H2O2/UV-C treatment of textile preparation wastewater: kinetic investigation on alternative combinations of commercial textile preparation auxiliaries

Abstract

Four different textile preparation effluents were simulated to examine the applicability of the hydrogen peroxide/ultraviolet-C (H2O2/UV-C ) advanced oxidation process for the treatment of real textile preparation (desizing, scouring and bleaching) wastewater bearing the non-ionic surfactant nonyl phenol decaethoxylate (NP-10). In the absence of any textile preparation chemical, NP-10 degradation was complete in 15 min (rate coefficient: 0.22 min−1) accompanied by 78% chemical oxygen demand (COD) (rate coefficient: 0.026 min−1) and 57% total organic carbon (TOC) (rate coefficient: 0.014 min−1) removals achieved after 60 min photochemical treatment. H2O2 consumption rates were not significantly affected by the introduction of carbonate and chloride ions (average rate coefficient: 0.032 min−1) at pH values<11.5, above which H2O2 dissociation to its conjugate base became pronounced. The organic, phosphonate-based sequestering agents competed with NP-10 for UV-C light absorption and HO• radicals. H2O2/UV-C oxidation of the simulated textile preparation effluent containing 3.0 g L−1 Cl−, 1.5 g L−1 NaOH and 1.0 g L−1 diethylenetriamine pentamethylene phosphonic acid (DTPMP) resulted in the worst treatment performance due to its high pH and organic carbon content. For this textile preparation effluent, NP-10 abatement was complete in 100 min (rate coefficient: 0.018 min−1), while COD and TOC removals dropped down to only 16% and 8%, respectively, achieved after 60 min treatment. The highest H2O2/UV-C oxidation efficiency resulting in 34% COD and 28% TOC removals was obtained for the simulated textile preparation effluent comprising of 3.0 g L−1 Cl−, 1.5 g L−1 NaOH and 1.0 g L−1 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). For this textile preparation effluent, NP-10 degradation was complete after 50 min (rate coefficient: 0.061 min−1) exposure to H2O2/UV-C treatment.