Wastewater sludge dewaterability enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation.
Chemical conditioning is one of the most important processes for improve the performance of sludge dewatering device. Aluminum salt coagulant has been widely used in wastewater and sludge treatment. It is generally accepted that pre-formed speciation of aluminum salt coagulants (ASC) has an important influence on coagulation/flocculation performance. In this study, the interaction mechanisms between sludge particles and aluminum salt coagulants with different speciation of hydroxy aluminum were investigated by characterizing the changes in morphological and EPS properties. It was found that middle polymer state aluminum (Alb) and high polymer state aluminum (Alc) performed better than monomer aluminum and oligomeric state aluminum (Ala) in reduction of specific resistance to filtration (SRF) and compressibility of wastewater sludge due to their higher charge neutralization and formed more compact flocs. Sludge was significantly acidified after addition Ala, while pH was much more stable under Alband Alcconditioning due to their hydrolysis stability. The size of sludge flocs conditioned with Alband Alcwas small but flocs structure was denser and more compact, and floc strength is higher, while that formed from Alais relatively large, but floc structure was loose, floc strength is relatively lower. Scanning environmental microscope analysis revealed that sludge flocs conditioned by Alband Alc(especially PAC2.5and Al13) exhibited obvious botryoidal structure, this is because sludge flocs formed by Alband Alcwere more compact and floc strength is high, it was easy generated plentiful tiny channels for water release. In addition, polymeric aluminum salt coagulant (Alb, Alc) had better performance in compressing extracellular polymeric substances (EPS) structure and removing sticky protein-like substances from soluble EPS fraction, contributing to improvement of sludge filtration performance. Therefore, this study provides a novel solution for improving sludge dewatering property by controlling aluminum speciation.
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Bingdi
B
Cao
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China. Electronic address: zhwj_1986@126.com.
Weijun
W
Zhang
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China.
Qiandi
Q
Wang
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China.
Yangrui
Y
Huang
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China.
Chenrui
C
Meng
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China. Electronic address: wgds@rcees.ac.cn.
Dongsheng
D
Wang
D000535:Aluminum; D005374:Filtration; D005427:Flocculation; D012722:Sewage / Q000737:chemistry*; D062065:Wastewater
D000535:Aluminum; D012722:Sewage; D062065:Wastewater
Aluminum salt coagulants; Aluminum speciation; Extracellular polymeric substances; Floc properties; Hydroxy aluminum speciation; Sludge conditioning