HOT SEAT
From appalling to appealing – wastewater sludge beneficiation Managing wastewater sludge represents a significant portion of total wastewater treatment plant (WWTP) costs. To reduce this expense, the volume of sludge can be reduced or alternatively beneficiated into biogas or a saleable product. WASA asks Chris Braybrooke, GM: Marketing at Veolia Services Southern Africa, about the treatment of wastewater sludge.
In 2020, Veolia produced nearly 43 million megawatt hours of energy and treated 47 million tonnes of waste
How is sewage sludge locally managed? Conventional practices related to wastewater sludge management include land disposal, waste piling, landfill disposal and, to a lesser degree, use in agricultural practices. These are becoming less viable, with a ban on liquids to landfill and the plan to reduce solid organic waste to landfill. Furthermore, transport costs and landfilling fees keep increasing. With sludge production increasing daily, the current practices are unsustainable. Unfortunately, on-site land disposal and waste stockpiling
Chris Braybrooke, GM: Marketing, Veolia Services Southern Africa
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have become the standard options for many WWTPs in South Africa. Some of these sludges also find their way into water resources and contaminate them. Bold steps must be taken to ensure that these volumes are reduced, made safe and valorised where possible. This would include looking at fertiliser production, materials of construction, and biosolids
A typical modern wastewater and sludge treatment diagram
used to produce energy or heat. Innovative solutions are available to reduce wastewater sludge and turn it into a resource. How can wastewater sludge create biogas? Anaerobic digestion (which forms part of the secondary step of sludge treatment) is one of the oldest and most
used processes for sludge stabilisation and biogas production. This is where microbes feed on the organic matter, transforming it into methane gas and carbon dioxide when digested. It is possible to increase biogas production by adding co-fermentation agents like grease, untreated (and highly concentrated) sewage and additional bio-waste to the digesters. Typical gas production for sewage sludges ranges from approximately 400-450 m3 per tonne. The biogas is removed from the digested sludge by air stripping in the gas removal unit before the sludge is fed further to the intermediate storage. Digester biogas would normally contain small amounts of water and hydrogen sulfide (< 0.01 %). This could cause corrosion
