Mass transfer coefficients within anaerobic biofilms: effects of external liquid velocity

This work concerns mass transport in anaerobic biofilms, formed under upflow liquid velocities similar to the prevailing conditions in anaerobic reactors used for wastewater treatment. During biofilm formation under liquid velocities of 1.5 and 13.2 m/h, internal mass transfer coefficients were routinely measured. Mass transfer coefficients attained pseudo steady-state values between 2–4×10−3 m/h, no dependence being observed between bulk flow and internal mass transport rates. However, a transient variation in the liquid velocity from 1.5 up to 13.2 m/h, imposed after the biofilm had reached the steady-state, increased the internal mass transport by 20% on average. This result suggests that periodic changes in the bulk fluid velocity can be used as a tool to increase the transport of soluble substrates inside already formed biofilms, although the effect seems to be limited.