Effect of photocatalysis on the transfer of antibiotic resistance genes in urban wastewater

The widespread use and abuse of antibiotics in human and animal medicine has produced a reservoir of antibiotic resistant bacteria (ARB) which persist and spread within many environments including natural and wastewater systems. This paper reports the first investigation into the effect of advanced oxidation technologies, photocatalysis, on the potential to induce antibiotic resistant gene transfer within sub-lethally injured ARB. The impact of photocatalytic disinfection (PCD) treatments on three strains of Escherichia coli, an antibiotic sensitive strain (K12) and two antibiotic resistant strains (J-53R (rifampicin resistant) and HT-99 (chloramphenicol resistant), within an immobilised titanium dioxide stirred tank reactor. When suspended in distilled water, viable cell numbers (CFU mL−1) of both ARB declined from 3 log10 to 0.5 log10 with 180 min PCD treatment. However, subsequent recovery to 3 log10 of both ARB was observed during post treatment incubation at 37 °C for 24 h. No E. coli K12 were recovered immediately after 150 min treatment, or after post treatment incubation. These observations suggest that the ARB are less sensitive to the oxidative stresses involved in PCD treatment than the antibiotic sensitive strain. Gene pair conjugant numbers in PCD treated mixtures of J-53R and HT-99 cells (a 9:1 ratio) were calculated to be four-fold greater than in the (no treatment) control experiments. Both surviving bacterial cell numbers and conjugant pair numbers were lower when ARB were PCD treated in final effluent from an urban wastewater treatment plant. In conclusion, the results of this study confirm the efficacy of PCD, but also highlight the importance of applying PCD treatment “long enough” to avoid post treatment recovery from sub-lethal injury and the highly undesirable transfer of antibiotic resistant genes amongst bacteria during wastewater treatment

Assessment of low-cost cartridge filters for implementation in household drinking water treatment systems

In regions where houses are sparsely located, traditional centralized water treatment plants are not economically feasible, with household water treatment (HWT) systems commonly used to provide potable water for a range of household activities. Filtration prior to disinfection is essential, and due to their ease of use and small footprint, cartridge filters are commonly employed. In this work, readily available commercial filter types (spun, wound and pleated) of different micron ratings (10, 5 and 1) were tested for the removal of turbidity either alone or in series via simulated large volume pilot trials. Water with an initial turbidity of 40 ± 10 NTU was prepared using fine test dust (ISO 12103-1, A2) with the turbidity removal efficiency, pressure drop, total capacity and lifespan of the filters evaluated. To increase useable filter lifetime upon reaching the 1 bar pressure limit, a series of washing steps were employed to regenerate the filters. Whilst pleated filters could be efficiently cleaned, spun and wound filters could not, and were discarded after single use. In pilot trials, the volume of turbid water filtered varied from 0.85 m3 with a 1 micron wound filter to 6 m3, with 5 and 1 micron pleated filters in series, which following regeneration could be used for three filtration cycles. For pleated filters, turbidity removal efficiency improved over time as a cake built up resulting in the effluent turbidity reaching acceptable quality (<5 NTU). This criterion continued to be achieved with repeated cycles of washed pleated filters, thereby significantly reducing the cost and improving sustainability of the HWT system. Field trials were carried out with a similar HWT system (5 and 1 micron spun filters) installed in households of rural communities in Curiti, Colombia. Turbidity was effectively removed from natural water (reduction to <1.2 NTU) with improved efficacy in comparison to synthetic water samples due to the large particle size distribution observed in the natural water. © 2020 Elsevier Lt