title: Improving the removal of anions by coagulation and dissolved air flotation in wastewater reclamation.
abstract: This study investigated the feasibility of improving the removal of anions from a secondary effluent by coagulation/flocculation (Coag/Floc) and dissolved air flotation (DAF) using a pilot-scale wastewater reclamation plant in a high-tech industrial park. The pilot plant was equipped with units of Coag/Floc, DAF, activated carbon beds (AC), microfiltration modules (MF) and a reverse-osmosis membrane (RO). It was operated in-situ continuously for around one year to evaluate the performance of anion removal in two processes - the AC-RO process and the DAF-AC-RO process. Long-term experimental results indicated that combining Coag/Floc, DAF and AC units increased the potential of pretreatment to remove anions. The removal efficiencies in Coag/Floc-DAF units were in the order phosphate > fluoride > chloride > sulfate > silicate. The charged complex of PACl flocs revealed a higher affinity for adsorption onto phosphate and fluoride than on chloride, sulfate and silicate. Comparison of the performance of Coag/Floc-DAF-AC units in the DAF-AC-RO process with that of a single AC unit in the AC-RO process demonstrated that adding Coag/Floc-DAF units increased the removal efficiencies of phosphate, fluoride and silicate by approximately 70.0%, 42.7% and 70.1%, respectively. Most of the phosphate and fluoride were removed in Coag/Floc-DAF units, while most of the silicate escaped from the Coag/Floc-DAF units, and was adsorbed and/or trapped in the AC unit. The quality of reclaimed water in the DAF-AC-RO process complied with the requirements of high-tech industries in cleaning processes. Combined units of Coag/Floc-DAF-AC were therefore recommended for use in pretreatment in wastewater reclamation in high-tech industrial parks.
authors.affiliation: Department of Environmental Engineering and Management, Chaoyang University of Technology, Taichung County, 413, Taiwan.
authors.forename: S H
authors.initials: SH
authors.lastname: Chuang
authors.forename: W C
authors.initials: WC
authors.lastname: Chang
authors.forename: T C
authors.initials: TC
authors.lastname: Chang
authors.forename: S J
authors.initials: SJ
authors.lastname: You
mesh_terms: D000388:Air; D000838:Anions / Q000302:isolation & purification*; D007220:Industrial Waste; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D000838:Anions; D007220:Industrial Waste; D014874:Water Pollutants, Chemical