| Petrochemical wastewater has characteristics of high concentration of pollutants, complicated components and difficultly biodegradable and so on, which is serious to water pollution. The processing technology has been the focus and difficulty of the research of the wastewater treatment. In this study, the inflow of one typical petrochemical sewage treatment plant is treated as the research object. Considering a series of problems existing in the practical petrochemical wastewater treatment process, such as poor hydrolysis acidification efficiency and serious equipment corrosion, micro-aerobic hydrolysis acidification and anaerobic hydrolysis acidification contrast test were designed to study hydrolysis acidification under different conditions, analysis of hydrolysis acidification effect under different conditions, determine the optimum operation conditions. At the same time, the characteristics of the influent and effluent of the hydrolytic acidification were determined using molecular weight classification and three-dimensional fluorescence spectrum, and the biodegradation of oxygen in the reactor effluent and hydrolysis acidification of sludge microbial population structure were also analyzed. With the study based on the actual petrochemical wastewater treatment project, the results of the research have important indicative function in promoting application of the micro-aerobic hydrolysis acidification process, as well as the difficultly biodegradable petrochemical wastewater treatment.The study on long-term performance comparison of micro-aerobic hydrolysis acidification and anaerobic hydrolysis acidification reactor showed that the metabolic activities of the facultative hydrolytic and acidogenic bacteria could be enhanced and that the removal of organics with aromatic and conjugated double bond could be improved at the micro-aerobic conditions. Micro-aerobic hydrolysis also could significantly inhibit the activity of sulfate reducing bacteria reduce the production of sulfate reduction and H2 S. Variation of COD and VFA/COD in the influent and effluent, specific ultraviolet absorbance(UVSA), determination of molecular weight distribution of dissolved organic matter and the investigation for the removal of COD of micro-aerobic hydrolysis acidification-A/O combined process were adopted to estimate the hydrolysis acidification function of difficultly biodegradable petrochemical wastewater treatment by micro-aerobic hydrolysis acidification and anaerobic hydrolysis acidification reactor, which is more objective and exact and exercisable in estimating the efficiency of the reactor application in the practicality projects.The study found that the removal rate of COD of micro-aerobic hydrolysis acidification decreased gradually with the shorting of HRT, the VFA in the effluent increased first and then decreased, both of the VFA and VFA/COD reached the maximum and the removal rate of COD was relatively high at HRT 12 h when the effect of hydrolysis acidification was to achieved the best. The longer of the HRT, the inhibition of sulfate reduction was more obvious; The removal of COD of anaerobic hydrolysis acidification increased with the increase of HRT, both of the VFA and VFA/COD reached the maximum at HRT12 h when the effect of hydrolysis acidification was the best but a low removal rate of COD. The longer of the HRT, the problem of the sulfate reduction was more serious.The study of the influence of DO concentration on the micro-aerobic hydrolysis acidification showed that, the removal rate of COD, VFA and VFA/COD increased first and then deceased with the increase of DO concentration(0.1~0.5mg/L), all of these indicators reached the maximum at 0.2~0.3mg/L DO concentration condition, respectively 30.1%, 53.7% and 0.635mg/mg, the hydrolysis acidification effect was the best. With the increase of dissolved oxygen concentration in water, the metabolic activities of the facultative hydrolytic and acidogenic bacteria could be enhanced and that the removal of biodegradable organic matter could be improved, but the inhibitory effect on anaerobic bacteria could be strengthened when the dissolved oxygen concentration reached a certain concentration, resulting in hydrolysis acidification decreased, at the same time, the degradation of the organic matter especially small molecule VFA by facultative bacteria increased, which lead to the decrease of VFA and VFA/COD.We could further analyze the differences between the micro-aerobic hydrolysis acidification and anaerobic hydrolysis acidification process from the basis of Microbiology by the analysis on the sludge microbial population structure of hydrolysis. The study found that the sludge population structure was similar between the micro-aerobic and anaerobic hydrolysis acidification reactor, but the microbial population abundance of micro-aerobic hydrolysis acidification was higher than anaerobic hydrolysis acidification and the microbial diversity of the anaerobic hydrolysis acidification was higher than micro-aerobic hydrolysis acidification. Bacteria belonging to Proteobacteria, Chloroflex and Actinobacterium dominated the microbial community in the micro-aerobic sludge with 39.7%, 20.3% and 1.9% of the total bacterial sequences, respectively. These values were higher than those in the anaerobic sludge(36.9%, 17.5% and 1.3%, respectively), which indicated that the macromolecular refractory organics could be degraded effectively at the micro-aerobic conditions. Bacteroidetes and Acidobacteria were highly enriched in the anaerobic reactor, leading to better acidification at the anaerobic conditions. At the genus level, the diversity and abundance of sulfate reducing bacteria in the micro-aerobic sludge were less than those in the anaerobic sludge, which was consistent with less effluent sulfide concentration of the micro-aerobic reactor. Sulfate reduction was therefore inhibited effectively at the micro-aerobic conditions. These results demonstrated that micro-aerobic hydrolysis acidification is a promising technique for pre-treatment of petrochemical wastewater. |
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