Biological oxygen demand (BOD) is a measure of the relative oxygen depletion effect of a waste contaminant and is widely used to assess the amount of pollution in a water source. The BOD in the effluent (Lc in mg/L) of a rock filter without recirculation is given by:
Lc = Lo/1 + (2.5D2/3)√Q
where L0 is influent BOD (mg/L), D is the depth of the filter (m), and Q is the hydraulic flow rate (U(m2-day)). Assuming Q = 300 L/(m2-day) plot the effluent BOD as a function of the depth of the filter ( 100 < D < 2000 m) for L0 = 5, 10, and 20 mg/L. Make the three plots in one figure and estimate the depth of filter required for each of these cases to obtain drinkable water. Label the axes and display a legend.