Ca(ClO)2 pretreatment enhancing suspended solids removal through flocculation from digested dairy wastewater and its mechanisms

Xinyue Ma; Ziyan Cheng; Wenjing Bai; Rui Tang; Guangxue Wu; Xinmin Zhan; Zhen-Hu Hu

doi:10.1016/j.scitotenv.2022.159080

Ca(ClO)₂ pretreatment enhancing suspended solids removal through flocculation from digested dairy wastewater and its mechanisms

Sci Total Environ. 2023 Jan 15;856(Pt 1):159080. doi: 10.1016/j.scitotenv.2022.159080. Epub 2022 Sep 28.

Authors

Xinyue Ma¹, Ziyan Cheng¹, Wenjing Bai¹, Rui Tang², Guangxue Wu³, Xinmin Zhan³, Zhen-Hu Hu⁴

Affiliations

¹ Anhui Engineering Laboratory of Rural Water Environment and Resource, School of Civil Engineering, Hefei University of Technology, Hefei 230009, China.
² Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, Shanghai University of Electric Power, Shanghai 200090, China.
³ Civil Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland.
⁴ Anhui Engineering Laboratory of Rural Water Environment and Resource, School of Civil Engineering, Hefei University of Technology, Hefei 230009, China; Anhui Province Key Laboratory of Industrial Wastewater and Environmental Treatment, Hefei 230024, China. Electronic address: zhhu@hfut.edu.cn.

PMID: 36179835
DOI: 10.1016/j.scitotenv.2022.159080

Abstract

Intensive animal farming produces large volume of digested liquid, and overdose application often causes the pollution of surface water and groundwater. Therefore, post-treatment is very necessary for the discharging of surplus digested liquid, but the removal of high concentrations of suspended solids (SS) in the digested liquid is a challenge. In this study, the effect of Ca(ClO)₂ pretreatment on SS flocculation removal of digested dairy wastewater was investigated. The results showed that, without Ca(ClO)₂ pretreatment, the flocculation by polyacrylamide (PAM), polyferric sulfate (PFS) or polymeric aluminum chloride (PAC) only removed 42.6 %-50.4 % SS from anaerobic digested liquid. With the combination of Ca(ClO)₂ pretreatment and PAC flocculation together, the SS removal efficiency can reach 80 %. The total chemical oxygen demand (TCOD) removal had a similar trend with SS removal, but soluble chemical oxygen demand (SCOD) removal was less affected by the pretreatment and flocculation. More than 75 % of orthophosphate (SRP) and total soluble phosphorus (TSP) was removed after Ca(ClO)₂ pretreatment and flocculation with PFS or PAC. Ca(ClO)₂ pretreatment also effectively inactivated fecal bacteria. The mechanisms of Ca(ClO)₂ pretreatment enhancing SS flocculation removal were further elucidated. The SS removal was the action of ClO^- and Ca²⁺ together. The function of ClO^- was to break down suspended particles, change the surface, and decrease the absolute Zeta potential, while the function of Ca²⁺ was to form precipitation. This result indicates that Ca(ClO)₂ pretreatment can effectively enhance the SS flocculation removal of anaerobic digested liquid.

Keywords: Calcium hypochlorite; Digested dairy wastewater; Flocculation; Pretreatment; Suspended solid.

MeSH terms

Biological Oxygen Demand Analysis
Flocculation
Waste Disposal, Fluid* / methods
Wastewater*

Substances

Waste Water
ferric sulfate