Effect of lipids on biomass development in anaerobic fixed-bed reactors treating a synthetic dairy waste

Abstract

The aim of this work was to follow the evolution in quantity and quality of the biomass developed during the operation of two anaerobic fixed bed reactors treating a synthetic dairy waste with different lipid contents. The feasibility of a special reactor design that allowed the biomass withdrawal with minimum operation disturbances was tested. The HRT was maintained at 1.5 days and the influent concentration was gradually increased from 3 to 12 g COD/l. Initially, one reactor was loaded with skim milk and the other one with whole milk, with equal organic loading rates (OLR). The effect of lipids was evaluated in terms of reactor performance, total, adhered and entrapped biomass and evolution of biomass quality determined in batch assays by: (i) measuring of potential specific methanogenic activity against direct (acetate, H2/CO2) and indirect (propionate and butyrate) substrates; (ii) measuring of the resistance of acetoclastic bacteria to the presence of sodium oleate. The lipids reduced the adhered fraction of biomass. The methanogenic activity against butyrate was enhanced in the presence of lipids, but no significant effect was detected on the other measured activities. The biomass taken from the reactor fed with lipids was more susceptible to the presence of sodium oleate, but, over the operation period, this susceptibility was reduced.