Boosting short chain fatty acids recovery and separation from waste activated sludge via synergistic activation of Na⁺ and lysozyme

Augmentation of the anaerobic treatment efficiency of waste activated sludge (WAS) to achieve better resource utilization is an effective approach for reducing carbon emissions and minimizing solid waste generation. However, resource recovery from WAS is often limited by the insufficient release and hydrolysis of organic matters within microbial cells. To overcome these issues, a novel Na⁺ and lysozyme co-pretreatment method has been used in this study to accelerate the production of short-chain fatty acids (SCFAs) by promoting cell lysis. Experimental results have revealed that the maximal SCFAs production of 302.8 ± 47.8 mg COD/g VSS is achieved with 10 % w/w lysozyme and 0.34 mol/L Na⁺ co-pretreatment on day 2, which is 7.6-fold higher than that of the control. Mechanism exploration has also exposed that Na⁺ and lysozyme exhibit a pronounced synergistic effect in cell lysis, where 1 + 1 > 2. The maximum sludge disintegration degree (DD_M) and SCFAs conversion efficiency have been achieved by combined pretreatment, reaching 68.5 % and 74 %, respectively. The structure of extracellular polymeric substance (EPS) including protein content and looseness are also modified by Na⁺ or Na⁺ + Lysozyme pretreatment, which further confirm the impact of Na⁺ on the permeability of EPS. The carbon sources generated through Na⁺ and lysozyme pretreated WAS can be efficiently recovered through PAC conditioning, with a high recovery rate of 87 %. The Na⁺ and lysozyme reagents implemented in the present study are all non-toxic and cost-effective, thereby promising a green and efficient solution for the carbon recovery and separation from the WAS.