High Methanogenic Activity Research Articles

Internal driving mechanisms of microbial community and metabolism for granular activated carbon enhancing anaerobic digestion of high-strength sulfate organic wastewater

In this study, the feasibility of enhancing high-strength sulfate organic wastewater anaerobic digestion by adding granular activated carbon (GAC) and the internal driving mechanisms were investigated in up-flow anaerobic sludge blanket (UASB) reactors. The UASB reactor with GAC (GAC reactor) was more stable in COD removal efficiency and CH4 production than that without GAC (non-GAC reactor). When the influent COD concentration increased to 12,000 mg/L with a COD/SO42− ratio of 4.0, the COD removal efficiency and CH4 yield increased by 10.45 % and 20.50 %, respectively. Under inhibition condition with sulfides of 800 mg/L, specific methanogenic activity of GAC reactor sludge increased by 41.8 % compared to that of non-GAC reactor sludge. Electron transport system and microbial community results showed that GAC enhanced microbial activity and improved direct interspecies electron transfer (DIET) between potential electroactive microorganisms and Methanosaeta. Functional enzyme gene analysis demonstrated that GAC enhanced microbial metabolic activity, covering glycolysis, pyruvate metabolism, sulfate reduction, and methanogenesis. Therefore, the enrichment of key microorganisms, the promotion of DIET methanogenesis, and the improvement of functional metabolism activity may be the important reasons for GAC reactor sludge with higher methanogenic activity. Furthermore, synergistic promotion of sulfate-reducing metabolism and methanogenesis may be due to the establishment of potential syntrophic partnership between sulfate-reducing bacteria (Desulfovibrio) and Methanosaeta. This study deciphered internal driving mechanisms of microbial community and metabolism for GAC enhancing anaerobic digestion of high-strength sulfate organic wastewater.

Bioelectrochemical system for enhancing anaerobic digestion of pharmaceutical-containing domestic wastewater

The unprecedented recent expansion in usage of paracetamol (AAP) has increased the need for suitable wastewater treatment technology. Furthermore, direct interspecies electron transfer promotion (DIET) offers simple and efficient approach for enhancing anaerobic digestion (AD). In this work, using AAP-containing domestic wastewater as feed, control AD reactor (RC) was operated, besides three DIET-promoted AD reactors (REV, RMC and REVMC, referring to electrical voltage “EV”-applied, nFe3O4-multiwall carbon nanotube (MCNT)-supplemented, and “EV applied + MCNT supplemented” reactor, respectively). Maximal treatable organic loading rates by RC, REV, RMC and REVMC were 3.9, 3.9, 7.8 and 15.6 g COD/L/d, corresponding to AAP loading rate of 26, 78, 156 and 312 μg/L/d, respectively. Methane production rate generated by RC, REV, RMC and REVMC reached 0.80 ± 0.01, 0.86 ± 0.04, 1.40 ± 0.07, and 3.01 ± 0.17 L/L/d, respectively. AAP expectedly followed hydroquinone degradation pathway, causing AD failure by acetate accumulation. However, this performance deterioration could be mitigated by DIET-promoted microbes with higher methanogenic activity and advanced electric conductivity. Economic evaluation revealed the favourability of MCNT addition over EV application, since payback periods for RC, REV, RMC and REVMC were 6.2, 7.7, 4.2 and 5.0 yr, respectively.

Effect of Varying Zinc Concentrations on the Biomethane Potential of Sewage Sludge

The anaerobic digestion of sewage sludge is highly sensitive to high zinc concentrations. Although sulfate-reducing bacteria (SRB) activity can negatively affect methanogenesis, SRB-mediated metal sulfide precipitation can alleviate zinc toxicity. A series of mesophilic anaerobic batch experiments was performed for the biomethane potential of three different sewage sludge samples for 74 days using the background sludge zinc content, alone or in combination with the external addition of 200, 300 and 400 mg Zn/L. The highest biomethane production was 165 ± 1 mL CH4/g VS using activated sludge (AS) with a background concentration of 93 mg Zn/L. A slight decrease in the biomethane yield (i.e., 157 ± 1, 158 ± 1 and 159 ± 1 mL CH4/g VS) was obtained in the presence of 293, 393 and 493 mg Zn/L, respectively. The potential reason for the high methanogenic activity at high inlet Zn concentrations could be that the AS used in this study was already acclimated to those conditions. Zinc was likely removed from the system by sulfide precipitation, and a removal efficiency above 99% was achieved under all zinc concentrations. A sulfate reduction efficiency of 99% was also obtained. Overall, this study details the potential utilization of biogenic sulfide as a metal detoxifying agent without detrimental effects on methane production from sewage sludge.

The Future Challenges of Anaerobic Membrane Bioreactor (AnMBR) for High Strength Wastewater

This article is to present a review of anaerobic membrane bioreactor (AnMBR), process, operational condition, fouling mechanism and future challenge for high strength wastewater. Since1969s, membrane filtration technology has been used and continuously developed for wastewater treatment and recovery. AnMBR has proposed for the economic feasibility owing to the low footprint, high yield production under the relatively low energy consumption. Continuous stirred tank reactor (CSTR) configuration is the widely used couple with a flat sheet or hollow fibre modules. The various factors of operating condition are influence on the performance such as hydraulic retention time (HRT= 6 – 12 d), solid retention time (SRT > 100 d) and operating temperature (T = 10 - 56oC). In addition, the increase in temperature is related to high methanogenic activity and high COD removal efficiency (85% - 99%). However, the limitation of this process is fouling that occurs from the soluble microbial product (SMP), exopolymer substance (EPS) and biopolymer cluster (BPC). Almost of appropriate operating conditions for high performance, anti-fouling, the majority of effective microorganisms and energy balance are discussed in detail. For the challenge work, improvement of the prevention membrane fouling and high energy recovery in the hybrid/combination system with forward osmosis (FO), membrane distillation (MD) and powder activated carbon (PAC)-AnMBR.

New insights into the effect of ethanol and volatile fatty acids proportions on methanogenic activities and pathways

During anaerobic digestion, methanogenic activities and pathways can be affected by intermediates. Here, the effects of intermediates acetate, propionate, and ethanol on methanogenesis were investigated. Four anaerobic sequencing batch reactors were acclimated with propionate (ASBR_P), ethanol/propionate (ASBR_EP), acetate/propionate (ASBR_AP), and ethanol/acetate/propionate (ASBR_EAP). Ethanol was the easiest one to be biodegraded, thereby enhancing the maximum methane production rate and shortening the lag phase, while the longest acclimation time and lowest methane production rate were observed in ASBR_P. Different microbial communities and syntrophic patterns existed in four reactors. Desulfovibrio and Geobacter were the dominant ethanol-oxidizing bacteria in ASBR_EP and ASBR_EAP, respectively. Both Desulfovibrio and Geobacter possessed the potential of extracellular electron transfer, which might be the advantage of ethanol dosage for enhancing methanogenesis through direct interspecies electron transfer. Methanosarcina was enriched in ASBR_P and ASBR_AP, while Methanosaeta in ASBR_EP and ASBR_EAP. Genes responsible for acetoclastic methanogenesis were significantly enriched in ASBR_EAP, possibly resulting in the highest methanogenic activity from acetate. Results from this study will advance the optimization of practical anaerobic systems, which can be achieved by regulating the intermediates with different fermenting pathways.

Thermal/alkaline pretreatment of waste activated sludge combined with a microbial fuel cell operated at alkaline pH for efficient energy recovery

Energy and resource recovery from waste activated sludge (WAS) is promising for WAS treatment. Microbial fuel cell (MFC) is an environmentally friendly technology for energy recovery from WAS. Low hydrolysis rate and high methanogenic activity of WAS restrained the efficient electricity production in MFC operated at neutral pH. In this study, a combination of thermal/alkaline sludge pretreatment (140 °C, pH 12.5, 40 min) with MFC was developed, aiming to achieve high electricity generation and sludge reduction. Results show that a high power density (1.24 W/m2) was obtained in the MFC operated under alkaline condition. Complete restriction of methane production was achieved using the supernatant of thermal/alkaline pretreated WAS as substrate. 49.0 ± 3.4% of chemical oxygen demand (COD) was removed in the MFC. A low external resistance was favorable for COD removal and the accumulation of electricigens. This work provides a promising strategy for efficient sludge reduction, enhanced energy and resource recovery, as well as reduced greenhouse gas emission.

High methanogenic activity of a three-stage UASB in relation to the granular sludge formation

A new UASB (upflow anaerobic sludge blanket) system with three-stage concept and granular sludge formation was developed to provide a very high process activity, in terms of a high energy yield and a large optimum COD loading rate, from ethanol wastewater at 37 °C and a controlled pH of 5.5 in the first bioreactor with recirculation of the final overflow from the third to the first two bioreactors to lower the amount of sodium hydroxide used for pH control in the first bioreactor and to increase the total alkalinity of the whole system. The proper volumetric ratio of the three-stage UASB with flocculant sludge provided the dominance of the three sequencial steps of acidogenesis, acetognesis and methanogenesis to occur in the respective bioreactors, causing a higher process performance and giving the optimum COD loading rate of 15 kg/m3d. The presence of granular sludge in all three bioreactors, resulted from the slow increment in the COD loading rate over a long operation period with high levels of microbial concentrations in all three bioreactors under the continuous feed operation and steady sate condition. This further increased the optimum COD loading rate from 15 to 25 kg/m3d (calculated from the total liquid volume) with an extremely high energy yield of 11,740 kJ/kg COD applied.

Methane formation and consumption by sediments in a cross-channel profile of a small river impoundment

Rivers are a natural source of methane (CH4) into the atmosphere and may contribute significantly to total CH4 emissions. Even though the details of sources of CH4 in rivers are not fully understood, weirs have been recognized as a hotspot of CH4 emissions. In this study, we investigated CH4 production and consumption in air-exposed river sediments along a cross-channel transect located upstream of a weir. Stable carbon isotopes were used for determination of individual methanogenic pathways. In order to understand the relationship between physicochemical and biological processes, additional parameters such as organic matter, grain median size, and carbon and nitrogen content were characterized as well. Generally, samples from the surface sediment layer (0-10 cm) had higher CH4 production than sediments from the deeper layer (10-20 cm) during the incubation experiments. Sediments near the bank zones and in the mid-channel were characterized by the highest organic carbon content (6.9 %) as well the highest methanogenic activity (2.5 mmol g-1 DW d-1). The CH4 production was predominated by H2/CO2 dependent methanogenesis in the surface sediment layer (0-10 cm), while the proportion of acetoclastic and hydrogenotrophic methanogenesis in the deeper sediment layer (10-20 cm) was balanced. The CH4 oxidation potential of sediments showed the same spatial pattern as observed for the CH4 production. Our results showed high spatial variability of sediment CH4 production and oxidation in the cross-channel profile upstream of the weir, whereas the highest CH4 dynamics were observed in the littoral zones. This variability was closely linked with the carbon and nitrogen content in the sediment samples.

Food waste treatment in an anaerobic dynamic membrane bioreactor (AnDMBR): Performance monitoring and microbial community analysis

The applicability of a dynamic membrane (DM) was examined in the anaerobic treatment of high-strength food waste. A DM was established on woven polyester with a pore size of 50 µm, which achieved a solids retention time to hydraulic retention time ratio of 2.1:12.1. The highest average rate of methane production (1.1 L CH4/L/d) was achieved with an organic loading rate (OLR) of 5.0 g chemical oxygen demand (COD)/L/d. Propionate was the most abundant volatile fatty acid (VFA) for OLRs above 3.1 g/L/d, but concentrations were maintained below 0.9 g/L. Up to 82% of the VFAs in the mixed liquor was reduced in the effluent, implying high methanogenic activity of the DM. Microbial assays confirmed a higher archaeal and bacterial content in the DM than in the mixed liquor at shear velocities above 1.0 cm/s. Methanolinea tarda, which is known to be propionate tolerant, was the predominant archaea in the DM.

A combination of ammonia stripping and low temperature thermal pre-treatment improves anaerobic post-digestion of the supernatant from organic fraction of municipal solid waste treatment

Municipal Solid Waste is mostly composed of organic material which is often treated in anaerobic reactors in waste treatment plants. In most cases, the obtained digestate undergoes a solid/liquid separation step, producing a liquid fraction (known as anaerobic supernatant) rich in ammonium nitrogen that has to be further treated in order to meet discharge standards. The objective of the present work was to evaluate the feasibility of anaerobic post-digestion (37 °C) of a supernatant rich in carbon and nitrogen from a municipal waste treatment plant. In order to increase the efficiency of the process, a combined pre-treatment consisting of a low-temperature thermal process (75 °C) and ammonia stripping (1.3 Lair Lsupernatant−1 min−1) was applied. The effects of pre-treatment contact time (4 and 8 h) and the hydraulic retention time (HRT) in the anaerobic reactor (20–40 d) were studied. Supernatant pre-treatment with 8-h contact time caused 13% organic matter solubilisation, thus improving methanisation by 18% when the HRT was 40 d. At the same time, ammonia stripping allowed to maintain ammonia concentration in the digester below inhibitory values (less than 100 mg N-NH3 L−1) enabling therefore high methanogenic activity (>0.23 g COD g−1 VS d−1). The final effluent characteristics (low total ammonia nitrogen and aerobically biodegradable organic matter levels) would permit implementing subsequent less energy intensive and more environmental-friendly technologies (such as partial nitritation/anammox) to comply with discharge limits.

Removal of nitrogen from chicken manure anaerobic digestion for enhanced biomethanization

The effects of side-stream ammonia stripping as a pre- and post-treatment on the anaerobic mono-digestion of chicken manure were investigated in laboratory-scale continuous stirred tank reactors. Ammonia stripping columns were operated at pH 10 but different temperatures (35, 55, 70 °C). Results showed that digestate stripping at 70 °C and pH 10 got the highest ammonia removing rate (18.2–45.2%), and under these conditions, the methane yield at OLR of 9 g VS L−1 d−1 reached 0.199 L g−1 VSadded which was significantly higher than that of other digesters (0.01–0.03 L g−1 VSadded), although no improvement of methane yield was observed at OLR 3 and 6 g VS L−1 d−1. The microbial community analysis revealed that hydrolytic and fermentative bacteria dominated all bacterial communities. Methanogenic pathway of feedstock stripping digester was predominant by hydrogenotrophic Methanimicrococcus, while hydrogenotrophic/aceticlastic Methanoscarcina was dominant in the archaeal structures of the rest digesters. However, a shift from Methanosarcina to Methanoculleus was observed in R3 (digestate stripping at 70 °C/pH 10) when dominant species were inhibited and decreased in other digesters, indicating that the high methanogenic activity in R3 was maintained by shifting to methanogens with high tolerance to inhibitors.

The Effect of Temperature on the Methanogenic Activity in Relation to Micronutrient Availability

In the view of microbial community, thermophilic microorganisms were reported to have faster biochemical reaction rates, which are reflected by a higher methane production rate. However, there has no research to discuss the effect of temperature on methanogenic activity in relation to micronutrient transport and availability. The objective of this study was to investigate the effect of temperature on methanogenic activity in relation to nutrient uptakes, micronutrient transports, and mass balance using anaerobic sequencing batch reactors (ASBR) with recycled biogas for treating ethanol wastewater at mesophilic (37 °C) and thermophilic (55 °C) temperatures. The increase in temperature from 37 to 55 °C increased in both of the optimum chemical oxygen demand (COD) loading rate and methanogenic activity, corresponding to the results of N and P uptakes, energy balance, and mass balance. The higher temperature of the thermophilic operation as compared to the mesophilic one caused a lower water solubility of the produced H2S, leading to lowering the reduction of divalent cation micronutrients. The thermophilic operation could prevent the deficit of micronutrients, thus causing a higher methanogenic activity, while the mesophilic operation still had the deficit of most micronutrients, leading to the lower activity.

Co-ensiling of cattle manure before biogas production: Effects of fermentation stimulants and inhibitors on biomass and methane preservation

Abstract The impact of formic acid and glucose addition on the co-ensiling of cattle manure with straw was assessed during 4 months at laboratory scale. Feedstock deprived of additives lost 67% of its methane potential for prolonged ensiling. This was mainly due to the lack of water-soluble carbohydrates and to the high methanogenic activity of cattle manure. The use of co-substrates enhanced biomass and energy conservation during ensiling. The best result was obtained for co-ensiling of cattle manure with glucose (100 g/kg of feedstock). For this condition, lactate production was extensive, which enabled biomass acidification, suppressed ammonia emissions and led to full preservation of methane potential after 4 months. Therefore, in field-scale storage, co-ensiling with a sugar-rich co-substrate appears to be the most resourceful method to optimize cattle manure preservation. Application of this promising technique will have a major impact on the methane yield of agricultural biogas plants where cattle manure has to be stored for long periods.

Methanogenic activity in the biomass from horizontal subsurface flow constructed wetlands treating domestic wastewater

The aim of this study was to evaluate the methanogenic activity of horizontal subsurface flow (HSSF) constructed wetlands treating domestic wastewater. The analysis was carried out in four 4.5m2pilot-scale HSSF systems, two planted with Phragmites australis and two planted with Schoenoplectus californicus. A specific methanogenic activity (SMA) assay was carried out with the microbial biomass attached to the gravel of the HSSF systems to account for the different seasons. Accumulated solids throughout the entire operational time were also assessed. Results showed that biochemical oxygen demand (BOD5) removal efficiencies averaged 67.6±9.9% with organic loading rates (OLR) of4.4–5.8g BOD5m−2d−1. Total suspended solids (TSS) removals were 92.9±3.4%. Solids accumulation rates ranged between0.7±0.3 and 1.5±0.6kgTSSm−2year−1, respectively. Microbial biomass extracted from the HSSF presented a SMA regarding volatile suspended solids (VSS) of 0.018–1.220g CODCH4g−1VSSd−1, corresponding to methane productions between 176 and 15227mgCH4m−2d−1. Methanogenic activity after 550d were significantly lower (73.6%) than after 1200d of operation. The influent inlet zone of the HSSF systems showed 14–39% higher methanogenic activity than the middle and exit zones in the first 550d of operation. However, after 1100d of operation, the middle and exit zones presented 18–55% higher methanogenic activity than the inlet zone. The plant species did not affected the methanogenic activity of the biofilm from the HSSF system. The results of the present study showed that microbial biomass development through operation time, seasonality and the applied OLR influence methane production in HSSF systems.

CH4 and CO2 production below two contrasting peatland micro-relief forms: An inhibitor and δ13C study.

Two peatland micro-relief forms (microforms) - hummocks and hollows - differ by their hydrological characteristics (water table level, i.e. oxic-anoxic conditions) and vegetation communities. We studied the CH4 and CO2 production potential and the localization of methanogenic pathways in both hummocks and hollows at depths of 15, 50, 100, 150 and 200cm in a laboratory incubation experiment. For this purpose, we measured CH4 and CO2 production rates, peat elemental composition, as well as δ13C values of gases and solids; the specific inhibitor of methanogenesis BES (2-bromo-ethane sulfonate, 1mM) was aimed to preferentially block the acetoclastic pathway. The cumulative CH4 production of all depths was almost one fold higher in hollows than in hummocks, with no differences in CO2. With depth, CO2 and CH4 production decreased, and the relative contribution of the hydrogenotrophic pathway of methanogenesis increased. The highest methanogenic activity among all depths and both microforms was measured at 15cm of hollows (91%) at which the highest relative contribution of acetoclastic vs. hydrogenotrophic pathway (92 and 8%, respectively) was detected. For hummocks, the CH4 production was the highest at 50cm (82%), where relative contribution of acetoclastic methanogenesis comprised 89%. The addition of 1mM BES was not selective and inhibited both methanogenic pathways in the soil. Thus, BES was less efficient in partitioning the pathways compared with the δ13C signature. We conclude that the peat microforms - dry hummocks and wet hollows - play an important role for CH4 but not for CO2 production when the effects of living vegetation are excluded.

Leachate flush strategies for managing volatile fatty acids accumulation in leach-bed reactors

In anaerobic leach-bed reactors (LBRs) co-digesting an easily- and a slowly-degradable substrate, the importance of the leachate flush both on extracting volatile fatty acids (VFAs) at the beginning of newly-started batches and on their consumption in mature reactors was tested. Regarding VFA extraction three leachate flush-rate conditions were studied: 0.5, 1 and 2Lkg−1TSd−1. Results showed that increasing the leachate flush-rate during the acidification phase is essential to increase degradation kinetics. After this initial phase, leachate injection is less important and the flush-rate could be reduced. The injection in mature reactors of leachate with an acetic acid concentration of 5 or 10gL−1 showed that for an optimized VFA consumption in LBRs, VFAs should be provided straight after the methane production peak in order to profit from a higher methanogenic activity, and every 6–7h to maintain a high biogas production rate.

An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter (AF) was introduced for the treatment of coal gasification wastewater (CGW), and effluent recirculation was adopted to enhance phenol removal and methane production. The results indicated that AF was reliable in treating diluted CGW, while its efficiency and stability were seriously reduced when directly treating raw CGW. However, its performance could be greatly enhanced by effluent recirculation. Under optimal effluent recirculation of 0.5 to the influent, concentrations of chemical oxygen demand (COD) and total phenol in the effluent could reach as low as 234.0 and 14.2mg/L, respectively. Also, the rate of methane production reached 169.0mLCH4/L/day. Though CGW seemed to restrain the growth of anaerobic microorganisms, especially methanogens, the inhibition was temporary and reversible, and anaerobic bacteria presented strong tolerance. The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater (GW). However, the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication. By analysis using the Haldane model, it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters, but only suitable effluent recirculation could result in high methanogenic activity.

On-site treatment of source separated domestic wastewater employing anaerobic package system

On-site treatment of black water generated at a residential school was investigated by employing an upgraded two-stage package system: a modified septic tank followed by an anaerobic filter. The findings revealed that the average removal efficiency for CODtot, CODss, BOD and TSS were 72.6, 90.2, 78.4 and 83.2%, respectively. Monthly septage characterization revealed a declining trend in VSS/TSS ratio, which indicated the progressive hydrolysis as well as stabilization of the sludge. The interrelationship between physico-chemical and microbial parameters revealed a linear relationship between the data with a good coefficient of correlation. High methanogenic activity of 0.386gCH4/gVSS. D was observed within the developed sludge. Thus the studied package system can be a suitable alternative to the conventional septic tank for on-site treatment of black water in the rural areas of developing regions.

Degradation of methanethiol in anaerobic sewers and its correlation with methanogenic activities

Methanethiol (MT) is considered one of the predominant odorants in sewer systems. Therefore, understanding MT transformation in sewers is essential to sewer odor assessment and abatement. In this study, we investigated the degradation of MT in laboratory anaerobic sewers. Experiments were carried out in seven anaerobic sewer reactors with biofilms at different stages of development. MT degradation was found to be strongly dependent on the methanogenic activity of sewer biofilms. The MT degradation rate accelerated with the increase of methanogenic activity of sewer biofilms, resulting in MT accumulation (i.e. net production) in sewer reactors with relatively low methanogenic activities, and MT removal in reactors with higher methanogenic activities. A Monod-type kinetic expression was developed to describe MT degradation kinetics in anaerobic sewers, in which the maximum degradation rate was modeled as a function of the maximum methane production rate through a power function. It was also found that MT concentration had a linear relationship with acetate concentration, which may be used for preliminary assessment of MT presence in anaerobic sewers.

Methanosaeta dominate acetoclastic methanogenesis during high‐rate methane production in anaerobic reactors treating distillery wastewaters

AbstractBACKGROUNDAnaerobic treatment of vinasses wastewater can result in high methane production rates, which depends on the ability to maintain a high specific methanogenic activity in the reactor. Here, it was investigated whether methane production could be increased by optimizing (1) temperature and (2) organic loading rate. It was expected that by maintaining high residual acetate concentrations, due to systematic overloading, anaerobic sludge with higher methanogenic activity would develop.RESULTSA pilot‐scale experiment of 180 days showed that Methanosarcina were unable to dominate acetoclastic methanogenesis in an upflow anaerobic sludge bed (UASB) reactor, despite the favorable conditions. This could be attributed to their reduced tendency to incorporate into sludge granules. Conversion rates of 40 to 50 kg COD m−3 d−1 were obtained for vinasses in mesophilic UASB reactors.CONCLUSIONThese high methane production rates open the possibility to achieve electricity production of more than 2 kW m−3 reactor, with concomitant economic perspectives. © 2013 Society of Chemical Industry