Combined membrane filtration and 265 nm UV irradiation for effective removal of cell free antibiotic resistance genes from feed water and concentrate

The removal of cell free DNA (plasmids) carrying antibiotic resistance genes (ARGs) was investigated at benchscale using ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes commonly applied in water reuse applications. The removal of the plasmid spiked to ultrapure water was determined using a direct qPCR method. More than 99% plasmid removal was achieved by membranes with 1 kDa molecular weight cut off (MWCO). Membranes with lower MWCO showed complete removal under the specific experimental conditions, reaching a maximum log reduction value above 6.6. The concentrate from membrane filtration was further subjected to UV-LED irradiation at 265 nm. The required fluence for 1 log damage was 73 mJ/cm(2) for the 267 target bp segment and 23 mJ/cm(2) for the 601 target bp segment, respectively. With these two DNA segments, the inactivation rate per segment length was higher for the larger segment, in accordance with a higher pyrimidine and TT content, compared with the smaller fragment. Target DNA was not detectable anymore when using 100 and 300 mJ/cm(2) for the 601 and 267 bp segments respectively. The results indicate that membrane filtration, combined with UV-LED treatment of the concentrate, can be an effective measure to remove and inactivate ARGs from water to prevent their release to the environment.