Environmental letters最新文献

A method of predetermining drainage wind velocities is derived in the form of an incremental velocity model. The model requires the topographical data and a general description of surface roughness. Using these fixed inputs with the model yields velocity factors. Velocity factors are determined as a function of height above the terrain and elapsed time since the occurrence of the maximum surface temperature. The velocity factors multiplied by a cooling factor give velocities. Time or space mean velocity may be found by summation techniques. By computing velocity factors for several points within an area of concern, one can determine drainage flow patterns and pollutant movements for any given night.

This paper describes a modified procedure for the determination of nitrate in sediments and some natural water samples. In the Water Quality Branch Laboratories where large numbers of samples are regularly analysed, it was found that existing methods1,4 do not give precise and accurate results particularly when applied to sediment samples and some natural waters. The reasons for such inaccuracies have sebsequently been found and a method for removal of such interfering substances have been devised. The proposed method essentially consist of two steps. In the first step the interfering substances such as sulfide and humic acid substances are removed by precipitation with copper. The resultant solution is then analysed by a colorimetric approach utilizing cadmium fillings as the reducing agent to reduce nitrate to nitrite, and analyse the resultant nitrite with sulfanilamide, and naphtylene diamine. The smallest amount of nitrate that can be detected with certainty is approximately 10 mug-at N/Kg and 50 mug/ at N/Kg in water and sediments respectively. The figures for sediments are based on dissolving 20 gms. of sediment, dry weight, in 100 ml volume. The proposed method has been tested on a wide variety of natural water samples, sediments, clays and sands.

Geothermal steam at the world's five largest power plants contains from 0.15 to 30% noncondensable gases including CO(2), H(2)S, H(2), CH(4), N(2), H(3)BO(3), and NH(3). At four of the plants the gases are first separated from the steam and then discharged to the environment; at the fifth, the noncondensables exhaust directly to the atmosphere along with spent steam. Some CO(2) and sulfur emission rates rival those from fossil-fueled plants on a per megawatt-day basis. The ammonia and boron effluents can interfere with animal and plant life. The effects of sulfur (which emerges as H(2)S but may oxidize to SO(2)) on either ambient air quality or longterm human health are largely unknown. Most geothermal turbines are equipped with direct contact condensers which complicate emission control because they provide two or more pathways for the effluents to reach the environment. Use of direct contact condensers could permit efficient emission control if coupled to processes that produce saleable quantities of purified carbon dioxide and elemental sulfur.

Adsorption of tryptophan onto CaCO3 at constant ionic strength (0.05 M Nacl) and from dilute aqueous solution (10(-4) M to 10(-3) M tryptophan) is reported. Adsorption was primarily determined by the charge characteristics of both the adsorbate amino acid and adsorbent CaCO3. When both adsorbate and adsorbent are semicharged, tryptophan ions are expelled away from the CaCO3-solution interface. Tryptophan is only removed by CaCO3 in a narrow pH range, 6.0 greater than pH less than 8.5 within which CaCO3 has positive charges, and tryptophan is negatively charged. The pH of zero point of charge, pHzpc, of CaCO3 was also determined by alkalimetric tritration and coagulation techniques and a value of 9.50 +/- 0.5 was found. These preliminary finding demonstrate primarily that interfacial chemical reactions play an important role in the temporal and spatial transformation of dissolved organic matter in natural water systems.