Hydrolysis and acidification of activated sludge from a petroleum refinery

The cost-effective treatment of activated sludge that is generated by refining petroleum is a challenging industrial problem. In this study, semi-continuous stirred tank reactors (CSTRs) containing petroleum refinery excess activated sludge (PREAS) were used to comparatively investigate hydrolysis and acidification rates, after the addition of heneicosane (C₂₁H₄₄) (R1) and 1-phenylnaphthalene (C₁₆H₁₂) (R2) to different and individual reactors. Operation of the reactors using a sludge retention time (SRT) of 6 days and a pH of 5.0, resulted in the maintenance of stable biological activity as determined by soluble chemical oxygen demand (SCOD), volatile fatty acids (VFAs) production and oil removal efficiency. The optimum conditions for hydrogen production include a SRT of 8 days, at pH 6.5. Under these conditions, hydrogen production rates in the control containing only PREAS were 1567 mL/L (R0), compared with 1365 mL/L in R1 and 1454 mL/L-PREAS in R2. Coprothermobacter, Fervidobacterium, Caldisericum and Tepidiphilus were the dominant bacterial genera that have the potential to degrade petroleum compounds and generate VFAs. This study has shown that high concentrations of heneicosane and 1-phenylnaphthalene did not inhibit the hydrolytic acidification of PREAS.