In waste water treatment, the use of a physico-chemical process by flotation would present some advantages compared to a separation by settling. However like each physico-chemical process, a separation by flotation needs a chemical destabilization. We have studied the use of an electrochemical destabilization coupled to a process of flotation (DAF). This paper presents the results obtained on an urban waste water treated by electrocoagulation and dissolved air flotation (DAF). To show the interest of coupling flotation and electrocoagulation, we have studied each process separately. Then we have combined the two processes. The role of each operation on pollution removal is presented. An effect of synergism between the two processes on the pollution abatement is shown. A reduction of 75% of the global COD is obtained. The results of the coupling are compared to the performance of an intensive treatment by flocculation-lamellar settler.