Calculation of the negative impact on water bodies from the pulp and paper mill based on mathematical modelling of pollutant flow

The modern system for standardizing the load on water bodies consists of three main elements: 1 calculation of technological standards for marker substances for the industry; 2 calculation of permissible discharge standards for substances of 1 and 2 hazard classes; 3 comparisons of the calculated standards of permissible discharges with the standards of permissible impacts for water management areas established on the basis of the decision of the state ecological expertise. The formulas given in the methodology for calculating the permissible discharge standards have a limited range of application. The paper proposes an algorithm for calculating the convectivediffusion transfer of pollutants from the wastewater discharges of Silvamo Corporation Rus into the Vuoksa river in the Lesogorskoye reservoir area. For the study, the main outlet of the enterprise was chosen, through which purified wastewater containing residual pollutants from the main production and wastewater of the city of Svetogorsk is discharged. The Vuoksa River is extremely heterogeneous in the area of wastewater discharge through the outlet. Therefore, the calculation of the transfer of pollutants according to the current method for calculating the permissible discharge standards ignores the formed alongshore stagnant zones and wind currents prevailing in these zones. For the calculations, a combined model of the transport of pollutants was proposed, taking into account two-dimensional and three-dimensional models of wind currents and models of convective-diffusion transport and transformation of substances. When calculating the concentration field according to the official method for calculating the permissible discharge standards, the length of the pollution spot was 15 meters, and according to the proposed calculation algorithm, taking into account the relief of the coastal zone and the direction of wind currents, 140 meters. For the release of Silvamo Corporation Rus with fine water into the Vuoksa River, the results of calculating the standards for permissible discharges according to the current methodology and based on the developed combined model of convective-diffusion transport of pollutants are presented, which gives heterogeneous results. According to the developed allowable model, the concentration of BOD in wastewater is 1.7 times higher than the required value according to the current methodology for calculating standards, discharges are allowed. The application of an individual approach to the calculation of standards for permissible discharges makes it possible to determine environmental standards for water quality in water bodies and determine the maximum levels of load from a pulp and paper mill.

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