Browsing by Author "Lundman, Ross Wade"

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Efficient sampling designs for microbial processes: a case study
(1993-07) Johnson, K. R.; Lundman, Ross Wade; Hamilton, Martin A.
We describe a method for determining optimal sampling designs for experiments involving subsampling in stages. An optimal sampling design either maximizes the precision of the results for a given amount of experimental effort (time, money) or minimizes the effort required to achieve a specified level of precision. The optimization method utilizes information on (i) the cost of obtaining a sample at each stage and (ii) the variability of the data attributable to each sampling stage. To illustrate the method, we use effluent suspended cell data from a packed-bed bioreactor. The sample design involved three stages. First, three primary samples were collected from the reactor. Second, each reactor sample was subsampled in triplicate and a specified volume of each subsample was passed through a filter. Third, the bacteria of the filter were counted in each of ten microscopic fields, each field representing the same proportion of the filter area. The optimization analysis, applied to the mean of the log-transformed bacterial counts, showed that the precision of the sample mean could be substantially improved by expending more sampling effort on the first stage and less on the second and thir stages. We also show how the optimization analysis can be applied to other response measurements (e.g., total organic carbon, soluble organic carbon and glucose concentration) and sampling designs involving other numbers of subsampling stages.
Modeling biofilm accumulation and mass transport in a porous medium under high substrate loading
(1995-09) Wanner, O.; Cunningham, Alfred B.; Lundman, Ross Wade
A packed bed biofilm reactor inoculated with pure culture Pseudomonas aeruginosa was run under high substrate loading and constant flow rate conditions. The 3.1-cm-diameter cylindrical reactor was 5 cm in length and packed with 1-mm glass beads. Daily observations of biofilm thickness, influent and effluent glucose substrate concentration, and effluent dissolved and total organic carbon were made during the 13-day experiment. Biofilm thickness appeared to rech quasi-steady-state condition after 10 days. A published biofilm process simulation program (AQUASIM) was used to analyze experimental data. Comparison of observed and simulated variables revealed three distinct phases of biofilm accumulation during the experiment: an initial phase, a growth phase, and a mature biofilm phase. Different combinations of biofilm and mass transport process variables were found to be important during each phase. Biofilm detachment was highly correlated with shear at the biofilm surface during all three phases of biofilm development.
Transport of substrate and biomass in a packed bed bioreactor
(Montana State University - Bozeman, College of Engineering, 1992) Lundman, Ross Wade