As mentioned earlier, every machinery system on the ship requires a proper procedure to be followed for starting and stopping and failure to follow this step-by-step procedure will lead to either failure in starting or stopping the machine or to some other fault.
Sewage treatment plant is one of such equipment in the ship’s engine room that requires a step-by-step procedure during starting and stopping.
STARTING
Generally, the sewage plant is running all the time while the ship is sailing. However, the plant might be required to be started manually if it is newly installed.
This is because the new plant needs to be stopped at regular intervals of time for improving its performance and maintenance procedures.
Following are the points that need to be followed for starting a sewage treatment plant:
Make sure if any maintenance is carried out on the sewage treatment system and all the openings have been closed properly before starting The sewage plant is be filled with fresh water inside the chamber At this stage, there are no aerobic bacteria inside the chamber, but the sewage would have started coming to the plant. In order to increase the efficiency and starting rate of the plant, a bio-pacis added to the plant by flushing the amount specified in the manual This bio-pacis mixed with warm water, which helps in the growth of bacteria and also in efficient functioning of the plant If the bio-pacis not added, the plant might take up to 5 to 7 days to become completely functional. However, with the bio-pacit becomes functional within 24 hours 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 Open the sewage overboard valve and close the holding tank valve when the ship is out of restricted waters The plant is to be continuously monitored and checked for the flow through the transparent plastic tubes Asample is taken for checking for suspended solids and chlorine content The test must be performed every week to check the performance of the system Some STPs are provided with 7 bar air line with solenoid valve in case the blower has to be stopped
“Do not turn off the power source of the aeration blower under any circumstances. If this happens, the micro-organism will die and thereby reduce the overall effectiveness of the device.”
STOPPING
Stopping of 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 For stopping the system, close the inlet valve to the sewage plant, then close the overboard valve and let the sewage go overboard Empty all the three chambers of the plant i.e. aeration, settling and chlorination chambers If the chambers are not emptied, it will lead to growth of anaerobic bacteria which forms the toxic H2S gas If entry has to be made inside the tank, the later should be checked for hydrogen sulphidegas H2S with the help of a dragortube by taking a continuous sample from the plant Entry needs to be made wearing mask and rubber gloves In case the ship is going to the dry dock, the overboard should be connected to the shore reception facilitiesReferences
The Ultimate Guide to Operating Procedures of Engine Room Machinery. Anish Wankhede [2014]