1.1 BACKGROUND TO THE STUDY
Bio-remediation is one of the most viable options for remediating soil contaminated by organic and inorganic compounds considered detrimental to environmental health. Bio-remediation is a process defined as the use of microorganisms/plants to detoxify or remove organic and inorganic xenobiotics from the environment. It is a remediation option that oers green technology solution to the problem of hydrocarbon and heavy metals contamination. The main advantage of bio-remediation is its reduced cost compared to conventional techniques. Besides cost-effectiveness, it is a permanent solution, which may lead to complete mineralization of the pollutant. Furthermore, it is a non-invasive technique, leaving the ecosystem intact (Perelo, 2010). Bioremediation can deal with lower concentration of contaminants where the cleanup by physical or chemical methods would not be feasible. For bioremediation to be eective, microorganisms must enzymatically attack the pollutants and convert them to harmless products. Bioremediation can be effective only where environmental conditions permit microbial growth and activity, its application oen involves the manipulation of environmental parameters to allow microbial growth and degradation to proceed at a faster rate (Vidali, 2001). Hydrocarbon considered to be one of the major sources of energy supply across the world usually constitutes major contaminants to both aquatic and terrestrial ecosystems. Various techniques has been employed to remediate soil environment contaminated by hydrocarbons, ranging from physical, to chemical and mechanical forms of treating or removing the contaminants.
Bio-remediation offers a better technique for treatment and removal of these contaminants into an innocuous substance. Eective bioremediation of hydrocarbons in the soil environment can be achieved by either or both of the following techniques: Biostimulation and Bioaugmentation. Microorganisms play a significant and vital role in bioremediation of heavy metal contaminated soil and wastewater. Though when microorganisms especially bacteria are exposed to higher concentration of metal, it may have cidal eects on them. Hence, microorganisms are eective only at low metal concentration in the soil. Microorganisms are usually used for the removal of heavy metals.
Microorganisms can interact with metals and radionuclides via many mechanisms, some of which may be used as the basis for potential bioremediation strategies (Lloyd et al., 2005). Mechanisms by which microorganisms act on heavy metals includes biosorption (metal sorption to cell surface by physiochemical mechanisms), bioleaching (heavy metal mobilization through the excretion of organic acids or methylation reactions), biomineralization (heavy metal immobilization through the formation of insoluble sulfides or polymeric complexes) intracellular accumulation, and enzyme-catalyzed transformation (redox reactions) (Lloyd, 2002). Biosorption seems to be the most common mechanisms (Haferburg and Knothe, 2007). It is the only option when dead cells are applied as bioremediation agent. However, systems with living cells allow more eective bioremediation processes as they can self-replenish and remove metals via dierent mechanisms (Malik et al., 2004). On the other hand, living cells shows higher sensitivity to environmental conditions and demand nutritional and energetic sources. Many genera of microbes like Bacillus,Enterobacter, Escherichia, Pseudomonas and also some yeasts and moulds help in bioremediation of metal and chromium-contaminated soil and water by bio-absorption and bioaccumulation of chromium (Kotas and Stasicka, 2000). The heavy metal removal by the bacteria Pseudomonas was attributed to the cellular growth of these organisms (Ray and Ray, 2009).
1.2 STATEMENT OF PROBLEMS
Bio-remediation of engine oil polluted soil through agrommeral fertilizer and fermented melon seed reveals that spent engine oil harden inhibitory or toxic effect on the growth of crops. The degree of toxicity on crops is attributed to the contact of the volatile and water soluble hydrocarbons in waste engine oil with the tissue of the tender crop of absorption of soluble toxic substance by the plants.