A.I. Radu, J.S. Vrouwenvelder, M.C.M. Van Loosdrecht, C. Picioreanu
Chemical Engineering Journal, 188, 30-39, (2012)
A two-dimensional mathematical model coupling fluid dynamics, salt and
substrate transport and biofilm development in time was used to
investigate the effects of cross-flow velocity and substrate
availability on biofouling in reverse osmosis (RO)/nanofiltration (NF)
feed channels. Simulations performed in channels with or without spacer
filaments describe how higher liquid velocities lead to less overall
biomass amount in the channel by increasing the shear stress. In all
studied cases at constant feed flow rate, biomass accumulation in the
channel reached a steady state. Replicate simulation runs prove that the
stochastic biomass attachment model does not affect the stationary
biomass level achieved and has only a slight influence on the dynamics
of biomass accumulation. Biofilm removal strategies based on velocity
variations are evaluated. Numerical results indicate that sudden
velocity increase could lead to biomass sloughing, followed however by
biomass re-growth when returning to initial operating conditions.
Simulations show particularities of substrate availability in membrane
devices used for water treatment, e.g., the accumulation of rejected
substrates at the membrane surface due to concentration polarization.
Interestingly, with an increased biofilm thickness, the overall
substrate consumption rate dominates over accumulation due to substrate
concentration polarization, eventually leading to decreased substrate
concentrations in the biofilm compared to bulk liquid.