Get the septic tank right

Martin Male, a businessman and resident of Kawanda in Wakiso district woke up to a foul smell in his house.

At first, he did not take it seriously, because he left his home very early and returned late. “But one weekend I asked a local builder to move around and look for the source of the smell and he discovered that the septic tank had filled and its contents spilled into the compound.”

Paul Bogere, a plumber says a septic system can be an efficient, inexpensive and convenient method for treating and disposing of household wastewater produced in the bathroom, kitchen and laundry. He says septic systems are used if sewage treatment plants are not accessible.

The septic system consists of three main parts: the septic tank, the drain field and the soil beneath the drain field.

Fred Lukoda, who is in the construction business, says a septic tank is an important facility, but some people do not give it enough attention during planning. “To set up a septic tank one, needs a big concrete, steel or plastic tank that must be placed underground to collect waste, which flows into the tank at one end and leaves at the other,” he explains.

Lukoda says septic tanks are meant to treat waste. They are used in places where there is no main connection to a public sewer provided by the local government or private corporations.

According to Bogere, the recommended distance of the septic tank from the house should be 30m. “It is better to put it in a garden. However, you can place a concrete tank in the compound and allow grass to grow over it,” he says

How the system works

Bogere says septic tanks naturally produce gases which emit a foul smell. “Sinks, therefore, must have loops of pipes called P-traps that hold water in the lower loop and block the gases from flowing back into the house.

The gases flow up a vent pipe,” Bogere explains. He says as new water enters the tank, it displaces the water that is already there. This water flows out of the septic tank and into a National Water and Sewerage Corporation drain field. According to Bogere, the drain field is made of perforated pipes buried in trenches filled with gravel.

Untreated waste water from the house flows into the septic tank, where the solids separate from the liquids. Some solids, such as soap, scum or fat, will float to the top of the tank to form a scum layer. Heavier solids, such as human and kitchen waste, settle to the bottom of the tank as sludge.

Bogere explains that the remaining liquid flows out of the tank to a land drainage system or drain field. Baffles built into the tank hold back the floating scum from moving past the outlet of the tank.

Costs

Bogere says the cost of a plastic septic tank depends on the size one wants. A tank that can hold 100 litres will cost between sh500,000 and sh650,000, 160 litres will cost about sh1m to sh1.3m and the largest one which can hold up to 5,000 litres will cost about sh4m.

However, he says this size is not recommended. The construction of a concrete or brick septic tank will cost more than the plastic tank because a lot of material is required. This includes stones, concrete, iron bars, bricks, sand, cement and labor inclusive. All this will cost about sh3 to sh4m.