Effect of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. Part I: Biofilm growth and activity

Two similar anaerobic fixed-bed bioreactors which allowed the biomass to be periodically withdrawn were run in parallel. After feeding each digester w ith synthetic dairy wastes of different lipid content (Period I), both dige sters were fed with increasing sodium oleate concentrations with skim milk as co-substrate (Period II) and oleate as the sole carbon source (Period II I). In Period I: the digester fed with lipids was more efficient and exhibi ted lower levels of volatile fatty acids than the digester fed without lipi ds. The biofilm built up in the presence of lipids was thinner, but more re sistant to the presence of oleate than the biofilm formed in the absence of Lipids. which lost 53% of its solids after contacting with oleic acid. The specific methanogenic activity with butyrate as substrate was enhanced in the presence of lipids, but no significant effect was detected on the aceto clastic and hydrogenophilic activities, which remained similar for both dig esters along the trial period. (C) 2000 Elsevier Science Ltd. All rights re served.