Assignment #3 – ENGI 2133 October 2015
Due: October 22, 2015.

1. Consider the air over a city to be a box 100 km on the two bottom sides that reaches up to an altitude of 1.0 km. Clean air is blowing into the box along one of its sides with a speed of 4m/sec. Suppose an air pollutant with a reaction rate K = 0.20/hr is emitted into the box at a total rate of 10.0kg/s. Find the steady state concentration if the air is assumed to be completely mixed.
Q = flow = velocity X Area, where units are in m3/sec
2. a) In the above problem if wind speed drops to 1m/sec, estimate the pollutant concentration 2 hours later.
b) In the above problem, what if the clean air blowing in is actually contaminated with the pollutant at a concentration of 1.5µg/m3. Find the steady state concentration if the air is assumed to be completely mixed.
3. A facultative sewage lagoon that has a surface area of 10 Ha and a depth of 1.0 m. is receiving 8,640 m3/d of sewage containing 100 mg/L of biodegradable contaminant. At steady state, the effluent from the lagoon must not exceed 20 mg/L of the biodegradable contaminant. Assuming the lagoon is well mixed and that there are no losses or gains of water in the lagoon other than sewage input, what biodegradable reaction rate coefficient (d-1) must be achieved?
A Ha = 100m X 100m
4. An aerobic sewage treatment pond with a volume 1200m3 has been receiving a steady flow of a non-conservative waste at a rate of 100m3/day for a long enough time to assume steady state conditions apply. The waste entering the treatment pond has a concentration of 200mg/L and a K = 0.20/day.
a) What would be the concentration of the effluent in the plume leaving the treatment pond?
b) If the input waste concentration suddenly decreased to 100 mg/L, what would be the concentration in the effluent 7 days later?