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Antibiotic use in animal husbandry is a potential entryway for antibiotics and antibiotic resistance genes (ARGs) to enter the environment through manure fertilizer application. The potential of anaerobic digestion (AD) to remove antibiotics and ARGs was investigated through tetracycline (TC) and sulfadimethoxine (SDM) additions into dairy manure digested for 44 d. This was the first study to evaluate antibiotics at concentrations quantified on-farm and relevant to field applications of manure. Triplicate treatments included a 1 mg L -1 TC spike, a 10 mg L -1 TC spike, a 1 mg L -1 SDM spike (SDM 1), a 10 mg L -1 SDM spike, a mixture of TC and SDM at 1 mg L -1 each (TC+SDM 1), and a manure-only treatment. The SDM spikes were reduced by >99% reduction during the AD processing, but TC additions had variable reductions (0-96%). Molecular analyses showed that decreases in tetM gene copies correlated with declines in TC; however, reductions in SDM concentration did not correlate with decreases in sul1 gene copy concentrations. The AD reactors containing 10 mg L -1 of TC and 10 mg L -1 of SDM both had CH 4 production reductions of 7.8%, whereas no CH 4 reduction was observed in other treatments (1 mg L -1 treatments). The study results were the first to confirm that AD can remove SDM when adding at concentrations observed in on-farm manure (<1 mg L -1 ) without compromising energy production. Because TC adsorbs to the solid particles and transforms into isomers, the decreases in TC concentrations were more variable and should be closely monitored., (© 2021 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

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.)

The use of antimicrobials by the livestock industry can lead to the release of unmetabolized antimicrobials and antimicrobial resistance genes (ARG) into the environment. However, the relationship between antimicrobial use, residual antimicrobials, and ARG prevalence within manure is not well understood, specifically across temporal and location-based scales. The current study determined ARG abundance in untreated manure blend pits and long-term storage systems from 11 conventional and one antimicrobial-free dairy farms in the Northeastern U.S. at six times over one-year. Thirteen ARGs corresponding to resistance mechanisms for tetracyclines, macrolides-lincosamides, sulfonamides, aminoglycosides, and β-lactams were quantified using a Custom qPCR Array or targeted qPCR. ARG abundance differed between locations, suggesting farm specific microbial resistomes. ARG abundance also varied temporally. Manure collected during the winter contained lower ARG abundances. Overall, normalized ARG concentrations did not correlate to average antimicrobial usage or tetracycline concentrations across farms and collection dates. Of the 13 ARGs analyzed, only four genes showed a higher abundance in samples from conventional farms and eight ARGs exhibited similar normalized concentrations in the conventional and antimicrobial-free farm samples. No clear trends were observed in ARG abundance between dairy manure obtained from blend pits and long-term storage collected during two drawdown periods (fall and spring), although higher ARG abundances were generally observed in spring compared to fall. This comprehensive study informs future studies needed to determine the contributions of ARGs from dairy manure to the environment.

Although there are a variety of commercially available biological and chemical treatments for removal of hydrogen sulfide (H2S) from biogas, managing biogas H2S remains a significant challenge for agricultural digesters where labor and operational funds are very limited compared to municipal and industrial digesters. The objectives of this study were to evaluate headspace aeration for reducing H2S levels in low cost plug flow digesters and to characterize the relationship between the liquid surface area and H2S oxidation rates. Experiments with replicate field scale plug flow digesters showed that H2S levels decreased from 3500 ppmv to <100 ppmv when headspace oxygen levels were 0.5 to 1%. Methane production was not affected by aeration rates that resulted in headspace oxygen levels of up to 1%. Pilot scale experiments using 65 to 104 L desulfurization units showed that H2S oxidation rates increased with increases in liquid surface area. These results support the hypothesis that H2S oxidation rates are limited, in part, by the surface area available for oxygen transfer, and can be increased by growth of biofilms containing H2S oxidizing bacteria. Maximum removal rates corresponded to 40 to 100 g S m-2 d-1 of liquid surface area at biogas retention times of 30 to 40 min.

The methanogenic communities in alternative inocula and their potential to increase CH 4 production in mesophilic and psychrophilic dairy manure-based anaerobic digesters were examined. Quantitative-PCR and terminal restriction fragment length polymorphism (T-RFLP) profiles were used to determine archaeal and methanogenic community changes when three inocula (wetland sediment (WS), landfill leachate (LL), and mesophilic digestate (MD)) were incubated at 15, 25, and 35 °C for 91 and 196 days. After each incubation period, the inocula were used in biochemical methane potential (BMP) tests at the incubation temperatures. There was no significant correlation between inoculum mcrA gene copy numbers and CH 4 produced in BMP tests, suggesting that population size was not a distinguishing characteristic for predicting CH 4 production. Archaeal composition in LL and WS reactors generally converged with MD reactors after incubation at 25 and 35 °C for 196 days. These MD reactors had high relative abundance of TRF 302, likely Methanosaetaceae, and low acetic acid (0.62-1.61 mM). At 15 °C incubation, most reactors were associated with high acetic acid (1.61-133.6 mM) and dominated by TRF 199, likely Methanosarcinaceae. The LL reactor incubated at 25 °C for 91 days had higher relative abundance of TRF 199 and produced significantly higher CH 4 than WS and MD reactors in BMP test. In the future, it may be possible to create enrichment cultures that favor particular methanogens and use them as inoculum to benefit digesters at low mesophilic temperatures. Our data provides evidence that tailoring the archaeal community could benefit digesters operating under different conditions.

Pilot-scale digesters (850 L) were used to quantify CH4 and H2S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish+manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH4 production by 11% and 39% in Trial 1 and 2, respectively. As H2S production rapidly declined in the radish+manure digesters, CH4 production increased reaching high levels of CH4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H2S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34-0.40%), although cumulative H2S production in the radish+manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150 m(3) CH4/month, providing a farmer additional revenue up to $3125/month in electricity sales., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Studies have shown that including food waste as a co-digestion substrate in the anaerobic digestion of livestock manure can increase energy production. However, the type and inclusion rate of food waste used for co-digestion need to be carefully considered in order to prevent adverse conditions in the digestion environment. This study determined the effect of increasing the concentration (2%, 5%, 15% and 30%, by volume) of four food-processing wastes (meatball, chicken, cranberry and ice cream processing wastes) on methane production. Anaerobic toxicity assay (ATA) and specific methanogenic activity (SMA) tests were conducted to determine the concentration at which each food waste became toxic to the digestion environment. Decreases in methane production were observed at concentrations above 5% for all four food waste substrates, with up to 99% decreases in methane production at 30% food processing wastes (by volume)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Co-digestion of food waste with dairy manure is increasingly utilized to increase energy production and make anaerobic digestion more affordable; however, there is a lack of information on appropriate co-digestion substrates. In this study, biochemical methane potential (BMP) tests were conducted to determine the suitability of four food waste substrates (meatball, chicken, cranberry and ice cream processing wastes) for co-digestion with flushed dairy manure at a ratio of 3.2% food waste and 96.8% manure (by volume), which equated to 14.7% (ice-cream) to 80.7% (chicken) of the VS being attributed to the food waste. All treatments led to increases in methane production, ranging from a 67.0% increase (ice cream waste) to a 2940% increase (chicken processing waste) compared to digesting manure alone, demonstrating the large potential methane production of food waste additions compared to relatively low methane production potential of the flushed dairy manure, even if the overall quantity of food waste added was minimal., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A co-digestion investigation was conducted using small-scale digesters in Costa Rica to optimize their ability to treat animal wastewater and produce renewable energy. Increases in methane production were quantified when swine manure was co-digested with used cooking grease in plug-flow digesters that operated at ambient temperate without mixing. The co-digestion experiments were conducted on 12 field-scale digesters (250 L each) using three replications of four treatment groups: the control (T0), which contained only swine manure and no waste oil, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. The T2.5 treatment had the greatest methane (CH(4)) production (45 L/day), a 124% increase from the control, with a total biogas production of 67.3 L/day and 66.9% CH(4) in the produced biogas. Increasing the grease concentration beyond T2.5 produced biogas with a lower percentage of CH(4), and thus, did not result in any additional benefits. A batch study showed that methane production could be sustained for three months in digesters that co-digested swine manure and used cooking grease without daily inputs. The investigation proved that adding small amounts of grease to the influent is a simple way to double energy production without affecting other digester benefits., ((c) 2010 Elsevier Ltd. All rights reserved.)

Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2,968 mg/L to 472 mg/L) and higher dissolved nutrient concentration (NH(4)-N increased by 78.3% to 82.2mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH(4)-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater.

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]

Highlights: [•] Emergy analyses of digesters for human waste in Haiti and dairy manure in the US. [•] New emergy indices (EEI and AYR) were created for comparisons of analogous products. [•] Food and waste emergy analyses were conducted to determine waste emergy values. [•] Inputs from wastes accounted for more than 99% of the emergy in digesters. [•] When emergy waste values were zeroed, apparent sustainability improved. [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]

Abstract: An emergy analysis was performed to assess the relative sustainability and environmental impact of small-scale energy production using Taiwanese model plug-flow anaerobic digesters to treat livestock manure in Costa Rica. Emergy analysis quantifies all inputs to a system by converting them to solar energy equivalents, thus allowing for direct comparison of the diverse inputs of renewable energies, human labor and economic goods needed to construct and maintain anaerobic digestion systems. The digesters were located on the campus of EARTH University, Costa Rica, and the biogas was utilized to power a 40kW generator that supplies electricity for farm operations. Separate emergy analyses were performed for the biogas production and the combination of biogas production and generation of electricity. Manure was the largest input in both analyses, accounting for 85.3% of the annual emergy input for biogas production and 66.9% for electricity generation from the biogas. The fraction of emergy inputs from renewable sources (ΦR) was 66% for biogas production and 52% for electricity generation from the biogas. The transformities of biogas and electricity generation from the biogas were 5.23E+04sej/J and 1.01E+06sej/J respectively. The emergy yield ratios (EYR) were 2.93 for biogas production and 2.07 for electricity generation indicating that these digesters efficiently match purchased resources and renewable energies to produce energy from livestock manure. The generation of electricity from the biogas resulted in a decrease in the emergy sustainability index (ESI) from 5.67 to 2.22 and an increase in the environmental loading ratio (ELR) from 0.52 to 0.93. Using a generator to convert the biogas to electricity does decrease the sustainability of the system, largely due to the high emergy value associated with the electrical generation equipment and machinery, but these results demonstrate that the production of biogas and the generation of electricity from Taiwanese model digesters in Costa Rica are environmentally sustainable processes that result in the production of energy that is largely dependent on renewable and recycled energies. [Copyright &y& Elsevier]

Anaerobic digestion (AD) is a biological-based technology that generates methane-enriched biogas. A microbial electrolysis cell (MEC) uses electricity to initiate bacterial oxidization of organic matter to produce hydrogen. This study determined the effect of energy production and waste treatment when using dairy manure in a combined AD and MEC (AD-MEC) system compared to AD without MEC (AD-only). In the AD-MEC system, a single chamber MEC (150 mL) was placed inside a 10 L digester on day 20 of the digestion process and run for 272 h (11 days) to determine residual treatment and energy capacity with an MEC included. Cumulative H2 and CH4 production in the AD-MEC (2.43 L H2 and 23.6 L CH4) was higher than AD-only (0.00 L H2 and 10.9 L CH4). Hydrogen concentration during the first 24 h of MEC introduction constituted 20% of the produced biogas, after which time the H2 decreased as the CH4 concentration increased from 50% to 63%. The efficiency of electrical energy recovery (ηE) in the MEC was 73% (ηE min.) to 324% (ηE max.), with an average increase of 170% in total energy compared to AD-only. Chemical oxygen demand (COD) removal was higher in the AD-MEC (7.09 kJ/g COD removed) system compared to AD-only (6.19 kJ/g COD removed). This study showed that adding an MEC during the digestion process could increase overall energy production and organic removal from dairy manure. [ABSTRACT FROM AUTHOR]