Study on short-chain fatty acids production from anaerobic fermentation of waste activated sludge pretreated by alkali-activated ammonium persulfate

Abstract

As a sustainable method for carbon recovery from waste activated sludge (WAS), anaerobic fermentation to produce short-chain fatty acids (SCFAs) is often limited by disintegration of WAS. A novel pretreatment method of alkaline-activated ammonium persulfate (AP/Alk), employing an initial pH of 10 and an ammonium persulfate dosage of 1 mM/g VSS (mmol per gram volatile suspended solids), was proposed in this study to enhance disintegration of WAS and yield of SCFAs. It was compared with one control and five pretreatment groups including alkali, persulfate, free ammonia, ammonium persulfate, alkali-activated sodium persulfate to elucidate the synergistic effects of free ammonia and radicals in WAS dissolution and acidogenesis within the AP/Alk system. The highest sludge disintegration degree with 30.3 % and maximum SCFAs production with 295.4 mg COD/g VSS were achieved by using the method. Comparative analysis showed that free ammonia primarily disrupted microbial cells to release intracellular organics, while radicals preferentially degraded tightly bound extracellular polymeric substances (TB-EPS) proteins. The synergistic effects of free ammonia and radicals accelerated accumulation of soluble proteins and polysaccharides, improved selectively enrichment of hydrolytic-acidogenic genera (e.g., Macellibacteroides, Proteiniclasticum, Desulfobulbus), and upregulated antioxidant genes to alleviate oxidative stress, but suppressed SCFAs consumers (e.g., unclassified_f__Comamonadaceae) including methanogens (e.g., Methanosaeta), thereby promoting the accumulation of SCFAs and acetic acid proportion. AP/Alk offers a sustainable strategy for WAS utilization and energy recovery.