Biomedical subjects

Mark C M Van Loosdrecht

Publications and source records attributed to Mark C M Van Loosdrecht.

4 recordsLinked to original sources

PubMed2004

Three-dimensional dual-morphotype species modeling of activated sludge flocs.

An individual-based model, originally developed for a biofilm system, was adapted to simulate three-dimensional formation of activated sludge flocs. The model was extended to two different bacterial morphotypes (floc-forming and filamentous bacteria), allowing spatial development of the floc according to the bacterial morphology, diffusion, reaction, and growth processes. The model needed also extension with a process for attachment of individual cells. Despite being in an early stage of development, the model is already a tool that enables us to obtain useful information about the microfloc environment. The model indicates that filamentous bacterial morphology and substrate microgradients are important aspects in the formation of bacterial structures. In mass transport-limited regimes filamentous bacterial structures prevail, whereas in growth-limited regimes irregular shaped flocs with fingerlike structures are dominant. These modeling results suggest that activated sludge flocs and biofilms might be different manifestations of the same phenomena. The model results support the hypothesis that floc-macrogradients can be the most important parameter for development of bulking sludge. The model suggests that attachment has a very strong effect on floc structure, leading to enhancement of the effect of substrate microgradients.

Bacteria, Aerobic↗

PubMed2004

Particle-based multidimensional multispecies biofilm model.

In this paper we describe a spatially multidimensional (two-dimensional [2-D] and three-dimensional [3-D]) particle-based approach for modeling the dynamics of multispecies biofilms growing on multiple substrates. The model is based on diffusion-reaction mass balances for chemical species coupled with microbial growth and spreading of biomass represented by hard spherical particles. Effectively, this is a scaled-up version of a previously proposed individual-based biofilm model. Predictions of this new particle-based model were quantitatively compared with those obtained with an established one-dimensional (1-D) multispecies model for equivalent problems. A nitrifying biofilm containing aerobic ammonium and nitrite oxidizers, anaerobic ammonium oxidizers, and inert biomass was chosen as an example. The 2-D and 3-D models generally gave the same results. If only the average flux of nutrients needs to be known, 2-D and 1-D models are very similar. However, the behavior of intermediates, which are produced and consumed in different locations within the biofilm, is better described in 2-D and 3-D models because of the multidirectional concentration gradients. The predictions of 2-D or 3-D models are also different from those of 1-D models for slowly growing or minority species in the biofilm. This aspect is related to the mechanism of biomass spreading or advection implemented in the models and should receive more attention in future experimental studies.

Anaerobiosis↗

PubMed2002

Proposed modifications to metabolic model for glycogen-accumulating organisms under anaerobic conditions.

Filipe et al. (2001) proposed an anaerobic metabolic model for glycogen-accumulating organisms (GAO) in which the succinate-propionate pathway was used to describe the production of propionyl-CoA. However, propionyl-CoA is only an intermediate product in the above pathway. Stopping at propionyl-CoA instead of propionate (the end product of the pathway) results in the consumption of one ATP from succinate to succinyl-CoA, which was not accounted for in the model of Filipe et al. (2001). This resulted in significant errors in the stoichiometric coefficients in the final metabolic model. A modified model is presented in this communication and is shown to fit the experimental data significantly better than the original model.

Acetyl Coenzyme A↗

PubMed2002

Model-based evaluation of temperature and inflow variations on a partial nitrification-ANAMMOX biofilm process.

A mathematical model describing nitrification (nitritification plus nitratification) and anaerobic ammonium oxidation (ANAMMOX) combined in a biofilm reactor was developed. Based on this model, a previously proposed one-reactor completely autotrophic ammonium removal over nitrite (CANON) process was evaluated for its temperature dependency and behaviour under variable inflow. The temperature-dependency of growth rates of the involved organisms is described by an Arrhenius-type equation. If temperature decreases, the activities of the involved organisms decrease. This means that thicker biofilms are needed or the ammonium surface load (ASL) to the biofilm should be decreased to maintain full N-removal at lower temperatures. Although the growth rate of nitrite oxidisers is higher than that of ammonium oxidisers at lower temperatures, these organisms can be effectively competed out due to a lower oxygen affinity. Variable inflow or dissolved oxygen (DO) concentration negatively affect the N-removal efficiency due to an unbalance between applied ASL load and required oxygen concentration. A variation of the dissolved oxygen concentration in a small range (+/- 0.2g O2/m3) has no significant influence on the process performance, which means that requirements on electrode sensitivity and a DO control scheme are not too stringent. A variable ASL has obvious influence on the process performance, at both constant and variable DO. A good adjustment of DO in accordance with the variable ASL is needed to optimise the N-removal efficiency. At T = 20 degrees C, an N-removal efficiency of 88% is possible at ASL = 0.5 g NH4+ - N/mr2 d, in a biofilm of at least 0.7 mm thickness and a DO level of 0.3 g O2/m3 in the bulk liquid.

Biofilms↗