Sewage Treatment Plant – Internal Inspection Procedure

After the sewage treatment plant has been stopped, isolated and completely emptied, the internal inspection should be carried out systematically. The OEM (Original Equipment Manufacturer) maintenance instructions and the vessel's SMS (Safety Management System) procedures must always be followed.

1. Preparation Before Inspection

1. Stop the sewage treatment plant and isolate it from the electrical power supply.
2. Apply Lock-Out/Tag-Out (LOTO) to prevent accidental starting or operation.
3. Close and secure all relevant inlet, outlet, air and chemical lines.
4. Drain and completely empty all tanks.
5. Thoroughly ventilate the tanks and connected spaces.
6. Test the tank atmosphere and confirm that it is safe for entry before anyone enters.

2. Internal Inspection

After confirming that the tank is safe for entry:

1. Carefully open the tank/manhole covers.
2. Inspect the tank walls, bottom and internal surfaces for:
   • Corrosion.
   • Cracks.
   • Structural damage.
   • Excessive sludge, scale or other deposits.
3. Inspect the air pipes, air diffusers and aeration system for blockage, damage or deterioration.
4. Inspect pumps, valves, pipes and connections for wear, leakage and damage.
5. Check the screens, filters and sludge-handling arrangements and clean them as required.
6. Inspect floats, level sensors and other internal fittings for damage and deterioration.
7. Check rubber seals, gaskets and manhole covers for deterioration and damage.
8. Inspect the internal coating/paint for peeling, blistering or other damage.
9. Remove accumulated sludge, scale and other deposits in accordance with the OEM instructions.
10. Check all accessible moving parts for free movement and signs of abnormal wear.

3. Specific Checks as per OEM Instructions

The following checks should be carried out as applicable to the particular sewage treatment plant and as specified in the manufacturer's maintenance manual:

• Check the condition and cleanliness of the aeration unit and diffusers.
• Check pump impellers, shafts and bearings, where accessible.
• Check all valves for correct operation.
• Check level switches and sensors for correct condition and operation.
• Check the air supply system for blockage or restriction.
• Replace damaged seals, gaskets and worn components with OEM-approved spare parts.
• Carry out any additional measurements, clearances, inspections or tests specified by the manufacturer.

4. Reassembly and Operational Test

After completing the internal inspection:

1. Ensure that all sludge, deposits, tools and foreign materials have been removed.
2. Reassemble the plant correctly and refit all covers, gaskets, fittings and connections.
3. Close and secure all openings.
4. Restore the piping connections and remove isolations in accordance with the approved procedure.
5. Fill the plant as required and carry out a leak test.
6. Start the plant and conduct a complete operational test.
7. Confirm correct operation of the pumps, aeration system, valves, level controls, alarms and other associated equipment before returning the plant to normal service.

5. Safety Precautions

A sewage treatment tank is a confined/enclosed space and may contain toxic, oxygen-deficient or flammable atmospheres. Safety must therefore be the first priority.

1. Never enter the sewage tank without following the vessel's approved enclosed-space entry procedure.
2. Obtain the required enclosed-space entry permit and carry out a proper risk assessment and toolbox meeting before starting the work.
3. Isolate and lock out all possible electrical, mechanical, pneumatic and hydraulic energy sources.
4. Ensure that all relevant sewage, air, chemical and other lines are isolated and secured against accidental flow or operation.
5. Test the atmosphere for:
   • Oxygen concentration.
   • Toxic gases.
   • Flammable gases/vapours.
6. Atmosphere testing should be carried out before entry and continuously during the entry.
7. Provide continuous forced ventilation throughout the work.
8. Keep a trained attendant outside the tank at all times and maintain reliable communication with the personnel inside.
9. Keep suitable rescue equipment, safety harness and lifeline immediately available.
10. Use appropriate PPE, including:
    • Safety helmet.
    • Protective gloves.
    • Safety shoes/boots.
    • Safety goggles/eye protection.
    • Protective clothing.
    • Suitable respiratory protection where required.
11. Never work alone inside the tank.
12. Stop the work immediately if:
    • Ventilation fails.
    • Gas readings become unsafe.
    • Any alarm is activated.
    • Any person feels unwell or experiences difficulty breathing, dizziness or other symptoms.
13. Provide adequate lighting and use only suitable, properly approved electrical equipment for the environment.
14. Avoid direct contact with sewage and contaminated surfaces as sewage may contain harmful microorganisms.
15. After completion, properly clean, wash and disinfect tools and PPE used during the inspection.