Problem

This plant is situated in the residential area in the town Bela Bela.  The old plant used Chlorine gas for post chlorination, but this type of disinfection is a high risk. Due to non compliance on the existing chlorine gas installation and high capital costs requirements for upgrading this facility, an alternative, safe, cost effective chlorination method was opted.

Problem

Fig 1 Schematic diagram of Ceratium-dinoflagellates

Ceratium-dinoflagellates, an algae specie, is most common in the upper depths of the Rietvlei Dam that are exposed to sunlight.  Their existence in this dam water is only at certain periods of the year, especially in winter periods, and cause a problem at the treatment works. This specie contain two mobile outgrowths (flagellae) that help these organisms to swim and are believed to be responsible for the filter blockages and subsequent production loss at the treatment works.

During this abnormal algal bloom it is very difficult, or at all, to maintain an optimum production level of 40 Ml/day. These blocked DAFF units need to be backwashed at more regular intervals and the normal flow of production of 40 Ml/day can no longer be achieved.

To prevent flooding and loss of water due to blockages, production needs to be reduced and the plant is unable to run at its optimum level.