Establishing Direct Interspecies Electron Transfer during Laboratory-scale Anaerobic Digestion of Waste Activated Sludge via Biological Ethanol-type Fermentation Pretreatment

Direct interspecies electron transfer (DIET) has been considered as an effective working mode to proceed with syntrophic metabolism, which is not yet established in the anaerobic digesters treating waste activated sludge (WAS), due to the lack of DIET-based syntrophs capable of producing the biological electrical connection and slow hydrolysis/acidification limiting the available substrates for DIET-based syntrophic partners. A strategy of initially pretreating WAS at pH 4.0–4.5 with ethanol-type fermentation enrichments (referred to as Biological Ethanol-type Fermentation Pretreatment, BEFP) for stimulating the methanogenic communities to perform DIET was proposed in this study. Under the SRT of 24 days, methane production and sludge reduction in the digesters treating WAS with BEFP were about 29.8% and 12.3% higher than that without BEFP, respectively. The digested sludge with BEFP presented a high conductance (0.9722 ± 0.0085 uS/cm/g/L-VSS), even more conductive than the aggregates in the digester init...