What happens when you flush!?

What happens when you flush!?

This is perhaps a topic we don’t give much thought and perhaps rightly so, but with thousands of passengers on-board there is going to be sewage to deal with, and can it just be pumped into the sea?

Anyone who has flushed a toilet on-board a ship can probably tell by the distinct sound that it is of course a vacuum system.  Using a vacuum system has advantages to a typical toilet flush, firstly the pipework to the collecting tank can be smaller, and secondly the flush uses considerably less water.  Water consumption on-board is already high so the more we save here the better!  Read about on-board water consumption and production here.

The vacuum is produced either by vacuum pumps or alternatively by water being pumped through a venturi ejector.  The waste is held in collecting tanks and then pumped to the sewage treatment plant.  Sewage treatment types are constantly being developed to keep up with regulations, I will describe the most up to date plant which is called a membrane bioreactor!  This I admit does sounds like something you would find in a nuclear power station, it is anything but.

I won’t go into the details behind the plant as I don’t think many people will want to read about it especially if having lunch.  The plant consists of pre filters, and then an aeration tank which has air lines running through it with nozzles, this ensures the effluent is aerated.  Within the tank are colonies of bacteria which respire aerobically to break down the waste into water and an innocuous sludge. The water then passes into a second aeration tank via an inter stage filter.  Again the bacteria is breaking down the waste, this part of the plant is known as the Bio-Reactor, not as hi tech as you previously thought.  From here the effluent is pumped through membrane filters which are similar filters to that used in reverse osmosis.  The pure water can fit through the filters but the bacteria cannot.  The result is what we called permeate.  This collects in a tank for discharge overboard.  Before discharged it is passed through an ultra violet lamp, this ensures any bacteria carried over is killed.

Would you drink it?

The manufacturers of the membrane bio reactor plants say the permeate is so clean that it is safe for drinking!  The permeate does get sent for testing in a laboratory regularly and I have seen the results from these tests.  The results came back with no traces of coliforms, which are a bacteria found in the human gut.  This is quite impressive considering in some ports around the world the drinking water has traces of coliforms!  The permeate no matter how clean will never end up in the drinking water supply there are plenty of regulations to protect us from that.

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