**5. Conclusions**

cost needed is high and skillful personnel to be in charge is required to ensure the

Basically, there are three stages involved in the process [32]. The first stage is heavy phase separation, where separated oils and solids are removed. In the second stage, the bacteria are used to convert the emulsified oil into non-harmful end products. This stage is known as emulsified oil degradation stage. Then, the third stage contains clarifier in order to remove the remaining solids and water.

Physicochemical sorption involved in absorption and adsorption processes can

eventually separate the oil from the bilge water. Absorption occurs when two discrete physical states of substances are fused together. Meanwhile, in adsorption, molecules adhere onto the surface of different phase [16]. Both absorption and adsorption involved absorbent sorption media and adsorbent, respectively. The oil is separated by pumping the bilge water through these media until their maximum sorption capacity is achieved, which then the oil is removed. Certain used media are possible to be regenerated onboard; meanwhile, some are regenerated or disposed of onshore. Somehow, the regenerated media is replaced once it is exhausted, where it can no longer absorb or adsorb the oil molecules. Having a few advantages which include low capital and operating cost as well as compact treatment unit, these two sorption techniques are suitable for vessels with less than 400 gross tonnages [16]. **Table 1** summarizes the comparison of the oil–water separation techniques.

Currently, many types of OWS for bilge from different manufacturers are available in the market. The separators consist of a number of separator units that

**No. Manufacturers Name of the products Separation techniques**

ULTRA-SEP Bilge Water Separator Ultrafiltration

ULTRA-SEP 1. Centrifugation

VG-SEP 1. Centrifugation

1 Alfa Laval PureBilge Centrifugation 2 EnSolve Biosystems, Inc. PetroLiminator OWS Biological

5 Compass Water Solutions CRP-SEP 1. Gravitational

6 Recovery Energy, Inc. BOSS Oily Water Separators 1. Filtration

*Examples of commercially available bilge water separator.*

3 Village Marine Tec. Village Marine Tec. Oily Water Separator (VMT OWS)

**applied**

Adsorption

(membrane)

2. Filtration 3. Ultrafiltration (membrane)

2. Adsorption

2.Centrifugation

2.Centrifugation

**4. Commercial OWS for bilge water treatment**

treatment functioned well.

*Resources of Water*

**3.6 Absorption and adsorption**

4 Separator Spares & Equipment, LLC.

**Table 2.**

**154**

Different techniques are available and being used in the oil–water separation techniques for bilge water treatment. Typically, more than one unit of separators is needed to meet the minimum allowable discharge limit value set by the regulatory bodies. Gravitational and centrifugal methods are said to be the first technique before undergoing further polishing separation. Polishing treatment unit caters smaller droplet of oil, or emulsified oil, which cannot be treated by gravitational and centrifugal methods. To conclude, oily bilge water can be treated with proper separation techniques so that the treated bilge water discharged to the sea comply with the limit and marine pollution can be minimized and prevented. Any other treatment techniques can as well be tested and introduced to enhance the oil–water separation process in treating bilge water.
