Simultaneous abatement of organics (2,4-dichlorophenoxyacetic acid) and inactivation of resistant wild and laboratory bacteria strains by photo-induced processes in natural groundwater samples

Abstract

Simultaneous abatement of 2,4-dichlorophenoxyacetic acid (2,4-D at 70 µg L−1), Escherichia coli and Klebsiella pneumoniae (laboratory and wild strains) cells from real groundwater samples containing natural iron concentrations (∼0.3 mg L−1) was studied by addition of H2O2 (10 mg L−1) using a 18-L compound parabolic collector-CPC solar reactor (under natural sunlight irradiation 150,000 J m−2) equipped with a UV-(A + B + Visible) lamp (15 W: UV-B and UV-A intensities were 0.74 and 6.47 W m−2 respectively) powered by a photovoltaic panel. Viability of E. coli K12 and K. pneumoniae laboratory strains at high initial concentrations of 106–107 cells mL−1 (followed by DVC-FISH) dropped 4.69 and 2.18 Logs, respectively after 30 min t30W of combined UV-A + B-Visible lamps and sunlight irradiation (SL + UV + H2O2). Moreover, the initial 2,4-D concentration underwent a strong reduction reaching concentrations below the detection limit after 5 min t30W of SL + UV + H2O2 treatment. Regarding real wild bacteria strains often present in natural well waters, which were at low initial concentrations, total culturability (initial concentration 101 CFU mL−1) and viability (initial concentration 102–103 cells mL−1) reductions were reached after 30 min (t30W) of combined treatment. Participation of several photochemical and dark events such as photocatalysis (by iron hydro-oxides and other metal oxides naturally present), Fenton and photo-Fenton (by natural dissolved iron), UV-A + B/NO3 −, Dissolved organic matter (DOM)/UV + Vis and UV-B photolysis of H2O2 are suggested as responsible of simultaneous 2,4-D abatement and microbial inactivation in natural groundwater samples.