City-Level Decoupling-Case Studies

provide an income to the city through the sale of electricity and carbon credits generated from the captured methane. 62

The design of the Mariannhill landfill thus included three core approaches:

• The ‘naturalistic' containment, treatment and reuse of leachate

Conventional landfill design is responsible for leachate, a liquid waste that can become toxic and contaminate land and water. 63 In collaboration with Enviros UK, Durban Solid Waste designed a treatment system whereby the cells of the Mariannhill landfill are lined with a geomembrane that prevents the escape of leachate, while above the lining a layer of rock and sand allows it to drain off and be collected in a reservoir. 64 Here 30 m 3 are treated by aeration and settlement daily, before being passed through a reedbed. 65 This ‘polished' leachate is reused for on-site irrigation and to settle landfill dust. 66 In addition, constructed wetlands help to remove toxic materials. 67 This closed-loop approach means that environmental contamination by toxic leachate is prevented, and water and energy costs of piped council water are significantly reduced. • The capture of landfill gas for electricity generation Traditional landfills are responsible for significant methane emissions from rotting organic waste. Methane is ten times as potent as carbon dioxide in its global warming effect, but its impact can be significantly reduced by burning it. The Mariannhill landfill turns this waste product into a resource by using it to generate between 450,000 kWh and 650,000 kWh of electricity per month. 68 This allows the site to generate approximately 200,000 – South Africa Rand – R- (approximately US$22,500 69 ) per month from the sale of electricity at a power purchase tariff of between R 0.24/kWh (off-peak) and R 0.36/kWh (peak). 70 Income from the sale of Certified Emission Reductions (CERs) has not yet been received due to the lengthy clean development mechanism process, but about R40 million (US$4.5 million) worth of CERs have been generated since 2007 by the 1MW Mariannhill and 6.5MW Bisasar Road plants together. 71 The Bisasar Road plant on its own has brought in more than R48 million (US$5.4 million) since commissioning. The capital cost of the combined gas-to-electricity project has been approximately R130 million (approximately US$14.5 million), with operational costs of about R10 million (US$1.125 million) per year. 72 These have been partly covered by a R58.74 million (US$6.6 million) loan from the French Development Bank, and a R17.7 million (approximately US$2 million) donation from the South African Department of Trade and Industry. 73 Subject to verification and the sale of CERs, the combined project is expected to break even in approximately 5 years. 74 • The protection and restoration of indigenous vegetation The restoration of the original vegetation to closed cells and border areas of the site is another example of how the Mariannhill design surpasses that of conventional landfills. 75 Existing vegetation is usually destroyed during construction, but the Mariannhill design included an onsite nursery called the Plant Rescue Unit (PRUNIT), to save displaced indigenous plants. The Plant Rescue Unit now also provides low-cost rehabilitation to other closed dumps in the area. 76 The saving and propagation of indigenous vegetation supports local biodiversity, and has also provided jobs for people previously unemployed. It has also saved the municipality more than

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