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Thursday, 15 August 2019 10:29

The technologies of the circular economy: Anaerobic digestion

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Veolia’s Biolbulk Completely Stirred Tank Reactor (CSTR) is used by Distell to treat effluent and harvest biogas for use as a fuel

The circular economy needs a commercially viable technology base capable of transforming and reprocessing our waste into usable products and resources. One such tried-and-tested technology family in the sewage and effluent treatment space is anaerobic digestion. In this article, Veolia Water Technologies South Africa’s Chris Braybrooke discusses the strategic importance of anaerobic digestion in South Africa’s energy, economic and environmental future.

Veolia Water Technologies’ goal for South Africa’s wastewater treatment facilities with suitable COD effluent conditions is to help these plants become 100% energy self-sufficient by utilising their waste as an energy source. In addition to the obvious advantages this will bring to operating and waste disposal costs, it will also help reduce energy demand on South Africa’s national power grid, and, by extension, reduce their requirements for coal-based energy, lowering carbon emissions.

 And yet the science behind one the key technologies of such plants is simple: using anaerobic biological digestion to compost organic matter, which produces biogas (mostly methane) that is then harvested and used as a fuel for the plant’s heating and cogeneration requirements.

Such systems have already been installed or are being piloted by Veolia South Africa for companies in the food and beverage and municipal sectors including Distell and Ethekwini Municipality.

Effluent treatment applications in biofuels, chemical processing, pharmaceutical and pulp and paper are also key industries that could utilise anaerobic digestion to optimise their treatment requirements, as well as achieve greater energy self-sufficiency.

 Veolia Water Technologies covers the complete range of anaerobic digestion applications with specialised technology solutions:

  • Anaerobic wastewater treatment Veolia’s Memthane® Anaerobic Membrane Bioreactor is designed for treating high-strength effluents such as high concentration streams (up to 250 000 ppm), ethanol waste, fat, oil and grease streams, starch slurries and high COD chemical applications. Memthane® is being used to achieve up to 100% energy and heat requirements in applications such as distilleries through biogas production, while efficiently treating complex compounds and reducing disposal costs.
  •  Completely Stirred Tank Reactor (CSTR) For industrial effluents with significantly high amounts of suspended solids, Veolia manufactures the Biobulk CSTR, the anaerobic equivalent to the conventional activated sludge digestion system. This solution is used by Distell to lower the COD load in the outfall to the Stellenbosch Municipality, harvest the energy in the wastewater for reuse and lower the overall cost of effluent treatment.
  • Upflow Anaerobic Sludge Blanket (UASB) Veolia’s Upthane™ UASB treatment system has been used to develop over 500 energy-neutral sewage treatment plants – and other low-strength wastewater applications – across the world utilising anaerobic microorganisms. The biogas contains approximately 75% methane and can be utilised to provide the energy needs of the entire WWTP in a combined heat and power unit.

Completing Veolia’s anaerobic treatment range is its Integrated Fixed Film Activated Sludge System (AnoxKaldnex™ Hybas™); Moving Bed Biofilm Modular Reactor (AnoxKaldnes™ Z – MBBR); and Expanded Granular Sludge Blanket (Biobed®) systems.

Completing Veolia’s anaerobic treatment range is its Integrated Fixed Film Activated Sludge System (AnoxKaldnex™ Hybas™); Moving Bed Biofilm Modular Reactor (AnoxKaldnes™ Z – MBBR); and Expanded Granular Sludge Blanket (Biobed®) systems.

 This family of treatment technologies is helping the wastewater treatment industry to be a pioneer of circular economy approach in our modern cities, where wastewater treatment plants produce their own energy and minimise their solid waste. With greater treatment efficiency, circular energy requirements and reduced demands on bulk electricity, these plants will be key assets in our sustainable future.

Creating syngas from sludgeVeolia’s Research & Development team in France is currently experimenting with a new tiered gasification technology to transform sewage sludge into energy-rich synthesis gas. In gasifying sewage sludge using a mixture of steam and oxygen at 700° – 1 000° C, results to date have demonstrated the technical feasibility of the process in terms of producing a high energy potential gas, rich in hydrogen and methane.

This research and innovation process responds to Veolia’s desire to gradually make its various wastewater treatment sites energy independent.

By using the energy generated from their own waste, wastewater treatment plants could in the future reduce their environmental impact along with their energy bills, ultimately becoming self-sufficient in their energy requirements.

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