Determining the Minimum Allowable Wastewater Purification before Discharging with Allowance for the Harmful Effect Summation

The procedure and examples of determining the standard (minimum allowable) wastewater purification η, the minimum allowable concentrations of substances in the discharged water c st , and the permissible discharge standards are considered. It is shown in the context of potential effect of several substances, taking into account the harmful effect summation, that it is possible to determine only one unknown ( c st ). Two analytical methods have been obtained for solving the problem of calculating the standard purification rate η: for all substances (subject to the unknown η 1 = η 2 = η 3 =… or the relations between them are equal) and for determining η only for one substance, for example, the first η 1 (subject to the value assignment for other η 2 , η 3 , …). In general, the problem of determining η does not have an unambiguous solution since the choice of one of two types of solutions, as well as substances for which the desired η should be set or calculated, requires an independent technical and economic study. The possibility is established for using the normalized concentration for the summation of substance effects in solving the inverse problems of calculating the wastewater dilution in water bodies. To illustrate the effect of harmful summation on the safety of discharges and methodology testing, a calculation example of the purification degree η of technical wastewater containing two substances, for example fluorine and hydrazine, is given. In addition to fluorine and hydrazine, the water body contained a third substance, formaldehyde, which was absent in wastewater. All the substances have the harmful effect summation. The possible ratios η 1 and η 2 are calculated (for fluorine and hydrazine, respectively), at which the discharge of these substances will be safe for the water body. It is shown that the harmful effect summation significantly affects the standard wastewater purification degree.