Water disinfection by persulfate activation using a nitrogen-doped reduced graphene oxide – PVDF membrane

Abstract

This work demonstrates the suitability of employing carbon-based catalytic membranes for persulfate activation and water disinfection in continuous flow mode of operation for the first time. Poly(vinylidene fluoride) (PVDF) membranes with and without nitrogen-doped reduced graphene oxide (rGO-M) were prepared and tested. The cumulative effect of each membrane component was assessed based on the persulfate activation capacity and the retention and/or elimination of faecal contamination indicator microorganisms in a defined suspension of Escherichia coli and Enterococcus faecalis. In the absence of persulfate, the pristine PVDF membrane enabled retention of 1.98 ± 0.51 log, while the rGO-M–PVDF membrane removed 3.71 ± 0.66 log of the initial microbial abundance (3.87 ± 0.01 log) after 6 h of operation. The catalytic features of the rGO-M–PVDF membrane were then demonstrated by adding a persulfate precursor to the feed suspension. This treatment system was able to reduce the abundance of cultivable microorganisms (total heterotrophs, enterobacteria, enterococci) of the defined suspensions and river water samples to values below the limit of detection (< 0.5 CFU mL−1) up to 24 h operation. In addition, the reactivation capacity of the cultivable microorganisms and representative specific genes (16S rRNA, intl1, blaTEM and sul1) after 7-day storage of the treated river water was studied. Among the parameters analysed, only total cultivable heterotrophic cells were able to regrow to values similar to those found in the feed. Therefore, the proposed system can be considered as a promising technology for the removal of harmful microbiota during drinking water production in continuous flow mode.