2 Important Drains in the Ship’s Engine Room

There are several drains provided in the ship’s engine room in order to prevent water clogging and damage to any machinery. Though all these are equally important, there are few that require regular attention.

Two most important drains in engine room are:

The Air bottle moisture drains and Water Drains from fuel oil settling and service tanks

Most of you would know this for sure, but the fact remains that several mishaps happen due to improper handling and infrequent draining of these tanks. Mentioned below are two instances which explain the importance of these drains in ship’s operations.

Lesson 1

On one of our previous ships, we had an anchorage of 24 days and in this period everyone in the engine room forgot to drain the water from Fuel Oil settling and service tanks in the ship’s engine room.

We then suddenly received orders to move the ship. After a few hours, the engine slowed down and an overload alarm appeared on the engine control room panel.

We immediately tried to find out the reasons for the overload alarm and realized that the viscometer was showing “high viscosity” level. After some brain-storming, it was decided to check the service tank drains.

The junior engineer, who was assigned the task of checking the drains, came back saying that oil and not water was coming from the drains. However, when asked to drain more, a large amount of water discharge was found.

Luckily the generators were on Diesel oil (D.O) which helped prevent the blackout on the ship. Moreover, we had two settling tanks, so removal of water was much faster, but we missed the convoy at Suez as the engine RPM did not increase until “good quality” oil came in the line and the viscosity reached near normal.

Lessons Learnt:

We should have drained the tanks every day until we saw (Collecting the drain in suitable container- half cut soft drink can) no water coming. In our case, the drain pipe end was ending too deep in the funnel so the contents could not actually be seen. It is thus extremely important that what is coming out of the drain is clearly seen.

In dry dock, while cleaning Fuel Oil service tanks, a senior engineer must carefully check the drain from both inside and outside. The steam heating coils must also be pressure tested at this occasion.

Lesson 2

Air bottles are important for supplying air to the marine engine air starting system and for other important purposes. On a new ship, it was found that we were draining water not from the Air bottle bottom drain but from a drain on the filling line.

Below the filling line drain, a funnel was installed which was quite familiar to the air bottle drain funnel. The motorman was so sure about the drain that no senior officer bothered to cross check. Then, one day we got a doubt about the quantity of water draining from the funnel, which was of course not of the quality we expected.

Upon opening the air bottle manhole door it was found that the water was filled up to quite a high level and luckily it did not find its way into the main engine, else there could have been a massive damage to the engine or even injury due to water hammer. The Air bottle was then cleaned and the defect was rectified.

Lessons Learnt

Nowadays, it is often seen that the tracing of pipelines in ship engine room is not done properly, mainly because of shortage of crew members and fast turnarounds. Efforts should thus be made to trace the pipelines once in a while.

While opening air to main engine, moisture must be drained from the bottom most point of the line. Air driers and control air line filters must also be regularly checked.

These days quarantine inspection has also become important. The cold room holding provisions thus must be kept clean. Meat room and fish room drains should be checked (put a handful of salt in them), along with the unit cooler pan heater and drain.

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Procedure for Starting and Stopping of Sewage Treatment Plant on a Ship

Any machine on the ship requires a proper procedure to be followed for starting and stopping it. Failure to follow this step-by-step procedure will lead to either failure in starting or stopping the machine or lead to some fault.  

Sewage treatment plant is one such equipment on the ship which requires a step-by-step procedure to be followed for starting and stopping it. In this article we will go through the procedure of starting and stopping a sewage treatment plant.

Starting of a Sewage Plant

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 treat plant which needs to be stopped at regular interval of time for improving 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 be 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 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 growth of these bacteria and also 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 holding tank valve when the ship is out of restricted waters.

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

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

Stopping of the plant

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.

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 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.

3. If entry has to be made inside the tank, the later should be checked for hydrogen sulphide gas H2S with the help of 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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Maintenance and Checks for Sewage Treatment Plant on Ship

An efficient running of a sewage treatment plant on a ship requires periodic maintenance and daily checks of the system. Failure to do so can lead to an output that cannot be discharged into the sea, blockage of pipelines, and even failure of some parts.

There are several factors that results in smooth working of a sewage treatment plant on a ship and this article enumerates all the maintenance and checks for that smooth running.

Routine Checks

1. During daily rounds the pressure of the system should be checked and should be within the limits.

2. The air lift return should be checked to make sure the system is working properly. This is usually checked by the flow through the clear plastic pipe present on the installation. A clear sludge can be seen flowing through the tubes back to the aeration chamber.

3. Over a period of time, the sludge content in the aeration tank due to the recycling of the sludge from settling tank and fresh sewage increases. This sludge content or suspended solid particle is measured in mg/liter. The method of checking it is to take sample in a conical flask provided by the manufacturer and filling it up to 1000ml mark. The sample is then allowed to be settled and reading of sludge content is checked.

 

The sludge content should not be above the 200 mark, but if it is above the 200 mark, the tank has to be emptied for increasing the performance. In some ships this is checked by filtering the sample through a pre-weighed pad which is dried and re-weighed. This also depends from manufacturer to manufacturer, but is done every week.

4. Also the bio-pac is added every week to the plant to increase efficiency. The bio-pac contains aerobic bacteria which get activated when mixed with hot water.

5. The chlorination of the sample should be between 1-5 ppm and accordingly the dosing has to be increased or decreased.

6. The level of biological oxygen demand (BOD) is also checked and it should not be above 50 mg/liter. The sample is checked by incubating the sample at 20 degrees and well oxygenating the same. The amount of oxygen absorbed over a period of five days is measured. This is done to check the oxygen required for full breakdown of sewage after it has been treated by aerobic bacteria.

7. The internal coating of the sewage treatment plant should be checked for cracking and blistering. If any kind of damage is found then we first need to empty the tanks and then necessary repairs to be performed. Special precautions should be taken before entering the tank as it may contain toxic gases that cause suffocation. The gases should be checked by dragor tube, a special tube in which samples of various gases are taken before entering.

When it is made sure of the absence of toxic gases, entry is made with the mask and gloves. After completion of work the area has to be disinfected. Later, hands should be properly scrubbed and overalls be thoroughly washed.

8. If the sewage treatment plant is fitted with UV disinfectant system instead of the chlorination system, the UV lamp has to be changed as recommended by the manufacturer.

9. High and low level limit switches should be checked for auto cut-in and cut-out of the discharge to over-board pump.

10. Make sure the stand-by sewage discharge pump is put on auto during the working of the sewage treatment plant.

Maintenance

In case of a blockage of the sewage line there is a connection for back flushing which uses sea water. This is to be used to unclog the sewage pipelines; however, it is to note that all valves are closed and only the necessary valves are open, for it might back flush from WC of the cabins.

Generally, stewards are instructed for using chemicals provided by various manufacturers such as Drew Marine and Unitor during washing so that no blockages of lines are caused. However, there shouldn’t be any overuse of these chemical as it would lead to killing of aerobic bacteria which will decrease the efficiency of the plant and other problems.  The amount of chemicals is to be as per manufacturer recommendation.

Reference: From marine auxiliary machinery by Mc George

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4 Important Terms Related to Sewage Treatment Plant on Ships

Sewage on board ships needs to be treated before it is discharged to the sea. Sewage treatment plant is used to treat the sewage and make it less harmful for the sea.

Marine engineers must know the operation of the sewage plant before using the same in order to comply with the rules and regulations of discarding sewage.

While operating the sewage plant, engineer must know:

However, apart from the above mentioned aspects, marine engineers should also know four important terms while dealing with sewage treatment plants on ships. They are:

Biochemical Oxygen Demand (BOD) Coliform Count Recommended levels of pumping out solids Bio-chemical digestion of sewage

1. Biochemical Oxygen Demand

Biochemical oxygen demand is a test to identify biological decomposable substances and to test the strength of the sewage. BOD depends on the activity of bacteria in the sewage. These bacteria feed on and consume organic matter in the presence of oxygen.

 

BOD can also be defined as the amount of oxygen required by the micro-organisms in the stabilization of organic matter. The results are generally expressed as the amount of oxygen taken by one litre sample (diluted with aerated water) when incubated at 20 degree for five days.

BOD of raw sewage is 300-600 mg/litre. IMO recommends BOD of less than 50 mg/litre after treatment through sewage treatment plant.

 

2. Coliform Count

Coliform is a type of organism which is present in human intestine and is recognized as indicator organisms of sewage pollution. Presence of these organisms in water is an indication of pathogen (pathogen count), which are diseases causing bacteria responsible for cholera, dysentery, typhoid etc.

The number of coliform organisms present in sewage on ship is very large, with each person contributing around 125 billion in winters and 400 billion in summer.

IMO recommends faecal coliform count of less than 250 faecal/100 ml. of affluent after treatment.

 

3. Recommended levels of pumping out solids

Dissolved solids – Solids which are dissolved in the solution

Suspended solids – Solids physically suspended in sewage that can be removed by laboratory filtration and are relatively high in organic matter.

Settle able solids – Suspended solids that will subside in quiescent liquid in a reasonable period of time (usually around an hour)

Suspended level of raw sewage – Around 300-400 mg/litre; IMO recommends 50 mg/ litre after treatment.

Residual disinfectant – After treatment residual disinfectant should be as low as possible. IMO recommends use of ultra violet exposure for chlorination method.

 

4. Biochemical digestion of sewage:

Anaerobic process

Anaerobic bacteria can only multiply in the absence of free oxygen as they utilize chemically bound oxygen to survive. Anaerobic bacteria break down the organic matter into water, carbon dioxide, methane, hydrogen sulphide and ammonia. This process is called putrefaction.

The products thus produced out of this process are noxious and toxic. The effluent is of poor quality and by-products are highly corrosive.

Aerobic process

Aerobic bacteria require free oxygen to survive. They break down the organic matter to produce safe products such as water, carbon dioxide, inert residue, and energy to synthesize new bacteria.

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