Colloidal silica removal in coagulation processes for wastewater reuse in a high-tech industrial park.

Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes.     

Radiographisch-densitometrische Holzeigenschaftsuntersuchungen an Douglasien aus unterschiedlich durchforsteten Versuchsflächen

From two experimental areas with different thinning grades of a mixed stand of Douglas-fir and spruce, increment cores were taken from 40 Douglas-fir trees, chosen at random in a height of 1.3 m. The properties ring width, latewood percentage, average density, maximum and minimum density were examined from one part of the material by the x-ray densitometric method. The oven-dry density of the remaining part of increment core was examined for additional control. Based on the existing sample data, a significantly higher ovendry density was determined in the untreated area of higher stand density (376 stems/acre) than for the thinned stand (214 stems/acre). The specific gravity (at 10% moisture content) determined by x-ray densitograms shows no statistically valid difference on the average. The possible factors for this result are still being discussed. Further investigations of interactions between individual properties of the Douglas-fir samples obtained by the x-ray densitometric method are being carried out by multiple linear regression analysis.     

Hydrogen peroxide: Control of its content in water objects

A brief review of existing methods designed to determine hydrogen peroxide in aqueous media has been presented. Particular attention has been given to biosensor devices enabling us to exercise simple and express control of concentration of the specified compound.     

High-temperature sensible-heat storage options

Alkali-metal carbonate salts meet the requirements for high-temperature solar central receiver systems, but because of their corrosiveness they present special problems in the design of storage tanks. In order to reduce corrosion and temperature sufficiently to retain strength in the storage containing wall, internal and thermal insulation is required. We present design options and operation criteria for sensible-heat, molten-salt storage with internal insulation.     

From practical methods to theoretical foundations

The year 2006 marks the ninetieth anniversary of the air navigation (later called navigation) service of the Air Forces of this country. The history of air navigation is investigated, and an opinion about its modern state and directions of further development is presented.