DTOC(mg/L) nu(0.01/cm) §50 Turbidity∝0.1NTU a Total bacteria(×1000)口 Colifom(10) 买 10 Ozone dose(mg/L) Figure 7 Effect of ozone dose on treated water quality zone dose on the quality of treated water. With no ozone dose(equivalent to pressured air flotation), the DOF separator could achieve a good removal of turbidity and certain removal of colour, organic matter and bacteria. As the ozone dose increased, the efficiency of colour, organic and bacteria removal was improved. For a further higher removal of coliform bacteria, a higher ozone dose would be needed Treated water quality. Table 3 compares the water quality of the DOF separator and the current conventional treatment process(coagulation sedimentation filtration chlorine disinfection)applied in Beishiqiao Wastewater Purification Centre for tertiary wastewater treatment for re-use. It can be seen that the DOF separator process can achieve the very high water quality. Regarding colour, odour and total bacteria, the treated water quality by the doF separator is better than that by conventional tertiary treatment. The treated water quality meets the Chinese Standard for Domestic Re-use(SAC, 2002). Moreover, the total hrt of the doF separation process is only 30min, in comparison with that for the conventional tertiary treatment 2-3h. High treatment efficiency is one of the important features of the DOF parasol Summary and conclusion This paper introduced a compact device for tertiary wastewater treatment utilising a dispersed ozone flotation technique. The DOF separator combines coagulation, ozonation and dispersed air flotation in one treatment unit within a total hydraulic retention time of approximately only 30 min. The following conclusions can be drawn from the current Table 3 Comparison of the water quality of the treated water between DOF separator and conventional DOF separator Conventional treatment Standard for non-drinkable domestic reus Colour (unit) 5-10 15-30 Slight uncomfortable sell No offensive odour Turbidity(NTU》 5-10 Ss(mg/L) 10-15 BOD(mg/L) 0-20 Coliform(cfu/100 mL) 3 HRT 30 minzone dose on the quality of treated water. With no ozone dose (equivalent to pressured air flotation), the DOF separator could achieve a good removal of turbidity and certain removal of colour, organic matter and bacteria. As the ozone dose increased, the efficiency of colour, organic and bacteria removal was improved. For a further higher removal of coliform bacteria, a higher ozone dose would be needed. Treated water quality. Table 3 compares the water quality of the DOF separator and the current conventional treatment process (coagulation þ sedimentation þ filtration þ chlorine disinfection) applied in Beishiqiao Wastewater Purification Centre for tertiary wastewater treatment for re-use. It can be seen that the DOF separator process can achieve the very high water quality. Regarding colour, odour and total bacteria, the treated water quality by the DOF separator is better than that by conventional tertiary treatment. The treated water quality meets the Chinese Standard for Domestic Re-use (SAC, 2002). Moreover, the total HRT of the DOF separation process is only 30 min, in comparison with that for the conventional tertiary treatment 2–3 h. High treatment efficiency is one of the important features of the DOF separator. Summary and conclusion This paper introduced a compact device for tertiary wastewater treatment utilising a dispersed ozone flotation technique. The DOF separator combines coagulation, ozonation and dispersed air flotation in one treatment unit within a total hydraulic retention time of approximately only 30 min. The following conclusions can be drawn from the current study: 0 10 20 30 40 50 60 70 Concentration TOC (mg/L) UV (× 0.01/cm) Colour (c.u.) Turbidity (× 0.1 NTU) Total bacteria (× 1000) Coliform (× 10) Raw water 0 0.4 0.8 1.2 1.6 Ozone dose (mg/L) Figure 7 Effect of ozone dose on treated water quality Table 3 Comparison of the water quality of the treated water between DOF separator and conventional process Parameter DOF separator Conventional treatment Standard for non-drinkable domestic reuse Colour (unit) 5–10 15–30 30 Odour None Slight uncomfortable sell No offensive odour Turbidity (NTU) ,0.5 ,0.5 5–10 SS (mg/L) ,10 ,10 10–15 BOD (mg/L) ,10 ,10 10–20 COD (mg/L) ,30 ,30 50–60 Total bacterial(cfu/mL) 25 30 – Coliform (cfu/100 mL) 3 3 5 HRT 30 min 2 – 3 h – P.K. Jin et al. 156