*Oil–Water Separation Techniques for Bilge Water Treatment DOI: http://dx.doi.org/10.5772/intechopen.91409*

float to the water body surface [23]. In froth flotation, the separation takes place when the oil adheres onto the fine bubbles generated when air is introduced into the system. Surfactant is added to adsorb the air or water interface of the bubbles of air with the head groups (hydrophilic) in the water and the tail groups (hydrophobic) in the air. Hence, when the bubbles rise through the solution, the oil will concen-

Meanwhile, dissolved air flotation (DAF) introduces micro gas bubbles into the flotation chamber that has been formed when water is saturated with gas under pressure [25]. The oil droplet will spread around the gas, and conglomerate will continue to rise to the surface of the solution. The advantages of flotation treatment are the following: less investment needed, low energy consumption, and easy to maintain [26]. However, the statement contradicts with Yu et al. [27] who stated that flotation requires high energy consumption and has repairing and maintenance

According to Yu et al. [27], coagulation process is a robust oil–water separation technology because it is able to separate dissolved and emulsified oil; hence, it is vastly applied in the latest oily wastewater treatment method [28]. In the coagulation process, coagulant, a chemical substance, is added to the wastewater to destabilize the charge of colloidal particles in the solution [29] which is too tiny for gravitational settling. When the particles are destabilized, larger flocs are formed making it easier to settle and then are skimmed off to the clarifier or sludge

Anyhow, many experiments might be needed if the coagulation method is going

Some bilge water treatment units include biological treatment, which is called as a bioreactor. In this method, microorganisms are used to eliminate or reduce the organic and inorganic compounds before the treated wastewater being discharged to the sea or to a collection system [29]. The microorganisms convert the dissolved and particulate carbonaceous organic matter, including oil, in the bilge water into

As can be seen from Eq. 1 above, the oxidation process needs oxygen (O2) and

organic matter to carbon dioxide (CO2) and water (H2O). Other than that, the new cells generated are referring to the biomass produced after the oxidation of organic

There are two principals of biological processes used to treat wastewater, which are suspended growth and attached growth, or also known as biofilm, processes.

<sup>3</sup>� ! new cells <sup>þ</sup> CO2 <sup>þ</sup> H2O (1)

<sup>3</sup>�), in order to convert the

to be used in treating oily wastewater. This is because of the complexity of oily wastewater, making it hard to choose the most suitable coagulants for effective separation of oil and water to take place [27]. In a study done by Zeng et al. [30], oil removal efficiency is improved up to 99% when aggregation of poly-zinc silicate (PZSS) with anionic polyacrylamide (A-PAM) is used as the coagulating and flocculating chemicals. Somehow, higher costs are needed, and it could cause water

bodies'secondary pollution and difficulties to the next process [27].

simple end products through the oxidation process. The equation below is representing the aerobic biological oxidation of organic matter [29].

Organic material þ O2 þ NH3 þ PO4

nutrients, which are nitrate (NH3) and phosphate (PO4

trate on the bubble surfaces and foam is formed [24].

problem as well as issue in manufacturing of the device.

**3.4 Coagulation and flocculation**

thickener.

*Resources of Water*

**3.5 Biological**

matter takes place.

**152**

Suspended growth process maintains the microorganisms in liquid suspension by proper mixing methods. Meanwhile, attached growth attach the microorganisms to an inert packing material, where the wastewater will flow past the biofilm to remove the organic materials [29]. For OWS onboard, biofilm is used, in which the bacteria are attached to a synthetic support media. In this bioreactor, aerators are installed under the media to supply oxygen to the bacteria for bacterial growth as well as for oxidation of the organic contaminants to take place. Other than that, a clarifier is needed in order to remove the biomass formed at the end of the processes [16].

Biological treatment, with flexible operation, simple maintenance and management, as well as stable effluent quality [26], is indeed a suitable method since no waste oil is produced by the process [16]. Small oil droplets of emulsified oil, which are hardly removed by physical and chemical treatment, can be degraded easily by the bacteria [31]. However, CO2 will be produced from the process, resulting in increment in greenhouse gases. Even though the operating cost is low, the capital

