Aeration Requirements of Bisolids Lysis and Modified Recycle in the Activated Sludge System, 2002 Environmental Conference Proceedings

H. B. Claus and A. Springer

If the excess biological solids produced in the activated sludge process could be recycled back into the system and used as a food source, sludge disposal costs could be significantly reduced. The Kady Mill has been shown as a potentially effective method for sludge lyse and recycle in the activated sludge process. The main thrust of this research was to determine the oxygen requirement and the variables that affect the oxygen transfer coefficient changes in the sludge lyse and recycle process. Originally it was assumed that the sludge lyse and recycle process would consume more oxygen due to the increase in the BOD load to the system. The stiochiometry of BOD removal dictates this to be true. For an additional load of 25% organic matter should require 25% more oxygen to accomplish the decomposition. However, not all organisms are equally efficient, and the decomposition environment makes a difference. In full-scale studies utilizing the lyse and recycle system, additional aeration power did not seem to be required. This thesis explores whether or not there is an increase in the oxygen requirement with the sludge lyse and recycle process. New bio-oxidation units manufactured by Challenge Environmental Inc. were used in this work because the units enable the oxygen uptake rate to be measured. Biological floc counts and measurements were made in an effort to relate the change in oxygen uptake rate to the difference that was seen in the oxygen transport coefficient.

Several conclusions could be made from this research. There is an additional oxygen requirement, but it is compensated for by an increase in aeration efficiency and an improvement in the degradation environment. Something must be released in the lysis process which influences the mass transfer coefficient (KLa). There was a 14% decrease in the specific oxygen uptake rate (SOUR) and a 30% increase in the oxygen transport coefficient (KLa) with the sludge lyse and recycle activated sludge system compared to the conventional system. These effects can be rationalized by the particle size reduction effect which makes the floc more aerobic. A 17% decrease in the average floc size diameter was measured in the sludge lyse and recycle unit. An 84% sludge yield reduction was measured in the unit operated in the sludge lyse and recycle mode compared to the conventional activated sludge unit.