Petrochemical slop wastewater treatment by means of aerobic granular sludge: effect of granulation process on bio-adsorption and hydrocarbons removal

The aim of this work is to study the mechanism for hydrocarbons removal from slop wastewater by means of aerobic granular sludge technology (AGS). Two sequencing batch reactors (SBRs), R1 and R2, worked for 150 days according to two different strategies: (i) slop treatment with mature salt-adapted granules (R1); (ii) cultivation of AGS with slop wastewater for its treatment (R2). Results revealed that, despite the similar physical properties of AGS at the end of experimental period (4.4–4.8 gTSS·L−1 and 2.2–2.5 gVSS·L−1, and mean dimensions of 1.15 mm and 1 mm, for R1 and R2 respectively), in R2 granules highlighted better total petroleum hydrocarbons (TPHs) removal efficiencies than R1 (83% vs 36%), when real slop was fed to the reactors. The direct cultivation of AGS with slop (R2) prompted a higher extracellular polymeric substances (EPSs) production that enhanced the bio-adsorption of TPH, thus favouring the adaptation of bacteria to hydrocarbons.