Treatment of Low Turbidity Water Using Poly-Aluminium Chloride (PAC) and Recycled Sludge: Case study Chinhoyi

Coagulation of low turbidity water using PAC and recycled sludge was studied using a bench scale sedimentation jar test operated at ambient temperature and pressure. Tests were done on low turbidity raw water samples from the river Manyame in Chinhoyi. The coagulants tested were aluminium sulphate (control), PAC and recycled sludge. The effects of the coagulants on the final physical properties of treated water (pH, conductivity, floc quality and most importantly turbidity) were analysed. It was observed that for 60 mg/L dosages, final pH was in the 8.2-8.4 range with an average of 0.24 unit change for PAC and 0.12 for aluminium sulphate, changes in conductivity were less than 20 μScm -1 for both coagulants and PAC was more efficient in turbidity removal at all dosages. The higher efficiencies of PAC where due to the poly-ions formed during hydrolysis. An improvement to the coagulating system was attempted by using settled sludge from clarifiers. At a constant 30 mg/L PAC dosage, the maximum turbidity removal efficiency, 73%, was observed at 6 ml sludge dosage.