Enzyme immobilization on amino-functionalized Fe3O4@SiO2 via electrostatic interaction with enhancing biocatalysis in sludge dewatering

Enzymes have important advantages in sludge dewatering, but their catalytic performance is limited by their poor activity and stability. To address this issue, we develop a series of immobilized enzymes (immobilized acid protease, IE 1; immobilized pectinase, IE 2; immobilized laccase, IE 3) prepared by the electrostatic interaction between the Fe3O4@SiO2-NH2 as immobilized carrier and the free enzyme, and used for sludge dewatering. As-obtained immobilized enzymes endowed high efficiency and stable sludge dewatering performance in a wide pH range, and had the best dewatering performance when the pH was 5. Specifically, the specific resistance filtration (SRF) performance of the immobilized enzyme at pH 5 was better than that of the control group, and the order was FE 3, 3.84 × 1013 m kg−1 > FE 1, 2.52 × 1013 m kg−1 > CL 1, 2.16 × 1013 m kg−1 > CL 2, 1.34 × 1013 m kg−1 > FE 2, 2.06 × 1013 m kg−1 > IE 2, 0.89 × 1013 m kg−1 > IE 1, 0.82 × 1013 m kg−1 > IE 3, 0.73 × 1013 m kg−1. Such improvement is attributed to two respects: Firstly, the immobilized enzyme has good activity, stability, and abundant functional groups on the surface, which is conducive to the attachment and continuous decomposition of organic matter. Secondly, the solid immobilized carrier can construct the skeleton structure in situ and effectively promote the release of water in sludge. This study provides a feasible way for the practical application of biological enzyme in sludge dewatering.