Dissolved oxygen concentration as a strategy to select type and composition of bacterial storage lipids produced during oilfield produced water treatment

Abstract

Oilfield produced water (PW) management and treatment represents a significant cost to oil producers. Alcanivorax borkumensis is a marine bacteria capable of converting hydrocarbons into storage lipids, currently of great interest as raw materials for biofuel or oleochemical industries. In this study, the effect of dissolved oxygen (DO) concentration on the production of storage compounds by A. borkumensis SK2 was investigated in a sequencing batch airlift reactor treating saline oilfield produced water (PW). Intracellular lipids accumulation decreased from 0.74 g/g cellular dry weight (CDW) (7–8 mg/L O2) to 0.51 g/g CDW under 2–3 mg/L O2 and 0.45 g/g CDW during alternated DO concentrations of 7–8/1–2 mg/L O2 (famine/feast stage). Triacylglycerols were the main lipids accumulated for DO of 7–8 and 2–3 mg/L O2. During alternated DO conditions, accumulation of polyhydroxyalkanoates (0.41 g/g CDW) was observed. Extracellular lipids production were mainly wax esters and not significantly affected by DO concentration. Fatty acid (FA) composition and relative proportions of saturated and unsaturated FA in the produced compounds was also affected by oxygen availability. The obtained results show that selection of DO concentration during PW treatment can be used as a strategy to direct bacterial metabolism to production of a particular compound of interest. Hydrocarbon removal efficiencies in the range of 90%–96% were achieved showing that is possible to reduce aeration costs without compromising PW treatment and concomitant production of valuable compounds.