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

Abstract

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.

Impact of granule size distribution on nitrous oxide production in autotrophic nitrogen removal granular reactor

“…To this end, a previously-developed N 2 O model capable of describing relevant mechanisms in autotrophic nitrogen removal systems (Chen et al, 2019) was applied in this work. With granule size distribution being considered in accordance with Baeten et al (2017), the impact of granule size distribution on N 2 O production was investigated for the autotrophic nitrogen removal granular reactor. This work is expected to gain useful insights into 1) future control over granule size characteristics in order to mitigate N 2 O production/emission from the autotrophic nitrogen removal granular reactor and 2) good practice in modelling N 2 O production/emission from the autotrophic nitrogen removal granular reactor based on the extent of granule size distribution.…”

“…1 was implemented in Aquasim (Reichert, 1998) through compartmentation of the reactor and utilization of the diffusive link. As explained by Baeten et al (2017), the introduced mass transfer rate (R d ) of a compound between two diffusively linked compartments, which is analogous to the well-known gas-liquid mass transfer model, is calculated by , where S 1 is the concentration in the first compartment, S 2 is the concentration in the second compartment, and q ex is a predefined, sufficiently high exchange coefficient. Specifically, depending on the number of granule size classes (n ≥ 2) to be considered, the implementation (i.e., Fig.…”

“…As discussed in Baeten et al (2017), this approach with diffusive links (i.e., Fig. 1) is advantageous over the previous advection-based approach proposed by Volcke et al (2012), which uses reasonably high advective links to connect the bulk liquid of compartments to mimic the mixing, in its elimination of the trade-off between mixing and correct mass balance, thus leading to higher reliability and efficiency, wider applicability, easier implementability, and a lower risk for numerical errors in Aquasim.…”

Influences of Longitudinal Heterogeneity on Nitrous Oxide Production from Membrane-Aerated Biofilm Reactor: A Modeling Perspective

“…2 As demonstrated in Figure 1, the compartmental model was implemented through the equal division of the biofilm reactor into a certain number of compartments and used a sufficiently high mass transfer between two diffusively linked compartments when the simulation of the biofilm reactor as a CSTR was required (Figure 1A,B). Such an artificial diffusion approach was first introduced by Baeten et al 27 to better represent biofilm systems as CSTRs in AQUASIM and has been successfully applied by Chen et al 28 to explore the N 2 O production from a codiffusional system (i.e., a granular biofilm system performing PN/A). By contrast, the advective links were directly used to simulate the biofilm reactor as a PFR (Figure 1C,D).…”

Bacterial cell-free expression technology to in vitro systems engineering and optimization

“…The protection of the gene of interest can be achieved by addition of extra base pairs, by supplementing DNA binding proteins, e.g. GamS, by chemical modification with PTO (phosphorothioate bonds modifications), or with short oligos blocking the RecBCD complex [74] , [75] . Besides, stabilization is also possible by DNA circularization strategies [76] , crosslinking into hydrogels [77] , or even by E. coli genome engineering [78] .…”