The water management system consists of two river reaches (A1-A2; A2-A3) and two point discharges of municipal wastewate

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The water management system consists of two river reaches
(A1-A2; A2-A3) and two point discharges of municipal wastewater
from M1 and M2. Wastewater is discharged in cross-sections A1 and
A2. The amount of sewage discharged from individual localities is:
S1 = 2 cu. m / s and S2 = 1 cu. m / s; the concentrations of
pollutants (e.g. BOD5) are CS1 = 1450 mg / l and CS2 = 925 mg / l,
respectively.
River flow upstream of the cross-section A1 is Q1 = 10 cu. m /
s; concentration of pollutants is CR1 = 32 mg / l.
To simplify the task, it is assumed that linear inflow (from
differential catchments) along the river reaches A1-A2
and A2-A3 is negligible. In these reaches, as a result of the water
self-purification process, the pollution load
is reduced. The values of the reduction coefficients α12 and α23
were determined with a model (α12 = 0,25; α23 = 0,60).
A swimming pool will be located in the cross-section A3, Therefore,
water quality standards were set in the A2 and A3
cross-sections
(CR2max = 20 ml / l and CR3max = 20 ml / l).
Building wastewater treatment plants (WWTP) in M1 and M2 is
planned; the costs depend on the assumed pollution load
reduction
coefficients x1 and x2. These relationships were assumed to be
linear: TC1 = c1x1 & TC2 = c2x2 (c1 = 5, c2 = 3).
Define pollution load reduction coefficients (x1 and x2) in such a
way
that the total costs are the smallest and water quality standards
are met.