title: A simple empirical model for the clarification-thickening process in wastewater treatment plants.
abstract: In wastewater treatment plants (WWTPs), activated sludge is thickened in secondary settling tanks and recycled into the biological reactor to maintain enough biomass for wastewater treatment. Accurately estimating the activated sludge concentration in the lower portion of the secondary clarifiers is of great importance for evaluating and controlling the sludge recycled ratio, ensuring smooth and efficient operation of the WWTP. By dividing the overall activated sludge-thickening curve into a hindered zone and a compression zone, an empirical model describing activated sludge thickening in the compression zone was obtained by empirical regression. This empirical model was developed through experiments conducted using sludge from five WWTPs, and validated by the measured data from a sixth WWTP, which fit the model well (R² = 0.98, p < 0.001). The model requires application of only one parameter, the sludge volume index (SVI), which is readily incorporated into routine analysis. By combining this model with the conservation of mass equation, an empirical model for compression settling was also developed. Finally, the effects of denitrification and addition of a polymer were also analysed because of their effect on sludge thickening, which can be useful for WWTP operation, e.g., improving wastewater treatment or the proper use of the polymer.
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: Y K
authors.initials: YK
authors.lastname: Zhang
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: H C
authors.initials: HC
authors.lastname: Wang
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: L
authors.initials: L
authors.lastname: Qi
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: G H
authors.initials: GH
authors.lastname: Liu
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: Z J
authors.initials: ZJ
authors.lastname: He
authors.affiliation: School of Environment & Natural Resource, Renmin University of China, No. 59 Zhongguancun Street, Haidian District, Beijing 100872, China E-mail: whc@ruc.edu.cn.
authors.forename: H T
authors.initials: HT
authors.lastname: Fan
mesh_terms: D018533:Biomass; D008962:Models, Theoretical; D012722:Sewage; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D012722:Sewage; D062065:Wastewater; D014874:Water Pollutants, Chemical