Evaluation And Application Research Of Petrochemical Wastewater Toxicity To Biological Treatment

Petrochemical wastewaters have toxic impacts on the microorganisms in biotreatment processes, which is prone to cause deterioration of effluent quality of the wastewater treatment plants. In this study, the inhibition effects of activated sludge’s oxygen consumption rate were tested to evaluate the toxicity of production wastewaters in a petrochemical industrial park. The evaluation covered the wastewaters from not only the process of sewage treatment plant, but also different production units in the park and different production nodes in each unit.The study developed a set of toxicity evaluation of petrochemical wastewater biological treatment system. The technical key points in operation was cleared and the operating conditions was optimized. In view of the variation of activated sludge sensitivity among different tests, the toxicity data were standardized according to the concentration effect relationships of the standard toxic substance 3,5-dichlorophenol in each day, in order to improve the comparability among the toxicity data. Furthermore, the Quality Emission Load(QEL) of corresponding standard toxic substance was calculated by multiplying the corresponding 3,5-dichlorophenol concentration and the wastewater flow quantity, to indicate the toxicity emission contribution of each wastewater to the wastewater treatment plant.The study also anylized the effects of petrochemical wastewater on microorganism in activated sludge, in which it was found that petrochemical wastewater had severe toxicity on the nitrifying bacteria in activated sludge, however accelerated the oxygen consumption of heterotrophic bacteria. As the former was covered by the later, directly testing the total oxygen consumption rate of the whole activated sludge would lead to undervalued toxicity results. The study also analyzed the influence of readily degradable substances on the heterotrophic oxygen consumption in activated sludge, and found out that in the petrochemical wastewater it was the readily degradable substances such as acetate that was responsible for promoting the heterotrophic oxygen consumption.The test was modified by adding 90 mg/L sodium acetate to avoide the acceleration of the readily degradable substances in petrochemical wastewaters to activated sludge, which proved the superiority of the modified method; according to different wastewater and sludge in inhibition tests of activated sludge’s oxygen consumption rate, it proved the feasibility and extensive applicability of the modified method.By evaluating the petrochemical wastewater toxicity to biological treatment on the process of sewage treatment plant, the study found out the toxicity of petrochemical wastewater on nitrifying bacteria in activated sludge reducted from 64.3% to 25.9%, and the Lead process reduced the toxicity effectively; but the inhibition did not kept decreasing during the process flow. It increased in aerated grit chamber, and decreased in the primary settling tank, the hydrolysis acidification process, and the anoxic zone of A/O process. The process of hydrolysis acidification made the largest contribution to the reduction of toxicity to biological treatment, followed by the anoxic zone. control and reduce the toxicity of aerated grit chamber stage of growth, is helpful to reduce the impact to the follow-up biological treatment effectThe developed method was also applied in the evaluation of production wastewaters in a petrochemical industrial park. No direct correlation was observed between the toxicity effects and the organic contents, so that it does not suggest to predict the toxic properties of the effluents by the organic contents. According to the rank list of the toxicity contribution of wastewater from different units and nodes by using the corresponding 3,5-dichlorophenol concentration and Quality Emission Load(QEL) of corresponding standard toxic substance, the sources of toxic wastewater in the petrochemical industrial park were clearly identified. This study provides effective guidances to the source control of wastewater toxicity in the large industrial park.