Precautions in Operating Biological Vacuum Sewage Treatment Plant
Following precautions in operating biological vacuum sewage treatment plant must be followed to maintain optimal process conditions and effluent quality.
- If there is no counter pressure for the discharge pump, a bend piping arrangement must be done with a pipe loop (goose neck) over tank’s water level to prevent siphoning.
- The unit must be in continuous operation to maintain biological activity.
- It will take about one month before effective biomass will overtake the process after first start-up or after maintenance break. During this bacteria breeding period unit is not working as designed.
- Never discharge both aeration chambers totally at same time. Ensure always that there is bacterial population left in either chamber I or chamber II to avoid collapse of the biological process.
- Amount of the needed dilution water can be calculated. Needed dilution water is 1 x incoming black water (vacuum system). The amount of black water in vacuum toilet system is 15 l/person/day. A total dilution water need can be calculated: Dilution water per day = (1 x 15 l/person/day) x persons on board.
- Dilution water can be fresh, brackish or technical water. Dilution water is added into aeration chamber I.
- Dilution is not needed, if vessel’s grey water is also processed in the treatment plant.
- Some antifoaming chemicals has a very high BOD5 value. It is recommended to use antifoaming chemicals which have low BOD5 value.
- All substances which might be harmful to the biological process such as large amounts of grease, acids, alkaline, etc. are not allowed to be led to treatment unit.
- Never let the pump run dry. Mechanical seals may be damaged.
- Effluent quality is within IMO’s limits after about one month of the start up.
- Take a sludge content test at least every week or every time when sludge “SLUDGE ALARM” is displayed.
- 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.
Alarms in Vacuum Sewage Treatment Plant
HIGH LEVEL ALARM
- Water level is over high level switch LSH over presetted time, timer setting 30s.
- Led is on (vacuum failure), ejector pump has been running over presetted time, timer setting 15min.
- Led is blinking (vacuum collapse), vacuum level below presetted value -0.2bar (Pressure switch alarm) over presetted
time, timer setting 2min.
- Emergency stop, emergency stop pressed down.
- High level alarm, see above.
- Blower overload, circuit breaker tripped.
- Discharge pump overload, circuit breaker tripped.
- Control voltage failure, circuit breaker tripped.
- Chlorination pump overload, circuit breaker tripped.
- Antifoaming pump overload, circuit breaker tripped.
- Presetted number of discharge times reached, counter setting 200 times.
Reference: EVAC Environmental Solutions Marine Sector Operation Manual