Tetrachlorobiphenyl removal from sludge matrix using mixed crystal Ti0.97Fe0.02Ni0.01O2 thin film

Abstract

In this study, 2,2',5,5'-tetrachlorobiphenyl removal from activated sludge matrix using thin film (TF)-based photocatalytic (PCT-TF+UVC+H2O2) and UVC+H2O2 (photolytic) treatment systems were investigated for three different initial sludge pH(i) values of 3.0 +/- 0.1; 7.3 +/- 0.1 and 10.0 +/- 0.1. A novel, visible light active Ti:Fe:Ni nano composite TF was successfully synthesized and used as catalyst. The fabricated TF was characterized by SEM, TEM, XRD, XPS and UV-vis spectroscopy methods. Experimental results indicated that while raw industrial sludge contains only 2,2',5,5''-tetrachlorobiphenyl, treated sludge samples contained more chlorinated PCB congeners in descending chlorination order from 2,2',3,3',4,4',5,5',6,6' decachlorobiphenyl to 2,3',4,4',5 pentachlorobiphenyl. Experimental results also indicated that 2,2',5,5'-tetrachlorobiphenyl was removed from the sludge matrix by only TF-based PCT that was carried out at neutral pH(i). In addition, UVC+H2O2 system caused significant PCB formation at all studied pH levels. PCB generation/degradation reactions followed pseudo-first order reaction kinetics. Obtained results also proposed that UV irradiation can induce C-Cl bond cleavage in chlorinated compounds yielding Cl-center dot radicals, responsible for further chlorination. The k(obs) value observed in 2,2',5,5'-tetrachlorobiphenyl degradation by TF-based PCT at pH(i) = 7.3 +/- 0.1 was 0.0169 +/- 10(-3) min(-1) and 1.5 times higher than at pH(i)=3.0 +/- 0.1. The observed k(obs) values in TF based PCT for PCB generation at pH(i)=3.0 +/- 0.1 and pH(i)=10.0 +/- 0.1 were 0.0037 +/- 10(-3) and 0.0015 +/- 10(-3) min(-1), respectively. (C) 2015 Elsevier B.V. All rights reserved.