Exam Question

(a) Principle of Operation of Sewage Systems
(i) Flow-Through System
A flow-through system operates on the principle of extended aeration , a biological sewage treatment process. The system consists of three interconnected chambers. Raw sewage first enters a chamber where it may be passed through a screen or comminuted. Air is then pumped into this chamber via a diffuser, creating fine bubbles that promote the growth of aerobic bacteria . This process forms a biological sludge. The mixture then flows into a settling tank where the activated sludge settles to the bottom, leaving a clear effluent on top. This clear effluent is then passed to a third chamber, where it is disinfected with a chlorination process before being discharged into the sea. The settled sludge is recirculated back to the aeration chamber to continue the treatment process.
(ii) Collection/Holding/Transfer System