investigation of the excess sludge reduction in sbr by oxidizing some sludge by ozone

the excessive biological sludge production is one of the disadvantages of aerobic process such as sbr. so the problem of excess sludge production along with its treatment , and disposal in aerobic processes in municipal and industrial waste water can be seen in many parts of the world even in our country . to solve the problem of excess sludge production , reducing in by oxidizing some of the sludge by ozone is a suitable idea , thus reducing the biomass coefficient as well as the sewage sludge disposal.   in this study, two sbr reactors with of 20 liter being controlled by on-line system are used. after providing the steady state in the reactors, along the 8 month research sampling and testing parameters such as cod, mlss, mlvss, do, sour, svi, residual ozone and yield coefficient were done. the results showed that during the solid retention time of 10 days the kinetic coefficient of y and kd was 0.58 (mg biomass / mg cod) and  0.058 (1/day) respectively. at the next stage of research, different concentrations of ozone in one liter of  the returned sludge to   reactor were used to reduced the excess biological sludge production. the results showed that the 20 mg ozone per gram of mlss in one liter of the returned sludge to   reactor is able to reduce yield coefficient from 0.58 to 0. 28 (mg biomass/mg cod),in other words, the biological excess sludge by 52 % .but the soluble cod increased slightly in the effluent and the removal percentage decreased  from 92 in blank reactor to 64 in test reactor. while the amount of svi and sour in this consumed ozone concentration reduced 9 mgo2/h.gvss and 20 ml/g respectively. no sludge was seen in the 25 mg ozone concentration per gram of mlss in one liter of  the  returned sludge to reactor.