Enhancement of waste activated sludge hydrolysate digestion efficiency via promotion of direct interspecies electron transfer

초록

Anaerobic digestion (AD) of waste activated sludge (WAS) yields low methane (CH4) because extracellular polymeric substances hinder hydrolysis and limit its biodegradability. Pretreatment methods such as alkaline or mechanical disruption can enhance solubilization; however, the resulting hydrolysate often contains recalcitrant compounds that inhibit further degradation. In this study, a combination of alkali along with ultrasonication was applied to enhance the solubilization of WAS, followed by CH4 production under AD. Pretreated results showed alkaline (pH = 12) + ultrasonication (30 min) showed 300 % higher solubilization compared to ultrasonication (60 min) alone. Batch experiments (with and without Fe3O4) were conducted, and the results showed that pretreated hydrolysate supplemented Fe3O4 showed higher CH4 yield than their control counterparts (up to 85 %). To validate the batch results of pretreated hydrolysate, a continuous operation was conducted without (Control) and with an electric voltage reactor (EVR) at different organic loading rates (OLR) up to 4 g chemical oxygen demand (COD)/L/d. The results showed that EVR enhanced the CH4 production by 28 % and COD removal by 19 % at 4 g COD/L/d compared to the control. Microbial community analysis highlighted the dominance of Syntrophomonas zehnderi (a fatty acid oxidizer) in EVR, which increased by 27 %, suggesting stronger syntrophic partnerships with methanogens. Genetic profiling further supported these findings, showing a 25 % upregulation in Adenosine triphosphatease related genes and a striking 69 % increase in pili-associated genes, both critical for direct interspecies electron transfer. These results demonstrated that the combined pretreatment (alkali + ultrasonication) offers a promising alternative for enhanced AD of WAS.

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