Reatores de discos rotativos e tubular helicoidal na degradação fotocatalítica de diclofenaco e carga orgânica de efluente hospitalar

Abstract

In this study, the advanced oxidation process heterogeneous photocatalysis were used for the degradation of diclofenac and decrease of the organic load in the effluent from the emergency sector (PA) of the University Hospital of Santa Maria (HUSM). Two different photoreactors were investigated: the rotative discs reactor, which employed TiO2 immobilized on ceramic discs (1800 mL), and the tubular helicoidal reactor (1000 mL), employing TiO2 in suspension. Both used as radiation source a mercury vapor lamp of medium pressure (125 W and 401 W m-2) that propitiated flow of photons of 2.22 x 10-6 ± 1.30 x10-7 mol s-1 and 1.77 x 10-6 ± 1.45 x 10-7 mol s-1 for the rotative discs and tubular helicoidal reactors, respectively. Potassium ferrioxalate was used as actinometer for these measurements. The experimental conditions were optimized by applying Response Surface Methodology. Reduction of chemical oxygen demand (COD) after 60 min was used for this evaluation. The temperature of the reactors was kept constant in 30 °C, while pH and discs rotation velocity; and pH, mass of TiO2 in suspension and recirculation rate were the variables for rotative discs and tubular helicoidal reactors, respectively. The better conditions found were: pH 5 and 9 rpm for rotative discs reactor (COD reduction of 30%) and pH 3, 600 mg L-1 TiO2 and recirculation rate of 15 L h-1 (COD reduction of 45%) for the tubular helicoidal reactor. The photonic efficiency of the rotative disc reactor was 2.69 ± 0.23%, lower than the 10.54 ± 0.37% reached by the tubular helicoidal. The efficiency of degradation of diclofenac in hospital effluent was assessed through high performance liquid chromatography with diode array detector (HPLC-DAD, lmáx = 279 nm), a mobile phase MeOH:Aqueous Na3PO4 0.01 mol L-1 (H3PO4 , pH 6) 70:30 (v/v). The diclofenac added to the hospital effluent (0.1 mg L-1) was 100% e 97% degraded by using using the rotative disc and tubular helicoidal reactors, respectively. Diclofenac environmental exposure in the hospital effluent was also carried out by mean of HPLC-DAD. Samples collected during 7 days were analyzed. Diclofenac concentration ranged from 0.8 to 3.6 mg L-1 (average: 1.7 mg L-1). The acute toxicity (LC50) of the hospital effluent and diclofenac solutions was evaluated by using bioassay Artemia salina. Inhibition of toxicity caused by the treatment of hospital wastewater using the rotative disc and tubular helicoidal reactors was 58% and 55%, respectively. Concerning diclofenac aqueous solutions, no mortality of Artemia salina was observed, which shows that this compound presents no acute toxicity for this bioindicator.