Effect of rhamnolipid on the aerobic removal of polyaromatic hydrocarbons (PAHs) and COD components from petrochemical wastewater

The removal efficiencies of 15 PAHs and some COD components (inert, readily degradable, slowly degradable and metabolic products) from a wastewater taken from a petrochemical industry treatment plant (İzmir, Turkey) have been determined using an aerobic completely stirred tank reactor (CSTR). Addition of rhamnolipid surfactant (15 mg l−1) increased the removal efficiencies of PAHs and soluble COD from 72% and 90% to 80% and 99%, respectively. The rhamnolipid treatment caused a significant increase of 5- and 6-ring PAH degradation. The soluble COD removal efficiency was 93%, in CSTR reactors with rhamnolipid added. The inert COD removal efficiency was 60% in a CSTR reactor containing rhamnolipid. Batch tests showed that removal arising from the adsorption of the PAHs was low (between 1.88% and 4.84%) while the removal of PAHs from the petrochemical industry wastewater via volatilization varied between 0.69% and 5.92%. Low sorption capacity (Kp) values for refinery activated sludge (approximately 2.98 l g−1) confirmed that bio-sorption was not an important mechanism controlling the fate of PAHs in aerobic CSTR reactors. Models proposed to simulate the PAH removal indicated that 94% of the PAHs were removed via biodegradation.