Comparison of methods for determination of microbial biomass in wastewater

Microbial biomass in wastewater was determined by methods used in environme ntal microbiology and by a method used in wastewater engineering based on a conceptual model simulating fundamental microbial processes in wastewater from measured oxygen uptake rates. The methods originating from environment al microbiology are based on staining and counting of cells for the determi nation of total cell biomass (acridine orange and DAPI), physiological stat e of cells (LIVE: DEAD(R) BacLight(TM) and activity of cells (reduction of the redox dye CTC and microautoradiography). Depending on the staining meth od applied, cell biomasses yielded 15-86% of the biomass defined by the mod el, and good correlations between cell biomass and model biomass were found . Cell biomass, oxygen uptake and acetate uptake were measured in wastewate r, where acetate was added. Substrate uptake rates were found not to be pro portional to the increases in cell biomass, suggesting that only a small fr action of the cell biomass was responsible for the main part of the substra te uptake. Despite the differences found between cell biomass and model bio mass, it was recommended to use the conceptual model as an engineering tool for simulation of microbial processes and wastewater quality changes. Howe ver, there should be a clear distinction between the terms 'model biomass', 'cell biomass' and different activity measurements of cells. (C) 2001 Elsev ier Science Ltd. All rights reserved