The effect of operational parameters on electrocoagulation-flotation process followed by photocatalysis applied to the decontamination of water effluents from cellulose and paper factories

Cellulose and paper pulp factories utilize a large amount of water generating several undesirable contaminants. The present work is a preliminary investigation that associates the electrocoagulation-flotation (EC) method followed by photocatalysis to treat such wastewater. For EC, the experiment with aluminium and iron electrodes showed similar efficiency. Iron electrodes (anode and cathode) were chosen. By applying 30 min of EC/Fe0, 153 A m−2 and pH 6.0, the COD values, UV-vis absorbance and turbidity underwent an intense decrease. For the subsequent UV photocatalysis (mercury lamps) TiO2 was employed and the favourable operational conditions found were 0.25 g L−1 of the catalyst and solution pH 3.0. The addition of hydrogen peroxide (50 mmol L−1) highly increased the photo-process performance. By employing the UV/TiO2/H2O2 system, the COD reduction was 88% compared to pre-treated effluents and complete sample photobleaching was verified. The salt concentration on EC (iron electrodes) showed that the electrolysis duration can be reduced from 30 to 10 min by the addition of 5.0 g L−1 of NaCl. The biodegradability index (BOD/COD) increased from 0.15 (pre-treated) to 0.48 (after EC) and to 0.89 (after EC/photocatalysis irradiated for 6 h), showing that the employed sequence is very helpful to improve the water quality. This result was confirmed by biotoxicity tests performed with microcrustaceous Artemia salina.