No abstract

Electrochemical tests of nitrate reduction on Boron-Doped Diamond cathode are investigated through a Design of Experiments (DOE) method. The results show good reduction of nitrate into almost exclusively N2. In the studied domain, the best experimental conditions are high initial nitrate content, low acidic pH values and low working current densities. The application of DOE conclusions on an agro-industrial wastewater gives really satisfying results: final nitrate contents lower than 50 mg/L without nitrite or ammonium formation, and with low energy consumption (under 25 kWh/kgNO3).

Emerging micropollutants have been recently the target of interest for their potential harmful effects in the environment and their resistance to conventional water treatments. Catalytic ozonation is an advanced oxidation process consisting of the formation of highly reactive radicals from the decomposition of ozone promoted by a catalyst. Nanocarbon materials have been shown to be effective catalysts for this process, either in powder form or grown on the surface of a monolithic structure. In this work, carbon nanofibers grown on the surface of a cordierite honeycomb monolith are tested as catalyst for the ozonation of five selected micropollutants: atrazine (ATZ), bezafibrate, erythromycin, metolachlor, and nonylphenol. The process is tested both in laboratorial and real conditions. Later on, ATZ was selected as a target pollutant to further investigate the role of the catalytic material. It is shown that the inclusion of a catalyst improves the mineralization degree compared to single ozonation.

Paper mill, chemistry, textile and food processing industries are high water consumers. Within the framework of the European project Aquafit4Use, the possibility to close the on-site water loop is studied. The aim is to find new technologies or innovative treatment trains to produce water that is 'fit for use' in the industrial process; an example of a paper mill is given. Laboratory-scale tests on nine technologies were carried out to determine the best suitable treatment train: anaerobic process (already on site) --> aerobic process (already on site) --> Flexible Fibre Filter Module --> softening --> nanofiltration --> evapoconcentration or ozonation on nanofiltration (NF) concentrate. This treatment train is currently compared on site at pilot scale to another treatment train including some modifications on the existing on-site biological treatment: anaerobic process --> softening --> membrane bioreactor --> nanofiltration --> evapoconcentration or ozonation of NF concentrate.

Degreasing waste effluents issued from a surface treatment plant were treated by electrochemical techniques in an attempt to reduce COD so that clean water can be returned to the rinse bath. Electrocoagulation, both with iron and aluminium anodes, and anodic oxidation with boron doped diamond (BDD) anodes were tested. In the electrocoagulation tests, the nature of the anodes did not impact significantly the reduction of COD. Electrocoagulation showed good COD removal rates, superior to 80%, but it was not able to reduce COD down to low levels. Anodic oxidation was able to reduce COD down to discharge limits; the oxidation efficiency was superior to 50%. Economical calculations show that anodic oxidation is best used as a polishing step after electrocoagulation. The bulk of the COD would be reduced by electrocoagulation and, then, anodic oxidation would reduce COD below discharge limits. The maximum treatable flow is somewhat hindered by the small sizes of current BDD installation but it would reach 600 m(3)/year if anodic oxidation is coupled with electrocoagulation, the operational cost being 2.90 Euros /m(3).