Modeling heterogeneous photocatalytic inactivation of E. coli using suspended and immobilized TiO2 reactors

A study was carried out to develop a kinetic model of the photocatalytic inactivation of Escherichia coli using different TiO₂ catalysts. The model developed is based on a reaction scheme that involves effectively coupling mass‐transfer fluxes between bacteria and catalyst surface on one hand and bacterial degradation reaction on the other. The photocatalytic results were derived from experiments led in a batch reactor under both dark and Ultra Violet (UV) irradiation conditions. Using a reference catalyst, the robustness of the developed model was tested under solar conditions. The experimental data validated the model as successfully able to reproduce evolutions in the viable bacteria concentration in the range of parameters studied without any further adjustment of the kinetic parameters. The model was used to simulate the bacterial degradation kinetics under different working conditions to describe the partitioning of both bacterial adhesion and photocatalytic reaction in the solution to be treated © 2015 American Institute of Chemical Engineers AIChE J, 61: 2532–2542, 2015     

Peracetic acid‐enhanced photocatalytic and sonophotocatalytic inactivation of E. coli in aqueous suspensions

BACKGROUND: Although chlorination is an effective and widely employed method of water disinfection, it suffers serious drawbacks such as the formation of toxic chlorinated by‐products. Therefore, other disinfection technologies have been researched and developed, including advanced oxidation. RESULTS: The efficacy of heterogeneous photocatalysis and sonophotocatalysis induced by UV‐A irradiation and low frequency (24–80 kHz) ultrasound irradiation in the presence of TiO₂ as the photocatalyst and peracetic acid (PAA) as an additional disinfectant to inactivate E. coli in sterile water was evaluated. PAA‐assisted UV‐A/TiO₂ photocatalysis generally leads to nearly complete E. coli inactivation in 10–20 min of contact time with the extent of inactivation depending on the photocatalyst type and loading (in the range 100–500 mg L^?1) and PAA concentration (in the range 0.5–2 mg L^?1). The simultaneous application of ultrasound and UV‐A irradiation in the presence of TiO₂ and PAA prompted further E. coli inactivation. CONCLUSIONS: The proposed advanced disinfection technology offers complete E. coli inactivation at short treatment times and low PAA doses. Copyright © 2010 Society of Chemical Industry     

Effect of pH, inorganic ions, organic matter and H2O2 on E. coli K12 photocatalytic inactivation by TiO2: Implications in solar water disinfection

The effect of different chemical parameters on photocatalytic inactivation of E. coli K12 is discussed. Illumination was produced by a solar lamp and suspended TiO₂ P-25 Degussa was used as catalyst. Modifications of initial pH between 4.0 and 9.0 do not affect the inactivation rate in the absence or presence of the catalyst. Addition of H₂O₂ affects positively the E. coli inactivation rate of both photolytic (only light) and photocatalytic (light plus TiO₂) disinfection processes. Addition of some inorganic ions (0.2 mmol/l) like HCO₃⁻, HPO₄²⁻, Cl⁻, NO₃⁻ and SO₄²⁻ to the suspension affects the sensitivity of bacteria to sunlight in the presence and in absence of TiO₂. Addition of HCO₃⁻ and HPO₄²⁻ resulted in a meaningful decrease in photocatalytic bactericidal effect while it was noted a weak influence of Cl⁻, SO₄²⁻ and NO₃⁻. The effect of counter ion (Na⁺ and K⁺) is not negligible and can modify the photocatalytic process as the anions. Bacteria inactivation was affected even at low concentrations (0.2 mmol/l) of SO₄²⁻ and HCO₃⁻, but the same concentration does not affect the resorcinol photodegradation, suggesting that disinfection is more sensitive to the presence of natural anions than photocatalytic degradation of organic compounds. The presence of organic substances naturally present in water like dihydroxybenzenes isomers shows a negative effect on photocatalytic disinfection. The effect of a mixture of chemical substances on photocatalytic disinfection was also studied by adding to the bacterial suspension nutrient broth, phosphate buffer and tap water.     

Regio‐ and Stereoselective Biohydroxylations with a Recombinant Escherichia coli Expressing P450pyr Monooxygenase of Sphingomonas Sp. HXN‐200

A recombinant Escherichia coli expressing P450_pyr monooxygenase of Sphingomonas sp. HXN‐200 was developed as a useful biocatalyst for regio‐ and stereoselective hydroxylations, with no side reaction and easy cell growth. The resting E. coli cells showed an activity of 4.1 U/g cdw and 9.9 U/g cdw for the hydroxylation of N‐benzylpyrrolidin‐2‐one 1 and N‐benzyloxycarbonylpyrrolidine 3 , respectively, being as active as the wide‐type strain. Biohydroxylation of N‐benzylpyrrolidin‐2‐one 1 with the resting cells gave (S)‐N‐benzyl‐4‐hydroxypyrrolidin‐2‐one 2 in >99% ee and 10.8 mM, a 2.6 times increase of product concentration in comparison with the wild‐type strain. Biohydroxylation of N‐tert‐butoxycarbonylpiperidin‐2‐one 5 , N‐benzylpiperidine 7 and N‐tert‐butoxycarbonylazetidine 9 with the E. coli cells afforded the corresponding 4‐hydroxypiperidin‐2‐one 6 , 4‐hydroxypiperidine 8 , and 3‐hydroxyazetidine 10 in 14 mM, 17 mM, and 21 mM, respectively. Moreover, hydroxylation of (−)‐β‐pinene 11 with the recombinant E. coli cells showed excellent regio‐ and stereoselectivity and gave (1R)‐trans‐pinocarveol 12 in 82% yield and 4.1 mM, which is over 200 times higher than that obtained with the best biocatalytic system known thus far. The recombinant strain was also able to hydroxylate other types of substrates with unique selectivity: biohydroxylation of norbornane 13 gave exo‐norbornaeol 14 , with exo/endo selectivity of 95%; tetralin 15 and 6‐methoxytetralin 17 were hydroxylated at the non‐activated 2‐position, for the first time, with regioselectivities of 83–84%.