Durban leads the country in generating electricity from waste through two landfill sites that are currently earning carbon credits and providing the blueprint for further plants in the province.

Waste Potential

Municipalities generate a lot of waste, often high in calorific value and with great potential for electricity generation. In Durban two landfill sites, Marianhill and Bisasar Road, are capable of producing electricity for thousands of middle-income households, which they have been doing since 2011 through the Durban Landfill Gas to Electricity Project (LG2EP).

The LG2EP consists of two sites – the Bisasar Road landfill near Claire Hills and the Marianhill landfill west of Durban. In total, the project’s capital expenditure has been in excess of R120 million, with an annual operating budget of over R10 million.

Owned by eThekwini Municipality, with Durban Solid Waste serving as the technical advisor and project operator, LG2EP features technology typical of landfill gas-to-energy projects in other parts of the world. Marianhill, the smaller of the two projects at 1MWp, was considered a pilot and construction started in January 2006. Marianhill Landfill takes between 450 and 700 tons daily, with Bisasar Road Landfill at 6.5MWp taking between 3500 and 5000 tons per day.

Landfill gas is emitted when bacteria decomposes waste in landfills – the general composition of the gas is about 50% methane and 42% carbon dioxide, with the rest comprising of nitrogen and oxygen compounds. Generally, peak production occurs a year after material has been deposited in the landfill, and has a generation lifespan of two decades.

Capturing the landfill gas means that instead of having methane released into the atmosphere, it is captured and used for generating electricity.

Waste to Energy: The Process

For the Durban project, large gas extraction wells, flare units and landfill gas generators were installed. At the Bisasar Road landfill, 90 horizontal and 72 vertical wells were installed. At Marianhill, 15 horizontal and nine vertical wells were installed. The wells are made of standard polyethylene pipes.

As gas is naturally produced in the landfill, the gas is extracted through a series of horizontal and vertical wells before reaching the gas collection pipework, which collects and transports the gas to the next stage of the electricity generation process at the extraction plant.

Once the gas reaches the extraction plant, it is supplied to generation engines. A centrifugal blower inside the extraction plant, which creates a lower air pressure inside the wells compared to that of the landfill, is essential. This difference in air pressure allows the gas to move from the landfill into the wells and from there to the extraction plant, before moving to the generation units.

During the extraction stage any excess gas that comes through the system is channelled through the flare units, where it is flared. A landfill gas flare with minimum capacity of 1000Nm3/hr was installed at each site. The Marianhill gas generator consists of a single 1MW unit, while the Bisasar Road Landfill consists of six 1MW and one 0.5MW Jenbacher type 320 engines.

The gas is burned in cylinder spark ignition engines, which in turn drive a generator to produce electricity that is then fed through the step-up transformer before supplying electricity to the eThekwini electricity grid.

eThekwini’s expansion plans

One of the project’s attractions for eThekwini Municipality was registering it through the Clean Development Mechanism (CDM). This allows them to earn carbon credits and enable selling it on the carbon market.

At the time of signing the CDM agreement, the price of carbon was higher than it is now. The project has so far racked up about 799 337 carbon credits, which the municipality has not yet sold in its entirety. Nedbank has purchased 124 884 voluntary credits and the World Bank buys Marianhill credits, so far totalling 180 864.

There’s a silver lining to the carbon market crash, says Parkin, if the National Treasury goes ahead with implementing a carbon tax. “We might be able to able to earn [rough estimate] R80 million a year for reducing CO2.” In addition to this, the project has signed a power purchasing agreement with eThekwini Electricity Unit where it receives income from electricity sold to the local grid. Since December 2006, the income revenue from electricity has been R115 million.

eThekwini plans to expand its programme and is currently doing an assessment at Marianhill, which could see the addition of another engine and more capacity. At Bisaser Road, Parkin notes that landfill gas will start dropping off around 2017.

The department has had to look at other landfills in the city, in particular Buffelsdraai. However, the approach might be slightly different, says Parkin. “Since the Buffelsdraai landfill is not located near the grid, we are looking at other uses for the gas generated there.” The project, still in a feasibility stage, plans to extract gas for fuel, specifically to power refuse vehicles owned by Durban Solid Waste.

A rough estimate shows that Buffelsdraai could produce approximately 2400 litres of fuel per day. Parkin says the cost of producing this fuel could be up to R5 or R6 cheaper per cubic metre of diesel, resulting in more savings for the municipality and for the environment.