Grey and Black Water Treatment on Ships

The concept for waste water treatment used today on ships is the one-stream solution which consists of mixing grey water (from showers, handbasins, laundry) and black water (from toilets) and combined treatment by membrane bio-reactors. Immersed membrane modules, which are also used in municipal waste water treatment, are applied. Ultrafiltration installations with externally arranged modules with open channels at the raw-water side have also been designed.

For large waste water volumes, e.g. on cruise liners with more than 1000 passengers, the two-stream solution can be more effective.

• The grey water is treated by low-pressure reverse osmosis membranes. The permeate is available for technical purposes.
• The black water, the concentrate from low-pressure reverse osmosis and the kitchen waste water are treated by a membrane bioreactor. The filtrate can be discharged or reused in applications with lower quality demands.

The development of the two-stream solution was influenced by knowledge and experiences from the treatment of industrial waste water by membrane processes and the “do-not-mix rule”. The “do-not-mix rule” says that, in general, it is easier and more efficient to treat waste water with different composition and clear concentration differences by different processes. The figure shows the two-stream solution which has been implemented on 25 ships.

The membrane technology from the company Rochem UF, presented by way of example, is based on ultrafiltration and ultrafiltration + low-pressure reverse osmosis. It is shown in Figure