Dissolved air flotation (DAF) was studied for treatment of 2 m-% oil-in-water emulsions (O/W emulsions) prepared from synthetic oils by adding chemicals such as the cationic surfactant CTAB (cetyltrimethylammonium bromide), the coagulant PolyDADMAC (polydiallyldimethylammonium chloride) (also studied for oily wastewaters) or Epi-DMA (epichlorohydrin-dimethylamine copolymer) directly into the saturator (PosiDAF) in two different concentrations, or by performing coagulation-flocculation followed by DAF. The efficiencies of various DAF treatments were evaluated by measuring the chemical oxygen demand (COD) and total surface charge (TSC). Flow cytometry (FCM) was used to measure the number of hydrophobic particles in the selected samples. According to the results, the performance of PosiDAF with CTAB was poor compared to that with PolyDADMAC and Epi-DMA. PosiDAF performed better with PolyDADMAC (with a dose of 334 ppm, the highest COD reduction was 100%) than with Epi-DMA (with a dose of 596 ppm, the highest COD reduction was 93%) for the treatment of O/W emulsions. The COD reduction was higher when the concentration of both the PolyDADMAC and Epi-DMA was higher in the saturator. The efficiency of PosiDAF with PolyDADMAC proved to be better than the efficiency of the conventional coagulation-flocculation followed by DAF for breaking up O/W emulsions. PosiDAF with PolyDADMAC also proved to perform very well for treatment of real oily wastewaters; the COD reduction was 70% with an optimal PolyDADMAC dosage of 200 ppm with the TSC value totally neutralized. FCM studies performed on O/W emulsions and oily wastewater samples were successful with repeatable results, thus proving to be a promising analysis method for waters containing oil emulsions. (c) 2013 Elsevier B.V. All rights reserved.