According to the Knowledge Product (KP) studies commissioned by the Department of Environmental Affairs (DEA), mechanical biological treatment (MBT) combines both mechanical and biological treatment methods (open windrow composting, materials recycling facilities, anaerobic digestion and in-vessel composting). These are supported by a combination of pre-treatment and sorting techniques at the beginning of the process, and a selection of emissions control and quality control techniques at the end of the process. The mechanical and biological processes can be arranged in either order, with mechanical treatment preceding biological treatment or vice versa. Typical mechanical treatments will include a range of sorting technologies, from simple sieve / trommel separation techniques through to more advanced positive selection techniques like near infrared (NIR) segregation.
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Read more: (http://www.fge.co.za/project/a-large-waste-to-energy-plant/) In the Western Cape, landfill airspace comes at a premium and as a result landfill tipping fees are higher there than in the rest of the country. Gas prices are also higher in the Western Cape because it is so far removed from the natural gas fields of Mozambique and industrial gases have to be trucked in from Gauteng and further afield. These two factors made it feasible to develop a plant that both a) reduces waste to landfill and b) produces a valuable industrial gas. The New Horizon Energy plant which is part of Clean Energy Africa is designed to process 480 tons/day of municipal solid waste (MSW) using mechanical means to extract the organic fraction. The first stage of the process is the recovery of plastic, glass and cans in a dirty material recovery facility (dMRF). The organic fraction of MSW will be supplemented with 70 tons / day of pure organic waste and processed in an anaerobic digestion (AD) plant to produce approximately 1,250 Nm3 / h of biogas. After hydrogen sulphide (H2S) and volatile organic compounds (VOC) removal and further upgrading, the biogas will be separated into its two main components – biomethane and CO2. After compression to 250 bar the biomethane will be tankered off site as compressed natural gas (CNG) and the liquid CO2 will be stored on site at -25°C, ready for dispatch to industrial clients. Specialised machinery and equipment is used to process the raw MSW to produce the following useful products:
As a result, only the crushed glass and minerals (grit, sand, etc.) from the original raw MSW stream will find their way back to landfill, thereby diverting as much as 90% by volume from landfill. After processing in the AD plant the organic digestate will be dewatered and processed into a nutrient-rich organic fertiliser, thereby ensuring that as little as possible goes to waste.
Western Cape Athlone Park MBT Plant (Photo Jenni Evans, News 24)
According to the Knowledge Product (KP) studies commissioned by the Department of Environmental Affa...