Abstract
A continuous stirred microbial electrochemical reactor (CSMER), comprising of a complete mixing zone (CMZ) and microbial electrochemical zone (MEZ), was used for brewery wastewater treatment. The system realized 75.4 ± 5.7% of TCOD and 64.9 ± 4.9% of TSS when fed with brewery wastewater concomitantly achieving an average maximum power density of 304 ± 31 m W m−2. Cascade utilization of organic matters made the CSMER remove a wider range of substrates compared with a continuous stirred tank reactor (CSTR), in which process 79.1 ± 5.6% of soluble protein and 86.6 ± 2.2% of soluble carbohydrates were degraded by anaerobic digestion in the CMZ and short-chain volatile fatty acids were further decomposed and generated current in the MEZ. Co-existence of fermentative bacteria (Clostridium and Bacteroides, 19.7% and 5.0%), acetogenic bacteria (Syntrophobacter, 20.8%), methanogenic archaea (Methanosaeta and Methanobacterium, 40.3% and 38.4%) and exoelectrogens (Geobacter, 12.4%) as well as a clear spatial distribution and syntrophic interaction among them contributed to the cascade degradation process in CSMER. The CSMER shows great promise for practical wastewater treatment application due to high pre-hydrolysis and acidification rate, high energy recovery and low capital cost.
Highlights
A continuous stirred microbial electrochemical reactor (CSMER), comprising of a complete mixing zone (CMZ) and microbial electrochemical zone (MEZ), was used for brewery wastewater treatment
Brewery wastewater are biodegradable (BOD5/COD > 0.5) and nontoxic containing high content of carbohydrate and protein, which would be suitable for biological treatment[2]
The CSMER operated at a hydraulic retention time (HRT) of 12 h with external resistance fixed at 10 Ω during the three experiment phases
Summary
Apart from Clostridium and Bacteroides, diverse fermentative bacteria including Bacillus, Acetobacterium and Enterococcus existed in CSMERCMZ and CSTRBottom[31,32] These observations suggested that bacterial communities in CSMERCMZ and CSTRBottom played a key role in the primary hydrolysis and acidification of macromolecular organic compounds, revealing by the fact that most s-protein and s-carbohydrates in brewery wastewater were degraded in the CMZ of CSMER and the bottom zone of CSTR. Removal of VFAs from anaerobic digestion of organic matter could accelerate their eventual decomposition to CO2 and H2O40,41, the relatively higher Syntrophobacter and Geobacter in MEZ could contribute to higher methane production rate in CSMER Real wastewater such as brewery and winery wastewater cannot be efficiently used by exoelectrogens because of a high fraction of particulate and fermentative substrate[14]. Effluent TCOD (909 ± 296 mg L−1) was unfavorable for aerobic post-treatment step because of high concentration, performance in terms of substrate removal need to be optimized by adjusting HRT, reducing external resistance, regulating functional microbial communities
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