Sequential treatment via Trametes versicolor and UV/TiO₂/Ru_xSe_y to reduce contaminants in waste water resulting from the bleaching process during paper production

An efficient sequential, biological and photocatalytic treatment to reduce the pollutant levels in wastewater due to the bleaching process during paper production is reported. For a biological pre-treatment, 800 ml of non-sterilized effluent was inoculated with Trametes versicolor immobilized in polyurethane foam, with 25 g l^-1 glucose, 6.75 mM CuSO₄, and 0.22 mM MnSO₄ added, and cultured at 25 °C with an air flow of 800 ml min^-1 for 8 d. The fungus did not inhibit growth of the heterotropic populations of the effluent. After 4 d of culture, the chemical oxygen demand (COD) reduction and colour removal (CR) were 82% and 80%, respectively, with laccase (LAC) and manganese peroxidase (MnP) activities of 345 U l^-1 and 78 U l^-1, respectively. The COD reduction and CR correlated positively (p < 0.0001) with LAC and MnP activities. Chlorophenol removal was 99% of pentachlorophenol, 99% of 2,3,4,6-tetrachlorophenol (2,3,4,6-TCP), 98% of 3,4-dichlorophenol (3,4-DCP) and 77% of 4-chlorophenol (4-CP), while 2,4,5-trichlorophenol (2,4,5-TCP) increased to 0.2 mg l^-1. The pre-treated effluent was then exposed to a photocatalytic treatment. The treatment with photolysis resulted in 9% CR and 46% COD reduction, 42% CR and 60% COD reduction by photocatalysis, and 62% CR and 85% COD reduction by heterogeneous photocatalysis with the system TiO₂/Ru_xSe_y (Fig. 4). With this treatment the bacterial and fungal populations also decreased by 5 logarithmic units with respect to the biological treatment alone (Fig. 5). The total sequential treatment resulted in a 92% CR (from 5800 UC), 97% COD reduction (from 59 g l^-1) and 99% chlorophenol removal at 96 h and 20 min.