Sewage on board ships must be treated prior being discharged to the sea. For this, ships are loaded with STP plant that is used for treating the sewage and making it less harmful for the sea. Engineers are having better knowledge about operating the sewage plant prior using the same to comply with the rules and regulations of discarding sewage. A marine engineer should possess these things:
There are important terms that marine engineer should know. We will discuss them in detail.
Biochemical oxygen demand is a test used by engineers to determine decomposable substances and to test the sewage strength. Biochemical Oxygen Demand depends on the activity of bacteria inside the sewage. These bacteria consume organic matter under oxygenated environment.
It can be also explained as the amount of oxygen needed by micro-organisms in the organic matter stabilization.
Coliform is an organism present in human intestine and is also used as indicator organism of sewage pollution. If this organism is present in the water, it reveals the pathogen count, which are disease causing bacteria and responsible for dysentery, cholera, typhoid, etc.
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There are dissolved solids, suspended solids, settle able solids, suspended level of raw sewage, and residual disinfectant. Dissolved solids cannot be seen through eyes but contaminate water.
Suspended solids are visible and can be removed by filtration process. These solids are high in organic matter.
Settle able solids will subside in quiescent liquid for about one hour.
Residual disinfectant should be low after treatment.
Biochemical digestion of sewage involves two processes- Anaerobic and aerobic processes. Anaerobic bacteria can grow in the absence of oxygen in air as they use chemically bound oxygen for survival. The bacteria break down the organic matter into water, methane, carbon dioxide, hydrogen sulphide, and ammonia. This process is known as putrefaction.
The products form out from the process are noxious and toxic. The effluent is quality less and by-products are extremely corrosive.
Aerobic bacteria need air for oxygen to survive. These bacteria break down the organic matter to generate safe products like carbon dioxide, water, energy, and inert residue to synthesize new bacteria.
These are the key terms used for STP plant on the ships. If you think we have skipped anything important, let us know in comments. Do feedback and ask if you have any confusion.
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