Operating Principle Biological Sewage Treatment System DVZ-SKA- BIOMASTER
The Biological Sewage Treatment system consists of three watertight compartments and other equipment:
1. Pre-treatment Tank
2. Treatment Tank
3. Disinfecting Tank
4. Other Equipment (pumps, blowers, dosing pumps, level sensor)
The “black water” is fed through the pipeline using gravity or a vacuum and flows through the sewage inlet into the pre-treatment tank, where intensive sedimentation and pre-treatment takes place using oxygen, a continuous supply of which is provided by a fan. The system is ventilated to the open deck via the ventilation system.
The pre-treated “Black water” flows through a special overflow into the treatment tank, containing the submerged fixed bed, which is at the center of the system.
The sewage to be treated must circulate through this bed. Fine oxygen bubbles are blown in by a special disperser keep the sewage in suspension and excite the micro-organism on the surface of the fixed bed into extreme activity, causing almost complete aerobic- biological degradation of faecal mass.
Remaining activated sludge is fed back into the pre- treatment tank using a sludge siphon and continues to serve as an active biomass within the system.
The biologically cleaned sewage is fed to the disinfecting tank via rising pipe. Adding disinfectant via the metering pump kills off germs and bacteria.
The Blower is operated by a manual switch on the control panel and should be switched on all the time when the unit is in operation.
The Discharge pump is controlled by a HAND/OFF/AUTO switch on the control panel. When the Discharge pump switch is in the AUTO position, it is under the control of the level switches situated in the Disinfectant tank. When the maximum filling level is reached, the level sensor activates the Discharge pump, which empties the tank down to a specified minimum level. The dosing pump is switched on when the water level in the Disinfectant tank is ‘LOW’ and is switched off automatically after the preset time.
GENERAL PROCEDURE FOR START UP
- Close all air and water valves, and inspect overall system visually.
- Check the motors rotation.
- Check all motors for current draw.
- Fill the treatment plant with water, NEVER start up a system with waste water. Use the same water source, if possible, as used for sanitary service. Fill treatment plant tank until water spills into contact tank and reaches a level ½ way up the contact tank sight glass. Check for leaks, if any, repair before start up.
- Start compressed air supply by starting any of the Air Blowers.
- Bleed air out of Discharge pump casing. Check pump action by hand- start (sight glass level falls) and, necessary, fill with water again. After checking put the pump in AUTO mode.
- Fill the chlorine container with 15 % Sodium Hypochlorite, and check pumping action of dosing pump (manual control switch).
- During the normal operation, the 2-way outlet valve for the Disinfectant Tank should be in open position. The valves for the Pre treatment and Treatment tank should be closed.
NOTE: it will take 5-10 days for the bacterial culture to grow to normal operating strength. During this period system, effluent may change from clear to cloudy. If bacterial culture has started properly it reverts to clear.
SLUDGE PUMP OUT
If the accumulated sludge at the bottom of the Treatment plant is not removed, it will spill over into the Contact Tank. In general, terms, if the water in the sight glass turns from clear to gray or brown, a pump out is required to keep the effluent quality above the required by IMCO standard.
It can anticipate, that the ship will go to restrict waters, a sludge pump out shall be performed a few days before, in open (unrestricted discharge) waters to ensure full operational time available without the need to de-sludging. The procedure outlined below is recommended if the system is to consistently produce a clear effluent. The frequency of pump out is determined by operating history and the requirements. The time period specified is average and based up on the system operating at 100% of rated capacity.
- Bypass sewage system or close inlet valve.
- Turn discharge pump off.
- Close disinfecting tank discharge valve.
- Open the pre-treatment tank valve or treatment vale.
- Start discharge pump manually and drain or pump contents overboard, if outside of regulated waters, or into a suitable receiver or disposal.
- Turn discharge pump off when tank is empty. DO NOT RUN PUMP DRY.
- Close the pre- treatment tank valve or treatment valve.
- Refill the treatment tank with water immediately after pump out to maintain the bacteria.
DO NOT ALLOW SYSTEM TO REFILL WITH SEWAGE WITHOUT FIRST FILLING WITH WATER.
For highest quality, drain Pre-treatment Tank, Treatment tank at 3-month intervals maximum.
Check level in chlorine tank regularly. De-aerate system after changing chlorine tank according to manufacturers’ documentation.
The system is set up for the use of liquid sodium hypochlorite in 15 % concentration.
WARNING: Liquid chlorine is aggressive and poisonous. Use proper protective clothing.
GUARDEX CHLORITE CALCIUM HYPOCHLORITE (SHOCK BRYTE) Keep only in the original container in a cool, well-ventilated pace.
Daily Routine Work
1. Check the general condition of the system.
2. Check the blower operation. Check for abnormal running noise.
3. Check the discharge pump operation.
4. Observe any abnormal equipment conditions. Confirm the chlorine pump is operating automatically.
5. Check that the Vacuum Pumps are maintaining the vacuum in the system properly and the cuts in and cuts off operation is as per the settings of the Pressure Switches provided.
Weekly Routine Work
1. Take the sample.
2. Determine the free chlorine value.
3. The cock valve should be carefully adjusted to give the required flow. Check the chlorine content of the effluent.
Monthly Routine Work
1. Visually check for leakage and condense water.
2. Check for all tanks after opening their respective cover for blockages, braid formations, deposits, leaking points and damage on components and machines, clean if required.
3. Clean the high-level alarm Sensor and the Discharge Pump Cut in and Cut Off Sensors.
4. Check the Blowers filter for dirt, replace if required.
Yearly Routine Work
1. Empty and Clean the Treatment Plant.
The Sewage Discharge Pump, the Air Blowers, the Dosing Pump and the Vacuum Pumps should always be maintained in good working condition and the maintenance should be carried out as per the vessel’s PMS.
Please observe the information in these operating instructions, to ensure that the unit functions satisfactorily and remains serviceable for a long period.
- Take suitable measure to prevent unintentional operation or impermissible impairment.
- Note that lines and valves must not be unscrewed from systems that are under pressure!
- Always switch off the voltage supply before working on the system!
- Always keep in mind during maintenance and repairs, that bacteria and viruses are present in the waste water. Health risks are minimal when good personal hygiene is observed and proper precautions are taken. Use protective clothes, gloves and rubber boots where necessary.
- Chlorine in tablet or liquid form can be hazardous. Do not inhale vapors.
- Vapors and gasses: Make sure tank is ventilated properly before entering.
- 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 and cabin’s toilets.
Find below extract from MARPOL 73/78
DISCHARGE OF SEWAGE Annex IV Of MARPOL 73/78
Regulations for the Prevention of Pollution by Sewage from Ships
Discharge of sewage
(1) Subject to the provisions of regulation 3 of this Annex, the discharge of sewage into the sea is prohibited, except when:
(.1) The ship is discharging comminuted and disinfected sewage using a system approved by the Administration in accordance with regulation 9.1.2 of this annex at a distance of more than 3 nautical miles from the nearest land, or sewage which is not comminuted or disinfected at a distance of more than 12 nautical miles from the nearest land, provided that in any case, the sewage that has been stored in holding tanks, or sewage originating from spaces containing living animals shall not be discharged instantaneously but at a moderate rate when the ship is en route and proceeding at not less than 4 knots; the rate of discharge shall be approved by the Administration based on standards developed by the Organization; or
(.2) the ship has in operation an approved sewage treatment plant which has been certified by the Administration to meet the operational requirements referred to in regulation 9.1.1 of this Annex, and
(.2.1) The test results of the plant are laid down in the ship’s International Sewage Pollution Prevention Certificate.
(.2.2) Additionally, the effluent shall not produce visible floating solids in, nor cause discoloration of, the surrounding water.
(2) The provision of paragraph 1 shall not apply to ships operating in the waters under the jurisdiction of a State and visiting ships from other states while they are in these waters and are discharging sewage in accordance with such less stringent requirements as may be imposed by such State.
(3) When the sewage is mixed with wastes or waste water covered by other Annexes of MARPOL, the requirements of those annexes shall be complied with in addition to the requirements of this Annex.
IF THE SEWAGE TREATMENT PLANT IS PUT OFF;
a- Prior entering territorial waters (12NM from nearest land), the discharge of raw sewage overboard is not permitted and is to be turned over to the sewage holding tank and the sewage overboard discharge valve is to be kept shut and padlocked to avoid any inadvertent discharge. After locking, the key is to be retained by Chief Engineer. This event is to be logged in the sewage discharge log.
b- All sewage generated during vessel’s course within territorial waters of a country and port stay is to be collected in the holding tanks.
c- Untreated Sewage overboard discharge is only to be resumed after the vessel is out of territorial waters (12NM from the nearest land) and underway at the speed of more than 4 knots, the position of the vessel is to be confirmed from bridge and event logged.
d- Discharge should be carried out at a moderate rate.
e- Capacity of the holding tanks is sufficient for above 5 days under normal use.
f- Holding tank is to be flushed with fresh water periodically.
g- Regular maintenance of all equipment is to be carried out as per maker instructions.
h- Holding tank must be emptied out at least 6 hours before entry into territorial waters; the position of the vessel must be confirmed with the bridge.
i- Also, when special port regulations prohibit discharge from a sewage treatment plant, the sewage must be retained in the sewage holding tank.
j- Discharge of untreated sewage is not allowed, EXCEPT IN EMERGENCY.
The provisions of this Annex shall apply to:
(a) (i) New ships of 400 gross tonnage and above;
(ii) New ships of less than 400 gross tonnages which are certified to carry more than 15 persons;
(b) (i) existing ships of 400 gross tonnage and above, 5 years after the date of entry into force of this Annex;
(ii) existing ships of less than 400 gross tonnage which are certified to carry more than 15 persons, 5 years after the date of entry into force of this Annex.
Note: The sewage Chlorine tests should be carried out everyday less than 12 nautical miles from the nearest land or all USA Coastguard territorial waters. A normal chlorine level of Discharged sewage should be between 1-4 ppm. In USA Coastguard territorial waters, chlorine level of discharged sewage should be between 0.2-0.5 ppm. The chlorine that is giving to a system can be stopped outside of the 12NM from the nearest land, consequently, the dosage pump set can be reduced to “0” zero level which means “off” condition.
Article Submitted By: NEERAJ RAHI