EXECUTIVE SUMMARY

The Balfour Wastewater Treatment Works (WWTW) is located to the north-west of Balfour town within the Dipaleseng Local Municipality (DLM) and falls under the jurisdiction of the Gert Sibande District Municipality (GSDM) and covers the town of Balfour, the neighbouring township of Siyathemba and a large local abattoir (2Mℓ/day). The existing works (4Mℓ/day) did not have sufficient capacity to properly treat the volume of effluent that it was receiving and urgently required to be upgraded. This project therefore dealt with the upgrading of the Balfour WWTW in order to accommodate current and future sewage loadings produced by the abovementioned areas over the project design horizon.

The existing infrastructure at the works has a theoretical capacity of 4Ml/day (ADWF). However, the current ADWF entering the works was in excess of 6Ml/day. The existing works therefore urgently required a capacity upgrade in addition to the refurbishment of the existing infrastructure. The future projected sewage design flow for the works over a 20 year design horizon (by year 2038) is estimated to be 12Ml/day ADWF undertaken in two phases.

The existing infrastructure namely an inlet works, biological reactor, clarifiers, chlorine contact chamber and drying beds would be supplemented with a new primary settling tank, digestor and pump sumps to form the first 6Ml/day module which would be operational upon completion of Phase 2. A new 6Ml/day would be constructed under Phase 3 with identical elements to provide a total of 12Ml/day.       

Process Design Considerations and Design Loadings

There where high levels of organic loads entering the works during times when peak flows are received from large local abattoir, resulting in major fluctuations in organic loading over the course of a day. The fluctuation in organic loading will detrimentally affect the ability of the works to successfully treat the effluent to the required discharge standards on an ongoing basis. A balancing facility has therefore been incorporated into the design of the works to allow for the diversion of flow during peak flow periods.

The concentration of most of the determinants was significantly reduced after the sample had been allowed to settle which indicated that the incorporation of primary settling tanks into the design would greatly assist the treatment process. This would be supplemented by the incorporation of a new coarse screen, primary settling tanks, biological reactor, concrete anaerobic digesters, gas handling facilities, secondary settling tanks, subsequent pump sumps, chlorine contact facilities and chamber and drying beds.

The effluent entering the works was an average COD of 1 500mg/l, the maximum loadings that the works is able to treat (to general limits), are provided below which is significantly higher than the industry norms and standard from DWS.

It was therefore imperative that more stringent pre-treatment requirements (than those currently allowed for within the MOA) are imposed on the large local abattoir and furthermore undertake to carry out pre-treatment of their effluent to within these revised limits before the effluent produced by the abattoir is discharged into the waterborne sewerage system.