Consulting engineering and project management company SSI, a subsidiary of the Nertherlands DHV Engineering group, has commissioned a demonstration-scale wastewater treatment plant featuring the Nereda technology, which it believes to be a breakthrough in wastewater treatment.
“Nereda is a revolutionary technology for the treatment of domestic and industrial wastewater,” SSI water sector GM Francis Gibbons tells Engineering News.
The technology was developed by DHV in partnership with the Delft University of Tech- nology, the Dutch Foundation for Applied Water Research and the Technology Foundation.
Gibbons notes that Nereda uses aerobic sludge granules as opposed to conventional activated sledge flocs. The granules settle much faster than conventional flocs and can operate at mixed liquor concentrations comparable with those of a membrane bio- reactor, while maintaining high settling velocities. The higher biomass concentration allows for a much smaller footprint compared with traditional activated sludge plants.
“The Gansbaai wastewater treatment works is a first-in-the-world project that is using the Nereda technology. We refer to the project as a demonstration-scale project. It was completed last year.”
Owing to the reduced footprint, the proposed plant was able to fit onto the existing site and allowance was made to increase the plant capacity by another 3 M∙/d on the same site of the town.
Gansbaai made use of the existing sewer- age works close to the municipal offices. One area is connected through a piped sys- tem; the other areas are serviced by tankers that deliver septic tank effluent to the works. The capacity of the old sewerage works was limited and the quality of the effluent did not conform to the standards set by the Depart- ment of Water and Environmental Affairs. Faced with increased development in the greater Gansbaai, the Overstrand municipality decided to upgrade the capacity of the old sewerage works to 2 M∙/d in the interim.
The existing site had very limited potential for conventional plant expansion, but was centrally located, whereas the intended new site would have been positioned outside the town where additional land would have had to be bought and an environmental-impact assessment conducted.
Nereda guarantees a 30% energy consumption saving.
“At Gansbaai, a 43% saving was achieved by using the technology, leaving the final project costs at R25-million. A capital cost saving of at least 20% can be expected, but varies from project to project,” says Gibbons.
The test results at Gansbaai revealed that a good-quality effluent had been produced, especially considering the variable nature of the sewage delivered to the works, as most of the effluent is carted by tanker from septic tanks.