Water treatment plant unit sizing for a growing town

Mopane Local Municipality supplies a town of about 62,000 people from a treatment works built in 1979 for 25,000. The works now runs above its capacity in summer, filters are backwashed by hand, and the town has had boil-water notices twice in two years after heavy rain made the river muddy. Several suburbs get water only on alternate days.

The municipality has funding for a feasibility design of a new works on the same site and wants it in eight weeks. You are the graduate engineer on the consultant's team, responsible for demand and unit sizing.

What you know: - population of 62,000 today, growing at about 2.4% a year; the design horizon is 30 years; - average domestic demand of about 150 litres per person per day, plus commercial and institutional demand of about 15% of domestic, and current non-revenue water of 32%, which the municipality wants to bring down to 20%; - raw water from a river weir, with turbidity between 15 NTU in winter and 400 NTU after summer storms, some colour, and occasional algae; - the plant must meet the national drinking water standard (SANS 241 in South Africa; IS 10500 if you adapt it for an Indian town); - 1.2 hectares of flat land beside the old works.

You will forecast demand, choose a conventional or alternative process, and size the units: rapid mixing, flocculation, clarification, rapid gravity filters, disinfection and clear water storage. You will draw a site layout and hydraulic profile and give a cost estimate.

Done means a feasibility design with a treatment capacity in Ml/day, each unit sized with its design criteria shown, a layout that fits the site, and a short report the municipality can use to apply for construction funding.