| The treatment of highly concentrated refractory wastewater is difficult all along because the wastewater has high concentration of organic matter and poor degradability. Pesticide wastewater is a typic highly concentrated refractory wastewater because of its complicated components and high toxicity. The treatment of pesticide wastewater always draw the attention of society. Pesticide industry plays an important role in economy of China . Quite a large quantity of pesticide is produced and consumed in China. Recent years, with the updating of pesticide products, traditional pesticide, due to its high toxic residue and poor performance,has been gradually replaced by new generation pesticide which is more friendly to environment. Imidacloprid becomes a typical representative of the new generation pesticide due to its great efficiency, low toxicity and low residue. Imidacloprid has a very good market. However, there is not an effective technology to treat the wastewater from imidacloprid production. The study of the treatment process of Imidacloprid production wastewater can not only solve the problem for enterprise but also provide a effective way for the treatment of high concentrated wastewater. In this article, by the study of imidacloprid production wastewater quality (pH 3～4, COD 60000～80000 mg/L, NH3-N 5000～6000 mg/L, PO43--P 6000～7000 mg/L), a pretreatment + biochemical treatment combined process is made according to the characteristic of imidacloprid wastewater which has high concentration of phosphorus,ammonia and COD. The key of design of the treantment of imidacloprid wastewater lies in the pretreatment process. The methods of Chemical precipitation by Ca(OH)2 and air stripping are used as the technology of removal of phosphorus and ammonia respectively. After the treatment, the phosphate in wastewater is almost completely removed, meanwhile the removal rate of ammonia can reach 90.3%～94.8%. Wastewater contains pollutant matters such as DMF, nitrile and Organic chlorid which tend to hydrolyze on the basic condition. So Alkaline hydrolysis is adopted following the process of phosphorus removal. The result shows that alkaline hydrolysis can reduce the COD of wastewater by 29.6% and increase the effect of microelectrolysis. The study of microelectrolysis proves that microelectrolysis is a effective way to treat the wastewater and can decrease COD by 47.2% on the optimum process conditions. The effect of microelectrolysis is increased further through adding catalystic A to Fe/C padding. The result of experiment shows that when the ratio of Fe to A is 5:1, COD is reduced to 13855mg/L, removal rate of COD reached 50.1%. Through the above pretreatment, the biodegradability of the wastewater improves. Effluent COD can reach the first class of wastewater discharge standard when the wastewater following pretreatment is diluted in certain proportion and treated by biochemical method. Now, the process has been put in project after several pilot-scale tests. It can be foreseen that this new process is not only applied to the treatment of imidacloprid production wastewater, but also suitable to the efficient treatment of refractory organic wastewater.
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