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The removal efficiencies and accumulated concentrations of oxytetracycline and ciprofloxacin in three pilot-scale constructed wetlands (CWs) with different flow configurations (surface, horizontal subsurface, and vertical subsurface flow) were investigated. The results indicated that the average mass removal efficiencies of the CWs for the target antibiotics in one year of treatment ranged from 85 to 99%, and the vertical subsurface flow constructed wetlands exhibited the highest and most stable removal efficiencies for oxytetracycline (99 ± 0.27%) and ciprofloxacin (97 ± 0.26%). The influence of seasonal changes on the removal efficiencies of oxytetracycline and ciprofloxacin in CWs was insignificant. The higher accumulated antibiotic concentrations and antibiotic-degrading bacteria abundances indicated that substrate adsorption and biodegradation were the predominant pathways affecting the antibiotic removal efficiency of wetlands. The concentration of accumulated ciprofloxacin in soil and oyster shell (84–124 and 83–115 μg kg−1) was significantly higher than that of oxytetracycline (37–81 and 3–17 μg kg−1). In addition, analysis results based on pilot-scale CWs also indicated that the influence of the type of CW on the bacterial community was more significant than the wetland substrate and residual concentration of antibiotics. • Flow configuration determine removal efficiencies of OTC and CIP in wetland. • Removal rate of antibiotic in wetland increased in following order: VSF > HSF > SF. • Neutral-pH level of substrate can enhance degradation rate of OTC in wetland. • Flow configuration show more effect on bacterial community in CW than antibiotic. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the nutrient removal and microbial response during the treatment of antibiotics-enriched swine wastewater by vertical flow constructed wetlands with different water flow directions and substrates. Better NH 4 -N and TN removal were achieved in down-flow and up-flow treatments, respectively. The concentrations of all the chemical properties including oxytetracycline (OTC), difloxacin (DIF), copper (Cu) and zinc (Zn), nitrite/nitrate, sulphate and total organic carbon (TOC) in down-flow treatment soils were significantly higher than those in up-flow treatments on day 30, 60 and 90 (p < 0.05). Bacterial α-diversity indices in soils were negatively correlated with the concentrations of OTC, DIF, Cu and Zn significantly (p < 0.05). Among experimental factors, substrate type significantly contributed to variation of bacterial communities in waters, while water flow direction and sampling time significantly contributed to those in soils (p < 0.01). Among environmental factors, OTC + DIF, Cu + Zn, nitrate/nitrite and sulphate significantly contributed to variation of bacterial communities in soils (p < 0.05). The taxonomy assignment indicated that antibiotics accumulation in soils promoted the growth of 19 dominant genera, including several antibiotic-resistant or degrading bacteria, which however were generally not dominant in effluents. In addition, although the TN and NH 4 -N removals were reduced when antibiotic concentrations in soils increased, the available community data cannot strongly support the inhibition effect of antibiotics on nitrogen transformation. Further assessment found that some dominant genera in water samples and those enriched under the stress of antibiotics in soils tended to increase their abundances in the effluents of oyster shell-based CWs. [ABSTRACT FROM AUTHOR]

The fate of antibiotics and antibiotic resistance genes (ARGs) in constructed wetlands has received more concerns recently. This study aimed to assess the influence of hydraulic flow direction (down-flow or up-flow) and substrate type (brick rubble or oyster shell) on removal of antibiotics and ARGs from swine wastewater. For antibiotic removal, all of treatments can remove more than 84% of oxytetracycline and difloxacin during two stages of operation. Brick-based columns had stronger antibiotic removal capacity due to properties of brick, including large porosity and micropore size and 32% of Fe 2 O 3 . The surface soils tended to adsorb much more oxytetracycline than difloxacin, as was opposite to brick and oyster shell. For ARGs removal, the removal efficiencies of tetracycline-resistance genes ( tet ) and integrase gene of Class 1 integrons ranged from 33.2 to 99.1%, without significant difference among treatments (p > 0.05). However, most of ∑ tet relative abundances in effluents of up-flow treatments were higher than those in influents, which indicated a risk to release relatively more antibiotic-resistant bacteria in proportion to total bacteria into environment. Significantly correlated with antibiotic concentrations, ARGs relative abundances in surface soils increased as the time progressed for all the treatments. Our results demonstrate that antibiotic removal using constructed wetlands is greatly affected by substrate type, whereas variation of ARG relative abundances in effluents and soils are determined by hydraulic flow direction. [ABSTRACT FROM AUTHOR]