Combined process of biofiltration and ozone oxidation as an advanced treatment process for wastewater reuse

The effluent of a wastewater treatment plant was treated in a pilot plant for reclaimed water production through the denitrification biofilter（DNBF） process,ozonation（O3）, and biologic aerated filtration（BAF）.The combined process demonstrated good removal performance of conventional pollutants, including concentrations of chemical oxygen demand(27.8 mg·L–1) and total nitrogen(9.9 mg·L–1) in the final effluent, which met the local discharge standards and water reuse purposes.Micropollutants（e.g., antibiotics and endocrine-disrupting chemicals） were also significantly removed during the proposed process. Ozonation exhibited high antibiotic removal efficiencies, especially for tetracycline（94%）.However, micropollutant removal efficiency was negatively affected by the nitrite produced by DNBF. Acute toxicity variations of the combined process were estimated by utilizing luminescent bacteria. Inhibition rate increased from 9% to 15% during ozonation. Carbonyl compound concentrations（e.g., aldehydes and ketones） also increased by 58% as by-products, which consequently increased toxicity. However, toxicity eventually became as low as that of the influent because the by-products were effectively removed by BAF. The combined DNBF/O3/BAF process is suitable for the advanced treatment of reclaimed water because it can thoroughly remove pollutants and toxicity.