Search

Using food waste (FW) as a co-substrate in anaerobic digestion (AD) results in increased energy production, decreases in greenhouse gas emissions, and recycles the FW nutrients back to the land for producing crops. This research investigated food waste AD systems in the United States (US) and Germany (DE) that co-digested FW with dairy manure at the lab and full-scale. In DE, the post-consumer FW had 32–49% more CH 4 potential (477–499 mL CH4 /g VS) than maize and grass silage (368 and 331 mL CH4 /g VS) and solid and liquid manure (243 and 91 mL CH4 /g VS). Methane production in the full-scale DE system with 66% FW (by volume) was 882 m3 CH4 /d, which was 37% higher than the laboratory results due to the 86-day retention and 42 °C AD conditions in the field. The pre-consumer FW in the US had a similar CH 4 potential (264–553 mL CH4 /g VS), but due to the lack of heating in the full-scale system, 62% less CH 4 was produced than the lab-based potential. While DE requires pasteurization of FW for AD and bans FW bans to landfills, the US does not have specific requirements for FW treatment in AD or federal FW landfill policies, with a few forthcoming FW bans in some municipalities and states. As FW diversion and utilization in AD systems is expected to grow, it is important to understand the effect of FW in biogas production and nutrient content, comparisons between lab and field-scale results, and the effect of policy on FW utilization. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic digestion (AD) is an economically viable manure treatment option for large dairies (>500 cows) in the U.S. However, roughly 90% of U.S. dairies have less than 200 cows, making this technology economically inaccessible to the vast majority of U.S. dairies. While there have been case studies of individual small dairies with anaerobic digesters, there are no comparative studies using cost data from these systems. The objectives of this study were to (1) determine the economic viability of small-scale U.S. digesters using cost data from nine existing 100 to 250-cow dairies and seven theoretical systems and (2) reevaluate the minimum size dairy farm needed for economically feasible AD in the U.S. Cash flow analysis results showed that total capital costs, capital costs per cow, and net costs per cow generally decreased with increasing herd size in existing systems. Among existing revenue streams, use of digested solids for bedding generated the highest revenue ($100cow−1 year−1), followed by biogas use for heating and/or electrical generation ($47 to $70cow−1 year−1) and CO2 credits ($7cow−1 year−1). No system had a positive cash flow under the assumed conditions (8% discount rate, 20-year term). However, six of the 16 systems had positive cash flows when 50% cost sharing was included in the analysis. Our results suggest that, with cost sharing, economically viable AD systems are possible on 250-cow dairies. Additional revenue streams, such as tipping fees for food waste, may reduce the minimum size to 100-cow dairies. [Copyright &y& Elsevier]

Combustion can concentrate phosphorus (P) from poultry litter into an ash product that is easier to transport for land application. This was the first life cycle assessment (LCA) study to investigate the efficacy and sustainability of a fluidized bed combustion (FBC) system using poultry litter to heat poultry houses and produce electricity, in the United States, to replace liquid propane gas (LPG) and natural gas (NG) use. The 'Baseline scenario' used results from a 16-month FBC monitoring study, and an 'Improved scenario' based on an increased biomass feed rate (0.246 tons/h), increased run-time (6720 h/y), and net positive electricity production. In the Baseline scenario, climate change potential was 32% and 44% lower than use of LPG and NG, respectively, for poultry house heating, but the low electricity production from the FBC system resulted in net electricity import and lower sustainability compared to LPG use in 12 of the 18 impact categories. The Improved scenario had 48–98% less environmental impacts than the Baseline scenario in the 18 categories. The sensitivity analysis showed that a 10% change in the electricity input for FBC operation resulted in the highest average change (4.8%) in the 18 impact categories, indicating the necessity of a net positive electrical energy output from the FBC unit for increased sustainability. The results also highlighted the impact of the replacement heating fuel type, as replacing NG through poultry litter combustion had a greater impact than replacement of LPG. • Combustion of poultry litter can be a sustainable form of manure management. • Climate change potential was 32% and 44% lower than using LPG and NG for heating. • The avoided use of LPG offset the impacts in 6 out of 18 categories analyzed. • Electricity input to the FBC system had the highest overall environmental impact. • If the FBC operated with a net electricity export, impacts decreased by >48%. [ABSTRACT FROM AUTHOR]

United States dairy operations use antibiotics (primarily β-lactams and tetracyclines) to manage bacterial diseases in dairy cattle. Antibiotic residues, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARG) can be found in dairy manure and may contribute to the spread of antibiotic resistance (AR). Although β-lactam residues are rarely detected in dairy manure, tetracycline residues are common and perhaps persistent. Generally, <15% of bacterial pathogen dairy manure isolates are ARB, although resistance to some antibiotics (e.g., tetracycline) can be higher. Based on available data, the prevalence of medically important ARB on dairy operations is generally static or may be declining for antibiotic-resistant Staphylococcus spp. Over 60 ARG can be found in dairy manure (including β-lactam and tetracycline resistance genes), although correlations with antibiotic usage, residues, and ARB have been inconsistent, possibly because of sampling and analytical limitations. Manure treatment systems have not been specifically designed to mitigate AR, though certain treatments have some capacity to do so. Generally, well-managed aerobic compost treatments reaching higher peak temperatures (>60°C) are more effective at mitigating antibiotic residues than static stockpiles, although this depends on the antibiotic residue and their interactions. Similarly, thermophilic anaerobic digesters operating under steady-state conditions may be more effective at mitigating antibiotic residues than mesophilic or irregularly operated digesters or anaerobic lagoons. The number of ARB may decline during composting and digestion or be enriched as the bacterial communities in these systems shift, affecting relative ARG abundance or acquire ARG during treatment. Antibiotic resistance genes often persist through these systems, although optimal management and higher operating temperature may facilitate their mitigation. Less is known about other manure treatments, although separation technologies may be unique in their ability to partition antibiotic residues based on sorption and solubility properties. Needed areas of study include determining natural levels of AR in dairy systems, standardizing and optimizing analytical techniques, and more studies of operating on-farm systems, so that treatment system performance and actual human health risks associated with levels of antibiotic residues, ARB, and ARG found in dairy manure can be accurately assessed., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)