Biological degradation of oil sludge: A review of the current state of development

Abstract

Oil sludge is a thick viscous mixture of sediments, water, oil and hydrocarbons, encountered during crude oil refining, cleaning of oil storage vessels and waste treatment. Polycyclic aromatic hydrocarbons (PAHs), which are components of crude oil sludge, constitute serious environmental concerns, as many of them are cytotoxic, mutagenic and potentially carcinogenic. Improper management and disposal of oil sludge causes environmental pollution. The adverse effects of oil sludge on soil ecology and fertility have been of growing interest among environmental scientist and an important consideration in the development of efficient technologies for remediation of contaminated land, with a view to making such land available for further use. Oil sludge can be treated by several methods such as physical, chemical and biological processes. The biological processes are mostly cost effective and environmentally friendly, as they are easy to design and implement, as such they are more acceptable to the public. Compost, the product of biological breakdown of organic matter is a rich source of hydrocarbon-degrading microorganisms such as bacteria and fungi. These microorganisms can degrade the oil sludge to less toxic compounds such as carbon dioxide, water and salts. Compost bioremediation, the application of composting in remediation of contaminated environment, is beginning to gain popularity among remediation scientists. The success or failure of compost bioremediation depends on a number of factors such as nutrients, pH, moisture, aeration and temperature within the compost pile. The bioavailability and biodegradability of the substrate to the degrading microorganisms also contributes to the success of the bioremediation process. This is a review on the biological remediation technologies employed in the treatment oil sludge. It further assesses the feasibility of using compost technology for the treatment of oil sludge, as a better, faster and more cost effective option.

A review- bioremediation of oil sludge contaminated soil

“…Bioremediation of contaminated soil is defined as the use of living organism (mainly bacteria, fungi, algae) to make environment free from toxicity of contaminant through transformation, degradation and mineralization of the contaminants to less harmful compound [13,14]. There are three basic processes involved in this technology.…”

“…Each of these process can occur at contaminant site (in situ) or out of contaminant site (ex situ) as well as aerobic (with oxygen) and anaerobic (without oxygen) [16]. In situ bioremediation involves the treatment of organic pollutants under natural conditions at original contaminated sites without relocation [7,14].Whereas Ex situ bioremediation excavation and transportation of pollutants from original contaminated site to be treated elsewhere to maintain the proper conditions of the bioremediation process more easily [14]. Though ex situ bioremediation is faster than in situ, due to relocation of pollutants it has increased cost and the chance of direct exposure of toxicity to public generally worker [7].…”

“…The acceleration and growth of microbial organism such as bacteria and fungi depends on carbon nutrient elements such as Nitrogen and Phosphorus, an electron acceptor and organic compound that supplies carbon and energy [17,18]. The growth of the microorganism is prevented if there is shortage of organic and inorganic compounds such as nitrates, sulphates, carbon dioxide, ferric iron, amino acids, vitamins and the metabolism of microorganisms will occur [14]. Microorganisms facilitate degradation of oil sludge depending on some certain forms of nitrogen and phosphorus (NH 3 , NO 3-, NO 2-, organic nitrogen and orthophosphate such as KNO 3 , NaNO 3 , NH 3 NO 3 , K 2 HPO 4 and MgNH 4 PO 4 ) and nutrients in the form of fertilizers, slow release and oleophilic are added to meet this requirement [19].…”

“…In most of cases microbial organism perform degradation activities at optimum nearly at neutral pH between 6 and 9 [22,23]. In some cases, liming is introduced to transform from acidic to alkaline state to facilitate bacterial more than fungal growth to avoid mutagenic intermediates produced by fungal decomposition of PAHs [14].…”

“…The viscosity is increased with decrease in temperature whereas the solubility in water and volatility is reduced which negatively affect the transformation of long chain n-alkanes from solid phase to water phase causing delaying the oil sludge biodegradation [24]. Though there is a variety range of temperatures for effective biodegradation of hydrocarbon it is found to be optimum between 30 to 40°C [14].…”