Technology And Application On Chemical Wastewater Treatment Of An Enterprise By Coagulation Flotation Combined With Biological Method

For wastewater with a high concentration of organic matter, suspended solids and salt in Jiangsu fine chemical plant, only a single biological treatment (anaerobic+aerobic) was used in the original process. The design capacity of the original process was as follows:the water flow rate was40t/d, the COD concentration was2470mg/L and the SS concentration was100mg/L. But the actual maximum flow rate was80t/d, the COD concentration was4000mg/L and the SS concentration was700mg/L. The expansion of the second phase of production scale and the long-term overload operation of original wastewater treatment system made it difficult to maintain a steady state and the original process showed a variety of problems. To solve these problems, the original process increased physico-chemical treatment uint—coagulation-flotation device and hydrolytic acidification tank2#,3#and reduced part of aerobic tank, and the system operation conditions were optimized. The scheme of "coagulation flotationâ†'hydrolysis acidification tank1#â†'hydrolysis acidification tank2#,3#â†'aerobic tank Aâ†'aerobic tank B" was used to transform the system for enhancing its capacity and making effluent can reach discharge standards at the same time.In laboratory coagulation test, when initial pH values were8.0,9.0,10.0and11.0, the optimal dosages of coagulant PAC were25,50,100and200mg/L respectively, and the removal rate of turbidity can reach99.5%. Due to the possible presence of substances which can react with coagulant in wastewater, when PAC was dosed, the wastewater pH decreased greatly, but the effluent pH can be maintained at the range from7.0to9.0, which met the influent pH of biochemical system. PAM coagulant dosing optimum pH was7.0and8.0, respectively, and under these pH conditions, the optimal dosage of PAM was0.25～0.50mg/L. During flotation operation, slag scraper optimum operating cycle was boot3min, stop20min, the water reflux ratio of dissolved gas cylinders was1/3, and the normal operating pressure of dissolved gas cylinders was between0.40～0.50MPa.The step feeding mode was used in the transformation process debugging.The influent flow rate increased from3t/h to4t/h and the concentration of COD increased from3000mg/L to6000mg/L. The abnormal change of nitrogen and phosphorus nutrients in Hydrolytic acidification tank was as follows:the ammonia nitrogen content in the hydrolysis acidification tank2#was the highest and the total phosphorus content of hydrolysis acidification tank3#was higher than that of hydrolysis acidification pool2#in late stage. PAM excessive dosing can clog water pipes, and also can cause the concentration tank sludge dewatering difficulty.After transformation, the handling ability of wastewater treatment system has upgraded. The water flow rate reached8Ot/d and the COD concentration reached5578mg/L. The removal effect of suspended solids (SS) by coagulation floatation was good, which can reach more than93%.The wastewater B/C increased from0.31to0.41, which greatly reduced the inhibitory effect of suspended matter on the activity of anaerobic microbe. The biochemical systems HRT decreased from8.05d to5.95d.The hydrolysis acidification HRT increased from l.55d to2.70d and the aerobic processes HRT decreased from6.50d to3.25d. The COD degradation rate of hydrolysis acidification upgraded from23.3%to48.0%and the aerobic tank B began to play a role in degradation of COD, the average amount of which can reach983mg/L. Gas collection system could effectively inhibit the escape of odors, which achieved the desired requirements. The degradation rate of COD was more than97%, and the monitoring effluent COD was142mg/L, which can meet emissions standards.