Development of an automation system to evaluate the three-dimensional oxygen distribution in wastewater biofilms using microsensors

In this paper the authors describe the development of an automation system applicable to environmental biofilm studies. The automation system controls a combined oxygen microsensor to measure the three-dimensional dissolved oxygen distribution in a wastewater biofilm sample. The biofilm is sampled from a rotating biological contactor in a municipal wastewater treatment plant. The automation system consists of a data acquisition system, a motion control system, and a computer program. The combined oxygen microsensor consists of a sensing electrode, a reference electrode, a guard cathode, an oxygen permeable membrane, and an electrolyte solution. The automation system allows the acquisition and storage of data from 4000 measurements from the microsensor and the precise positioning of the microsensor in order to measure 100 dissolved oxygen profiles in a 1000 μm × 1000 μm biofilm area. The three-dimensional profile shows that the dissolved oxygen concentration in the biofilm sample is highly heterogeneous and it revealed “pockets” of dissolved oxygen in deep sections of the biofilm sample. The automation system and the combined oxygen microsensor were proven to be tools that improve the quantity and quality of experimental results needed to understand important functions in biofilms used in wastewater treatment.