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The discharge of effluents rich in sulphate and nitrate is of increasing concern, as the former leads to mineralisation of surface water, and the latter is a plant nutrient. A process is described whereby sulphate is reduced to sulphide under anaerobic conditions with producer gas as substrate. Sulphide stripped off is then converted to elemental sulphur by reacting it with biologically produced iron(III). The study consisted of laboratory batch and continuous experiments, as well as pilot scale studies. Sulphate was reduced to sulphide at a rate of 1.2 g SO4 1−1 d−1 with H2/CO as substrate, and 2.4 g SO4 1−1 d−1 with only CO as substrate. Nitrate was converted to ammonia in the anaerobic reactor. Sulphide was removed from 2 000 mg 1−1 (as SO4) to less than 90 mg 1−1. The iron(II), produced after reduction of iron(III) with H2S, was oxidised biologically to iron(III). The volumetric reaction rate was 5.5 g Fe 1−1 d−1.

When the operation of 18 waste water treatment plants was taken over by ERWAT, improved sludge management was identified as one of the key objectives. After evaluations, operational strategies were formulated and implemented to align biosolids management with international trends as well as South African Guidelines on permissible utilization and disposal of sludge. Improved sludge management includes minimizing intake of heavy metals from industry through cooperation with local municipalities. Beneficial use of sludge from the Olifantsfontein waste water treatment works was increased through establishing a partnership with the local farming community. Rehabilitation of mine dumps was identified as an option for beneficial use of biosolids.

More than 120 on-line instruments were installed in specially designed instrumentation kiosks throughout the Rand Water purification works during the past three years. This forms part of an ongoing expansion programme in which instrumentation is increasingly used for: (i) process monitoring, (ii) process automation and (iii) monitoring of final water quality. This programme is planned to cover the whole distribution network within the next ten years. Output signals from all instrumentation are relayed via PLCs to run time servers and through the Ethernet to Hewlett Packard Unix systems in the control rooms where continuous monitoring and corrective action will be taken. The real time data will also be directly available via viewer nodes to Scientific and Engineering personnel in the near future for quality monitoring, trend analyses and feedback to consumers.

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