title: Investigating the effect of hardness cations on coagulation: The aspect of neutralisation through Al(III)-dissolved organic matter (DOM) binding.
abstract: Hardness cations are ubiquitous and abundant in source water, while the effect of hardness on the performance of coagulation for dissolved organic matter (DOM) removal in water treatment remains unclear due to the limitation of methods that can characterise the subtle interactions between DOM, coagulant and hardness cations. This work quantified the competition between coagulant Al3+and hardness cations to bind onto DOM using absorbance spectroscopy acquired at different Al3+concentrations in the absence and presence of Ca2+or Mg2+. The results indicate that, in the presence of either Mg2+or Ca2+, an increasing depression of the binding of Al3+-DOM could be observed in the differential spectra of DOM with the increasing of Mg2+or Ca2+at a level of 10, 100 and 1000 μM, with the observation being more significant at higher pH from 6.5 to 8.5. The results of zeta potentials of DOM indicate that the competition of hardness cations results in the negative DOM being less efficiently neutralised by Al3+. This study demonstrates that the removal of DOM by coagulation would significantly deteriorate with the presence of hardness cations, which would compete with coagulant Al3+to neutralise the unsaturated sites in DOM.
authors.affiliation: Department of Environmental Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China.
authors.forename: Yuxuan
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Environmental Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China. Electronic address: yanmq@pku.edu.cn.
authors.forename: Mingquan
authors.initials: M
authors.lastname: Yan
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, CAS, POB 2871, Beijing 100085, China.
authors.forename: Ruiping
authors.initials: R
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, CAS, POB 2871, Beijing 100085, China.
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, CAS, POB 2871, Beijing 100085, China.
authors.forename: Jiuhui
authors.initials: J
authors.lastname: Qu
mesh_terms: D002412:Cations; D006244:Hardness; D009930:Organic Chemicals / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry; D018508:Water Purification
chemical_list: D002412:Cations; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical
keywords: Aluminum; Coagulation; Differential absorbance spectra; Dissolved organic matter; Hardness cation; Neutralisation