Research On Heavy Oil Sewage By Hydrolysis Acidification-MBR

Currently, steam soak is the main method of development and production of heavy oil. Sewage pollution has become a serious problem along with the increase proportion of the production of heavy oil. It was difficult to deal with the heavy oil wastewater due to the complex composition, poor biodegradability, high salinity, and density difference between oil and water. Therefore, reasonable disposal of the huge amounts of heavy oil sewage is a serious economic and technical problem needed to be resolved.The methods including physical,chemical and biochemical are major techniques used to treat heavy oil wastewater. Physical and chemical techniques could not dispose the wastes thoroughly with low efficiency and high cost. On the contrary, biochemical technique has the virtue of efficiency and low cost without secondary pollution. Because of the above reasons, the biochemical technique is the favorite method to deal with heavy oil sewage.This paper was supported by"The National 11th Five-year Key Project"(2006BAB04B02). Heavy oil sewage in Chenzhuang was the object of this study. According to the characteristics of anti-biodegradable and high content of effluent suspended matter, method of hydrolysis acidification-MBR was adopted, replacing the existing bio-contact oxidation-sedimentation- double media filtration technology. Through the experiments, hydrolysis acidification tank could operated steady at 15³5℃when the hydraulic retention time was greater than 16h. Temperature influenced on the COD_Cr removal rate slightly. The COD_Cr of effluent which was treatment by hydrolysis acidification is between 220 mg/L to 240mg/L. And the removal rate was between 25% and 33%. Oil concentration in effluent was about 2.00⁵.00mg/L and the removal rate was above 75%. The BOD5 of influent was between 54 mg/L and 75mg/L. BOD5/COD_Cr was between 0.17 and 0.23. It showed that the poor biodegradability before hydrolysis acidification. The BOD5 of effluent was between 95 mg/L to 112mg/L and the BOD5/COD_Cr is between 0.45 and 0.49. The biodegradability increased after hydrolysis acidification. So hydrolysis acidification played an important role in improving the biodegradability of the heavy oil sewage. It was good to shorten the hydraulic retention time as the biodegradability increased, making the organic degradation completely in the following treatment.The active sludge of MBR bank was acclimated by the effluent of hydrolysis acidification. The protozoan which can test the performance of activated sludge was easy to be observed by microscope. Results reflected that there were a large number of bacteria existed in the active sludge. A lot of paramecium, colpidium and metopus were observed at first. COD_Cr was above 150mg/L. After amoeba and trachelophyllum appeared the number of paramecium, colpidium and metopus decreased. Water quality improved and the COD_Cr was below 150mg/L. When vorticella, rotifer and euplotes could be observed, amoeba was disappeared. The amount of metopus rostratus and trachelophyllum declined. Transmittance of effluent was better than before and the COD_Cr was below 130mg/L. when arcella was observed, the transmittance of effluent was not very well. The COD_Cr was below 120mg/L and hydraulic retention time was too long.After aerobic activated sludge was matured, the COD_Cr of the supernatant performed between 117 and 130mg/L.Removal rate was between 40% and 47%. Oil concentration was lower than 1.00mg/ L. The removal rate was above 90% and the BOD5 of the supernatant was less than 10mg/L. At that time, MBR membrane could be used. When the hydrolytic acidification-MBR system displayed stable, CODcr in effluent was between 69mg/L to 90 mg/L. Removal rate of CODcr under the operation of this system could reach up to 70%. Oil concentration of the effluent was about 0.09 0.30mg/L. The average removal rate of oil was over 99%.Suspended solids in the effluent was less than 1.00mg/L while the average removal rate could reach up to 95%.Under the operation of hydrolysis acidification-MBR system, COD_Cr, oil content and the suspended solids in effluent reduced by 32%, 95% and 88% compared with the existed double media filtration treatment.