Variations in sludge organic composition and dewatering behaviors through visible light driven photocatalysis: In-situ O2 generation

Abstract In this research, carbon and nitrogen doped TiO 2 nano-particles were successfully synthesized and immobilized onto inner surface of a tubular thin film reactor (TTFR). CO 3 -N x O y -TiO 2 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 CO 3 -N x O y -TiO 2 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, H 2 O 2 , 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 H 2 O 2 and OCl mixing dosage for photocatalytic and photolytic experiments was determined to be 0.02 g H 2 O 2  g −1 DS and 4 × 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.