There are numerous industrial activities where large amounts of water become contaminated to a slight extent by oil or oil-based substances. For example, water used as ballast in the holds of oil tankers gives substantial quantities of oil contaminated water. Oil can also be present in bilge water from a ship. In many cases, the degree of contamination is slight, but the volumes of water involved are large. In view of the fact that oil and the like have a severe effect on the environment, disposal of such contaminated water poses a considerable problem. It is unacceptable to simply dispose of such contaminated water into rivers or other water courses. Further, in view of the present increasing awareness of the damage that various pollutants can do to the environment, in various jurisdictions the regulations etc. governing disposal of contaminated water are becoming stricter.
One known disposal technique is to pass the water through water/oil separators. In many cases, these consist simply of tanks with a series of baffles. They are based on the principle that oil and like substances float on the surface of water. Thus, by causing the water to flow under a series of baffles, the oil and other substances with a retarded or retained behind the baffles. The intention is that after the water has passed under a series of baffles, then it should be relatively clean. However, in many cases this technique is less than effective, and it does not reduce the oil content below that required. In particular, in the case of oils emulsified in water, this technique is ineffective. Further, where a mixture of oils is involved, there is usually at least one oil having a density close to that of water, preventing it from being separated by such a technique. In any event, such a technique requires the large volumes of water involved to be collected and transported to an installation with the baffled tanks, etc.
Other techniques include the use of membranes, to separate the oil from the water, but these have the disadvantage that they tend to clog quickly.
Another technique is to use filters, but this is ineffective where the oil has a similar molecular size to that of water.
A further technique is to use a settling tank, but this again relies upon the fact that the contaminants will float or otherwise separate from the water, which is not always the case.
All the foregoing techniques involve relatively large scale and expensive installations. As a consequence, the water has to be collected and transported to the installation for processing. This adds to the cost. At the present time, in Canada, it can cost Cdn. $1.00 per gallon to dispose of contaminated water. Since many marine operations and the like generate contaminated water in quantities of millions of gallons, the costs involved in disposal are considerable.
It is therefore desirable to provide some disposal technique for oil-contaminated water, which reduces the oil content well below any level required by regulation, etc., which is simple and economical, and which preferably does not require any large, complex or expensive equipment. It is desirable that the method can be carried out in a simple and economic apparatus, so that it becomes feasible to supply such equipment or apparatus to a location where any significant quantity of contaminated oil is collected, e.g. individual ports, docks, etc.