title: Variation in water density related to pollutants removal in wastewater treatment processes and its use in explaining the working principles of the Unifed SBR.
abstract: The wastewater quality of several municipal wastewater treatment plants (MWTPs) in Beijing was studied, and the water densities of different processing units were also measured during the wastewater treatment process. The results clearly showed that the water density declined from influent to effluent of the wastewater treatment process. Meanwhile, the variation in water density had good statistical correlation with the concentrations of total organic carbon, total phosphorus, suspended solids and total solids. Furthermore, the variation in water density could be used to explain the working principles of the Unifed sequencing batch reactor (SBR). Tracer tests were conducted in the Unifed SBR to investigate the hydraulic characteristics of the reactor. The experimental results showed that the variable values of water density from influent to effluent in the Fangzhuang MWTPs were greater than those caused by the temperature difference of >3 °C between the influent and the liquid in the reactor at 13 °C. Moreover, the flow regime of wastewater in the Unifed SBR was affected by the variation in water density, which may lead to stratification or a density current. Ascribed to the appearance of stratification in the Unifed SBR reactor, the water quality of the effluent could not be affected by that of the influent.
authors.affiliation: Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail: songyh@craes.org.cn.
authors.forename: Liancheng
authors.initials: L
authors.lastname: Xiang
authors.affiliation: Beijing University of Civil Engineering and Architecture, Beijing 100044, China.
authors.forename: Junqi
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail: songyh@craes.org.cn.
authors.forename: Yonghui
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail: songyh@craes.org.cn.
authors.forename: Ruixia
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail: songyh@craes.org.cn.
authors.forename: Huibin
authors.initials: H
authors.lastname: Yu
authors.affiliation: Beijing Drainage Group Co., Ltd, Beijing 100044, China.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Gao
authors.affiliation: Beijing Drainage Group Co., Ltd, Beijing 100044, China.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail: songyh@craes.org.cn.
authors.forename: Yunrong
authors.initials: Y
authors.lastname: Dai
mesh_terms: D019149:Bioreactors; D010758:Phosphorus / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D010758:Phosphorus; D062065:Wastewater; D014874:Water Pollutants, Chemical