Application of ozone in reducing the health effects of irrigation with urban wastewater

Wastewater produced in urban and industrial can be purified and refined enough that it can easily be used as sources of fresh water in agriculture. In many countries, the treated wastewater is used for irrigation and aquaculture. The most important issue in the use of urban wastewater for irrigation is to ensure the efficiency of water disinfection process in the reduction of pathogenic microorganisms. Ozonation as an advanced technology with high performance in a reduction of viruses and parasites can be environmentally friendly alternative to the chlorination of wastewater. In this pilot plan with a reactor at a height of 6 m and 1 m in diameter performance of ozone in the elimination of coliforms, fecal coliforms and in the effluent COD reduction was studied in the wastewater treatment plant of Mianeh city. Capacity of ozone generator that is used to disinfect the wastewater treatment plant was about 500 grams per hour. The hydraulic retention times of 6, 10, 15 and 25 minutes and transferred ozone doses of 1 to 50 mg per liter was used. The results showed that the ozone doses of 4 mg per liter and the retention time of more than 10 minutes are enough to adapt with the standards irrigation water regarding to coliforms and fecal coliforms. Ct values obtained for the removal of fecal coliforms is about 1 mg per liter per minute. Transferred ozone doses to reduce the COD of wastewater need to be more than 20 milligrams per liter. Finally, ozone can be technically and economically viable alternative to chlorination of municipal wastewater treatment plant and reuse for agricultural purposes.