Introduction: Titanium dioxide nanoparticles (TiO 2 NPs) are commonly used in industry (e.g. cosmetics, sunscreens, food products, paints and drugs). But, they have different adverse cellular effects including oxidative stress and cellular damage. Aim of the work: To evaluate the possible toxic effect of titanium dioxide nanoparticles on the structure of the spleen of rats. Materials and Methods: Forty-five adult male rats were divided into three groups. Group I served as the control group. Group II (low-dose group) rats were given oral dose of TiO 2 (600 mg/kg/day) daily for 8 weeks. Group III (high-dose group) rats were given a daily oral dose of TiO 2 (1200 mg/kg/day) for 8 weeks. Spleen specimens were taken after 4 weeks, 8 weeks and 12 weeks from the start of the experiment. Thereafter, spleen specimens were processed for histological and immunohistochemical examinations. Results: The low-dose group showed slight disturbance in architecture of white pulp, slight congestion in red pulp and significant increase (P< 0.01) in CD4 and CD68 immuno-expression only after 8 week specimens compared with control group. The high-dose group showed marked disturbance in architecture of white pulp and significant increase (P< 0.01) in CD4 and CD68 immuno-expression after 4 week specimens, CD4 and CD68 immuno-expression significantly decreased (P< 0.01) in the 8 and in the 12 week specimens. No obvious improvement occurred after 12 weeks (withdrawal specimens). Conclusion: Prolonged exposure to daily high oral dose of TiO 2 NPs has deleterious and toxic effects on the spleen of rat, besides disruption of its structure.

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Hydrogen sulfide (H2S) is one of the main contaminants found in biogas which is one of the end products of the anaerobic biodegradation of proteins and other sulfur-containing compounds in solid waste. The presence of H2S is one of the factors limiting the valorization of biogas. To valorize biogas, H2S and other contaminants must be removed.This study evaluated the performance of a pilot-scale biotrickling filter system on H2S removal from landfill biogas. The biotrickling filter system, which was packed with stainless-steel pall rings and inoculated with an H2S-oxidizing consortium, was designed to process 1 to 10 SCFM of biogas and used to determine the removal efficiency of a high concentration of hydrogen sulfide from landfill biogas. The biofiltration system consisted of two biotrickling filters connected in series. Results indicate that the biofiltration system reduced H2S concentration by 94% to 97% without reduction of the methane concentration in the outlet biogas. The inlet concentration of hydrogen sulfide, supplied to the two-phase bioreactor, was in the range of 900 to 1500 ppmv. The hydraulic retention times (HRT) of the two biotrickling filters were 3.9 and 0.9 min, respectively. Approximately 50 ppmv of H2S gas was detected in the outlet gas. The maximum elimination capacity of the biotrickling filter system was found to be 272 g H2S.m -3 .h -1 . During the biological process, the performance of biotrickling filter was not affected when the pH of the recirculated liquid decreased to 2-3. The overall performance of the biotrickling filter system was described using a modified Michaelis-Menten equation, and the Ks and Vm values for the biosystem were 34.7 ppmv and 200 mg H2S/L.h -1 , respectively.