A FIELD STUDY ON OXYGEN PENETRATION IN WASTEWATER BIOFILMS

Due to the importance of oxygen in biofilm reactors for wastewater treatment, a lot of laboratory studies have been done so far on oxygen transfer in biofilms. However, no field study in this area has ever been reported yet. In order to disclose how oxygen penetrates in biofilms in full-scale wastewater treatment systems and to collect experimental evidence to verify results of laboratory studies, a field study was conducted using a unique oxygen microelectrode. In this study, in-situ oxygen measurements in biofilms were conducted directly under field conditions at each stage in two typical 4-stage rotating biological contactor (RBC) systems for municipal wastewater treatment. All experimental results have shown the existence of oxygen depletion phenomenon in the biofilms under field conditions and the partial oxygen penetration took place even under a favorable condition in terms of oxygen availability. It was observed that among all biofilm oxygen profile measurements in this field study, only a shallow depth, less than 0.6 mm, in the biofilms was penetrated by oxygen. Significant influence on oxygen penetration depth from the location of oxygen measurement on the biofilms has indicated the heterogeneous nature of the biofilm structure. The length of the operation time of the biofilm reactor appeared to have impacts on oxygen penetration in the biofilms. The longer the operational period of the biofilm reactor, the shallower the oxygen penetration depth in the biofilms. This correlation needs further verification in study under well-controlled conditions though.