Photochemical degradation of organic pollutants in wastewaters

Abstract

In the present work, the photochemical treatment of a synthetic wastewater in a batch recycle photochemical reactor using ultraviolet irradiation (254 nm, 6 W), hydrogen peroxide and ferric ions was studied. The wastewater was composed of peptone, lab lemco, glucose, ammonia hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and had initial total carbon 1080 mg L-1. Its volume was 250 mL, and the active (irradiated) volume in the annular photoreactor was 55.8 mL. The effect of initial total carbon, initial hydrogen peroxide amount, and Fe(III) added, on total carbon removal was studied aiming at optimizing operating parameters. Each experiment lasted 120 min, and the process was attended via pH, total carbon and HPLC analysis (for determination of phenolic compounds conversion). The results obtained showed that the addition of Fe(III) markedly increased the mineralization of the wastewater, especially during the first 60 min. Specifically, for initial carbon concentration 528 mg L-1, hydrogen peroxide 2664 mg L-1, without any Fe(III) added, the total carbon removal achieved after two hours was 50%, whereas after adding 240 mg L-1 Fe(III) the total carbon removal observed was 87%. The difference was even more pronounced during the first 60 min since the total carbon removal was increased from 19% in the absence of Fe(III) to 79% in the presence of 240 mg L-1 Fe(III). The effect of phenol presence (0-100 mg L-1) on total carbon removal was also examined. In all experiments, complete removal of phenol was observed, whereas TC removal was around 75%. The results obtained were applied for the treatment of real wastewater (landfill leachate) with initial carbon concentration 2650 mg L-1, and pH 8.3. It was observed that pH adjustment markedly increased the percentage of carbon removal. With pH adjustment from 8 to 5 the results for total carbon removal improved from 3% (using only 13320 mg L-1 H2O2) to 75% after pH adjustment with HCl (using 13320 mg L-1 H2O2, 400 mg L-1 Fe(III)).