TY JOUR TI THE RATIO OF CHEMICAL OXYGEN DEMAND TO SUSPENDED SOLIDS CONCENTRATION AS AN INTEGRATED INDICATOR OF POLLUTION SOURCES IN SURFACE WATERS KW chemical oxygen demand KW suspended solids KW COD/TSS ratio KW surface water quality KW environmental monitoring KW wastewater KW drainage water KW marginal filter KW environmental indicator JO MOSCOW ECONOMIC JOURNAL AU Kuznecov, E.A. PY 2026 IS 11 PB Electronic science