Hydroxylamine enhanced Fe(Ⅱ)-activated peracetic acid process to promote short-chain fatty acid production during sludge anaerobic fermentation

Short-chain fatty acids (SCFAs) production was limited by low organic matters solubilization and methanogens rapid consumption during sludge anaerobic fermentation. The HA/Fe(Ⅱ)/PAA pretreatment system was employed to solve these issues in this study. Results showed that HA/Fe(Ⅱ)/PAA pretreatment significantly enhanced the disintegration of sludge cells and EPS, improved the dissolution of organic matter and the biodegradability of sludge, thereby promoting the production of SCFAs. The optimal SCFAs production achieved with HA/Fe(Ⅱ)/PAA pretreatment was 2527.62 mg COD/L, approximately 5.14 times that of the blank group, with acetic acid accounting for 64.94 %. Further research indicated that for HA/Fe(Ⅱ)/PAA system, the introduction of HA can accelerate Fe(Ⅱ)/Fe(Ⅲ) cycle, and promote the production of active species, as ·OH, R-O·, and Fe^IVO²⁺. Moreover, HA/Fe(Ⅱ)/PAA pretreatment significantly increased the activity of hydrolysis and acidification enzymes and inhibited the activity of methanogenic enzymes. Meanwhile, the microbial community analyses further confirmed that HA/Fe(Ⅱ)/PAA can enrich the SCFAs-forming microorganisms and inhibit SCFAs-consuming microorganisms. All of these factors were conducive to the accumulation of SCFAs. This study demonstrated that HA/Fe(Ⅱ)/PAA pretreatment can effectively promote high-level SCFAs production, providing new insights for high-value resource recovery from sludge.