3.1 What is the structure called? 3.1.1 Briefly describe how the organic matter decomposes in the structure - NSC Civil Technology Civil Services - Question 3 - 2017 - Paper 1

The organic matter decomposes in the septic tank through the action of anaerobic bacteria and other biological organisms such as maggots and worms. This process breaks down the waste without the need for oxygen, resulting in a clearer effluent.

The purpose of the inlet pipe opening at 3.1.B is to allow wastewater to flow into the septic tank for treatment and subsequent decomposition.

The inflow at 3.1.B must be lower than the liquid level to prevent any backflow of sewage and to ensure efficient treatment within the tank. This also maintains the necessary pressure balance within the tank.

The effluent at 3.1.D is typically discharged into a drainage field or leach field, where it can further percolate through the soil for filtration and treatment.

Without a ventilation pipe, a drain system can experience pressure fluctuations that lead to siphoning of traps, resulting in sewer gases entering the living spaces. This can cause unpleasant odors and health hazards, as well as disrupt the proper flow of wastewater.

An S-trap is constructed in a zigzag shape, allowing liquid waste to flow while creating a water seal that prevents sewer gas from escaping. This design is essential for ensuring proper drainage while maintaining hygiene.

STRAIGHT

SLIGHTLY SMALLER

6 mm