Siza water at Frasers Works Ballito treats about 5 Ml of sewage water per day.

Problem

There are two main concerns at this plant:

1. The operation of the Chlorine gas chlorination system is unsafe if it is not properly operated and maintained by skilled staff.
2. The control system to ensure sufficient residual Chlorine levels in the final water, was not difficult to operate and not accurate to comply to the discharge requirements set by Department of Water Affairs (DWA). 

Picture 1 Siza WWTW in Ballito

Solution

Amanzi-Amahle (on behalf of Arch Chemicals) installed a safe, reliable and easy to operate chlorination system that replaced the Chlorine gas system.  This system consists of a HG102 controller and a 180-kg HTH Scientific Chip Doser (see picture 2).

Picture 2 HG102 controller and 180-kg HTH Scientific Chip Doser

This setup involves the installation of a dedicated re-circulating line on the contact chlorine tank which will circulate the final effluent water continuously. The water is re-circulated at a rate of around 16 m³ per hour in order to ensure proper mixing of chemicals and final effluent water.

Linked to the HG102 Controller is a 180-kg HTH Scientific Chip dosing unit that will dissolve automatically an amount of fresh chlorine for dispensing into the re-circulating line. The Doser works on the principle of a water flow directly onto the HTH Scientific Chips and thus dissolving it. The fresh solution is dosed by gravity directly into the chlorine contact tank. 

The HG-102 Controller measures the following parameters: 

• pH
• Redox (Oxidation Reduction Potential)

pH and Redox is done on a continuous basis with probes.

A sample of this water is continuously taken from this re-circulated water line and analyzed by the HG102 controller for ORP level.  Specific set points are entered into the HG-102 Controller for Redox (ORP) in order to keep the Chlorine residual at a constant level of 0.3 mg/l (ppm). 

*Fluctuation in pH level of the water is minimal (between 6.9 – 7.1) and therefore any variation in ORP level will open or close a solenoid valve accordingly which supply water to the HTH Scientific Chip doser. 

This Chlorine residual level will ensure sufficient bacteriological kill and meet the requirements as set by DWA. 

Any variations due to ammonia breakthrough are coped with by this Chlorine controlling system. 

Picture 3 HG102 controller

*Note:

If there is a dramatic fluctuation in pH level of the water, the HG102 system is NOT recommended unless pH control of the water is done together with Chlorine control.

Benefits

• Enhanced operator safety
• Ease of use
• Automatic control
• Cost Effective
• Low maintenance
• Easily calibrated
• Easily sized for all flow rates
• Chemicals -Easily and safely stored