Harold Ayodo
19 June 2006
Nairobi — Kenya Medical Research Institute (Kemri) has unveiled a simple aerobic sewage treatment plant that would reduce pollution of the environment.
Kemri scientists say the Sh1.5 million project that took them four years of research is cost-effective and has many advantages. Environmental experts say the invention would reduce pollution within municipalities in East Africa - the main culprits in the pollution - especially in Lake Victoria.
The recycled water, they say, is certified fit for human consumption, is odour-free and can save colossal amounts of money that hotels and agro-chemical factories incur to purchase water. The innovation comes at the same time as a Sh2 billion French Government-sponsored project to upgrade the dilapidated water and sewerage system in Kisumu.
To illustrate its efficacy, the institute's centre in Kisumu uses the recycled waste to water lawns and flowerbeds and in cleaning and sanitation. The centre initially relied on septic tanks to dispose of its waste over the years, before realising that the black cotton soil, where the centre stands, was being affected.
Municipalities like Kisumu and Homa Bay, whose sewerage treatment plants broke down decades ago, and now discharge raw sewage into Lake Victoria, stand to benefit from the new invention. For instance, the Kisumu Water Treatment and Sewerage Plant at Kisat was designed to handle 9,000 cubic metres of effluent but receives 15,000 cubic metres.
Kisat was constructed in 1966 and rehabilitated in 1986 to serve a population of 150,000 people. The population today, however, is slightly above 500,000. Over the same period, the sewage treatment plants at Nabongo and Shirere in Kakamega remain neglected and are in poor conditions.
Purifying wastewater
But just how does the Kemri invention work? Bacteria, which the scientists have coded as WWT-C, are used to eat waste and transform it into non-polluting material.
Researchers say eight different types of organisms are used in the process. These heavy-duty bacteria break down waste and sewerage in many Western nations.
Kemri Principal Electronic Technologist, Mr Winston Olwande, says the institute started researching on possible recycling of waste after concerns were raised over its septic tanks in Kisumu.
"We have a population of over 300 people generating waste water of approximately 10,000 gallons per day. Therefore, recycling the waste was a prerequisite," says Olwande.
The aerobic treatment plant that sits on less than a quarter acre piece of land has four main components that work together to purify wastewater.
"The waste from our residential houses and offices is channeled to the pre-treatment tank that removes microbes that cannot degrade," Olwande explains.
Waste, which includes rags, sticks, condoms, sanitary towels and fruit seeds, are removed manually using a rake.
"The next component is the aeration chamber where the microbes decompose waste in water. The aerobic digestion is a process occurring in the presence of oxygen," he says.
He explains that bacteria consumes organic matter and converts it into carbon dioxide under aerobic conditions.
"The aeration system consists of an air pump, piping and diffusers that force air into the aeration chamber," Olwande says.
Aerobic treatment
The bacteria changes dissolved and solid pollutants into cell mass, non-degradable material and gases such as carbon dioxide, hydrogen and methane.
"It is important to maintain an active population of microbes in the system to break down solids," says Olwande.
The variety of aerobic microorganisms living together in this mixed state decomposes assorted materials. The air pump located at the aerobic tank compresses air to flow into the aeration chamber before the diffuser forces air into water.
"Air is bubbled and the rising bubbles mix with the water the aerobic digestion is a bacterial process occurring in the presence of oxygen," he explains.
Treated water moves from the aeration chamber into a settling chamber or clarifier. The clarifier allows the cell mass and non-degradable materials to settle from the water before it leaves the treatment system. Olwande adds that the separation of microbial cells from treated effluent is an important part of the process.
Aerobic treatment processes lower the bio-chemical oxygen demand - a common measure of pollution.
"The process reduces the suspended solids that do not settle to the bottom of the clarifier," says Olwande.
The clarifier that provides a place for the microbes that have treated the waste to settle out of water is the third chamber.
"The clean water is then channeled from a land application system to a disposal tank and eventually to water sprinklers," Olwande says.
The plant, which the engineer proposes to be set up in estates, requires simple maintenance. This includes periodic removal of solids in the aeration chamber.
"Checking the air pump to ensure the air flow rate entering the aeration chamber is constant is important. Cleaning the air filter on the compressor inlet to remove dust and fibres and looking for air leaks are overriding prerequisites," says Olwande.
If adopted, the simple and cost-effective technology will ensure efficient water and sewerage treatment in towns and municipalities.
There is now hope of a clean up of the heavily polluted Lake Victoria, which is the largest fresh water mass in Africa.
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