The Sewage treatment plant (STP) is used onboard to treat and disinfect the sewage generated on ships before discharging overboard into the sea. It is very important machinery on a ship in respect to environmental and Marpol regulations.
The STP mainly consists of three chambers –
- Aeration– the sewage from lavatories directly flow into the aeration compartment. The air from the blower instigate the circulation of the liquid and break up the solids and also providing oxygen to the bacteria’s present there.
- Settling Tank – The slurry gets collected and water drives back to the aeration chamber and the water get separated
- Sterilization– In this chamber sewage is treated with chlorine tablets and Ultra Violet sterilization.
There are two types of bacteria used in the sewage treatment plant
- Aerobic – These bacteria require free oxygen to survive. They break down the organic matter to produce safe products such as H2O, CO2, residue and energy to synthesise new bacteria. These bacteria become more dangerous when we are doing maintenance, hence we always do in presence of ventilation.
- Anaerobic – These bacteria only multiply in absence of free oxygen as they utilise chemically bond oxygen to survive. They break down the organic matter to produce H2O, CO2, CH4, H2S and NH3. This process is known as PUTREFACTION. The products thus formed are noxious and toxious . The effluent is of poor quality and highly corrosive.
What is Coliform Count ?
The coliform is a kind of organism which holds a chunk of the human intestine and is acknowledged as “INDICATOR ORGANISMS OF SEWAGE POLLUTION”
The presence of these organisms in water is an indication of “Pathogen” which is a disease-causing bacteria responsible for Cholera, Dysentry, Typhoid etc.
Maintenance done in Sewage Treatment Plant
- Check the treated water and UV lamp indicator daily.
- Monitor the quantity of oil and clean the filter of the aeration blower.
- Inspect the condition of V- belt.
- Clean the aeration chamber tank screen.
- Replace the UV lamp of STP yearly.