Hidrológiai Közlöny 1971 (51. évfolyam)

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

40 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. extended and flocs were made to grow to greater size. For this latter purpose auxiliary coagulants, namely poly-acrylamide, earboxy-methyl-cellulose, sodium alginate and activated silicic acid have been tested in both laboratory and model experiments. In the experiments performed at the Research Institute for Water Resources Development both carboxy-methyl-cellulose and sodium alginate failed to yield the desired results. Activated silicic acid pro ved most effective, polyacrylamide was found effective at médium concentrations (50 to 100 mg/lit) only. At lower concentrations of suspended matter it was found to impair the quality of water, while at higher concentrations the results were no better than with the basic coagulant alone. It was alsó established that the flocculant must be added 0.5 —1.5 minutes after the addition and thorough mixing of the coagulant, i. e., at the beginning of the llocculation process. The experimentál results have been plotted on graphs, showing positively the relationships between the various treatment processes. Plánt scale experiments on the application of activated silica have alsó been conducted by M. Nvilassy. The particular plánt design permitted the parallel treatment of twice 20,000 cu.m per day. The arriving flow is divided already before the sand trap and can be treated separately. The two streams are combined again after clarifiers only. Parallel experiments have thus been conducted in identical equipment, but using different chemicals. The efficiency of clarification could be compared immediately. Experiments have been performed with water of 8 to 10 and 0.5 to 2 Centigrades temperature, i. e., at temperatures where the effect of clarification is generally known to be poorest. Alumínium sulphate alone was fed into one system, while alumínium sulphate and 3 to 6 g/cu.m activated silica was fed into the other. Activated siheie acid was added about 30 seconds after the introduction and mixing of alumínium sulphate. The results attained were favourable. The transparency of water treated with alumínium sulphate alone was 30 to 40 cm, which figure rose to 150 to 180 cm when activated silica was alsó added. The quality of treated water was similarly improved alsó as regards suspended solids, organic matter and alumínium ion content. Plant-scale experiments have alsó demonstrated the efficiency of clarification and subsequent filtering to be appreaciably improved by the addition of activated silica. The drawback of activated silica is that it must be produced at the site by a process that is laborious, calls for close laboratory supervision and plánt control. A further disadvantage is that it cannot be stored as a semi-product, i. e., without dilution after seasoning. The diluted, complete solution can be stored for 2 to 3 days, as it tends to form a gelatinous precipiate in the tanks and piping, which is difficult to remove. Successful experiments are under way for eliminating this drawback. Essentially the method consists in treating water glass in an H cycle on an ion exchanger, rather than with acid, or an acidic salt. The time of activation is thus reduced and storage for 1 to 2 weeks is made possible without involving the risk of gel formát ion. From practical experiences gained so far it seems safe to conclude that of all materials promoting clarification, the best results have been attained with activated silica. Of the different organic polymers health autliorities are reluctant to permit more than minute quantities for the treatment of drinking water, since most products are detrimental to humán health. For instance, more than 2000 such materials are produced in the United States, but of these only about 30 are allowed for the treatment of drinking water. Further research is of course required to make available a clarifying agent, which is capable of bonding practically all of the mainly organic substances present in surface water and of removing it together with the precipitate. In this respect the micro-pollutants, such as pesticides, oils, etc., would be of interest. The problems associated with pretreatment and the preparation of chemicals are deseribed by G. Nagy, who listed the contemporary items of equipment, pointing out the conditions and limitations to their application. Practical hints are alsó given for the use of chemicals and the conditions for their applications. The reporter is in full agreement with the statement that the prerequisite for an adequate control over the variety of equipment needed for the preparation and application of chemicals and thus for the production of good quality water is that a technological laboratory and adequately trained personell should be available at the water-works. The primary funetion thereof is to adjust the treatment process to any change in the quality of raw water and to be prepared adequately for effecting the necessary measures. This requirement is basically correct, although in Hungary continued efforts are necessary to train and edueate such personell. This personell should be available already at the inauguration of new waterworks and training opportunity should be offered to them at similar plants before an investment is actually realized. The settling of suspended solids and relevant phenomena are dealt with in the paper "The zeta potential and its adjustment" by A. G. Curev. The Brownian movement of colloidal particles in surface water cannot be stopped within a short time, unless chemicals are added. The suspended particles usually carry a negative charge. According to his experiments, in surface waters the electro-negative zeta-potential between the colloids ranges from 15 to 30 mV. The agglomeration of colloidal particles is prevented by this electric repulsive force. Agglomeration and settling of the colloids can be attained by reducing the zetapotential to zero, or to about ±5 mV. The experimentál results obtained by the author are in full agreement with the generally accepted view that the removal of colloidal matter with the help of