Oxygen transfer in trickling filters

Insufficient oxygen transfer can result in anaerobic biofilms and odor generation during biochemical oxygen demand (BOD) removal in trickling filters, and can limit ammonia oxidation in nitrifying trickling filters. Since oxygen transfer to biofilms in plastic media trickling filters occurs by diffusion of oxygen through thin fluid films, previous models used solutions based on penetration theory to calculate BOD removal. However, it is shown in this paper that penetration theory is not valid for typical hydraulic conditions in trickling filters since oxygen can diffuse through the fluid film and reach the biofilm surface. As a result, numerical solutions are required to solve the equations describing oxygen mass transport to the biofilm. Computer models are therefore used to calculate the maximum oxygen transfer during BOD and ammonia oxidation in plastic media trickling filters. These models can be used by design engineers to minimize conditions that may cause odor generation in trickling filters, and to provide an upper limit to the efficiency of nitrifying trickling filters.