1.7. Mass Balance for Pollutant in the Lake

Try these first

1. 1.

   Define what is meant by mass balance.

   Hint

   Think about how we measure inputs and outputs in a system.

2. 2.

   What are the two main components of mass balance?

   Hint

   Consider the flow of materials.

3. 3.

   What is the formula for mass balance?

   • Rate of Output = Rate of Input
   • Rate of Accumulation = Rate of Input - Rate of Output
   • Rate of Accumulation = Rate of Input + Rate of Output

   Hint

   Think about what accumulates over time.

4. 4.

   True or False: Evaporation can directly contribute to the input of pollutants into a lake.

   • True
   • False

   Hint

   Consider where pollutants go.

5. 5.

   A lake with a depth of 2 meters and a surface area of 5000 m^2 has an initial concentration of pollutant A of 1 kg/m^3. If a factory discharges 200 kg/day into the lake and evaporation removes 50 kg/day, calculate the concentration after three days.

   Hint

   Consider the overall mass accounting across the time in your calculations.

6. 6.

   If a pollutant is continuously added to a well-mixed lake, and after three days the concentration is observed to be 1.5 kg/m^3 with continuous inputs of 75 kg/day and evaporation of 25 kg/day, calculate the initial concentration prior to any discharge.

   Hint

   You will need to set up the mass balance equation to find initial values.