Comparison of AC/O3–BAC and O3–BAC processes for removing organic pollutants in secondary effluent

AC (activated carbon)/O3–BAC (biological activated carbon) process was employed to treat secondary effluent and compared to O3–BAC process. The effects of ozone dosages and empty bed contact time (EBCT) in BAC on dissolved organic carbon (DOC) removal were investigated. The results showed that the presence of AC improved ozone utilization and biodegradability of the effluent. DOC removal increased with ozone dosage and EBCT in BAC, however, 3 mg l−1 ozone dosage with 15 min oxidation time and 15 min EBCT in BAC were more economical and efficient. For DOC removal, AC/O3–BAC was more efficient than O3–BAC and its synergetic effect was more than that in O3–BAC process. The biomass of the subsequent BAC unit in AC/O3–BAC process was more than that in O3–BAC process and much more than that in BAC alone. Except for organic pollutants with molecular weight (MW) >10 kDa, those of other MW range were decomposed much more by AC/O3 process than by O3 process. GC/MS analysis showed that dibutyl phthalate, bis(2-ethylhexyl) phthalate, 4-bromo-3-chloroaniline, 2-propanone-ethylhydrazone and phenol derivatives were prevalent organic compounds in the secondary effluent. Some aromatic compounds, such as 4-bromo-3-chloroaniline and 2,4-dichloro-benzenamine disappeared after AC/O3 treatment. However, some small molecules were generated, after further biological treatment by BAC, the kinds and concentration of organic compounds were greatly reduced.