Procedure for Starting and Stopping


The sewage plant is generally running all the time during sailing, but it might need to be started when the ship is installed with a new sewage treatment plant which needs to be stopped at regular intervals of time to improve its performance and maintenance procedures. Below are the points that need to be followed for starting a sewage treatment plant:


1. Make sure if any maintenance is carried out on the sewage treatment system, all the openings have been closed properly before starting.


2. The sewage plant is filled with fresh water inside the chamber.


3. At this stage, there are no aerobic bacteria inside the chamber, but the sewage has started coming to the plant. Thus, in order to increase the efficiency and starting rate of the plant bio-pac is added to the plant by flushing the amount specified in the manual.  This bio-pac is mixed with warm water which helps in the growth of these bacteria and also the efficient functioning of the plant.


4. If the bio pac is not added, the plant might take up to 5 to 7 days to be completely functional. However, with the bio-pac, it becomes functional within 24 hours.


5. Start the air compressor or open the air valve as per the design of the plant. The pressure is maintained as per the manual. Generally 0.3-0.4 bars.


6. Open the sewage overboard valve and close the holding tank valve when the ship is out of restricted waters.


7. The plant is continuously monitored and checked for flow through the transparent plastic tubes.


8. The sample is taken for checking for suspended solids and chlorine content.



Stopping the sewage treatment plant is generally done either before entering the dry dock or in case some maintenance has to be carried out inside the treatment plant.


1. For stopping the system, close the inlet valve to the sewage plant and close the overboard valve and let the sewage go overboard.


2. Empty all three chambers of the plant i.e. aeration, settling, and chlorination chambers. If the chambers are not emptied, it will lead to the growth of anaerobic bacteria which forms the toxic H2S gas.


3. If an entry has to be made inside the tank, the latter should be checked for hydrogen sulphide gas H2S with the help of a dragor tube by taking a continuous sample from the plant. Entry is made with the help of mask and rubber gloves should be put on.


4. In case the ship is going to dry dock the overboard should be connected to shore reception facilities.




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