Cetyltrimethylammonium Bromide Enhances Anaerobic Fermentative Production of Short-Chain Fatty Acids from Waste Activated Sludge

Anaerobic fermentation for short-chain fatty acid (SCFA) production has attracted much attention in the field of waste activated sludge (WAS) treatment. However, the SCFA yield is limited. This study reports a new, efficient, and cost-effective strategy to improve SCFA production from anaerobic fermentation of WAS by cetyltrimethylammonium bromide (CTAB) intervention. Experimental results proved that CTAB improved the yield and quality of SCFAs: a SCFA yield of 273.5 mg of COD/g of volatile suspended solids (VSS) was obtained at 0.03 g/g total suspended solid CTAB addition, which improved by 443% compared with the control (50.3 mg of COD/g of VSS); the percentage of acetic acid raised from 5.6% (without CTAB) to 33.7-44.2% (with CTAB). Mechanism exploration established that CTAB enhanced the disintegration of WAS and improved the biodegradability of released organics, thus offering more available substances for SCFA production. Microbial community analyses showed that CTAB increased the relative abundance of hydrolytic microorganisms (e.g., IMCC26207 and unclassified_f__Enterobacteriaceae) and SCFA producers (e.g., Romboutsia and Escherichia-Shigella), and reduced the relative abundances of SCFA consumers (e.g., Candidatus_Competibacter), which were conducive to SCFA accumulation. The economic analysis showed that CTAB intervention exhibited a comparable or higher economic benefit over some traditional pretreatment approaches (e.g., thermal and CaO₂-based advanced oxidation) for WAS anaerobic fermentation. The findings of this study expand the application field of CTAB and provide new insights into WAS anaerobic fermentation technology.