Cumulative CH4 Production Research Articles

Metagenomic Analysis during Co-Digestion Buffalo Sludge and Tomato Pomace Post Thermal Stress: A Case Study

The tomato industry and buffalo farming generate waste, including sludge (BS) and tomato pomace (TP), which can significantly impact their economic and environmental sustainability. The case study tracked changes in microflora composition after a thermal shock during anaerobic co-digestion. The inoculum-to-substrate ratio was 0.5 based on volatile solid content under mesophilic conditions. An Automatic Methane Potential Test System was used to monitor the process before and after thermal stress (50°C) occurred for three days. Next-generation sequencing analyzed the bacterial and archaeal communities. The pH decreased, and methane production plateaued due to the high volatile solid content (87 g/L). After thermal stress, the pH returned to neutral, and the batch resumed biogas production. The cumulative CH4 production reached 3,115 Nml. The biogas had a maximum methane peak of 78.5% compared to 58.4% in BS. The taxonomic classification showed that Firmicutes (51.7%) and Bacteroidetes (29.9%) represented 81.6% of the total OTUs among the bacteria. Fonticella, the most abundant Clostridiaceae (average 4.3%), was absent in BS and increased (up to 17.1%) in TP during methane production. Methanocorpusculum was the most abundant in the archaeal community. However, Metanosarcina showed a stronger correlation with methane production. Brief thermal stress significantly altered bacterial and archaeal populations and allowed to resume biogas production.

Liquid Phase Parameter Analysis of Methanogenesis in Anaerobic Digestion of Coal Promoted by Kitchen Waste

In order to study the effect of food and kitchen waste on promoting methane production by collaborative fermentation of coal, this paper selected lignite and food and kitchen waste as the research objects, and carried out the gas production experiment of mixed fermentation of coal and food and kitchen waste with different ratios at 35 ℃ with mine water as the bacteria source. The results showed that the cumulative CH4 production was the highest in the mixed fermentation with the ratio of 1:4 (coal: kitchen waste). Therefore, exploring the optimal mixture ratio of coal and food waste fermentation can not only effectively improve the gas production effect, but also broaden the diversified utilization ways of coal and food waste, which has a good development potential.

Efficient methane production from anaerobic co-digestion of lignin-based feedstock and waste plastic: Digester performance and microbial community structures

Waste plastic (WP) and lignocellulosic biomass (LCB) are both refractory polymers that can provide feedstocks for the production of fuels. Anaerobic digestion (AD) is a widely recognized technology utilized in waste management and renewable energy production. It involves the utilization of microorganisms to decompose organic matter into methane (CH4). Nevertheless, mono-digestion, which refers to AD utilizing a single feedstock, encounters difficulties related to the properties of the feedstock. Therefore, the utilization of co-digestion with multiple feedstocks provides the potential to overcome these limitations. This study might be the first to examine the impact of co-digestion of low-density polyethylene (LDPE) with rice straw (RS) for biogas and CH4 production. The cumulative CH4 production for AD-1, AD-2, AD-3, AD-4, AD-5, and AD-6 was 154.9, 177.4, 52.0, 81.2, 98.43, and 135.15 NmL/g VS. The methane energy yields varied between 2.29 and 7.64 MJ/m3, while their respective βece values spanned from 17.6 to 58.8 %. Volatile solid removal was enhanced for the treated RS-LDPE mixture, as demonstrated in AD-6, in comparison to the untreated substrate in the AD-2 digester. There is a notable disparity in the composition of bacterial communities within the bioreactors that were constructed prior to and subsequent to the AD process. The proliferating Firmicutes, Bacteroidetes, and Protobacteria were crucial to the AD of RS and LDPE. The three predominant methanogenic genera present in the constructed digesters and inoculum were Methanobacterium, Methanolinea, and Methanosarcina, each with a distinct abundance level. The findings open up the possibility of better understanding the effect of co-digestion of WP and LCB on enhancing CH4 production, which is critical for developing strategies for bioremediation and waste valorization simultaneously with biofuel production.

Methane Production from Poly(lactic Acid) (PLA) and Polyhydroxybutyrate (PHB) Biodegradable Plastics with Anaerobic Granulated Sludge

- In this study, using Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria under mesophilic (38 ± 1oC) and thermophilic (58 ± 1oC) conditions in anaerobic granulated sludge taken from Pakmaya Yeast Factory in Izmir, Turkey; Methane production from biodegradable plastics with poly(lactic acid) (PLA) and polyhydroxybutyrate (PHB) was investigated. Effect of different operating parameters, increasing biodegradation times (from 10 days to 500 days), different inoculumsubstrate ratios (ISRs) (16, 8, 4, 2, 1) and increasing biochemical methane potential (BMP) times (between 10 day and 500 days) for the production of methane gas from PLA and PHB biodegradable plastics in anaerobic granular sludge waste; Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria were operated during the anaerobic digestion process under anaerobic conditions at mesophilic (38 ± 1oC) and thermophilic (58 ± 1oC) experimental temperatures. PLA biodegradable plastics were operated at optimum pH=7.6. PHB biodegradable plastics were carried out at optimum pH=8.1. Predicting the biodegradation behavior of PLA and PHB biodegradable plastics with BMP tests; It is found that the ISR parameter plays a very important role. This study showed that temperature plays a key role in the aging of microorganisms (Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria) during anaerobic digestion, the degradation of bioplastic materials (PLA and PHB) and the degradation of their natural properties. The increase in temperature from mesophilic conditions to thermophilic conditions increased the activities of methanogenic bacteria such as Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224. The maximum cumulative CH4(g) production was measured at 630 NL CH4 / kgVS for PHB biodegradable plastics in anaerobic granulated sludge with inoculum culture (the mixture of Methanosarcina barkeri DSM 800 and Methanococcus vannielii DSM 1224 methanogenic bacteria), at ISR=16 value, after 100 days, at pH=8.1 and at 58±1oC, respectively. The maximum 97% biodegradation efficiency was observed for PHB biodegradable plastics after 100 days, at pH=8.1 and at 58 ± 1oC thermophilic conditions, respectively.

Analysis of biogas production from sewage sludge combining BMP experimental assays and the ADM1 model.

The Anaerobic Digestion Model No. 1 (ADM1) was employed to simulate methane (CH4) production in an anaerobic reactor (AR), and the associated bench-scale biochemical methane potential (BMP) assay, having sewage sludge (SWS) from a municipal wastewater treatment plant (WWTP) as feedstock. The SWS presented the following physical-chemical characteristics: pH (7.4-7.6), alkalinity (2,382±100mg CaCO3 L-1), tCOD (21,903±1,000 mg L-1), TOC (895±100 mg L-1), TS, TVS, and VSS (2.0%, 1.1%, and 0.8%, respectively). The BMP assay was conducted in six replicates under anaerobic mesophilic conditions (37±0.1°C) for 11 days with a CH4 yield registered of 137.6±6.39 NmL CH4 or 124±6.72 CH4 g-1 VS-1. When the results obtained with the BMP bench-scale reactors were compared to the output generated with computational data by the ADM1 model having as input data the same initial sewage tCOD, similar cumulative CH4 production curves were obtained, indicating the accuracy of the ADM1 model. This approach allowed the characterization of the sludge and estimation of its biogas production potential. The combination of BMP assays, experimental data, and ADM1 model simulations provided a framework for studying anaerobic digestion (AD) processes.

Bioconversion of carbon dioxide and zero valent iron to methane by anaerobic sludge: Kinetics and archaeal consortium

Using carbon dioxide (CO2) as a carbon source for renewable energy production has potential applications for CO2 sequestration and greenhouse gas (GHG) emission reduction. In biological conversion, CO2 can be transformed into methane (CH4) by hydrogenotrophic methanogens with hydrogen (H2) as an energy source. In this study, zero-valent iron (ZVI) of 16, 32, 64, and 96 g/L was used as the H2 energy source for a bioconversion of CO2 to CH4. When the ZVI dosage was increased, a decrease in CO2 in the headspace occurred simultaneously with the increase in CH4. The presence of CH4 in both CO2/H2 and CO2/ZVI indicates that hydrogenotrophic methanogens can utilize both ZVI and H2 as electron donors and convert CO2 to CH4. The highest methane yield of 1.728 mmol CH4/mmol CO2 was observed for the CO2/ZVI 96 g/L. The modified Gompertz equation fitted the cumulative CH4 production curves of CO2/H2 and CO2/ZVI very well, where R2 was 0.9915 and 0.9903-0.9968, respectively. 16S rDNA high-throughput sequencing results revealed that ZVI addition facilitated the increase of the family Methanobacteriaceae, which became the most abundant among other archaea. It points out that this family favors ZVI and utilizes electrons more effectively from ZVI than H2.

Surface electron-polarized biochar-enhanced anaerobic digestion mechanism revealed by metagenomic binning strategy

Inefficient electron transfer is a key bottleneck for anaerobic digestion (AD), which often leads to system instability. Here, we propose for the first time a new strategy to solve the problem by adding surface electron-polarized biochar to enhance methanogenesis by providing electrons to methanogens through surface electron-poor/rich regions. Pyrolysis conversion of pigeon manure to conductive materials (CM) containing electron-poor/rich regions is realized. Different levels of CM (2.5, 5 and 7.5 g/L) are used to enhance methane production from pig manure and rice straw co-digestion systems. It is found that the addition of 5 g/L CM results in the highest cumulative CH4 production (187.4 ± 8.0 mL/g VS substrate), 35.4% higher (P < 0.05) than the control (0 g/L). Methanogenic archaea are enriched. Synergistic metabolic mechanisms between the functional microorganism bin.CM52.160 (cellulose degradation) and bin.CM03.101 (methane production) are revealed by the metagenomic binning strategy. A large number of potentially unculturable electroactive microorganisms have been identified. This work provides important insights into the construction of micro-electric fields on material surfaces and offers a practical approach to improving AD performance.

Effect of waste mango silage on the in vitro gas production, in situ digestibility, intake, apparent digestibility, and ruminal characteristics in calf diets.

Mexico is the fifth largest producer of mangoes in the world. For the conservation of agro-industrial waste and crop residues, the ensiling technique has shown good results. This study aimed to evaluate the effect of increasing the level of mango silage (86% waste mango and 14% pangola grass hay) in calf diets on in vitro gas production, in situ digestibility, intake, apparent digestibility, and ruminal characteristics. The diets contained 0 (T0), 30 (T1), 45 (T2), and 60% (T3) mango silage. The partial (24, 48, and 72 h) and cumulative (72 h) biogas, CH4 production, and degradation were determined in the in vitro evaluation. In situ digestibility and estimators of fermentation kinetics of dry matter (DM) and organic matter (OM) were determined. Intake, apparent nutrient digestibility, and rumen parameters of calves (200 kg) were evaluated in a 4 × 4 Latin square design. Response to increased mango silage was calculated by linear and quadratic orthogonal contrasts. In vitro partial and cumulative biogas production decreased linearly (p < 0.05), and the partial and cumulative CH4 production did not show linear or quadratic contrast (p > 0.05); in vitro DM degradation, in vitro neutral detergent fiber degradation, and in vitro acid detergent fiber degradation showed a linear increase (p < 0.05). In situ dry matter digestibility (DMDis), in situ organic matter digestibility (OMDis), b, a + b, c, and effective digestibility (ED) of DMDis, a, a + b, c, and ED of OMDis increased linearly (p < 0.05). Dry matter intake, OM intake, and crude protein intake showed a linear increase (p < 0.05); NDF intake and ADF intake presented a quadratic behavior (p < 0.05). Apparent digestibility of DM, OM, CP, and hemicellulose, pH, N-NH3, total bacterial count, acetate, propionate, butyrate, volatile fatty acids, acetate: propionate ratio, cellulolytic bacteria, and protozoa did not present a linear or quadratic orthogonal effect (p > 0.05). The in vitro, in situ, and in vivo variables demonstrated that up to 60% mango silage can be used for the intensive fattening of calves in confinement.

Anaerobic digestion of lignocellulosic waste for enhanced methane production and biogas-digestate utilization

Lignocellulosic biomass is an important source for nutrient management in agricultural systems and has a largely unexploited potential for biogas production. The digestates from the anaerobic digestion (AD) process are widely used in agriculture systems due to their nutrient composition and organic matter, making them a valuable source for plants. As a result, methane (CH4) production from AD of lignocellulosic biomass waste, such as rice straw, corn stalk, and grape stalk, was determined in this study, and their anaerobic digester residues were studied at various concentrations to investigate their potential on tomato plant growth and fruit yield. The biogas and CH4 yields of the pretreated rice straw, corn stalk, and grape stalk were determined through the AD process for 72 days, and the results revealed a gradual increase in the cumulative biogas and CH4 production until the end of the AD process (72 days). The cumulative biogas from rice straw, corn stalk, and grape stalk was 359.3, 309.9, and 215.1 L/kg VS, respectively. However, the biogas production of rice straw was higher than that of corn stalk, and grape stalk by 15.6% and 67%, respectively. The cumulative CH4 yield of rice straw was higher than that of corn stalk, and grape stalk by 21.1% and 76.3%, respectively. The results also showed that tomato growth significantly increased under grape stem residue (GSR) more than under rice straw residue (RSR) and corn stalk residue (CSR), as well as under untreated control and control infected with Fusarium oxysporum f. sp. lycopersici (FOL). The increase in bioreactor residue concentration resulted in a significant increase in tomato growth parameters, crop yield, and tomato quality. The results confirmed that 20% of GSR increased the tomato's physical and chemical properties compared with control, RSR, and CSR. The soil content of total nitrogen, phosphorus, and potassium gradually increased with the increase in residue concentrations before and after AD, and the maximum concentration was obtained at 25% of GSR. Therefore, anaerobic digestate could be economically viable, which can be a good solution for sustainable lignocellulosic biomass waste management and plant growth.

Novel nitrogen-doped biochar supported magnetite promotes anaerobic digestion: Material characterization and metagenomic analysis

Although different conductive materials have been applied to anaerobic digestion, there has not been a material that can really combine their merits and make up their shortcoming from each other. In this study, a novel nitrogen-doped biochar supported magnetite (Fe3O4@N-BC) was synthesized. Various material characterizations confirmed that nitrogen atoms were successful doped into the biochar and magnetite precipitated on its surface. 5 g/L Fe3O4@N-BC achieved the highest promotion of cumulative CH4 production by 1.75 times compared with the blank group. Further metagenomic analysis revealed that Fe3O4@N-BC could increase the gene abundances of pilA, MmcA, Fpo, Rnf and HdrEd in bacteria Clotridium, Pseudomonas and Syntrophomonas and archaea Methanosarcina. Redundancy analysis showed that it was electrical conductivity and electron exchange capacity that were the key physicochemical characteristics for Fe3O4@N-BC to facilitating direct interspecies electron transfer. This study provides a reference for future conductive material synthesis and its application for anaerobic digestion.

Dissimilatory manganese reduction facilitates synergistic cooperation of hydrolysis, acidogenesis, acetogenesis and methanogenesis via promoting microbial interaction during anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) of waste activated sludge (WAS) is commonly limited to poor synergistic cooperation of four stages including hydrolysis, acidogenesis, acetogenesis and methanogenesis. Dissimilatory metal reduction that induced by metal-based conductive materials is promising strategy to regulate anaerobic metabolism with the higher metabolic driving force. In this study, MnO2 as inducer of dissimilatory manganese reduction (DMnR) was added into WAS-feeding AD system for mediating complicated anaerobic metabolism. The results demonstrated that main operational performances including volatile solid (VS) degradation efficiency and cumulative CH4 production with MnO2 dosage of 60 mg/g·VS reached up to maximum 53.6 ± 3.4% and 248.2 ± 10.1 mL/g·VS while the lowest operational performances in control group (38.5 ± 2.8% and 183.5 ± 8.5 mL/g·VS) was originated from abnormal operation of four stages. Furthermore, high-throughput 16 S rRNA pyrosequencing revealed that enrichment of dissimilatory manganese-reducing contributors and methanogens such as Thermovirga, Christensenellaceae_R_7_group and Methanosaeta performed the crucial role in short-chain fatty acids (SCFAs) oxidation and final methanogenesis, which greatly optimized operational environment of hydrolysis, acidogenesis and acetogenesis. More importantly, analysis of functional genes expression proved that abundances of genes encoding enzymes participated in acetate oxidation, direct interspecies electron transfer (DIET) and CO2 reduction pathway were simultaneously up-regulated with the optimum MnO2 dosage, suggesting that DMnR with SCFAs oxidation as electron sink could benefit stable operation of four stages via triggering effective DIET-based microbial interaction mode.

Biogas generation potential of discarded food waste residue from ultra-processing activities at food manufacturing and packaging industry

There is a tremendous increase in the demand for efficient and productive food supply chain due to rapid increase in the world population. At the same time, anaerobic digestion (AD) of discarded food waste residue (FWR) along with buffer substrate (BS) could be a sustainable way to transform waste to energy. In this study, substrate combinations (SCs) were prepared using pre (OFPre), and post (OFPost) processed FWR; anaerobic sludge (AS) as BS. The Biochemical methane potential test (BMPT) was performed for SCs prepared at varying proportion. The decline in substrate biodegradability ratio (SBR) and C/N ratio was also determined. The study was performed under three different temperature condition ranging from 35 °C to 73 °C over 90 days. It was found that SC of C5 and C6 had maximum biogas generation potential (BGP) under thermophilic (45 °C to 52 °C) temperature condition, and the cumulative CH4 production was 997 and 880 ml/g of VS. The artificial neural network (ANN) and random forest regression (RFR) were the two-machine learning (ML) tools used to predict and correlated the CH4 yield using input data series of SCs, SBR and C/N ratio. The ANN-CH4 prediction model was found to have best possible prediction efficiency.

Insight into magnetite effects on anaerobic digestion of waste activated sludge with thermal hydrolysis pretreatment: From reactor performance to metagenomics analysis

Although the promotion of magnetite in anaerobic (AD) has been widely reported, the role of magnetite plays in the AD of waste activated sludge (WAS) and the mechanism of the promotion effect are still needed to be explored. This study investigated the effects of magnetite in AD of WAS with thermal hydrolysis pretreatment (THP) from four aspects including reactor performances, sludge characteristics, microbial community structures and gene abundance. Results showed that magnetite is able to enhance the consumption of soluble protein (SPN) and soluble polysaccharide (SPS) by increasing the activities of α-glucosidase and protease. With the addition of 0.5–5 g/L magnetite, the cumulative CH4 production could be increased by 38.25 %–85.34 %. The sludge electrical conductivity (EC) grew with the increase of magnetite dosage, which were 3.02, 8.65, 13.00, 15.46 and 17.97 μS/cm for G0-G4 respectively. In the presence of magnetite, the abundance of Proteobacteria increased which contained many genera of electroactive bacteria, such as Pseudomonas. By further metagenomics analysis, hydrogenotrophic methanogenesis pathway was shown to be enhanced with the addition of magnetite. The increasing abundance of pilA genes from Clostridium and Pseudomonas in bacteria and Methanospirillum in archaea confirmed that magnetite stimulated DIET in the AD of WAS.

Effect of Substrate-to-Inoculum Ratio and Temperatures During the Start-up of Anaerobic Digestion of Fish Waste

The high protein and lipid content of fish waste makes mono-digestion a difficult bioprocess for an anaerobic digestion (AD) system. On the other hand, the massive increase in fish and seafood consumption worldwide has led to an inevitable fish waste mono-AD. Therefore, this study was conducted to investigate the effects of food-to-microorganisms (F/M) ratios and temperatures during the start-up period of fish waste mono-digestion. F/M ratios of 0.5, 1, 2, and 3 on a g-COD/g-VSS basis were operated at 35°C and 45°C, representing mesophilic and hyper-mesophilic conditions, respectively. The increase in F/M ratio improved the maximum methane (CH4) production rate at both temperatures. However, F/M ratio of 0.5 generated the highest CH4 yield in mesophilic and hyper-mesophilic conditions (0.23±0.00 L-CH4/g-CODinput). Further increase in F/M ratio decreased CH4 yield up to 21.74% and 39.13% when the reactors were operated at 35°C and 45°C, respectively. When reactors were supplied with FM ratios of 0.5, 1, and 2, hyper-mesophilic temperature improved methanogenesis by up to 2.61% and shortened the lag phase by 22.88%. Meanwhile, F/M ratio 3 at 45°C decreased cumulative CH4 production by up to 26.57% and prolonged the lag phase by 10.19%. The result of this study is beneficial to managing the input substrate of a batch-AD system that treats fish waste as a sole substrate.

Neglected effect of transportation on the property of municipal biowaste and the subsequent biomethane potential

Long-distance transportation of municipal biowaste can influence its physio-chemical characteristics and the subsequent anaerobic digestion (AD) performance. However, the effect of whole transportation processes on the characteristics of municipal biowaste from upstream source separation/collection to downstream storage remains poorly documented. To this end, this study presented the relevant work by sampling in practical conditions. Results showed that transportation led to a high hydrolysis rate of 33.4%–35.5%, and an acidification rate of 15.8%–17.3%. Simultaneously, lactic acid was produced to a concentration of 18.1 g/L, occupying approximately 20% of dissolved organic carbon. Furthermore, the highest cumulative CH4 production was observed at the samples of source separation/collection (398 ± 52–519 ± 117 mL/gVS for FW, 276 ± 51–332 ± 41 mL/gVS for KW), and then accompanied by a decrease (299 ± 31 mL/gVS for FW and 285 ± 39 mL/gVS for KW) after downstream storage. The results indicated that the subsequent anaerobic digestion would be inclined to appear perturbation caused by the lactic acidification of the initial feed and it is imperative to avoid further conversion of lactic acid to propionic acid, which could provide vital guideline reference for the optimization of biogas production process. Moreover, the lactic acid-rich property also highlights other value-added pathways for the resource recovery of municipal biowaste.

Effect of anthraquinone-2,6-disulfonate (AQDS) on anaerobic digestion under ammonia stress: Triggering mediated interspecies electron transfer (MIET)

The underlying mechanisms by which humic-like substrates affect anaerobic digestion under ammonia stress are insufficiently understood so far. In this study, anthraquinone-2,6-disulfonate (AQDS), a representative analogue of humic acid, was adopted at a 100 μM concentration as the exogenous additive during anaerobic digestion process along with 5.0 g NH4+-N/L stress. The results showed that AQDS could improve the cumulative CH4 production and the maximum CH4 production rate by 7.3 and 10.8%, respectively, and shorten the methanogenic lag phase by 13.8%. Acetate-related production and methanation were both facilitated, during which the biological rather than the chemical mechanism played a crucial role. The microbial diversity distribution revealed that electroactive Anaerolinea and Methanosaeta were significantly enriched in response to AQDS amendment. Herein, AQDS was presumed to serve as an electron shuttle to trigger a mediated interspecies electron transfer (MIET) network among electroactive consortia, thus accelerating acetate methanation and ameliorating methanogenesis under ammonia stress.

The influence of closed pores and stacked coal grains on gas transport in CO2 injection enhanced CH4 recovery process

CO2 injection enhanced coalbed methane (CH4) recovery technology can achieve the enhancement of CH4 production and the effective geological storage of carbon dioxide in coal seams. A coal seam is composed of matrix and fractures. Matrix has open pores and closed pores and fractures may have stacked coal grains. However, the influences of closed pores in matrix and stacked coal grains in fractures on CO2 injection enhanced CH4 recovery have rarely been studied. This paper develops a numerical simulation model to explore the hydraulic-mechanical coupling responses in CO2 injection enhanced coalbed methane (CO2-ECBM) recovery process. This model considers the binary gas displacement and transport in ternary pores, the deformation of coal with different porosity, and fractal stacked coal grains in fractures. After verification with the data available from literature, this model is used to simulate a field trial in the Qinshui Basin. The simulation results show that the contribution of gas in closed pores to the total CH4 production enhanced by CO2 injection is more than 60% in high-rank coal and is proportional to the volume fraction of closed pores. The stacked coal grains in fractures affect the effective roughness and can be expressed by three structural parameters. Higher effective roughness induces lower cumulative CO2 injection and lower cumulative CH4 production and the conical bottom diameter of cone-like element has the largest influence. These findings can promote our understanding for the influence of closed pores and stacked coal grains on gas transport in coalbed gas reservoirs from a multi-scale perspective.

Comparison of metabolic kinetics during high and low solids anaerobic digestion of fecal sludge.

High solids anaerobic digestion (HS-AD) is an attractive energy-producing technology; however, high total solids (TS) content may inhibit methanogens due to high volatile fatty acid (VFA) and total ammonia nitrogenconcentrations. The objective of this paper is to quantify rate-limiting metabolic kinetic parameters to determine the influence of TS content during anaerobic digestion of fecal sludge. Two TS content:11% and 17% microcosms were analyzed. Good performance was observed in both systems, with volatile solid(VS) removalgreater than 50%, CH4 yield between 0.44 and 0.56 m3 CH4 /g VS added and cumulative CH4 production between 1.78 and 2.03 m3 CH4 /m3 digester-day. At 11% TS VFA consumption and VS removal had a positive correlation to CH4 production while the 17% TS microcosm had a negative correlation with both. This is the first study to determine the kinetic parameters for hydrolysis, VFA consumption, and methanogenesis during digestion of fecal sludge. These kinetic parameters are necessary in the design and operation of anaerobic digestion systems treating fecal sludge.

Wetland microtopography alters response of potential net CO2 and CH4 production to temperature and moisture: Evidence from a laboratory experiment

Coastal wetlands store significant amounts of carbon (C) belowground, which may be altered through effects of rising temperature and changing hydrology on CO2 and CH4 fluxes and related microbial activities. Wetland microtopography (hummock-hollow) also plays a critical role in mediating plant growth, microbial activity, and thus cycling of C and nutrients and may interact with rising seas to influence coastal wetland C dynamics. Recent evidence suggests that CH4 production in oxygenated surface soils of freshwater wetlands may contribute substantially to global CH4 production, but comprehensive studies linking potential CH4 production to environmental and microbial variables in temperate freshwater forested wetlands are lacking. This study investigated effects of temperature, moisture, and microtopography on potential net CO2 and CH4 production and extracellular enzyme activity (β-glucosidase, xylosidase, phenol oxidase, and peroxidase) in peat soils collected from a freshwater forested wetland in coastal North Carolina, USA. Soils were retrieved from three microsites (hummock, hollow, and subsurface peat soils (approximately 20–40 cm below surface)) and incubated at two temperatures (27 °C and 32 °C) and soil water contents (65% and 100% water holding capacity (WHC)). Hummocks had the highest cumulative potential net CO2 (13.7 ± 0.90 mg CO2-C g soil−1) and CH4 (1.8 ± 0.42 mg CH4-C g soil−1) production and enzyme activity, followed by hollows (8.7 ± 0.91 mg CO2-C g soil−1 and 0.5 ± 0.12 mg CH4-C g soil−1) and then subsurface soils (5.7 ± 0.70 mg CO2-C g soil−1 and 0.04 ± 0.019 mg CH4-C g soil−1). Fully saturated soils had lower potential net CO2 production (50–80%) and substantially higher potential net CH4 production compared to non-saturated soils (those incubated at 65% WHC). Soils incubated at 32 °C increased potential net CO2 (24–34%) and CH4 (56–404%) production under both soil moisture levels compared to those incubated at 27 °C. The Q10 values for potential net CO2 and CH4 production ranged from 1.5 to 2.3 and 3.3–8.8, respectively, and did not differ between any microsites or soil water content. Enrichment of δ13CO2-C was found in saturated soils from all microsites (−24.4 to − 29.7 ‰) compared to non-saturated soils (−31.1 to − 32.4 ‰), while δ13CH4-C ranged from −62 to −55‰ in saturated soils. Together, the CO2 and CH4 δ13C data suggest that acetoclastic methanogenesis is an important pathway for CH4 production in these wetlands. A positive relationship (Adj. R2 = 0.40) between peroxidase activity and CH4 production was also found, indicating that peroxidase activity may be important in providing fermented C substrates to acetoclastic methanogenic communities and contribute to anaerobic C mineralization. These results suggest that changes in temperature and hydrology could stimulate CO2 and CH4 emissions from surface hummock soils, and to a lesser extent from hollow soils, and provide preliminary evidence that hummocks may be a spatially important and unrecognized hotspot for CH4 production.

In Vitro Assessment of Enteric Methane Emission Potential of Whole-Plant Barley, Oat, Triticale and Wheat.

Simple SummaryThere is an increasing interest in finding effective but economical strategies for mitigating enteric methane (CH4) emissions from ruminants. Small-grain cereal forages including barley, oat, triticale, and wheat, unlike maize, are widely grown in temperate locations and may be economical to use for ruminant production. However, the starch and fiber composition and concentrations of whole-plant cereal forages affect rumen degradability, and hence may cause differences in the CH4 production potential among these forages. Therefore, the objective of this study was to determine the enteric CH4 emission potential of various whole-plant cereals and evaluate whether the variability in emissions could be explained by variations in nutrient profiles, degradability, and rumen fermentation characteristics. The results indicate that feeding whole-plant oat forage to ruminants may decrease CH4 emissions but adversely affect animal performance due to lower degradability, whereas barley forage may ameliorate emissions without negative effects on animal performance.The study determined in vitro enteric methane (CH4) emission potential of whole-plant cereal (WPC) forages in relationship to nutrient composition, degradability, and rumen fermentation. Two varieties of each WPC (barley, oat, triticale, and wheat) were harvested from two field replications in each of two locations in central Alberta, Canada, and an in vitro batch culture technique was used to characterize gas production (GP), fermentation, and degradability. Starch concentration (g/kg dry matter (DM)) was least (p < 0.001) for oat (147), greatest for wheat (274) and barley (229), and intermediate for triticale (194). The aNDF concentration was greater for oat versus the other cereals (531 vs. 421 g/kg DM, p < 0.01). The 48 h DM and aNDF degradabilities (DMD and aNDFD) differed (p < 0.001) among the WPCs. The DMD was greatest for barley, intermediate for wheat and triticale, and least for oat (719, 677, 663, and 566 g/kg DM, respectively). Cumulative CH4 production (MP; mL) from 12 h to 48 h of incubation was less (p < 0.001) for oat than the other cereals, reflecting its lower DMD. However, CH4 yield (MY; mg of CH4/g DM degraded) of barley and oat grown at one location was less than that of wheat and triticale (28 vs. 31 mg CH4/g DM degraded). Chemical composition failed to explain variation in MY (p = 0.35), but it explained 45% of the variation in MP (p = 0.02). Variation in the CH4 emission potential of WPC was attributed to differences in DMD, aNDFD, and fermentation end-products (R2 ≥ 0.88; p < 001). The results indicate that feeding whole-plant oat forage to ruminants may decrease CH4 emissions, but animal performance may also be negatively affected due to lower degradability, whereas barley forage may ameliorate emissions without negative effects on animal performance.