59 / 2021-06-30 10:17:48

New insight into sludge dewatering by bioleaching using acidified sludge as inoculum: Extracellular polymeric substance and microbial community succession

Bioleaching; Acidified sludge; Dewatering; Extracellular polymeric substances; Bacterial community

Bioleaching is a biological conditioning technology for sludge, which not only improves sludge dewatering performance but also removes heavy metals from sludge. The study proposed the acidified sludge as a novel inoculum to enhance sludge dewaterability during bioleaching process. The distribution of extracellular polymeric substance and microbial community diversity were investigated to elucidate the dewatering mechanism. Three treatments including: blank group (T1), Fe²⁺ addition group (T2) and acidified sludge and Fe²⁺ addition group (T3) were conducted. Results demonstrated that the acidified sludge can effectively improve the dewatering performance of sludge. After 48 h conditioning, the capillary suction time (CST) and specific resistance of filtration (SRF) of T3 decreased from 157.6 s and 125.3 ×10¹¹m/kg of raw sludge to 40.9 s and 5.27×10¹¹m/kg. The blank group and Fe²⁺ addition did not result in significant improvement in sludge dewaterability. A positive correlation was found between CST/SRF and PN in TB-EPS with the correlation coefficients were R=0.985 (P<0.05) and R=0.972 (P<0.05), respectively. However, the PS in TB-EPS showed a rather poor correlation with CST and SRF and the R values were only 0.22 and 0.20. Furthermore, based on the results of 3D-EEM, the decrease of tyrosine and tryptophan protein-like substances in bioleached sludge played an important role in improving sludge dewaterability. The results of microbial diversity revealed that about 3.35 % Acidithiobacillus was found, which was the most commonly bioleaching microbes. In addition, other acid-tolerant microorganisms were observed in acidified sludge, such as Acidocella.sp (3.47%), Romboutsia sp. (5.11%), Competibacter sp. (6.27%) and so on. These microorganisms played a crucial role in destruction of sludge floc structure by altering EPS composition and decomposing dissolved organic matter presented in EPS. Therefore, the acidified sludge has potential and application prospects to improve sludge dewatering and reduce the environmental risk for sludge land utilization.