Improving the accuracy of granular sludge and biofilm reactor simulations in Aquasim through artificial diffusion.

Aquasim is public-domain and user-friendly software that is widely used for biofilm modeling. The program uses built-in process unit blocks, such as biofilm and mixed compartments. In the literature, often several of these compartments are linked with artificial advective flows to represent a single physical well-mixed system, such as a granular sludge reactor. This work shows that caution should be exercised with this popular approach because numerical errors occur when too high artificial advective flows are used. These errors could stay unnoticed if mass-balances of the simulation results are not checked. A solution to this problem is proposed in this work. A new method based on diffusive links between compartments instead of advective links leads to more reliable and faster simulations and is much easier to implement. Biotechnol. Bioeng. 2017;114: 2131-2136. © 2017 Wiley Periodicals, Inc.