Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Varró István: Felszíni vizek tisztításának korszerű módszerei és anyagai

Special Conference Number, Szebellédy, L. Hidrológiai Közlöny 1971. 1. sz. 39 Endrey. In this method air is introduced under pressure into the filter at the bottom, while water is sprinkled on the top of the sand so thatintrickling down between the particles it should have ample opportunity for contacting with the air. The oxidizing médium in this process is again air, but other, more powerful substances, such as ozone, chlorine oxidé and the mixtures thereof with air, may alsó be used. In practical reahzations efforts should be made to ensure an as large as possible a contact surface between the gaseous oxidizing agent, the water and the granular médium, the latter acting as the contact catalvst. The development of a coherent water film must be prevented by appropriately controlling the feed of air and water. After passage through the granular médium, the air is discharged into the atmosphere. Flushing of the filter can be omitted, since the oxidized ironand manganese compounds are adsorbed on the filter sand particles. Depending on the iron- and manganese content of water, replacement of the filter sand may become necessary only after several months, but sometimes after 1 to 2 years. The load of 0.3 to 0.4 kg iron/cu.m sand can be increased — as demonstrated by practical experience — to as high as 20 kg/cu.m. Practical experiences in plants using this method have shown the process to be successful. Promted by the favourablereports several treatment plants using this method are being built in Hungary. It is to be regretted that no economic analysis has been attached on this technically sound method so that no information is as vet available on the relatíve economics. Experimentál and theoretical results are quoted by Z. Novak in demonstrating that the ozone process is superior to conventional treatment technologies in removing iron- and manganese from groundwater. The advantages are claimed to be: 1. The chemical required, i. e., ozone, is produced at the site from air, consequcntly, no transportation, handling, storage are necessary. 2. The treatment process is aecelerated. 3. The acid content is reduced. 4. The quality and taste of water are improved. 5. Iron- and manganese compounds are oxidized together with hydrogen sulphide and nitrites. 6. Ozone-feed rates can be controlled without undue difficulties. The above statements appear to be correct, since ozone — owing to the considerable advantages attainable by its application — is likely to gain growing significance in water treatment technology. On the one hand, it is a highly effective oxidizing agent, and on the other, the observable parameters of water are greatly improved. This is mentioned alsó by L. Kolin, A. Pálhidy and I. Horváth in their paper to be deseribed subsequently. Investigations into the potential applications of ozone have been achieved. It should be noted, however, that water treatment with the help of ozone calls for high investment and operating costs, so that careful economic estimates are necessary before anv decision is adopted. Application cannot be justified, unless all of the conventional methods of iron- and manganese removal pro ve unsuccessful. Drum filters From the point of view of economics microstrainers of polyamide were found superior to such of stainless steel (they are eheaper by about 90 percent) for the mechanical filtering of surface water, as deseribed by W. Starke. Polyamide filters, however, need protection from sunshine, since the ensuing photochemical reaction tends to reduce the strength of the filter material. The strainers have meshes 35 to 50 microns wide, but meshes up to 140 microns may alsó be used. The mesh width applied depends on the suspended material and the quantity thereof, which it is desired to remove from water. Micro strainers may prove economical even in the case of water containing up to 150 to 300 mg/lit live organic matter in suspension. Drum filters with micro mesh strainers are considered applicable: 1. for waters of reservoirs and lakes containing plancton, 2. for river waters up to 150 to 300 mg/lit suspended matter, 3. for river waters containing 150 mg/lit detritus and a large quantity of plancton, but then a settling basin must be provided before the filter. About 2% of the filtered water are required for flushing the drum filters and the pressure needed is about 4 kp/sq.cm. Mechanical treatment of surface waters before clarification has been studied intensively in Hungary. Several types of open and closed (pressurized) drum filters have been developed by designers and contractors alike. These filters have meshes of minimum 0.3 mm width but are unsuited for microfiltration. Drum filters can be used effectively in the case of surface waters. Practically each major industrially developed country has accepted an originál type of drum filter, which can be used successfullv. Mechanical pre-treatment with appropriately selected drum filters may result in the following advantages: 1. micro sediment, givingoften rise to complaints can be removed from water, 2. using correctly selected mesh openings, the living suspended matter content of water can be reduced effectively and thus the technology of treatment may be simplified. Clarification In their paper on the clarification of cold waters L. Bulkai and Z. Körösi concluded that the rate of clarification is reduced on the one hand by the reduced rate of hydrolysis of metál ions, on the other, by the higher viscosity of water. To overcome these difficulties the mixer speed of the flocculator was increased, the time of residence