Solar energy driven photocatalytic membrane modules for water reuse in agricultural and food industries. Pre-industrial experience using s-triazines as model molecules

Ignazio Renato Bellobono,Paola Maria Tozzi,Riccardo Bianchi,Rodica Stanescu,Emilia Simona Mangone,Cristina Costache,Franca Morazzoni

doi:10.1155/s1110662x05000139

Abstract

A membrane module, utilizing photocatalytic membranes, has been employed in a pilot plant, in conditions of solar irradiation, to investigate photomineralisation of atrazine, propazine, terbutylazine, symazine, prometryn, and ametryn, as model molecules ofs-triazine herbicides, at a standard concentration (1.0 ppm) simulating those of contaminated aquifers, by using ozone as oxygen supplier. Photocatalytic composite membranes immobilised30±3wt.% ofTiO2and 6 wt.% of a synergic mixture of tri-(t-butyl)- and tri-(i-propyl)vanadate(V). Photomineralisation was followed by analysis of substrate disappearance, as such, and by total organic carbon (TOC) analysis. A four parameters kinetic model was employed, as set up in previous studies of this series, to interpret the whole photomineralisation curve. Quantum yields, as indicative of catalytic and photocatalytic mechanisms, were evaluated satisfactorily: they are discussed, and compared with those of previous studies on the same substrates, carried out in the same module, but in conditions of practically monochromatic irradiation (254 nm) within the range of optical absorption of semiconductor. Finally, in order to compare effectiveness of composite photocatalytic membranes, described above, prepared by photografting, either in the presence or in the absence of an added photopromoter, as well as that of metallic membranes, onto which the semiconductor without any photopromoter was present as a 3–4μm thick surface layer, directly produced on the nanotechnologically treated surface, with those of other commercial materials, parallel experiments were carried out, by using commercial sheets in which the semiconductor was immobilised, by a method based substantially on glueing by colloidal silica. All of these comparison experiments were carried out at a laboratory scale, by using, in these experiments, dioxygen of air, or ozone as oxygen donors.

Highlights

In six preceding works of this series [1,2,3,4,5,6], the TiO2-mediated, pilot-plant photomineralisation of atrazine, propazine, terbutylazine, symazine, prometryn, prometone, and ametryn, as model molecules of s-triazine herbicides, was thoroughly studied, onto photocatalytic composite membranes immobilising 30 ± 3 wt.% of TiO2 with or without 6 wt.% of a synergic mixture of tri-(t-butyl)- and tri-(i-propyl)vanadate(V), as photopromoter of semiconductor photocatalyst
In the current debate on the amendment of the 80/778 European Drinking Water Directive [11], the issue most controversially discussed is the parameter which sets the maximum concentration of any pesticide or herbicide to occur in drinking water at 0.1 ppb
If an assessment approach similar to that adopted by the World Health Organization [12] will prevail everywhere, the limit values for s-triazine herbicides in human drinking water will be of a few ppb

Summary

INTRODUCTION

In six preceding works of this series [1,2,3,4,5,6], the TiO2-mediated, pilot-plant photomineralisation of atrazine, propazine, terbutylazine, symazine, prometryn, prometone, and ametryn, as model molecules of s-triazine herbicides, was thoroughly studied, onto photocatalytic composite membranes immobilising 30 ± 3 wt.% of TiO2 with or without 6 wt.% of a synergic mixture of tri-(t-butyl)- and tri-(i-propyl)vanadate(V), as photopromoter of semiconductor photocatalyst. Methylthio - 1, 3, 5 - triazine - 2, 4 - diamine) (IV), ametryn (N2 - ethyl - N4 - iso - propyl - 6 - methylthio-1,3,5-triazine2,4-diamine) (V), and atrazine (N2-ethyl-N4-iso-propyl6-chloro-1,3,5-triazine-2,4-diamine) (VI) (IUPAC names between parentheses)

MATERIALS AND METHODS

Apparatus and procedures

RESULTS AND DISCUSSION

CONCLUSIONS