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. 

Solution 

Fig 2  Industrial Feeder at conditioning canals

A HTH® 250-kg Industrial Doser unit was installed at the beginning of the conditioning canals just after the lime and flocculant dosage point at the raw water inlet of this plant. It was filled with HTH® Scientific™ Chips (68% available Chlorine Calcium hypochlorite) and dosed into both canals (A & B) at an initial rate of 9 ppm. The dosage was controlled on the measured Chlorine residual level at the end of the canals, prior to the DAFF units. The optimum Chlorine residual was controlled at 0.4 – 0.6 ppm.

Chlorine residual measurements after the DAFF units were measured at 0 ppm which is the ideal level due to the GAC filers that follow the treatment process. 

The Rietvlei Potable water treatment plant was able to effectively mitigate the effects of ceratium plagued water on the filter run cycle and backwash frequency resulting in substantial cost savings based on consistent plant throughput of 40 - 46 Ml/day together with water savings on backwash water reductions.

Filter blockages and thus backwash cycles were reduced dramatically and optimum production capacity of up to 46 Ml/day can now be maintained continuously.

This pre-chlorination with HTH® Scientific™ Chips has proved to be more financially viable than the cost of the loss of production and the compromised water quality.

Benefits

1. No handling of liquid chemicals.
2. Tailor made for every application need.
3. No electricity needed; gravity feed.
4. Low risk installation.
5. Easy, cost effective installation.
6. Continuous chemical dosing ensures safe drinking water.
7. The HTH® Industrial feeder has proven reliability.
8. Dosage can be regulated with flow through rotameter.

To learn more about the proven advantages of the HTH® Controller, Pulsar® System or HTH® Chips, please contact the ICM Group on +27 (11) 393 9000 or visit our website at hthscientific.co.za