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Biogas could save wastewater plants 30MW of energy

biogas plant overview image

An overview of WEC Project’s biogas-to-energy plant.

Wastewater treatment plants could depend less on Eskom by using the biogas formed onsite. This is according to wastewater solutions company WEC Projects.

The company explains that methane rich biogas, which is formed as a by-product of sewage treatment, can be used to fuel gas engine generators and contribute towards a percentage of the electricity used to operate water and wastewater plants.

South Africa has around 50 major municipalities. WEC said that these municipalities have wastewater treatment plants large enough to operate an effective biogas plant, which in turn, could possibly save about 30MW of electricity.

“As far as energy savings go, a figure of this size will have a pretty significant impact on both their own costs and on the electricity provider’s drive towards energy efficiency,” Jason Gifford, WEC Projects’ energy division spokesperson said.

The company is exploring the possibilities of biogas as an alternative energy source to achieve “true energy efficiency”.

Biogas power plant

The company first implemented a biogas power plant at Johannesburg Water’s wastewater treatment plant.

“Our goal is to make this initial plant a shining example of how true energy efficiency can be achieved,” Gifford said. Once the case can be effectively made for biogas, the company plans to build other treatment plants like this one.

Biogas production

Gifford explained that their wastewater treatment plant uses a process of anaerobic digestion (a natural process involving the decomposition of organic matter in the absence of oxygen) to produce biogas or raw fuel. Traditionally however, sewage treatment plants use this process to convert a large proportion of the solid sewage sludge, produced in the mainstream treatment processes, into biogas.

“This reduces the sludge volume prior to disposal as well as ensuring that a stable sludge is disposed of,” Gifford explained. He added that due to the massive electricity price increases recently, it now makes financial sense to use biogas to produce electricity.

One of the main aims of the biogas solution is to provide a wastewater treatment plant with an onsite energy source that should also be able to offset a portion of the plant’s operation costs.

Using biogas as fuel

In order for the biogas to be used as a fuel source, running in the engines of generators, it has to be clean. “Part of WEC Projects’ role is to clean the biogas so that it can serve as a fuel,” Gifford said.

He explained that the biogas in its raw fuel state contains water, hydrogen sulphide and a variety of volatile organic compounds (VOCs) and siloxanes. These chemicals can damage moving parts in an engine.

“For the gas to be effective as a fuel, it therefore needs to be conditioned and have these contaminants removed,” he explained. In the long run, the cleaner fuel, the longer the lifespan of the engine and the lower running costs will be.

Johannesburg Water’s wastewater biogas-to-energy project was the first of its kind in the country, Gifford said. The company now aims to set up similar biogas plants at other wastewater plants that operate anaerobic digesters.

“Suggesting that the 50 largest wastewater treatment plants in the country could save a combined 30MW through this process is a conservative estimate,” Gifford said. “But even taking the conservative estimate, this is no small figure in these energy-constrained times.”

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