Phenolic refinery wastewater biodegradation by an expanded granular sludge bed reactor

Refinery spent caustics (SC) were diluted with sour waters (SW) in a ratio 1:7, neutralized with CO₂ (SC/SW_CO2) and 83% of H₂S was striped during this procedure, remaining an aromatic portion that contained 2123, 2730 and 1379 mg L⁻¹ of phenol, p-cresol and o-cresol, respectively. The mixture was treated anaerobically in an EGSB reactor fed with 1.5 gCOD L⁻¹ d⁻¹, without mineral supplements causing loss of COD removal efficiency that dropped to 23%, methane production ceased and no phenol or cresols were biodegraded. The EGSB experiments were resumed by feeding the reactor with nutrients and phenol at 1.0 gCOD L⁻¹ d⁻¹. The mixture SC/SW_CO2 added to the phenol load, was step increased from 0.10 to 0.87 gCOD L⁻¹ d⁻¹ maximum. When total organic load was increased to 1.6, COD removal efficiency was 90% and at the highest load attained, 1.87, efficiency dropped to 23% attributed to the toxic effect produced by cresols.