One of the most essential requirement in every building is the mechanism of managing waste. A functional system that gets rid of the grey and soil water is a key feature to make any building habitable.Although there has been innovation on various aspects of construction over time, the use of septic tanks to deal with household wastes has remained popular for over 150 years.
The system, which has gained roots in Kenya since 1940s, in areas lacking established sewer lines was convenient when there was ample space and many developers and construction consultants readily recommended it almost all the time, creating a belief this system, to an extent that it has no other alternative.
Today, there are viable options, cheap, economical with space and very efficient ones.One such system is the Biodigester, an emerging alternative for waste management, slowly replacing the traditional septic tanks in Kenya.
A number of providers are developing innovative ways towards installation of this system which is essentially a biological means that employs enzymes to accelerate the bacterial breakdown of the waste. Soil and grey water from the house is directed to the biodigester via an inlet piping, it gets broken down naturally, producing methane gas and water as by-products.
According to Mr Harrison of Herritech Ventures, the process starts by excavation and getting rid of any black cotton soil. The amount of space required is determined by the occupancy of the house or building (population).
“For the 2 years of our service in biodigester installation, we have served over 65 clients, including institutions. Majority of the clients however involve residential houses who simply need 1M3 of space for biodigester.
The installation takes about 2 days, after which we wait for 5 days to introduce enzymes and the biodigester is then considered ready for use.”
Water and methane gas produced from the process can both be harvested if the user desires. However, according to Mr Langat of HPD Consult, the methane gas produced in cases of single domestic units is quite insignificant. It is therefore just released and escapes to the atmosphere.
“A biodigester for single residential dwelling is classified to serve up to 30 users while one for an institution serves about 200-2000 users. From the latter, the biogas can be harvested for cooking since the biomass is sufficient to produce enough gas. The water can however be harvested in both cases for gardening or domestic cleaning, or the user can let it seep through the soak pit.”
Interestingly, the water can also be purified for human consumption, although this requires elaborate purification systems, as Mr Thairu of Wonder Biodigesters advises.
Biodigester technology has several benefits over the traditional septic system.
Mr Thairu explains that biodigester takes lesser space, sentiments also shared by Mr Langat:
“Septic tank takes more space, which wastes your valuable land, especially for the popular 50×100 plots common in urban setup.”
Needless to say is the economic advantage resulting from the recycled water and harvested gas, which saves you cooking energy costs by appreciable margins.
No exhauster needed
Although many people still doubt the ability of this technology to keep away the need for exhauster services in your home, Mr Harrison assures that the system is full proof, at least from the projects he has undertaken across the country.
In addition, the bad odours experienced in septic tanks is a gone story, since the biodigester ensures complete breakdown of the waste as opposed to septic tanks which simply stores the waste.
Sampled installation costs from different providers prove more viable than septic tanks, contrary to the fears that many have always expressed regarding the costs. The installation cost of a biodigester for single domestic unit ranges between Ksh 85,000 to 95,000 while for an institution with more than 2,000 users, the cost is about Ksh 800,000. The users will however need to invest a little more in case they want to harvest the biogas, to include the gas storage chamber, according to Mr. Thairu.
Things to avoid
It is advisable for users to ensure chemicals, plastic materials and other items like diapers are not directed to the biodigester.
“This causes clogging and interferes with the biological action of the bacteria. In uncontrollable cases, the installed grease traps serve to get rid of the chemicals as waste water from bathrooms is directed there” Says Mr Thairu.
This system is a worthy investment for homeowners, institutional and commercial buildings. It is prudent to view the long term and since the cost-benefit analysis proves positive, why not consider it for your waste management?
Although there is the question of environmental effects of the methane gas that escape to the air especially for single dwelling units where it is insignificant to harvest, still this cannot rule out the overriding benefits.