Optimization of Ozone Application in Post-Treatment of Cattle Wastewater from Organic Farms

In this study, an advanced oxidation process using ozone application in a fixed-bed reactor filled with bio-rings was used for purification and disinfection of cattle wastewater (CWW) previously treated in a UASB reactor. The O3 concentration applied to the reactor was 7.8 mg L−1 (±1). Four ozonation times were tested in a batch process: T1 = 0.5 h, T2 = 1 h, T3 = 1.5 h and T4 = 2 h. The pH values tended to increase with the time of contact between liquid and gas. COD and BOD5 removal of 55 and 64% was recorded in T4. Color and turbidity were reduced by 88.5 and 93.4%, while total solids and total suspended solids were reduced by 65.7 and 93.5%, respectively. Oils and greases were completely removed from the wastewater. Electrical conductivity did not vary significantly between treatments, and its association with the presence of cations, such as Na+, Ca2+ and Mg2+, suggests good quality of the water ozonated in T4 for application in the soil, with no risk of salinization. High concentrations of nitrogen compounds were removed, but the efficiency in removing phosphate compounds was low. Coliform removal of above 99% was achieved with T3. Only the CWW ozonated in T4 is recommended for irrigation of raw-consumed crops. Based on most parameters analyzed, the CWW treated in T4 would also be suitable for discharge into water bodies according to Brazilian legislation, suggesting that this technology could be applied in the near future.