Removal of faecal indicator pathogens from waters and wastewaters by photoelectrocatalytic oxidation on TiO(2)/Ti films under simulated solar radiation

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

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

A promising technology based on photoelectrocatalysis against Mycobacterium tuberculosis in water disinfection

Mycobacterium tuberculosis is highly infectious, persistent and has been detected in more than one quarter of the world's population. It is notoriously resistant to sterilization and disinfection procedures, largely due to an unusual hydrophobic cell wall and effective defense mechanisms against oxidative stress. This work shows an effective method to reduce M. tuberculosis quantity in water by using Ti/TiO₂ nanotubes electrodes bare and coated with Ag nanoparticles by using photoelectrocatalytic oxidation process. The results have indicated 99.999% of inactivation of a solution spiked with standard and resistant strains of 1×10⁴ CFU mL^-1 M. tuberculosis after 5 min of treatment at Ti/TiO₂ photoanode in 0.05 mol L^-1 Na₂SO₄ (pH 6) under applied potential of + 1.5 V versus Ag/AgCl and UV irradiation. The mycobacteria degradation was monitored by dissolved total organic carbon (TOC) removal, carbohydrate release, chromatography coupled to mass spectroscopy measurements and it is slightly superior to photocatalysis and photolysis processes. All the results corroborated with the complete inactivation and degradation of the byproducts generated during cell lysis.

A comprehensive review on the use of second generation TiO2 photocatalysts: Microorganism inactivation

Photocatalytic disinfection practices have been applied for decades and attract current interest along with the developments in synthesis of novel photocatalysts. A survey based investigation was performed for elucidation of photocatalytic treatment details as well as disinfection mechanism of microorganisms. The present work brings significant information on the utilization of second generation TiO₂ photocatalysts for inactivation of microorganisms typically using E. coli as the model microorganism. Special interest was devoted to the role of organic matrix either generated during treatment or as a natural component. Studies on photocatalytic disinfection were extensively reviewed and evaluated with respect to basic operational parameters related to photocatalysis, and types and properties of microorganisms investigated. Degradation mechanism and behavior of microorganisms towards reactive oxygen species during disinfection and organic matrix effects were also addressed. For successful utilization and effective assessment of visible light active photocatalysts, standard protocols for disinfection activity testing have to be set. Further improvement of the efficiency of these materials would be promising for future applications in water treatment processes.

A photoelectrocatalytic process that disinfects water contaminated with Mycobacterium kansasii and Mycobacterium avium

Nontuberculous mycobacteria are resistant to conventional water treatment; indeed, they have been recovered from a wide variety of environmental sources. Here, we applied the photoelectrocatalytic technique using a Ti/TiO2-Ag photoanode to inactivate mycobacteria. For a mycobacteria population of 5 × 10(8) CFU mL(-1), we achieved 99.9 and 99.8% inactivation of Mycobacterium kansasii and Mycobacterium avium with rate constant of 6.2 × 10(-3) and 4.2 × 10(-3) min(-1), respectively, after 240 min. We compared the proposed method with the photolytic and photocatalytic methods. Using a mycobacteria population of 7.5 × 10(4) CFU mL(-1), the proposed Ti/TiO2-Ag photoanode elicited total mycobacteria inactivation within 3 min of treatment; the presence of Ag nanoparticles in the electrode provided 1.5 larger degradation rate constant as compared with the Ti/TiO2 anode (1.75 × 10(-2) for M. kansassi and 1.98 × 10(-2) for M. avium). We monitored the degradation of the metabolites released during cellular lysis by TOC removal, sugar release, chromatography, and mass spectrometry measurements; photoelectrocatalysis and Ti/TiO2-Ag photoanodes furnished the best results.