Variations in sludge organic composition and dewatering behaviors through visible light driven photocatalysis: In-situ O-2 generation

Abstract

In this research, carbon and nitrogen doped TiO2 nano-particles were successfully synthesized and immobilized onto inner surface of a tubular thin film reactor (TTFR). CO3-NxOy-TiO2 nano-composite thin films (NCTF(s)) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Characterization results indicated that the CO3-NxOy-TiO2 NCTF has a broad adsorption edge in the visible light region. Decorated TTFR was used to observe the impacts of visible light irradiation on sludge dewatering characteristics and organic structure. In the experiments, H2O2, NaOCl and their various gravimetric combinations were added to the sludge as electron acceptor combination (EAC). Obtained experimental results revealed a photocatalytic synergy between hydrogen peroxide and chlorite molecules. The optimum H2O2 and OCl mixing dosage for photocatalytic and photolytic experiments was determined to be 0.02 g H2O2 g(-1) DS and 4 x 10(-3) g(-1) NaOCl g(-1) DS, respectively. The pseudo-first order kinetic constants (k(obs)) for volatile solids (VS) removal observed in EAC(3) (with NCTF), EAC(2) (with NCTF) and photolysis were 0.140 min(-1), 0.045 min(-1) and 0.025 min(-1), respectively. The average VS removal rate depending on the applied unit photonic power to unit TTFR area was 218 +/- 14 mgVS(removed) W-1 h(-1) cm(-2). Experimental results obtained using different EAC(s) dosage schemes revealed that O-2 was the main active specie and HO radicals also contributed to sludge treatment. Naphthalene, pyrene, anthracene and phenanthrene were detected in raw sludge and removed 87 +/- 1% by the method.