Category Archives: Sewage Treatment

Troubleshooting of Biological Vacuum Sewage Treatment Plant on Ships

 Troubleshooting of Biological Vacuum Sewage Treatment Plant on Ships

Trouble

Cause

Remedy

Vacuum is not created
even though pump is
running.
  1. Tank empty
  2. Foam instead of liquid in tank
  3. Valves are shut
  4. Incorrect rotation of motor
  5. Blockage or leakage in piping system.
  1. If the tank is empty, fill to at least to the low level switch. Check the condition of the pump according to the manufacturer´s instruction.
  2. If the pump is pumping foam instead of liquid, this will be evident due to severe vibration. Add water to the tank and try
    again. If adding water does not help, reduce the level of foam by pouring antifoam agent into the tank (1 cup per 2 cubic metres of foam and sewage).
  3. Check that shut-off valves are fully open and not clogged.
  4. If the direction of rotation of the pump is wrong, change wiring accordingly.
  5. Close the valves that isolate the collecting unit from the piping system and start the pump again. If vacuum now builds up, there
    must be a leak in the piping system.
The ejector pumps do not
create enough vacuum.
Sewage plug in the ejector.
  1. Make sure that pump is stopped and shutoff valve is closed.
  2. Remove plug and clean out ejector. If this procedure is unsuccesful, the following
    steps should be taken.
  3. Dismantle flange connections and remove bend.
  4. Dismantle flange connections and remove ejector from tank.
  5. Dismantle flange connections and remove connection cone.
  6. Withdraw non-return valve from ejector.
  7. Clean sealing surfaces and if necessary replace rubber flap.
  8. While the ejector is dismantled, it is advisable to check the nozzle and the inside of the ejector housing for sludge and impurities.
  9. Refit ejector and non-return valve in reverse order to dismantling, at same time checking the condition of all seals and replacing as
    necessary.
  10. Make sure that non-return valve is correctly positioned.
Discharge pump does not start.
  1. Motor defect
  2. No power
  3. Automatic fuses off
  4. Impeller defect
  5. Failure in float switch.
  1. Replace motor.
  2. Check the electrical system.
  3. Check reason for this before
    switching fuses on.
  4. Measure clearance of impeller.
  5. Check float switch and wiring, repair or replace.
Discharge pump does not stop.
  1. Failure in float switch.
  2. Too much water enters the plant.
  1. Check float switch and wiring, repair or replace.
  2. Allowed in peak periods. Try to
    reduce peak flow.
Discharge pump is running but not
pumping.
  1. Wrong rotation direction.
  2. Impeller defect.
  3. Valve in discharge system closed
    or defect.
  1. Change phases on electrical motor.
  2. Replace impeller.
  3. Check valves in discharge system.
There is overflow in system.
  1. Pump is clogged.
  2. Discharge pump defect.
  3. Too much water enters the plant.
  1. Open and clean pump.
  2. Open bypass and repair/replace
    discharge pump.
  3. Allowed in peak periods. Try to
    reduce peak flow.
Air blower does not run. Screen in aeration chamber clogged.
• Timer wrongly adjusted.
• No power.
• Automatic fuses off .
• Motor defect.
• Impeller defect.
• Defect non-return valve and water in
air blower.
Clean screen and remove dirt.
• Check and adjust timer .
• Check the electrical system.
• Check reason for this before
switching fuses on.
• Replace or repair.
• Replace impeller.
• Repair and replace valve.
! NOTE: In case of emergency, use
vessel’s air system, but pressure
must be less than 1.5 bar.
Air blower is running, but not creating
sufficient pressure. Air blower is running, but low pressure.
  1. Defect non-return valve.
  2. Wrong direction of rotation.
  1. Repair or replace.
  2. Change phases on electrical motor.
Air blower is running , but no surface
bubbles in the activation tanks.
  1. Hose or pipe defect.
  2. Air distributors clogged or defect.
  1. Repair or replace.
  2. Clean or replace air distributors.
Plant smells.
  1. Too much mineral sludge.
  2. Bacterias killed. Brown sludge
    indicates normal bacteria life. Black sludge indicates that bacterias are killed.
  1. Check sludge content and discharge if required.
  2. Check air blower function by opening the man holes. Surface bubbles must be seen during blower operation.
Discharge water is dirty.
  1. Too much water enters the plant,
    thereby creating too high hydraulic loading.
  2. From newly started plants, bacterias not yet formed.
  3. Bacterias killed.
  1. Allowed in peak periods. Try to
    reduce peak flow.
  2. Check start up date. Time required
    for bacteria formation is approximately 4 (four) weeks.
  3. See “plant smells”.
There is too much black sludge on
surface in settling tank III.
  1. Insufficient operation of sludge
    return pump.
  1. Check and adjust return sludge air
    valve. Check air hoses.
There is no residual chlorine in the
discharge water.
  1. Dosing pump is not operating.
  2. Disinfectant tank is empty.
  3. Dosage rate is too low.
  4. Disinfection chlorine is obsolete.
  1. Check pump operation.
  2. Fill it up with approved disinfectant.
  3. Increase dosage by adjusting dosing pump.
  4. Replace with “fresh” chlorine.

Reference: EVAC Environmental Solutions Marine Sector Operation Manual

Related Links:

Biological Vacuum Sewage Treatment Plant on Ships

Maintenance of Biological Vacuum Sewage Treatment Plant on Ships

Troubleshooting of Biological Vacuum Sewage Treatment Plant on Ships

Working and Maintenance of Air Ejector, Pressure Switch and Level Switch

Sewage Testing in Biological Vacuum Sewage Treatment Plant

Precautions in Operating Biological Vacuum Sewage Treatment Plant