Fast responding biosensor for on-line determination of nitrate/nitrite in activated sludge

A microscale biosensor for nitrate/nitrite was used for in-situ monitoring in an activated sludge plant. The biosensor is based on diffusion of nitrat e/nitrite through a tip membrane into a dense mass of bacteria converting t he ions into nitrous oxide with subsequent electrochemical detection. The b iosensor signal was in very close agreement with the nitrate/nitrite concen tration in the plant as analysed by conventional laboratory techniques. The concentration of the only interfering substance, nitrous oxide, was so low that it did not have any effect. The response time of the applied biosenso rs was less than 30 s, and the detection limit was less than 50 mu g N l(-1 ). Detachment of the ion-permeable membrane in the tip ol these first-gener ation biosensors limited the period with continuous monitoring to 5 days. ( C) 2000 Elsevier Science Ltd. All rights reserved.