Oxygen transfer in trickling filters

Abstract

Very little is known about oxygen transfer in trickling filters. Oxygen transfer in trickling filters must be studied in correlation with hydrodynamics. We suggest a method to quantify oxygen transfer in such a system. The hydrodynamics is studied using a random plastic media when it is clean and when it is covered with biomass. Concerning oxygen transfer, different equations may be proposed depending on the hydraulic model: plug flow or axial dispersion. These equations must be solved by successive iterations to find the oxygen transfer coefficient and finally the oxygen transfer performance expressed in kgO 2/kWh. Another way to quantify gas transfer in the presence of biochemical reaction is to utilize a tracer gas. Propane was used in our experiments. On clean media the results give an oxygen transfer performance of 2 kg O 2/kWh. The results are similar for the plug flow model and for the axial dispersion model. When the biomass respiration is endogeneous, the oxygen balance on the tower results in a much greater oxygen transfer performance, the minimum calculated is 22 kg O 2/kWh. We must consider that in this case oxygen transfer is amplified, by around a factor of 10, due to biomass respiration. Unfortunately there is another fact that seems contradictory to those experimental measurements. The liquid at the outlet of the tower is generally saturated with oxygen. This state of saturation should be incompatible with an enhancement factor for oxygen transfer greater than 1. Our explanation is proposed based on hydrodynamics.