Abstract

As a general trend in the Oil and Gas industry, thetreatment and disposal of waste is a serious environmentalissue. During Exploration and Production activities, drilling operations may generate oily waste as drill cuttings.Hydrocarbons may also enter the soil ecosystem in the caseof accidental oil pollution. These wastes are usuallydisposed of in a variety of methods including thermal andphysico-chemical treatments. Over the last ten years, bioremediation has been considered as a possiblealternative to "classical" treatments since it has been wellestablished that hydrocarbons are prone to be biodegraded.This paper presents the scientific principles ofbioremediation and on-site applications illustrated withcases of studies : landfarming of drill cuttings, biocomposting of hydrocarbons-polluted soils and oilycuttings, natural attenuation hydrocarbons-polluted soil, development of biodegradable oil-based mud andphytoremediation processes. This publication aims atdemonstrating that oily waste can be depolluted bybiological treatments; however, in-situ biodegradation mustnot be over-estimated. Our experience demonstrates that incertain local conditions the biological activity is notefficient, and the treatment duration becomes a criticalissue. Systematically, a detailed waste management study, including feasibility, cost, logistics and regulations has tobe completed to verify that bioremediation is the keysolution for the oily waste treatment and disposal.

Introduction

Large amounts of hydrocarbons (HC) are extracted, produced, refined and handled on land every year anddespite, improvements in careful handling, transport andcontainment, there is the possibility that some may enterthe soil environment. Oil can reach the soil from many sourcesfor example oil spills, blowouts, road accidents, leaking ofunderground storage tanks, and non-controlled landfilling.Onshore and offshore drilling operations generate oilywastes like the drill cuttings that are composed of thedrilling fluid mixed with the subsoil material (mineralmatter). There are three major types of fluids or "muds" :water-based (WBM), oil-based (OBM) and synthetic-based(SBM). The release of oily waste has been shown to causeserious damage to natural ecosystems. The vegetation canbe totally eliminated for a long period of time in the case ofhigh inputs of HC(1). In the soil, HC are subjected to physical (evaporation, leaching, adsorption) and biological(biodegradation) processes(2,3). Residual HC may persist fora long time in case of no treatment.

Physicochemical and biological treatments involvingmicroorganisms can be used in the decontamination of oilywastes. Natural attenuation has been proposed as aremediation technique in specific cases of soil and groundwaterpollution. Bioremediation, i.e. the stimulation ofmicrobial degraders for the remediation of contaminatedenvironments, has been also proposed as an alternative orcomplementary technique to treat soil pollution and oilywastes(4). It mainly consist in optimising the environmentalconditions for the development of naturally occurringpollutant degraders by adding nutrients and maintainingaerobic conditions if deemed necessary. The concentrationof nutrients has to be adjusted to an optimal ratio expressedas C/N/P. Bioremediation practices are usually site-specific(type and concentration of HC, wastes characteristics, technical equipment available, type of fertilisers...).Landfarming and composting in piles have beensuccessfully used to treat oily wastes (sludges, soils, cuttings). Phytoremediation, i.e. the use of plants for theremediation of contaminated environments, has beenrecently proposed to treat soils polluted by mineral andorganic compounds(5). The action of plants may consist inthe direct uptake of pollutants. Plant roots also releaseexudates, which stimulate the activity of microorganisms inthe rhizosphere thus increasing the rates of microbialbiodegradation in the root zone.

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