Oil Spill
Authors: Ghazaly O.M. , Sayed E. 
Published: December 2007

Crude oil and refined petroleum products are mixtures of a large numbers of components, each with its own chemical and physical properties. Once oil is spilled, it immediately begins to undergo many natural physical, chemical and biological changes.

Oil and oily wastes can sometimes be broken down using biological process. Biodegradation of oil by microorganisms can only take at oil-water interface, so that on land the oil must be mixed with a moist substrate.

The rate of degradation depends upon temperature and availability of oxygen and appropriate nutrients containing nitrogen phosphorous.

There are a number of products on the market which contain oil degrading bacteria and other micro- organisms. And addition of oil soluble nutrients to accelerate the process of natural degradation these nutrients are more likely remain at the oil water interface rather than become dissolved in the sea. Although degradation rates can often be increased by regular aeration of the soil and by the addition of fertilizers, such as urea and ammonium phosphate. The method is only likely to be applicable to relatively small spills because of the amount of land required.

The contaminated material should not contain more than 20% oil, the oily debris is the spread over the surface to a depth of no more than 0.2 meters, the maximum application rate being about 400 tones of oil per hectare of land the oil should be left to weather until it is no longer sticky before being thoroughly mixed in with the soil using a plough or rotavator mixing should repeated at intervals of 4–6 weeks for the first six months but less frequently thereafter the biodegradation is suitable to applicable on artificial island at Belayim.

Introduction

Water and sediments through the world contain microorganisms (bacteria, yeasts, and fungi) which utilize and degrade petroleum components.

A very large number of species of micro- organisms, which can degrade petroleum, have been identified in open and coastal areas. Biodegradation is the most important of the processes in determining the ultimate fate of oil in the marine environment, although it does not immediately decrease the volume of oil or its impact on the environment after it is spilled.

Biodegradation is promoted by dispersion of oil slicks into small particles of high surface area. This applies whether dispersion occurs naturally or is induced by application of dispersants.

It is interesting to note that biodegradation enhances the rate of natural dispersion of oil. For biodegradation to proceed at reasonable rates, nutrines such as nitrogen and phosphorus must be present.

Thus, biodegradation proceeds more rapidly in costal waters (which contain many of these nutrients) than in the open sea.

Microorganism can degrade most components of crude oil, but the lighter, lower molecular weight components are degrated faster than the heavier ones.

Higher temperatures accelerate biodegradation, but this process still proceeds at significant rates even in arctic regions. Asphaltenes a class of compounds which is usually a small component of crude oils, are degrated at rates which are so slow as to be insignificant. Fortunately, however it is widely accepted that asphaltenes are virtually non- toxic.

Lighter components are degraded faster than high molecular weight ones, the most favourable temperatures for the microbial growth are above 25° C. Below 5° C virtually any growth ceases.

Solubility of oxygen in sea water is low (6 to 8 mg per liter) compared to quantities required for complete oxidation of hydrocarbons:3 to 4 mg of o2 per mg of hydrocarbon for conversion into CO2 and H2O.