Hidrológiai Közlöny 1977 (57. évfolyam)

1. szám - Dr. Bora Gyula–Hock Béla–Mucsy György–Pintér János–Dr. Réczey Gusztáv–Röszler Károly: A Sajó vízminőségi műszaki-közgazdasági modellje

Dr. Bora Gyula és mlsai: A Sajó vízminőségi műszaki-közgazdasági modellje Hidrológiai Közlöny 1977. 1. sz. 37 The technico-economic model of water quality in the Sajó Rirer By dr. Bora, Gy.

—Hock, B.—Mucsy, Gy.

— Pintér, J.

—dr. Réczey, G. — Röszler, K. The Sajó Valley is one of the most congested industrial areas of Hungary including a number of industries (siderurgy, chemical industry, paper mills, sugar refineries), which produce largo effluent volumes, further urbanized settlements with communal sewage. The aim of the technico-economic model for the Sajó River is to control the quality of water in the river by meeting the technico-economic requirements simultaneously. The model is intended to provide the basic information needed for decision making on the construction of sewage treatment facilities. For formulating the model it was found necessary to clear a number of fundamental hydrological-, technical- and economic problems. The first problem was to decide what component to adopt as the basis for modelling the oxidizable substances. For characterizing pollution in the river which is the recipient of mainly industrial effluents the dissolved 0

2 content proved inadequate. Owing to the high level of toxic pollution of industrial origin the application of the BOD had to be discarded. For this reason the chemical oxygen demand COD, characterized by the diehromate oxygen consumption was adopted as the basis of modelling the oxidizable substances. The basic assumption underlying the model is that after the water in the recipient and the effluent are mixed, the decrease of the COD mass current in the direction of flow is proportionate to the existing COD (1). For combining the effects of recipient water and of the effluents to be discharged, the mass current values are expressed in terms of the streamflow rate in the recipient (4). For the mouth cross-sections of the tributaries of the Sajó River and of the effluent discharges mass balance equations have been written in terms of the COD mass current (Fig. 1, Eqs. (5)—(7)). The removal and assimilation conditions between two successive cross-sections are represented by transformation coefficients (8). The nine greatest streams in the catchment, representing 98 per cent of the COD mass current have been taken into consideration in formulating the model. The effluent discharges producing less than 30 cons COD mass current annually have been neglected, having 17 sources of effluents which produce 98.9 per eent of the annual mass current in the system (Fig. 2). The basic aim of the model is to optimize the costs of pollution control (construction and running costs) with allowance for the assimilation and decomposition processes in the recipient. Tn contrast to currentdomestie practice the model prescribes COD standards for the recipient, rather than for the effluent. For optimal results several treatment methods were required to be available for oach source of pollution with different construction- and operating cost implications. Thus several alternative technologies have been developed for the individual polluting sources (for all sources altogether 53) and the related costs have been computed. The final objective of the computations is the choice of a set of technologies from among the 53 alternatives related to the 17 sources of pollution, by which the set of limit values represented by the boundary conditions specified for the COD values can be realized at the minimal economic effort. The model indentifies thus discrete technologies according to the lowest investment costs, so that the criteria specified for the COD be satisfied for all effluent dischargesand tributary streams. In formulating the model allowance has been made for the fact that further industrial development is under way and urbanization will accelerate in the Sajó Valley. The year 1985 has been adopted as the time range of analysis. For this year estimates have been made by individual polluting sources on the perspective figures of water consumption and effluent discharge. As far as mathematics is concerned, the problem to be solved was one in discrete programming (Eqs. (15)—(18)). The method of solution is known to be more complicated than for the conventional linear programming problems, since the optimal solution of the discrete problem is found by solving a series of problems in linear programming. The data used in the model are classified into two groups

: a ) The technical data needed for writing the boundary conditions (Tables 1 to 6), or the boundary conditions proper (Tables 7 and 8). b

) The economic data needed for writing the target function (Table 2 ). Prior to optimization an examination has been made to see whether under the present initial condition (218 g COD/cu.m in the Czechoslovakian — Hungarian border cross-section) a solution can be found at all to the problem (Fig. 3 J. It was concluded that in the entrance cross-section the upstream neighbour must ensure at least 60 g COD/cu.m value in order that the problem of pollution control could be solved over the Hungarian section, under a realistic set of limit values. Investment strategies have been developed in the model for two main situations, depending on whether constraints are specified for the tributaries, or not. For the former sensitivity tests have also been performed by modifying the basic load by ±15 per cent. The corresponding investment requirements were thus found to be 816 and 961 million Ft (Table 12). The model departs in several respects from the current Hungarian specifications, since where "free capacity" was available in the recipient for additional COD mass currents, lower treatment efficiencies were considered "satisfactory" (which require evidently lower costs), while in other instances higher standards were specified. Both informations may be relevant to the state water administration. It should be noted in conclusion that owing to space limitations a rough outline of the project activities could only be presented in this paper. Some subjects had to be excluded from the description even in the abbreviated form, such as the optimal scheduling of project realization in the optimized solution, the checking of the optimized solution with respect to other water quality components, the verification of the model against several-years long records, the test of sensitivity, etc.