Improvement of wastewater sludge dewatering performance using titanium salt coagulants (TSCs) in combination with magnetic nano-particles: Significance of titanium speciation

In this study, the effects of chemical conditioning using titanium salt coagulants (TSCs) of different hydrolysis speciation in combination with magnetic nano-particles on dewatering performance of waste activated sludge were evaluated by means of specific resistance to filtration (SRF) and capillary suction time (CST). The morphological and extracellular polymeric substances (EPS) properties under chemical conditioning were investigated in detail to understand the reaction mechanisms involved. The results showed that the TSC with basicity of 0.5 performed better in improving sludge dewatering performance than other TSCs. Sludge floc formed by TSC0.5 treatment was characterized by larger floc size and higher floc strength than that conditioned by other TSCs. EPS compression and densification were the major mechanisms of sludge conditioning, and TSC0.5 had better performance in compressing EPS structure. In addition, reduction of soluble EPS concentration, especially protein-like substances contributed to improvement of sludge filterability under conditioning. Furthermore, addition of Fe2O3 nanoparticles could further improve dewatering performance and decrease compressibility of sludge system by acting as skeleton builders and enhancing floc strength. The sludge particles aggregation efficiency was effectively improved with addition of nano-Fe2O3. They also were able to bind with protein-like substance in EPS component, which might contribute to promotion of sludge filterability. (C) 2016 Elsevier Ltd. All rights reserved.