Photoelectrocatalytic disinfection of water and wastewater: performance evaluation by qPCR and culture techniques

Abstract

Photoelectrocatalytic oxidation (PEC) was evaluated as a disinfection technique using water and secondary treated wastewater spiked with Escherichia coli and Enterococcus faecalis. PEC experiments were carried out using a TiO(2)/Ti-film anode and a zirconium cathode under simulated solar radiation. Bacterial inactivation was monitored by culture and quantitative polymerase chain reaction (qPCR). Inactivation rates were enhanced when the duration of the treatment was prolonged and when the bacterial density and the complexity of the water matrix were decreased. E. coli cells were reduced by approximately 6 orders of magnitude after 15 min of PEC treatment in water at 2V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to about 5 log reduction, while electrochemical oxidation alone resulted in negligible inactivation. The superiority of PEC relative to PC can be attributed to a more efficient separation of the photogenerated charge carriers. Regarding disinfection in mixed bacterial suspensions, E. coli was more susceptible than E. faecalis at a potential of 2V. The complex composition of wastewater affected disinfection efficiency, yielding lower inactivation rates compared to water treatment. qPCR yielded lower inactivation rates at longer treatment times than culture techniques, presumably due to the fact that the latter do not take into account the viable but not culturable state of microorganisms.

Sequential ionic layer adsorption and reaction (SILAR) deposition of Bi4Ti3O12 on TiO2: an enhanced and stable photocatalytic system for water purification

“…55 Previous work has demonstrated that under the same conditions Gram-negative bacteria take significantly longer to be de-activated than Gram-positive. 56 We suggest that the BTO-TiO 2 system affects rapid deactivation of E. coli, but would warn against assuming such efficient bactericidal action against other micro-organisms.…”

“…It can be concluded that BTO is acting in this capacity as an electron sink, similarly to the traditional model of electron transfer on P25. 56 Given that removal of oxygen from a test solution somewhat abated the photocatalytic efficiency however, it can be concluded that not all photoexcited electrons in the anatase conduction band are transferred to BTO/rutile, and that some electrons are trapped as superoxide ions.…”

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

“…Considering that the major groups of pathogenic organisms are: (a) bacteria, (b) viruses, (c) protozoans and (d) helminths ( Sperling, 2008 ) it is important to point out that the initial microorganism density as well as the nature of mixed bacterial populations in water play an important role in the selection of a disinfection process, since the combination affects the type, cost and required treatment time for complete microbial inactivation ( Venieri et al, 2012 , 2013 ). In this regard for example, while bacteria are physically protected at high population density values, suspended solids and turbidity can decrease the performance of the photo-assisted EAOPs due to irregular light intensity scattering ( Rather and Lo, 2020 ).…”

“…In Eq. (2) the subscripts cb and vb denote the conduction and valence bands, respectively ( Domínguez-Espíndola et al., 2019 ; Venieri et al., 2013 ).…”

Simultaneous removal of estrogens and pathogens from secondary treated wastewater by solar photocatalytic treatment

“…Genomic DNA was extracted performing chemical lysis and phenol/chloroform/isoamyl alcohol (25:24:1) extraction using lysozyme and proteinase K, according to our previous work (Venieri et al, 2013 quantity and purity of all DNA samples were determined measuring their absorbance at 260 nm and estimating the ratio of absorbance values at 260 nm and 280 nm, respectively.…”