Abstract
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.
Highlights
Petroleum refinery excess activated sludge (PREAS) is a major by-product produced after the biological treatment of wastewater that is generated by the petroleum industry
PREAS contains a wide range of petroleum hydrocarbons (PHCs)
Heneicosane and 1-phenylnaphthalene were used as controlled supplements to model and assess the impacts that PHCs have on hydrolysis and acidification with PREAS
Summary
Petroleum refinery excess activated sludge (PREAS) is a major by-product produced after the biological treatment of wastewater that is generated by the petroleum industry. Anaerobic digestion is a commonly used sludge treatment that removes recalcitrant contaminants and. State Key Laboratory of Heavy Oil Processing, State Key Laboratory of Petroleum Pollution Control, China University of Petroleum, Beijing 102249, China. Anaerobic digestions are often characterized by four general biological processes: (1) hydrolysis, (2) acidogenesis, (3) acetogenesis, and (4) methanogenesis (Appels et al 2008). A two-phase anaerobic digestion process that separates hydrolysis–acidogenesis and methanogenesis results in the development of distinct environments having improved total bioactivity (Rajagopal and Béline 2011).
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