STUDIES ON A UASB REACTOR

Abstract

UASB (Upflow Anaerobic Sludge Blanket) Reactor is one of the latest technologies in the field of wastewater treatment. It was first used by Lettinga et.al. in late 1980's since then it has been used by most of the countries for the treatment of different type of wastes. As the name suggests UASB is the anaerobic treatment process in which the wastewater flows in upward direction through the bed of sludge whereby the different type of anaerobes present in the sludge treats it thus resulting in the reduction of COD of the wastewater. The reduction in COD is used mainly for the biogas production, which is the specialty of any anaerobic process. The gas bubbles produced in the reactor as they pass through the sludge bed acts as a good mixer, thus reducing the cost for mixing. These bubbles carry along with them the sludge particles that got detached from the bubbles at GLS (Gas-Liquid-Solid) separator. The biggest advantage of the UASB over the other anaerobic process is that of high OLR that can be applied. Reason for this is the presence of special type of sludge called granulated sludge inside the reactor, this sludge has high density and high COD removal efficiency when compared with ordinary sludge. Several authors have given the reason for granulation inside the reactor while others have given the factors that can affect the granulation process. Samsoon et.al. along with the other factors has given that nitrogen in the excess of the metabolic requirement of microbes is essential for the granulation to occur. While several authors have developed models for the UASB reactor ranging from the Integral dynamic modeling to the sludge production but none of the above models take into account the process of granulation in their model. Since granulation is the phenomenon that differentiates it from other anaerobic processes and is also necessary for the smooth operation of UASB it becomes imperative to study the phenomenomon of granulation. In this dissertation the phenomena of granulation is studied during the start-up and the steady state operation of the UASB reactor for the treatment of Molasses. Since the granulation phenomenon is dependent on various factors such as COD removal efficiency, VSS content and pH of the sludge bed along with the iii biogas production rate, so these parameters were carefully noticed during current study. Maintenance of prerequisite facilitated in the phenomenon of granulation on 65`" day of operation at an OLR of 12g COD/1.day.The growth of granules were then noticed and growth rate calculated at two different OLRs was then fitted in "Birth & Spread" model for crystal growth by assuming that granules are actually crystals, growing under the super saturation of total nitrogen supplied into the sludge bed through influent molasses solution.