Question

The best available affordable technology (BAAT) to remove Turbidity from water is the coagulation-flocculation process in potable water treatment schemes. Chemical coagulants used include Alum (hydrated Aluminum Sulphate) and Ferric Chloride (FeCl₃).

Zai WTP is an important plant providing treatment for Yarmouk River water (through King Abdalla Canal) to supply part of the water requirements of our capital, Amman.

The plant used Alum to accomplish coagulation-flocculation process from its start until the year 2000 when a decision was made to replace Alum by FeCl₃.

Do some research and prepare a ONE-page write up explaining the reasons behind that switch in the type of the chemical used?

Answer 1

Coagulation process is important in water treatment and the most widely used coagulant examples are Alum and ferric chloride. As by its name aluminium based coagulant and iron based coagulant have different chemical and physical charecterstics while treating water. Here we are discussing the advantage or reason for selectin FeCl3 over Alum for a specific wateer treatment process.

Ferric chloride is a way more superior than Alum and it seems to form a heavy floc that settles nicely. In common understanding it is pretty cheap. But in case of alkanity is a heavy concern then Alum might works better than Ferric chloride.

To determine the effectiveness of these two caogulants in removing both suspended solids and phosphorus , tests were conducted. The orthophosphate removal efficiency for Alum and Ferric chloride were 89% and 93% respectively. Optimum turbidity removal was achieved with 60 mg/l dosage for both Alum and Ferric chloride. Alum is most effective over the limited range of pH 6.5 to 7.5. But in the case of Ferric chloride its effectivenes lies in between the pH range of 4- 11. The ferric floc is is heavier than Alum Floc. Over these advantage alum has been replaced over ferric chloride.