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ENGINEERING: Project In Gansbaai Scoops Major Awards


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SSI’s recently commissioned Gansbaai wastewater treatment plant featuring the breakthrough Nereda technology, has scooped top technical excellence awards in 2009 from the SA Institution of Civil Engineers (SAICE) – both regional and national, and won a commendation at the CESA (Consulting Engineers of South Africa) Glenrand-MIB awards.

SSI has introduced a new technologically advanced process in South Africa for the treatment of sewage and industrial wastewater and have completed the first full scale 3Ml/day demonstration plant in the world, for the Overstand Municipality in the Western Cape.

The design of the plant is based on the pioneering Nereda technology introduced by SSI Engineers and Environmental Consultants (SSI). This innovative technology is so efficient that it has eliminated the need for a new 5Ml/d works planned by the municipality. In addition to major capital cost savings of 43%, the new Nereda plant will also achieve operational cost benefits of up to 50% compared with equivalent conventional installations.

The new technology was developed by SSI’s Dutch parent company, the DHV Group, in cooperation with the Delft University of Technology.

The Gansbaai project is the world’s first full scale domestic demonstration sewage treatment works that uses Nereda technology, a major breakthrough in secondary wastewater treatment that forms granules instead of flocs in the reactor.

SSI’s project principal, Pieter Jordaan, says the granules’ settling speed is 10 times faster than that of conventional flocs and can operate at mixed liquor concentrations comparable to that of a membrane bioreactor, whilst maintaining these high settling velocities. The higher biomass concentration allows for a much smaller footprint than is possible with traditional activated sludge plants, an important factor where space for plant expansion is limited.

One of the major process benefits of granular sludge is that simultaneous denitrification is possible due to the ‘anoxic core’ in the granule i.e. both nitrification and denitrification during the aerobic phase,” he adds. “Capital costs for Gansbaai WWTW are calculated to be some 20% lower than the equivalent conventional systems and operating costs about 50% lower. The Gansbaai plant is already producing an extremely high quality effluent” he said.

The initial required upgrade to 2Ml/d was based on standard sequential batch reactor technology which could be easily adapted to the new alternative technology. The installed Nereda plant can treat 4.5Ml/d, making it possible for the municipality to suspend its plans for a new 5Ml/d works planned on another site. “The inlet and disinfection portions of the works have been designed for 5Ml/d, while the reactors and fine bubble aeration system have been designed for the 4.5Ml/d capacity but will require standby units to be added to the system to ensure uninterrupted treatment capability. The existing reactor has been adapted for operation as a sludge thickener. Effluent from the treatment works is being used to irrigate adjacent sports fields with excess final effluent being released to an existing reed bed as a polishing step. The system is controlled by a programmable logic controller set up especially for Nereda and tested by DHV.

Jordaan says a 12-month testing and monitoring programme is currently underway to monitor both the start up performance (growing granular sludge from conventional activated sludge seed) and the long term stability and performance of the granular sludge.

Nereda technology is a major breakthrough in the aerobic treatment of both industrial and municipal wastewater and this project has proved that it is highly appropriate for the upgrading of existing treatment plants, many of which are in a highly distressed state,” Jordaan says.

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