A lagoon with volume 1,200 m^3 has been receiving a steady flow of a conservative waste at a rate of 100 m^3/day for a long enough time to assume that steady-state conditions apply. the waste entering the lagoon has a concentration of 10 mg/L. Assuming completely mixed conditions,
a) what would be the concentration of pollutant in the effluent leaving the lagoon?
b) if the input waste concentration suddenly increased to 100 mg/L, what would the concentration in the effluent be 7 days later?