PREINDUSTRIAL EXPERIENCE IN ADVANCED OXIDATION AND INTEGRAL PHOTODEGRADATION OF ORGANICS IN POTABLE WATERS AND WASTE-WATERS BY PHOTOPERM(TM) MEMBRANES IMMOBILIZING TITANIUM-DIOXIDE AND PROMOTING PHOTOCATALYSTS

A membrane module, utilizing photocatalytic membranes, has been employ ed in a pilot plant both to investigate integral photodegradation of t richloroethene and atrazine, as model molecules of chloroaliphatics an d chloro-triazine pesticides, and to transform typical industrial non- biodegradable wastes into fully biodegradable ones. In the first kind of experiments, by Langmuir-Hinshelwood plots relative to the pilot pl ant itself, with dioxygen as oxidising agent, the kinetic constants fo r degradation at 'infinite' concentration, k, and the apparent adsorpt ion equilibrium constants, K, have been evaluated. Kinetic constants k were (3.68+/-0.25)X10(-5) and (6.67+/-0.65)X10(-4) mol/min for trichl oroethene and atrazine respectively, and corresponding values of K (11 .2+/-0.6)X10(3) and 150+/-45 M(-1) respectively. Apparent reaction ord er was substantially zero for trichloroethene over the entire range of initial concentrations examined (9.1X10(-5) to 1.0X10(-2) M); for atr azine, in contrast, it was close to unity at concentrations lower than about 10(-3) M, but it decreased progressively, approaching 0.2 at hi gher concentrations. Variation of apparent reaction order with concent ration is discussed on the basis of a kinetic character of parameter K . Advantages brought about by immobilization of titanium dioxide semic onductor, with respect to its use in aqueous suspensions (rate factor 2.5), and by co-immobilization of suitable promoting photocatalysts to gether with titanium dioxide (rate factor 28) are shown. In the second kind of experiments, times necessary to reach a BOD/COD ratio of 2/3 have been measured for some characteristic wastes containing: i) non-b iodegradable surfactants; ii) phenolic components; iii) organic solven ts and paint components from wood and metal finishing; iv) lubricating fluids and refinery effluents. By employing ozone, instead of dioxyge n, as oxidizing species during the photocatalytic transformation, reac tivity was higher by a factor ranging from 1.1 to 1.7, but, even with dioxygen, times for complete induction of biodegradability were satisf actorily low (from 8.5 to 26 h per m(3) of effluent containing 10,000 ppm COD, in a pilot plant fitted with 1.2 m(2) of photocatalytic membr ane, and a nominal irradiating power of 80 W).