Exam Question
(a) Describe, with the aid of a sketch a sewage system that operates by natural processes (10)
(b) State, with reasons FOUR operational circumstances that may adversely affect the quality of the output of the plant in (a). (10)
Class 4 (4th Engineer)
SSEP
📅 Dec 2022
Reference Answer
### (a) Biological Sewage Treatment Plant (Natural Processes)
A biological sewage treatment plant utilizes natural aerobic decomposition processes to treat raw sewage, rendering it safe for discharge overboard in compliance with MARPOL Annex IV regulations. The core principle is the cultivation of a healthy colony of aerobic bacteria which digest the organic matter in the sewage.
#### Principle of Operation
The system is based on the **extended aeration** process. Raw sewage is introduced into an environment rich in oxygen and populated with aerobic microorganisms. These bacteria use the organic waste as food and, through respiration, break it down into simple, stable, and inoffensive end products: primarily Carbon Dioxide (CO2), Water (H2O), and inorganic mineralized sludge. The process requires a controlled environment with sufficient oxygen, retention time, and a stable temperature to be effective.
A biological sewage treatment plant utilizes natural aerobic decomposition processes to treat raw sewage, rendering it safe for discharge overboard in compliance with MARPOL Annex IV regulations. The core principle is the cultivation of a healthy colony of aerobic bacteria which digest the organic matter in the sewage.
#### Principle of Operation
The system is based on the **extended aeration** process. Raw sewage is introduced into an environment rich in oxygen and populated with aerobic microorganisms. These bacteria use the organic waste as food and, through respiration, break it down into simple, stable, and inoffensive end products: primarily Carbon Dioxide (CO2), Water (H2O), and inorganic mineralized sludge. The process requires a controlled environment with sufficient oxygen, retention time, and a stable temperature to be effective.
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