Coupling of biological methods with membrane filtration using ozone as pre-treatment for water reuse

This work focused on the advanced treatment of the biologically treated wastewater of a textile plant. Nowadays, treatment methods for water reuse are mainly membrane technologies. According to the difficulty of concentrate stream treatment and fouling problem in membrane process, a combination pre-treatment process including ozonation, biological aerated filter (BAF) and reverse osmosis was developed for textile wastewater treatment. Comparing different ozone dosing methods, the ozone–BAF integrated device allowed a higher COD (chemical oxygen demand) and color reduction. The optimal ozone dosage in the integrated device was 20–30 mg/L. After the two-stage BAF treatment, an effluent was obtained with an average COD of 27.4 mg/L, a turbidity of 4.2 NTU, a SS (suspended solid) of 3.0 mg/L, an ammonia nitrogen of 0.7 mg/L and a color of 2 degree.After being steadily treated by the reverse osmosis (RO) unit preceded by ultrafiltration, the pH value of permeate water was 7.4–7.9, conductivity was 50–200 μs/cm, total hardness was 2–10 mg/L, and total alkalinity was 25–60 mg/L. The results showed that the membrane permeates could be reused as dyeing process water. Moreover, the pH value of concentrated stream was in the range of 7.3–8.3, a color of 32 degree, and a COD of 45.7–97.9 mg/L. The concentrate water could be discharged directly without additional treatment since it had already met the discharge standard.

Research Highlights
► Membrane filter with pre-treatment including ozone and biological aerated filter was chosen as the treatment technology for textile wastewater reuse.
► Comparing the ways of adding ozone into the water, the integrated device, allowed higher COD and color reduction.
► The concentrated stream could be discharged directly without additional treatment since it had already met the discharge standard.