Biogas: A viable energy source

the Herald 06/01/2010

ZIMBABWE, like other Sadc countries, faces energy challenges, and these are adversely affecting the overall performance of the economy.

The manufacturing and agricultural sectors have not been spared by this shortcoming.

Electricity shortages have led to power cuts that have retarded industrial activities, while the rate of deforestation has been accelerated as more people resort to firewood as an alternative source of fuel.

This has prompted stakeholders in the energy sector to look for alternative energy sources like the shelved methane gas project in Lupane, ethanol in Chiredzi, solar energy, mini-hydro plants and biogas.

Professor Christopher Chetsanga, who is the president of Zimbabwe Academy of Sciences and also the chairman of Zesa Holdings, said the methane gas from different sources has to be tapped as fossil fuels are soon to deplete while biogas, which is green energy, can be the solution for the country’s power shortages.

The use of biogas also known as mash gas, landfill gas or digester gas, depending on the site it has been produced, can be part of the answer to the country’s perennial energy challenges.

Urban areas have been seriously affected by energy challenges and yet these areas have the potential of producing large amounts of biogas as they have the feedstock for biogas plants in the form of sewage.

Biogas is produced by anaerobic digestion or fermentation of organic matter such as manure, sewage sludge, municipal waste, or bio-degradable waste at temperatures between 3 degrees and 70 degrees Celsius.

With the big sewage treatment plants in the country, especially in large cities like Harare, the production of biogas becomes a more viable project, which the city council and the private sector can invest in.

Engineers working with the city council established biogas plants at Firle and Crowborough Sewer Works several years ago.

Firle Sewer Works in the capital has the capacity of producing about 97000 cubic metres of biogas in three hours.

Experts from BOC Gases said methane in biogas has more heat-producing capacity than coal, which is usually used in thermal power stations; hence the city councils can generate electricity using the gas.

However, the biogas plant equipment in Harare is now in a state of disrepair.

Mr Leslie Gwindi, the spokesperson for the City of Harare, said they had thrown a tender for the refurbishment of the sewer works, which are currently not working efficiently.

He said there is need for financing the biogas project as the city council is facing financial challenges to resuscitate the project.

Biogas production and use is not new in the in the country.

According to a 1986 journal published by the then Department of Energy and Water Resources, the Government assisted towards the construction of more than a hundred biogas plants in rural areas and tertiary institutions in the 1980s.

Currently, the Ministry of Energy and Power Development has revived the projects and over 400 plants have been constructed at homestead level in Wedza, Sanyati, Chirumanzu, Gutu and Chipinge.

According to the ministry’s spokesperson, the beneficiaries provide labour and finance towards setting up the biogas plants while the ministry provides the technical expertise.

In countries like Thailand, Rayong Municipality produces organic fertilizer from biogas plant wastes while the gas is used to generate at least 5 000Mwh of electricity per year at its sewer plant.

Another typical example of a large-scale biogas plant is Vestal Farm in Kenansville, North Carolina, in America, which rears pigs.

The farm produces biogas from pig manure, which is used to generate electricity.

At the project biogas is compressed and used to operate a 30Kw micro turbine.

The energy produced results in reduction of annual electricity bills for the farm.

The expert at BOC Gases said the biogas could be piped to the end users or put in a canister, though it needs to be liquefied first before packaging.

He said the best and most cost-effective way is to pipe the gas straight to the end users like the Mozambique to Sasol pipe in South Africa.

Industries and domestic users can also tape the gas thereby generating revenue for the city council.

The expert said packaging the gas is an expensive venture, which requires the establishment of an air separation plant, which liquefies the gas using liquid nitrogen before it is filled in gas bottles and canisters.

Professor Chetsanga encouraged the private sector to participate fully in energy production for the development of the country.

"The human resources and the raw materials are available, and urban centres have to utilise their effluent in energy production rather than dumping it and causing an environmental threat

"This will also reduce the strain on the over burdened local power utility company," he said.

According to the Ministry of Energy and Power Development, funding and maintenance of the plants is the major stumbling block in rural areas.

The ministry is urging the corporate sector and donors to venture into these projects to assist in power generation for the rural population in order to stop the rampant deforestation caused by the use of firewood.

The spokesperson said it costs about US$600 to US$1 000 to set up a viable household biogas plant.

The cost includes raw materials and labour.

Given the current situation of incessant power cuts, there is great need for use of alternative renewable energy sources.

According to Professor Chetsanga this will widen the industrial base and create employment for the youths.

Local authorities can generate revenue by proper waste management whilst rural areas can retain their forests.

Even dumpsites dotted around several cities and towns can produce biogas if proper machinery is used to tap the gas.

l Article courtesy of the Ministry of Science and Technology Development.