No abstract

A kinetic model for anaerobic digestion of insoluble solid-state substrates was developed. Rate equations for cell growth and substrate consumption were derived based on the assumption that the microorganisms assimilate the substrate mainly at the point of contact where they grow. The model emphasizes effects of substrate particle size, organic loading, and cell concentration on the rates of cell growth and substrate utilization. Batch digestion of a stearic acid emulsion with a mean particle size of 2.0 microm and a biological sludge was conducted at 30 and 37 degrees C to verify the proposed model. Agreement between the experimental and calculated results indicated the validity of the model for describing the microbial degradation of insoluble solid-state substrates. Further examination of the model revealed that with low cell substrate affinity or at low cell concentration, it coincided with a Michaelis-Menten type kinetics in which the effect of particle size was taken into consideration.

Performance equations for the fed-batch digestion of insoluble solid-state substrates were developed based on a verified interfacial kinetic model for microbial uptake of these substrates. Fed-batch anaerobic digestions of a suspension of stearic acid with a mean particle size of 2 pm were conducted to verify the derived equations. Agreement between the experimental and calculated results indicated the validity of these equations. The performance equations should be useful for describing the time courses of cell growth, substrate consumption and product accumulation in a fed-batch digestion system with insoluble solid-state organics as substrate.Des equations de performance pour la digestion en alimentation discontinue de substrats B I'Ctat solide ont CtC etablies B partir d'un modkle sQr de cinitique interfacial pour I'absorption microbienne de ces substrats. On a procede B des digestions anatrobiques en alimentation discontinue d'une suspension d'acide sttarique avec une taille moyenne de particules de 2 pm afin de vtrifier les equations calcultes. L'accord entre les risultats experimentaux et les risultats calculks montre la validit6 de ces equations. Ces Cquations de performance devraient Ctre utiles pour dtcrire les Ctapes de la croissance des cellules, la consommation des substrats et I'accumulation des produits dans le systbme de digestion en alimentation discontinue avec des matibres organiques B I'Ctat solide insolubles comme substrats.