UV/O3-BAC process for removing organic pollutants in secondary effluents

The UV/O3-BAC (biological activated carbon) process was employed to treat secondary effluents and compared to the O3-BAC process. The effects of ozone dosage and empty bed contact time (EBCT) in BAC unit on dissolved organic carbon (DOC) removal were investigated. The results showed that the presence of UV improved ozone utilization and biodegradability of the effluent. DOC removal increased with ozone dosage and EBCT in BAC, however, 3 mg/L ozone dosage with 15 min oxidation time and 15 min EBCT in BAC were more economical and efficient. The synergetic effect in UV/O3-BAC process is more than that in O3-BAC process for DOC removal. Except for organic pollutants with MW >10,000 Da, those of other MW range were decomposed much more by UV/O3 process than by O3 process. GC/MS analysis showed dibutyl phthalate, bis(2-ethylhexyl) phthalate, 4-bromo-3-chloroaniline and other phenol derivatives were prevalent organic pollutants found in the secondary effluent. After UV/O3 treatment, some aromatic compounds including 2,4-dichloro-benzenamine, 4-bromo-3-chloroaniline and 3,5-dimethoxy-acetophenone disappeared and some small molecules were formed, but the kinds and concentration of organic pollutants including phthalate esters were greatly reduced by the subsequent BAC unit.