Since achieving mechanical completion of the sewage treatment plant at SASOL’s Shondoni Mine, in April 2016, Prentec has been responsible for the operation of the plant and consistently achieving Special Limits effluent water quality standards.
Original equipment manufacturer Prentec was responsible for the detailed design, procurement, project management, construction, commissioning and as is currently operating the plant on behalf of SASOL for a period of two years.
Due to the unique integration of Biological Nutrient Removal (BNR) into the design of the Sequential Batch Reactors (SBRs), the plant is able to meet the South African National Standards’ special limits for treated effluent, ensuring that phosphate and nitrate released back into circulation are lower than for conventional STPs.
By scheduling regular sludge re-cycles and including system specific chemical dosing, this becomes an effective, reliable solution for handling sewage from the mining complex, as well as soapy water and coal fines from change houses, workshops and offices.
The plant treats 200 cubic metres of sewage per day on a 50m x 30m footprint and is fully automated via its comprehensive Human Machine Interface (HMI) control system. The STP requires a considerable amount of integrated instrumentation for the purposes of careful plant monitoring for extra assurance that the special limits are met.
Site features include an inlet works with screens and grit channels, and a main raw sewage sump which acts as a buffer tank for incoming sewage. The 200 cubic metres per day is treated with two 8.6m diameter SBR tanks with surface aerators. These lead into a surge tank which, combined with the sump assists with buffering and handling peak flows.
Tertiary treatment has been provided by means of Deep-bed Upflow or “DUP” filters followed by final disinfection with chlorine. The plant’s waste handling is conducted entirely on-site by means sludge drying beds and a small incinerator – thus drastically reducing sludge volumes while also eliminating the need for sludge-transport logistics.
Although SBRs are typically associated with conventional domestic sewage treatment, projects such as this show that the BNR-SBR integrated technology is applicable for technically exceptional applications and provide a novel capability in the local market.