Advances in Water Treatment and Enviromental Management

NON-POINT DISCHARGES FROM URBAN AREAS 225DO concentration along the river was determined by the following equations:(1(2where δ- DO concentration at a distance (m) from the sewage treatment works,mg O 2 /1; a-limiting solubility of oxygen in water at a given temperature, mg O 2 /l;kpreaeration coefficient, days -1 ; , -constants of xygen consumption by effluentsand river water organics, days- 1 ; -oxygen concentration in effluents and theriver O 2 background above the sewage treatment works, mg O 2 /1.(3S g ,S p -oxygen concentration in NP discharge and in the river above city, mg O 2 /l;Q g ,Q p rates of discharge of NP and the river above the NP inflow m 3 /s; Q-sum of theriver and NP dischargesof effluents and the river waterand NP mixture above the sewage treatment works, mg O 2 /1;(4of the NP discharge and the river water prior to NP inflow, mgeffluent rate, m 3 /s; V and —rate of river flow below the sewage treatment works,in m/s and m/day, respectively:(5Kg—constant of NP oxygen consumption rate, day-1;coefficient of mixing.effluents dilution ratio,Experimental data allowed to assign kg=0.3 day -1 . Computing produced a fileapplicable to evaluation of BOD and DO in the river water in a wide range ofcombinations.The rate and BOD of NP discharge were set corresponding to towns with populationsranging from 50000 to one million inhabitants. The design storm was set at 12 mmrain, providing for 90% wash off of solid particles built-up on impervious surfacesaccessible to the rain flow (Khvat, 1988).