Commercial Biogas Plants Research Articles

Improving biogas production with application of trimetallic nanoparticle using response surface methods

The potential of trimetallic nanoparticles (TMNPs) to enhance biogas production through microbe-to-microbe interactions and boost biogas yield is evident. This present study employed the central composite design (CCD) of response surface methods (RSM) to determine the optimal conditions of iron-cobalt-zinc TMNPs influenced anaerobic digestion for higher biogas yield. The impact of initial pH (6.6–7.4), TMNPs concentration (0–30 mg L−1), temperature (25-45 °C), and hydraulic retention time (HRT) (0-4 days) were modelled for improved biogas production. The results indicated that the linear model terms of pH and TMNPs concentration, and quadratic model terms of temperature and HRT, significantly affect the biogas production. Linear model terms of TMNPs, temperature, pH, and HRT have significant interactive effects and the numerical analysis identified the best conditions for the evaluated parameters. Ideal anaerobic process settings generated a maximum cumulative biogas production of 3700 mL−1POME than blank (2000 mL−1), corresponding to an 85 % yield. Optimizing the initial pH, TMNPs concentration, temperature, and HRT can significantly improve biogas yield and could be helpful for developing more efficient AD processes at large volume and commercial biogas plants. Promoting TMNPs as catalysts positively improves an AD process towards sustainable biogas production.

Operational process stability in pilot dry anaerobic digester of source‐sorted organic fraction municipal solid waste

AbstractThe organic fraction of municipal solid waste (OFMSW) is a major portion of solid waste in Malaysia, with 44.5% of the total waste being food waste‐derived sources. This study investigates the performance of dry anaerobic digester (DAD) operation using the pilot dry anaerobic digester (PDAD), a plug flow reactor, in treating source‐sorted organic fraction municipal solid waste (SS‐OFMSW) for biogas production. A commercial Malaysian food waste (CMFW) sample has been used to represent SS‐OFMSW. The anaerobic digestion was performed in a semi‐continuous operation using a 15 m3 PDAD with organic loading rates (OLRs) ranging from .63 to 5.46 kg volatile solid (VS)/m3·day under mesophilic conditions. The maximum methane composition was achieved at 56.0% at OLR 5.17 kg VS/m3·day with specific methane production (SMP) of .57 m3·CH4/kg VSfed and gas production rate (GPR) 5.27 m3·gas/m3·digester·day. As indicated by a pH and alkalinity ratio, the PDAD system was stable ranging from pH 6.7 to 8.3, alkalinity ratio of .3 with an inclination of total ammonia nitrogen (TAN) up to 1056 mg/L. The SMP achieved is between 1.58 and .4 m3·CH4/kg VSfed and potentially to fuelled 475 MW commercial biogas plant fed by CMFW. The DAD deployment strengthened the circular economy and decarbonization initiatives.

A Case Study on Small- and Centralized Biogas Plants and Energy Production Capacities in South Gyeongsang Province

Objectives : The primary goals of this research were to assess the viability and practicality of small-scale village facilities as well as central commercial biogas plants. Additionally, the study aimed to create predictive models by exploring various codigestion scenarios.Methods : The study conducted a comprehensive analysis of available biomass and its maximum energy potential through anaerobic digestion in every city, county, and village within South Gyeongsang province. Five distinct codigestion scenarios were explored, encompassing assessments of processing capacity, energy production potential, and the necessary digester capacity for anaerobic digestion. At the village level, the scenarios comprised: C1, which involved sole digestion of manure; C2, codigestion of manure and food waste in a 7:3 ratio; C3, codigestion of pig slurry and slaughterhouse waste in a 9:1 ratio; C4, multiple codigestion with PS:FW:SW=6.5:2.8:0.8; and finally, C5, involving the addition of sewage and sewage sludge to the codigestion process of C4's biomass.Results and Discussion : The biomass generated in South Gyeongsang province was 9430 tons/day, with a methane production potential of 167 million cubic meters/year. This biomass had an energy production potential of 156,000 TOE/year and a potential electricity generation of 732.7 GW/year, based on the annual petroleum conversion ton. Codigestion (C5) enabled up to 720% more electricity generation compared to sole digestion of manure (C1). Mixing pig slurry and food waste in a 7:3 ratio resulted in approximately 18% more electricity production compared to the case where manure was mixed with slaughterhouse by-products in a 9:1 ratio.Conclusion : Biomass imbalance was significant in most regions, particularly due to high variations in food waste generation between regions. Obtaining alternative resources and integrating various biomass for anaerobic digestion, especially in rural areas, is crucial for achieving stable anaerobic digestion and high methane production. Regions with high biomass density are predicted to support large-scale biogas facilities following European standards, while 25 villages showed the potential for small-scale biogas facilities.

Socio-Economic Benefits of Biogas for Women in Household Cooking In Nepal

The bio-gas is viable technology as household cooking solution to reduce smoke related diseases, accidents of burning, good source of organic fertilizer, save time for collection of fuel wood and change the kitchen environment. It is important energy source. Women empowerment is possible through bio-gas in Nepalese kitchens and promotes changes in cooking practice. The bio-gas programme is most effective and successful programme in rural Nepal. By studying and understanding the potential of biogas, the research can provide valuable insights into the potential of biogas to improve the lives of semi-urban communities and contribute to sustainable development with a specific focus on women’ welfare. The researcher collected primary data and information through survey questionnaire and secondary data were gathered from relevant reports and documents published by government and bio-gas companies. The study employed both quantitative as well as qualitative techniques of data analysis. For the study, the respondents were broadly categorized in two distinct categories: households with privately owned biogas plants and the households connected to commercial biogas plant recently launched in Ghorahi Sub-Metropolitan City. For quantitative data, questionnaire was distributed among 60 randomly selected households having privately owned biogas plant, and 40 respondents were also randomly selected from among the 50 households connected to commercial biogas plant. Finally, qualitative findings from key informant interview (KII) and observation were also applied to justify and strengthen the quantitative findings. For this purpose, interviews were conducted among the Mayor of Ghorahi Sub-Metropolitan City, DE and Ward Chairman of project site. Major proportion of waste in Ghorahi is biomass that includes kitchen waste, farm residue and livestock dung that has been utilized to produce flammable methane gas. Bio-gas is cost effective, so, households of all income groups can afford the technology. Bio-gas as clean fuel enhances Nepalese women’s culinary practice, plays crucial role in women’s welfare; which is the first step towards women empowerment. The study has shown that women and girls have greatly relieved from the drudgery of fuel wood collection and smoke related diseases.

Sustainability of large-scale commercial biogas plants in Nepal

Interest in large-scale compressed biogas (CBG) and biogas for electricity generation is increasing due to these technologies’ potential for addressing dual energy and waste management challenges. However, sustainable operation of large-scale commercial biogas plants requires attention to numerous factors, including technical aspects (feedstock types, plant size, operational parameters, and biogas and fertilizer utilization strategies), costs (capital investment and operational), and affordability, as affected also by subsidies. This study conducts a case study of the sustainability of an existing operational large-scale biogas plant in Nepal, considering its operational condition, financial status, and environmental benefits under designed capacity and actual operating conditions. Design parameters related to biogas and digestate production, financial viability, and greenhouse gas (GHG) emission reduction potential were compared with the realized outcomes of the plant. Operational and financial data for the plant were obtained through visits to the plant supplemented by interviews of the plant manager. The analysis reveals that both the feedstock and digester efficiencies are much lower than the design expectations, by 55% and 62%, respectively. This has led to reductions in the production of biogas and biofertilizers by 72% and 90%, respectively. Moreover, while the internal rate of return (IRR) of the plant at design capacity was 23%, it is indeterminate for the actual operating condition, as the net present value is negative for all discount rates. The biogas plant does generate environmental benefits; the GHG emissions avoided are estimated to be around 274 tons of CO2 equivalent per year under the actual operating conditions. Given these results, it is clear that improving the operational performance of large-scale biogas plants in contexts such as this one should be a priority. Moreover, the findings can help policymakers, investors, and other stakeholders make better plans for future development of biogas facilities, insisting on more realistic and careful assessments of technical and financial viability.

Anaerobic digestion: A promising technology of utilizing radioactively contaminated plant biomass

Anaerobic digestion (AD) is a widely used technology that allows for the reprocessing and reduction of waste biomass. A study was conducted to see if the AD technology might be used to process radioactively polluted agricultural biomass. For this purpose, laboratory tests were carried out with a 20-liter model biogas plant (BGP) with the radionuclide 134Cs and operational tests with the South Bohemian commercial biogas plant monitoring the radionuclide 137Cs. The activities of 134Cs in inputs, contaminated grass or maize silage and in emerging fractions were investigated in the model fermenter. The activity of 134Cs in the dry matter during the fermentation process increased by 46% on average, which corresponds to a reduction of dry matter by 43% due to the production of biogas. 137Cs activities were measured in commercial BGP maize, grass, and whole plant silage, wheat, digestate, biogas, and aerosol samples. The commercial BGP fermentation process was more efficient, with an 80% reduction in dry mass weight. Dry biomass (1.37 Bq/kg) had a 137Cs massic activity that was 4.4 times lower than the activity of dry digestate mass (6.01 Bq/kg). The activity of the 137Cs in biogas aerosol was 1.1 × 10−7 Bq/m3 or less, and the decontamination factor was 6.9 × 106 or greater. Most Cs remain in the digestate. No other ways of radioactivity leakage have been identified.

Life cycle assessment of environmental impacts for two-stage anaerobic biogas plant between commercial and pilot scales

This study presents the detailed life cycle assessment (LCA) of environmental impact potential for two-stage anaerobic biogas plants between commercial and pilot scales. It provides a comprehensive and systematic approach to evaluating the environmental impacts of producing biogas from livestock wastes in several phases: collecting, processing, and production. The commercial biogas plant (C-BP) system is located in Central Taiwan's pig farm, with 1500–2000 pigs a year. The Symnergy (symbiosis bioenergy model) biogas pilot plant (S-BP) is installed in Manado City, Indonesia. The Institute of Green Products, Feng Chia University, designed both C-BP and S-BP systems. The environmental impacts of both systems' gate-to-grave life cycles were assessed and compared using Simapro 9.0.0 software. The pilot-scale biogas plants produce bioenergy from the wastewater of the slaughterhouse. Therefore, 10,950 tonne/year of slurry feedstock flowing into the commercial biogas plant was considered a functional unit equal to 21 times larger than the pilot scale biogas plant. The LCA analyzes the impacts of three processes for feedstock collection, biogas production, and digestate production. It was found that Photochemical Ozone Creation Potential had the highest total impact on C-BP (33%), and Eutrophication had the highest impact on S-BP (33%). Both the biogas production systems of C-BP and S-BP showed very low environmental impacts, and the impacts of C-BP are lower than the S-BP. However, implementing digesters considerably reduced the potential environmental impacts of well manure feedstock handling and fertilizer applications. The LCA analysis among the three individual processes is developed to allow critical points and environmental impacts for local government. Consequently, the LCA report could help establish regional sustainability strategies for the management of livestock wastes by anaerobic two-stage biogas plant from manure.

Bioaugmentation with cold-tolerant methanogenic culture to boost methane production from anaerobic co-digestion of cattle manure and corn straw at 20℃

Low methane yield and long digestion period are common issues encountered in psychrophilic anaerobic digestion (AD). To address these challenges, this study successfully acclimatized a cold-tolerant methanogenic consortium and applied it as bioaugmentation seed to enhance the psychrophilic AD. Various doses (4%, 8%, 12%, 14%, and 16%) of the bioaugmentation seed were introduced to boost the batch psychrophilic AD of cattle manure and corn straw. Results demonstrated that bioaugmentation increased the methane yield by 3.4–4.8-fold, shortened T80 time by 28–34 d, and reduced VFAs contents by 21.61%-49.23%. The optimal dose for bioaugmentation on psychrophilic AD was 12%, increasing methane yield from 15.40 mL g-1VS to 73.01 mL g-1VS. Microbial community analysis revealed that increase in relative abundance of propionate-oxidizing bacteria and the dominant methanogens (Methanosarcina, Methanothrix) were the key to accelerating the rate-limiting step, i.e., conversion of accumulated propionate and acetate to methane. These findings suggest that bioaugmentation with cold-tolerant methanogenic consortium is a potential approach to boost the psychrophilic AD process, and provide theoretical guidance for commercial biogas plants in cold regions.

Performance of biogas plant analysis and policy implications: Evidence from the commercial sources

This study investigates the potential of biogas as a commercially viable alternative energy source in Pakistan due to her large agricultural base. The production of biogas is a source of utilizing enriched livestock manure resulting in smell reduction, village sanitation, and environmental improvement. The cost-benefit analysis approach is adopted to explore the empirical findings. The analysis is carried out on four different commercial biogas plants with capacities ranging from 20 to 200 m3 that have been erected in various parts of Pakistan, the majority in Punjab province due to their agricultural and animal capacity. Total inflows are calculated which include installation, administrative, operation, and maintenance costs. Although benefits extracted are examined in terms of monetary value. Meanwhile, it is concluded through quantitative assessment that 8 out of 9 plants are giving good returns, which can cater to the energy needs. Furthermore, it can be suggested that commercial use of biogas is feasible and profitable with an acceptable rate of returns with proper operating and feeding of the plant is essential for success. Therefore, training should be provided to agriculture and livestock farmers so that they can perform better in the development of biogas plants.

Integrated multi-omics analyses reveal the key microbial phylotypes affecting anaerobic digestion performance under ammonia stress

Ammonia inhibition is one of the most common causes of instability during the operation of commercial biogas plants. Here, the sensitivity of different functional bacteria to ammonia stress, the ability of functional bacteria to adapt to ammonia stress, and the key phylotypes affecting anaerobic digestion (AD) performance were studied by evaluating the process performance, active microbiome, and protein expression patterns during endogenous ammonia accumulation using integrated metagenomics and metaproteomics analyses. Acetate metabolism was most sensitive to ammonia stress, and the expression activity of methyl-CoM reductase of Methanothrix was inhibited at relatively low ammonia concentrations, which resulted in the accumulation of acetate and other short-chain volatile fatty acids (VFAs) through feedback effects. As the AD process progressed, the abundance of active Methanosarcina with high ammonia tolerance increased, and the activity of their enzymes related to acetoclastic methanation was significantly up-regulated, which resulted in the complete restoration of acetate metabolism and AD performance. Thus, microbial communities can cope with acetate metabolic repression through self-optimization. In contrast, when the total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) increased to 4846.95 mg N/L and 337.46 mg N/L, respectively, propionate (and no other VFAs) accumulated in the digester, which was accompanied by a decrease in methane yield by more than 65%. At this time, the abundance of active syntrophic propionate-oxidizing bacteria (SPOB) decreased by 52%, and the expression of key enzymes related to propionate degradation was significantly down-regulated. The proportion of down-regulated differentially expressed proteins in the dominant Pelotomaculum was as high as 94%, indicating the severe suppression of the growth of these functional bacteria as well as their inability to easily acclimate to ammonia stress. Thus, SPOB appeared to be the key microbial phylotypes affecting AD performance under ammonia stress. Ammonia inhibited the methylmalonyl-CoA pathway of Pelotomaculum by inhibiting the expression of succinyl-CoA synthase, which resulted in the suppression of syntrophic propionate oxidation. The results of this study provide new insights into the microbial mechanism of ammonia inhibition and identify the key phylotypes affecting AD performance under ammonia stress. Our findings also shed light on the microbial regulatory targets of nitrogen-rich waste anaerobic digesters.

Characterization of Blf4, an Archaeal Lytic Virus Targeting a Member of the Methanomicrobiales.

Today, the number of known viruses infecting methanogenic archaea is limited. Here, we report on a novel lytic virus, designated Blf4, and its host strain Methanoculleus bourgensis E02.3, a methanogenic archaeon belonging to the Methanomicrobiales, both isolated from a commercial biogas plant in Germany. The virus consists of an icosahedral head 60 nm in diameter and a long non-contractile tail of 125 nm in length, which is consistent with the new isolate belonging to the Siphoviridae family. Electron microscopy revealed that Blf4 attaches to the vegetative cells of M. bourgensis E02.3 as well as to cellular appendages. Apart from M. bourgensis E02.3, none of the tested Methanoculleus strains were lysed by Blf4, indicating a narrow host range. The complete 37 kb dsDNA genome of Blf4 contains 63 open reading frames (ORFs), all organized in the same transcriptional direction. For most of the ORFs, potential functions were predicted. In addition, the genome of the host M. bourgensis E02.3 was sequenced and assembled, resulting in a 2.6 Mbp draft genome consisting of nine contigs. All genes required for a hydrogenotrophic lifestyle were predicted. A CRISPR/Cas system (type I-U) was identified with six spacers directed against Blf4, indicating that this defense system might not be very efficient in fending off invading Blf4 virus.

Influence of inoculum/substrate ratio on biogas yield and kinetics from the anaerobic co-digestion of food waste and maize husk

The study reports for the first time, the influence of inoculum/substrate (I/S) ratios on biogas yield and kinetics of food waste (FW) and maize husk (MH) anaerobic co-digestion. The study was investigated in six anaerobic digesters, D-0, D-0.25, D-0.5, D-1, D-2, and D-4 at 36 ± 2 °C. D-1 with I/S ratio of 1 had the largest cumulative biogas yield of 9.99 L/gVS. Results from the modified Gompertz model revealed a decrease in lag phase (λ) by 20.4% at I/S ratio 1, hence, shows that the amount of time needed for active methanogenesis to commence was hugely decreased. Maximum specific biogas production (Rm) and maximum biogas production potential (A) increased with increase in I/S ratio. Also, D-1 yielded the highest values of 0.37 L/gVS/day and 9.99 L/gVS for Rm and A, respectively. A decrease in biogas yield at D-0.25 and D-0.5 was however obtained with respect to the control experiment. The study recommends confirmation of optimum I/S ratio prior to establishment of commercial biogas plants.

Microbiological Surveillance of Biogas Plants: Targeting Acetogenic Community.

Acetogens play a very important role in anaerobic digestion and are essential in ensuring process stability. Despite this, targeted studies of the acetogenic community in biogas processes remain limited. Some efforts have been made to identify and understand this community, but the lack of a reliable molecular analysis strategy makes the detection of acetogenic bacteria tedious. Recent studies suggest that screening of bacterial genetic material for formyltetrahydrofolate synthetase (FTHFS), a key marker enzyme in the Wood-Ljungdahl pathway, can give a strong indication of the presence of putative acetogens in biogas environments. In this study, we applied an acetogen-targeted analyses strategy developed previously by our research group for microbiological surveillance of commercial biogas plants. The surveillance comprised high-throughput sequencing of FTHFS gene amplicons and unsupervised data analysis with the AcetoScan pipeline. The results showed differences in the acetogenic community structure related to feed substrate and operating parameters. They also indicated that our surveillance method can be helpful in the detection of community changes before observed changes in physico-chemical profiles, and that frequent high-throughput surveillance can assist in management towards stable process operation, thus improving the economic viability of biogas plants. To our knowledge, this is the first study to apply a high-throughput microbiological surveillance approach to visualise the potential acetogenic population in commercial biogas digesters.

Biochemical process evaluation of an anaerobic digester: a case study on long sustain commercial biogas plant

The anaerobic digestion technology has been established decades ago but still the commercial biogas industries are facing some challenges like process imbalance and failure of the digester, which has to be addressed by monitoring and identifying early warning indicators essential in the operation and maintenance. The aim of present study is to evaluate the early warning indicators during start-up: optimization, full load, and gradual overload phases of an 18-m3 commercial food waste biogas plant. The plant was operated by applying the optimal operation limits of FOS/TAC, TVFA/TA, IA/PA (Reply’s), and BA/TA ratios in the optimization of the AD process. The plant performance was studied in terms of methane yield, reduction in OLR, HRT, VS, and COD. The plant was operated for a span of 12 months at different OLRs ranging from 0.32 kg COD/m3/day (start-up) to 2.03 kg COD/m3/day (overload) in a mesophilic condition. Results showed that performance of AD at full load, in terms of biogas yield (m3/day) and methane yield (m3 CH4/(kg VS reduced) and m3 CH4/(kg COD reduced)), was found to be average of 32.65, 0.55, and 0.57, respectively. The process imbalance was observed from day 114 to day 119 of optimization period. The values of FOS/TAC, IA/PA, and TVFA/TA ratios were detected to be slightly more than the regular values, whereas bicarbonate alkalinity (BA) was abruptly reduced to 0.37 (kg CaCO3/m3). On the other hand, intermediate alkalinity (IA) value has been increased to 3.2 (kg CaCO3/m3), which was defined as limit for process instability. The gradual overload (0.6% more VS addition for 28 days) has no significant affect on the AD process and biogas production, but methane yield was slightly decreased.

Economic evaluation of a hybrid renewable energy system (HRES) using hybrid optimization model for electric renewable (HOMER) software—a case study of rural India

Abstract This paper unveils a sustainable energy plan for optimal utilization of available electrical energy resources for an energy-deficient village. The chosen village is Nangal, near Barnala, Punjab, India. Primarily, the requirements of electric energy are recorded and elaborated for around 450 households. Aiming this, the potential to harness electric power and its effective utilization has been identified from the available resources of energy: biomass, agriculture waste and solar photovoltaic (PV) technology. In order to achieve this, a hybrid renewable energy system (HRES) model is proposed whose performance is evaluated by implementing it in hybrid optimization model for electric renewable (HOMER) software. HOMER software provides optimal solution for a commercial biogas plant for catering cooking gas demand. Also, a coordinated solution for solar PV-operated water pumps used for irrigation, village water supply and solar PV street lights is presented and analyzed. In this way, the accurateness of proposed model is investigated by estimating the optimal electric power demand and its economic benefits. It has been revealed that the computed cost of energy and total net present cost are $0.032/KWh and $76,837, respectively, by the parametric assessment of proposed HRES system. It is envisaged that the proposed model can be a road map for future research engineers in designing an effective energy utilization for villages.

Membrane-based technologies for biogas upgrading: a review

Global warming caused by increasing CO2 atmospheric levels is calling for sustainable fuels. For instance, biomethane produced by biogas upgrading is a promising source of green energy. Technologies to upgrade biogas include chemical absorption, water scrubbing, physical absorption, adsorption, cryogenic separation and membrane separation. Historically, water scrubbing was preferred because of the simplicity of this operation. However, during the last decade, membrane separation stood out due to its promising economic viability with investment costs of 3500–7500 €/(m3/h) and operational costs of 7.5–12.5 €/(m3/h). Here we review biogas upgrading by membrane separation. We discuss gas permeation, membrane materials, membrane modules, process configurations and commercial biogas plants. Polymeric materials appear as most adequate for membranes aimed to upgrade biogas. Concerning membrane modules, hollow fibers are the cheapest (1.5–9 €/m2). Multistage configurations provide high methane recovery, of 99%, and purity, of 95–99%, compared to single-stage configurations.

Determination of biogas process efficiency - a practice-oriented alternative to the biomethane potential test

The energy efficiency of biogas plants is fundamentally based on the biochemical degradation of input materials. This paper introduces a novel method of efficiency determination based on the gross calorific value (GCV), a very common method in conventional power generation. GCV investigation of five commercial biogas plants in northern Schleswig Holstein were conducted by a one-year time series analysis with weekly sample taking. Although initially a simple model was used to estimate the lignin content, the plausible results indicate the suitability of the proposed method. For comparison, methods like the FoDM and the classical biomethane potential test are highlighted to point out their traditional usage and their adaption for the biogas sector. Also the laboratory efforts they cause is taken into account.

A Review of Commercial Biogas Systems and Lessons for Africa

Many African countries have vast biomass resources that could serve as feedstock for methane production through the adoption of commercial biogas plants. However, due to many inhibiting factors, these resources are under-utilised. This article reviews commercial biogas systems that treat organic waste from municipalities, large livestock farms, large plantations/crop farms, food/beverage production facilities, and other industries, to identify essential lessons which African countries could use to develop/disseminate such biogas systems. The review identified the critical barriers to commercial biogas development to be high initial capital costs, weak environmental policies, poor institutional framework, poor infrastructure and a general lack of willpower to implement renewable energy policies and set challenging targets. In African countries where feed-in-tariffs, quota obligations and competitive bidding programmes have been instituted, implementation has been poor, and most state-owned utilities have been unsupportive. Using knowledge from more experienced countries such as Germany and China, some key lessons have were identified. Among the key lessons is the need to institute and enforce environmental management policies to ensure that waste from medium and large livestock farms and industries are not disposed of indiscriminately, a tool China has recently used to promote commercial biogas plants to a high degree of success.

Assessment of the degradation efficiency of full-scale biogas plants: A comparative study of degradation indicators

Increasing popularity and applications of the anaerobic digestion (AD) process has necessitated the development and identification of tools for obtaining reliable indicators of organic matter degradation rate and hence evaluate the process efficiency especially in full-scale, commercial biogas plants. In this study, four biogas plants (A1, A2, B and C) based on different feedstock, process configuration, scale and operational performance were selected and investigated. Results showed that the biochemical methane potential (BMP) based degradation rate could be use in incisively gauging process efficiency in lieu of the traditional degradation rate indicators. The BMP degradation rates ranged from 70 to 90% wherein plants A2 and C showed the highest throughput. This study, therefore, corroborates the feasibility of using the BMP degradation rate as a practical tool for evaluating process performance in full-scale biogas processes and spots light on the microbial diversity in full-scale biogas processes.

Assessment of hydrogen metabolism in commercial anaerobic digesters.

Degradation of biomass in the absence of exogenous electron acceptors via anaerobic digestion involves a syntrophic association of a plethora of anaerobic microorganisms. The commercial application of this process is the large-scale production of biogas from renewable feedstock as an alternative to fossil fuels. After hydrolysis of polymers, monomers are fermented to short-chain fatty acids and alcohols, which are further oxidized to acetate. Carbon dioxide, molecular hydrogen (H2), and acetate generated during the process are converted to methane by methanogenic archaea. Since many of the metabolic pathways as well as the syntrophic interactions and dependencies during anaerobic digestion involve formation, utilization, or transfer of H2, its metabolism and the methanogenic population were assessed in various samples from three commercial biogas plants. Addition of H2 significantly increased the rate of methane formation, which suggested that hydrogenotrophic methanogenesis is not a rate-limiting step during biogas formation. Methanoculleus and Methanosarcina appeared to numerically dominate the archaeal population of the three digesters, but their proportion and the Bacteria-to-Archaea ratio did not correlate with the methane productivity. Instead, hydrogenase activity in cell-free extracts from digester sludge correlated with methane productivity in a positive fashion. Since most microorganisms involved in biogas formation contain this activity, it approximates the overall anaerobic metabolic activity and may, thus, be suitable for monitoring biogas reactor performance.