Investigating the residual aluminum elimination from conventional and enhanced coagulation by phosphate compounds in wastewater treatment process

Aluminum salts are important chemical materials which are extensively used next to in water treatment processes. High concentration of Al in drinking water may produce health problems. Post coagulant addition of phosphate compounds could reduce the concentrations of residual metals without the need of installing new unit processes in existing water treatment plants. Concentrations of residual metals in conventional coagulation were different in various pHs and minimum and maximum concentrations of Al were in pHs of 6.5 and 5.5. Maximum removal of Al took place in pH = 5.5 with 0.37 mg/l reduction. Maximum and minimum concentrations of residual phosphate were detected at pHs of 8.5 and 5.5 respectively. In natural pH concentrations of Al in enhanced coagulation had been increased versus coagulant dose increase (from 0.21 mg/l to 0.35 mg/l). Maximum removal of Al took place by alum dosage of 20 mg/l which reduce the concentration from 0.28 mg/l to 0.07 mg/l. Residual Al concentration in enhanced coagulation at pH of 5.5 increased from 0.55 mg/l to 2.4 mg/l with the increase of coagulant dosages from 10 to 50 mg/l. Maximum removal of residual Al happened in coagulant dosage of 50 mg/l. Temperature increases permanently increased the concentrations of soluble metals and consequently removal efficiency.