HETEROGENEOUS PHOTOCATALYSIS ASSOCIATED WITH ELECTRO-OXIDATION IN THE PRE-TREATMENT OF EUTROPHIC WATER IN A PILOT STATION OF WATER TREATMENT

Abstract

The pre-chlorination is a practice performed in many water treatment plants in order to reduce the organic load. However, this practice leads to the formation of chlorinated products considered carcinogenic. This fact has raised interest in the development or improvement of techniques that can eliminate or reduce the use of chemical pre-oxidation. In this context, the aim of this research was to study the electrooxidation performance associated with heterogeneous photocatalysis (photoreactor) comparing to the employment of chlorine and chlorine dioxide, evaluating the quality of treated water in terms of chemical oxygen demand, chlorophyll a, turbidity and trichlormethane formation. After the pre-oxidation of the samples, they were subjected to coagulation with HCA (5.4 mg.l-1), cationic polymer (2.0 mg.l-1), descending direct filtration and post chlorination (5.0 mg.l-1). Samples were collected at 30 and 90 minutes after the beginning of the career filtration and were analyzed according to Standard Methods for Examination of Water and Wastewater. The average results for turbidity removal reached 95.57% (chlorine), 96.23% (chlorine dioxide) and 99.5% (with the photoreactor). For COD removal was obtained an average of 37.45% (chlorine), 49.45% (chlorine dioxide) and 65.5% (photoreactor). The average of chlorophyll removal was 91.94% (chlorine), 94.04% (chlorine dioxide) and 98.97% (photoreactor). TTHM produced reached concentrations of 104.07 μg.l-1 (chloro), 88.85 μg.l-1 (chlorine dioxide) and 77.20 μg.l-1 (photoreactor). The photoreactor was capable of producing water within the standards established for water quality. In the meantime, the photoreactor is presented as a technology which enhances coagulation, by increasing the precipitation capacity of dissolved compounds, thus increasing the filtration efficiency, and minimizes by-products of chlorination.

Key Words: electro-oxidation; heterogeneous photocatalysis; pre-treatment of eutrophic water