Sludge dewaterability improvement with microbial fuel cell powered electro-Fenton system (MFCⓅEFs): Performance and mechanisms

Throughout the entire process of sludge treatment and disposal, it is crucial to explore stable and efficient techniques to improve sludge dewaterability, which can facilitate subsequent resource utilization and space and cost savings. Traditional Fenton oxidation has been widely researched to enhance the performance of sludge dewaterability, which was limited by the additional energy input and the instabilities of Fe2+ and H2O2. To reduce the consumption of energy and chemicals and further break the rate-limiting step of the iron cycle, a novel and feasible method that constructed microbial fuel cell powered electro-Fenton systems (MFCⓅEFs) with ferrite and biochar electrode (MgFe2O4@BC/CF) was successfully demonstrated. The MFCⓅEFs with MgFe2O4@BC/CF electrode achieved specific resistance filtration and sludge cake water content of 2.52 × 1012 m/kg and 66.54 %. Cellular structure and extracellular polymeric substances (EPS) were disrupted, releasing partially bound water and destroying hydrophilic structures to facilitate sludge flocs aggregation, which was attributed to the oxidation of hydroxyl radicals. The consistent electron supply supplied by MFCⓅEFs and catalytically active sites on the surface of the multifunctional functional group electrode was responsible for producing more hydroxyl radicals and possessing a better oxidizing ability. The study provided an innovative process for sludge dewaterability improvement with high efficiency and low energy consumption, which presented new insights into the green treatment of sludge.

Response of microbes to biochar strengthen nitrogen removal in subsurface flow constructed wetlands: Microbial community structure and metabolite characteristics

Four subsurface flow constructed wetlands (SFCWs) were constructed on the basis of the volume ratio of biochar in common gravel (0%, 10%, 20%, and 30%) for the evaluation of microbe and metabolite characteristics response to biochar addition. The results showed that the biochar added SFCWs provided higher removal efficiencies for ammonium (49.69%-63.51%) and total nitrogen (81.83%-86.36%), compared with pure gravel packed SFCWs for ammonium (47.40%) and total nitrogen (80.75%), respectively. Illumina MiSeq sequencing results revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Firmicutes. Biochar addition can improve the removal of nitrogen by altering microbial community and increasing the relative abundance of Thauera, Candidatus Competibacter, Dechloromonas, Desulfobulbus, Chlorobium, and Thiobacillus. Protein and humic substances were the primary components of extracellular polymeric substance (EPS) in SFCWs. The amount of total EPS considerably decreased with biochar addition, which caused a shift in the EPS functional groups including carbonyl of protein, amide, and hydroxyl groups. Moreover, biochar could enhance the high molecular weight compounds metabolized into low molecular compounds. The results can provide new insights into the use of biochar in the enhancement of nitrogen removal by microbial community and metabolic product characteristics.