Bio-ozonation technology for treatment of mixed industrial and domestic wastewater for reuse in agriculture

A 2-stage bio-ozonation treatment process (SGBP-O₃) was studied for purification of complex mixed industrial and domestic wastewater. Suspended growth biological process (SGBP) reactors (2nos) were inoculated with activated sludge and real wastewater from municipal wastewater treatment plant and adapted to model mixed wastewater (MWW) conditions. Domestic, pharmaceutical, textile, petroleum and agricultural runoff wastewaters were simulated into a model MWW and treated with SGBP operated at constant operating parameters and varying aeration conditions. Effluents were exposed to 71±17 mg/L fixed dose of ozone streams at different contact times ranging from 1 to 60-min.  The results show that the SGBP performance was maximum under alternated aeration conditions (60/30-min) achieving up to 92.1, 90.6, 83.3 and 83.8% reduction in COD, BOD₅, TN and PO4-P respectively. Nitrification was not inhibited and transition to pulse aeration cycles (60/30-min) did not interrupt the metabolic activities of autotrophic bacteria as nitrification up to 64.1% was reached. Diesel oil and Methylene blue (MB) dye compounds were degraded considerably to 83.6 and 93.5% removals respectively. Post-ozonation of SGBR 60/30-min effluent decreased the residual COD from 45.8 to 36.7 mg/L and increased residual BOD₅ from 5.0 to 9.9 mg/L with increased ozone contact time. Residual diesel oil and MB dye compounds in SGBR effluents were both degraded and mineralized leading to reduction by 35.6 and 64.1% respectively. The results indicate that SGBR has great potential to treat and improve the quality of complex mixed wastewater considerably even at less operating costs. Post-ozonation at fixed ozone dose of 71 mg/L and contact time less than 30-min enhance the biodegradability of the mixed wastewater and improve the water quality considerably for possible reuse applications. The water reuse studies conducted show positive indication for reuse of bio-ozonation treated mixed industrial and domestic wastewater in agriculture. However, downstream biodegradation is desirable to further improve the quality of ozonated effluent.