Determination of the microbial population in thermophilic anaerobic reactor: Comparative analysis by different counting methods

This paper describes the determination of the microbial population, in term s of the number, biomass and composition, of single and two-phase, laborato ry-scale thermophilic (55 degreesC) anaerobic reactors, under steady-state conditions. Epifluorescence microscopy with DAPI (4 ' ,6-diamidine-2-phenyl indole) as fluorochrome was used to determine the total number of micro-org anisms in the reactors, and autofluorescence microscopy for the number of t he autofluroescent methanogenic populations. The results obtained by the di rect count methods were compared to the quantity of biomass contained in th e system, determined by volatile suspended solids. The viable bacterial pop ulation was determined by plating techniques using an anaerobic chamber. Th e total bacterial and F420 autofluorescent populations of single-stage dige sters increase when the hydraulic retention time decreases; nevertheless, t he percentages of the autofluorescent methanogens remain constant at 13%. I n the two-stage reactors, the percentages of this group are 99% and 26% of the total population in the acidogenic and methanogenic factors, respective ly. In the single-stage reactors, biomass determinations can be used to est imate microbial concentrations, and vice versa, as there is a high positive correlation between microorganism concentration and biomass. It was obtain ed a high correlation between direct counts by epifluorescence microscopy a nd viable plate counts for the combined system studied. (C) 2001 Academic P ress.