Small-scale Anaerobic Digestion Research Articles

Multiple-criteria decision analysis techniques for anaerobic digester technology assessment

Effective decision-making requires the evaluation of several criteria rather than a single, preferred criterion. The best decision options (alternatives) are recommended to decision-makers when a multi-criteria decision problem is addressed. This study develops a multi-criteria selection method for the assessment of small-scale anaerobic digester technology by combining two existing methods. The Simple Multi-Attribute Rating Technique (SMART) and the Analytical Hierarchy Process (AHP) approaches of multiple-criteria decision analysis were used as a decision support tool, and the preferred anaerobic digester technology was selected from a list of eleven potential small-scale digester technologies used in low to middle-income countries. These techniques were applied under two scenarios for a case study in the South African smallholder farmers. Scenario 1 involves a subsistence smallholder farming context, while scenario 2 involves a commercially oriented smallholder farming context. The overall results revealed that the DIY Biobag and Puxin digester design models achieved 82.1 and 73.7 % preference in comparison to other digester technologies for scenarios 1 and 2, respectively. The Biobag digester technology achieved the highest ranking, which is consistent with the significant cost advantage and technical characteristics of the technology. However, for those households with sufficient access to funds for the initial expenditure, the method identifies the Puxin digester as the most appropriate alternative, excluding cases where underground construction is not possible. The AGAMA BiogasPro digester was ranked in the second position in both scenarios. A sensitivity analysis was conducted to determine the effect of changes in the assessment criteria weights and found the selected alternatives stable and robust. Finally, it can be concluded that the developed technology selection model contributed a knowledge-based framework to be used in various situations by different decision-makers, thereby providing a method applicable to particular local conditions to identify the most suitable technology choices.

Life cycle assessment and cost-benefit analysis of small-scale anaerobic digestion system treating food waste onsite under different operational conditions

This study employed life cycle assessment and cost-benefit analysis to evaluate the environmental and economic profile of a real decentralized small-scale anaerobic digestion (AD) system treating food waste (FW). Different operational conditions, including temperature, biochar addition, biogas engine efficiency, and FW loading, were compared via scenario analysis. Biochar addition could potentially obtain carbon reduction and save fossil fuel. Moreover, at high FW loading and biogas engine efficiency, biochar addition achieved 1–3190% better performance than the system without biochar in all the nine impact categories. The system under mesophilic conditions performed worse than ambient conditions due to high energy demand. All the current scenarios resulted in a monetary loss at US$ 480 k-681 k, while profit was possible if the capital cost and operator salary decreased significantly. Overall, operating the small-scale AD system under ambient temperature with biochar addition was preferred due to its potential environmental benefits and economic profits.

Innovative high-pressure water scrubber for biogas upgrading at farm-scale using vacuum for water regeneration

Biogas upgrading is becoming essential in the valorization path for biogas. Biomethane from anaerobic digestion is identified to be one of the main resources to decarbonize the energy requirement. However, small-scale (especially farm-scale) applications suffer from a lack of implementation worldwide, mainly limited by the cost of the upgrading process. As one of the most used technologies, High Pressure Water Scrubbing presents a great margin for improvement. The most expansive items in this technology remain the packing column used for absorption and the stripping column used for water regeneration. In this work, the stripping column is replaced by a flash tank submitted to a rough vacuum (up to 0.2 bar in absolute pressure) associated to a static mixer to promote the gas desorption and thus the complete regeneration of the water. The implementation of an anisotropic packing, with properties evolving with the height of the column and adapted to the reduction of the gas flowrate due to absorption, is also investigated in order to reduce the size of the absorption column. A full-scale prototype was developed and implemented on a farm anaerobic digester. The range of application is from 20 to 40 Nm3/h of raw biogas. These field experiments associated to a complete description of the gas fluxes allowed to characterize the device in terms of carbon dioxide absorption efficiency, biomethane purity and methane recovery. Influences of six parameters (absorption pressure, desorption pressure, temperature, water flowrate, biogas flowrate, column height) were elucidated regarding those performances. Results highlight the great improvement of the water regeneration conducted under rough vacuum. From 0.8 to 0.2 bar in absolute pressure, the biomethane purity increased by 10%, the carbon dioxide elimination rate by 14%, and the methane recovery by 19%. With an increase in the packing height using an anisotropic configuration (modification of the packing properties with the column height) suited to the gas flowrate decrease into the column, a biomethane purity over 97% was obtained. The energy consumption associated was measured at 0.8 kWh/Nm3 of raw biogas but can be reduced to 0.3 kWh/Nm3. The overall energy efficiency for biogas upgrading can reach up to 91%. These results could pave the way for gas grid injection and vehicle fuel applications for small-scale anaerobic digestion.

Techno-Economic Assessment of On-Site Production of Biomethane, Bioenergy, and Fertilizer from Small-Scale Anaerobic Digestion of Jabuticaba By-Product

Bioenergy recovery from biomass by-products is a promising approach for the circular bioeconomy transition. However, the management of agri-food by-products in stand-alone treatment facilities is a challenge for the low-capacity food processing industry. In this study, the techno-economic assessment of a small-scale anaerobic digestion process was evaluated for the management of jabuticaba by-product and the production of biomethane, electricity, heat, and fertilizer. The process was simulated for a treatment capacity of 782.2 m3 y−1 jabuticaba peel, considering the experimental methane production of 42.31 L CH4 kg−1 TVS. The results of the scaled-up simulated process demonstrated the production of biomethane (13,960.17 m3 y−1), electricity (61.76 MWh y−1), heat (197.62 GJ y−1), and fertilizer (211.47 t y−1). Economic analysis revealed that the process for biomethane recovery from biogas is not profitable, with a net margin of −19.58% and an internal rate of return of −1.77%. However, biogas application in a heat and power unit can improve project feasibility, with a net margin of 33.03%, an internal rate of return of 13.14%, and a payback of 5.03 years. In conclusion, the application of small-scale anaerobic digestion can prevent the wrongful open-air disposal of jabuticaba by-products, with the generation of renewable energy and biofertilizer supporting the green economy toward the transition to a circular economy.

Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan

The Integrated Agriculture System in Indonesia was established in 2009. By the end of 2018, 752 small-scale anaerobic digestion (AD) systems treating beef cattle manure were successfully installed. In this study, the system was studied comprehensively at the first attempt by considering the current operating conditions, the actual performance of the digester, and site-specific factors for biogas production. Compost and bio-urine were produced at approximately 0.13 t/day and 4.8 L/day, respectively. The digester produced an unstable biogas amount of 0.109 to 0.521 m3/day. However, digester in Japan produces biogas 980 m3/day. This observed difference was due to the difference in the inputs and technological peculiarities. The main purpose for installation of the AD system was also different. Producing compost and bio-urine were the aimed in Indonesia, while producing biogas and reducing sawdust usage were the target in Japan. Thus, this study suggested that monitoring and controlling the operational parameters of digester in Indonesia could increase the biogas production as a first step without installing any additional temperature controller or mixing equipment. This approach might also be useful for improving the quality of compost and bio-urine by providing stable treatment conditions.

The influence of coagulant type on the biological treatment of sewage sludge

Anaerobic digestion (AD) and composting are commonly utilized sludge management methods however, the influence of different coagulant types on these biological processes and their stabilized biomass characteristics have not been fully explained. In this study, the effect of the coagulant used in municipal wastewater treatment on the biological stabilization of sludge was investigated. Fully controlled and monitored small-scale AD and composting bioreactors were utilized. The coagulants tested included an inorganic coagulant (IC), polyaluminium chloride (PAC), and organic coagulants, (OC) polyamine (pAmine) and chitosan (Chit). Overall, the coagulant applied showed a measurable influence on the biological stabilization of sludge. The presence of complex organics compounds from OC in the sludge biomass was found to decrease biomass biodegradability while increasing gas production. During AD, Chit-sludge achieved higher biogas production than pAmine- and PAC-sludges (13 % and 16 %, respectively, in Nm3 CH4 t−1VS). In composting, pAmine-sludge achieved the highest feedstock temperature (34–35 °C) and CO2 gas emissions, followed by Chit- (33 °C) and PAC-sludges (32 °C). Generally, tot-P concentration in PAC-sludge was higher than in pAmine and Chit-sludges both before (20, 17 and 15 g/kg DM, consecutively) and after AD (23, 21 and 20.5 g/kg DM, consecutively), and during the composting (31, 29.5 and 26 g/kg DM, consecutively) process. Tot-N concentrations (g/kg DM) showed a substantial increase after AD (pAmine and PAC ca 50 % and Chit 81 %), while a decrease was observed after composting, specifically in PAC-sludge (PAC 28 %, pAmine and Chit ⁓5 %). The selection of the most suitable coagulant by wastewater treatment facilities depends on the objective of the biological stabilization process. In cases where AD is applied and biogas yield is selected as the target output, the semi-natural OC Chit was found to be the best option among the coagulants tested. Comparably, when the nutrient content of resulting biosolids (AD or composting) is more relevant, it was found that OC-produced sludge contained higher N concentrations, while IC-produced sludge contained slightly higher P concentrations.

The Design, Development and Assessment of a Novel De-centralised IoT-Based Remote Monitoring of a Small-Scale Anaerobic Digester Network

The implementation of community-level de-centralised anaerobic digestion (AD) systems offers a sustainable solution for organic waste management and energy provision, but there is currently a need for low-cost methods of system control and management at this scale. The problem becomes accentuated with increasing deployment, as greater complexities are created by the need to both monitor and control a wider network of smaller, community-scale plants. This paper describes research to design, deploy and test such a system by creating a network of two independent biogas generation AD reactor sites situated in the United Kingdom and Thailand. Internet of things (IoT) aspects such as inexpensive and widely available open-source control electronics was used in combination with small commercial gas analysers to log, transfer and share data with a central station, achieving real-time monitoring of performance for both networked digesters. The design proved beneficial for collaboration and knowledge exchange purposes along with providing off-site observations on reactor status. This information was used for early intervention to maintain biogas yields and enable the dynamic assessment of process economics. The concept showed potential for upscaling to larger multi-site networks of AD reactors that could maintain process optimisation without the need for skilled staff on site.

Techno-economic analysis of a micro-scale biogas plant integrated with microalgae cultivation for the treatment of organic municipal waste

The deployment of small-scale anaerobic digestion (AD) plants for the treatment of the organic fraction of municipal solid waste (OFMSW) and associated production of renewable energy at a local level has recently attracted attention as opposed to full-scale centralized plants. In this work, we evaluate the technical and economic feasibility of an integrated process comprising small-scale AD of OFMSW followed by microalgae cultivation, to valorise the waste streams of the former (off-gases produced by combined heat and power generation and liquid digestate) for the production of valuable biomass to be destined to either the biofertilizers or the biostimulants markets, in agreement with a circular economy perspective. The material and energy balances were obtained by means of process simulation for a plant located in Northern Italy, taken as a reference. The analysis revealed that, although the high turbidity of the digestate strongly hinders biomass production, the process is profitable from a techno-economic perspective, with discounted payback time ranging from 3.3 to 7.1 years, and profitability indexes greater than 1. The low market price of biofertilizers makes it the less profitable choice, even compared to the AD process alone, while selling the biomass for biostimulants applications could strongly increase the process profitability.

Co-occurrence network analysis reveals loss of microbial interactions in anaerobic digester subjected to repeated organic load shocks

Fluctuations in the anaerobic digestion (AD) organic loading rate (OLR) cause shocks to the AD microbiome, which lead to unstable methane productivity. Managing these fluctuations requires a larger digester, which is impractical for community-scale applications, limiting the potential of AD in advancing a circular economy. To allow operation of small-scale AD while managing OLR fluctuations, we need to tackle the issue through elucidation of the microbial community dynamics via 16S rRNA gene sequencing. This study elucidated the interrelation of the AD performance and the dynamics of the microbial interactions within its microbiome in response to repeated high OLR shocks at different frequencies. The OLR shocks were equivalent to 4 times the baseline OLR of 2 g VS/L/d. We found that less frequent organic load shocks result to deterioration of methane productivity. Co-occurrence network analysis shows that this coincides with the breakdown of the microbiome network structure. This suggests loss of microbial interactions necessary in maintaining stable AD. Identification of species influencing the network structure revealed that a species under the genus Anaerovorax has the greatest influence, while orders Spirochaetales and Synergistales represent the greatest number of the influential species. We inferred that the impact imposed by the OLR shocks shifted the microbiome activity towards biochemical pathways that are not contributing to methane production. Establishing a small-scale AD system that permits OLR fluctuations would require developing an AD microbiome resilient to infrequent organic loading shocks.

An Innovative Solid-State Micro-Anaerobic Digestion Process to Valorize Food Waste: Technical Development Constraints and Consequences on Biological Performances

To face the increase of waste production and meet the energy demand of urban areas, municipal waste management systems should be rethought. Innovative solutions such as decentralised small-scale anaerobic digestion could be developed. This work presents the design, operation and performances of a new micro-scale anaerobic digester (AD) developed to degrade food waste (FW) in urban areas i.e. highly compact and with low water and energy demand. To meet these objectives, the new micro-scale AD is a semi-continuous and two-stage process built vertically to take advantage of the gravity to mix and move the digested matter instead of using mechanical devices. The first stage consists in a tubular reactor fed weekly with FW and periodically watered with leachate from the second stage reactor located below the tubular reactor. Results show that AD performances were highly correlated to the efficiency of hydric transfer between the tubular reactor and the leachate tank. Indeed, pH, volatile fatty acids and microbial community analysis showed that the hydrolysis occurred in the tubular reactor, while the methanogenesis step occurred in the leachate tank. Overall, the average methane production was 143 ± 87 NL/kgvs with an average methane content of 44 ± 10% and the operation mode of the process has still to be improved.Graphic

Anaerobic Digestion of Food Waste, Brewery Waste, and Agricultural Residues in an Off-Grid Continuous Reactor

Small-scale anaerobic digestion (AD) can be an effective organic waste management system that also provides energy for small businesses and rural communities. This study measured fuel production from digestions of single and mixed feedstocks using an unheated, 2 m3 digester operated continuously in a temperate climate for over three years. Using local food waste, brewery waste, grease waste, and agricultural residues, this study determined that small-scale AD co-digestions were almost always higher yielding than single feedstocks during psychrophilic operation and seasonal temperature transitions. Agricultural residues from Miscanthus x giganteus had the greatest impact on biomethane production during co-digestion (4.7-fold greater average biogas %CH4), while mesophilic digestion of brewery waste alone produced the most biogas (0.76 gCH4 gVS−1 d−1). Biogas production during the transition from mesophilic to psychrophilic was temporarily maintained at levels similar to mesophilic digestions, particularly during co-digestions, but biogas quality declined during these temperature shifts. Full-time operation of small-scale, unheated AD systems could be feasible in temperate climates if feedstock is intentionally amended to stabilize carbon content.

Operational parameters of small-scale anaerobic digester for rural areas in Indonesia to support sustainable development goals (SDGs)

Small-scale anaerobic digester (AD) has been widely used by society in rural areas of Indonesia to produce biogas. The use of biogas as a renewable energy source is in line with the Sustainable Development Goals (SDGs) program, especially regarding Affordable and Clean Energy. In rural areas, biogas produced by small-scale AD is needed to produce fuel for cooking, produce the fertilizer for agriculture activities and as solution to environmental problems related to livestock manure disposal. This paper discusses the operational parameters of small-scale AD in Indonesia. These operational parameters are important to establish for standardizing the quality requirements of small-scale AD installed in rural areas of Indonesia. The research was conducted by review the literature from several previous studies that related to similar topic and discussed with biogas experts and practitioners to determine operational parameters for small-scale AD. The results of this research are obtaining the hydraulic retention time, pH value, temperature, and loading rate as operational parameters with respective range values. Information on the operational parameters of small-scale AD can be used as input for developing the Indonesian National Standards for the quality requirements of low-pressure biogas that is in line with this research.

Small Farms Using Anaerobic Digestion: A Viable Technology Education and Outreach Effort

ABSTRACT Anaerobic digestion (AD) on farms is receiving increasing attention as a technology for minimizing greenhouse gas emissions, reducing odors and pathogens, and generating energy. Although AD technology in the U.S. has been considered appropriate only for larger scale, especially livestock, farms, there has been growing interest in adapting the technology for smaller farms and greater variety of feedstocks. A series of three workshops used farmer-participatory research methodologies to assess attitudes and perceptions of small-scale anaerobic digesters in New York State by smaller scale livestock and crop operations. Results indicate a diverse group of farmers are interested in using anaerobic digester systems. Participants who attended the tour and workshop also increased their level of knowledge and understanding of anaerobic digester systems. Participant discussion revealed a need for more information for AD establishment on small farms including detailed economic data and a greater number of example AD systems. Additionally, results showed improved funding sources for adoption of this sustainable technology will likely increase farmer’s rate of adoption.

Greenhouse gas mitigation and rural electricity generation by a novel two-stroke biogas engine

Small-scale anaerobic digestion of wet organic wastes can make positive contributions to climate mitigation, energy security and nutrient cycling in agri-food systems. However, the environmental sustainability of small-scale anaerobic digestion is undermined where lack of capacity to utilize the biogas fuel results in biomethane venting to the atmosphere, contributing to climate change. Policy support for improved manure management in Bali, Indonesia, has resulted in the installation of small (6 m3) anaerobic digesters across 752 Bali cattle breeding units. These 752 remote rural digesters annually vent approximately 75 482 ± 37 741 m3 of biomethane into the atmosphere as a waste, owing to lack of practical means to convert this potential fuel into useful energy. Meanwhile, most of these cattle farms lack access to electricity. This paper describes the performance of a novel, compact and versatile “BioMiniGen” system that provides convenient electricity generation from small-scale biogas production. This innovative system comprises: (i) a simple biogas desulfurizing system; (ii) a two-stroke, single cylinder (63 cc) air-cooled engine; (iii) an electric generator; (iv) an optional CO2 removal unit. Lifecycle assessment indicated that bioelectricity generated by the BioMiniGen would have a smaller environmental footprint than Indonesian grid electricity across 11 impact categories, including a negative global warming burden owing to avoidance of biogas venting. Trade-offs included a larger abiotic depletion burden associated with manufacture of the generators. Over a five-year lifetime, each unit, costing US$500, could generate up to 5971 kWh of electricity and mitigate up to 65.1 Mg CO2 eq., with a greenhouse gas abatement value up to US$13023. Across Bali, up to 898 ± 449 MWh yr−1 bioelectricity could be generated, and 1.92 ± 0.96 Gg CO2 eq. saved. Further pilot trials are needed to ascertain realistic biogas yields from cleaned digesters managed for bioenergy generation alongside manure management. BioMiniGen technology could make an important contribution to energy security for the 1.4 billion people globally who lack access to electricity.

Comparing Hydrogen Sulfide Removal Efficiency in a Field-Scale Digester Using Microaeration and Iron Filters

Biological desulfurization of biogas from a field-scale anaerobic digester in Peru was tested using air injection (microaeration) in separate duplicate vessels and chemical desulfurization using duplicate iron filters to compare hydrogen sulfide (H2S) reduction, feasibility, and cost. Microaeration was tested after biogas retention times of 2 and 4 h after a single injection of ambient air at 2 L/min. The microaeration vessels contained digester sludge to seed sulfur-oxidizing bacteria and facilitate H2S removal. The average H2S removal efficiency using iron filters was 32.91%, with a maximum of 70.21%. The average H2S removal efficiency by iron filters was significantly lower than microaeration after 2 and 4 h retention times (91.5% and 99.8%, respectively). The longer retention time (4 h) resulted in a higher average removal efficiency (99.8%) compared to 2 h (91.5%). The sulfur concentration in the microaeration treatment vessel was 493% higher after 50 days of treatments, indicating that the bacterial community present in the liquid phase of the vessels effectively sequestered the sulfur compounds from the biogas. The H2S removal cost for microaeration (2 h: $29/m3 H2S removed; and 4 h: $27/m3 H2S removed) was an order of magnitude lower than for the iron filter ($382/m3 H2S removed). In the small-scale anaerobic digestion system in Peru, microaeration was more efficient and cost effective for desulfurizing the biogas than the use of iron filters.

Field testing of a small-scale anaerobic digester with liquid dairy manure and other organic wastes at an urban dairy farm

Anaerobic digestion has been acknowledged as an appropriate technology to tackle climate change and support sustainable development. In general, biogas installation in developed countries involved a high investment cost due to the size and complexity of the technology, while small and simple technologies are often used in developing countries. In this study, an 8 m3 commercial portable biodigester was modified by installing a mixing device and a heating element coil wire, and fed with liquid dairy manure, dairy by-products and food wastes. The results showed that the mixing device and heating element were effective to keep biodigester temperature around 37.7 °C at an ambient temperature between − 8 and + 25 °C. Higher temperature and longer hydraulic retention time (HRT) were related to higher digestion performance, while the opposite was observed with organic loading rate (OLR). Biodigester performance was not influenced by temperature and HRT, while it was increased with the increase of OLR. The highest biogas yield was observed during the co-digestion of liquid manure with waste milk and food waste, while the highest volumetric production of biogas was observed with liquid dairy manure co-digested with camembert cheese waste and food wastes.

Economic and Environmental Analysis of Small-Scale Anaerobic Digestion Plants on Irish Dairy Farms

The European Union’s (EU) climate and energy package requires all EU countries to reduce their greenhouse gas (GHG) emissions by 20% by 2020. Based on current trends, Ireland is on track to miss this target with a projected reduction of only 5% to 6%. The agriculture sector has consistently been the single largest contributor to Irish GHG emissions, representing 33% of all emissions in 2017. Small-scale anaerobic digestion (SSAD) holds promise as an attractive technology for the treatment of livestock manure and the organic fraction of municipal wastes, especially in low population communities or standalone waste treatment facilities. This study assesses the viability of SSAD in Ireland, by modelling the technical, economic, and environmental considerations of operating such plants on commercial Irish dairy farms. The study examines the integration of SSAD on dairy farms with various herd sizes ranging from 50 to 250 dairy cows, with co-digestion afforded by grass grown on available land. Results demonstrate feedstock quantities available on-farm to be sufficient to meet the farm’s energy needs with surplus energy exported, representing between 73% and 79% of the total energy generated. All scenarios investigated demonstrate a net CO2 reduction ranging between 2059–173,237 kg CO2-eq. yr−1. The study found SSAD systems to be profitable within the plant’s lifespan on farms with dairy herds sizes of >100 cows (with payback periods of 8–13 years). The simulated introduction of capital subvention grants similar to other EU countries was seen to significantly lower the plant payback periods. The insights generated from this study show SSAD to be an economically sustainable method for the mitigation of GHG emissions in the Irish agriculture sector.

Determination of the Potential Impact of Domestic Anaerobic Digester Systems: A Community Based Research Initiative in Rural Bangladesh

This research examines the potential impact of domestic anaerobic digester (AD) systems adopted in Bangladesh and similar developing countries. Cattle dung and poultry litter feed stocks were specifically investigated, because these were freely available and plentiful to people living within agricultural areas of rural Bangladesh. Data was collected to ascertain whether these two representative AD facility types provide tangible social, economic and environmental impact that benefits homeowners. Primary quantitative and qualitative data was obtained by field data collection, and meeting with expert groups and stakeholders. Empirical analysis conducted revealed that variations were found in the biomass feedstocks available on different sites but also differences were apparent in terms of the operations and maintenance (O and M) systems of the biogas plants operated. The biogas and methane yield variation was also measured, and variations were found in the cattle dung and poultry litter AD yield capacity. Overall, 64% of feedstock was utilised, 91% of biogas plants remain underfed and energy yield efficiency was 57% from cattle smallholdings’ AD and 28% from poultry farms’ AD. These results showed that small scale AD can offer a significant impact upon rural lifestyles through augmented economics, improved social activities, relationship building with neighbours and improved lifestyle achieved via time savings accrued. These results could help rural entrepreneurs, AD equipment providers and government institutions to develop a road map to implement future AD installation on a much wider geographical scale.

Life cycle assessment of portable two-stage anaerobic digestion of mixed food waste and cardboard

Biogas produced from organic waste can reduce waste and produce renewable energy and is a viable waste treatment alternative for remote encampments. Portable, small-scale anaerobic digestion (AD) units can be used to sustainably produce biogas in remote areas and reduce landfilled waste. This project investigated the life cycle impacts of a portable AD unit and the effects of organic loading rate (8–32 g chemical oxygen demand (COD) L−1 d−1) and waste composition (food versus cardboard waste ratios of 35:65 and 65:35) on biogas production efficiency. Optimal biogas production was obtained using a 65% food to 35% cardboard waste mixture and a mid-range organic loading rate (16 g COD L−1 d−1); this scenario also yielded the lowest climate change impact [37.4 ± 0.7 g CO2 eq per kg COD waste] due to greater biogas conversion efficiency. However, the overall life cycle impacts of biogas production were not significantly affected by waste mixtures or feed rates in the AD portable system and experiments evaluated. Life cycle impacts due to portable AD processing were overall agnostic to feedstock variability. Thus, waste type and volume variations generated by encampments with fluctuating populations can likely be accommodated by the portable AD system without substantially affecting short term process sustainability. Portable AD system biogas generation rates were comparable to conventional, full-scale waste to energy facilities, while combustion impacts were more sustainable than those associated with conventional fossil fuels. Portable AD units represent a sustainable energy resource, waste reduction, and landfill alternative for remote areas.

Measuring the results of a workshop on installing anaerobic digesters on smaller livestock farms

AbstractIt is accepted generally that anaerobic digesters (AD) are efficacious technologies for reducing greenhouse gas emissions from livestock operations (Pronto and Gooch, 2009). In addition, AD technology has a number of other potential benefits including: energy production for use on the farm and for sale, separation of manure solids for ease of use or export off-farm, pathogen reduction leading to healthier labor and herd outcomes and odor control. It is also clear that in the USA, research and extension efforts, including public financing of AD technology installations, have disproportionally been focused on larger farms- e.g., dairy farms with at least 500 milking cows. The latter has begun to change as more resources are being invested in AD technology for smaller livestock farms. We present the results of a pre and post survey implemented at four workshops on small-scale AD technology for livestock farmers in northeastern New York State. Results indicate that information presented shifted farmers’ attitudes such that they viewed AD technology as not overly complex; and, they became less interested in selling generated surplus power off-farm.