Impact of dosing order of the coagulant and flocculant on sludge dewatering performance during the conditioning process

Hou-Feng Wang; Hao Hu; Hua-Jie Wang; Raymond Jianxiong Zeng

doi:10.1016/j.scitotenv.2018.06.161

Impact of dosing order of the coagulant and flocculant on sludge dewatering performance during the conditioning process

Sci Total Environ. 2018 Dec 1:643:1065-1073. doi: 10.1016/j.scitotenv.2018.06.161. Epub 2018 Jun 28.

Authors

Hou-Feng Wang¹, Hao Hu², Hua-Jie Wang³, Raymond Jianxiong Zeng⁴

Affiliations

¹ Centre of Biological Wastewater Treatment and Resource Recovery, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China; CAS Key Laboratory for Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China.
² CAS Key Laboratory for Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China.
³ CAS Key Laboratory for Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China; School of Environmental and Chemical Engineering, Anhui Vocational and Technical College, Anhui 230011, China.
⁴ Centre of Biological Wastewater Treatment and Resource Recovery, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China; CAS Key Laboratory for Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China. Electronic address: rzeng@ustc.edu.cn.

PMID: 30189523
DOI: 10.1016/j.scitotenv.2018.06.161

Abstract

The combined use of coagulant and flocculant can achieve excellent dewatering performance. In this study, we investigated the impact of dosing order of the coagulant and flocculant on sludge dewatering performance. The results showed that capillary suction time (CST) values during the coagulation-flocculation process decreased 20-25% compared to those during the flocculation-coagulation process using the same doses of additives. Moisture content of the sludge during the coagulation-flocculation process was lower. The dosing order of coagulants and flocculants during the conditioning process was clearly important for sludge dewatering, and the coagulant should be dosed before the flocculant. Furthermore, a mechanism for the different dewatering performance was proposed: larger agglomerated and destabilized colloid particles formed, and more bound water was released into the sludge bulk solution during the coagulation-flocculation process, compared with the flocculation-coagulation process, which resulted in better dewatering performance, as reflected in the CST value and moisture content of the sludge cake. These results enable a better understanding of combined conditioning with coagulants and flocculants on sludge dewatering.

Keywords: Coagulation-flocculation process; Combined conditioning; Dosing order; Flocculation-coagulation process; Mechanism; Sludge dewatering.