Kinetic study on fermentation from CO2 and H2 using the acclimated-methanogen in batch culture

Methane was produced from H₂ and CO₂ using the acclimated-mixed methanogens in a 3.71 fermentor in batch culture at pH 7.2 and 37°C. The Fermentation kinetics parameter for the growth of methanogens, overall mass transfer coefficient of the reactor, and the conversion rate of H₂ and CO₂ to CH₄ by the acclimated-mixed culture were determined using the technique of Vega et al. The maximum specific growth rate (μ_max) and H₂ specific consumption rate (q_max) were found to be 0.064(h⁻¹) and 104.8 (mmol h⁻¹ g⁻¹) respectively. Monod saturation constants for growth (Kp) and for inhibition (K′p) were found to be 3.54 (kPa) and 0.57 (kPa), respectively. These findings indicate that without very low dissolved H₂ levels, the fermentations are carried out under μ_max, and the specific uptake rate (q) was almost not affected at any dissolved H₂ level in the range studied. The yield of CH₄ (Yp/s) was calculated to be 0.245 (mol CH₄ mol⁻¹ H₂), which is near the stoichiometric value of 0.25. DH₂ was also measured using the Teflon tubing method and was in good agreement with those estimated by kinetic calculations.     

Methanogenesis control by electrolytic oxygen production in microbial electrolysis cells

High purity H₂ production using microbial electrolysis cells (MECs) is often limited by methanogenesis. Here methanogenesis was effectively controlled by electrolytic oxygen production. Oxygen production was induced intermittently using two stainless steel electrodes, which were used as the MEC cathode during Normal operation. It was found that oxygen should be produced every 12 h or more frequently because of rapid hydrogenotrophic methanogen growth with available pure H₂. This method was also effective in an initially methanogen-dominated MEC. However, the growth of aerobic biofilms in MECs weakened methanogen control. Residual oxygen after fed-batch cycles was found to be the key indicator for effective methane control. Methane content was consistently smaller than 10% at the threshold residual oxygen volume (3 mL) or greater. MEC operation at such threshold conditions will allow high purity H₂ production, low energy consumption for O₂ production and minimal O₂ exposure on bioanodes, enabling sustainable wastewater treatment and energy recovery using MECs.     

利用微生物促进煤层间CO2甲烷化的新方法

为了在提高煤层气采收率的同时促进二氧化碳的资源化利用,在分析现有煤层气采收率方法作用机理的基础上,提出了一种利用微生物促进ECBM埋藏CO2甲烷化的新方法.该方法将注入二氧化碳趋采煤层气、微生物降解煤技术集约整合,通过产甲烷菌将因驱替煤层气而吸附在煤层表面的二氧化碳转化为甲烷,从而达到提高煤层气采收率同时减排二氧化碳的目的.煤层间微生物菌群降解煤的机理说明,产甲烷菌本身就具有利用煤分解生成的二氧化碳和氢气合成甲烷的能力,而外加二氧化碳可以在微生物降解煤的早期就启动消耗氢气生成甲烷气体的过程,并同时促进煤组分分解生成氢气的速度.由二氧化碳对产甲烷菌的影响、氢的来源、微生物激活和注入二氧化碳的先后顺序等角度的理论分析结果进一步论证了此种技术方案的可行性.     

Biogeochemical factors influencing net mercury methylation in contaminated freshwater sediments from the St. Lawrence River in Cornwall, Ontario, Canada

The activity of various anaerobic microbes, including sulfate reducers (SRB), iron reducers (FeRP) and methanogens (MPA) has been linked to mercury methylation in aquatic systems, although the relative importance of each microbial group in the overall process is poorly understood in natural sediments. The present study focused on the biogeochemical factors (i.e. the relative importance of various groups of anaerobic microbes (FeRP, SRB, and MPA) that affect net monomethylmercury (MMHg) formation in contaminated sediments of the St. Lawrence River (SRL) near Cornwall (Zone 1), Ontario, Canada. Methylation and demethylation potentials were measured separately by using isotope-enriched mercury species (²⁰⁰Hg²⁺ and MM¹⁹⁹Hg⁺) in sediment microcosms treated with specific microbial inhibitors. Sediments were sampled and incubated in the dark at room temperature in an anaerobic chamber for 96 h. The potential methylation rate constants (K_m) and demethylation rates (K_d) were found to differ significantly between microcosms. The MPA-inhibited microcosm had the highest potential methylation rate constant (0.016 d⁻¹), whereas the two SRB-inhibited microcosms had comparable potential methylation rate constants (0.003 d⁻¹ and 0.002 d⁻¹, respectively). The inhibition of methanogens stimulated net methylation by inhibiting demethylationand by stimulating methylation along with SRB activity. The inhibition of both methanogens and SRB was found to enhance the iron reduction rates but did not completely stop MMHg production. The strong positive correlation between K_m and Sulfate Reduction Rates (SRR) and between K_d and Methane Production Rates (MPR) supports the involvement of SRB in Hg methylation and MPA in MMHg demethylation in the sediments. In contrast, the strong negative correlation between K_d and Iron Reduction Rates (FeRR) shows that the increase in FeRR corresponds to a decrease in demethylation, indicating that iron reduction may influence net methylation in the SLR sediments by decreasing demethylation rather than favouring methylation.     

温度对产甲烷菌代谢途径和优势菌群结构的影响

产甲烷菌是严格厌氧的古菌,由其完成的产甲烷过程通常是厌氧微生物生化代谢中最重要的限速步骤。温度作为影响产甲烷菌的产甲烷速率重要因素,其变化会改变生物环境中的产甲烷的代谢途径和优势菌群分布。目前已知甲烷生物合成有3条途径：乙酸代谢途径、CO₂还原途径和甲基营养型途径。理论上乙酸途径生成的甲烷约占甲烷生成总量的2/3,CO₂还原产甲烷途径则约占1/3,甲基营养型途径只在少数情况下考虑其影响,例如盐湖。在低温条件下产甲烷菌以利用乙酸代谢为主;在中温条件下,产甲烷途径以乙酸代谢和H₂/CO₂还原一定比例存在;在高温和超高温条件下,以只利用CO₂还原途径的菌群为主。     

非常规微量元素对厌氧发酵性能的提升作用

厌氧发酵是有机废弃物和高浓度有机废水处理的重要技术手段,缺乏必需的微量元素会显著降低厌氧微生物的代谢活性,进而影响工艺的处理效果.如何维持厌氧系统微量元素的平衡和有效供给是重要的研究课题.关于Fe、Co和Ni在厌氧系统的作用已有大量的文献报道,而对于Se、W、Mo、Cu和Zn等非常规微量元素的作用还缺少总结和分析.产甲...     

Process kinetics of UASB reactors treating non‐inhibitory substrate

The degradation of a non‐inhibitory substrate (sucrose) in upflow anaerobic sludge bed (UASB) reactors with different superficial flow velocites (u_s) was performed to generate experimental data. Additionally, a kinetic model accounting for the mass fraction of methanogens (f) and granule size distribution in UASB reactors is also proposed. At the volumetric loadings of 2.65–21.16 g COD dm^?3 day^?1, both the COD removal efficiency and granule size of the UASB reactors increase with increasing u_s. The f values determined experimentally increase from 0.13–0.24 to 0.27–0.43 if the volumetric loading is increased from 2.65 to 5.29 g COD dm^?3 day^?1. With a further increase in volumetric loading, the f values decline because of the accumulation of volatile fatty acids (VFAs). The predicted residual concentrations of VFAs and COD are in fairly good agreement with the experimental data. From the calculated effectiveness‐factor values, the influence of mass transfer resistance of the substrate sucrose on the overall substrate removal rate should not be neglected. From parametric sensitivity analyses together with the simulated concentration profiles, methanogenesis is the rate‐limiting step. Copyright © 2003 Society of Chemical Industry     

沁水煤田赵庄矿区煤微生物产甲烷能力分析

为提高沁水煤田赵庄矿区的煤层气井产量,以煤地质微生物产甲烷理论为基础,采取本矿区煤层气井水,在荧光显微镜及古菌16s r DNA V6高变区宏基因组测序验证菌源可靠性后,采用厌氧培养的方法,分别在小型玻璃瓶和中型发酵罐中开展了为期49 d的煤炭生物转化模拟试验,分析了成气过程中菌群数量变化、成气规律,进行了产气试验后煤的工业分析、煤表面扫描电子显微镜观察。结果显示,小型和中型模拟试验中所产甲烷气体含量分别高达25%、31%;2个模拟试验菌液中菌群数量的变化均为缓慢增长、显著增加、趋于减缓3个阶段,与成气规律基本一致;对试验前后煤样工业分析进行比对后,发现固定碳含量和挥发分都有所下降;且观察到附着在煤表面进行煤降解的产甲烷菌群落。山西沁水煤田赵庄矿区的本源产甲烷微生物菌群可以对煤进行有效降解,并产生甲烷。     

厌氧序批式反应器处理青霉素制药废水

为研究厌氧序批式反应器(AnSBR)处理青霉素制药废水的效能与机制,依次考察了不同进水浓度(1、10、100、1 000 mg/L)青霉素G钠盐对AnSBR有机物去除、甲烷转化和污泥特性的影响。结果表明,低浓度(1、10 mg/L)青霉素G钠盐对有机物去除和甲烷转化无显著影响,100 mg/L青霉素G钠盐产生了短期负面但可逆影响,1 000 mg/L青霉素G钠盐产生了持续负面且不可逆影响,青霉素G钠盐主要影响厌氧污泥沉降性。在容积负荷2.5 g COD/(L·d)和进水青霉素G钠盐不超过100 mg/L的条件下,AnSBR的有机物去除率和甲烷转化率可达到85%和0.25 L/g COD,出水青霉素G钠盐低于检测限。甲烷杆菌属和甲烷八叠球菌属等具有耐受高浓度青霉素G钠盐环境的相对优势,使得AnSBR处理青霉素制药废水具有良好的应用潜力。     

3D-Printed Methane-Producing Electrodes for Microbial Fuel Cells Developed Using Biogel Ink Containing Live Methanogens and White Charcoal

Methanogens are used as catalysts for cathodes in microbial fuel cells, to reduce CO₂ to CH₄. However, the attachment of microbes to the electrodes via culturing is time-consuming, and inadequate biofilm formation can lead to lesser surface area coverage, resulting in reduced methane formation. This study aims to improve the production efficiency and performance of methanogen cathodes developed using 3D printing of bioink containing live methanogens. A progressive cavity pump is used for the 3D gel-printing of methanogens and micro-sized white charcoal particles into the desired structure. Despite the absence of anaerobic conditions during printing, the 3D-printed cathodes with higher concentrations of microbial inoculum in the bioink produce more methane gas. Even with an unconcentrated inoculum, the methanogens multiply 800-fold during incubation, resulting in increased methane gas production. The predominant methanogens in the electrodes included the hydrogenotrophic Methanobacterium spp. Therefore, the technique used in this study can be used to successfully develop 3D-printed biocathodes catalyzed by methanogenic microbes with verifiable practical applicability. This study is the first to report the growth of methanogens and their methanogenic activity in 3D-printed cathodes.