Microbial electrolysis contribution to anaerobic digestion of waste activated sludge, leading to accelerated methane production

Methane production rate (MPR) in waste activated sludge (WAS) digestion processes is typically limited by the initial steps of complex organic matter degradation, leading to a limited MPR due to sludge fermentation speed of solid particles. In this study, a novel microbial electrolysis AD reactor (ME-AD) was used to accelerate methane production for energy recovery from WAS. Carbon bioconversion was accelerated by ME producing H-2 at the cathode. MPR was enhanced to 91.8 gCH(4)/m(3) reactor/d in the microbial electrolysis ME-AD reactor, thus improving the rate by 3 times compared to control conditions (30.6 gCH(4)/m(3) reactor/d in AD). The methane production yield reached 116.2 mg/g VSS in the ME-AD reactor. According to balance calculation on electron transfer and methane yield, the increased methane production was mostly dependent on electron contribution through the ME system. Thus, the use of the novel ME-AD reactor allowed to significantly enhance carbon degradation and methane production from WAS. (C) 2016 Elsevier Ltd. All rights reserved

Microbial network for waste activated sludge cascade utilization in an integrated system of microbial electrolysis and anaerobic fermentation

Background: Bioelectrochemical systems have been considered a promising novel technology that shows an enhanced energy recovery, as well as generation of value-added products. A number of recent studies suggested that an enhancement of carbon conversion and biogas production can be achieved in an integrated system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) for waste activated sludge (WAS). Microbial communities in integrated system would build a thorough energetic and metabolic interaction network regarding fermentation communities and electrode respiring communities. The characterization of integrated community structure and community shifts is not well understood, however, it starts to attract interest of scientists and engineers. Results: In the present work, energy recovery and WAS conversion are comprehensively affected by typical pre-treated biosolid characteristics. We investigated the interaction of fermentation communities and electrode respiring communities in an integrated system of WAS fermentation and MEC for hydrogen recovery. A high energy recovery was achieved in the MECs feeding WAS fermentation liquid through alkaline pretreatment. Some anaerobes belonging to Firmicutes (Acetoanaerobium, Acetobacterium, and Fusibacter) showed synergistic relationship with exoelectrogens in the degradation of complex organic matter or recycling of MEC products (H-2). High protein and polysaccharide but low fatty acid content led to the dominance of Proteiniclasticum and Parabacteroides, which showed a delayed contribution to the extracellular electron transport leading to a slow cascade utilization of WAS. Conclusions: Efficient pretreatment could supply more short-chain fatty acids and higher conductivities in the fermentative liquid, which facilitated mass transfer in anodic biofilm. The overall performance of WAS cascade utilization was substantially related to the microbial community structures, which in turn depended on the initial pretreatment to enhance WAS fermentation. It is worth noting that species in AD and MEC communities are able to build complex networks of interaction, which have not been sufficiently studied so far. It is therefore important to understand how choosing operational parameters can influence reactor performances. The current study highlights the interaction of fermentative bacteria and exoelectrogens in the integrated system

Statistical Optimization of Operational Parameters for Enhanced Naphthalene Degradation by Photocatalyst

The optimization of operational parameters for enhanced naphthalene degradation by TiO2/Fe3O4-SiO2 (TFS) photocatalyst was conducted using statistical experimental design and analysis. Central composite design method of response surface methodology (RSM) was adopted to investigate the optimum value of the selected factors for achieving maximum naphthalene degradation. Experimental results showed that irradiation time, pH, and TFS photocatalyst loading had significant influence on naphthalene degradation and the maximum degradation rate of 97.39% was predicted when the operational parameters were irradiation time 97.1 min, pH 2.1, and catalyst loading 0.962 g/L, respectively. The results were further verified by repeated experiments under optimal conditions. The excellent correlation between predicted and measured values further confirmed the validity and practicability of this statistical optimum strategy

Electrode Microbial Communities Associated with Electron Donor Source Types in a Bioelectrochemical System Treating Azo-Dye Wastewater

Bioelectrochemical systems (BESs) have been acknowledged to be an efficient technology for refractory pollution treatment. An electron donor is as an indispensable element of BES, and domestic wastewater (DW) has been proved as a cost-efficient and accessible alternative option to expensive carbon sources (such as acetate and glucose), yet its effect on microbial community evolution has not been thoroughly revealed. In this study, the electrode microbial communities from BESs treating azo dye wastewater fed by DW (RDW), acetate (RAc), and glucose (RGlu) were systematically revealed based on 16S rRNA Illumina MiSeq sequencing platform. It was found that there were significant differences between three groups in microbial community structures. Desulfovibrio, Acinetobacter, and Klebsiella were identified as the predominant bacterial genera in RDW, RAc, and RGlu, respectively. Methanosaeta, the most enriched methanogen in all reactors, had a relative lower abundance in RDW. Microbial communities in RAc and RGlu were sensitive to electrode polarity while RDW was sensitive to electrode position. Compared with pure substrates, DW increased the diversity of microbial community and, thus, may enhance the stability of electrode biofilm. This study provides an insight into the microbial response mechanism to the electron donors and provides engineering implications for the development of BES

Methane Promotion of Waste Sludge Anaerobic Digestion: Effect of Typical Metal Meshes on Community Evolution and Electron Transfer

Anaerobic digestion of waste activated sludge (WAS) to produce methane is a promising pathway for biomass energy recovery. However, a slow organic biodegradation rate and weak microbial cooperation between fermentation bacteria and methanogens lead to low methane production from WAS. Considering the reuse of conductive materials for the regulation of microbial communities, this study chose three kinds of high-mesh metal materials (nickel, copper, and stainless steel) to promote the anaerobic digestion process. All three kinds of metal mesh could effectively increase methane production, and the highest methane production was increased by 61%, reaching 77.52 mL gVSS−1. The poor biocompatibility of the stainless steel mesh was the least effective in promoting methane production compared to the biocompatible copper mesh and nickel mesh. The microbiological analysis found that the metal mesh with good biocompatibility can effectively induce and promote the enrichment of key microorganisms in the process of synergistic methane production, and the direct electron transfer process (DIET) of microorganisms on the metal surface contributes to the further improvement of the methane production efficiency. Therefore, the application of metal conductive materials in sludge anaerobic fermentation is feasible to achieve the retention of syntrophic bacteria and methanogens in the system

Methane Promotion of Waste Sludge Anaerobic Digestion: Effect of Typical Metal Meshes on Community Evolution and Electron Transfer

Anaerobic digestion of waste activated sludge (WAS) to produce methane is a promising pathway for biomass energy recovery. However, a slow organic biodegradation rate and weak microbial cooperation between fermentation bacteria and methanogens lead to low methane production from WAS. Considering the reuse of conductive materials for the regulation of microbial communities, this study chose three kinds of high-mesh metal materials (nickel, copper, and stainless steel) to promote the anaerobic digestion process. All three kinds of metal mesh could effectively increase methane production, and the highest methane production was increased by 61%, reaching 77.52 mL gVSS−1. The poor biocompatibility of the stainless steel mesh was the least effective in promoting methane production compared to the biocompatible copper mesh and nickel mesh. The microbiological analysis found that the metal mesh with good biocompatibility can effectively induce and promote the enrichment of key microorganisms in the process of synergistic methane production, and the direct electron transfer process (DIET) of microorganisms on the metal surface contributes to the further improvement of the methane production efficiency. Therefore, the application of metal conductive materials in sludge anaerobic fermentation is feasible to achieve the retention of syntrophic bacteria and methanogens in the system

Biocathodic Methanogenic Community in an Integrated Anaerobic Digestion and Microbial Electrolysis System for Enhancement of Methane Production from Waste Sludge

Understanding the microbial community structure relative to enhancement of methane production from digestion of waste-activated sludge (WAS) coupled with a bioelectrochemical system is a key scientific question for the potential application of bioelectrochemistry in biogas production. Little has been known about the influence of electrode on the structure and function of microbial communities, especially methanogens in a bioelectrochemical anaerobic digestion (AD) reactor. Here, a hybrid reactor, which coupled bioelectrolysis and AD, was developed to enhance methane recovery from WAS. The methane production rate reached up to 0.0564 m³ methane/(m³ reactor*d) in the hybrid reactor at room temperature, which was nearly double than that of the control anaerobic reactor (0.0259 m³ methane/(m³reactor*d)) without bioelectrochemical device. Microbial community analysis revealed that hydrogenotrophic methanogen <i>Methanobacterium</i> dominated the cathode biofilm, which was the predominant contributor to accelerate the methane production rate from WAS. While acetoclastic methanogen <i>Methanosaeta</i> was enriched in the sludge phase of all reactors, shifts of the microbial community structure of the biocathode was in significant correlation with the methane production. This study suggested a potential way to utilize a bioelectrochemical system with the regulated microbial community to enhance methane production from WAS