Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Valló Sándor: Összefüggés a felszíni vizek minősége és a hidrológiai viszonyok között

Special Conference Number, Szebellédy, L. Hidrológiai Közlöny 1971. 1. sz. 13 deficiency the maximum permissible wastes load can be determined in terms of the full biochemical oxygen demand. Owing to the factors neglected the method was mucii criticised, different authors suggesting different methods for taking these factors into consideration. A procedure for the highest permissible wastes-load concentration has been developed at V1TUKI. The modified mathematical model for the oxygen line has been simplified and thus the actually permissible wastes load can be determined in g/sec units from the dissolved oxygen content. Aside from the above method the permissible wastes load can be estimated directly, based on the BOD

5 or oxygen consumption. However, water quality is controlled besides oxygen conditions, alsó by other components. The relationship between streamflow and water quality can be formulated mathematically as: T = C-Q = nQ + b+cQ(Q - Qj),' where T and C are particular components of load and water quality, respectively, while Q is a given streamflow rate. Accordingly, for a given rate of streamflow, the pollution load due to a particular component of quality is composed of three terms: 1. the base load proportionate to streamflow {a-Q), 2. the load independent of streamflow (b), 3. highwater load, proportionate to streamflow or more correctly to change in streamflow rate, and reflecting the influence of pollution washed from the flood plain. III. Measures for improving the quality of surface waters Control of gradually increasing pollution in watercourses is relegated principaliy into the domain of the science of wastes treatment technology. The methods reviewed in the preceding section yield positive information on the permissible load in recipients, the necessarv treatment efficiency of plants, and by considering the combined influence of several wastes discharges, even the aggregate optimum efficiency of several treatment plants. However, the technological aspects of watersupply call not only for forecasts on quality of raw water based on hydrological conditions in the broader sense, or for ensuring an acceptable water quality by proper wastes treatment. The effectiveness of water treatment and last but not least, the minimization of investment and operating costs make it imperative to have optimum quality of raw water obtained from surface diversions. This requirement is especially pronounced in standing waters (natural and artificial lakes) where individual components of water of given quality are adversely influenced by natural factors, resulting in grave difficulties during water treatment. It is for this reason that paramount importance should be attributed to the measures, aiming at a) improving the oxygen supply to surface waters, b) controlling eutrophication, c) preventing thermal stratification, d) the optimum design of intakes for obtaining raw water of the optimum possible quality. a) The most important of the factors positively influencing oxygen household is the oxygen uptake across the watersurface. The principles of aeration, somé interesting designs and operational experience gained on the Ruhr river are deseribed in the paper submitted by H. W. Koenig, K. fi. Imhoff and D. Albrecht. The aeration methods can be classified into two broad groups, namely 1. aeration by gravity, and 2. aeration by mechanical means. Aeration by gravity is not a növel method on rivers. Considerable improvement in quality has been observed downstream of steep sections, rapids or weirs built for purposes other than air entrainment. This method of aeration has become more regular lately by the construction of cascades, mainly on highly polluted watercourses. Diagrams are given in the paper for dimensioning cascades with due allowance for water-quality and hydrological conditions. The methods of mechanical aeration have been developed essentially after the technology of wastes treatment (introduction of air under pressure, surface aeration by vertical-shaft impellers). Intensive aeration has recently been accomplished by the turbines of power stations. Experiences gained on the Ruhr river are of considerable interest. From the river receiving a wastes load corresponding to 4 millión population equivalent, 1.7 miihon cu.m are used on daily average for communal- and industrial watersupply. One of the most important projects in the system consisting of waterworks, treatment plants and weirs is the Baldeney hydroelectric station. Aeration equipment had to be provided in the backwater reach to control sudden oxygen deficiency caused by alga decay. Of the three turbines in the power station twexare of 75, one of 15 cu.m/ sec discharging capacity. Air has been introduced under a pressure of 0.4 kp/sq.cm at the rate of 3500 cu.m/hour. As a consequence of aeration, the discharging capacity of the turbine dropped to 14 cu.m/sec. Taking into consideration alsó the power loss in the station, 178 kg/hour dissolved oxygen could be introduced into the flow of 14 cu.m/sec at the cost of 126 kW power, corresponding to 1.41 kg 0

2/kWh. These values apply to water of 20 °C and 50 percent average oxygen deficiency between liaedwater and tailwater. At an other aeration system using the turbines at the Pixley Dam (US), air was introduced by atmospheric overpressure under the turbine runner, through suction pipes. Under conditions identical with those at the Baldeney Dam, the energy consumption was 0.45 kg 0

2/kWh. Two other methods of aeration have alsó been used in the Baldeney reservoir; on one location flexible plastic hoses have been placed on the bot-