Abstract
Additional treatment of wastewater, such as constructed wetlands (CWs), is a possible solution to reduce the discharge of antibiotics and antibiotic resistance genes (ARGs) from households and industry to the environment. This study aims to investigate the occurrence and removal of antibiotics and ARGs by two full scale CWs operated at different hydraulic retention times (HRT), namely 1 day and 3 days. Both CWs were receiving the same wastewater treatment plant (WWTP) effluent. Temporally and spatially distributed sampling of water and sediment was conducted for one year and samples were analyzed for antibiotics and ARGs by using LC-MS/MS and qPCR. Results showed that both CWs removed antibiotics significantly with a comparable overall removal of 28%–100%, depending on the type of antibiotics. However, some of the antibiotics showed higher concentration after the CW treatment. Five antibiotics (tiamulin, tylosin, oxytetracycline, sulfamethoxazole and trimethoprim) were the most abundant (>1500 ng/l on average) in winter. Meanwhile, ermB was the most abundant (average of 5.0 log) in winter compared to summer (average of 3.5 log). Other ARGs did not show a significant increase or decrease between winter and summer. ARGs were removed from the wastewater by 0.8 to 1.5 log. The HRT did not influence the removal of either the antibiotics or the ARGs. A strong correlation was found between sul genes and intI1. The results also revealed a positive and a negative relationship from sampling point 1 to sampling point 5: a positive relation between abundance of antibiotics, ARGs, and of NO3–N, NH4–N, TP, COD and a negative relation between antibiotics, ARGs and temperature. This relationship showed the effect between antibiotics and ARGs concentrations with physicochemical parameters and nutrients. The ability of CWs to reduce the input of micropollutants into the environment makes CWs a potential post treatment to WWTP.
Highlights
Antibiotics are widely used to treat and prevent diseases in humans and for livestock but has gained attention since antibiotic resistance is becoming a serious threat to global public health and the environment (Chee-Sanford et al, 2009; WHO, 2014)
This study aims to investigate the occurrence and removal of antibiotics and antibiotic resistance genes (ARGs) by two full scale constructed wetlands (CWs) operated at different hydraulic retention times (HRT), namely 1 day and 3 days
There was more variation and fluctuation within the sampling points in the CW with HRT-1 compared to the CW with HRT-3 for chemical oxygen demand (COD) and total phosphate (TP)
Summary
Antibiotics are widely used to treat and prevent diseases in humans and for livestock but has gained attention since antibiotic resistance is becoming a serious threat to global public health and the environment (Chee-Sanford et al, 2009; WHO, 2014). 30–70% of antibiotics are partially or not metabolized by the human body, and antibiotics enter WWTP via the sewage system (Bouki et al, 2013; Kümmerer, 2004). WWTPs are designed to treat wastewater to meet quality requirements before being discharged into the environment, by reducing the concentration of chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN) and total phosphate (TP). WWTPs are not sufficiently tailored to remove micropollutants such as pharmaceuticals, personal care products, and antibiotics (Margot et al, 2015). These micropollutants are detected in the effluents in the range of ng/l (norfloxacin) (Dong et al, 2016) to mg/l (ciprofloxacin) (Larsson et al, 2007). Additional treatment is needed to ensure the high quality of wastewater effluent, before it is released into the surface water
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