The Effect of Calcium on Microbial Aggregation during UASB Reactor Start-Up

The dynamics of granule formation were studied using cells from two bench-scale UASB Reactors. The objective was to elucidate factors which influence formation and maintenance of highly active self-agglomerated microbial biomass. Simultaneous examination of biological and physical parameters was performed during the start-up of a calcium-positive (100 mg/1) reactor and a reactor without added calcium. The influence of carbon nutrients and Ca⁺⁺ on the cell surface and microbial aggregation was studied. The granules formed in both reactors but were larger in the calcium-positive reactor in which they settled 3-4 times faster. A higher rate of biomass accumulation also was evident in the calcium-positive reactor and this allowed a more frequent increase in the substrate loading rate and earlier development of the granular sludge.