ENGINEERING: SSI's Breakthrough At Wemmershoek
Recent Western Cape Business News
DURING 2009 SSI Engineers and Environmental Consultants made a breakthrough at Gansbaai, where it commissioned the first full-scale domestic sewage treatment project in Africa implementing the cost-effective and sustainable Nereda® wastewater treatment technology.
This was a major departure in secondary wastewater treatment where the biomass forms granules instead of flocs in the reactor - importantly resulting in major capital cost savings on the 5Ml/d project of around R19-million, compared to a traditional treatment process. Operational costs too are considerably less (typically 30 to 50%), according to Pieter Jordaan, SSI’s sector area manager Water: Western Cape.
Now SSI is to repeat the technology with the Stellenbosch Municipality who has appointed the company for the design and project implementation of the upgrade to the existing Wemmershoek Waste Water Treatment Works.
Project principal Jordaan says the R70-m project entails the construction of the upgraded 5Ml/d sewage works at Wemmershoek as well as a new main transfer sewer pipeline from Franschhoek to Wemmershoek and an outfall pipeline to the Berg River. Treated effluent will be pumped back to Franschhoek through a separate rising main to irrigate parks and sports fields.
The upgraded treatment works will replace the existing Franschhoek and La Motte plants and incorporate the existing Wemmershoek works.
The design period was preceded by various investigations and public participation for the selection of the pipeline routes and treatment process. Very strict requirements were set for the quality of the effluent water to be released into the Berg River. Conventional sewage treatment technology cannot be utilised on this site due to space restrictions at the existing Wemmershoek treatment works.
This is not an issue with Nereda® installations as this technology uses a much smaller plant footprint compared to equivalent capacity conventional plants, which in many cases will eliminate the need to purchase additional land for an upgraded wastewater facility.
Two technologies were originally considered; Membrane Bio Reactor (MBR) and the Nereda® Granular Biomass process used at the new Gansbaai treatment works.
The Nereda® option includes a 7km outfall pipeline to below the Berg River Supplemental Pump Station. The projected operating costs of the Nereda® option are substantially lower than MBR due to better energy efficiency which lead to the Nereda® option being selected for implementation, Jordaan says.
Nereda® technology was developed by DHV (SSI’s parent company) in conjunction with the Delft University in the Netherlands. It comprises a process where granular biomass is grown whereas conventional processes make use of activated sludge flocs. The granules settle much faster than conventional flocs and can operate in mixed liquor concentrations comparable to MBR whilst maintaining high settling velocities.
Higher biomass concentrations allow for much smaller reactor tanks and smaller overall plant footprint and as simultaneous denitrification occurs (where both nutrients and phosphates are removed) this usually means chemical-free operations. This win-win process is more environmentally friendly and sustainable, with an attendant cost saving. The Gansbaai plant has proved that the technology is very robust and has produced excellent quality effluent.
Nereda® technology has received various prestigious overseas awards and the Gansbaai project received the 2009 SAICE (SA Institution of Civil Engineers) Technical Excellence Award and a CESA (Consulting Engineers SA) Engineering Excellence commendation.
Jordaan says work on the Wemmershoek project will commence in the first quarter of next year, with the construction period being 18 months.
So confident is he about the Nereda® process, and the economic and environmental savings so compelling, that he believes SSI could well be involved in various similar projects in the future. “A lot of interest is being shown in the technology,” he says.
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