La Marie Treatment Plant - New Rapid Filters
La Marie New Treatment Works
The construction of the new 70,000 m3/day capacity treatment plant and associated works which started in March 2003 were completed in July 2005 at a cost of 352 million rupees.
General Description of the Installation
Raw water from Mare aux Vacoas impounding reservoir which is conveyed to La Marie Treatment Plant through two 800 mm diameter Ductile Iron Pipes is first utilised to turn the turbines of a hydro-generator thereby producing a power of 200 kw. this power is utilised by CWA to run the pumps which force water up to la Brasserie Berthaud, Didier and Trou aux Cerfs service reservoirs located at higher levels than that at la Marie. By so doing, savings on the cost of electricity is obtained.
After turning the turbines the water from the hydro-generator goes to the Rapid Mixing Tank where Aluminium Sulphate (commonly called Alum) and Lime are added in order to combine the minute soil particles into big lumps called flocs so that thay can be removed with more ease. These chemicals are fed from a chemical store house where they are safely stored in bags.
The water then travels to the flocculating chamber, containing flocculator, where polyelectrolytes are added to improve the formation of flocs. After this process the water goes to the two settling tanks, each having a capacity of 1400 m3. the flocs settled down therein and are regularly removed through a system of valves at the bottom of the tanks and canal to the sludge drying beds (60 Nos). the clear water from the settling tanks goes to the filter whilst the sludge goes to the sludge drying beds and the spent water from these beds goes to the river. The sludges are then disposed to a dumping area on the site itself in order to fill in a sunken zone on the site. in case it becomes necessary later on, the sludge may be disposed to Mare Chicose.
The eight filters are regularly backwashed to prevent clogging and the backwashed water goes to the spent wash water tank where the fine particles settled down whilst the spent water is recycled through the slow sand filters. The filtered water is then chlorinated and stored in the pure water tanks ready for distribution.
A is noteworthy to emphasize that the new and special feature of this treatment plant is the automatic scada system which records all data pertaining to the plant.