Improper sewage disposal is one of the major contributors to environmental pollution that affect human health and aquatic ecosystems.
And the rapidly growing population has worsened the situation as it has led to the release of partially treated effluent into rivers and streams. The pollution caused downstream, leads to an imbalanced ecosystem.
However, it is a different story in Nyeri town.
Proper sewage disposal has seen a sewerage treatment plant turn into a source of organic fertiliser for thousands of farmers and a source of fish for Nyeri town and its environs. The plant has also birthed a recreation centre for parties, weddings and photo sessions.
The plant located at Kangemi slums is operated by Nyeri Water and Sanitation Company (Nyewasco), under the Tana Water Works Development Agency (TWWDA). The agency is responsible for the development, maintenance and management of water and sanitation infrastructure in Embu, Kirinyaga, Meru, Nyeri and Tharaka Nithi counties.
At the conventional wastewater treatment plant, solid waste is separated from liquid waste and turned into sludge through anaerobic or fermentation process.
George Kamunya, the plant manager, explained that although wastewater management has been a thorn in the flesh of the water sector, the sewerage plant has done wonders.
"The process entails strict filtration and sedimentation to ensure that we get the dry sludge which is the organic fertiliser, and the treated water, which is then released to the river," he said.
According to Kamunya, after receiving sewage from the mains, screening is done to remove timbers, rags, plastic, stones and sometimes carcasses before it is allowed to pass on to the grit chamber where inorganic fine stones and pieces of glass are separated.
"The grit chamber is emptied after accumulation, in seven days. The wastewater is then allowed to go for the second stage known as the primary sedimentation tank or the clarifiers tank, where separation of sludge and liquid water takes place," the plant manager explained.
After desludging, Kamunya said, the sludge is pumped to the lagoon tank or the digesters tank to undergo anaerobic digestion between 90 to 120 days to kill the bacteria.
"The sludge is then released to the drying beds to undergo the drying process, where after analysis is done, we sell the sludge at Sh500 per 1,000 kilogrammes which is way below the market price for organic fertiliser," he said.
The market price for a 50-kilogramme bag of inorganic fertiliser is Sh3,500, implying that 1,000 kilogramme will require a farmer to spend Sh70,000.
Kamunya said in a month, they harvest at least 150,000 kilogrammes, but they are not able to meet the demand from farmers, who come from as far as Muranga and Kiambu counties.
"The process has been affected by the ongoing rains, keeping over 50 farmers waiting. What this means is that any person who orders the sludge at this time will have to wait for close to two months because we have to meet the demand of the farmers in the queue," Kamunya.
Nyeri Youth and Women Self-help Group is among the many groups that have joined the lucrative venture where they buy the sludge, sieve it and sell it as fine organic fertiliser to farmers. They also carbonise it and process it into charcoal briquettes.
The self-help group's vice chairperson Dennis Muriithi said the sewage treatment plant has been a source of revenue to the 52 members who have established outlets to sell their products. Their clients, he said, include farmers and the slum dwellers who depend on charcoal for cooking.
"A 50-kilogramme bag of ordinary charcoal goes for Sh2,500, but we sell ours at Sh800 where five pieces of briquettes can last for eight hours while cooking, but the other charcoal can last for one hour only," Muriithi said.
Muriithi said, since they approached Nyewasco as a group, they negotiated and bought the sludge at half the price, a move that has made his group make major strides, such as putting Wi-Fi in their premises which gives youth from the community a chance to connect to technology.
"We have also bought two motorbikes to reach our clients and this has led to job creation directly and indirectly," he said.
The sewage treatment process is quiet elaborate; where solid waste is separated from liquid waste. The liquid waste is filtered through high-rate trickling filters, intermediate sedimentation tanks and low-rate trickling filtration to the final humus tank before the final stage known as the tertiary stage.
"The detailed process is to ensure that water is treated and all the bacteria is killed. At the tertiary stage, wastewater retention has 21 days for the aeration process. To ensure that the treatment has been successful, we rear tilapia fish which can't survive in contaminated water before we discharge the effluent back to the river," Kamunya said.
They later sell the fish to Nyeri and its environs at Sh100 per kilogramme, providing a great source of minerals, such as iron, zinc, iodine, magnesium and potassium to the locals.
The process, he added, contributes immensely to environmental conservation as pollution is avoided hence the protection of biodiversity.
"The recreational park is popular for weddings, for the ceremony and photo sessions. We charge Sh3,000 per session. Learning institutions also visit the sewerage plant to understand our operations," Kamunya added.
TWWDA Chief Executive Officer Phillip Gichuki hailed the project, saying it has complimented the agency's diverse climate-smart efforts by providing an alternative source of green energy.
"We have planted 109,875 indigenous trees in the past three years and an additional 23,232 in the Financial Year 2022-2023. Studies show that 60 per cent of trees are cut for energy, this is a game changer in environmental conservation because access to water is highly dependent on the environment," Gichuki said.
The agency, he said, is also constructing Biodomes in three secondary schools (Siakago Girls, Ngaru High School and Gatuanyaga Secondary School) to harness green energy to enhance their operations.
"We are constructing a Decentralised Treatment Facility (DTF) at Kiawara since there is currently no sewerage system... we are at the same time equipping all our boreholes with solar power because we prioritise the use of green energy in realising our vision of universal access to quality water and sanitation services," he said.
"The success of Nyewasco's sewerage treatment plant shows that construction of a wastewater treatment plant in our communities will not lead to permanent bad smell contrary to the stigma from our communities. We are encouraging other water service providers to follow suit," Gichuki said.
