Higher Methane Production Research Articles

A comparative long-term operation using up-flow anaerobic sludge blanket (UASB) and anaerobic membrane bioreactor (AnMBR) for the upgrading of anaerobic treatment of N, N-dimethylformamide-containing wastewater

Synthetic industrial wastewater containing approximately 2000 mg/L N, N-dimethylformamide (DMF) was treated using a lab-scale anaerobic sludge blanket (UASB) and an anaerobic membrane bioreactor (AnMBR) in this study. The inoculum consisted of two sources of sludge: Co-culture of anaerobic digested sludge (ADS) with DMF-hydrolyzing activated sludge (DAS) for the AnMBR, and co-culture of anaerobic granular sludge (AGS) with DAS for the UASB. Effective DMF methanogenic degradation of nearly 100% removal was achieved in both reactors on the first day. Both reactors obtained excellent DMF removal efficiency and high methane production under a low organic loading rate (OLR) of around 3–4 g COD/L/d. However, excessive elevation of OLR significantly limited DMF hydrolysis. When OLR exceeded 6 g COD/L/d, the removal efficiency and methane production in both reactors dramatically dropped. Despite their different forms and shapes, the ADS and AGS both provide methanogens which are responsible for methanogenesis. The UASB tolerated a higher OLR while the AnMBR was limited by membrane fouling due to the increased sludge concentration. However, the AnMBR obtained high-quality effluent without suspended solid. Whether DMF can be effectively degraded depends on DAS, in which abundant DMF-hydrolyzing bacteria (DHB) provide sufficient quantities of the hydrolytic enzyme for effective hydrolysis of DMF. However, these DHB were facultative and were also identified as denitrifying bacteria which require nitrate as the electron acceptor or otherwise survive under the aerobic condition. They gradually decayed rather than proliferated and were outcompeted by methanogens. Therefore, it is conceivable that a slight dosage of nitrate would enrich the abundance of DHB in both the UASB and the AnMBR, and provide a sufficient quantity of enzymes for the DMF hydrolysis. The cultivation of the anaerobic DMF-degrading granular sludge using the UASB is considered an upgraded solution to the effective treatment of DMF-containing wastewater.

Anaerobic biodegradability test for Lantana camara to optimize the appropriate food to microorganism (F/M) ratio

ABSTRACT Invasion of Lantana camara all over the world and its management is a global problematic issue. Its rapid growth and competition with natural resources such as space, water, and nutrients of other plants, reasons for the demand to manage this noxious weed. This study was done to optimize the ideal food to microorganism (F/M) ratio. Different food to microorganism (F/M) ratios of 1, 1.5, 2 and 2.5 were studied along with one control where only cow dung was kept. Highest methane production was obtained from the F/M ratio of 1.5 (195.5 ± 8 mL CH4/g VS) and cumulative methane production from it was 4801.5 mL followed by ratios 2 and 2.5 respectively. In control, methane production was relatively low as compared to all the F/M ratios (2151.5 ± 8 mL). 20 L capacity batch reactor was performed with a working volume of 15.5 L where substrate and cow dung were fed according to the best ratio found during biochemical methane potential trial (BMP). Maximum methane yield was observed on the 19th day (2650 ± 18 ml CH4/g VS). Maximum volatile solids (VS) reduction was observed in the F/M ratio 1.5 (49.63%) followed by 2 and 2.5 respectively. The maximum amount of volatile fatty acid (VFA) was produced in F/M ratio 1.5 (715 ± 10) and 2 (715 ± 15) followed by ratios 2.5 and 1 respectively. Maximum soluble chemical oxygen demand (sCOD) was found in F/M ratio 1.5 (8000 mg/L). Morphological changes were captured in FESEM and XRD.

Evaluation of lactulose, lactose, and fructose breath testing in clinical practice: A focus on methane.

Background and AimBreath testing (BT) is used to identify carbohydrate malabsorption and small intestine bacterial overgrowth. Measuring methane alongside hydrogen is advocated to reduce false‐negative studies, but the variability of methane production is unknown. The aim of this study is to examine the effect of high methane production on hydrogen excretion after ingesting lactulose, fructose, or lactose.MethodsA retrospective audit was performed of patients with gastrointestinal symptoms who underwent BT. Following a low fermentable carbohydrate diet for 24‐h, a fasting BT before consuming 35 ml lactulose, 35 g fructose, or lactose in 200 ml water, followed by BT every 10–15 min for up to 3‐h, was performed. A positive test was defined as a ≥20 ppm rise of hydrogen or methane from baseline. A high methane producer had an initial reading of ≥5 ppm. Breath hydrogen and methane production were measured as area under the curve. Chi‐squared tests were used to compare proportions of those meeting the cut‐off criteria.ResultsOf patients, 26% (28/106) were high methane producers at their initial lactulose test. The test–retest repeatability of methane production was high, with the same methane production status before ingesting lactose in all (70/70) and before ingesting fructose in most (71/73). Methane production was highly variable during testing, with 38% (10/26) having ≥1 reading lower than baseline. Hydrogen produced by high or low methane producers did not differ (1528 [960–3645] ppm min vs 2375 [1810–3195] ppm min [P = 0.11]). Symptoms and breath test results were not positively related.ConclusionThe validity of including an increase of ≥20 ppm methane to identify carbohydrate malabsorption or small intestine bacterial overgrowth should be questioned due to the variability of readings during testing.

Anaerobic treatment of LCFA-containing synthetic dairy wastewater at 20 °C: Process performance and microbial community dynamics.

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assessed at 20 °C. The effects of the LCFA concentration (33-45% of COD) and organic loading rates (2-3 gCOD/L·d) were determined using three parallel expanded granular sludge bed reactors. For the first time, long term anaerobic treatment of LCFA-containing feed at 20 °C was shown to be feasible and was linked to the microbial community dynamics in high-rate reactors. During a two-month operation, a soluble COD removal of 84-91% and COD to methane conversion of 44-51% was obtained. However, granular sludge flotation and washout occurred after two months in all reactors without volatile fatty acids (VFA) accumulation, emphasizing the need for sludge retention for long-term granular sludge reactor operation with LCFA-containing feed at low ambient temperatures. The temporal shifts in microbial community structure were studied in the high-rate treatment of SDW, and the process disturbances (elevated LCFA loading, LCFA accumulation, and batch operation) were found to decrease the microbial community diversity. The relative abundance of Methanosaeta increased with higher LCFA accumulation in the settled and flotation layer granules in the three reactors, therefore, acetoclastic methanogenesis was found to be crucial for the high-rate treatment of SDW at 20 °C. This study provides an initial understanding of the continuous anaerobic treatment of LCFA-containing industrial wastewaters at low ambient temperatures.

Methane productivity evaluation of an invasive wetland plant, common reed

This study aims to investigate the potential of substrate for producing biogas from common reed (Phragmites australis), a perennial grass, and provide the techniques to select optimal and reasonable materials with high methane production. By determining the parameters such as chemical oxygen demand (COD), volatile solids (VS), and percentage of element chemicals, carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S) of raw materials henceforth through the TBMP (theoretical biochemical methane potential) via calculations give the maximum methane potential of particular available in feedstock and present by methane yield per unit of mass of feedstock (mlCH4/gVS). In this study, the results were obtained from TBMPThEC and TBMPThCOD that were highest at 460.890 mlCH4/gVS and 130.88 mlCH4/gVS, respectively. The results showed that based on COD calculations, the results were consistent with the ability to create methane in the experiment and based on elemental compositions showed that the further potential to produce methane of feedstock.

Improvement of Sugarcane Stillage (Vinasse) Anaerobic Digestion with Cheese Whey as its Co-substrate: Achieving High Methane Productivity and Yield.

This study investigated methane production in an anaerobic sequencing batch biofilm reactor (AnSBBR) by co-digesting sugarcane vinasse and cheese whey. The assessment was based on the influence of feed strategy, interaction between cycle time and influent concentration, applied volumetric organic load (OLRA), and temperature over system stability and performance. The system showed flexibility with regard to the feed strategy, but the reduction of cycle time and influent concentration, at the same OLRA, resulted in lower methane productivity. Increasing organic load, up to the value of 15.27gCODL-1day-1, favored the process, increasing methane yield and productivity. Temperature reduction from 30 to 25°C resulted in worse performance, although increasing it to 35°C provided similar results to 30°C. The best results were achieved at an OLRA of 15.27gCODL-1day-1, cycle time of 8h, fed-batch operation, and temperature of 30°C. The system achieved soluble COD removal efficiency of 89%, methane productivity of 208.5molCH4m-3day-1 and yield of 15.76mmolCH4gCOD-1. The kinetic model fit indicated methanogenesis preference for the hydrogenotrophic route. At the industrial scale estimative, considering a scenario with a sugarcane ethanol plant with ethanol production of 150,896m3year-1, it was estimated energy production of 25,544MWhmonth-1.

Thermophilic anaerobic digestion: Effect of start-up strategies on performance and microbial community

Effects of two different start-up methods were compared during conversion from mesophilic to thermophilic anaerobic digestion of sewage sludge. During the batch operation, a transient increase in both total bacterial concentration and relative abundance of thermophilic bacteria in R1 (a one-step increase method) resulted in 34% higher volatile solids (VS) removal efficiency by R1 compared to R2 (a step-wise increase method). Meanwhile, higher total archaeal concentration and increased relative abundance of thermophilic archaea in R2 were attributed to 65% higher methane production by R2 compared to R1. The same trends for VS removal and methane production were observed during the subsequent continuous mode, although the microbial composition of the two reactors became similar. These findings may prove helpful for determining the preferred start-up method for thermophilic anaerobic digestion: a one-step method can be proposed for higher VS removal efficiency, or a step-wise method can be selected for enhanced methane production.

Impact of total carbon/sulfate on methane production and sulfate removal from co-digestion of sulfate-containing wastewater and corn stalk

During the process of preparing furfural by straw depolymerization with dilute sulfuric acid, large amounts of high temperature sulfate-rich organic wastewater were produced. It cannot be treated directly by anaerobic digestion and converted to bioenergy due to high concentrations of sulfate. In this study, anaerobic co-digestion of sulfate containing wastewater and corn stalk was performed at thermophilic conditions to investigate the influences of total carbon (TC)/sulfate (6, 16, 35 and 110) on methane production and sulfate removal. The results showed that the highest methane production of 260.14 mL g−1 volatile solid (VS) was achieved at TC/sulfate of 35, which was significantly higher than 12.53 mL g−1 VS obtained at TC/sulfate of 6. Moreover, the results of sulfate balance analysis showed a maximum sulfate removal of 93.43% was achieved at TC/sulfate of 16, and sulfate concentration in biogas slurry was less than 0.1 g/L regardless of TC/sulfate after 28 days of co-digestion. The microbial community was analyzed using 16S rDNA sequencing technology, the results showed that methane was mainly produced by Methanoculleus and Methanosarcina, and sulfate was removed via Desulfotomaculum, and the relative abundance of methanogenic archaea (MA) and sulfate reducing bacteria (SRB) were significantly correlated with methane production and sulfate removal. It can concluded that higher methane production and sulfate removal can be obtained by anaerobic co-digestion of sulfate containing wastewater and corn stalk at properly TC/sulfate.

Effects of ferric oxide on the microbial community and functioning during anaerobic digestion of swine manure

Iron-based materials have been suggested as environmentally-friendly additives that can enhance methane production during anaerobic digestion (AD). In this study, the effects of ferric oxide (Fe2O3) addition on methane production were investigated during swine manure AD. In addition, the effects of Fe2O3 addition on the AD ternary pH buffer system and microbial community were evaluated. Fe2O3 could improve the accumulative methane production by maximum 11.06% when adding 75 mmol of Fe2O3. Higher methane production could be attributed to the enhancement of direct interspecies electron transfer (DIET) and the formation of Fe-S precipitates, but not the addition of Fe2O3 as a nutrient. Furthermore, Fe2O3 addition enhanced methanogenesis rather than acetogenesis, as evinced by analysis of functional genes. Nevertheless, high-throughput sequence analysis of microbial community composition revealed the lack of a significant influence by Fe2O3 addition, and Fe2O3 addition did not significantly affect the ternary pH buffer system.

Sulfate deprivation triggers high methane production in a disturbed and rewetted coastal peatland

Abstract. In natural coastal wetlands, high supplies of marine sulfate suppress methanogenesis. Coastal wetlands are, however, often subject to disturbance by diking and drainage for agricultural use and can turn to potent methane sources when rewetted for remediation. This suggests that preceding land use measures can suspend the sulfate-related methane suppressing mechanisms. Here, we unravel the hydrological relocation and biogeochemical S and C transformation processes that induced high methane emissions in a disturbed and rewetted peatland despite former brackish impact. The underlying processes were investigated along a transect of increasing distance to the coastline using a combination of concentration patterns, stable isotope partitioning, and analysis of the microbial community structure. We found that diking and freshwater rewetting caused a distinct freshening and an efficient depletion of the brackish sulfate reservoir by dissimilatory sulfate reduction (DSR). Despite some legacy effects of brackish impact expressed as high amounts of sedimentary S and elevated electrical conductivities, contemporary metabolic processes operated mainly under sulfate-limited conditions. This opened up favorable conditions for the establishment of a prospering methanogenic community in the top 30–40 cm of peat, the structure and physiology of which resemble those of terrestrial organic-rich environments. Locally, high amounts of sulfate persisted in deeper peat layers through the inhibition of DSR, probably by competitive electron acceptors of terrestrial origin, for example Fe(III). However, as sulfate occurred only in peat layers below 30–40 cm, it did not interfere with high methane emissions on an ecosystem scale. Our results indicate that the climate effect of disturbed and remediated coastal wetlands cannot simply be derived by analogy with their natural counterparts. From a greenhouse gas perspective, the re-exposure of diked wetlands to natural coastal dynamics would literally open up the floodgates for a replenishment of the marine sulfate pool and therefore constitute an efficient measure to reduce methane emissions.

Effects of Bacterial Bio-augmentation on the Methane Potential from Facultative Digestion of Palm Oil Mill Effluent and Empty Fruit Bunch

The methane productivity and biodegradability of facultative single- and co-digestion samples with palm oil mill wastes was evaluated on the effect of bacterial bio-augmentation. The single- and co-digestion substrates were bio-augmented with Bacillus subtillis and a methanogenic mixed culture of anaerobic microorganisms at different loading percentage. The highest methane production was recorded at 0.95 LCH4 from co-digestion sample augmented with 10% (v/v) B. subtilis while the highest methane yield of 0.7 mLCH4/g volatile solid, attained by single-digestion of palm oil mill effluent with addition of mixed methanogens at 5% (v/v). Cumulative methane production for single-digestion increased from 0.17 LCH4 to 0.32 LCH4 in response to the bio-augmentation treatment with 5% mixed methanogens. Conversely, additional mixed methanogens to co-digestion substrate resulted 75% reduction in methane production compared to non-augmented co-digestion substrate. Addition of B. subtilis into co-digestion was more beneficial than mixed methanogens due to the cellulolytic degradation ability of B. subtilis to digest the lignocellulolytic substances in empty fruit bunch.

Autoinducer-2-mediated quorum sensing partially regulates the toxic shock response of anaerobic digestion

This study discovered a strong correlation between the autoinducer-2 (AI-2)-mediated quorum sensing (QS) with the performance of a submerged anaerobic membrane bioreactor during its recovery from a pentachlorophenol (PCP) shock: a decrease in AI-2 levels coincided with a reduction in volatile fatty acid concentrations, and corresponded significantly to a decrease in the relative abundance of Firmicutes, and to an increase in the relative abundance of Bacteroidetes and Synergistetes. Further batch experiments with the addition of an AI-2-regulating Escherichia coli mutant culture showed that a reduction in AI-2 levels resulted in the highest biogas production rate during a PCP shock. In contrast, an increase in AI-2 levels via addition of the E. coli wild type strain or an AI-2 precursor showed no obvious effects on biogas production. These results suggest that the AI-2 level in anaerobic sludge was governed primarily by Firmicutes, and the AI-2-mediated QS partially regulates the toxic shock response of anaerobic sludge via tuning the activities of Firmicutes and Synergistetes. A decrease in the AI-2 level might reduce acetogenesis and favor hydrogenotrophic methanogenesis, thus resulting in less VFA accumulation and higher methane production during the PCP shock. This study is the first of this type that exploits the role of quorum sensing in the toxic shock response of anaerobic sludge; it demonstrates a novel approach to shortening the recovery period of anaerobic processes via manipulating the AI-2-mediated QS.

The macro- and micro-prospects of the energy potential of the anaerobic digestion of corn straw under different storage conditions

This study demonstrated the efficiency of storage conditions for corn straw is very important in maintaining high methane production. Using data from lab-scale experiments with fresh, silage and dry corn straw, the relationships among the different materials, microbial changes and methane production were analyzed. Moreover, the economic evaluation of three different straw types was conducted. The results showed a cumulative methane production of 207 mL/g total solids (TS) for silage straw. This yield was 9.34% less than that of fresh straw and 17.08% more than that of dry straw. The silage straw with higher organic acids successfully reduced the loss of dry matter (DM) to 3.77%, and the loss of DM was 15.6% for dry straw. The dominant Spirochaeta, Treponema and Methanosaeta in silage straw were reasonable for high methane production. Furthermore, the economic evaluation suggested silage should completely replace traditional dry storage prior to anaerobic digestion in North China.

Extraction of phenolic compounds and production of biomethane from strawberry and raspberry extrudates

This study proposes a biorefinery approach system to treat two berry extrudates generated by the berry-tasted products industry. The berry extrudates studied were strawberry extrudate (SE1 and SE2) and raspberry extrudate (RE), both of them processed in the same industrial plant. The proposed biorefinery approach consists in the extraction of bioactive compounds after hydrothermal pre-treatment followed by anaerobic digestion of the remaining biomass after extraction. A high concentration of valuable phenolic compounds was extracted from each extrudate through the absorption-desorption processes, i.e. 876, 392 and 2402 mg of gallic acid equivalents/kg extrudate in SE1, SE2 and RE, respectively. Anaerobic digestion of the remaining biomass after extraction led to high methane production, between 371 and 503 mL CH4/g VS. The economical evaluation showed that the proposed biorefinery approach would offer higher benefits than just anaerobic digestion of the untreated extrudate, although this last option would be economically feasible as well.

Kinetic analysis of methane production from anaerobic digestion of water lettuce (Pistia stratiotesL.) with waste sludge

AbstractBACKGROUNDIncreasing demand on energy sources has motivated research studies on renewable energy originating from biomass. Water lettuce (Pistia stratiotes L.) as an invader lignocellulosic biomass with high crop yield can be utilized in anaerobic digestion to produce biomethane. Substrate and inoculum concentrations, and temperature are important parameters for kinetic analysis of methane production that was performed with water lettuce and waste sludge for the first time. Kinetic analysis can be used in reactor design, scale up and identification of optimum conditions.RESULTSIn the present study, anaerobic digestion of water lettuce with waste sludge as inoculum was performed in a batch system. Substrate concentration [30, 40 and 50 g total solid (TS) L−1], waste sludge concentration (3.4 and 6.8 g TS L−1) were investigated at different digestion temperatures (35, 45, 55 and 65 °C). In the studied range, the highest biogas yield [321 mL g–1 volatile solid (VS) with 72.5% of methane content) was reached at substrate concentration of 30 g TS L−1 and waste sludge concentration of 6.8 g TS L−1 at 35 °C. The Cone model fitted well to the actual methane production compared to the modified Gompertz model. The effect of digestion temperature on methane production potential was described by the Ratkowsky model (R2 = 0.91) and optimum digestion temperature was found as 45 °C. Experimental methane yields were 81.5–232.7 mL methane g–1 VS which were 27.7–79.0% of theoretical maximum methane yield. Energy conversion efficiency was reached up to 78.4%.CONCLUSIONThe results revealed that anaerobic digestion of water lettuce with waste sludge for high methane production rate was accomplished at certain substrate and inoculum concentrations and temperature. © 2019 Society of Chemical Industry

Effect of nitrogen fertilization on the production of biogas from sweet sorghum and maize biomass

ABSTRACT The aim of the study was to determine the biogas productivity from selected cultivars of sorghum (Sorghum bicolor Moench) and maize (Zea mays L.) depending on the dose of mineral fertilization with nitrogen. The topic is novelty in the northern Poland area due to the fact that this crop is not very widespread here. The silage samples were derived from two experiments: (1) two factors experiment with sorghum varieties (Arbatax, KWS Maja, Herkules) and two doses of mineral nitrogen fertilization (0 and 150 kg ha−1 N) in split-plot design. (2) one-factor experiment with fodder maize, variety NK Magitop, and two doses of mineral nitrogen fertilization (0 and 150 kg ha−1 N) in a randomized complete block design. The experiment was performed in four replications in the split-plot design. Methane fermentation was carried out under mesophilic conditions. The temperature of the process was 37°C ± 1°C, while pH 7 ± 0.1. The content of total solids in the bioreactor was 7.0%. The composition of the gas produced was measured once a day with the use of an automatic biogas analyser (GFM 416, GasData). The trial was run in triplicate until the daily yield was less than 1% of the cumulative biogas yield [DIN 38 414-S8. Sediments and sediments. Determination of fermentation characteristics; 1985]. Sorghum was characterized by higher average biogas productivity (about 12%), higher methane content in biogas (about 10%), and higher methane productivity (about 43%). It can, therefore, be stated that sorghum represents as an alternative plant to maize for the purpose of biogas production.

Impacts of mixing on foaming, methane production, stratification and microbial community in full-scale anaerobic co-digestion process

This study investigated the impact of mixing on key factors including foaming, substrate stratification, methane production and microbial community in three full scale anaerobic digesters. Digester foaming was observed at one plant that co-digested sewage sludge and food waste, and was operated without mixing. The lack of mixing led to uneven distribution of total chemical oxygen demand (tCOD) and volatile solid (VS) as well as methane production within the digester. 16S rRNA gene-based community analysis clearly differentiated the microbial community from the top and bottom. By contrast, foaming and substrate stratification were not observed at the other two plants with internal circulation mixing. The abundance of methanogens (Methanomicrobia) at the top was about four times higher than at the bottom, correlating to much higher methane production from the top verified by ex-situ biomethane assay, causing foaming. This result is consistent with foaming potential assessment of digestate samples from the digester.

Optimizing biomethane production of mesophilic chicken manure and sheep manure digestion: Mono-digestion and co-digestion kinetic investigation, autofluorescence analysis and microbial community assessment

Optimization of mesophilic methane production from Chicken manure (CM) and Sheep manure (SM) at total solid (TS) of 8% and 1.6% were obtained by sequence tests in mono-digestion. However, the positive synergy of co-digestion with an optimum CM/SM of 2.5 (310 mLCH4/gVSadded) resulted in a high hydrolytic capacity and methane production. The modified Gompertz model (R2 > 0.98) and modified Aiba model (R2 > 0.88) illustrated co-digestion significantly improved the methane generation rate with strong ammonia tolerance. Dissolved Organic Matter (DOM) variation in response to the metabolic rate of microbial community illustrated that the SMP-like and protein-like components half-split by EEM–PARAFAC were significantly negative corresponded to bio-methane production. Moreover, the canonical correlation analysis (CCA) resulted a significant difference between the substrate and DOM composition. Potential functional metabolic illustrated statistically significance difference between mono and co-digestion, however, Methanosaeta and Syntrophobacter predominated the syntrophic methanogenesis. The constructed complex metabolic cooperation caused the co-digestion stable and high efficiency.

Towards determining spatial methane distribution on Arctic permafrost bluffs with an unmanned aerial system

Arctic permafrost stores vast amounts of methane (CH4) in subsurface reservoirs. Thawing permafrost creates areas for this potent greenhouse gas to be released to the atmosphere. Identifying ‘hot spots’ of methane flux on a local scale has been limited by the spatial scales of traditional ground-based or satellite-based methane-sampling methods. Here we present a reliable and an easily replicable design using only off-the-shelf, cost-effective methane sensor components and an Unmanned Aerial System (UAS). Our results demonstrate the high efficiency of the design and the advantages of this methodology for environmental methane studies that are subjected to the high spatial variability of methane levels. On Barter Island, NE Alaska, we noted spikes in CH4 concentrations coincident with topographic features or anomalies. Such spikes may be attributed to enhanced land/air transfer and may reveal zones of high methane production and/or minimal oxidation in areas of thermoerosional gullies along thawing coastal zones. Thermoerosional gullies represent hotspots that release significantly higher levels of methane than the surrounding areas, thus suggesting that point sampling is inadequate in characterizing methane releases and that increasing rates of permafrost thaw may result in increasing point sources of high CH4 emissions.

Impact of biochar-supported zerovalent iron nanocomposite on the anaerobic digestion of sewage sludge

Anaerobic digestion (AD) is an attractive technology for sludge treatment as it stabilizes sludge and produce renewable energy. However, problems such as low organic matter content and high heavy metals level are often encountered which severely limits the effectiveness of AD. In this study, the biochar-supported nanoscale zerovalent iron (nZVI-BC) was synthesized and used as additives during AD of sewage sludge to investigate the enhancement effects for methane production and its impacts on microbial structure at mesophilic temperature. nZVI-BC addition enhanced process stability by improving the generation and degradation of intermediate organic acids, but inhibitory effects were observed at high dosage. The methane content and cumulative methane yields were increased by 29.56% and 115.39%, respectively. Compared with AD without nZVI-BC, the application of nZVI-BC showed positive effect on improvement of metals (Cu, Cd, Ni, Cr, and Zn) stabilization in the digestate. Microbial community analysis illustrated that nZVI-BC addition could significantly increase the Shannon diversity index and Chao1 richness index of archaea, and meanwhile archaea were more diverse in nZVI-BC amended digesters than in control. It was notable that Methanosaeta dominated in all the digesters at genera level, while the relative abundance of hydrogenotrophic methanogens (Methanobacterium and methanospirillum) increased 35.39% in nZVI-BC amended digesters compared to the control, resulting in higher methane production. The results will guide development of microbial management methods to enhance the stability of AD process.