Vízügyi Közlemények, 2003 (85. évfolyam)
1. füzet - Somlyódy László: Az értől az óceánig - a víz: a jövő kihívása
Az értől az óceánig — a viz: a jövő kihívása 93 water shortage, drought and floods. Consequently one must manage the resources of water, an activity which has been successfully performed since several centuries by the Hungarian water professionals. Life in natural waters is of highly diverse type: For example in frcshwaters several ten thousands of plant and animal species arc found. Among these the smallest ones bacteria, downward-most along the food-chain, and algae (suspended microscopic plants) are of micron size. (Viruses, things of hardly larger size than the water molecule and causing much trouble, are not living thins, and therefore they arc difficult to detcct). Algae can also be of the size of several hundred microns: their size cover two-, while their volume 4-5 orders of magnitude. The largest specimen of the freshwater food-web are the fish, that can grow to several meters length. In course of the biological production the matter cycles continuously (affected also by pollution) via the producers and the decomposers of the aquatic life. In this cycling the various substances arc also spatially trans-located and may interact with each other, the sediment, the soil and with the atmosphere. The multiple physical, chemical and biological processes, which vary in time and space, affect the state of the quality of water and the biogeochemical cycling of matter. Waste waters differ substantially from natural waters, due to their chemical and biological properties and to the species-poor life of them. They frequently contain pathogens. Waste water is a "spent medium" regarding industrial, communal and agricultural water use objectives. They contain various inorganic and organic polluting substances and plant nutrients in a condensed way, at high concentrations. Every substance which was used by the society will sooner or later appear in these waste waters (Figure I). The impact of waste waters, when discharged into natural waters, may be of varying types: For example: too low or too high concentrations of elements, substances and compounds; the modification of the chemical and physical environment; the distortion of the biological cycling and thus the ecosystem; domination of certain life forms and thus the decrease of biodiversity; toxicity; health-deteriorating effects and so on (these may appear simultaneously and in interacting manner). All these hinder, make very expensive, or even eliminate the use of waters and may result in serious damages even on the long term (Figures 2—3). Presently almost all large European rivers show the signs of eutrophication. The internal seas, the Baltic and Black seas, are also suffering from this impact (Figure 4). We face two problems: a) The largest part of the pollution load, casing this problem, stem from the agriculture and is of non-point source character; b) Investigations indicated that unlike in freshwater lakes, here the limiting factor is not the phosphorus but the nitrogen or the two together. Therefore there is a need for removing nitrogen from waste waters. The solution was found, more than two decades ago, in biological denitrification (the principle was know already in the 19 l h Century). The need for the protection of the internal seas and the successful technological development resulted in the sewage treatment directive of the EU. For the so called sensitive areas this directive requests, from the waste water treatment of large cities, the simultaneous removal of compounds containing C, N, and P. In Hungary the cost-requirements corresponding to the compliance with this directive amounts to 1000 billion HUF (including the respective sewerage). A substantial part of global worries are connected to the increase of the population and to the decrease of the specific, per capita, resources. The growth is exponential: by the end of the 21 s 1 Century the population of our planet will exceed 10 billion. Presently about 4—6% of the population is facing problems that stem from physically insufficient amount of water, but another 20% has no access to safe drinking water, due to economic reasons, mainly in the Near-East and in Africa. Since population growth is also concentrated in the Asian and African
