Surface Environment, Mine Ventilation and Underground Hazards · Surface Environment · 1 mark · Numerical answer
A washery discharges 300 m³/day of water at DO 4 mg/L into a stream flowing 0.04 m³/s at DO 8.5 mg/L. Ignoring temperature effects, find immediate mixed DO in mg/L to two decimals.
Convert stream flow to 0.04×86400=3456 m³/day. Conservation of dissolved oxygen gives C=(3456×8.5+300×4)/(3456+300)=8.140575 mg/L. Round to 8.14. No downstream oxygen consumption is included in this instantaneous mixing balance.
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