Electrochemical microsystem for continuous monitoring of nitrification activity of microbial complexes

Nitrification activity of a microbial complex was monitored continuously using a microdevice with integrated NH₄⁺ ion-selective electrodes. The device consisted of a glass substrate with sensing electrodes, polydimethylsiloxane (PDMS) substrates with chambers for cell culture and an internal electrolyte solution, and a polymethylmethacrylate (PMMA) substrate with NH₄⁺ ion-selective membranes. To stabilize the potential of Ag/AgCl electrodes used for sensing for a long time, a small current was flowed continuously between the Ag/AgCl electrode and a surrounding gold electrode to grow AgCl during the monitoring. The consumption of NH₄⁺ ions accompanying the nitrification of the active sludge was monitored for 48 h. Furthermore, signal molecule to promote the nitrification activity was examined using three acyl homoserine lactone molecules.