In the present process, a biofilm of 0.5 cm thickness is immobilized around a rod of 3 cm diameter. What is the constant concentration of the toxic contaminant in the bulk aqueous phase?
a) 0.002 mol m⁻³
b) 0.5 mol m⁻³
c) 0.3 mol m⁻³
d) 0.05 mol m⁻³