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Nuclear magnetic resonance (NMR) techniques are ideally suited for the study of biofilms and for probing their microenvironments because these techniques allow for noninvasive interrogation and in situ monitoring with high resolution. By combining NMR with simultaneous electrochemical techniques, it is possible to sustain and study live biofilms respiring on electrodes. Here, we describe a biofilm microreactor system, including a reusable and a disposable reactor, that allows for simultaneous electrochemical and NMR techniques (EC-NMR) at the microscale. Microreactors were designed with custom radio frequency resonator coils, which allowed for NMR measurements of biofilms growing on polarized gold electrodes. For an example application of this system we grew Geobacter sulfurreducens biofilms on electrodes. EC-NMR was used to investigate growth medium flow velocities and depth-resolved acetate concentration inside the biofilm. As a novel contribution we used Monte Carlo error analysis to estimate the standard deviations of the acetate concentration measurements. Overall, we found that the disposable EC-NMR microreactor provided a 9.7 times better signal-to-noise ratio over the reusable reactor. The EC-NMR biofilm microreactor system can ultimately be used to correlate extracellular electron transfer rates with metabolic reactions and explore extracellular electron transfer mechanisms. [ABSTRACT FROM AUTHOR]

In our previous papers we have demonstrated that biofilm structure never reaches a steady state in biofilm reactors; in this paper we link this fact to biofilm detachment and to the oscillating pattern of biofilm accumulation. In one respect reactors supporting suspended microbial growth and reactors supporting attached microbial growth (biofilms) are similar: in both the biomass accumulates in the reactor and is disposed of with the effluent. However, while in reactors with suspended microbial growth biomass accumulation and disposal occur simultaneously, in biofilm reactors these two processes are separated in time. Biomass accumulation in biofilm reactors shows a distinct pattern composed of three phases: (1) growth, (2) detachment, (3) regrowth. Despite this distinct pattern of biofilm accumulation observed at the microscale, biofilm reactors do reach a steady state of substrate removal. [ABSTRACT FROM AUTHOR]

Hexavalent uranium [U(VI)] was immobilized in biofilms composed of the sulfate reducing bacteria (SRB), Desulfovibrio desulfuricans G20. The biofilms were grown in two flat-plate, continuous-flow reactors using lactate as the electron donor and sulfate as the electron acceptor. The growth medium contained uranium U(VI) and the pH was maintained constant using bicarbonate buffer. The reactors were operated for 5 months, and during that time biofilm activity and uranium removal were evaluated. The efficiency of uranium removal strongly depended on the concentration of uranium in the influent, and was estimated to be 30.4% in the reactor supplied with 3 mg/L of U(VI) and 73.9% in the reactor supplied with 30 mg/L of U(VI). TEM and SAED analysis showed that uranium in both reactors accumulated mostly on microbial cell membranes and in the periplasmic space. The deposits had amorphous or poor nanocrystalline structures. [ABSTRACT FROM AUTHOR]

The goal of this presentation is to identify biofouling mechanisms that cause undesirable effects to the membrane separation processes of flux decline and pressure drop. The underlying assumption of this presentation is that biofouling is unavoidable and that the operator cannot eliminate it entirely. This premise justifies research efforts toward understanding the mechanisms by which biofouling affects the membrane processes, rather than expecting that technology can entirely eliminate membrane biofouling in the near future. An improved understanding of biofouling mechanisms may lead to better membrane design, better membrane modules, and better membrane cleaning procedures. [ABSTRACT FROM AUTHOR]

The need for reproducing biofilm processes is undisputable -- the quality of biofilm research depends on this reproducibility. However, as many biofilm researchers know, long-term biofilm processes are notoriously difficult to reproduce. To avoid problems related to biofilm reproducibility two strategies are used: (1) to study very young biofilms that have accumulated for a few hours to a few days only, and (2) to run biofilm experiments only once. The first approach trades reproducibility for relevance because natural biofilms are usually older, often much older than a few days. This approach can be applied to answer questions relevant to initial events of biofilm formation but not questions relevant to long-term biofilm accumulation. The second approach conceals the problem of biofilm reproducibility. To assure reproducibility of biofilm processes, we methodically followed a procedure for growing biofilms in terms of microbial makeup, media composition, temperature, surface preparation, etc. Despite all this effort the reproducibility of our results for long term growth is unimpressive. Consequently, the question had to be asked: Are biofilm processes reproducible? The experiments described in this paper address this question. Biofilms grown in two identical and identically operated biofilm reactors had comparable structure only until the first sloughing event. After that, biofilms had different patterns of accumulation. [ABSTRACT FROM AUTHOR]

Focuses on monitoring biofilms and the interpretation of data. Problems associated with biofilm heterogeneity, which causes monitored parameters to vary from location to location in the same biofilm; How researchers used the concept of discretized biofilms, which is an integrated system of biofilm monitoring and data interpretation, to assess the effect of biofilm heterogeneity on biofilm activity; Data indicating that heterogeneous biofilm can be ten times more active, in terms of glucose consumption rate, than a homogeneous biofilm of the same thickness but with uniformly distributed density.

Develops a technique to measure local effective diffusivity distribution in heterogenous biofilms. Relation between local effective diffusivity and biofilm density; Calibration of the effective diffusivity microelectrode; Surface averaged effective diffusivity profiles.

In this study, a pure culture of Zoogloea ramigera was film-wise grown on activated carbon particles in a differential fluidized bed biofilm reactor (DFBBR). In biofilm, effective diffusion coefficients of the essential substrates; glucose, ammonium chloride and dissolved oxygen were simultaneously calculated. The multi-substrate biokinetic expression used to calculate effective diffusion coefficients was derived by nonlinear regression analysis of the data of continuous fermenter experiments. This equation was utilized to solve diffusion & reaction model for effective diffusion coefficients in active biofilm. The results of the model solution revealed that the effective diffusion coefficient for all three substrates through the biofilm decreased with increasing biofilm density. [ABSTRACT FROM AUTHOR]