Biofilms, description

It should be noticed that biomass growth and respiration for bulk water phase include details that are not taken into account in the simple half-order biofilm description. As an example and a consequence, the two yield constants, YHw and Yup are differently interpreted in terms of the substrate requirement of the biomass (Figure 5.5). 

The microbial transformations of the wastewater described in the concept shown in Figure 5.5 deal with the COD components defined in Section 3.2.6. The figure also depicts the major processes that include the transformations of the organic matter (the electron donors) in the two subsystems of the sewer the suspended wastewater phase and the sewer biofilm. The air-water oxygen transfer (the reaeration) provides the aerobic microbial processes with the electron acceptor (cf. Section 4.4). Sediment processes are omitted in the concept but are indirectly taken into account in terms of a biofilm at the sediment surface. Water phase/biofilm exchange of electron donors and dissolved oxygen is included in the description. 

When considering the details of the sewer process concept, the processes of the subsystems are theoretically described at different levels. The most detailed description is done for the water phase by including the biomass/substrate relationship. Fewer details in terms of a description at an empirical level are included for the reaeration and the processes in the biofilm. 

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. 

Investigations have been performed to exemplify the DO surface removal rates from biofilms grown on different types of wastewater (Bjerre et al., 1998b). Such investigations may indicate if Equation (5.3) can be considered an appropriate description of the aerobic activity. The wastewater for these studies originates from an open sewer system, the Emscher river, Germany. The results of the experiments are outlined in Table 5.2, and further details are shown in Figures 5.6 and 5.7. 

As shown in Figure 6.8, the most important part of the anaerobic sulfur cycle in terms of the sulfate respiration process can be integrated with the anaerobic carbon cycle. A fractionation of the readily biodegradable substrate (Ss) into SF and SA fits well to the anticipation that mainly SF is used by the sulfate-reducing biomass in sewer biofilms. By integrating the sulfide formation in this way, a simple conceptual approach is obtained instead of the traditional empirical descriptions as depicted in Table 6.1. 

A simplification of the aerobic heterotrophic in-sewer microbial processes is depicted in Table 5.3. By omitting the reaeration and the growth of the biofilm biomass in this description, the remaining processes proceed interactively in the water phase under the conditions established in the OUR experiments. Furthermore, the processes take place at a constant temperature and at DO nonlimiting growth conditions affecting the formulation of the relevant rate expressions (see Table 7.1). 

The biofilm concept, applied to sediment-water interactions, breaks with classical strategies to model early diagenesis (i.e., the vertical redox zonation). Although far from completely developed, this concept may overcome modeling problems, such as an adequate description of recycling of substances. 

Description for any type of bacteria found freely in cooling water rather than bound up in biofilm and most commonly tested by means of dip-slides. A poorly maintained cooling system may contain 1 x 106 or more colony forming units (cfu) per milliliter of water. 

A description of any type of bacteria found attached or bound-up in slimes or biofilm. Potentially more of a problem than planktonic bacteria due to the difficulty of biocides penetrating the slime and the potential for rapid system re-infection. 

In order to demonstrate how CV is applicable to studying electron transfer in G. sulfurreducens biofilms or EABs in general, we first formulate the conditions prior to a CV being run the reason(s) for acquiring CVs of the biofilm will become apparent to the reader. The following is a brief description of the conditions for a... 

The first description of electroactive microorganisms can be dated back to Potter in 1911 [2].From there on and till the late 1990 it was generally assumed that artificial substances, mostly redox dyes like neutral red, are required to serve as mediators between the microbial cell and the conductive substratum - the electrode surface [3, 4]. However, after the discovery that electroactive biofilms can be formed without the help of exogenous substances [5, 6] the research... 

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