Antibiotic removal promoted by partial saturation in vertical flow constructed wetlands
To achieve the green and efficient removal of antibiotics from domestic sewage,four species of antibiotics(sulfamethoxazole(SMX),methotrexate(TMP),oxytetracycline(OTC),and ciprofloxacin(CIP))were selected as the targeted pollutants.Small-scale vertical flow constructed wetlands(VFCWs)were established to compare the water purification performance of two saturation levels of constructed wetlands(fully saturated,2/3 partially saturated)under two different concentration ranges of antibiotics(3.77 to 11.5 μg·L-1;185 to 350 μg·L-1),and to explore the internal rules of antibiotics'removal.The results showed that the 2/3 partially saturated VFCW had a larger variation in dissolved oxygen and oxidation-reduction potential,the removal efficiencies of chemical oxygen demand(COD)and total nitrogen(TN)were 77.9%to 88.4%and 66.1%to 80.3%,which were 2.31 to 3.40 times and 1.44 to 1.73 times of those in the fully saturated VFCW,respectively.Each VFCW exhibited significant efficacy in removing antibiotics,with removal rate ranging from 72.8%to 99.5%.Under the higher concentration of antibiotics,the partially saturated VFCW demonstrated an advantage in removing antibiotics.The average concentrations of SMX,TMP and OTC in the effluent were 20.8,3.73 and 3.96 μg·L-1,respectively,which represented a reduction of 32.5%,71.1%and 33.0%compared with those of the fully saturated VFCW.The vertical distribution of antibiotic concentration showed that antibiotics were primarily removed in the unsaturated layer and the upper 20 cm of the saturated layer.In the 2/3 partially saturated VFCW,those two regions accounted for 41.4%to 78.1%and 22.5%to 51.1%of the total removal contribution,respectively.Partial least squares path analysis indicated that the oxidation-reduction condition was the primary factor affecting the purification efficiency of the VFCW in this study.
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