EFFECT OF AGITATION ON COD REMOVAL IN A CONTINUOUS STIRRED BIOLOGICAL REACTOR

Abstract

In an aerobic waste water treatment process, aeration is the backbone of the proccess, which supplies oxygen In the form of air to the biological reactor, needed for COD removal. Surface aerators whose work is to create turbulence at the water surface are generally used for this purpose, so that oxygen transfer in the waste water from the air can be facilitated. For getting maximum efficiency from a surface aerator, it's proper design, placement and speed are very important factors, so that it can give maximum oxygen transfer utilizing minimum energy. In the present study the performance of—aerators was studied at various working conditions in a complete mixing biological waste treatment system, working continuously. Two standard types of agitators, were studied for the purpose namely 'flate blade turbine' and 'vaned disc turbine'. Effect of various speeds and submergences on COD removal was tested for both the agitators. It was found that with increasing speed COD removal efficiency of reactor increases but at very high speeds (above 100 rpm.), increase in speed had no appriciable improvement in efficiency. Also agitators worked best at zero submergence level. In general, flate blade turbine was found superiour than vaned disc turbine for maximum COD removal. Maximum COD removal obtained was 93.6% with flat blade turbine at zero submergance and 110 rpm speed, and 92% with vaned disc turbine at same operating conditions.