# Waste water mass balance problem

Info:

BOD: Biochemical Oxygen Demand

BOD5 is the total amount of oxygen consumed by microorganisms during the first five days of biodegradation

BOD5 = (DOi - Dof)/(P) this is the five-day BOD of a diluted sample

Where DOi = the initial dissolved oxygen (DO) of the diluted wastewater

DOf = the final DO of the diluted wastewater, 5 days later

P = the dilution fraction = (volume of wastewater)/(volume of wastewater plus dilution water)

A standard BOD bottle holds 300 mL, so P is just the volume of wastewater divided by 300 mL

5.36)

Consider a lake with 100 X 10^6 m^2 of surface area for which the only source of phosphorus is the effluent from a wastewater treatment plant. The effluent flow rate is 0.4 m^3/s and its phosphorus concentration is 10.0 mg/L (10.0 g/m^3). The lake is also fed by a stream having 20 m^3/s of flow with no phosphorus. If the phosphorus settling rate is estimated to be 10 m/yr, estimate the average phosphorus concentration in the lake. What level of phosphorus removal at the treatment plant would be required to keep the average lake concentration below 0.010 mg/L?

https://brainmass.com/chemistry/environmental-chemistry/waste-water-mass-balance-problem-86793

#### Solution Preview

Although not stated in the problem, I would assume an outflow to keep the lake level unchanged. Then this is essentially a mass balance problem. Draw a diagram showing the input from the wastewater treatment plant and the stream. Fill in each of the numbers given in the problem, and leave blanks for those you're ...

#### Solution Summary

Waste water mass balance problem