¼ Rmax AT3:2; ð7Þ
where AT3.2 is the sum of biofilm surface area of the walls and the
baffles until the depth x at which the oxygen concentration was
above 3.2 g m3. The biofilm N-conversions where the oxygen concentrations
were lower than 3.2 g m3 were calculated using Eq. (8):
Biofilm N-conversions ðg d1
Þ ¼ W
Z 0:8
x3:2
RNitr biofilmðxÞdx; ð8Þ
where RNitri biofilm is biofilm nitrification rates (g m2 d1) at oxygen
concentration below 3.2 g m3, x3.2 is depth at which oxygen concentration
was below 3.2 g m3.
In order to obtain an expression for RNitr biofilm(x), Rmax for biofilm
was divided by 3.2 to obtain slope ‘‘a’’ (Fig. 1). The slope
was multiplied with the oxygen concentrations at different depths
to obtain nitrification rates at these depths and fitted with an exponential
equation of the type y = c exp (dx). This equation was
integrated (Eq. (9)) to give biofilm N-conversions (for oxygen concentration
less than 3.2 g m3) as:
Biofilm N-conversions ðg d1
Þ
¼ W cð1=dÞ expðd x3:2Þ W cð1=dÞ expðd 0:8Þ;