Abstract: Enzymatic pretreatment can promote the degradation of organic components in sludge and thereby enhance its anaerobic digestion efficiency. Nevertheless, the high cost of commercial enzymes and the limited hydrolysis efficiency of single enzymes restrict their large-scale promotion and application. In this study, a strain of fungus, Aspergillus tamarii FM2, was isolated and screened from excess sludge (ES)， which could rapidly produce compound enzymes using multi-source organic solid wastes. The hydrolysis and anaerobic digestion efficiency of ES were enhanced by optimizing enzyme production and hydrolysis conditions, and the underlying mechanism was systematically elucidated. The results showed that soybean residue was the optimal solid-state fermentation substrate for Aspergillus tamarii FM2. The optimal enzyme production conditions were determined as follows: a temperature of 30 ℃, a moisture content of 90% of fermentation substrate, and a fermentation duration of 3 days. Under these conditions, the activities of protease, amylase, and cellulase in the compound enzyme-containing fermentation substrate reached 89.8, 89.0, and 17.2 U/g, respectively. The optimal dosage of compound enzyme substrate for pretreatment was 10%. At this point, the soluble chemical oxygen demand and soluble protein content in ES increased by 41.9% and 23.3%, respectively, compared with the control group. Further mechanism analysis revealed that compound enzyme pretreatment effectively promoted the dissolution of organic matter in ES and significantly improved the biodegradability of the pretreated liquid. Meanwhile, it disrupted the surface structure of ES. The preferential degradation order of the main constituents in the pretreated solid changed from structural carbohydrates to protein-amide substances, with the relative content of protein-N decreasing from 71% to 63%. After compound enzyme pretreatment, the methane yield from ES anaerobic digestion reached 209.0 mL/g, which was 84.0% higher than that of the raw sludge. Preliminary analysis of operational costs showed that, compared with other processes, the integrated process of compound enzyme preparation combined with hydrolytic pretreatment for enhancing sludge anaerobic digestion featured low cost and low energy consumption in operational economy, and presented high potential for popularization and practical application.

Key words: organic solid wastes, compound enzyme, excess sludge, pretreatment, anaerobic digestion