A Study On Dispersed-Ozone Floation (DOF) For Wastewater Reclamation

Tertiary treatment of domestic wasterwater was conducted in pilot scale at Beishiqiao Wastewater Purification Center, Xi'an, China, using a process of dissolved-ozone floatation(DOF). It is an integrated process for coagulation, separation and disinfection. Ozonation is a common practice nowadays for the removal of offensive smell and odour, and dispersed air flotation is usually used to separate light pollutants in water/wastewater treatment. The idea in this paper is to combine flotation and ozonation in the same unit, where ozone is introduced by a pump as dispersed gas. device (DOFD) can separate the suspended matters that were coagulated and remove the offensive smell, odour and colour by ozonation. The effluent from an activated sludge process was firstly led to a contact column for coagulation with a contact time for 30 seconds. The coagulated water then flowed into a DOFD at a rate of 1 m3/h.Compared with the conventional treatment process (Coagulation + Sedimentation + Filtration + Chlorine disinfection), The dispersed ozone floatation(DOF) process could achieve a very high removal of colour, offensive odour, and total organic matter, and resulted in high quality treated water, about 80% of colour, 70% of turbidity, 55% of TOC and UV254 can be removed. It also apparently achieved a remarked bacteria and coliform removal, more than 99% of bacteria and coliform can be removed.In addition, this paper also investigated the effect of different operation condition on the water quality of effluent. It is found that coagulation condition, air flotation condition and ozone dose play an important role in the effect of this process. In a appropriate coagulation condition, enough coagulated substance can adhere to the suspended matters and tiny air bubbles. Flotation condition decided the producing of tiny air bubbles, andthis is very important in air flotation process. At lower ozone dose, ozone in the process is to oxidize the unsaturable structure of organic matters to saturable one and hence to remove the odour and colour from the treated water. At higher ozone dose, the bacteria and coliform number is dramatically decreased. The removal of TOC and UV254 also can be change with the ozone dose. From lots of experimental datas, we can ascertain the best operation condition in DOF.