Influence of Extrinsic Factors on Granule Size in Uasb Reactor

The aim of this paper is to synthesize and analyze information on how the process of granulation is affected by environmental and operational conditions in the reactor. Various factors affecting granulation process as gleaned from the literature are organic loading rate (OLR), upflow velocity (Vup), sludge volume index (SVI), specific methenogenic activity (SMA), VSS/SS ratio, liquid in flow rate (Q), gas production rate (Qg), settling velocity (SV), temperature, pH, nutrients and trace metals, quantity of seed sludge, exocellular polymer, reactor configurations, its geometry and characteristics of wastewaters etc. The divalent cations such as calcium and iron may enhance granulation by ionic bridging and linking exo-cellular polymers. However, their presence in excess may lead to cementation due to precipitation leading to increased ash content and mass transfer limitation. The addition of external additives such as ionic polymers may enhance granulation in the upflow anaerobic sludge blanket reactors. Among the various factors and reported experimental results, the factors OLR, Vup, SVI, SMA, and VSS/SS ratio are identified as important factors for which experimental results are available in the literature. Comparision of results on granule size variations are presented and analyzed in this work. From the results, it is concluded that these factors are playing major roles in enhancing the granule size development, if regulated, monitored and maintained properly during initial phases of operation of UASB reactor.