An improved procedure for characterization of spatial and temporal evolution of immobilized cells in gel membranes

An improved procedure that allows the simple and reproducible characterizat ion of spatial and temporal distribution of immobilized biomass in gel memb ranes was developed. This procedure involves three main steps in the prepar ation of membrane samples, the use of a standard microtome to obtain membra ne slices, and the measurement of cell concentration by spectrophotometry. The key improvement in this procedure is to prepare the membrane samples by clamping them between two glass plates and storing them in a -80 degreesC freezer for a specified period of time depending on the membrane thickness. With this simple pre-treatment, the membrane samples were frozen in an ide al physical state to be cut into flat, consistent, slices using a commercia l freezing sledge microtome. thus providing accurate and reproducible resul ts. As a validation case study, a gel membrane bioreactor was constructed i n which an alginate gel membrane with immobilized Lactobacillus rhamnosus c ells was flanked by two well-mixed chambers with identical fermentation med ia. The improved procedure was employed to experimentally determine the int ra-membrane cell distribution in the alginate membranes during fermentation . The experimental results showed a heterogeneous "U-shape" biomass distrib ution across the membrane, with the highest cell concentration at the membr ane-solution interface. High reproducibility and accuracy were verified by a low average standard deviation (<5%) and a high biomass recovery ratio (> 90%), respectively.