New analytical pourpose to study the impact of water potabilization on humic substance activity

The drinking water disinfection procedures may affect the water quality. The addition of Na hypochlorite induces strong modifications in the chemical-physical characters of drinking waters, that involve the humic substances (HS) activity and, indirectly, the fate of the elements associated to HS. The case studied is a drinking water distribution net in Italy, in the town of Castelfranco Emilia (Modena, Northern Italy). Ten water samplings were performed from June 2000 to July 2001. The drinking water samples were collected at the input of the net, before the addition of disinfectants (station 1), and at two sites corresponding to 2 hours (station 2) and 10 hours (station 3) of way for the water flow from the input of the net. The experimental approach here presented is based on the enrichment of HS at the water-air interface, obtained by means of a suitable laboratory apparatus in which the water sample aerosolization is produced. The original samples, the collected aerosols and the water samples depleted by the aerosolization process were submitted to PIXE (Particle Induced X-ray Emission) analysis for the element determination at concentration level of fractions of μg/l, and to spectrofluorimetric and dynamic surface tension measurements. The largest volumes of aerosol were obtained in the treatment of the samples collected at the first station, before the addition of Na hypochlorite, while a lower mass of elements was evaluated in the aerosol produced by the samples of the second station respect to the other two stations. The wavelength values of the fluorescence intensity maximum suggested the presence of lignin and aromatic groups for the first and the second station samples, and of terrestrial humic acids for the third station samples. The dynamic surface tension values resulted generally anti-correlated with the fluorescence intensities. It may be concluded that, in the tested aqueduct net, the disinfection procedure depletes the HS activity, but, ten hours after the addition of disinfectants, the HS have reproduced humic acids in solution.