The influence of structural components of alkyl esters on their anaerobic biodegradation in marine sediment

Ester-based organic compounds are one type of synthetic base fluid added to drilling mud used during off-shore oil-drilling operations in the Gulf of Mexico. Concern over the environmental impact of synthetic base fluid (SBF) contaminated rock cuttings discharged into the Gulf of Mexico has prompted the promulgation of EPA regulations requiring that all SBF be tested for biodegradability in marine sediment prior to their use in the Gulf. In order to allow the design or selection of suitably biodegradable esters, the anaerobic biodegradability of a variety of ester compounds was tested using a marine sediment inoculum to reveal the effect of: (a) increasing the chain length of the acid moiety, (b) increasing the chain length of the alcohol moiety; (c) alternating the relative size of the alcohol and acid moieties, (d) branching in the alcohol moiety, and (e) the presence of an unsaturated bond in the acidic moiety. The chemical structure of esters was found to affect the completeness and rate of anaerobic biodegradation, and would affect their ability to be certified for use as an SBF in the Gulf of Mexico. Recommendations for ester usage include using esters that have a total carbon number of between 12 and 18 and avoiding the use of branched alcohols (or acids by inference). The presence of an unsaturated bond in the acid (or alcohol by inference) increased biodegradability of the ester.