Significantly enhanced dewatering performance of drinking water sludge from a coagulation process using a novel chitosan–aluminum chloride composite coagulant in the treatment of cyanobacteria-laden source water

Abstract

The enhanced dewatering performance and the fate of cyanobacterial cells in the filtration of cyanobacteria-laden sludge, generated by a coagulation process using a novel composite chitosan–aluminum chloride (CTSAC) coagulant, were systemically studied. Two other cyanobacteria-laden sludge, aluminum chloride (AC) sludge and chitosan (CTS) sludge, were also studied to compare dewater performance with CTSAC sludge. Results showed that the dewatering process did not cause cell lysis and microcystins (MCs) release. The level of MCs and extracellular organic matter (EOM) in the filtrate were decreased by adsorption and sieving onto the cake layer formed on the membrane, but dewatering at high vacuum pressure reduced the rejection efficiency. The sludge from the coagulation process using the CTSAC composite displayed better sludge dewaterability and obtained a better quality of filtrate (fewer MCs and EOM) than those from AC and CTS coagulation processes independently. A three-dimensional excitation–emission matrix (EEM) fluorescence measurement indicated that protein-like substances in soluble extracellular polymeric substances (EPS) played a negative role on cyanobacteria-laden sludge dewatering. In addition, CTSAC sludge showed a more compact structure and larger floc sizes than AC sludge and CTS sludge for a strong improvement in the charge neutralization and bridge ability of AC by combining CTS in the composite coagulant. It was further observed that floc size played a more significant role on sludge dewaterability than the degree of compactness. Overall, the preferable dewater performance of CTSAC sludge demonstrated the CTSAC composite coagulant has great potential for the treatment of cyanobacteria-laden source water.