There is a need for alternative, less costly wastewater treatment concepts. Upgrading existing treatment units by the inclusion of a precipitating and coagulating stage has proven an economically attractive alternative. The technological boundary conditions are well known and can be described in terms of necessary chemical dosages and resulting reduction ratios in pertinent wastewater constituents. Decision makers can be convinced of the significant savings in economic and ecological terms when such upgrading or phase-wise construction of needed treatment capacity is effected by chemicals dosing, using existing installations for the necessary liquid-solid separation. The costs of such pollution control measures are well-known and can be calculated for given boundary conditions. The benefits in a broader ecological sense are difficult to quantify. Direct cash savings result, however, when wastewater charges, owed for the discharge of less treated wastewater streams can be significantly reduced by the addition of such chemical stages. If the incremental costs of such additional stages are lower than the saved wastewater charge expenses, then real net benefits result. These have been calculated for two proven concepts of treatment plant upgrading.

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