24 February 2008

Zimbabwe: Zinwa to Revive Biogas Digesters

The Herald, Harare 11 February 2008

THE Zimbabwe National Water Authority will soon revive the biogas digesters that have been lying idle at Firle and Crowborough waterworks in Harare to cut down on energy costs.

Some of the biogas digesters that have been lying idle for years need to be de-sludged of sand accumulated over the years.

The digesters have the potential of producing enough biogas to run four of the water authority's five sewage treatment works and cut down on electricity costs that now run into several billions of dollars each month.

If revived, the digesters also have the capacity of producing enough energy to drive several other industrial operations that require large amounts of power.

According to water experts Crowborough wastewater in Kuwadzana, currently consumes almost 215 000 kilowatts each month, costing the water authority billions of dollars yet it has the potential of producing about 12 500-cubic metres of biogas a day.

Zinwa spokesperson Mrs Marjory Munyonga, who took the media and several engineers on a tour of the wastewater facilities last week, said studies done on Crowborough revealed that the gas produced has a chemical composition of 66,4 percent methane, 32,2 percent carbon dioxide and the rest hydrogen sulphide.

"Only a third of the gas produced in the digesters is used in gas boilers for heating digested sludge for stabilisation purposes and the rest of the gas is captured and disposed of as waste gas.

"We are inviting all those interested in biogas-related projects to come forward and work with us," Mrs Munyonga said.

Zinwa wastewater management manager Engineer Simon Muserere, who was part of the entourage, said the revival of the digesters had various advantages.

"The opportunities of utilising the plant are immense and these include using gas-run vehicles that can also be used as service vehicles at the sewage treatment plants," he said.

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