Problem:

The Johannesburg Water Company treats most of the residential waste water in the Northern Suburbs of Johannesburg, and current treats some 800 Million liters of domestic effluent per day. Using gaseous Chlorine the obvious safety risks were identified and a decision was made to look for an alternative source of disinfection material. All of the treatment plant final effluent flows into rivers and streams which presented another challenge in terms of which type of chemistry could be used.

Solution:

After several months of test work on site and evaluating both the economic viability as well as the product efficacy in terms of proper disinfection properties, DBF (Di Basic Filtrate – a waste stream from the local Arch manufacturing facility in Kempton Park) proved to be the most cost effective and safest way of doing the disinfection on site. 

Currently Arch supplies around 35Mt of DBF to Joburg Water and another 35Mt to ERWAT which treats a combination of industrial and residential effluent. DBF is delivered in tankers to site into bulk tanks (see picture) from where it is pumped into the final chlorine contact chambers and the dosing rate is controlled through measuring free chlorine, Total Bacteria Counts and testing for E Coli. 

Benefits:

The benefits of using DBF at these effluent plants were following: 

• Significant reduction of TBC’s and reduction in E Coli
• Safer product on site
• Dosing and control is easier than gaseous chlorine
• Cost savings to both the customer and Arch were significant
• Product proved to have high commercial value