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Antibiotic distribution and analysis within liquid and solid fractions of manure are highly variable due to each compound's respective physiochemical properties. This study developed and evaluated a uniform method extracting 10 antibiotics from 4 antibiotic classes (tetracycline, sulfonamides, macrolides, and β-lactam) from unprocessed manure, solid–liquid separated manure, and composted solids. Through systematic manipulation of previously published liquid chromatography tandem mass spectrometry methods; this study developed an extraction protocol with optimized recovery efficiencies for varied manure substrates. The method includes a two-step, liquid-solid extraction using 10 mL of 0.1 M EDTA-McIlviane buffer followed by 10 mL of methanol. Antibiotics recoveries from unprocessed manure, separated liquids, separated solids, and heat-treated solids using the two-step extraction method had relative standard deviations < 30% for all but ceftiofur. Total antibiotic recoveries were 67–131% for tetracyclines, 56% for sulfonamide, 49–53% for macrolides, and 1.3–66% for β-lactams. This is the first study to use one protocol to assess four classes of antibiotics in liquid and solid manure fractions. This study allowed for more precise risk assessment of antibiotic transport in manure waste stream applied to fields as a liquid or solid compost. [ABSTRACT FROM AUTHOR]

The small-scale digesters treating agricultural wastewater and producing energy are analyzed in order to explore different ways for increasing the efficiency of the systems. The analysis has shown that the small-scale digesters can provide methane and electricity to meet household needs resulting in increase in household income and decrease in water pollution and deforestation.

BACKGROUND Poultry litter (PL) has a high solid and organic nitrogen content that is converted into NH3 during anaerobic digestion (AD), requiring the dilution of PL influent prior to AD. With nutrients extracted from the AD effluent, the water could be reused for influent dilution or for other purposes, while creating a designer nutrient product from the PL matrix. The study goal was to determine the effectiveness of an ammonia (NH3)‐stripping and scrubbing system to remove and capture NH3 from anaerobically digested PL. After NH3 stripping, a novel, patent‐pending dual‐vessel NH3‐scrubber system was designed to simultaneously capture the stripped NH3 while producing higher quality biogas through partial removal of non‐combustible carbon dioxide (CO2) and corrosive hydrogen sulfide (H2S). RESULTS: The stripping reactor reduced total ammonia nitrogen (TAN) by 84.6–90.4% when loaded with an ammonium chloride solution or screened PL digestate after 4 h, while the scrubber captured 73.3–76.2% of the stripped NH3 when proxy biogas streams (59–60% CH4, 40% CO2) with two H2S concentrations (0.1 or 1% H2S) were used. The scrubber reduced CO2 and H2S concentrations in the biogas by 3.9% and 23–29%, respectively. CONCLUSION: The study demonstrated a novel NH3 stripping‐and‐scrubbing system that successfully reduced TAN in anaerobic digestate, captured the stripped NH3, and reduced CO2 and H2S concentrations in biogas. The novel design can be used to increase the adoption of AD for PL by providing a useful NH3 fertilizer, wastewater with less NH3, and a biogas stream with less H2S. © 2020 Society of Chemical Industry (SCI) [ABSTRACT FROM AUTHOR]

The article discusses the design, construction and the advantages of a biodigester that is used to produce electricity by the action of anaerobic digestion of livestock manure. The equipment is found to produce high quality biogas while increasing the fertilizer quality of the manure but needs some technical improvements for better results.

Graphical abstract Highlights • Metal nanoparticles (NPs) were added to anaerobic digestion (AD) of poultry litter. • Adding Ni NPs (12 mg/L) increased CH 4 production by 38.4% (368 mL CH 4 /g VS). • Fe, Co and Fe 3 O 4 NPs added individually also increased CH 4 with no effect on H 2 S. • Higher concentrations of NP mixtures greatly reduced H 2 S with no effect on CH 4. • A method for extraction of NPs from digestate for SEM detection was developed. Abstract The effects of metal nanoparticle (NP) addition during anaerobic digestion (AD) of poultry litter was tested using two sequential experiments: Exp. A) four NPs (Fe, Ni, Co, and Fe 3 O 4) at three concentrations; and Exp. B) NP combinations (Fe, Ni, and Co) at four concentrations. Scanning electronic microscopy (SEM) and elemental analysis were used to confirm NP inclusion after dispersion (before AD) and track nanoparticles post-AD, and new technique for NP extraction post-AD was developed. Before AD, NPs ranged from 30.0 to 80.9 nm for Fe, Ni, and Co, and 94.3 to 400 nm for Fe 3 O 4. Methane production increased with NPs addition compared to poultry litter-only, with the highest increases observed with NPs concentrations (in mg/L) of 12 Ni (38.4% increase), 5.4 Co (29.7% increase), 100 Fe (29.1% increase), and 15 Fe 3 O 4 (27.5% increase). Nanoparticle mixtures greatly decreased H 2 S production. The SEM post-AD detected Fe, Ni, and Fe 3 O 4 at concentrations ≥100 mg/L. [ABSTRACT FROM AUTHOR]

Lasalocid is an antibiotic from the group of carboxylic ionophores, and it is commonly used in cattle and poultry as a coccidiostat and for growth promotion. The widespread use and persistence of lasalocid have led to its detection in the environment. The objective of this study was to determine the fate and effect of veterinary ionophore lasalocid during the anaerobic digestion of dairy manure. Duplicate plug flow field-scale digesters were operated using either non-amended dairy manure or dairy manure amended with 1 or 5 mg/L lasalocid. Results showed that lasalocid was reduced approximately 75% during anaerobic digestion. Methane production from digesters treating manure amended with 1 and 5 mg/L lasalocid were comparable with CH4 production from the duplicate digesters operated without added lasalocid. These results suggest that anaerobic digestion can be used to reduce lasalocid levels in dairy manure, and lasalocid did not affect digester stability at concentrations expected in dairy manure. [ABSTRACT FROM AUTHOR]

There is growing concern about residual antibiotics and feed additives in the manure of treated animals because of the effects of these residues in the environment. Monensin is the most widely used ionophore coccidiostat in the U.S. The objective of this study was to determine the fate and effect of monensin during the anaerobic digestion of dairy manure. Duplicate plug flow field-scale digesters were operated using non-amended dairy manure and dairy manure amended with monensin to 1 and 10 mg/L for 56 days at 30°C at an organic loading rate of 1.4 kg VS/m3-d and 17-day hydraulic retention time. Results showed that monensin was reduced approximately 70% during anaerobic digestion. Methane production from digesters using manure amended with 1 mg/L monensin was comparable to that from digesters operated without added monensin. However, digesters using manure amended with 10 mg/L monensin yielded 75% less methane than digesters using manure without added monensin. These results suggest that anaerobic digestion is an effective treatment for reducing, but not eliminating, monensin in dairy manure. Monensin did not reduce methane production at concentrations expected in dairy manure at recommended dosage rates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In anaerobic digestion, methane (CH 4 ) production decreases as temperature decreases, resulting in a lower CH 4 production at psychrophilic (≤25 °C) digestion temperatures. Previous studies at mesophilic temperatures (30–35 °C) have shown that manure separation and digesting only the liquid fraction could result in the reduction of digester volume without sacrificing CH 4 production. In this research, biochemical methane potential (BMP) tests were used to quantify CH 4 production of unseparated and separated manure at two psychrophilic temperatures: 14 and 24 °C. The results showed that CH 4 production decreased by approximately 70% when the temperature was decreased from 24 °C to 14 °C. Between days 20–216 at 24 °C, higher VS content of the unseparated manure resulted in significantly higher CH 4 production (29–40% more) compared to separated manure, on a volumetric basis, but at digestion times of ≤16 days, faster VS to CH 4 conversion rates in separated manure resulted in no significant differences in CH 4 production between the manure types. Similarly, at 14 °C, the higher VS content of the unseparated manure resulted in significantly higher CH 4 production (56–147% more) throughout most of 216-day experimental period, when normalized by volume. On a VS basis (mL CH 4 /g VS), the separated manure at 24 °C produced significantly more CH 4 than the other treatments. The study suggests that at 24 °C, there will be higher CH 4 production, per volume of manure added, from unseparated manure due to the higher VS content, but when operating at a shorter digestion time, the differences could be insignificant. [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]

Bioplastics have emerged as a viable alternative to traditional petroleum-based plastic (PET). Three of the most common bioplastic polymers are polyhydroxybutyrate-valerate (PHBV), polylactide (PLA), and cellulose-based bioplastic (CBB). This study assessed biodegradation through anaerobic digestion (AD) of these three bioplastics and PET digested with food waste (FW) at mesophilic (35 °C) and thermophilic (55 °C) temperatures. The four plastic types were digested with FW in triplicate batch reactors. Additionally, two blank treatments (inoculum-only) and two PHBV treatments (with FW + inoculum and inoculum-only) were digested at 35 and 55 °C. The PHBV treatment without FW at 35 °C (PHBV-35) produced the most methane (CH4) normalized by the volatile solids (VS) of the bioplastics over the 104-day experimental period (271 mL CH4/g VS). Most bioplastics had more CH4 production than PET when normalized by digester volume or gram substrate added, with the PLA-FW-55 (5.80 m3 CH4/m3), PHBV-FW-55 (2.29 m3 CH4/m3), and PHBV-55 (4.05 m3 CH4/m3) having 848,275 and 561%, respectively, more CH4 production than the PET treatment. The scanning electron microscopy (SEM) showed full degradation of PHBV pellets after AD. The results show that when PHBV is used as bioplastic, it can be degraded with energy production through AD. [ABSTRACT FROM AUTHOR]

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]

Abstract: 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 (250L 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 (CH4) production (45L/day), a 124% increase from the control, with a total biogas production of 67.3L/day and 66.9% CH4 in the produced biogas. Increasing the grease concentration beyond T2.5 produced biogas with a lower percentage of CH4, 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. [Copyright &y& Elsevier]

Abstract: Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and were operated in the lower portion of the mesophilic range (25–27°C). The dairy digester produced 27.5m3/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0m3/day of biogas with 76.4% methane and reduced COD by 92%. Combining biogas from a swine and dairy digester, increased electricity production due to the higher biogas production rate of the dairy farm and the higher quality biogas obtained from the swine farm. The farm’s 2-h peak electricity demand (12.9kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs remaining in corrals 100% of the time. The $21,000 capital cost of the digester project will be recovered in 10.1 years through electricity savings and reductions in wastewater fines. If the generator were more appropriately sized for the farm, the capital recovery time would have been 7.6 years. [Copyright &y& Elsevier]

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 2968mg/L to 472mg/L) and higher dissolved nutrient concentration (NH4-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, NH4-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. [Copyright &y& Elsevier]

Abstract: Ecological Treatment Systems (ETS) are composed of a series of anaerobic and aerobic reactors, clarifiers, and wetlands, and have been used for the removal of nutrients from municipal and industrial wastewaters. The design of ETS enhances nutrient removal by providing both aerobic and anaerobic environments and steep gradients between the two environments. The ability of an ETS to treat wastewater from a dairy farm was investigated with a 20-week study in Columbus, OH, USA. The Waterman Ecological Treatment System (WETS) had four replicate treatment lines. Together, the four lines treated 1310L/day of diluted wastewater from a dairy facility with over 99% removal of ammonium-nitrogen (NH4-N) and carbonaceous biochemical oxygen demand (CBOD), and 79% removal of orthophosphate (PO4-P). The average influent/effluent concentrations of NH4-N, CBOD, and PO4-P were 52.1/0.07mg/L, 517/5.2mgO2/L, and 21.0/4.4mg/L, respectively. Nitrate+nitrite (NO x -N) was produced and removed within the system, and had an average effluent concentration of 0.53mg/L. The multiple anaerobic–aerobic interfaces in the WETS design enhanced biological removal of nitrogen and phosphorus. NH4-N, CBOD, and NO x -N were consistently removed throughout the 20-week study, but PO4-P removal efficiency decreased over time in one of the four treatment lines. [Copyright &y& Elsevier]

This study quantified the potential of farm-scale composting to degrade antibiotics in dairy manure. The compost windrow, consisting of sick cow bedding from a 1000-cow US dairy farm, was managed using the dairy farm's typical practices and monitored for tetracycline and nutrient composition. Samples were collected over 33 days, which was the time from compost pile formation to land application as fertilizer, and analyzed for solids, antibiotics, and nutrient content. Average tetracycline concentrations at the beginning of the study (452 ng/g DW) were lower than at the end of composting (689 ng/g DW), illustrating that antibiotic degradation was not greater than degradation of the compost solids. Total Kjeldahl nitrogen (TKN) increased from 15.3 to 18.4 g/kg during the composting period due to decreases in solids and likely inhibition of N-mineralization due to the presence of antibiotics. The results indicated that antibiotics were not completely degraded when using the farm's compost pile management techniques, with antibiotics possibly impacting nitrogen transformation in the compost, which should be considered in nutrient management when using sick cow bedding. Additionally, the results showed that antibiotic degradation during farm-scale composting can vary from reported laboratory-scale due to differences in management, composting duration, and temporal conditions, illustrating the need for more extensive on-farm research including common farm practices and real-world conditions. [ABSTRACT FROM AUTHOR]

The success of a One Health approach to combating antimicrobial resistance (AMR) requires effective data sharing across the three One Health domains (human, animal, and environment). To investigate if there are differences in language use across the One Health domains, we examined the peer-reviewed literature using a combination of text data mining and natural language processing techniques on 20,000 open-access articles related to AMR and One Health. Evaluating AMR key term frequency from the European PubMed Collection published between 1990 and 2019 showed distinct AMR language usage within each domain and incongruent language usage across domains, with significant differences in key term usage frequencies when articles were grouped by the One Health sub-specialties (2-way ANOVA; p < 0.001). Over the 29-year period, "antibiotic resistance" and "AR" were used 18 times more than "antimicrobial resistance" and "AMR". The discord of language use across One Health potentially weakens the effectiveness of interdisciplinary research by creating accessibility issues for researchers using search engines. This research was the first to quantify this disparate language use within One Health, which inhibits collaboration and crosstalk between domains. We suggest the following for authors publishing AMR-related research within the One Health context: (1) increase title/abstract searchability by including both antimicrobial and antibiotic resistance related search terms; (2) include "One Health" in the title/abstract; and (3) prioritize open-access publication. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) in biogas is produced during anaerobic digestion of organic wastes and can lead to corrosion of generators used for energy production. Recently, there has been interest in utilizing biochar as a substitute for activated carbon (AC) to adsorb and remove H 2 S from biogas. This study was the first to test iron (Fe)-impregnation of biochar to increase H 2 S removal from biogas using a biogas scrubbing column. Two biochar substrates, corn stover biochar (CSB) and maple wood biochar (MB), with and without Fe-impregnation were evaluated for H 2 S adsorption from biogas. The H 2 S adsorption capacity was quantified using dynamic breakthrough experiments. Iron-impregnated maple biochar (MB-Fe) had the highest H 2 S saturation adsorption capacity (23.9 mg H 2 S g−1 biochar), which was 3.9 times higher than the unmodified MB (6.1 mg H 2 S g−1 biochar). The Fe-impregnated corn stover biochar (CSB-Fe) saturation H 2 S sorption capacity (8.2 mg H 2 S g−1 biochar) was 2.5 times higher than the unmodified CSB (3.3 mg H 2 S g−1 biochar). The presence of iron oxide (Fe 3 O 4) was observed through X-ray diffraction and scanning electron microscopy in the Fe-impregnated biochar substrates, with ferrous sulfate (FeSO 4) as one of the end products in the saturated biochar surface and elemental sulfur in the pores. The study showed how Fe-impregnation can result in a multifold increase in H 2 S adsorption from biogas compared to unmodified biochar. ga1 • Iron-impregnation resulted in up to 3.9 times increase in H 2 S adsorption capacity. • Adsorption capacity of unmodified MB was 2.5 times higher than CSB. • H 2 S adsorption capacity of unmodified biochar was comparable to activated carbon. • Iron impregnation increased the Fe content of biochar from 1100 ppm to 29,700 ppm. • Fe 3 O 4 in the impregnated biochar was converted to FeSO 4 after reaction with H 2 S. [ABSTRACT FROM AUTHOR]

Crop yield depends on multiple factors, including climate conditions, soil characteristics, and available water. The objective of this study was to evaluate the impact of projected temperature and precipitation changes on crop yields in the Monocacy River Watershed in the Mid-Atlantic United States based on climate change scenarios. The Soil and Water Assessment Tool (SWAT) was applied to simulate watershed hydrology and crop yield. To evaluate the effect of future climate projections, four global climate models (GCMs) and three representative concentration pathways (RCP 4.5, 6, and 8.5) were used in the SWAT model. According to all GCMs and RCPs, a warmer climate with a wetter Autumn and Spring and a drier late Summer season is anticipated by mid and late century in this region. To evaluate future management strategies, water budget and crop yields were assessed for two scenarios: current rainfed and adaptive irrigated conditions. Irrigation would improve corn yields during mid-century across all scenarios. However, prolonged irrigation would have a negative impact due to nutrients runoff on both corn and soybean yields compared to rainfed condition. Decision tree analysis indicated that corn and soybean yields are most influenced by soil moisture, temperature, and precipitation as well as the water management practice used (i.e., rainfed or irrigated). The computed values from the SWAT modeling can be used as guidelines for water resource managers in this watershed to plan for projected water shortages and manage crop yields based on projected climate change conditions. [ABSTRACT FROM AUTHOR]

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]

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. [ABSTRACT FROM AUTHOR]

Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H2S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H2S reduction potential. For this work, biogas H2S, CO2, O2, and CH4 concentrations were quantified for two existing H2S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H2S concentration (average: 1938 ± 65 ppm) correlated with the O2 concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H2S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems. [ABSTRACT FROM AUTHOR]