By Sifelani Tsiko
Rapid urbanisation and a steadily rising population in cities and towns has left decades — old sanitation infrastructure in Zimbabwe under pressure.
The deteriorating state of municipal wastewater and sewage treatment management in the country is clear for everyone to see.
Raw sewage from cities and towns across the country continues to be discharged into nearby wetlands, streams, rivers and open spaces.
Residents continue to complain over raw sewer that flows from their homes into streets posing environmental and public health risks.
The stinking overflow causes severe headaches and forces people to stay indoors. Typhoid, dysentery and cholera remain a major public health threat.
Very few sludge plants in the country are still able to screen, sediment, aerate, clarify, disinfect and process the sludge.
Sewage engineers say less than 50 percent of the faecal matter generated in most cities and towns safely reaches waste treatment plants.
The bulk of the sewer remains in homes and other premises. Most local authorities have failed totally to find a lasting solution to the sewer crisis.
In the midst of it all, Dr Ephrem Whingwiri, head and founder of Zim Earthworm Farms, likes to think outside the box.
He has some interesting technological innovation that uses earthworms and microbes to treat wastewater.
Dr Whingwiri feels strongly that his innovations can solve the numerous pollution problems — stinking human waste from overflowing septic tanks and burst sewer pipes.
“At source sewer bursts are a serious challenge to many local authorities in Zimbabwe. Sewage streams flowing around homes and outbreaks of water borne disease such as typhoid, dysentery and cholera are common. The solution seems elusive and communities have lost hope,” he said.
Dr Whingwiri said several studies by the University of Zimbabwe’s Civil Engineering Department show that the major causes of sewer bursts in the country include disposal of insoluble materials such as sand into the sewer system, increase in population, vandalism of sewer components, poor maintenance of sewer components and use of old infrastructure.
In newly rehabilitated systems, he said improper design of sewers and the absence of water had led to sewer bursts as some material hardened and blocked the flow.
“These factors decreased efficiency of collection of sewage. Although sewage is being collected from households, most of it does not reach the wastewater treatment plant because of blockages and leaking pipes,” he said.
Given the complexity of the crisis and lack of investment, Dr Whingwiri advocates for simple low cost technologies to manage sewer.
He developed and patented a decongester sewer system which prevents sewer bursts, recycles, provides more water and many more benefits to residents, land developers and local authorities.
“The decongester sewer system for managing wastewater is based on an understanding of what earthworms, – environmental engineers, do for mankind,” he said.
“A decongester is installed at the source of generation of wastewater. Wastewater stabilisation is started in this device by earthworms. A decongester receives wastewater from source of generation. Solids are trapped and processed by earthworms to a rich organic fertiliser, vermicompost, while partially treated water carrying no sludge leaves the decongester to a sewer network or a new common trunk pipe.”
Dr Whingwiri said the use of decongesters reduces smell and pathogens.
“When the decongesters are connected to an existing sewer network, the load in the pipe is reduced, preventing bursts. When most of what flows in the sewer pipe is partially treated water, some of the water can be diverted to a communal treatment and recycling plant where the water is further treated by earthworms to a quality allowing for reuse in flushing toilets and irrigating plants.”
Excess water is discharged into ponds. Treated water, he said, can be taken back to houses for flushing toilets and irrigating plants or into water reservoirs.
“Because the wastewater carries no sludge and stabilisation is started in the decongester, there is no need for a primary anaerobic pond. The partially treated water can be discharged into a facultative pond. If an agricultural project is nearby, the wastewater can be used directly in irrigating plants and a maturation pond may not be necessary,” Dr Whingwiri said.
The vermicompost produced can be pelletised, bagged and sold to agricultural estates as organic fertiliser.
He said there were numerous benefits to residents.
Residents previously not connected to the sewer network can now be connected and the residents do not experience any sewer bursts.
They have options to use the water for flushing toilets and this way they reduce water bills.
In addition to this, they can use recycled water to irrigate plants helping to green the environment at no cost.
“In new settlements where there is no water reticulation, residents will always have water for flushing toilets,” the earthworm technologist said.
“The system conserves water in the reservoir and no sewer bursts are expected due to a reduced load in the sewer system. Additional houses due to increased population can be connected to the system.”
Furthermore, no sludge is deposited in sewage ponds while excess water generated, allows councils to use it to irrigate plants such as trees and lawns thus greening the cities.
“The use of earthworms technology can reduce sewer bursts and the workload for plumbers, in terms of overtime, fuel and manpower costs to councils,” Dr Whingwiri said.
“It also prevents the contamination of underground water such as boreholes and wells — common in new settlements that have mushroomed in and around major cities and towns.”
The earthworms technology, he said, could be applied in rehabilitating existing sewer systems, setting up of new sewer systems based on decongester technology, rural schools which use pit latrines, refugee camps and institutions with water shortages and poor sanitation as well as growth points.
“Zimbabwe generates about one million tonnes of biodegradable waste per annum which currently is a nuisance to local authorities who lack sufficient capacity to manage it,” Dr Whingwiri said.
“Most of the waste is disposed of at landfills, illegal dumpsites or is burnt yet 70 percent of Zimbabwean soils are sandy, prone to leaching, have low humus and are inherently infertile. Earthworms are a possible backbone of a green revolution. They decompose organic waste into a bio-fertiliser called vermicompost (earthworm faeces or excreta) on the market in Zimbabwe.”
Zimbabwe and most other developing countries still face a dire sanitation crisis with some 2,5 billion people, most of them in Africa or Asia, lacking access to toilets, United Nations figures show.
The annual global municipal solid waste (MSW) generation rate is projected to reach 2,2 billion tonnes per annum by 2025 from 1,3 billion tons per annum in 2012, according to the UN. And, low cost technologies such as earthworms decongesters could help the country manage human waste in towns and cities that were never planned to handle so many people.
Improvements in municipal solid waste management could reduce problems related to eutrophication, global warming, human health and acidification.