Sequencing batch airlift reactors (SBAR): a suitable technology for treatment and valorization of mineral oil wastewaters towards lipids production

Abstract

Produced water (PW) and spent oil-based wastewaters are some of the largest mineral oil wastewaters produced. Due to the high toxicity of hydrocarbons, several countries set stringent discharge limits and its treatment is compulsory before discharge. In this work, biological treatment of mineral oil wastewaters coupled with the production of bacterial lipids is demonstrated in sequential batch airlift reactors (SBAR). Two SBAR (2 L working volume) were used for treatment of PW and lubricant-based wastewater (LW), inoculated with Alcanivorax borkumensis SK2 (SBARAb+PW) and Rhodococcus opacus B4 (SBARR.o+LW), respectively. A total petroleum hydrocarbon removal (TPH) efficiency up to 96% and 80% were achieved for SBARAb+PW and SBARR.o+LW, respectively. Intracellular lipids production in SBARAb+PW increased when lower TPH/N ratios and higher feast stage duration were applied (up to 0.74 g g-1 cell dry weight (CDW)), whereas in SBARR.o+LW higher lipids production was observed for higher TPH/N ratios (0.94 g g-1 in CDW). Triacylglycerols (TAG) were the main intracellular lipid accumulated in both SBARAb+PW and SBARR.o+LW operations, while wax ester (WE) production was only observed extracellularly in the SBARAb+PW.