Investigating opportunities for use of alternative coagulants for drinking water treatment at Morton Jaffray Water Treatment works, Harare, Zimbabwe

Drinking water treatment at Harare's main water works, Morton Jaffray Water Treatment Works (MJWTW), has been a challenge due to source (Lake Chivero) pollution, and the efficacy of some of the processes and chemicals including aluminium sulphate (alum) has been questioned. This study investigated the use of an alternative coagulant to the traditional use of alum at MJWTW. The effectiveness of five coagulants, namely Anhydrous Poly Aluminium Chloride (APAC), Poly Aluminium Chloride (PAC), Primco 100, Zetafloc 4030 and alum (control) was investigated by flocculation tests in a laboratory using Lake Chivero water. Parameters analysed included pH, turbidity, Electrical Conductivity (EC) and chlorophyll-a for raw water and treated water. Raw water mean pH was 7 ± 0.4, turbidity (3.3 ± 0.2 NTU), EC (337 ± 5.0 μS/cm) and chlorophyll-a concentration (2.28 μg/L). Primco 100 had the best performance with the lowest optimum dosage of 25 mg/L while alum had the highest dosage of 55 mg/L. APAC, PAC, Primco 100 and Zetafloc 4030 did not change the pH of water significantly but alum did. The study concluded that Primco 100 was the most suitable coagulant and could be an alternative to alum.