The raw sludge (influent) was collected from an oil-refinery wastewater treatment plant in Yanshan petrochemical company (Beijing, China) with processing crude oil capacity of 8.5 million tons/ year. Its main characteristics are (all values are expressed in mg/L except pH): pH 7.53, TS (total solids) 2.8 × 104, SCOD (Soluble Chemical Oxygen Demand) 181, VSS (Volatile Suspended Solids) 2 × 104, SS (Suspended Solids) 2.67 × 104, ammonium nitrogen (NH3-N) 15.1, Total Nitrogen (TN) 56.8, VSS/SS near about 75%, which indicates that the sludge has favourable biodegradability. The hydrolysis inoculate was obtained from activated sludge in an aerobic sludge tank. The metanogenic inocula used in this experiment were obtained in an anaerobic digestion tank from Qinghe wastewater treatment plant (Beijing, China) with a population equivalent of 814,000 p.e. The main features
The activated sludge process is identified as the most effective technique in the municipal and industrial wastewater treatment plants . However, a significant amount of sludge is produced in the process, which causes severely impact on both environment and human health . Excess sludge produced from oil-refinery wastewater treatment plant contains various refractory organic contaminants and high calorific value . It is dangerous and a waste of energy without treatment. Anaerobic digestion has to be proven as an appropriate technique for the treatment of sludge as well as energy recovery. However, hydrolysis as the rate-limited stage always reduces the treatment efficiency . Two-phase anaerobic digestion separates hydrolytic acidification and methanogenesis, and provides optimum operating conditions for each phase, in which the treatment efficiency can be much improved [5-6]. In this study, two-phase anaerobic digestion was applied to the treatment of oil-refinery excess sludge for the first time. By optimizing conditions of hydrolytic acidification and adopting appropriate pre-
of them are pH value of 6.8, alkalinity 700 mg/L, water ratio 95.4%.