The basic principle of working of a biological treatment plant is decomposition of the raw sewage. This process is done by aerating the sewage chamber with fresh air. The aerobic bacteria survive on this fresh air and decompose the raw sewage which can be disposed of in the sea.

A typical aerobic STP consists of 4 chambers

• Primary: The raw sewage enters the primary chamber via a coarse mesh filter where large solids are broken down
• Aeration: From primary chamber sewage enters the aeration compartment where it is digested by aerobic bacteria and microorganisms in the presence of oxygen.
• Settling: The sewage then flows into the settling compartment where the activated sludge is settled out. Any solids that settle out are returned via an air lift to the aeration chamber which ensures that they are fully broken down.
• Chlorination: The clear liquid then overflows from the settling tank to the chlorination chamber, and the chlorinator disinfects the liquid.

Every day

• Observe that the treatment unit is operating normally and there is no alarms displayed.
• Check if the blowers are running.
• Check if the chlorine dosing pump is operating.
• Check that sludge flows through the sludge return hose (by air lift) when the air blower is running.
• Check for smell of the unit. If the unit is smelling, it is most probably that aeration is not working and treatment process has changed to anaerobic.

Every week

• If the chemical dosing system is in use, check the chlorine content in the effluent water regularly.
• Test sludge content in activation chamber I to ensure that mineral sludge content is within acceptable limits.
• Take a sludge content test at least every week or every time when “SLUDGE ALARM” is displayed.

Every month

• Check that there is no obstruction in the aeration piping and in the air distributors.
• Check the overflow between the aeration chamber II and the settling chamber.
• There should be no obstruction in the overflow between the settling chamber and the disinfection chamber.
• Check that there is no obstruction in the venting line. Inspect the tank’s external and internal coatings for corrosion.
• STP should be back washed with fresh water and new batch of bacteria added.

Every year

• Empty and clean the unit.
• Make sure that the unit is well ventilated and there is enough fresh air in the chamber if you have to go inside to avoid inhaling toxic fumes and suffocation. One person must stay outside of the tank and keep eye on person who is working inside the unit.
• Make sure that the waste water is lead to a proper holding tank (hull tank or collection tank) during shutdown or maintenance break. Perform the maintenance for the components of the unit according to the component maintenance program.