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As an example of the importance and the potential of in situ structure/function studies, nitrifying aggregates from different zones of a lab-scale fluidised bed reactor were analysed by microelectrode measurements of O2, NH4+, NO2−, and NO3− and in situ hybridisation targeting the 16S rRNA of the nitrifying bacteria. A shift from an ammonia oxidising to a nitrite oxidising community is present along the reactor. In the single aggregates an active nitrifying shell of about 100 μm could be related to the maximum abundance of nitrifiers in this zone. Interestingly, the main actors in this system are not representatives of the well-described genera Nitrosomonas and Nitrobacter but some other ammonia oxidisers from the beta subclass of Proteobacteria and a thus far unknown nitrite oxidising population.

As an example of the importance and the potential of in situ structure/function studies, nitrifying aggregates from different zones of a lab-scale fluidised bed reactor were analysed by microelectrode measurements of O2, NH4+, NO2−, and NO3− and in situ hybridisation targeting the 16S rRNA of the nitrifying bacteria. A shift from an ammonia oxidising to a nitrite oxidising community is present along the reactor. In the single aggregates an active nitrifying shell of about 100 μm could be related to the maximum abundance of nitrifiers in this zone. Interestingly, the main actors in this system are not representatives of the well-described genera Nitrosomonas and Nitrobacter but some other ammonia oxidisers from the beta subclass of Proteobacteria and a thus far unknown nitrite oxidising population.

Subject of discussion : “Studies on less defined wastewater treatment systems” versus “More fundamental research on biofilm processes”.

A glucose oxidase-based needle-type microsensor is described that is independent of the local oxygen concentration. The sensor consists of an enzyme-coated platinum microelectrode that is inserted in a glass capillary with a tip of 5–25 μm, and connected to the environment via an agar membrane. Oxygen is supplied to the enzyme coating from the shaft of the capillary. Depending on the electrode configuration, the sensor has a response time of 1–10 s, and the measuring range extends from 0.01 to 0.4 mmol l −1 or from 0.4 to 10 mmol l −1 . The signal is not affected by stirring.