Scrit critical substrate concentration (kg.m−^3 )
Sf substrate concentration inside the biofilm (kg.m−^3 )
dimensionless concentration inside the biofilm (Sf^ /Si)
Si substrate concentration at the biofilm-liquid interface
Sox concentration of oxidant substance (kg.m−^3 )
Sred concentration of reductant substance (kg.m−^3 )
S 1 substrate concentration at reactor inlet (kg.m−^3 )
S 2 substrate concentration at reactor outlet (kg.m−^3 )
t time (s)
T temperature (°C)
VR reactor volume
(Xf)a active cell density in the biofilm (kg.m−^3 )
Xv cell density within the biofilm (kg.m−^3 )
y distance inside the biofilm measured from the liquid-biofilm interface (m)
y+ dimensionless distance in the biofilm (y/Lf)
Yf/s mass of dry biofilm (kg)
Z depth of the trickling filter (m)
Greek Symbols
α parameter defined by equation (33)
β degree of substrate penetration in the biofilm
ε reactor porosity
ø Thiele modulus
ηi biofilm internal efficiency
η biofilm efficiency based on external substrate concentration
λ external mass transfer rate/internal coupled diffusion-reaction rate
μ specific growth rate (s−^1 )
μmax maximum specific growth rate (s−^1 )
μp dry biofilm production rate per unit mass of biomass (s−^1 )
(μp)a specific dry biofilm production rate per unit mass of active biomass (s−^1 )
(μp)max maximum specific biofilm production rate (s−^1 )
ψ dimensionless observable modulus, defined in equation (34)
Biofilm reactors 321