1. Field of the Invention
This invention relates to a process and apparatus for enhancing the growth of biomass within a reaction vessel and, in particular, enhancing biomass growth in reaction vessels which handle effluent and sewage.
2. Discussion of the Prior Art
In recent years, a process for treating industrial effluent and sewage involving the use of biomass support bodies has shown itself as an attractive alternative to the conventional activated sludge treatment process. In the conventional process, sewage or industrial effluent in a reaction vessel is aerated and agitated to stimulate the metabolism of a biological population within the vessel with various impurities in the effluent. The secondary sludge produced by this interaction is removed by sedimentation
In the biomass support body process, the reaction vessel is a vertical structure and it contains a number of free moving biomass support bodies Effluent and air are introduced at the base of the vessel and, as the effluent is oxygenated and propelled upward by the air, the biological population in the biomass support bodies reacts with the oxygenated effluent to produce carbon dioxide and additional biomass. This process is described in detail in U.S. Pat. No. 4,419,243 which also describes a suitable apparatus for accomplishing the process.
The biomass support body process has demonstrated that the capacity of the reaction vessel used in the process for a given through flow of effluent can be approximately one fifth of that of a conventional aeration tank and so the process offers commensurate savings in the cost of an effluent treatment plant. However, even more savings could be achieved if the critical variables of the biomass growth process, such as the pH level, control of recirculated solids and control of biomass populations, could be more precisely controlled. Additionally, it would be desirable to completely control the movement of the biomass support bodies through the vessel independent of the flow of effluent as opposed to relying on the upward flow of the effluent to suspend or fluidize the bodies, as is required in the existing biomass support processes. Furthermore, a wider choice of materials and construction of the support bodies could be available if there were no requirement that biomass support bodies be suspended or fluidized.