Polishing of water treated by a biological process with heterogeneous photocatalysis

Effluent from a vegetal extraction plant situated in the region of Botucatu, state of São Paulo, Brazil was treated by combining a biological process and heterogeneous photocatalysis. The biologically pretreated effluent was polished by heterogeneous photocatalysis on a laboratory scale, using TiO2 in suspension as catalyst. The heterogeneous photocatalysis experiments were carried out with natural pH (~7.5) and pH adjusted to 3 and 4. An analysis was made to ascertain how the addition of potassium persulfate inhibited the recombination of the e-/h+ pair and incremented the generation of hydroxyl radicals. Coagulation-flocculation to remove the catalyst in suspension reduced the effluent 's initial turbidity of more than 4000 NTU to 2 NTU in 30 min. The photocatalysis reduced the sample 's initial TOC (Total Organic Carbon) from about 40 mg L-1 (in O2 demand) to approximately 3 mg L-1 in 180 min, rapidly removing the odors from the sample and disinfecting the water.