Study on VFAs production of sludge fermentation with the immobilization of lysozyme on Noria-PEI modified PVA carrier

Sludge anaerobic digestion promoted by enzymes has the advantages of mild reaction, high efficiency and environmental protection etc. However, the difficulty of recovery and poor catalytic stability seriously restrict its application. Enzyme immobilization is the key to solve the above problems. A new type of polyvinyl alcohol(PVA) carrier was prepared by Noria and polyethylenimide(PEI) co-deposition. The effect of lysozyme immobilized with Noria-PEI modified PVA carriers on the efficiency of sludge anaerobic fermentation for VFAs production was studied. The results showed that immobilized lysozyme could enhance sludge fermentation to promote SCOD, and SCOD reached the highest concentration of 2 892.4 mg/L within 36 h, which was 3.4 times higher than in the blank(day 6). VFAs concentration peaked at 2 130.8 mg/L on day 4, mainly comprised of acetic acid and propionic acid, accounting for 61.8%-80.7%. The average particle size and specific surface area of sludge in the immobilized enzyme system were 42.957 μm and 0.413 m2/g, indicating that immobilized enzyme enhanced the hydrolysis of granular sludge. Microbial community analysis showed that the hydrolytic acid-producing phyla of Firmicutes, Proteobacteria and Bacteroides accounted for high proportion in the immobilized enzyme system. At the genus level, Macellibacteroides, Petrimona, Lactobacillu, and Clostridium_sensu_stricto_1 were the main genera, which revealed the mechanism of enhanced VFAs production by the immobilized enzyme at microscopic level.