Biolysed Sludge Composting for Nitrogen Conservation and Humification Improvements and Mechanisms

Aerobic composting of conventional municipal sludge has always had the problems of nitrogen loss and low humification. In this study, biolysed sludge (BS), polyacrylamids-added sludge (PS) and Fe (III)/CaO-added sludge (FS) were used for composting, respectively, and their effect on the physical-chemical parameters, nitrogen conversion and humification during composting were investigated. The results showed that the dissolved organic matter (DOM) concentration of the BS pile (23.1 ± 0.4 g/kg) was 48.4% and 48.4% higher than the PS (15.5 ± 0.4 g/kg) and FS piles (15.5 ± 0.0 g/kg) in the initial stage of composting and became the lowest after composting, suggesting that the degradation of DOM was promoted in the BS pile. BS can also increase the retention rate of total nitrogen (TN) (27.8% ± 0.8%), higher than that in PS (22.7% ± 1.1%) and FS (24.6% ± 0.5%), which may be due to the lower production of ammonia nitrogen in the BS pile. Compared with PS and FS, BS provided more humic substance (HS) and humic acid (HA) for composting and the HA contents of the compost products were 34.4 ± 1.0, 35.4 ± 0.2 and 34.0 ± 0.3 mg/g in the PS, BS and FS treated piles, respectively. Fourier transform infrared and the excitation-emission matrix revealed that BS and FS promoted the aromaticity and stability of HA. The degree of polymerization (DP) of the products from the BS (1.48) and FS piles (1.56) was higher than that of the PS pile (1.36). However, the germination index (GI) value (133.4% ± 6.0%) of FS was lower than that of PS (152.3% ± 6.2%) and BS (158.3% ± 0.8%), showing that the products of FS composting contain more plant biotoxicity. Thus, compared with PS and FS, BS can increase the nitrogen retention rate and the maturity of the compost.