Resistance and induction of viable but non culturable states (VBNC) during inactivation of E. coli and Klebsiella pneumoniae by addition of H2O2 to natural well water under simulated solar irradiation.

Inactivation of E. coli and Klebsiella pneumoniae by addition of H2O2 10 mg L-1 into natural well water samples containing natural total iron concentrations (around 0.3 mg L-1) under simulated solar light was followed by bacterial culturability (plate count) and viability (DVC-FISH). Results showed that culturability of both bacteria was totally reduced while viability was only completely depleted for E. coli in well water samples depending of total iron concentration. Post-irradiation effects in presence of residual H2O2 showed that viability of both bacteria kept dropping being totally reduced for E. coli cells while K. pneumoniae decreased only 1-log. SEM micrographs showed that E. coli and K. pneumoniae cells underwent morphological changes and size reduction according to VBNC states. Different dark and photo-induced processes where physical-chemical features of groundwater samples play an important role could be responsible of bacteria abatement.

Photo-Fenton process at natural conditions of pH, iron, ions, and humic acids for degradation of diuron and amoxicillin.

Effect of ferric ions at concentrations typically found in natural waters (0.05 to 1.06 mg L-1) and low H2O2 concentrations (between 0.5 and 17.9 mg L-1) on simulated sunlight-induced (300 W m-2) photo-Fenton degradation at initial neutral pH (7.0) of amoxicillin and diuron in Milli-Q water was studied using an rotatable central composite experimental design 22 with a central and two axial points. H2O2 concentration was the parameter playing the key role on the degradation of both pollutants. Despite that initial pH was 7.0 in Milli-Q water, this latter decreased rapidly in the first minutes, reaching values of 3.5 and 5.0 for diuron and amoxicillin respectively after 15 min of simulated sunlight irradiation. In contrast, in presence of bicarbonate/carbonate (HCO3-/CO3=), fluoride (F-), and humic acids (HAs) at concentrations found often in surface and well waters with ferric ion and H2O2 concentrations of 0.3 and 9.7 and 15.2 mg L-1 respectively, both pollutants exhibited a strong degradation keeping the circumneutral pH. Amoxicillin and diuron degradation byproducts found by HPLC/MS were compatible with HO• and/or CO3-• radical attack. Several photo-induced processes such as photo-Fenton (by dissolved ferric-HA complexes), heterogeneous photocatalysis (by colloidal iron), UV-B H2O2 photolysis, irradiated-dissolved organic matter, and their reactions with pollutants would be the main oxidative route responsible of degradations. These findings demonstrated that it could be possible using iron concentrations often found in natural waters to oxidize via photo-Fenton processes among other events, organic pollutants at natural pH conditions.

2,4-D abatement from groundwater samples by photo-Fenton processes at circumneutral pH using naturally iron present. Effect of inorganic ions.

This study evaluated, at laboratory scale, if the using iron naturally present (0.3 mg L-1) and adding 10 mg L-1 of hydrogen peroxide was effective to remove 24.3 mgL-1 of 2,4-dichlorophenoxyacetic acid (2,4-D) from groundwater samples by simulated solar irradiation (global intensity = 300 W m-2). Under these conditions, the degradation of 2,4-D reached 75.2 % and the apparition of its main oxidation byproduct 2,4-dichlorophenol (DCP) was observed. On the other hand, pH exhibited an increasing from 7.0 to 8.3 during the experiment. Experiments using Milli-Q water at pH 7.0, iron, and H2O2 concentrations of 0.3 and 10 mg L-1, respectively, were carried out in order to study the effect of ions such as carbonate species, phosphate, and fluoride in typical concentrations often found in groundwater. Ion concentrations were combined by using a factorial experimental design 23. Results showed that carbonates and fluoride did not produce a detrimental effect on the 2,4-D degradation, while phosphate inhibited the process. In this case, the pH increased also from 7.0 to 7.95 and 8.99. Effect of parameters such as pH, iron concentration, and hydrogen peroxide concentration on the 2,4-D degradation by the photo-Fenton process in groundwater was evaluated by using a factorial experimental design 23. Results showed that the pH was the main parameter affecting the process. This study shows for the first time that using the photo-Fenton process at circumneutral pH and iron naturally present seems to be a promising process to remove pesticides from groundwater.