WASTEWATER SLUDGE
WASTEWATER SLUDGE – a growing liability or existing resource? Largely driven by legislation, wastewater sludge is increasingly viewed as a resource. Rudi Botha, senior water sector analyst at GreenCape*, talks to WASA about wastewater sludge beneficiation and its circular economy solutions.
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he Department of Forestry, Fisheries and the Environment, and the waste management divisions of municipalities largely consider waste as a resource. This perception has filtered into the water industry, where the energy and resource recovery from wastewater sludge is regarded as an attractive business model. However, our sector has not yet made the requisite shift where wastewater sludge transitions from a growing liability to a resource. Wastewater sludge is still a nuisance in terms of water management and is seldom a focus of the treatment process,” explains Botha. “If sludge were viewed as a valuable resource and there were an emphasis on how to harness that resource, the treatment process would change.
Rudi Botha, senior water sector analyst, GreenCape
This would make it easier to recover the treated water from wastewater, as well as nutrients, energy and soil conditioners,” adds Botha.
Growing liability
The City of Tshwane has an agreement with a fertiliser manufacturer to process their sludge into compost for blending Transportation and disposal costs of wastewater sludge per metro by disposal method into fertiliser products. (GreenCape Water MIR 2021) However, the other metros are facing transport and disposal costs of about R330 million per year. The disposal of wastewater sludges is an enormous cost to the operations of wastewater treatment works (WWTWs). The City of Cape Town (CCT), for example, currently spends around R60 million per year to
dispose of (or apply to land) about 200 dry tonnes per day of dewatered primary and waste activated sludge (WAS) it generates, with an average moisture content of 83% (ranging between 58% and 92%). This amounts to 74% of provincial sludge production. Half of the CCT’s sludge (the WAS) is in dry mass and applied to agricultural land, while the other half (primary and blended sludge) is treated and sent to the Vissershoek private landfill.
Legislation – a driver to a more circular economy
Waste and wastewater discharge regulations, such as the ban on landfilling of liquid waste, and the Western Cape plan to divert organic waste from landfill (50% diversion targeted this year and 100% by 2027) are key drivers for resource recovery projects at WWTWs. Furthermore, the 2017 amendment to Schedule 2 of the Electricity Regulation Act (No. 4 of 2006) provides the policy and regulatory framework for municipalities to develop their own electricity generation, such as biogas and combined heat and power (CHP) projects. “A circular economy minimises waste; regenerates ecosystems; and keeps products, components, and materials, including biological materials, at their highest use and/or value for as long J A N /F E B 2022
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