Thermophilic bioconversion of cellulose to volatile fatty acids

Abstract

This paper reports on experiments carried out on cellulose (α-floc) hydrolysis and concomitant acidogenesis in a single-stage thermophilic bioreactor. The bioreactor was operated at various loadings (0.33 – 2.5 g cellulose l −1 day −1) and retention times (4 – 6 days). Increase in either the retention time or loading boosted the total fatty acid concentration, but the extent of the cellulose conversion decreased as the loading increased. Acetic acid was the major product. High loading rates promoted the relative abundance of higher fatty acids. It was found that Monod-type kinetics failed to model the bioconversion process whereas a logistic equation did so statisfactorily. The parameters of the logistic model included the maximum specific growth rate and a finite cellulose conversion efficiency (expressed as a maximum attainable volatile fatty acid concentration) characteristic of a given cellulose loading. The model implies that cellulose conversion is inhibited even at high retention times. This aspect has been supported by microscopic examination of the reaction broth, showing the formation of a mucoid matrix at high loading.