Enrichment Of Hydrogenotrophic Methanogens Research Articles

Mathematical model of anaerobic propionate degradation by incorporating the r/K selection theory

Although anaerobic digestion mathematical model (ADMM) has been widely applied for system optimization and mechanism understanding, the selection of key kinetic and stoichiometric parameter values for ADMM is still a challenge. An ADMM incorporating the r/K selection theory was proposed to examine the enrichment of r- and K-strategists in completely mixed reactors (CMRs) and sequencing batch reactors (SBRs). With the influent propionate concentration (PC) of 0.75 g COD/L, K-strategists predominated at the sludge retention time (SRT) higher than 13 d for propionate oxidizing bacteria (POB) and 9 d for acetoclastic methanogens (AM) in CMRs, while r-strategists dominated at the SRT less than 20 d for POB and 5 d for AM in SBRs. Under the SRT of 20 d, in CMRs, both K-strategists of POB and AM increased with increasing PCs, while r-strategists of POB only appeared when the PC exceeded 6 g COD/L and r-strategists of AM could not be enriched under all PC conditions; in SBRs, K-strategists of POB and AM showed the superiority when the PC was lower than 0.5 and 1.5 g COD/L, respectively. Only K-strategists of hydrogenotrophic methanogens (HM) were enriched in all simulated scenarios. Based on sensitivity analysis, SRT and the first order decay rate had a high influence on the enrichment of HM, AM, and POB. Overall, the selection of r-/K-strategists of POB and AM could be achieved by regulating SRT, operational mode, and PC.

Improved net energy recovery in a sludge anaerobic digestion process by coupling an electrochemical system: electrode material and its impact on suspended microbial community.

Despite its great potential to recover energy from waste sludge, anaerobic digestion (AD) still needs to solve issues such as slow hydrolysis and H2 inhibition. This study investigated the effects of coupling microbial electrolysis cell (MEC) with AD on the CH4 yield. Results and analysis show that the CH4 yield was significantly improved in MEC-AD reactors by two factors, i.e., enhanced and accelerated hydrolysis and acidogenesis, and enrichment of hydrogenotrophic methanogens in suspended culture. Compared with graphite rod and carbon fiber brush, carbon felt (CF) as an electrode showed the best performance in terms of net energy output. The CH4 yield of MEC-AD-CF was 40.2 L CH4/kg VS, 92.3% higher than in the control group, and the VS removal rate was also increased by 47.2%. Acetoclastic methanogens were dominant in the control AD reactor, while the relative abundance of Methanobacterium, which is electroactive and known as hydrogenotrophic methanogen, increased to 24.6% in MEC-AD with CF as electrodes.

Impact of biochar supported nano zero-valent iron on anaerobic co-digestion of sewage sludge and food waste: Methane production, performance stability and microbial community structure

This work evaluates the effects of biochar supported nano zero-valent iron (nZVI-BC) on anaerobic co-digestion (co-AD) of sewage sludge and food waste. Kinetic model analysis suggested that nZVI-BC addition significantly increased the methane production potential (R0) and daily methane production rate (Gm) by 42.87% and 49.87%, while the raw biochar only increased R0 and Gm by 5.11% and 6.73%, respectively. Supplementation of higher concentrations of nZVI-BC was not preferable as inhibition of methane productivity was appeared. nZVI-BC addition remarkably improved organics degradation efficiency, as the reduction rate of TCOD, VSS and TSS were increased by 34.93%, 11.44% and 13.96%, respectively. The microbial analysis demonstrated that nZVI-BC facilitated the growth of hydrogentrophic methanogens, while acetotrophic methanogens which can only use acetate as electron donor were restrained. The study demonstrated nZVI-BC can effectively strengthen methanogenesis mainly through the enhancement of DIET between bacteria and methanogens, and the enrichment of hydrogenotrophic methanogens.

The underlying mechanism of enhanced methane production using microbial electrolysis cell assisted anaerobic digestion (MEC-AD) of proteins

Anaerobic digestion (AD) is a promising technology capable of converting waste matter into bio-energy. Recent studies have reported that microbial electrolysis cell assisted anaerobic digestion (MEC-AD) is an effective system for methane production from organic waste, via enhanced electron transfer. However, little is known about the effects of applied voltage on the AD of proteins. Herein, the mechanism of MEC-AD on protein digestion was investigated using varying concentrations of bovine serum albumin (BSA) as the protein substrate (500 mg/L, 4 g/L, and 20 g/L BSA). Experimental results showed that the applied voltage can not only enhance the methane production rate from 23.8% to 45.6% at low and medium organic loading (BSA concentration of 500 mg/L and 4 g/L), but also improve the methanogenesis efficiency increased by 225.4% at high BSA concentration (20 g/L) with the applied voltage of 0.6 V compared to that with open circuit. Mechanism explorations revealed that the applied voltage significantly enhanced the acidogenesis and methanogenesis processes in the AD of proteins. Microbial community characterization showed that with the applied voltage, the abundance of fermentative bacteria increased by 46.7 % at the anode, while, the abundance of Methanobacterium at the cathode increased from 10.4 to 84.3%, indicating the methanogenesis pathway transformed from acetoclastic to hydrogenotrophic. External circuit electron transfer calculations demonstrated that only 10% of the produced methane could be attributed to direct interspecies electron transfer (DIET). From a thermodynamic perspective, the applied external voltage led to a reduction in the cathodic potential to -0.9 V, which is beneficial for enhanced methane production via mediated interspecies electron transfer (MIET) by enrichment of hydrogenotrophic methanogens. The findings reported here reveal the previously unrecognized contribution of proteins to MEC-AD, while also furthering our understanding of the role of applied voltage in the MEC-AD process.

Effects of Sludge Retention Time on the Performance of Anaerobic Ceramic Membrane Bioreactor Treating High-Strength Phenol Wastewater

Anaerobic ceramic membrane bioreactor (AnCMBR) is an attractive alternative for the treatment of high-strength phenol wastewater, but the effects of sludge retention time (SRT) on the performance and membrane fouling are still unclear. The results indicated that the AnCMBR was successfully employed to treat high-strength wastewater containing 5 g phenol L−1. The removal efficiencies of phenol and chemical oxygen demand (COD) reached over 99.5% and 99%, respectively, with long SRT and short SRT. SRT had no obvious effect on the performance of the AnCMBR treating high-strength phenol wastewater with long time operation. The strong performance robustness of AnCMBR benefited from the enrichment of hydrogenotrophic methanogens and syntrophic phenol-degrading bacteria. However, the decline of SRT led to a more severe membrane fouling in the AnCMBR, which was caused by the small size of sludge flocs and high concentration of protein in the biopolymers. Therefore, this work presented a comprehensive insight to the feasibility and robustness of the AnCMBR for treating high-strength phenol wastewater.

Redox mediator-modified biocathode enables highly efficient microbial electro-synthesis of methane from carbon dioxide

Regulating cathodic interface properties towards highly effective CH4 production from CO2 is of great importance for energy storage using microbial electro-synthesis (MES). Herein, the feasibility and mechanism of two typical redox mediators, neutral red (NR) and anthraquinone-2, 6-disulfonate (AQDS), were evaluated for the improvement of CH4 formation from CO2 reduction in mixed-culture biocathodes of MESs. Results showed that the CH4 formation rates of biocathodes after modification with NR and AQDS were 5.8 and 3.5 times higher than that of unaltered cathodes. Moreover, the coulombic efficiency of CH4 formation improved from 44.27 ± 4.01% of the control cathode to 64.30 ± 4.83% and 62.26 ± 2.87% after modification with NR and AQDS, respectively. Consequently, the energy efficiency of MESs after cathode modification with NR and AQDS increased to 58.33 ± 3.17% and 53.21 ± 4.11% compared to 38.20 ± 3.12% without modification. Such improvements were likely attributed to the enhanced extracellular electron transfer of microbes, the reduction in internal resistances and the enrichment of hydrogenotrophic methanogens in the mixed-culture biocathodes after modification with NR and AQDS. This study provides an alternative strategy to regulate cathodic interface in MESs for renewable energy storage and biomethane production from CO2.

Enrichment of hydrogenotrophic methanogens by means of gas recycle and its application in biogas upgrading

Biomethanation by hydrogenotrophic methanogens has been proven as a potential process for managing renewable power intermittency and upgrading biogas. The present work aimed to enrich hydrogenotrophic methanogens under different mixing conditions (gas recycle vs. mechanical mixing) and temperatures (mesophilic vs. thermophilic conditions) for biogas upgrading. The synthetic gas (H2:CO2 = 4:1) was fed to the reactor bottom at a hydrogen injection rate (HIR) of 1.6 L H2 L−1 d−1. The gas recycle (100 L L−1 d−1) under thermophilic condition was found to be the most effective, reaching over 96% H2 conversion to CH4 within 15 d of operation. Archaea community analysis performed by 454 pyrosequencing showed that the sequence of Methanosaeta sp. decreased while obligate-hydrogenotrophic methanogens increased: Methanoculleus chikugoensis (19.5%) and Methanothermococcus thermolithotrophicus (28.1%) under mesophilic and thermophilic condition, respectively. To the thermophilic enriched culture, the biogas produced from an up-flow anaerobic sludge blanket reactor with additional hydrogen (four times of CO2) was fed at various HIRs for 200 d. As HIR increased, H2 consumption rate also increased with CO2 removal contained in the biogas. Up to an HIR increase to 19.2 L H2 L−1 d−1, the high calorific biomethane (96% of CH4) could be obtained at gas recycle rate of 200 L L−1 d−1.

Enrichment of Hydrogenotrophic Methanogens in Coupling with Methane Production Using Electrochemical Bioreactor

Anaerobic digestion sludge was cultivated in an electrochemical bioreactor (ECB) to enrich the hydrogenotrophic methanogens. A modified graphite felt cathode with neutral red (NR-cathode) was charged with electrochemical reducing power generated from a solar cell. The methane and carbon dioxide collected in a Teflon bag from the ECB were more than 80 ml/l of reactant/day and less than 20 ml/l of reactant/day, respectively, whereas the methane and carbon dioxide collected from a conventional bioreactor (CB) was around 40 ml/l of reactant/day, respectively. Moreover, the maximal volume ratios of methane to carbon dioxide (M/C ratio) collected in the Teflon bag from the ECB and CB were 7 and 1, respectively. The most predominant methanogens isolated from the CB on the 20th, 80th, and 150th days of incubation were hydrogenotrophs. The methanogenic diversity analyzed by temperature gradient gel electrophoresis (TGGE) of the 16S rDNA variable region was higher in the ECB than in the CB. The DNA extracted from the TGGE bands was more than 95% homologous with hydrogenotrophic methanogens in the CB. In conclusion, the ECB was demonstrated as a useful system for enriching hydrogenotrophic methanogens and increasing the M/C ratio of the gas product.