Journal of Microbial & Biochemical Technology

Abstract

A Method for Exploring Suspended Particles Interactions by Means of Optical Density Measurements: Application to Bacterial Floc and Solid Nutrients

Thierie J

In experiments, we observed that, surprisingly, the optical density (OD) of a mixture made up of various particles could decrease when the number of particular particles is increased. Our aims were first to understand this unexpected result, and second to see if we can use these results for practical purposes. We derived a simple but realistic expression giving the optical density resulting from light scattering of mixed suspended particles. The equation we obtained is a linear relation of the product of the particles number by their cross section. We showed that the total OD (obtained by summing over the OD’s of the independent particles) is different from the OD of the same system when the particles are interacting when put together. Using a static model with two types of particles (“the binary model”), we showed which conditions are necessary to explain this apparently paradoxical phenomenon. This simple calculation already makes it possible to optimize strategies of flocculation/coagulation of solids. We then used this methodology to investigate the biodegradation kinetics of municipal wastewater (MWW) particles by activated sludge (AS) of a wastewater treatment plant. We obtained a good representation of the assimilation of the slowly biodegradable particulate nutrients.