Effects of suspension dispersity and concentration on its flocculation efficiency in static and dynamic flocculators

Flocculation presents one of the most effective methods for enhancing separation of both anthropogenic and natural suspensions by sedimentation, filtration and flotation techniques.The flocculation effectiveness much depends on the medium shear rate in a flocculator. The objective of this research comprises the study how the suspension dispersity and concentration effect the efficiency of its flocculation in a static tubular flocculator and in a dynamic Couette flocculator. The studies used aqueous suspensions of ultra-fine calcium carbonate (<7 μm) and fine silica (<90 μm) as objects. It was established that treatment of ultra-fine calcium carbonate suspension in a static flocculator produced in the range 400-450 s-1 a pronounced primary maximum in the dependence "flocculation efficiency/shear rate". The increase of the suspension concentration to 70 g/l and above resulted in a small secondary maximum of the flocculation efficiency in the region of around 950 s-1. This can be due to a higher dissolution rate of flocculant and a corresponding increase of particles adhesion forces in flocs, which counteract viscous forces destroying them. In silicon dioxide suspension treatment, the primary and secondary peaks occur at both small and high suspension concentrations, but in a latter case, they are by far more pronounced and comparable in magnitude.

TITANIUM DIOXIDE SUSPENSION PHOTOCATALYSIS IN A TUBULAR PHOTOREACTOR AND TITANIUM DIOXIDE REUSE ON THE REMOVAL OF PHENOL

We studied flow rate, electrolytes effects, titanium dioxide separation and reuse and sunlight application on photocatalysis in a tubular photoreactor integrated with the titanium dioxide separation/reuse. The circulative flow treatment was preferred over the single pass treatment. Phenol and TOC removals in tap and deionized waters were a maximum at the circulative flow rate of 600 ml min-1 and the transmittance of 0.26%. At low flow rate, titanium dioxide particles were sedimented in tap water, but those were perfectly suspended in deionized water. The titanium dioxide slurry was sedimented spontaneously by standing and was repeatedly reused without decreasing the degradation efficiency. Keywords : Photocatalytic, Optimum flow, Electrolytes, Separation, Solra

PHOTOCATALYTIC REMOVAL OF TR I- AND HEXA-VALENT CHROMIUM IONS FROM CHROME-ELECTROPL ATING WASTEWATER

A novel technique based on photocatalysis was applied to eliminate chromium ions, a toxic hazardous environmental pollutant. The photoreduction of each species of chromium (total, hexavalent, and trivalent chromiums) from chrome-electroplating wastewater was investigated using a titanium dioxide suspension under irradiation by a low-pressure mercury lamp. The initial concentration of total chromium was 300 mg/l. The applied conditions were the direct photocatalytic reduction process at pH 3.65 and the indirect photocatalytic reduction with added hole scavengers at the same solution pH. Results from both processes were comparatively discussed. Result show that chromium was not efficiently removed by direct photoreduction. In contrast, with the adding of hole scavengers, which were formate ions, the photoreduction of chromium was very favorable. Both hexavalent and trivalent chromiums were efficiently removed. The photocatalytic mechanism is purposed in this study.

Research on the Ultra-Fine Titanium Dioxide Suspension Stability and Fractal

Using scanning electron microscope, the microscopic pictures of the surface on sediment have been obtained from the sub-micron titanium dioxide suspensions without dispersant or adding different types of dispersants. Deposits of titanium dioxide suspension have been observed and the mechanism of the dispersant has been analyzed. Meanwhile, deposits of titanium dioxide gray distribution figure have been gained by self-compiled Matlab program, which proved that the surface sediments is fractal, and the fractal dimension has been calculated under different conditions. The rules between suspension stability and fractal dimension have been achieved.