Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Abos Bruno: A talajvízdúsítás vízminőségi problémái

28 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. quality of water to be recharged is deteriorated in Hungary. The hot summers and relatively long duration of sunshine are beneficial to the rapid prolifieation of living organisms in water pumped from rivers and lakes. In England, on the other hand, where the climate is much less favourable, the quality of surface water to undergo slow filtration can certainly be improved. In their paper, Pusztai, Bérezik and Mrs. Végh (I) consider the favourable biological conditions due to meteorological factors in Hungary, and the related causes hindering filtration. Research results achieved with recharging Danube-water are deseribed. The processes are likely to occur wherever groundwater is recharged with the water of any major Hungárián river. Their conclusions regarding preliminary settling with a long dwelling time are striking. In favourable weather the decrease in inorganic, suspended matter is accompanied by an increase of organic (living) substances. Extensive experiments liave shown the organic matter to be mainly responsible for the rapid clogging of the upper layer of filter surfaces. The influence of inorganic suspended matter on the rate of infiltration is much smaller. In agreement with other authors they conclude that the efficiency of slow filtration groundwater recharging is difficult to improve without complex studies requiring further experiments. The application of the two desiccation methods suggested by the authors, is, however, questionable. The gravel bed will probably extend the periods, during which a good efficiency can be achieved in recharging. At the same time it will make seraping the filter bed more difficult as the gravel will have to be removed from the desiccating basin, whashed, and then replaced. This additional work will increase the operating costs of recharging, which the water-works will. be unwilling to accept. Recharging by inverted wells is alsó impossible in waters containing many living organisms, due to the small filter surface of the wells. This was proved both abroad and in Hungary. The living creatures clog the well filters in 1 or 2 days. Neitlier the preliminary settling of surface water, as suggested by the authors, is likely to be succesful. Settling was found to decrease the living organism content of water by 90%. At the same time, the secondary coagulation of the clarifier alsó acts adversely. The hydroxide-residue is precipitated in the well filters, elosing the pores of the filter layer, as in the case of rapid filters. The above statements are essentially confirmed by the paper of Schiefner (2). In October, 1964, when the number of planctons in the water of the Bodva river was 33 million/litre, the number of organisms in the recharging basin grew to the 100 millión order. In one basin even 400 million/litre were observed. A major problem of groundwater recharging in the vicinity of wells is alsó pointed out in the paper. In closed-basin artificial slow filtration the prefiltrate can always be wasted as long as the quality of filtered water is objectionable. In groundwater recharging in the vicinity of wells, the water produced is usually needed in the system. The waterworks are consequently compelled to feed the objectionable water into the distribution network even in the initial stages of recharging, which may last for a few days, but may attain as much as one, or two months. This problem can be solved only at high capacity waterworks, where individual groups of wells can be excluded from produetion and their yield can be wasted after groundwater recharging has been started. The paper by Gefferth—Préssler (3) is devoted to eutrophication processes in presettling- and recharging basins. It is confirmed that the prolifieation of organic life, the blooming of zoo- and phytoplancton is mainly responsible for clogging the path of filtration. The main subjects of the paper are the biological, chemical and physical processes occurring in natural waters and deseribed by many. The objective is to prevent eutrophication by clearing the fundamental relationships involved. Unfortunately, no method is indicated by which the prolifieation of organic life could be impeded. The mechanism of slow filtration and the experiences gained with the groundwater recharging system at Borsodszirák are compared in the paper by Á. Fázold (6). Certain theories concerning slow filtration and the results of practical experiments imply that the purification process ensuing in the course of filtration cannot be deseribed by any single theory. The alternatives of theories proposed by different authors must be combined and environmental factors taken into consideration to arrive at the mechanism of slow filtration. This conclusion appears to be correct, although slow filtration is believed to be influenced by many factors not fullv understood yet, as regards both biology and physico-chemistry. The changes in water quality attainable with groundwater recharging from basins along wells are considered in the paper by L. Hegyessy [5]. Hard water of high iron content was pumped at Nagybátonv from the Zagyva river to recharge groundwater. Before this operation was started the wells yielded very hard water, containing ironmanganese and aggressive carbonic acid. Favourable changes in the quality of water produced from the wells were observed, in that hardness decreased, iron, manganese and aggressive carbon dioxidé increased slightlv together with pH. This favourable experience is believed to be of considerable interest for the future applications of groundwater recharging. Under particular conditions waters high in iron and manganese can be used without filtration, if the water flowing in the soil is mixed and improved with surface water recharged into the ground along the wells. The improving effect on quality of groundwater recharging must be considered under two aspects — according to E. Paris [9] — since the quality of both surface and groundwater in improved thereby. Surface water is purified by slow filtration, while the quality of groundwater is improved by the infiltrating surface water. The improve-