Optimization of biogas production from cattle manure by pre-treatment with ultrasound and co-digestion with crude glycerin

Biogas production by co-digestion of cattle manure with crude glycerin obtained from biodiesel production was studied after pre-treatment of the cattle manure or mixtures of cattle manure with different amounts of added glycerin with ultrasound. Batch experiments with 1750 mL of medium containing 1760 g of screened cattle manure or mixtures of cattle manure (screened or ground) and 70-140 mL or crude glycerin were incubated under mesophilic and thermophilic condition in stirred tank reactors. Under mesophilic conditions, the addition of 4% glycerin to screened manure increased biogas production by up to 400%. Application of sonication (20 kHz, 0.1 kW, and 4 min) to a mixture of manure + 4% glycerin increased production of biogas by up to 800% compared to untreated manure. The best results were obtained under thermophilic conditions using sonicated mixtures of ground cattle manure with 6% added glycerin (348 L methane/kg COD removed were obtained).     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

A new algorithm to characterize biodegradability of biomass during anaerobic digestion: influence of lignin concentration on methane production potential

We examined the influence of fibrous fractions of biomass on biochemical methane potential (BMP) with the objective of developing an economical and easy-to-use statistical model to predict BMP, and hence the biodegradability of organic material (BD) for biogas production. The model was developed either for energy crops (grass, maize, and straw) or for animal manures, or as a combined model for these two biomass groups. It was found that lignin concentration in volatile solids (VS) was the strongest predictor of BMP for all the biomass samples. The square of the sample correlation coefficient (R(2)) from the BMP versus lignin was 0.908 (p<0.0001), 0.763 (p<0.001) and 0.883 (p<0.001) for animal manure, energy crops and the combined model, respectively. Validation of the combined model was carried out using 65 datasets from the literature.     

Nitrogen in global animal production and management options for improving nitrogen use efficiency

Animal production systems convert plant protein into animal protein. Depending on animal species, ration and management, between 5% and 45 % of the nitrogen (N) in plant protein is converted to and deposited in animal protein. The other 55%-95% is excreted via urine and feces, and can be used as nutrient source for plant (= often animal feed) production. The estimated global amount of N voided by animals ranges between 80 and 130 Tg N per year, and is as large as or larger than the global annual N fertilizer consumption. Cattle (60%), sheep (12%) and pigs (6%) have the largest share in animal manure N production.The conversion of plant N into animal N is on average more efficient in poultry and pork production than in dairy production, which is higher than in beef and sheep production. However, differences within a type of animal production system can be as large as differences between types of animal production systems, due to large effects of the genetic potential of animals, animal feed and management. The management of animals and animal feed, together with the genetic potential of the animals, are key factors to a high efficiency of conversion of plant protein into animal protein.The efficiency of the conversion of N from animal manure, following application to land, into plant protein ranges between 0 and 60%, while the estimated global mean is about 15%. The other 40%- 100% is lost to the wider environment via NH3 volatilization, denitrification, leaching and run-off in pastures or during storage and/or following application of the animal manure to land. On a global scale, only 40%-50% of the amount of N voided is collected in barns, stables and paddocks, and only half of this amount is recycled to crop land. The N losses from animal manure collected in barns, stables and paddocks depend on the animal manure management system. Relative large losses occur in confined animal feeding operations, as these often lack the land base to utilize the N from animal manure effectively.Losses will be relatively low when all manure are collected rapidly in water-tight and covered basins, and when they are subsequently applied to the land in proper amounts and at the proper time, and using the proper method (low-emission techniques).There is opportunity for improving the N conversion in animal production systems by improving the genetic production potential of the herd, the composition of the animal feed, and the management of the animal manure. Coupling of crop and animal production systems, at least at a regional scale, is one way to high N use efficiency in the whole system. Clustering of confined animal production systems with other intensive agricultural production systems on the basis of concepts from industrial ecology with manure processing is another possible way to improve Nuse efficiency.     

Nitrogen in global animal production and management options for improving nitrogen use efficiency

Animal production systems convert plant protein into animal protein. Depending on animal species, ration and management, between 5% and 45 % of the nitrogen (N) in plant protein is converted to and deposited in animal protein. The other 55%-95% is excreted via urine and feces, and can be used as nutrient source for plant (= often animal feed) production. The estimated global amount of N voided by animals ranges between 80 and 130 Tg N per year, and is as large as or larger than the global annual N fertilizer consumption. Cattle (60%), sheep (12%) and pigs (6%) have the largest share in animal manure N production. The conversion of plant N into animal N is on average more efficient in poultry and pork production than in dairy production, which is higher than in beef and sheep production. However, differences within a type of animal production system can be as large as differences between types of animal production systems, due to large effects of the genetic potential of animals, animal feed and management. The management of animals and animal feed, together with the genetic potential of the animals, are key factors to a high efficiency of conversion of plant protein into animal protein. The efficiency of the conversion of N from animal manure, following application to land, into plant protein ranges between 0 and 60%, while the estimated global mean is about 15%. The other 40%-100% is lost to the wider environment via NH3 volatilization, denitrification, leaching and run-off in pastures or during storage and/or following application of the animal manure to land. On a global scale, only 40%-50% of the amount of N voided is collected in barns, stables and paddocks, and only half of this amount is recycled to crop land. The N losses from animal manure collected in barns, stables and paddocks depend on the animal manure management system. Relative large losses occur in confined animal feeding operations, as these often lack the land base to utilize the N from animal manure effectively. Losses will be relatively low when all manure are collected rapidly in water-tight and covered basins, and when they are subsequently applied to the land in proper amounts and at the proper time, and using the proper method (low-emission techniques). There is opportunity for improving the N conversion in animal production systems by improving the genetic production potential of the herd, the composition of the animal feed, and the management of the animal manure. Coupling of crop and animal production systems, at least at a regional scale, is one way to high N use efficiency in the whole system. Clustering of confined animal production systems with other intensive agricultural production systems on the basis of concepts from industrial ecology with manure processing is another possible way to improve N use efficiency.     

Nitrogen in global animal production and management options for improving nitrogen use efficiency

Animal production systems convert plant protein into animal protein. Depending on animal species, ration and management, between 5% and 45 % of the nitrogen (N) in plant protein is converted to and deposited in animal protein. The other 55%–95% is excreted via urine and feces, and can be used as nutrient source for plant (= often animal feed) production. The estimated global amount of N voided by animals ranges between 80 and 130 Tg N per year, and is as large as or larger than the global annual N fertilizer consumption. Cattle (60%), sheep (12%) and pigs (6%) have the largest share in animal manure N production.The conversion of plant N into animal N is on average more efficient in poultry and pork production than in dairy production, which is higher than in beef and sheep production. However, differences within a type of animal production system can be as large as differences between types of animal production systems, due to large effects of the genetic potential of animals, animal feed and management. The management of animals and animal feed, together with the genetic potential of the animals, are key factors to a high efficiency of conversion of plant protein into animal protein.The efficiency of the conversion of N from animal manure, following application to land, into plant protein ranges between 0 and 60%, while the estimated global mean is about 15%. The other 40%–100% is lost to the wider environment via NH₃ volatilization, denitrification, leaching and run-off in pastures or during storage and/or following application of the animal manure to land. On a global scale, only 40%–50% of the amount of N voided is collected in barns, stables and paddocks, and only half of this amount is recycled to crop land. The N losses from animal manure collected in barns, stables and paddocks depend on the animal manure management system. Relative large losses occur in confined animal feeding operations, as these often lack the land base to utilize the N from animal manure effectively. Losses will be relatively low when all manure are collected rapidly in water-tight and covered basins, and when they are subsequently applied to the land in proper amounts and at the proper time, and using the proper method (low-emission techniques).There is opportunity for improving the N conversion in animal production systems by improving the genetic production potential of the herd, the composition of the animal feed, and the management of the animal manure. Coupling of crop and animal production systems, at least at a regional scale, is one way to high N use efficiency in the whole system. Clustering of confined animal production systems with other intensive agricultural production systems on the basis of concepts from industrial ecology with manure processing is another possible way to improve N use efficiency.     

Phosphorus loss from land to water: integrating agricultural and environmental management

Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased society's awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.     

Challenges and innovations on biological treatment of livestock effluents

Intensification of animal production led to high amounts of manure to be managed. Biological processes can contribute to a sustainable manure management. This paper presents the biological treatments available for the treatment of animal manure, mainly focusing on swine manure, including aerobic processes (nitrification, denitrification, enhanced biological phosphorus removal) and anaerobic digestion. These processes are discussed in terms of pollution removal, ammonia and greenhouse gas emissions (methane and nitrous oxide) and pathogen removal. Application of emerging processes such as partial nitrification and anaerobic ammonium oxidation (anammox) applied to animal manure is also considered. Finally, perspectives and future challenges for the research concerning biological treatments are highlighted in this paper.     

Microbial Community Dynamics of a Continuous Mesophilic Anaerobic Biogas Digester Fed with Sugar Beet Silage

The aim of the study was to investigate the long‐term fermentation of an extremely sour substrate without any addition of manure. In the future, the limitation of manure and therefore the anaerobic digestion of silage with a very low buffering capacity will be an increasing general bottleneck for energy production from renewable biomass. During the mesophilic anaerobic digestion of sugar beet silage (without top and leaves) as the sole substrate (without any addition of manure), which had an extreme low pH of around 3.3, the highest specific gas production rate (spec. GPR) of 0.72 L/g volatile solids (VS) d was achieved at a hydraulic retention time (HRT) of 25 days compared to an organic loading rate (OLR) of 3.97 g VS/L d at a pH of around 6.80. The methane (CH₄) content of the digester ranged between 58 and 67 %, with an average of 63 %. The use of a new charge of substrate (a new harvest of the same substrate) with higher phosphate content improved the performance of the biogas digester significantly. The change of the substrate charge also seemed to affect the methanogenic population dynamics positively, thus improving the reactor performance. Using a new substrate charge, a further decrease in the HRT from 25 to 15 days did not influence the digester performance and did not seem to affect the structure of the methanogenic population significantly. However, a decrease in the HRT affected the size of the methanogenic population adversely. The lower spec. GPR of 0.54 L/g VS d attained on day 15 of the HRT could be attributed to a lower size of methanogenic population present in the anaerobic digester during this stage of the process. Furthermore, since sugar beet silage is a relatively poor substrate, in terms of the buffering capacity and the availability of nutrients, an external supply of buffering agents and nutrients is a prerequisite for a safe and stable digester operation.     

Stirring and biomass starter influences the anaerobic digestion of different substrates for biogas production

Here, we present the results of lab‐scale experiments conducted in a batch mode to determine the biogas yield of lipid‐rich waste and corn silage under the effect of stirring. Further semi‐continuous experiments were carried out for the lipid‐rich waste with/without stirring. Additionally, it was analyzed how the starter used for the batch experiment influences the digestion process. The results showed a significant stirring effect on the anaerobic digestion only when seed sludge from a biogas plant was used as a starter. In this case, the experiments without stirring yielded only about 50% of the expected biogas for the investigated substrates. The addition of manure slurry to the batch reactor as part of the starter improved the biogas production. The more diluted media in the reactor allowed a better contact between the bacteria and the substrates making stirring not necessary.     

京郊典型集约化"农田-畜牧"生产系统氮素流动特征

城郊畜牧业的集约化发展在满足人们日益增长的肉蛋奶等动物性产品需求的同时,也带来了巨大的环境压力。本文利用养分流动和模型分析的方法,分析北京市郊区某村三种不同类型"农田-畜牧"生产系统(大型集约化种猪场、种养结合小规模生态养殖园和集约化单一种植区)的氮素流动特征。结果表明:饲料是集约化种猪场和生态养殖园氮素输入的主要来源,饲料投入氮量分别为12469.0和9268.5 kg.hm-.2a-1);集约化种猪场农牧体系间生产脱节,致使农田氮素输入主要依赖于化肥投入,化肥氮输入量(435.0 kg.hm-.2a-1)占农田氮素输入量的82.7%。相反,生态养殖园农牧体系结合紧密,猪粪尿氮还田比例达28.6%,这使得园区化肥氮输入量仅为135.0 kg.hm-.2a-1,因此畜禽粪尿的合理循环利用可作为减少化肥投入的有效途径;集约化种猪场、生态养殖园和单一种植区农牧生产系统氮素利用效率分别为18.8%、20.6%和17.3%,均处于较低水平;集约化种猪场猪粪尿在猪舍和储藏处理过程的氮素损失率为15.8%和25.4%,分别低于小规模生态养殖园相应损失率约8.7和4.8个百分点;生态养殖园粪肥氮还田量高,导致农田氮素盈余量高达1962.8 kg.hm-.2a-1,未能实现生态型养殖的理想效果,优化氮素管理、确定合理的消纳畜禽粪尿的农田面积和调整畜禽养殖密度是解决该问题的关键。     

Effects of pig manure and wheat straw on growth of mung bean seedlings grown in aluminium toxicity soil

Crop production in red soil areas may be limited by Al toxicity. A possible alternative to ameliorate Al toxicity is the application of such organic manure as crop straw and animal manure. A pot experiment was conducted to investigate the effects of organic materials on the alleviation of Al toxicity in acid red soil. Ground wheat straw, pig manure or CaCO3 were mixed with the soil and incubated, at 85% of water holding capacity and 25 degrees C, for 8 weeks. After the incubation, 14 seedlings of mung bean (Phaseolus aures Roxb) were allowed to grow for 12 days. Results showed that application of organic material or CaCO3 increased soil pH and decreased soil monomeric inorganic Al concentrations. Growth of mung bean seedling was improved sustantially by the application of organic material or CaCO3. Pig manure or wheat straw was more effective in ameliorating Al toxicity than was CaCO3. Mung bean plants receiving pig manure or wheat straw contained relatively high concentrations of P, Ca and K in their leaves. It is suggested that the beneficial effect of organic manure on mung bean is likely due to decreasing concentrations of monomeric inorganic Al concentrations in soil solution and improvement of mineral nutrition.     

Physicochemical and microbiological indicators of surface water body contamination with different sources of digestate from biogas plants

Transition from fossil energy sources to biogas production has resulted in a strong increase of leakage accidents from fermenters, but knowledge on the effects of fermentation product runoff into freshwater systems is currently restricted to direct toxicity due to oxygen depletion. This study provides first information about the influence of digestate runoff on the physicochemical habitat properties and the bacterial community composition of the hyporheic interstitial which is important in determining ecosystem functioning. We exposed natural stream beds to different concentrations of two different digestates from fermenters (corn and manure feedstock), hypothesizing that the digestate addition causes acute changes of the physicochemical parameters and has distinct effects on microbial community composition of the hyporheic interstitial depending on concentration and type of digestate. In line with the hypotheses, pH value, conductivity, redox potential and ammonium differed significantly from controls and among treatments after digestate addition, but only for a maximum of two days. pH values (controls: 7.8; corn: 7.9; manure: 7.9) and conductivity (controls: 813 μS/cm; corn: 969 μS/cm; manure: 1097 μS/cm) increased, the redox potential (controls: 153 mV; corn: 145 mV; manure: 144 mV) decreased the first two days. A high peak of ammonium-N was detected in the corn and manure treatments (controls: 5 mg/l, corn: 80 mg/l; manure: 60 mg/l) at day 1. In contrast, changes in bacterial community composition were detectable for longer periods of time (>5 days). Seventeen unique T-RF fingerprints of bacterial community response to each of the different digestate treatments (11 unique T-RFs in manure and 6 unique T-RFs in corn treatments) were found, suggesting that this approach provides a suitable ecological indicator for source tracking, e.g. in case of a biogas power plant leakage accident.     

Biotechnological intensification of biogas production

The importance of syntrophic relationships among microorganisms participating in biogas formation has been emphasized, and the regulatory role of in situ hydrogen production has been recognized. It was assumed that the availability of hydrogen may be a limiting factor for hydrogenotrophic methanogens. This hypothesis was tested under laboratory and field conditions by adding a mesophilic (Enterobacter cloacae) or thermophilic hydrogen-producing (Caldicellulosyruptor saccharolyticus) strain to natural biogas-producing consortia. The substrates were waste water sludge, dried plant biomass from Jerusalem artichoke, and pig manure. In all cases, a significant intensification of biogas production was observed. The composition of the generated biogas did not noticeably change. In addition to being a good hydrogen producer, C. saccharolyticus has cellulolytic activity; hence, it is particularly suitable when cellulose-containing biomass is fermented. The process was tested in a 5-m³ thermophilic biogas digester using pig manure slurry as a substrate. Biogas formation increased at least 160–170% upon addition of the hydrogen-producing bacteria as compared to the biogas production of the spontaneously formed microbial consortium. Using the hydrogenase-minus control strain provided evidence that the observed enhancement was due to interspecies hydrogen transfer. The on-going presence of C. saccharolyticus was demonstrated after several months of semicontinuous operation.     

Anaerobic Co-digestion of Swine Manure and Microalgae <Emphasis Type="Italic">Chlorella</Emphasis> sp.: Experimental Studies and Energy Analysis

Integration of algae production with livestock waste management has the potential to recover energy and nutrients from animal manure, while reducing discharges of organic matter, pathogens, and nutrients to the environment. In this study, microalgae Chlorella sp. were grown on centrate from anaerobically digested swine manure. The algae were harvested for mesophilic anaerobic digestion (AD) with swine manure for bioenergy production. Low biogas yields were observed in batch AD studies with algae alone, or when algae were co-digested with swine manure at ≥43 % algae (based on volatile solids [VS]). However, co-digestion of 6–16 % algae with swine manure produced similar biogas yields as digestion of swine manure alone. An average methane yield of 190 mL/g VS_fed was achieved in long-term semi-continuous co-digestion studies with 10?±?3 % algae with swine manure. Data from the experimental studies were used in an energy analysis assuming the process was scaled up to a concentrated animal feeding operation (CAFO) with 7000 pigs with integrated algae-based treatment of centrate and co-digestion of manure and the harvested algae. The average net energy production for the system was estimated at 1027 kWh per day. A mass balance indicated that 58 % of nitrogen (N) and 98 % of phosphorus (P) in the system were removed in the biosolids. A major advantage of the proposed process is the reduction in nutrient discharges compared with AD of swine waste without algae production.     

Biochar from animal manure: A critical assessment on technical feasibility,economic viability,and ecological impact

Animal manure has been used to manage soil fertility since the dawn of agriculture. It provides plant nutrients and improves soil fertility. In the last decades, animal husbandry has been significantly expanded globally. Its economics were optimized via the (international) trade of feed, resulting in a surplus of animal manure in areas with intensive livestock farming. Potentially toxic elements (PTEs), pathogenic microorganisms, antibiotic residues, biocides, and other micropollutants in manure threaten animal, human, and environmental health. Hence, manure application in crop fields is increasingly restricted, especially in hotspot regions with intensive livestock activities. Furthermore, ammonia volatilization and greenhouse gas (GHG) emissions during manure storage, field application, and decomposition contribute to air pollution and climate change. Conventional manure management scenarios such as composting and anaerobic digestion partially improve the system but cannot guarantee to eliminate sanitary and contamination risks and only marginally reducing its climate burden. Hence, this review discusses the potential of pyrolysis, the thermochemical conversion under oxygen-limited conditions as an alternative treatment for animal manure providing energy and biochar. Manure pyrolysis reduces the bioavailability of PTEs, eliminates pathogenic microorganisms and organic micropollutants, and reduces GHG emissions. Pyrolysis also results in the loss of nitrogen, which can be minimized by pretreatment, that is, after removing soluble nitrogen fraction of manure, for example, by digestion and stripping of ammonia–nitrogen or liquid–solid separation. However, conclusions on the effect of manure pyrolysis on crop yield and fertilization efficiencies are hampered by a lack of nutrient mass balances based on livestock unit equivalent comparisons of manure and manure biochar applications. Hence, it is essential to design and conduct experiments in more practically relevant scenarios and depict the observations based on the amount of manure used to produce a certain amount of biochar.     

Shifts in microbial community,pathogenicity-related genes and antibiotic resistance genes during dairy manure piled up

The uncomposted faeces of dairy cow are usually stacked on cow breeding farms, dried under natural conditions and then used as cow bedding material or they may be continuously piled up. However, no information is available to evaluate variations in the human and animal pathogen genes and antibiotic resistance during the accumulation of fresh faeces of dairy cow to manure. Here, we present the metagenomic analysis of fresh faeces and manure from a dairy farm in Ning Xia, showing a unique enrichment of human and animal pathogen genes and antibiotic resistance genes (ARGs) in manure. We found that manure accumulation could significantly increase the diversity and abundance of the pathogenic constituents. Furthermore, pathogens from manure could spread to the plant environment and enphytotic pathogens could affect the yield and quality of crops during the use of manure as a fertilizer. Levels of virulence genes and ARGs increased with the enrichment of microbes and pathogens when faeces accumulated to manure. Accumulated manure was also the transfer station of ARGs to enrich the ARGs in the environment, indicating the ubiquitous presence of environmental antibiotic resistance genes. Our results demonstrate that manure accumulation and usage without effective manure management is an unreasonable approach that could enrich pathogenic microorganisms and ARGs in the environment. The manure metagenome structure allows us to appreciate the overall influence and interaction of animal waste on water, soil and other areas impacted by faecal accumulation and the factors that influence pathogen occurrence in products from dairy cows.     

A sustainable pathway of cellulosic ethanol production integrating anaerobic digestion with biorefining

Anaerobic digestion (AD) of animal manure is traditionally classified as a treatment to reduce the environmental impacts of odor, pathogens, and excess nutrients associated with animal manure. This report shows that AD also changes the composition of manure fiber and makes it suitable as a cellulosic feedstock for ethanol production. Anaerobically digested manure fiber (AD fiber) contains less hemicellulose (11%) and more cellulose (32%) than raw manure, and has better enzymatic digestibility than switchgrass. Using the optimal dilute alkaline pretreatment (2% sodium hydroxide, 130°C, and 2 h), enzymatic hydrolysis of 10% (dry basis) pretreated AD fiber produces 51 g/L glucose at a conversion rate of 90%. The ethanol fermentation on the hydrolysate has a 72% ethanol yield. The results indicate that 120 million dry tons of cattle manure available annually in the U.S. can generate 63 million dry tons of AD fiber that can produce more than 1.67 billion gallons of ethanol. Integrating AD with biorefining will make significant contribution to the cellulosic ethanol production. Biotechnol. Bioeng. 2010;105: 1031–1039. © 2009 Wiley Periodicals, Inc.     

Activities in nonpoint pollution control in rural areas of Poland

Agriculture can contribute to water quality deterioration through the release of sediments, pesticides, animal manure, fertilisers and other sources of inorganic and organic matter. Nonpoint pollution control activities in rural areas of Poland are insufficient to meet the demands of the recovering agricultural production. There is still a need for agricultural runoff monitoring programs for identification, quantification and control of nonpoint sources. Special efforts are required to familiarise farmers with environmental friendly agricultural production technologies and ‘good agricultural practices’. This paper describes typical nonpoint sources from Polish agriculture. It presents all these activities and achievement in nonpoint pollution control after 1989, when systemic changes began and environmental problems became more visible.     

Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure

The objective of this work was to examine the feasibility of biogas production from the anaerobic co-digestion of herbal-extraction residues with swine manure. Batch and semi-continuous experiments were carried out under mesophilic anaerobic conditions. Batch experiments revealed that the highest specific biogas yield was 294 mL CH₄ g⁻¹ volatile solids added, obtained at 50% of herbal-extraction residues and 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Specific methane yield from swine manure alone was 207 mL CH₄ g⁻¹ volatile solid added d⁻¹ at 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Furthermore, specific methane yields were 162, 180 and 220 mL CH₄ g⁻¹ volatile solids added d⁻¹ for the reactors co-digesting mixtures with 10%, 25% and 50% herbal-extraction residues, respectively. These results suggested that biogas production could be enhanced efficiently by the anaerobic co-digestion of herbal-extraction residues with swine manure.