5.(a) With reference to sewage treatment systems, explain EACH of the following terms:
(i) aerobic;(2)
(ii) anaerobic.(2)
(b) Sketch a Biological Sewage Treatment Plant, labelling the MAIN compartments and indicating the direction of flow through the plant.(6)
(a) Sewage Treatment Terms
(i) Aerobic (2 marks)
- Refers to microorganisms that require oxygen for survival.
- They break down sewage efficiently into stable products (CO₂, water, non-harmful sludge) with minimal odour.
(ii) Anaerobic (2 marks)
- Refers to microorganisms that survive without oxygen.
- They break down sewage producing harmful gases (e.g. methane, hydrogen sulphide), unpleasant odours, and corrosive by-products.
(b) Biological Sewage Treatment Plant – Sketch (6 marks)
Your sketch should include three main compartments with arrows showing flow:
- Aeration Tank – where sewage is mixed with air (bubbles supplied by blowers/diffusers) and aerobic bacteria break down organic matter.
- Settlement/Clarifier Tank – solids (sludge) settle out, some sludge is recirculated, and clarified effluent flows onward.
- Disinfection/Chlorination Tank – calcium hypochlorite or chlorine is added before discharge overboard.
➡ Flow: Inlet → Aeration → Settlement → Disinfection → Overboard discharge