title: Microbial network for waste activated sludge cascade utilization in an integrated system of microbial electrolysis and anaerobic fermentation.
abstract: 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 pretreated 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 (H2). 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.
authors.affiliation: Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085 China.
authors.forename: Wenzong
authors.initials: W
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Zhangwei
authors.initials: Z
authors.lastname: He
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Chunxue
authors.initials: C
authors.lastname: Yang
authors.affiliation: College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan, 030024 China.
authors.forename: Aijuan
authors.initials: A
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Zechong
authors.initials: Z
authors.lastname: Guo
authors.affiliation: Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085 China.
authors.forename: Bin
authors.initials: B
authors.lastname: Liang
authors.affiliation: Department of Chemical and Biochemical Engineering, Center for BioProcess Engineering, Technical University of Denmark, Lyngby, Denmark.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Varrone
authors.affiliation: Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085 China ; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Ai-Jie
authors.initials: AJ
authors.lastname: Wang
keywords: Anaerobic digestion; Biogas; Microbial electrolysis cell; Waste activated sludge