Can ozone inactivate SARS-CoV-2? A review of mechanisms and performance on viruses.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has challenged societies around the globe. Technologies based on ozone, a powerful oxidant, have been evaluated to inactivate this virus in aerosols and fomites. However, the high data diversity hinders the possibility of establishing a common ground for determining best practices for the use of these technologies. Furthermore, there is a lack of consensus regarding which are the main mechanisms of ozone virus inactivation. This critical review examined the most relevant information available regarding ozone application in gas-phase for different viruses inactivation (including recent publications dealing with SARS-CoV-2), and pointed towards envelope alteration as the main reaction pathway for enveloped viruses, such as is the case of SARS-CoV-2. It could also be concluded that gaseous ozone can be indeed an effective disinfectant, successfully inactivating viruses such us influenza A H1N1, MERS-CoV, SARS-CoV-1 or even SARS-CoV-2 in aerosols or fomites. In reviewed works, low ozone exposures, just around 0.1-0.4 mg L-1 min, achieve about 4 log10 of inactivation in aerosols, while exposures between 1 and 4 mg L-1 min may be needed to guarantee an inactivation of 3-4 log10 in different fomites. Although further studies are required, ozone is an effective candidate to be used against SARS-CoV-2 or other viruses in surfaces and indoor locations.

Effect of COD on mainstream anammox: Evaluation of process performance, granule morphology and nitrous oxide production.

The effect of COD addition into an anammox reactor was assessed during short and long term exposure. The short term exposure was assessed via batch tests and lasted 48 h. Results indicated the presence of a very active denitrifying community able to consume COD using nitrate and nitrite as electron acceptors. However, the presence of COD did not result in an increase of the ammonium concentration at the end of the tests indicating that anammox activity was not suppressed by the addition of COD. Different COD concentrations (125, 225 and 175 mg COD/L) were also added in the reactor during 3 periods within its operation (period II, III and V respectively). Long term COD addition (up to 102 d of continuous addition during period II and III) caused a decrease of the anammox activity and a shift on the microbial community, with a decrease on the anammox fraction. However, the anammox process was never lost and it fully recovered as soon as COD addition stopped. Finally, dissolved N2O was monitored under periods with and without COD addition, showing higher concentrations during transient periods from COD addition to no addition. The results of this paper provide evidence of how a long term COD exposure into an anammox reactor affect the overall nitrogen removal process, the granular structure of the anammox biomass, its microbial composition and for the first time, its N2O emissions.

Produced water treatment by advanced oxidation processes.

Different Advanced Oxidation Processes (AOPs) such as photocatalysis, Fenton-based processes and ozonation were studied to include one of these technologies within an integrated solution for produced water (PW) polishing. Synthetic PW was prepared adding toluene, xylene, naphthalene, phenol, acetic and malonic acids to a seawater matrix. Despite that in all AOPs studied in this work BTEX and naphthalene were removed, the efficiency (in terms of TOC removal) of each treatment varied largely. Among these techniques, photocatalysis was found to be the less effective for the treatment of PW, as TOC removals lower than 20% were obtained for the best scenario after 4 h treatment. In the contrary, best results were obtained by ozonation combined with H2O2, where all the organic components were removed, including a high percentage of acetic acid, which was not abated by the rest of the AOPs studied. The optimum conditions for ozonation were 4 g h-1 O3 and 1500 mg L-1 H2O2 at pH 10, where after 2 h a 74% of TOC removal was achieved and the acetic acid elimination was 78%. This condition enabled that ozonation process accounted for the lowest electric energy consumption per order of target compound destruction regarding total organic carbon (TOC).

Integrated processes for produced water polishing: Enhanced flotation/sedimentation combined with advanced oxidation processes.

In this study, bench scale dissolved air flotation (DAF) and settling processes have been studied and compared to a novel flotation technology based on the use of glass microspheres of limited buoyancy and its combination with conventional DAF, (Enhanced DAF or E-DAF). They were evaluated as pretreatments for advanced oxidation processes (AOPs) to polish produced water (PW) for reuse purposes. Settling and E-DAF without air injection showed adequate turbidity and oil and grease (O&G) removals, with eliminations higher than 87% and 90% respectively, employing 70 mg L-1 of FeCl3 and 83 min of settling time, and 57.9 mg L-1 of FeCl3, 300 mg L-1 of microspheres and a flocculation rate of 40 rpm in the E-DAF process. A linear correlation was observed between final O&G concentration and turbidity after E-DAF. In order to polish the O&G content of the effluent even further, to remove soluble compounds as phenol and to take advantage of residual iron after these treatments, Fenton and photo-Fenton reactions were essayed. After 6 h of the Fenton reaction at pH 3, the addition of 1660 mg L-1 of H2O2 and 133 mg L-1 of iron showed a maximum O&G elimination of 57.6% and a phenol removal up to 80%. Photo-Fenton process showed better results after 3 h, adding 600 mg L-1 of H2O2 and 300 mg L-1 of iron, at pH 3, with a higher fraction of elimination of the O&G content (73.7%) and phenol (95%) compared to the conventional Fenton process.

High salinity effect on bioremediation of pretreated pesticide lixiviates from greenhouses.

Hydroponics culture greenhouses usually work in closed and semi-closed irrigation systems for nutrients and water-saving purposes. Photo-Fenton reaction has been revealed as an efficient way to depollute that kind of recycled effluents containing pesticides, even for high salinity concentrations. However, the inefficacy of organic matter chemical depletion imposes the use of a subsequent treatment. This work proposes the suitability of an integration of advanced oxidation process with a subsequent bioreactor to treat greenhouse lixiviates effluents at high or extremely high conductivity (salts concentration: up to 42 g L⁻¹). As a first step in this study, the performance of a series of sequencing batch reactors was monitored in order to check the biocompatibility of photo-Fenton pretreated effluents depending on their salinity content. In the second step, those same pretreated effluents were loaded to a biofiltration column filled with expanded clay. Finally, bacterial 16S rRNA gene sequencing was carried out to analyse microbial diversity of the biomass developed in the column. Results stated that the chemical-biological coupled system is effective for the treatment of water effluents containing pesticides. The integrated system is able to deplete more than 80% of the organic load, even under extremely high salinity.

Fosetyl-Al photo-Fenton degradation and its endogenous catalyst inhibition.

Interferences from many sources can affect photo-Fenton reaction performance. Among them, catalyst inhibition can be caused by the complexation and/or precipitation of iron species by the organic matter and salts present in the reaction media. This is the case of the oxidation of effluents containing organophosphorous fosetyl-Al. The degradation of this fungicide generates phosphate anions that scavenge iron and hinder Fe(II) availability. Experimental design was applied to artificially enlighten photo-Fenton reaction, in order to evaluate fosetyl-Al degradation. The performed experiments suggested how iron inhibition takes place. The monitoring of photo-Fenton reaction over a mixture of fosetyl-Al with other two pesticides also showed the interferences caused by the presence of the fungicide on other species degradation. Solar empowered photo-Fenton was also essayed for comparison purposes. Artificial and solar light photo-Fenton reactions were revealed as effective treatments for the elimination of tested fungicide. However, the phosphate ions generated during fosetyl oxidation decreased iron availability, what hampered organic matter degradation.

Experimental design applied to photo-Fenton treatment of highly methomyl-concentrated water.

This work is focused on the study of the suitability of the photo-Fenton process as a pretreatment for water highly contaminated with a methomyl commercial formulation in Advanced Greenhouses devices. Initial concentrations of reagents and pesticide were evaluated according to a central composite experimental design, with methomyl depletion and biocompatibility of the final effluent as response functions. A triad of optimal operation conditions could be determined, [Met.](0)=50 mg L(-1), [H(2)O(2)](0)=254 mg L(-1) and [Fe(2+)](0)=77 mg L(-1) for the best elimination yield and an acceptable BOD(5)/COD value, and initial concentration of methomyl can be established as the most important parameter for the performance of the treatment due to the limitations that impose on the hydrogen peroxide doses in the presence of the excipients of the commercial formulation.