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Energy from effluent

October 2015 News

Veolia Water Technologies South Africa has been awarded the contract to design, build and operate South Africa’s first Biobulk wastewater treatment facility. The plant, owned by Distell in Stellenbosch, will be ready for commissioning in March 2016. On commissioning, a 10-year BOT (build, operate, transfer) agreement comes into force.

Distell has three operational sites in the Stellenbosch area – Adam Tas, Van Ryn and Bergkelder. Over the last four years, Distell has developed its Green Plan to install a common anaerobic water treatment facility that will lower the COD (chemical oxygen demand) load in the outfall to the municipality, harvest the energy in the wastewater and lower the overall cost of effluent treatment.

The selected Veolia Biobulk CSTR (Continuous Stirred Tank Reactor) technology is a green technology and is a robust and proven process that treats industrial effluents with significant amounts of suspended solids. It is the anaerobic equivalent to the conventional activated sludge digestion system. Following an anaerobic suspended bacteria treatment process, the majority of the soluble and solid organic content, measured in COD, is converted into biogas. The Biobulk can be operated as a once-through system or, alternately, biomass can be returned after a clarification stage. The key to the Biobulk design is the manner in which the reactor vessel is mixed and the design of the degassing stage prior to clarification. The biogas is a source of renewable energy and converted into steam for the Distell site.

“The Biobulk system,” says Jaco Oosthuizen, technical manager industrial, Veolia Water Technologies, South Africa, “represents a long term capital savings investment. It brings with it an operating cost saving whereby solids in the effluent need not be removed; they can be converted to biogas (energy) in the reactor.” The effluent in this plant will be treated by the Biothane Biobulk Anaerobic Digester, the heart of the plant. Ancillary equipment includes storage buffer tanks, clarifiers, the centrifuge, boiler and biogas flare. First, the digester reduces the effluent COD content by 94,1%. Next, a clarifier removes suspended solids, in turn followed by Veolia Hydrotech drum filtering for tertiary treatment. This ensures the total suspended solid (TSS) concentration is less than 150 mg/l.

The 10-year BOT contract will enable Veolia to assume full ownership of the plant’s functions for the agreed period. This will ensure an appropriate transition from Veolia’s commissioning teams to its operations team. “Once the plant has been commissioned it will be handed over to our Operations & Maintenance division in the Western Cape. This division will perform all operations and maintenance functions for 10 years,” Oosthuizen explains.

Veolia is mandated to deliver the specified quality of water; carry out ongoing mainten-ance; and ensure the plant’s operating performance is in accordance with set objectives. For this project, Veolia will treat 1000 m³ of effluent per day with an organic load of 8,6 tons COD per day. The treated water will be discharged to the municipal wastewater works. During the process of anaerobic digestion, COD is converted into biogas, which will be transferred from the Biobulk, directly to the biogas boiler. The final effluent discharged to the municipality will contain less than 500 kg COD per day and the suspended solids concentration will be less than 150 mg/l.

“Another advantage of having a BOT contract in place,” Oosthuizen points out, “is that the client pays a set monthly fee for the water treatment.” Veolia finances the plant, which means it retains its interest in the plant. “This ensures the plant remains in peak condition – and we also produce biogas for resource recovery. It is a win-win for both parties.”

Veolia’s operation and maintenance personnel, along with Veolia engineers from Biothane Netherlands, who developed the Biobulk solution, will form part of the commissioning team. Veolia’s operational personnel will be trained, via on-the-job coaching and theoretical training modules, to take over full plant responsibility.

Oosthuizen is of the opinion that Veolia’s pricing structure; the operating cost benefits accrued by the client; the income from the additional biogas produced; and the fact that Biothane Netherlands has extensive experience in anaerobic treatment, are the drivers for being awarded the BOT contract. “Distell took careful consideration of offers on the table,” he concludes, “and with this bold step into green technologies, we feel really proud to be part of such a dominant player in the market place.”

For more information contact Jaco Oosthuizen, Veolia Water Technologies, +27 (0)21 871 1877, jaco.oosthuizen@veolia.com, www.veoliawaterst.co.za





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