Lysozyme coupling protease pretreatment to relieve the humic acid inhibition on excess sludge anaerobic fermentation.

[Display omitted] • Enzyme combination behaved better than single enzyme in relieving HA inhibition. • Lysozyme triggered higher hydrolase activities and soluble contents conversion. • Protease enhanced SCFA production via higher EEC and acidogenesis communities. • The balance between hydrolysis and fermentation communities is essential for AF. • Eneyzme cocktail facilitated substrate metabolism and SCFAs synthesis. The asynchronous dosed protease and lysozyme combination pretreatment was proved to be effective in enhancing the anaerobic fermentation of waste activated sludge (WAS). However, humic acid (HA) in the sludge could interact with hydrolase and restrain the hydrolysis efficiency, thus inhibiting short-chain fatty acids (SCFAs) production. This study investigated the effectiveness and mechanism of enzymatic pretreatment against HA. Results showed that the enzyme cocktail method increased the extracellular bioavailable contents by 34 %, which raised SCFAs production by 89.69 % (1269.65 mg COD /L). The balanced ratio of hydrolysis and fermentation communities suggested that the small molecular organics generated by the hydrolysis community could be sufficiently utilized by fermentation communities. The metabolism of amino acids and glucose was facilitated, and the activities of key enzymes were enhanced. These results clarified the effect of asynchronous enzyme cocktail pretreatment against HA inhibition and contributed to SCFAs production, which offered fresh perspectives on carbon recovery. [ABSTRACT FROM AUTHOR]