Biochemical Oxygen Demand Microelectrode for Quantifying Concentration Gradients in Anaerobic Biofilms

Abstract

Biochemical oxygen demand (BOD) is one of the widely used parameter to determinate the level of organic pollution in water. The standard method, BOD5 assay, is commonly used to measure BOD concentration but it takes a long time and cannot be integrated for online measurements. Additionally, BOD5 cannot be used to measure BOD in microscale systems, especially in anaerobic biofilms where the oxygen is absent. Because of the limitation of available tools for quantifying BOD concentration within anaerobic biofilms, a new, simple and miniaturized tool is needed for measuring local BOD concentrations in biofilms. The goal of this work is to develop a BOD microelectrode for quantifying concentration gradients in anaerobic biofilms. The developed BOD microelectrode uses an anaerobic mixed-culture-anodic biofilm as a transducer, which is grown on a carbon fiber tip diameter. The carbon fiber microelectrode acts as the working electrode, which is polarized using a potentiostat. A 100 µm platinum wire counter electrode and a Ag/AgCl-wire pseudo reference electrode are used to complete the electrochemical cell. The BOD microelectrode components are enclosed in a glass outer case. The BOD microelectrodes were calibrated using a standard BOD solution. The performance of the BOD microelectrode was assessed including response time and the linear BOD concentration range. Finally, concentration profiles in an anaerobic biofilm were measured to demonstrate its use.