Chapter 5, Problem 38P

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 (L_cin mg/L) of a rock filter without recirculation is given by:

$L_c=\frac{L_0}{1+\frac{(2.5D^{2/3})}{\sqrt{Q}}}$

where L₀is the influent BOD (mg/L), D is the depth of the filter (m), and Q is the hydraulic flow rate [L/(m²-day)]. Assuming Q = 300 L/(m²-day) plot the effluent HOD as a function of the depth of the filter $100\le D\le 2000$ 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.