Biofilm parameters

Design parameters reactor parameters—horizontal area. A expanded bed height, Hx—and support media parameters—media density, media diameter, d total volume of media, Fixed parameters liquid phase parameters—diffusivity of substrate S in liquid, liquid density, Pl liquid viscosity, Vl—biofilm parameters—diffusivity of substrate in biofilm, Dsx maximum rate constant, < s,max Michaelis constant, —and... 

Quantifying Biofilm Parameters As the amount of biofilm biomass is proportional to current production, quantifying biomass is important to assess BES performance. The anode biofilms can be detached from the electrode with a spatula or razor, and the biofilm biomass can be calculated from the total cell protein [21]. Alternatively, the cells can be stained with fluorescence dyes such as the BacLight viability kit (Invitrogen) and examined by Confocal Laser Scanning Microscopy (CLSM). The... 

The basic biofilm model149,150 idealizes a biofilm as a homogeneous matrix of bacteria and the extracellular polymers that bind the bacteria together and to the surface. A Monod equation describes substrate use molecular diffusion within the biofilm is described by Fick s second law and mass transfer from the solution to the biofilm surface is modeled with a solute-diffusion layer. Six kinetic parameters (several of which can be estimated from theoretical considerations and others of which must be derived empirically) and the biofilm thickness must be known to calculate the movement of substrate into the biofilm. 

Table 3 Model equations (mass balance on liquid phase and on biofilm) and parameter values ... 

Structure and function need to be jointly considered in the assessment of effects of stressors on river systems. It has been shown that the two sets of parameters offer complementary information since they cover different time scales and responses. This being shown in the case of biofilms is not a unique characteristic of them, but it might be applied to all other biological communities (e.g. macroinvertebrates, fish). These differ from the biofilm in its higher size and life span, and therefore in their integrative capacity to reflect effects in one part of the ecosystem. Higher traffic levels in addition to biofilms should be considered to study the whole ecosystem. In all of these biological compartments, the combined use of descriptors may amplify our ability to predict the effect of stressors on river basins. 

Theoretical knowledge is available for a detailed description of the biofilm processes (Characklis, 1990 Gujer and Wanner, 1990). However, a fundamental requirement to establish applicable experimental procedures for determination of components and process parameters delimits the use of details. A simple description of the biofilm processes in terms of a surface flux model according to the description in Section 3.2.2 is selected. 

These four procedures are all recommended to be performed in the order shown to achieve optimal parameter estimation followed by a final validation of the gravity sewer process model (Figure 7.7). In the case of design of a new sewer system, procedure number 4 is, of course, not relevant and kinetic parameters for the sewer biofilm must be evaluated and selected based on information from comparative systems. 

Procedures 1 to 3 described in the previous three subsections have typically been performed on wastewater samples at an upstream point of a sewer. The objective of these procedures has been to characterize the incoming wastewater to the sewer system in terms of COD fractions and process-relevant parameters. Contrary to this, the present procedure number 4 is performed with the overall objective of determining sewer process-related characteristics including the biofilm and reaeration. The characteristics of the water phase considered in procedures 1 to 3 are hereby extended to include all major processes relevant for the microbial transformations in gravity sewers, especially when dealing with aerobic processes. Further detailed characterization that is needed when including the anaerobic transformations will be dealt with in Section 7.2.5. 

Simulation procedure 4 is basically a calibration of the sewer process model for aerobic microbial transformations as described in the matrix formulation (Table 5.3). Both the biofilm processes and the reaeration are included. Initial values for the components and process parameters for this simulation originate from the sample taken at the upstream sewer station. When simulated values of the downstream COD components are acceptable, i.e., approaching the corresponding measured values, the calibration procedure is successfully completed. The major model parameters to be included in the calibration process are those relevant for the biofilm, especially km and K. After calibration, the model is ready for a successive validation process and later use in practice. 

A rather simple 1/2-order flux model for the biofilm processes was selected, although more detailed formulated models are well known, e.g., Gujer and Wanner (1990). The reason is that a simple and sound parameter estimation and calibration procedure that can be easily performed has been emphasized. 

Among organic constituent measurements, that of aggregate properties (BOD and COD) and specific parameters (TOC for example) has been well developed for more than 20 years. Concerning BOD, a recent review on biosensors [33] has been published. BOD biofilm-based sensors as well as respirometric systems, other measuring principles, and the commercial BOD instruments are discussed and compared regarding their performance characteristics like linearity, response time, precision, agreement between BOD values obtained from the biosensors and the conventional 5-day test, as well as toxic resistance to various compounds and operational stability. 

Observe the response time of the reactor for changes in the operating parameters SF, F and KLa. Is the biofilm always the slowest to respond Relate the response to the diffusion time constant L2/D. 

Because of the similarity of transport in biotilms and in stagnant sediments, information on the parameters that control the conductivity of the biofilm can be obtained from diagenetic models for contaminant diffusion in pore waters. Assuming that molecular diffusion is the dominant transport mechanism, and that instantaneous sorption equilibrium exists between dissolved and particle-bound solutes, the vertical flux ( ) through a stagnant sediment is given by (Berner, 1980)... 

Ellis, B. D., P. Butterfield, W. L. Jones, G. A. McFeters, and A. K. Camper. 2000. Effects of carbon source, carbon concentration, and chlorination on growth related parameters of heterotrophic biofilm bacteria. Microbial Ecology 38 330-347. 

The principle of the mass transport of substrates/nutrients into the immobilized enzyme/cells, through a solid, porous layer (membrane, biofilm) or through a gel layer of enzyme/cells is the same. The structure, the thickness of this mass-transport layer can be very different, thus, the mass-transport parameters, namely diffusion... 

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