feed. Quite a bit of research has been undertaken growing larvae on livestock manure, and with some success. However, it seems unlikely that these larvae or their protein meal would be approved by CFIA for use in animals destined for human consumption, but there are other companion species where there may be a market. Therefore, a trial was set up to establish whether BSF larvae would grow in a medium of composted mink waste, and to what extent the bioconversion would take place, in terms of value addition from waste.

MethodsBSF larvae were introduced at the very early larval stage (post egg hatch) into a medium of 100% mink waste compost (23.1% DM). No adjustment was made for nutrient content of the medium, nor for the moisture content, as the product was quite dry relative to other comparative products that the larvae have been grown on in our lab. Larvae were fed daily in increasing, measured increments, over a period of two weeks, until planking was observed, which is a stage pre-pupation. At this stage the larvae turn from a cream-white colour to a dark brown, and become immobile, while eating ceases. Representative numbers of larvae were dried and analysed for protein and oil content, and growth rate recorded during the two-week trial for comparison with two other known feed ingredients.

ObservationsAlthough it was possible for the larvae to grow successfully on the mink compost, their performance did not match that of larvae grown on a standard vegetable based diet. It did however exceed the performance of larvae grown on potato waste, which have previously been shown to do quite well. Growth rates and body composition data are shown below, and it should be noted that the oil composition in compost fed larvae was also lower than that of the vegetable fed larvae, but higher than the starch based potato diet. It has previously been observed that the oil content of larvae is directly influenced by diet nutrient composition, and it is likely that the low oil content in this case is a result of high protein nitrogen and low carbohydrate content of the mink compost. Previous work


has also demonstrated that blending feed ingredients can create a more ideal diet for optimizing the protein to oil ratio of BSFL. Ideal diets have led to a 40% protein and 35% lipid content in the larvae, maximizing the value proposition from both oil and meal.

Additionally, the “frass” residue following BSFL bioconversion is an ideal potting medium, with potentially beneficial properties similar to vermiculture casts. This provides a second revenue stream to the bioconversion, but most importantly greatly reduces the volume of compost to be sold as frass (generally up to 60%). Hence a lower volume, higher value product is left behind by the BSFL.

Larvae consumed (270 larvae) around 500g over the period of growth (16 day) and appeared to thrive sufficiently. Performance was intermediary between the vegetable and potato organic wastes.

0

0.02

0.04

0.06

0.08

0.1

0.12

A B C D E F

Aver

age

Wei

ght (

g)

Larvae Group Figure 1. Average weights calculated from ten randomly selected larvae post-feeding period for

experiment five. (A,B vegetable; C,D potato; E,F mink compost)

Figure 2. Comparative percentage oil content of larvae fed different diets and mink compost.

0

5

10

15

20

Lipi

d Pe

rcen

tage

(%)

Substrate


ConclusionBasic, well composted mink waste was a moderately good organic food source for larvae from the Black Soldier fly. From growth rates and compositional data, it would appear that potentially the ratio of protein to energy available in the compost, and possibly the high cellulose content were limitations to higher performance. However, blending the compost with other organics would certainly enhance larval growth and body composition.

It is likely the frass would perform well as a potting mix alone, due to the low moisture content and residual cellulose content. Use of the oil from larvae fed mink waste might be possible for inclusion in non-food livestock & companion animals, and similarly it would require further testing for pathogen transfer before application could be made to use protein meal from mink waste BSFL into non-food livestock diets. There are alternative uses for protein meals which could be explored if the economics of this bioconversion were attractive.

6.0 Appendix 6.1 Batch calculation excel sheetTable 1 shows part of an excel sheet for calculating the methane yield of a

Figure 2. Methane potential batch test of avicel cellulose after 31 days of digestion (yield 370 ml CH4/g VSadded). The theoretical methane potential of carbohydrate is about 415 ml CH4/g VSadded. However, 10% of the energy of the substrate is used for growth and heat by anaerobic microbes (Nkemka & Murto, 2013).

Inoculum AvicleInoc. 1 Avicel 1 Net Sub-Ino Daily CH4 yield Cum. Yield

Time /daysarea units %CH4 gas vol/mlTemp oC N l CH4 area units%CH4 gas vol/mlml CH4 Temp oC N l CH4 N l CH4 N l CH4/gVSadded N l CH4/gVSadded


6.2 Theoretical calculations and estimates1 g VS of carbohydrate = 1.07 g COD1 g VS protein = 1.5 g COD1 g VS lipid = 2.91 g COD1 g COD yields 350 ml CH41 g VS carbohydrate yields 415 ml CH41 g VS protein yields 495 ml CH41 g VS fat yields 1011 ml CH4PV = nRT (where P is the pressure in Pascals, V is the volume in m3, n is the number of moles, R= 8.314 J/(mol.K) and t is the temperature in Kelvins.1 m3 CH4= 9.8 KWh or 35.315 MJ

6.2 Appendix 2.Preliminary Report on Nutrient Extraction Prospects from Digestate. The goal of this report was to highlight some of the ways nutrients can be utilized from mink manure post anaerobic digestion. Mink manure is definitely a newer and less common type of manure being used for digestion. There has not been a great deal of work on mink manure digestion but there appears potential for it to be useful in the ways that dairy, chicken etc. manures have been used. The main issue with mink manure aa with all manures for that matter, is that they are extremely rich in specific nutrients, that, if not properly utilized posed considerable environmental degradation risk, hence strict guidelines exist that vary from place to place, dictating specific application rates for nutrients such as nitrogen and potassium for land application. In Nova Scotia, it typically only takes about 3.5kg of phosphorus added to the land to change the amount in the soil by 1.0 kg per hectare and about 4.5 kg of potassium to do the same. This poses quite the issue considering lots of soils already have practically all the nutrients available that plants have the potential to use. If high levels of phosphorus and potassium are applied to the land it increases the chances of run off into nearby water systems, causing further problems in the surrounding environment. These regulations alongside the elevated nutrient levels in manure make transport costs for nutrient solutions such as anaerobic digestate very costly, limiting the economic radius for disposal from the digester. However, there may be methods to lower these transport costs and in turn bring profitability through nutrient extraction and value creation in these by products.

Anaerobic digestion refers to a sequence of biological processes that occur inside a bio tank (with the help of microorganisms and lack of oxygen) that successfully biodegrade materials such as mink manure into a nutrient rich digestate, producing biogas, comprising methane and carbon dioxide. The digestate can be used as directly as a fertilizer as it consists of the leftover indigestible material and dead microorganisms from the process but comprises generally about 94% water, which is costly to transport. Digestates retain much of the original input nutrients and macronutrients.

With the constant depletion of gases, coal, and other naturally occurring energy sources, the importance of renewable biogas will steadily rise in coming years. Therefore, the advantages of operating a bio-methane system such as anaerobic digestion warrant attention. Though the methane gas suggests a profitable proposition, disposal of digestate can represent a considerable cost. Though the digestate has obvious fertilizer values, a large land base is required to stay within the prior mentioned nutrient guidelines for crop production. It is critical also to note that there are substantial risks when running this type of operation as bio-methane output is very much proportional to substrate and recipe formulation, as well as specific control of operating. For example co-digestion of manure mixed with crushed dairy products causes considerable increase in production of methane gas


(Figure 1), within limits. In excess, these products can cause a system to crash. Little data exists on the bio-methane potential (BMP) of mink manure in terms of whether this is a favourable substrate for digestion or co-digestion and its impact on digestate nutrient profile.

Figure 1. Biogas yield from dairy manure and food mixtures from a study performed by El-Mashad and Zang. Adding dairy manure to an anaerobic digestion mix of feed increased the biogas production substantially.

One key aspect about the digestate product after undergoing the digestion process is the presence of the nutrients from the original material. Typically, all the nitrogen, phosphorus and potassium present in the material placed in the anaerobic digester tends to stay in the digestate. This simplifies the capability to perform solid nutrient extraction and capture downstream to some extent. Digestate nutrient extraction involves physically removing and therefore reducing the nutrient levels in the digestate material so that it can be applied over smaller portions of land without causing any environmental harm. Nutrient extraction will be very important to reduce hauling costs but the nutrients themselves also hold important value, especially phosphorus if they can be captured in a format that presents other market products. Phosphorus is an essential nutrient in all cellular growth. It is however, over time, becoming increasingly scarce and expensive. This increases the value of having the ability to reprocess and reclaim phosphorus from secondary sources. Nutrient extraction from manures and digestates is needed due to regulations and guidelines that restrict the amount of phosphorus that can be applied per hectare of land. As per Nova Scotia Agriculture it has been determined that on average in Nova Scotian soils only 3.5 kg of phosphorus added/removed to/from the soil is required to change the level in the soil by 1.0 kg per hectare. Whereas, similar amounts of nitrogen and potassium will do the same. This is considerably less than the large nutrient requirements of typical crops grown in productive areas of Nova Scotia. When looking at typical nutrient levels for some common types of manure (Table 1) and keeping in mind the optimal carbon nitrogen level for digestion of use as fertilizer is 25:1 (Table 2), it is quite obvious that in order to stay within nutrient regulations, reduce transport costs, and close the nutrient cycle, some degree of nutrient extraction is needed. It is shown that mink manure composition falls within similar ranges of other more commonly used types of manure.


Table 1. Average nutrient levels in ppm for some typical wet and dry forms of manure. Information gathered from http://www.gov.mb.ca and Ontario Ministry of Agriculture and Food.

Manure Type Total N (ppm) Ammonium N (ppm)

Organic N (ppm)

Total P (ppm) Dry Matter (%)

Liquid Pig 4320 2640 1680 1440 4.3

Liquid Dairy 3720 1800 1920 984 7.1

Liquid Chick 9480 6960 2520 3000 8.3

Solid Dairy 5500 1300 4100 1500 20

Solid Beef 5500 600 4800 1150 28

Solid Chicken 22,500 7000 15,000 10,000 48

Mink 5105 2605 2500 1000 -

Table 2. Typical carbon nitrogen ratio values for different types of manure along with optimal carbon nitrogen ratios so that the manure can work most efficiently as a fertilizer and produce the most methane gas during anaerobic digestion.

Manure Type C:N Ratio Optimal C:N Ratio

Dairy 20:1 25:1

Mink 7:1 25:1

Pig 12:1 25:1-30:1. The general practice for primary nutrient extraction from a digestate is to first perform a mechanical separation of solids and liquids. The high water content in most manure makes the separation of liquids and solids an important tool to allow better handling, analysis, and manipulation of the manure. There are several techniques and pieces of equipment that can be used to achieve this, such as belt filter presses, screw presses or centrifuges. Screw presses and/or decanter centrifuges are simple techniques that will efficiently separate the material into liquids and solids with very little suspended material in the liquid portion. This helps avoid any potential blocking issues in further treatment. Mechanical separation has also shown to be able to successfully retain up to 98% of the phosphorus in the solid portion along with the organic source of nitrogen, while the ammonium form of nitrogen can be found in the liquid (Lebuf et al., 2012). A study performed in both Manitoba and Quebec on pig manure was able to successfully use a centrifuge to separate liquids and solids. On average, solids separation removed 61% of the phosphorus into the solid but up to 90 % may be removed by additional measures. Around 27% of nitrogen on average was removed in the solids fraction, ranging up to 34%. The solid fractions had up to 12 kg/tonne of phosphorus, and 11kg/tonne of nitrogen (Ackerman & Cicek, 2013). Once the manure has been separated into liquids and solids further treatment of the liquid fraction can achieve additional nutrient and mineral. A few techniques that have been used to date with some degree of success include fluidized bed crystallization forming struvite crystals, membrane separation procedures paired with reverse osmosis, and biomass production techniques using algae and macrophytes.


Struvite (NH4MgPO4·6H2O) crystallization has been used as a wastewater treatment technique for many years. More recently it has been looked at as a way to recover phosphorus from manures and digestates. Phosphate can be precipitated out of solution given the appropriate addition of ions. Adding magnesium or potassium to the liquid portion of the digestate will cause phosphorus and ammonium to precipitate out of solution as struvite crystals. As long as calcium levels are low this should be quite a simple process. If calcium levels are increased phosphorus will precipitate out as orthophosphate which has less value. One study showed up to 58% of dissolved phosphorus was removed using struvite precipitation methods (Marti et al., 2008). By adding a bed of struvite crystals or magnesium chloride into a crystallizer or fluidized bed reactor along with liquid digestate, a controlled system of struvite precipitation can be established. This technique has been performed on wastewater sludge in Canada by a company called Pearl. Pearl has been able to successfully remove 90% of dissolved phosphorus and 40% of the dissolved ammonia. Other studies have shown that with the addition of magnesium and an adjusted pH range to 7.7-8.2 up to 70% of total phosphorus could be removed as struvite crystals. There is market value to struvite crystals as shown from studies on struvite as a fertilizer.

Struvite has been tested as a fertilizer on rye grass. It has been described as a slow release fertilizer. The nutrients are released only as the grass begins to deplete the soils nutrients. Struvite has been very effective as a fertilizer for grass because it not only provides a great source of phosphorus (essential for cell growth) but also magnesium which is the fundamental element in chlorophyll which gives grass its strong green colour and allows plants to absorb light as their primary energy source.

There are many different ways membrane technologies have been used to remove and capture nutrients from a digestate system. Membrane-based techniques include microfiltration and ultrafiltration followed by reverse osmosis. Microfiltration and ultrafiltration are basically the same technique with different sized pores in the membrane itself. The liquid portion of the digestate is forced through the membrane using a precise pressure system. Each or both of these membrane techniques are used prior to performing reverse osmosis so that no dissolved solids block and interfere with the osmotic membrane. Reverse osmosis uses a hydrostatic pressure greater than the naturally occurring osmotic pressure to pass a liquid through a semi permeable membrane in the opposite way it would naturally travel (Lebuf et al., 2012). Using different membrane techniques along with a reverse osmosis procedure would allow the screening and extraction of nutrients such as phosphorus, nitrogen and potassium. These nutrients can then be generated into profit, however membrane costs remain high and likely overall prohibitive to use of these processes for low value digestate nutrients.

Figure 2. Struvite precipitated from swine manure. Struvite precipitation is a simple yet effective way at extracting phosphorus and nitrogen from a digestate. http://wastemgmt.ag.utk.edu/ResearchPrograms/struvite_2.htm


Another suggested application for nutrient extraction or reduction from digestates is to grow algal biomass, appropriate for further end use. There have been a few studies indicating that a digestate or manure does not interfere with but actually aids in the growing of algal media (Mulbry et al., 2002) by providing supplemental micronutrients. Xu and Shen also showed in one of their experiments growing duckweed that, it too can use the nutrients in a manure digestate to aid with growth. They showed that up to 89.4% of phosphorus and 83.7% of the nitrogen was taken up and used by the duckweed. The duckweed total biomass was 5.3 times greater than the starting amount and it was shown that nutrients were still being removed in the winter months even with minimal growth. The biomass of algae or macrophytes can then have quite a few applications, depending on strain, for example for chemical extraction industries, as animal feed, or also as a fertilizer material.

Table 3. Summary of three possible nutrient extraction methods for the mink digestate including how much phosphorus, nitrogen, and potassium can be removed and captured for other uses.

Nutrient Extraction Method

% Phosphorus removed % Nitrogen Removed % Potassium Removed

Crystallization (Struvite) 90.0 53.0 -

Membranes/Reverse Osmosis

35-45 70-80 70-80

Biomass Production 89.4 83.7 -

Technology Available in CanadaThe technologies mentioned above are available in Canada and would allow these nutrient extraction methods to be performed include; pearl struvite forming process (fluidized bed reactors); magnesium, calcium, potassium sources; decanter centrifuges, belt presses and screw presses; and reverse osmosis tanks and systems. In addition, novel technologies are being explored here and in Europe in particular, since anaerobic digestion occurs to a greater magnitude in these countries.

Figure 3. Algal biomass can be grown using the nutrients found in an anaerobic digestate. http://biomassmagazine.com/articles/11742/


Resources:Amon, T., Amon, B., Kryvoruchko, V., Zollitsch, W., Mayer, K., and Gruber, L., 2007. Biogas production from maize and dairy cattle manure-Influence of biomass composition on the methane yield. Agriculture, Ecosystems and Environment 118. 173-182. Battistoni, P., Fava, G., Pavan, P., Musacco, A., and Cecchi, F., 1997. Phosphate removal in anaerobic liquors by struvite crystallization without addition of chemicals: Preliminary results. Water Research 31. 2925-2929. El-Mashad, H. and Zhang, R., 2010. Biogas production from co-digestion of dairy manure and food waste. Biosource Technology 101. 4021-4028. Fuchs, W. and Drosg, B., 2013. Assessment of the state of the art of technologies for the processing of digestate residue from anaerobic digesters. Water Science & Technology 67.9.Gerardo, M., Aljohani, N., Oatley-Radcliffe, D., and Lovitt, R., 2015. Moving towards sustainable resources: Recovery and fractionation of nutrients from dairy manure digestate using membranes. Water Research 80. 80-89. Hills, D. and Roberts, D., 1981. Anaerobic Digestion of Dairy Manure and Field Crop Residues. Agricultural Wastes 3. 179-189. Lebuf, V., Accoe, F., Vaneeckhaute, C., Meers, E., Michels, E., and Ghekiere, G., 2012. Nutrient recovery from digestates: techniques and end-products. Venice, 2012 Fourth International Symposium on Energy from Biomass and Waste. Mulbry, W., Westhead, E., Pizzaro, C., and Sikora, L., 2004. Recycling of manure nutrients: use of algal biomass from dairy manure as a slow release fertilizer. Biosource Technology 96. 451- 458.Xu J. and Shen G., 2011. Growing duckweed in swine wastewater for nutrient recovery and biomass production. Bioresource Technol., 102, 848 – 853.

Websites:http://www.gov.mb.cahttp://biomassmagazine.com/articles/11742/http://wastemgmt.ag.utk.edu/ResearchPrograms/struvite_2.htmhttp://www.eliquo-we.com/en/pearl.html

Verschuren Centre for Sustainability in Energy and the EnvironmentCape Breton UniversityP.O. Box 5300Sydney, Nova ScotiaCanada B1P 6L2www.verschurencentre.ca

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