Pros, cons of plastic and concrete septic tanks

Concrete septic tanks have their advantages and disadvantages. Knowing the good and bad sides of this type of home-sewage system is important if you plan to install one. 

Architect Abdu-Wahab Nayanzi says, to use the toilet facility more appropriately, users should understand the toilet and septic tank system.

The septic tank is a small-scale sewage treatment system used in areas which have no access to the main sewage system. 

In Uganda, there are mainly two types of septic tanks, plastic and concrete septic tanks. 

The concrete septic tank is built underground with bricks, sand, cement, iron-bars and wire mesh and has a concrete slab on top with some openings, like manholes. On the other hand, the plastic septic tank is like a plastic drum. 

Timothy Balyejusa, the president of the Uganda Young Plumbers Association says plastic septic tanks are cheaper than concrete ones. 

According to him, plastic septic tanks are usually bought by people who are rushing to enter new houses. 

Balyejusa says the size of the septic tank is determined by the number of users of the toilet facility. 

“If you are building a residential house, you may construct a septic tank of 10 feet deep and 10 feet wide,” he says. 

Nyanzi says, a small septic tank for one family may consume 2,500 to 3,000 bricks. Fifteen iron-bars, three wire-meshes and three lorries of building sand. 

He says a septic tank for a toilet used by a big family consumes more iron bars. 

He adds that to find the right position for the septic tank; the architect who draws the plan for the main house should include it (the septic tank) from the beginning. 

Balyejusa maintains that pipes carrying waste into the septic tank should also be inclined at a certain angle to allow the smooth flow of waste. 

He adds that septic tanks work hand-in-hand with the soak pit. The soak pit is the catchment for water from the septic tank, bathroom and kitchen. 

Balyejusa explains that an overflow pipe is fixed on the septic tank leading to the soak pit. 

“Whenever the septic tank is filling up, water flows through the overflow pipe into the soak pit, helping to drain it,” Balyejusa says. 

Muhammad Nsereko, a construction expert, says the soak pit must be dug adjacent to the septic tank and inclined at an angle. 

Nsereko observed that, while constructing the septic tank, the builder must ensure it is completely sealed so that no oxygen enters in because it affects the proper composition of waste. 

He adds that between the toilet and septic tank, it is important to construct manholes in relation to the distance so that waste cannot travel a long distance before reaching the septic tank. 

Statistics show that about 25% of Ugandans live in urban and semi-urban areas and that 80% of that population uses septic tanks. 

Balyejusa says concrete septic tanks are more expensive to construct than plastic ones. 

“The plastic septic tank is cheaper by almost 50% to construct compared to the concrete tank. And it is also easy to transport, install and maintain,” Balyejusa says. 

The tanks are available in different sizes for between six and 100 users and can last for 11 months before filling up. 

Balyejusa adds that the challenge with concrete tanks is that when leakages occur due to poor pressure, it is difficult to identify the leak. 

“And the result will be waste into the groundwater resources which may cause waterborne diseases like cholera and dysentery,” he says. 

Costs

Depending on the capacity of the septic tanks, the price ranges from sh1m to sh5m. 

· 2000 litre capacity concrete septic tank for 20 people 

· 2,500 bricks –sh300,000

· Two medium size lorries of building sand sh450,000

· One lorry of plaster sand –sh160,000

· 15 Iron bars –sh550,000

· 3 wire mesh –sh75,000

· Excavation –sh300,000

· Construction labour –sh1.5m

· Aggregate stones-sh250,000

· Kilograms of binding wire –sh12,000

· Total –sh3.597.000