Hidrológiai Közlöny 1971 (51. évfolyam)

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

Hidrológiai Közlöny 1971. 1. sz. 37 Contemporary methods and materials in the treatment of surface watqrs By VARRÓ, ISTVÁN Department Head (Enterprise tor Soil ICxploration and Surveying, Budapest) The demand for water of drinking quality increases from day to day all over the World. This phenomenon can be traced back to particular positive and negatíve causes. Among the positive causes the growth of population and the rising standard of living are to be mentioned, whereas the careless waste of water and technical defects such as leakage in the network etc., are the most important negatíve factors. Bv eliminating these latter or at least by a considerable reduction of them the per capita water consumption would be appreciably lower. The supply of drinking water of the required volume and quality is restricted by the increasing pollution of the main water sources, that is surface water, by effluents of industrial, domestic, agricultural and other origin. The only effective measure of prevention in this respect is strict legislation in each country for pollution control. In recognition of this fact international co-operation has been established in the field of science, technology and water management for conserving the purity of surface waters. Hungary was among the first to promulgate such legislation and to strictly enforce the relevant provisions. It will most probably take a long time until these measures will eventually prove entirely successful and we, waterworks operators must undertake continuous efforts toward producing the required volumes of good-quality drinking water. One of the fundamental operations in water supply consists of the treatment of water. Reference is made here not only to the sanitary but alsó to the technological consequences of treatment (deposits in the pipeline, corrosion phenomena, etc.). Allowance should be made for these in the design stage already. Before any treatment technology is adopted for surface waters, experiments should be performed on laboratory- and pilot plánt scale. Any planning should be based on the results obtained. This apparent excess cost will be offset amply during subsequent operation. Prompted by the deterioration of water quality, the complex problem of surface water treatment is receiving attention alsó in Hungary. Somé advance is believed to have been achieved in the technology of treatment during the past decade. These he mainly in the field of new flocculants and in the introduction of new filtration methods, but the combined application of several filter materials may alsó be mentioned here. It should be noted, however, that the problem of micro-pollutants was not as severe as it is now, that is the watercourses were not polluted to this extent by oil, phenoles, detergents, pesticides and other chemicals. No successful attempt could be undertaken towards the removal of these substances until suitable and reliable analytical methods had been developed for their chemical determination. Investigations into these problems are still being continued. The main (lifference between the treatment technologies applied to surface waters in Hungary and abroad consist essentially in the greater popularity abroad of alumínium and iron compounds aceompained by the more widespread use of auxiliary eoagulants. Few remarks on auxiliary eoagulants are deemed necessary in this eontext. These substances will dissociate in aqueous solutions and consequently the anionic ones carry a r.egative, while the cationic ones a positive charge. Anionic flocculants are used mostly in combination with inorganic flocculants only. Cationio flocculants may be used alone. Non-ionic flocculants do not carry an eleetric charge and are used alone or together with their minerals. According to Prof. Mints (Congress IWSA, 1969) flocculants are mostly effective if their quantity is in a certain proportion with the quantity of colloidal particles. The difficulties resulting therefrom should alsó be mentioned here, these include the neeessity for the constant supervision of suspended matter and accurate dosage. As demonstrated by the experiments in Hungary, deseribed in the paper by L. Bulkai and Z. Körösi (VITUKI), auxiliary eoagulants can be applied between certain limit values of suspended matter-concentration. In Hungary activated silica is prefered as auxiliary coagulant and with good results. This is in agreement with (he conclusion by Chojnaki, deseribed in Fortschritt Wasserchemie, 1968. Good results have been reported in No. 10, 1968 of the "Journal American Water Works Association" by Pittmar and Wells on the application of activated silica for filter conditioning. Alsó, favourable experiences have been deseribed by Kulszkij in No. 9, 1968 of Vodosznabzsenije i Szanitarnaja Technika, gained with the use of activated silica for adjusting the operation of filters. Another difference in comparison with domestic technology is the necessity of applying coinplementary treatment by ozone and activated carbon to combat prevailing pollution conditions. By the combined applications of these two methods and of course the conventional ones, a treatment efficieney of round 98% can be attained concerning micro-pollutants. Considerations of eeonomics will decide whether or not the combined application of the two methods is necessary. This was the conclusion arrived at in report No. 2 submitted by Coutris and Gomella to the 1969 Congress of IWSA. Moreover it should be taken into considerat ion that preliminary treatment using activated carbon in volves a reduction in the chemical ozone demand of water. It should be noted further that conflicting opinion has been voiced in different countries concerning the sequence of ozone and activated carbon treatment. In this respect the quality of water is believed to be essential. Detailed investigations on this problem have not been concluded yet so that no positive relationships can be reported. The factors involved appear to be the fundamental quality of raw water, the content of organic and inorganic pollutants, micro-pollution and the relatíve proportions thereof. F. Meucci (Torino) is e. g. of the opinion that water treatment is facilitated by applying ozone first. This experience appears to be logical, since any ozone effect observed in the preliminary experiments may be due to any one of the following three phenomena. Under the influence of ozone water is either discoloured, it may become turbid, or the precipitation of colloids occurs in the form of micro-fioccules. These substances aro