A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.
The principle mechanisms of chloramine residual decay in drinking water distribution systems is examined using a comprehensive model of chloramine reactions calibrated to distribution system data. The results reveal that four principle chloramine decay mechanisms must be considered, including:
reactions with hypochlorous acid/ion (HOCl/OCl-); an auto- catalytic reaction in which chloramines spontaneously decay in the absence of other reactants; oxidation reactions with reduced forms of organics and iron; and biologically-catalyzed reactions, such as the reactions with nitrite produced by nitrifiers as well as the direct cometabolism of chloramines by nitrifiers. The chloramine reaction model fits the distribution system data best when all of these reactions, including cometabolism of chloramines by nitrifiers, are included in the model.
principal investigator at Cornel1 University is Philippe Baveye.The University of Illinois also has a closely coupled subcontract, entitled -moaering zne iransport o f trioiogicar ry ana wemica ly Reactive Solutes in a Two-Dimensional, Heterogeneous Intermediate Scale Exper mental System", from Battelle Pacific Northwest Laboratory (PNL). Progress of the DOE and PNL projects is reported herein.The project's reporting structure contains two types of reports. The first type is a quarterly internal progress report. The purpose of the internal reports is to keep all members of the research team abreast with developments in each area. The second type is a semi-annual report that is transmitted to DOE and PNL. Its main purpose is to inform the project sponsors of the researchteam's progress and plans. This report is the semi-annual progress report for the second half of the third year.The project has four primary areas: (1) biodegradation of poorly soluble organic contaminants, (2) dual -1 imitation kinetics of-electron donors and acceptors, (3) two-dimensional modeling o f biofilm reactions in nonhomogeneous porous media, and (4) biologically induced clogging in porous media. For each area, the following sections give a brief summary of the previous progress, report this period's progress, and indicate plans for future work. , "I 2 2. BIODEGRADATION OF POORLY SOLUBLE CONTAMINANTS The key goal of this portion of the project is to define and quantify fundamental mechanisms control 1 i ng in situ biodegradation of nonaqueous-phase liquids (NAPLs) in porous media. The P.I. is Bruce Rittmann, and the research assistants are Eric Seagren and Robert Bowen. The fundamental hypothesis of this portion of the project is that biodegradation can significantly speed up NAPL removal by lowering the liquid-phase concentration of the dissolved NAPL near the NAPL interface. Furthermore, bacteria able to locate near the NAPL interface will give the greatest effect. Previous AccomDlishments This portion of the research was initiated approximately six months after the beginning o f the overall project. In the first 24 months of study, significant results were achieved in 0 identifying the mechanisms control1 ing dissolution/biodegradation of NAPLs. For very low solubility compounds, direct contact of the bacterium with the NAPL interface often is necessary, but biodegradation of di ssol ved species is more likely when the NAPL component is more soluble. 0 selecting experimental systems for study. One system uses Pseudonomas putida PpG9 and toluene, while the second system uses P. putida PpG6 and decane. 0 designing and fabricating a two-dimensional column for experiments in NAPL dissolution with biodegradation. 0 developing analytical methods for substrates and biomass. 0 developing and utilizing a two-dimensional model for dissolution from a NAPL. This model was used to design the column to ensure adequate plume formation. 'I .. 3 0 application of a one-dimensional model of advection, dispersion, dissolution, and biodegradation in a doma...
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