Improving the removal of anions by coagulation and dissolved air flotation in wastewater reclamation

S. H. Chuang, W. C. Chang, T. C. Chang, S. J. You

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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.

Original languageEnglish
Pages (from-to)493-500
Number of pages8
JournalEnvironmental Technology (United Kingdom)
Issue number5
StatePublished - May 2006


  • Anion
  • Coagulation
  • Dissolved air flotation
  • Polyaluminum chloride
  • Wastewater reclamation


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