Impacts of free nitrous acid on stabilizing food waste and sewage sludge for anaerobic digestion

This work investigated the effectiveness of free nitrous acid (FNA) in enhancing organic waste solubilization to improve biogas production in anaerobic digestion (AD). The results indicated that FNA pretreatment can enhance soluble organic content and control H2S odor in tested organic wastes, including food waste, sewage sludge, and their combination. However, a significant decrease (>50 %) in FNA concentration was found in the reactors, possibly due to denitrifier-driven NO2- consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH4 production in the reactors fed with mixed substrate pretreated with 2.9 mg FNA-N/L. However, the presence of NO2- (325.6-2368.0 mg N/L) in some BMP reactors, due to carryover from FNA pretreatment, adversely affected CH4 production (>55 %) and prolonged lag time (>4.2 times). These findings are valuable for researchers and practitioners in waste management, offering insights for implementing FNA pretreatment to enhance the biodegradability of organic wastes in AD.

Anhydrous volatile fatty acid extraction through omniphobic membranes by hydrophobic deep eutectic solvents: Mechanistic understanding and future perspective

Volatile fatty acids (VFAs) derived from arrested anaerobic digestion (AD) can be recovered as a valuable commodity for value-added synthesis. However, separating VFAs from digestate with complex constituents and a high-water content is an energy-prohibitive process. This study developed an innovative technology to overcome this barrier by integrating deep eutectic solvents (DESs) with an omniphobic membrane into a membrane contactor for efficient extraction of anhydrous VFAs with low energy consumption. A kinetic model was developed to elucidate the mechanistic differences between this novel omniphobic membrane-enabled DES extraction and the previous hydrophobic membrane-enabled NaOH extraction. Experimental results and mechanistic modeling suggested that VFA extraction by the DES is a reversible adsorption process facilitating subsequent VFA separation via anhydrous distillation. High vapor pressure of shorter-chain VFAs and low Nernst distribution coefficients of longer-chain VFAs contributed to DES-driven extraction, which could enable continuous and in-situ recovery and conversion of VFAs from AD streams.

Two-stage anaerobic digestion: State of technology and perspective roles in future energy systems

Two-stage anaerobic digestion (TSAD) systems have been studied on a laboratory scale for about 50 years. However, they have not yet reached industrial scale despite their potential for future energy systems. This review provides an analysis of the TSAD technology, including the influence of process parameters on biomass conversion rates. The most common substrate (35.2% of the 38 selected studies) used in the analysed data was in the category of rapidly hydrolysable industrial waste with an average dry matter content of 7.24%. The highest methane content of 85% was reached when digesting food waste in a combination of two mesophilic continuously stirred tank reactors with an acidic (pH 5.5) first stage and alkaline (pH 7) second stage. Therefore, the review shows the limitations of the TSAD technology, future research directions, and the effect of integration of TSAD systems into the current strategy to reduce greenhouse gas emissions.

Impact of electro-conductive nanoparticles additives on anaerobic digestion performance - A review

Anaerobic digestion (AD) is a biochemical process that converts waste organic matter into energy-rich biogas with methane as the main component. Addition of electric electro-conductive, such as that nanoparticles (NP), has been shown to improve biogas generation. Interspecies electron transfer and direct interspecies electron transfer (DIET) using conductive materials is one of the mechanisms responsible for observed increases in CH₄. This article discusses the effect of the type and size of electro-conductive NPs on improving microbial degradation within AD systems, as well as the effect of electro-conductive NPs on microbial community shifts and syntrophic metabolism. Limitations and future perspectives of using NPs in an AD system is also discussed.

Tetracycline, sulfadimethoxine, and antibiotic resistance gene dynamics during anaerobic digestion of dairy manure

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 CH₄ production reductions of 7.8%, whereas no CH₄ 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.

Finding What Is Inaccessible: Antimicrobial Resistance Language Use among the One Health Domains

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.

Effect of metal nanoparticles in anaerobic digestion production and plant uptake from effluent fertilizer

Nanoparticle (NP) use can increase biological activity and adversely impact the environment. This study was the first to quantify biogas increases with NP mixtures during continuous anaerobic digestion (AD) of poultry litter and NP uptake in crops through tracking: 1) CH₄ and H₂S production from a NP mixture (Fe, Ni, and Co) in 30 L continuous digester (AD1) for 278 days compared to a control digester (AD2) without NP addition, 2) NP degradation during digestion, 3) using AD effluent with and without NP addition as a fertilizer, and 4) plant uptake of NPs. With NP inclusion, CH₄ production increased by 23.7%, and H₂S was reduced by 56.3%. The AD1 effluent had 1,160-19,400% higher NP concentrations and the lettuce biomass had 21.0-1,920% more NPs than lettuce fertilized with the AD2 effluent. This study showed that the effects of NPs remaining in the AD effluent must be considered.

Biochar addition with Fe impregnation to reduce H2S production from anaerobic digestion

Corn stover biochar (CSB) and maple biochar (MB) were added into anaerobic digesters and evaluated for hydrogen sulfide (H2S) reductions. This was the first study to show Fe-impregnated biochar can eliminate H2S production. The novel study evaluated biochar addition on H2S reduction and nutrient concentrations using three experiments to test the effect of: 1) biochar concentration, 2) biochar particle size, and 3) Fe-impregnated biochar using triplicate lab-scale reactors. At the highest biochar dose (1.82 g biochar/g manure TS), H2S production was 90.5% less than the control treatment (351 mL H2S/kg VS). Biochar particle size did not significantly affect H2S concentration. The Fe-impregnated biochar (0.5 g biochar/g manure TS) reactors had no H2S detected in the CSB-Fe system. Methane (CH4) in the biochar and control treatments were not significantly different in all three experiments. The results show that biochar added to digesters can significantly reduce H2S production without affecting CH4 production.

Effect of anaerobic digester inoculum preservation via lyophilization on methane recovery

A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH₄). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH₄ production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144-146 mL CH₄/g volatile solids (VS) and 194-225 mL CH₄/g VS at a 2:1 and 4:1 ISR, respectively, with 33-57% more CH₄ at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH₄ production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH₄ recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH₄ recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum.

Trends in Antimicrobial Resistance Genes in Manure Blend Pits and Long-Term Storage Across Dairy Farms with Comparisons to Antimicrobial Usage and Residual Concentrations

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.

Impact of metal nanoparticles on biogas production from poultry litter

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 Fe₃O₄) 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 Fe₃O₄. 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 Fe₃O₄ (27.5% increase). Nanoparticle mixtures greatly decreased H₂S production. The SEM post-AD detected Fe, Ni, and Fe₃O₄ at concentrations ≥100 mg/L.

Waste treatment and energy production from small-scale wastewater digesters

Three tubular anaerobic digestion (AD) systems were installed in Haiti to treat black water (toilet-based wastewater), including a three cell 36m³ clinic digester (CD), a two cell 2m³ hotel digester (HD), and a three-cell 3m³ farm digester (FD) for worker use. During digestion, total coliforms were reduced by 99.1%, E. coli by 98.5%, and chemical oxygen demand (COD) by 93.6%. Nutrients in the effluent averaged 99.4mg/L NH₄⁺ and 10.6mg/L PO₄^2-, producing an effective organic fertilizer. Average biogas production in CD was 108L/d, with 65.4% CH₄. Survey participants (n=573) were willing to pay $0.10-0.30 per use for sanitation facilities. Seventy-two percent of the rural population surveyed in Cange, Haiti lacked access to improved sanitation due to financial constraints. The economic analysis calculated an investment cost for a shared toilet AD systems of $16-$47 (USD) per person based on daily use at design capacity.

Effect of liquid surface area on hydrogen sulfide oxidation during micro-aeration in dairy manure digesters

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.

Effect of temperature on methane production from field-scale anaerobic digesters treating dairy manure

Temperature is a critical factor affecting anaerobic digestion because it influences both system heating requirements and methane production. Temperatures of 35-37°C are typically suggested for manure digestion. In temperate climates, digesters require a considerable amount of additional heat energy to maintain temperatures at these levels. In this study, the effects of lower digestion temperatures (22 and 28°C), on the methane production from dairy digesters were evaluated and compared with 35°C using duplicate replicates of field-scale (FS) digesters with a 17-day hydraulic retention time. After acclimation, the FS digesters were operated for 12weeks using solids-separated manure at an organic loading rate (OLR) of 1.4kgVSm(-3)d(-1) and then for 8weeks using separated manure amended with manure solids at an OLR of 2.6kgVSm(-3)d(-1). Methane production values of the FS digesters at 22 and 28°C were about 70% and 87%, respectively, of the values from FS digesters at 35°C. The results suggest that anaerobic digesters treating dairy manure at 28°C were nearly as efficient as digesters operated at 35°C, with 70% of total methane achievable at 22°C. These results are relevant to small farms interested in anaerobic digestion for methane reduction without heat recovery from generators or for methane recovery from covered lagoon digesters.

Anaerobic co-digestion of forage radish and dairy manure in complete mix digesters

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.

Evaluating the toxicity of food processing wastes as co-digestion substrates with dairy manure

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).

Characterizing food waste substrates for co-digestion through biochemical methane potential (BMP) experiments

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.

A new integrative conjugative element detected in Haitian isolates of Vibrio cholerae non-O1/non-O139

The presence of SXT/R391-related integrating conjugative elements (ICEs) in Vibrio cholerae O1 and non-O1/non-O139 isolated from clinical and environmental samples in Haiti in 2010 was studied. The main finding of this work was the identification of the novel ICEVchHai2 among closely related V. cholerae non-O1/non-O139 clinical strains. The mosaic structure of this element confirms the role of ICEs as efficient recombination systems whereby new genetic material can be acquired and exchanged, according V. cholerae strains new accessory functions.

Methane production in low-cost, unheated, plug-flow digesters treating swine manure and used cooking grease

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.

Waste treatment and biogas quality in small-scale agricultural digesters

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.