Investigation of the flocculating activity of oyster shell powders on Microcystis aeruginosa with varying particle size and mechanical conditions.

Harmful algal blooms have been a serious environmental problem. The flocculation of Microcystis aeruginosa by oyster shell powders prepared by aerobic calcination (CO), anaerobic calcination (CN), acidification anaerobic calcination (CAN), and deacetylation anaerobic calcination (CHN) was studied. The CO800 (100 mesh) and CN800 (160 mesh) presented the highest flocculation rate of 89.46% and 77.39% when they were stirred for 1 min with speed of 750 r/min and 250 r/min, respectively. The photosynthesis and viability of the algae cells flocculated by CO800 with particle size of 100 mesh were not significantly damaged. The phosphorus nutrient could be removed by CO800 and CN800 effectively due to the presence of Ca2+, which also limited Microcystis aeruginosa growth. The study showed that the processing of oyster shell powder could be used as an effective flocculating material.

Photocatalyst-coated carbon microtube electrodes: Preparation and characterization of their properties and photocatalytic degradation of methylene blue.

Photocatalysis is a potential technology for removing pollutants from water. As the recombination of the photogenerated electron-hole pairs can hinder the photocatalytic efficiency in the treatment of wastewater, the surface of the carrier is usually coated with a semiconductor. In this study, carbon microtube electrode prepared from corncob was coated with either titanium oxide (TiO2) or bismuth phosphate (BiPO4) and then used as a photocatalyst (C-TiO2 or C-BiPO4) to investigate the photodegradation of methylene blue (MB). The two photocatalysts, C-TiO2 and C-BiPO4, were characterized by phase determination, microstructure observation, water contact angle measurement, and base site analysis. The influences of reaction time, stability, MB concentration, initial pH, and OH radicals quenching on the degradation of MB were also evaluated. The degradation of MB by C-TiO2 and C-BiPO4 was mainly dominated by OH radical oxidation. The carbon microtube increased both the mass transfer rate and the photogenerated electron-hole pairs separation rate, thereby increasing the photocatalysis of both C-TiO2 and C-BiPO4 as revealed by an increase in the rate of MB degradation. The rate constants obtained for the degradation of MB by C-TiO2 and C-BiPO4 at 20 °C were 9.739 × 10-7 mM min-1 and 1.111 × 10-7 mM min-1, respectively. The coating of TiO2 and BiPO4 on the surface of the carbon microtube electrode enhanced their photocatalytic performance, and therefore, C-TiO2 and C-BiPO4 could be developed into a novel material to be used in the photodegradation of dye pollutants.