| A novel coagulation-flotation system was developed and investigated. The performance of coagulation-flotation system was evaluated through both theoretical and experimental means. The present investigation included: the amount of air precipitation and bubble size in the depressurization process of gas-saturated water as well as chemistry oxygen demand (COD) and suspended solid (SS) removal in the process of treating washing wastewater.The novel coagulation-flotation system was designed according to the principles of coagulation and flotation and the attachment theory of micro-bubble and flocs. The measuring method of air precipitation was based on measuring the precipitated air volume with a batch system. The amount of air precipitation was increased with the air-water ratio increased when the pressure was constant. The stable time of bubble was used to indicate the size of bubble. The results of the study on the stable time showed that when the pressure was higher than 0.4MPa, the stable time increased slowly and would get the same value when the air-water ratio enough high. It was better that the gas-liquid pump worked in the pressure of 0.4MPa. The diameter of micro-bubble was figured out about 3040 μm by means of Stokes' Expression in the pressure of 0.4MPa.The coagulation-flotation system was a viable method for the treatment of washing wastewater. The experimental results showed that the average COD removal rate was beyond 80%, SS removal rate was beyond 90% with PAC addition of 250mg·L-1 and PAM addition of 6 mg·L-1 when the dissolved air pressure was 0.30.6MPa ,the flow recycle ratio was 40%50%. The effluent concentration of COD and SS could meet the water-reuse standard. After disinfection, it could be reuse. By using the coagulation-flotationsystem, reclaimed water system became easier to operation and the cost decreased in a certain extent.
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