Enhanced direct interspecies electron transfer and methane production during anaerobic digestion of fat, oil, and grease by coupling carbon-based conductive materials and exogenous hydrogen

Coupling Fe3O4 and micro-hydrogen for enhancing the anaerobic bio-conversion of phenol: Methanogenesis pathway and interspecies electron transfer

Low anaerobic biological conversion rate is a challenge in the anaerobic biological treatment of phenol wastewater. The dominant syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway is expected to solve the problem. However, there are raw studies on artificially simulating a dominant SAO-HM pathway for enhancing the anaerobic bio-conversion of phenol. In this study, Fe3O4 and micro-hydrogen (Fe3O4/H2) was used to strengthen the anaerobic bio-conversion of phenol by simulating the dominant SAO-HM pathway. The results suggested Fe3O4 and H2 had a coupling promotion on the anaerobic bio-conversion of phenol and Fe3O4/H2 increased the relative abundance of Syntrophus (29.35%), Syntrophorhabdu (3.27%), Clostridium (3.01%) and Methanobacterium (65.74%), indicating Fe3O4/H2 formed a dominant SAO-HM pathway. However, Fe3O4/H2 obviously reduced the conductivity of sludge, the extracellular protein and the functional gens pilA, pilB and OmcS, implying direct interspecies electron transfer (DIET) generated by Fe3O4 was interfered by micro hydrogen in extracellular electron transport process which reduced the efficiency of extracellular electron transport. This study remind that extracellular electron transport cannot be ignored in the dominate SAO-HM pathway for the anaerobic bio-conversion of phenol.

An in-situ biochar-enhanced anaerobic membrane bioreactor for swine wastewater treatment under various organic loading rates

A biochar-assisted anaerobic membrane bioreactor (BC-AnMBR) was conducted to evaluate the performance in treating swine wastewater with different organic loading rates (OLR) ranging from 0.38 to 1.13 kg-COD/(m3.d). Results indicated that adding spent coffee grounds biochar (SCG-BC) improved the organic removal efficiency compared to the conventional AnMBR, with an overall COD removal rate of > 95.01%. Meanwhile, methane production of up to 0.22 LCH4/gCOD with an improvement of 45.45% was achieved under a high OLR of 1.13 kg-COD/(m3.d). Furthermore, the transmembrane pressure (TMP) in the BC-AnMBR system was stable at 4.5 kPa, and no irreversible membrane fouling occurred within 125 days. Microbial community analysis revealed that the addition of SCG-BC increased the relative abundance of autotrophic methanogenic archaea, particularly Methanosarcina (from 0.11% to 11.16%) and Methanothrix (from 16.34% to 24.05%). More importantly, Desulfobacterota and Firmicutes phylum with direct interspecific electron transfer (DIET) capabilities were also enriched with autotrophic methanogens. Analysis of the electron transfer pathway showed that the concentration of c-type cytochromes increased by 38.60% in the presence of SCG-BC, and thus facilitated the establishment of DIET and maintained high activity of the electron transfer system even at high OLR. In short, the BC-AnMBR system performs well under various OLR conditions and is stable in the recovery energy system for swine wastewater.

Differentiated cognition of the effects of human activities on typical persistent organic pollutants and bacterioplankton community in drinking water source

Accelerated urbanization in developing countries led to a typical gradient of human activities (low, moderate and high human activities), which affected the pollution characteristics and ecological functions of aquatic environment. However, the occurrence characteristics of typical persistent organic pollutants, including organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs), and bacterioplankton associated with the gradient of human activities in drinking water sources is still lacking. Our study focused on a representative case - the upper reaches of the Dongjiang River (Pearl River Basin, China), a drinking water source characterized by a gradient of human activities. A comprehensive analysis of PAHs, OCPs and bacterioplankton in the water phase was performed using gas chromatography-mass spectrometry (GC-MS) and the Illumina platform. Moderate human activity could increase the pollution of OCPs and PAHs due to local agricultural activities. The gradient of human activities obviously influenced the bacterioplankton community composition and interaction dynamics, and low human activity resulted in low bacterioplankton diversity. Co-occurrence network analysis indicated that moderate human activity could promote a more modular organization of the bacterioplankton community. Structural equation models showed that nutrients could exert a negative influence on the composition of bacterioplankton, and this phenomenon did not change with the gradient of human activities. OCPs played a negative role in shaping bacterioplankton composition under the low and high human activities, but had a positive effect under the moderate human activity. In contrast, PAHs showed a strong positive effect on bacterioplankton composition under low and high human activities and a weak negative effect under moderate human activity. Overall, these results shed light on the occurrence characteristics of OCPs, PAHs and their ecological effects on bacterioplankton in drinking water sources along the gradient of human activities.

Kinetic study on anaerobic digestion of long-chain fatty acid enhanced by activated carbon adsorption and direct interspecies electron transfer

This study applied granular activated carbon (GAC) to improve the anaerobic digestion of long-chain fatty acid (LCFA). New kinetics were considered to describe the effect of GAC on the LCFA degradation, including i) The adsorption kinetics of GAC for LCFA, ii) The β-oxidation pathway of LCFA, iii) The attached biomass improved by direct interspecies electron transfer (DIET). The developed model simulated the anaerobic digestion of stearic acid, palmitic acid, myristic acid, and lauric acid with 1.00 and 2.00 g l-1 of GAC. The simulation results suggested that adding GAC led to the increase of km,CnGAC and km,acGAC. As the concentration of GAC increased, the values of kinetic parameters increased while the accumulated acetate concentration decreased. Thus, GAC improved the kinetic parameters of the attached syntrophic communities.

Material and microbial perspectives on understanding the role of biochar in mitigating ammonia inhibition during anaerobic digestion

With the increasing adoption of carbon-based strategies to enhance methanogenic processes, there is a growing concern regarding the correlation between biochar properties and its stimulating effects on anaerobic digestion (AD) under ammonia inhibition. This study delves into the relevant characteristics and potential mechanisms of biochar in the context of AD system under ammonia inhibition. The introduction of optimized biochar, distinguished by rich CO bond, abundant defect density, and high electronic capacity, resulted in a significant reduction in the lag period of anaerobic digestion system under 5.0 g/L ammonia stress, approximately by around 63 % compared to the control one. Biochar helps regulate the community structure, promotes the accumulation of acetate-consuming bacteria, in the AD system under ammonia inhibition. More examinations show that biochar promotes direct interspecies electron transfer in AD system under ammonia inhibition, as evidenced by diminished levels of bound electroactive extracellular polymeric substances, increased abundance of electroactive bacteria, and notably, the up-regulation of direct interspecies electron transfer associated genes, including the conductive pili and Cytochrome C genes, as revealed by meta-transcriptomic analysis. Additionally, gene expression related to proteins associated with ammonium detoxification were found to be up-regulated in systems supplemented with biochar. These findings provide essential evidence and insights for the selection and potential engineering of effective biochar to enhance AD performance under ammonia inhibition.

Co-digestion approach for enhancement of biogas production by mixture of untreated napier grass and industrial hydrolyzed food waste

The co-digestion of untreated Napier grass (NG) and industrial hydrolyzed food waste (FW) was carried out in the batch reactor to investigate the effect of substrate ratios on biogas production performance. Two-stage anaerobic digestion was performed with an initial substrate concentration of 5 g VSadded/L and a Food to Microorganism Ratio (F/M) of 0.84. The 1:1 ratio of the NG and FW showed the optimum performances on biogas production yield with a value of 1,161.33 mL/g VSadded after 60 days of digestion. This was followed by the data on methane yield and concentration were 614.37 mL/g VSadded and 67.29%, respectively. The results were similar to the simulation results using a modified Gompertz model, which had a higher potential methane production and maximum production rate, as well as a shorter lag phase and a coefficient of determination of 0.9945. These findings indicated that the co-digestion of Napier grass and hydrolyzed food waste can enhance biogas production in two-stage anaerobic digestion.

Influence of applied voltage on bioelectrochemical enhancement of biomethanation for low-rank coal and microbial community distribution

The performance of peat biomethanation was investigated in bioelectrochemical anaerobic digestion at different applied voltages, and compared to conventional anaerobic digestion. The methane yield was stabilized at 16 mL/g peat in the conventional anaerobic digestion. However, in the bioelectrochemical anaerobic digestion, the methane yield was significantly increased to 264 mL/g peat at the applied voltage of 4 V, followed by 1 V, 2 V, 0.5 V and 0 V. The bioelectrochemical system could enrich more electroactive microorganisms on the electrode, as well as in the bulk solution, and further improve the direct interspecies electron transfer for methane production. The 16S rRNA analysis showed a significant increase in the abundance of specific microorganisms in the bulk solution, including Firmicutes phylum and Proteobacteria phylum, in addition to a gradual increase in acetoclastic methanogenesis with an increase in applied voltage. These results provide a solution to turn low-rank coal into a new alternative energy.