Anaerobic Digestion Of Manure Research Articles

Bacterial community structure and metabolism response to antibiotic residue levels in pig manure anaerobic digestion

Bacterial community succession in pig manure anaerobic digestion and its correlation with antibiotic residues under combinations of digestion time, temperature, moisture, acidity, and alkalinity are unknown. In this study, bacterial communities and antibiotic residues in compost were analyzed under combinations of these influencing factors (digestion time, temperature, moisture, and acidity and alkalinity). The results showed a decrease in antibiotic residues in the digestion, including tetracycline, oxytetracycline, chlortetracycline, norfloxacin, ciprofloxacin, penicillin, cephalosporin, sulfamethoxypyrimidine, sulfamethazine, tylosin, and erythromycin. These combined conditions resulted in changes in the structure and composition of the dominant and rare bacterial communities. However, there were bacterial populations (containing 13 genera) that presented a stable composition. Antibiotic residue levels were significantly associated with the genus numbers of dominant bacterial communities (containing 29 genera), but not with rare and stable bacterial communities. Antibiotic residue levels were significantly negatively correlated with the abundance of microbial genes encoding carbohydrate-active enzymes, negatively correlated with the abundance of genes involved in main metabolic pathways, and positively correlated with the abundance of genes associated with resistance to environments. Our findings suggest insight into correlations between bacterial community structure and metabolism and antibiotic residues in pig manure anaerobic digestion under effects of key influencing factors.

The Path to Net-Zero in Dairy Production: Are Pronounced Decreases in Enteric Methane Achievable?

Achieving net-zero greenhouse gas (GHG) emissions in dairy production will require >50% reduction in enteric methane (CH4) emissions together with elimination of emissions from feed production, additional carbon sequestration, reduction in manure emissions, anaerobic digestion of manure, and decreased reliance on fossil fuel energy. Over past decades, improved production efficiency has reduced GHG intensity of milk production (i.e., emissions per unit of milk) in the United States, but this trend will continue only if cows are bred for increased efficiency. Genetic selection of low-CH4-producing animals, diet reformulation, use of feed additives, and vaccination show tremendous potential for enteric CH4 mitigation; however, few mitigation strategies are currently available, and added cost without increased revenue is a major barrier to implementation. Complete elimination of CH4 emissions from dairying is likely not possible without negatively affecting milk production; thus, offsets and removals of other GHGs will be needed to achieve net-zero milk production.

How the USA can feasibly cut methane emissions 30% by 2030: anaerobic digestion of organic waste and various measures in oil and gas production

AbstractThe USA has committed to cutting its emissions of methane, an extremely potent greenhouse gas, by at least 30% by 2030 (‘30 × 30’). This is part of the Global Methane Pledge, signed by 155 countries, to keep global warming within 1.5 °C and thereby to forestall the disastrous effects of ‘runaway climate change’. It will be a major challenge for the USA to reach 30 × 30 and there is no consensus on how to do so. This paper provides a concrete, data‐driven roadmap to indicate how to reach 30 × 30 feasibly, focusing on two enormous sources of methane emissions: organic waste and oil and gas production. It calculates that building approximately 4700 anaerobic digesters (ADs) to process food waste and animal manure would cost about $74.2 billion in capital expenditure (capex) and cut 13.6% of total US methane emissions per year. On average, each project would take roughly 2–6 years to build. Of the various methane mitigation measures analyzed in the oil and gas sectors, the most impactful would be full compliance with the US Environmental Protection Agency's (EPA's) revised New Source Performance Standards (NSPS) for oil and gas production by 2029. This would cut 17.5% of total US methane emissions annually, at a cumulative capex of $20.7 billion from 2024 to 2029. Together, the 13.6% cut from food waste and manure ADs and the 17.5% cut from full NSPS compliance would amount to a 31.5% reduction, exceeding the 30 × 30 goal. Greater clarity from the federal government on funding eligibility and additional incentives would accelerate the buildout of ADs.

Effect of Monensin Supplementation in the Bovine Diet on the Composition and Anaerobic Digestion of Manure with and without Screening

Effect of Monensin Supplementation in the Bovine Diet on the Composition and Anaerobic Digestion of Manure with and without Screening

Prolonging the time of manure by water soaking can alleviate the inhibition of lime disinfection wastewater in a batch anaerobic digestion of swine manure

The African swine fever poses significant challenges for swine farms using lime-based disinfectants, leading to pronounced inhibition of anaerobic digestion systems due to the influx of lime disinfection wastewater. This study focuses on treating swine manure containing lime through water soaking (2d, 4d, 6d, 8d) before biogas digestion. An 8-day water soaking period significantly reduces Ca2+ and PO43--P concentrations by 20.36 % and 56.79 %, respectively. Batch tests show enhanced performance, with T1, T2, T3, and T4 witnessing increases in biogas production of 25.73 %, 114.36 %, 119.59 %, and 181.83 %, and Ca2+ sedimentation rates escalating by 6.59 %, 13.47 %, 28.94 %, and 35.64 %, respectively, compared to the control group (CK). In continuous tests, the pre-treated sample C1 maintains Ca2+ at 4.1 g/L, leading to a 104.86 % increase in biogas production compared to the control group. The study advocates extending water soaking durations as a strategy to mitigate lime disinfectant inhibition in swine manure anaerobic digestion systems, highlighting its potential for enhancing acidification, hydrolysis, and ultimately, the efficiency of biogas production.

Denaturing Gradient Gel Electrophoresis Approach for Microbial Shift Analysis in Thermophilic and Mesophilic Anaerobic Digestions.

To determine the evolution of microbial community and microbial shift under anaerobic processes, this study investigates the use of denaturing gradient gel electrophoresis (DGGE). In the DGGE, short- and medium-sized DNA fragments are separated based on their melting characteristics, and this technique is used in this study to understand the dominant bacterial community in mesophilic and thermophilic anaerobic digestion processes. Dairy manure is known for emitting greenhouse gases (GHGs) such as methane, and GHG emissions from manure is a biological process that is largely dependent on the manure conditions, microbial community presence in manure, and their functions. Additional efforts are needed to understand the GHG emissions from manure and develop control strategies to minimize the biological GHG emissions from manure. To study the microbial shift during anaerobic processes responsible for GHG emission, we conducted a series of manure anaerobic digestion experiments, and these experiments were conducted in lab-scale reactors operated under various temperature conditions (28 °C, 36 °C, 44 °C, and 52 °C). We examined the third variable region (V3) of the 16S rRNA gene fingerprints of bacterial presence in anaerobic environment by PCR amplification and DGGE separation. Results showed that bacterial community was affected by the temperature conditions and anaerobic incubation time of manure. The microbial community structure of the original manure changed over time during anaerobic processes, and the community composition changed substantially with the temperature of the anaerobic process. At Day 0, the sequence similarity confirmed that most of the bacteria were similar (>95%) to Acinetobacter sp. (strain: ATCC 31012), a Gram-negative bacteria, regardless of temperature conditions. At day 7, the sequence similarity of DNA fragments of reactors (28 °C) was similar to Acinetobacter sp.; however, the DNA fragments of effluent of reactors at 44 °C and 52 °C were similar to Coprothermobacter proteolyticus (strain: DSM 5265) (similarity: 97%) and Tepidimicrobium ferriphilum (strain: DSM 16624) (similarity: 100%), respectively. At day 60, the analysis showed that DNA fragments of effluent of 28 °C reactor were similar to Galbibacter mesophilus (strain: NBRC 10162) (similarity: 87%), and DNA fragments of effluent of 36 °C reactors were similar to Syntrophomonas curvata (strain: GB8-1) (similarity: 91%). In reactors with a relatively higher temperature, the DNA fragments of effluent of 44 °C reactor were similar to Dielma fastidiosa (strain: JC13) (similarity: 86%), and the DNA fragments of effluent of 52 °C reactor were similar to Coprothermobacter proteolyticus (strain: DSM 5265) (similarity: 99%). To authors' knowledge, this is one of the few studies where DGGE-based approach is utilized to study and compare microbial shifts under mesophilic and thermophilic anaerobic digestions of manure simultaneously. While there were challenges in identifying the bands during gradient gel electrophoresis, the joint use of DGGE and sequencing tool can be potentially useful for illustrating and comparing the change in microbial community structure under complex anaerobic processes and functionality of microbes for understanding the consequential GHG emissions from manure.

Global potential nitrogen recovery from anaerobic digestion of agricultural residues

Meeting the anticipated 50% increase in global food demand by 2050 requires a crucial reassessment of agricultural practices, particularly in terms of nitrogen fertilizers inputs. This study analyzes the technical potential of nitrogen recovery from livestock manure and crop residues, bringing attention to the often-overlooked resource of digestate derived from anaerobic digestion. Our analysis highlights the significant capacity of the anaerobic digestion process, yielding approximately 234 ± 5 million metric tons (Mt) of nitrogen annually, sourced 93% from livestock manure and 7% from crop residues. Additionally, we estimated that substituting synthetic nitrogen with nitrogen from anaerobic digestion has the potential to reduce greenhouse gas emissions by 70% (185 Mt CO2-eq yr−1). Lastly, 2.5 billion people could be sustained by crops grown using nitrogen from anaerobic digestion of manure and crop residues rather than synthetic nitrogen fertilizers. Although agricultural residues have double the technical potential of current synthetic nitrogen fertilizer production, 30% of croplands encounter difficulties in satisfying their nitrogen needs solely through crop residues and anaerobic digestion manure. This deficiency primarily results from inefficient reuse attributed to geographical mismatches between crop and livestock systems. This underscores the urgent need to reconnect livestock and cropping systems and facilitate the transport and reuse of manure in crop production. In conclusion, the mobilization of these large amounts of nitrogen from livestock manure and crop residues will require to overcome the nitrogen from anaerobic digestion green premium with incentives and subsidies.

Microbial analysis of anaerobic digester reveals prevalence of manure microbiota

Anaerobic digestion of swine manure reduces farm greenhouse gases emissions and provides a renewable gas in the agricultural sector. The particular composition of manure, with high concentrations of ammoniacal nitrogen and volatile fatty acids, often threatens the stability of the process through inhibition of methanogens. In this work, continuous production of biogas was tested under relative short hydraulic retention time (15 days). Although a strong inhibition period was detected, adaptation of the microbiota and displacement of bacteria and archaea present in the inoculum by microorganisms present in the animal manure resulted in biogas production close to the values found in standardized batch tests in absence of inhibitions. These findings suggest that in anaerobic digestion of manure, it is not necessary to inoculate, as manure itself contains a large number of active fermentative microorganisms that can even resist long-term digestion inhibition.

Renewable natural gas: A case study of Minnesota

Renewable natural gas (RNG) often generates usable energy from waste products, reduces methane emissions, and creates new revenue streams. However, not all RNG projects are financially or technically feasible. We assessed the total RNG potential of currently available local waste feedstocks in the state of Minnesota and analyzed the financial and technical limitations for project development. We found that under ideal production conditions the RNG potential from municipal solid waste, dairy and hog farm manure, and municipal wastewater solids in the state could replace approximately 7.5% of current Minnesota natural gas use. We find that technical and financial factors such as project size, financing, and distance to an existing pipeline further reduce the number of feasible RNG project sites in Minnesota. Virtual pipelines – trucking RNG short distances to pipeline injection stations – improved the modeled profitability of 124 out of 175 projects (71%) by decreasing transmission costs. No projects are financially feasible without state or federal renewable fuel credit programs because direct sale of RNG alone does not cover project costs. Dairy manure projects have the lowest levelized cost of energy, the highest total revenue, and the shortest payback period compared to municipal solid waste landfill and wastewater treatment plant projects of similar size. This difference is because manure anaerobic digestion projects are eligible for larger credits under renewable fuel credit programs than municipal solid waste landfills and wastewater treatment plants, but this credit system limits end-use of the RNG to vehicle fuel. Our contribution helps provide an outline for the magnitude of current natural gas use in Minnesota replaceable via RNG projects.

Characterization and anaerobic digestion of manure from pigs submitted to feed restriction or supplemented with ractopamine or chromium

Resumo Realizou-se este estudo com o objetivo de caracterizar a produção e a digestão anaeróbia de dejetos de suínos em terminação submetidos a restrição alimentar ou suplementados com ractopamina ou cromo. Os dejetos foram provenientes de 50 suínos machos castrados, em fase de terminação, com ± 154 dias de idade, com peso inicial de 99,0 ± 4,4 kg e final de 117,2 ± 5,8 kg. As dietas experimentais foram: controle (dieta convencional); restrição qualitativa (redução de 7,5% de energia líquida em relação à dieta controle); restrição quantitativa (redução de 15% no fornecimento de ração); cromo (0,8 mg); e ractopamina (10 ppm). Os dados foram submetidos à análise de variância por meio do delineamento em blocos ao acaso, no qual as semanas de análises foram consideradas como blocos (cofator). Não foram observadas diferenças entre as dietas nas produções de dejetos na matéria natural (MN), matéria seca (MS), matéria mineral (MM) e matéria orgânica (MO). Animais que receberam a dieta controle apresentaram o maior coeficiente de resíduo e não houve diferença entre as demais dietas. Não foram observadas diferenças entre as dietas para sólidos totais, pH e nitrogênio total dos afluentes e efluentes. O maior rendimento de biogás (574 mL g-1 de SV adicionados) foi obtido com os digestores abastecidos com dejetos de animais alimentados com dieta qualitativamente restrita. Conclui-se que a dieta com restrição qualitativa resulta em maior produção de dejetos, porém com menores excreções de nitrogênio e fósforo e maior rendimento de biogás.

Caracterização e digestão anaeróbia dos dejetos de suínos submetidos a restrição alimentar ou suplementados com ractopamina ou cromo

Abstract The aim of this study was to characterize the production and anaerobic digestion of manure from finishing pigs subjected to feed restriction or supplemented with ractopamine or chromium (Cr). The waste came from 50 barrows in the finishing phase, aged ± 154 days, with a starting weight of 99.0 ± 4.4 kg and a final weight of 117.2 ± 5.8 kg. The experimental diets were as follows: control (conventional diet), qualitative restriction (7.5% reduction in net energy compared to the control diet), quantitative restriction (15% reduction in feed supply), Cr (0.8 mg), and ractopamine (10 ppm). The data were subjected to an analysis of variance using a randomized block design, in which the weeks of analysis were considered blocks (cofactors). There were no differences in manure production between the diets regarding natural matter (NM), dry matter (DM), mineral matter (MM), or organic matter (OM). Animals fed the control diet had the highest residue coefficient, and there was no difference among the other diets. No differences were observed among the diets regarding total solids, pH, or total nitrogen in the tributaries or effluents. The highest biogas yield (574 mL g-1) of added volatile solids (VS) was obtained in the digesters supplied with manure from animals fed a qualitatively restricted diet. It can be concluded that a qualitatively restricted diet results in higher manure production but with lower nitrogen and phosphorus excretion and higher biogas yields.

CO2 bubbling pretreatment to remove the inhibition of lime disinfection wastewater in a swine manure anaerobic digestion system

Under the African swine fever epidemic, the extensive use of lime disinfectants has seriously inhibited anaerobic digestion (AD). In this study, the subject was swine manure containing lime disinfectant wastewater. The research set up a carbon dioxide (CO2) bubbling pretreatment device before it entered AD to explore the effect of breaking the inhibition of lime disinfectant. The results showed that the initial pulmonary hypertension (pH) of 11.0 and CO2 bubbling time of 8 h had the best effect, which could reduce calcium ion (Ca2+) by 73.0%, and the biogas production of the batch AD test increased by 28 times. In the continuous AD test, the Ca2+ of CK increased to 7.67 g/L, while the S1 pretreated by CO2 bubbling stabilized at 2.6 g/L, the biogas production in S1 was 112.4% higher than in CK. CO2 bubbling pretreatment reduces the concentration of Ca2+ in swine by utilizing the combination of exogenous CO2 and Ca2+, breaking the inhibitory effect on AD, and thereby improving the performance of the AD system. The test used CO2 in biogas to break the inhibition of lime disinfectants on AD, which was a convenient and feasible pretreatment process.

Metagenomic comparison of effects of mesophilic and thermophilic manure anaerobic digestion on antimicrobial resistance genes and mobile genetic elements

This study evaluated the long-term effects of mesophilic (MAD) and thermophilic (TAD) anaerobic digestion on the fate and evolution of antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs) in cattle manure following a metagenomic approach. The results indicated that MAD and TAD lowered ARG levels in fresh cattle manure by over 50 % and MGEs by over 65 %. However, no statistically significant difference was observed between the MAD and TAD processes in terms of their ability to reduce ARG and MGE. Co-occurrence analysis suggested facultative anaerobic species belonging to the Bacillota and Actinomycetota phyla as the primary potential hosts of ARGs and MGEs. Analyses of co-assembled contigs revealed the presence of transposon and toxin-antitoxin systems in close proximity to ARGs typically found in anaerobic digesters. The identification of these systems near ARGs is particularly significant, as it highlights a potential mechanism for the persistence and spread of ARGs in such environments. Overall, the results indicated that digested cattle manure (whether under mesophilic or thermophilic conditions) would pose a much lower risk of dissemination of antimicrobial resistance than untreated manures. Since TAD did not outperform MAD at reducing ARGs and MGEs, thermophilic temperatures may not be necessary to improve ARG reduction rates in cattle manure AD. These valuable insights could help develop strategies to reduce the dissemination of antibiotic resistance due to manure treatment and disposal.

Effect of reactor operation modes on mitigating antibiotic resistance genes (ARGs) and methane production from hydrothermally-pretreated pig manure

Numerous efforts have been made to enhance the performance of anaerobic digestion (AD) for accelerating renewable energy generation, however, it remains unclear whether the intensified measures could enhance the proliferation and transmissions of antibiotic resistance genes (ARGs) in the system. This study assessed the impact of an innovative pig manure AD process, which includes hydrothermal pretreatment (HTP) and a two-stage configuration with separated acidogenic and methanogenic phases, on biomethane (CH4) production and ARGs dynamics. Results showed that HTP significantly increase CH4 production from 0.65 to 0.75 L/L/d in conventional single-stage AD to 0.82 and 0.91 L/L/d in two-stage AD. This improvement correlated with a rise in the relative abundance of Methanosarcina, a key methanogenesis microorganism. In the two-stage AD, the methanogenic stage offered an ideal environment for methanogens growth, resulting in substantially faster and higher CH4 production by about 10% compared to single-stage AD. Overall, the combined use of HTP and the two-stage AD configuration enhanced CH4 production by 40% compared to traditional single-stage AD. The abundance and diversity of ARGs were significantly reduced in the acidogenic reactors after HTP. However, the ARGs levels increased by about two times in the following methanogenesis stage and reached similar or higher levels than in single stage AD. The erm(F), erm(G), ant(6)-Ia, tet(W), mef(A) and erm(B) were the six main ARGs with significant differences in relative abundances in various treatments. The two-stage AD mode could better remove sul2, but it also had a rebound which elevated the risk of ARGs to the environment and human health. Network analysis identified pH and TVFAs as critical factors driving microbial communities and ARG proliferation in the new AD process. With the results, this study offers valuable insights into the trade-offs between AD performance enhancement and ARG-related risks, pinpointing essential areas for future research and practical improvements.

47 Feeding Pigs with Low Crude Protein Diets: Impact of Pig Manure Nitrogen Content on Biogas Production and Digestate Quality

Abstract Lowering dietary crude protein levels is a nutritional strategy recognized to both decrease the use of high-impact feed ingredients and reduce nitrogen (N) excretion. Improved pig manure management practices can further mitigate the environmental impacts associated with pig production towards net-zero emissions. Anaerobic digestion (AD) is a promising technology for transforming pig manure into energy as biogas and into bio-based fertilizers (i.e., digestate from AD). However, little is known about the effects of pig manure N content on AD. Thus, this study aimed to evaluate the impact of pig manure N content on biogas production and digestate quality through the AD of manure from pigs fed low crude protein diets. Three pig manure N concentrations were tested: T1 = 5873, T2 = 5421, and T3 = 5149 total Kjeldahl nitrogen (TKN, mg/L). Throughout 5 sequential fed-batch cycles (25 ± 4 days/cycle), biogas production and its composition (CH4, CO2, and H2S) were measured, while raw manure and weekly digestate samples were analyzed for total solids (TS, %), volatile solids (VS, %), pH, chemical oxygen demand (COD, mg/L), TKN, and ammoniacal nitrogen (NH3-N, mg/L). In a temperature-controlled room (20 ± 1ºC), 6 digesters (3 treatments x 2 replicates) were operated as single-stage reactors to digest pig slurry (mixture of urine and feces, TS: 5.6%) inoculated with a liquid inoculum (TS: 2.3%) to improve manure-microbe interactions. Data were analyzed by ANOVA using PROC MIXED with repeated measures and comparison of means through the Tukey test (SAS software). In addition, both correlation and regression analyses were performed with R to evaluate the relationship among variables. Decreasing pig manure N content showed a tendency to reduce biogas (-20% in T3 vs T1; P = 0.0782) and methane (-22% in T3 vs T1; P = 0.0576) production per cycle, as shown in Table 1. Regarding biogas composition, CH4/biogas and CH4/CO2 decreased with N content (-3 and -4% in T3 vs T1; P ≤ 0.0082). There were strong positive correlations between the N content of pig manure and the amount of NH3-N (linear: r = 0.94, R2 = 0.88) and TKN (linear: r = 0.90, R2 = 0.81) present in the digestate at the end of each cycle. These results suggest that a reduction in pig manure N content reduces biogas production and its quality (ratio of CH4 to CO2). This latter variable is important for biogas efficiency; thus, reducing crude protein in pig diets may impair the production of biogas in AD. However, a decreased N content may cause less emissions into the environment, but when using the digestate as fertilizer, it may not entirely fulfill the N requirements of fast-growing crops for a given application rate.

Biogas and biomethane production potential via anaerobic digestion of manure: A case study of Portugal

Anaerobic digestion is a promising technology that can be part of the solution to meet the increasing energy demand while reducing the harmful effects on the environment. The objective of this work is to assess Portugal’s potential to produce biogas or biomethane via anaerobic digestion of manure. First, a spatial analysis of manure availability was done using ArcGIS. Then, a thermodynamic model of the production system was created in MATLAB, which includes three proposed production paths. The outputs of the thermodynamic model served as inputs for an economic analysis, also performed in MATLAB, and a life cycle assessment done using SimaPro software. Findings from the spatial analysis revealed that the centre and south areas (excluding Algarve) of Portugal have the highest manure availability, 73.6% of the national amount, and the Azores archipelago has high availability of cattle manure, 17.88% of the national amount. The total possible amount of production plants was estimated as 743. The thermodynamic model results show that the region of Lezíria do Tejo has the highest biogas and biomethane production potential, at 557172 t/year and 352364 t/year. Furthermore, the total potential biogas and biomethane production in Portugal was estimated as 3561947.05 t/year and 1791402.48 t/year. Regarding energy, the calculated efficiencies of biogas and biomethane production were 62.96% and 51.82%. The economic analysis yielded national average selling prices of 0.8174 €/kg and 1.290 €/kg for biogas and biomethane. The life cycle assessment showed that the main concerns regarding this type of systems are toxicity impacts and resource consumption.

Characterization of Proteus mirabilis and associated plasmids isolated from anaerobic dairy cattle manure digesters.

Proteus mirabilis is an opportunistic pathogen associated with a variety of human infections, including urinary tract infections. The prevalence of P. mirabilis in foods of animal origin and in the manure by-products created in animal production is not well documented. Further, the prevalence and persistence of extended-spectrum cephalosporin (ESC) resistant P. mirabilis is largely unknown. In this study, we characterized ESC-resistant P. mirabilis recovered from various stages of dairy manure anaerobic digestion. Isolates were screened by PCR for blaCTX-M, blaCMY and blaSHV, and antimicrobial susceptibility testing was performed. Fifty-six P. mirabilis carrying CTX-M were sequenced with short and long read sequencing technologies, and the assembled chromosomes and plasmids were compared. ESC-resistant Proteus was found in four of the six manure digesters, an indication that not all digesters were colonized with resistant strains. Both CTX-M-1 and CTX-M-15 plasmids were found in P. mirabilis isolates. Transfer of plasmid DNA by conjugation was also explored, with ESC-resistance plasmids able to transfer to Escherichia coli at high frequency. We concluded that P. mirabilis can harbour and transfer ESC-resistance genes and plasmids, and may be an overlooked reservoir of antimicrobial resistance.

Improvement of cow manure anaerobic digestion performance by three different crop straw biochars

Anaerobic digestion (AD) is an effective bioconversion technology widely used to treat agricultural waste and reduce environmental pollution. Although AD has been commonly applied to practical social needs, low yield and reactor instability limit its performance. In this study, potato, rape, and wheat straw were pyrolyzed to biochar at 600 °C and added to a batch AD system to improve biogas yield. Biochemical methane potential test was used to assess the methane production. The results showed that the three straw biochar had similar efficiency that increased cumulative methane production (35.45%–52.66%) compared with that in the control group (818.5 mL). Potato straw biochar presented the highest cumulative methane production (1249.5 mL). Significant differences in microbial communities between biochar and control groups were noticed. The microbial community structure in the AD system was significantly related to the biochar properties. The addition of biochar increased the abundance of Methanobrevibacter in the biochar group by 2–147 times. This study provides reference for the application of straw biochar to promote methane production.

Use of reverse osmosis concentrate for mitigating greenhouse gas emissions from pig slurry.

Due to the high global warming potential (GWP) in a short time scale (GWP100 = 28 vs. GWP20 = 86), mitigating CH4 emissions could have an early impact on reducing current global warming effects. The manure storage tank emits a significant amount of CH4, which can diminish the environmental benefit resulting from the anaerobic digestion of manure that can generate renewable energy. In the present study, we added the reverse osmosis concentrate (ROC) rich in salt to the pig slurry (PS) storage tank to reduce CH4 emissions. Simultaneously, pure NaCl was tested at the same concentration to compare and verify the performance of ROC addition. During 40 days of storage, 1.83 kg CH4/ton PS was emitted, which was reduced by 7-75% by the addition of ROC at 1-9 g Na+/L. This decrease was found to be more intensive than that found upon adding pure sodium, which was caused by the presence of sulfate rich in ROC, resulting in synergistic inhibition. The results of the microbial community and activity test showed that sodium directly inhibited methanogenic activity rather than acidogenic activity. In the subsequent biogas production from the stored PS, more CH4 was obtained by ROC addition due to the preservation of organic matter during storage. Overall, 51.2 kg CO2 eq./ton PS was emitted during the storage, while 8 kg CO2 eq./ton PS was reduced by biogas production in the case of control, resulting in a total of 43.2 kg CO2 eq./ton PS. This amount of greenhouse gas emissions was reduced by ROC addition at 5 g Na+/L by 22 and 65 kg CO2 eq./ton PS, considering GWP100 and GWP20 of CH4, respectively, where most of the reduction was achieved during the storage process. To the best of our knowledge, this was the first report using salty waste to reduce GHG emissions in a proper place, e.g., a manure storage tank.

The Antibiotics Degradation and Its Mechanisms during the Livestock Manure Anaerobic Digestion.

Antibiotics are administered to livestock at subtherapeutic levels to promote growth, and their degradation in manure is slow. High antibiotic concentrations can inhibit bacterial activity. Livestock excretes antibiotics via feces and urine, leading to their accumulation in manure. This can result in the propagation of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs). Anaerobic digestion (AD) manure treatment technologies are gaining popularity due to their ability to mitigate organic matter pollution and pathogens, and produce methane-rich biogas as renewable energy. AD is influenced by multiple factors, including temperature, pH, total solids (TS), substrate type, organic loading rate (OLR), hydraulic retention time (HRT), intermediate substrates, and pre-treatments. Temperature plays a critical role, and thermophilic AD has been found to be more effective in reducing ARGs in manure compared to mesophilic AD, as evidenced by numerous studies. This review paper investigates the fundamental principles of process parameters affecting the degradation of ARGs in anaerobic digestion. The management of waste to mitigate antibiotic resistance in microorganisms presents a significant challenge, highlighting the need for effective waste management technologies. As the prevalence of antibiotic resistance continues to rise, urgent implementation of effective treatment strategies is necessary.