Investigating the Removal of Residual Aluminum Resulting from Water Coagulation Process by Phosphate Compounds

High concentration of aluminum in drinking water may cause adverse health effects. But adding phosphate compounds after coagulant can reduce the concentrations of residual metals. The aim of this study was to apply phosphate compounds to remove residual aluminum resulting from water coagulation process. In this research، Jar tests were used to investigate residual Al removal by use of phosphate compounds in conventional and enhanced coagulation and to determine its affecting parameters. Phosphate compounds were added during rapid mixing. Dosage of alum in conventional coagulation test was 10 mg/l and the tests were done at different temperatures (i. e. 35، 22، and 5o C) and pHs (i. e. 8. 5، 7. 5، 6. 5، and 5. 5). For enhanced coagulation tests، alum at dosages of 10، 20، 30، 40، and 50 mg/l were applied in different pHs (i. e. 5. 5 and normal pH of water). This research showed that phosphate compounds are effective in reducing residual metals. The maximum removal of residual Al was observed at coagulant dosage of 50 mg/l. Concentration of residual metals in conventional coagulation was different at various pHs. Minimum and maximum concentrations of Al were observed in pHs of 6. 5 and 5. 5، respectively. This study showed that addition of phosphate at rapid mixing stage reduces the residual Al. However، the required dosages of phosphate should be increased at pH=5. 5.