Biological septic tank will save you space and money

FROM LEFT: a partially installed biological septic tank, which is comparatively smaller than the traditional and and an illustration of the biological septic tank. PHOTO| LUKORITO JONES

What you need to know:

  • Measuring only a metre cubed for a domestic house, the modern biological tank is relatively small. With a capacity of 1,000 litres, the tank, can serve up to 40 users.

  • A slightly larger tank, measuring cubic metres can serve a building of up to 100 users.

  • Larger biological tanks are available for institutions and commercial buildings.

Concerned about the crowding in some urban estates and the need for a clean environment, a city-based company has come up with an improved method of waste disposal.

For eight years now, Kenya Cast Products Ltd (KCP) has re-invented the way households handle sewage. Instead of the traditional septic tanks, which are usually smelly, fill up after a couple of years and take up considerable space, KCP has

introduced  biological septic tanks that use bacteria to digest organic waste on site.

“We felt it was time to design a system that could dispose of waste in a more eco-friendly way, and with fewer headaches for our consumers,” says Mr Joseph Kamau, the director of the Kahawa Sukari-based firm.

Ms Irine Maranga, a marketer with the waste-water management firm, says their septic tanks are becoming popular, with some users even opting to convert their septic tanks into the modern biological ones by fitting a bio-digester.

The increased demand, she says, is because the biological septic tanks are comparatively smaller, don’t smell, and never get filled up, so there is no need for exhauster services. 

“All these result in big savings for a homeowner in the long run,” she notes.

KCP’s rectangular tanks are made of highly vibrated concrete. They consist of a body, inlet and outlet baffles (devices used to restrain the flow of the water). The tanks are designed to be gravity powered and are suitable in high water table and inundating

areas. They are structurally sound, water-tight, corrosion and buoyancy resistant.

The biological septic system consists of three parts: A grease interceptor, a biological tank and a soakage drain. The system also divides the waste into grey water and black water. The latter is effluent that has come into contact with faecal matter, while the

former is water from the bathroom and kitchen sinks and laundry machines.

“Grey water is a combination of fats, oils, grease, waxes and detergents, which makes it chemically unstable” explains Ms Maranga. “It is thus not allowed into the digester. Instead, it is passed through a grease interceptor to rid it of oils, which can be

harmful to the environment. Thereafter it is directed to the soakage pit.”

The soakage pit (or French drain as it is also known), is a tank where the accumulated water seeps into the ground

Black water, on the other hand, is chanelled into a bio digester. Here, the bio digester uses naturally occurring anaerobic bacteria to treat the black water by digesting the faecal matter while eliminating pathogens (disease-causing organisms). The faecal matter

and other organic matter settle at the bottom of the tank through sedimentation and are converted by the bacteria into water and gases.

BIOLOGICAL DEGRADATION

“The sanitation system,” Ms Maranga explains, “works through a process called bacterial biodegradation. This process completely breaks down organic matter into water, carbon dioxide, nitrogen and methane. It takes only two weeks for the effluent to be

completely broken down. The carbon dioxide and methane gases produced are released while nitrogen dissolves in the water.”

She adds that the nitrogen-rich water, which is displaced to the soakage pit, is good for irrigation. However, further treatment is required to make the water fit for more domestic use.

The methane gas produced can be harnessed to cater for energy needs. However, this is only applicable to large institutions. For single domestic users, the quantity of waste is too little to produce sufficient amounts to harvest biogas.

The biodegradation takes place  as soon as waste water is flushed in. As a result, when using a biological septic tank, the characteristic foul odour usually associated with composting toilets and other septic tanks is eliminated. “This makes it easy for our

customers to install our KCP tanks anywhere within the compound,” says Mr Kamau.

“The tank applies the displacement principle, whereby the amount of waste water that is flushed into the tank displaces an equal volume of water from the tank to the French drain (soakage pit). Therefore, our clients do not have to exhaust the system time

and again,” he offers.

Measuring only a metre cubed for a domestic house, the modern biological tank is relatively small. With a capacity of 1,000 litres, the tank, can serve up to 40 users. A slightly larger tank,

measuring cubic metres can serve a building of up to 100 users.

Larger biological tanks are available for institutions and commercial buildings.

“Nowadays, many urban dwellers do not have the luxury of space, thus the need to save as much of it as possible. Our soakage system also eliminates the costs of excavation,” says Ms Maranga.

“With an installation fee of Sh90,000, our costs are easy to meet as the tanks require no maintenance thereafter.”