Enhanced Anaerobic Wastewater Treatment by a Binary Electroactive Material: Pseudocapacitance/Conductance-Mediated Microbial Interspecies Electron Transfer

Abstract

Anaerobic digestion (AD) is a promising method to treat organic matter. However, AD performance was limited by the inefficient electron transfer and metabolism imbalance between acid-producing bacteria and methanogens. In this study, a novel binary electroactive material (Fe 3 O 4 @biochar) with pseudocapacitance (1.4 F/g) and conductance (10.2 μS/cm) was exploited to store-release electrons as well as enhance the direct electron transfer between acid-producing bacteria and methanogens during the AD process. The mechanism of pseudocapacitance/conductance on mediating interspecies electron transfer was deeply studied at each stage of AD. In the hydrolysis acidification stage, the pseudocapacitance of Fe 3 O 4 @biochar acting as electron acceptors proceeded NADH/NAD + transformation of bacteria to promote ATP synthesis by 21% which supported energy for organics decomposition. In the methanogenesis stage, the conductance of Fe 3 O 4 @biochar helped the microbes establish direct interspecies electron transfer (DIET) to increase the coenzyme F 420 content by 66% and then improve methane production by 13%. In the complete AD experiment, electrons generated from acid-producing bacteria were rapidly transported to methanogens via conductors. Excess electrons were buffered by the pseudocapacitor and then gradually released to methanogens which alleviated the drastic drop in pH. These findings provided a strategy to enhance the electron transfer in anaerobic treatment as well as guided the design of electroactive materials.

Geobacter grbiciae—A New Electron Donor in the Formation of Co-Cultures via Direct Interspecies Electron Transfer

“…This stimulatory effect may be ascribed to the establishment of DIET between G. grbiciae and M. barkeri 800 with conductive particle materials acting as electron conduits. Previous studies on DIET have indicated that some (semi) conductive materials (including magnetite, carbon cloth, GAC, and biochar) can accelerate the direct electron transfer between microbes [7,10,13,[18][19][20][21][22][23][24][25][26][27]34,35]. Methane was generated at a faster rate and higher levels in co-cultures supplemented with GAC than in co-cultures supplemented with magnetite during the early growth phase.…”

“…Subsequently, various co-cultures that exchange electrons through DIET have been reported [5,[12][13][14][15][16][17][18] and primarily involve Geobacter species and methanogens. Moreover, the effects of various conductive materials on DIET have also been reported [7,10,[18][19][20][21][22][23][24][25][26][27]. The continuing increase in the number of microbes identified to carry out electron exchange through DIET indicates that DIET is a syntrophic metabolism that is more prevalent in nature than previously thought.…”

Insight into the Pseudocapacitive Behavior of Electroactive Biofilms in Response to Dynamic-Controlled Electron Transfer and Metabolism Kinetics for Current Generation in Water Treatment

“…It was reported that biopseudocapacitance exhibited by EBs enables rapid biofilm enrichment and facilitates efficient nitrate reduction in a bioelectrochemical denitrification system . It was also demonstrated that the pseudocapacitive and conductive mediators regulated the interspecies electron transfer rates (acid-producing bacteria and methanogens) and highly improved methane production in anaerobic digestion systems . These findings provide a new understanding of the regulation of biological metabolism processes involving electroactive biofilms centered on exoelectrogens.…”

Distinct Mechanisms on Accelerating Electron Transfer to Facilitate Two-Stage Anaerobic Digestion Modulated by Various Microalgae Biochar

“…Due to the poor capacity of methanogens to degrade organic macromolecules and bacteria (anaerobic microorganisms and acidogenic bacteria) can hardly generate methane, an efficient AD process requires balanced syntrophic metabolism between various microorganisms with fast electron exchange. A higher electron transfer rate during AD can lead to a faster mutualistic metabolism process between various functional bacterial species, improving the VFAs and H 2 production rate during the acidification process and the VFAs consumption rate to produce CH 4 during the methanogenesis process. , In another word, the electron transfer rate during the AD process is a principal factor that influence the functional bacteria activity as well as the VFAs generation and consumption rate, thus determining the final biohythane production rate …”