Performance of full scale constructed wetlands in removing antibiotics and antibiotic resistance genes.

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.

Fate of antibiotics and antibiotic resistance genes during conventional and additional treatment technologies in wastewater treatment plants.

Information on the removal of antibiotics and ARGs in full-scale WWTPs (with or without additional treatment technology) is limited. However, it is important to understand the efficiency of full-scale treatment technologies in removing antibiotics and ARGs under a variety of conditions relevant for practice to reduce their environmental spreading. Therefore, this study was performed to evaluate the removal of antibiotics and ARGs in a conventional wastewater treatment plant (WWTP A) and two full-scale combined with additional treatment technologies. WWTP B, a conventional activated sludge treatment followed by an activated carbon filtration step (1-STEP® filter) as a final treatment step. WWTP C, a treatment plant using aerobic granular sludge (NEREDA®) as an alternative to activated sludge treatment. Water and sludge were collected and analysed for 52 antibiotics from four target antibiotic groups (macrolides, sulfonamides, quinolones, tetracyclines) and four target ARGs (ermB, sul 1, sul 2 and tetW) and integrase gene class 1 (intI1). Despite the high removal percentages (79-88%) of the total load of antibiotics in all WWTPs, some antibiotics were detected in the various effluents. Additional treatment technology (WWTP C) showed antibiotics removal up to 99% (tetracyclines). For ARGs, WWTP C reduced 2.3 log followed by WWTP A with 2.0 log, and WWTP B with 1.3 log. This shows that full-scale WWTP with an additional treatment technology are promising solutions for reducing emissions of antibiotics and ARGs from wastewater treatment plants. However, total removal of the antibiotics and ARGS cannot be achieved for all types of antibiotics and ARGs. In addition, the ARGs were more abundant in the sludge compared to the wastewater effluent suggesting that sludge is an important reservoir representing a source for later ARG emissions upon reuse, i.e. as fertilizer in agriculture or as resource for bioplastics or bioflocculants. These aspects require further research.