Kinetics, diffusional limitation and microscale distribution of chemistry and organisms in a CANON reactor.

In the Completely Autotrophic Nitrogen removal Over Nitrite (CANON) process, aerobic and anaerobic ammonia oxidizing bacteria cooperate to remove ammonia in one oxygen-limited reactor. Kinetic studies, microsensor analysis, and fluorescence in situ hybridization on CANON biomass showed a partial differentiation of processes and organisms within and among aggregates. Under normal oxygen-limited conditions ( approximately 5 microM O2), aerobic ammonia oxidation (nitrification) was restricted to an outer shell (<100 microm) while anaerobic ammonia oxidation (anammox) was found in the central anoxic parts. Larger type aggregates (>500 microm) accounted for 68% of the anammox potential whereas 65% of the nitrification potential was found in the smaller aggregates (<500 microm). Analysis with O2 and NO2- microsensors showed that the thickness of the activity zones varied as a function of bulk O2 and NO2- concentrations and flow rate.

New concepts of microbial treatment processes for the nitrogen removal in wastewater.

Many countries strive to reduce the emissions of nitrogen compounds (ammonia, nitrate, NOx) to the surface waters and the atmosphere. Since mainstream domestic wastewater treatment systems are usually already overloaded with ammonia, a dedicated nitrogen removal from concentrated secondary or industrial wastewaters is often more cost-effective than the disposal of such wastes to domestic wastewater treatment. The cost-effectiveness of separate treatment has increased dramatically in the past few years, since several processes for the biological removal of ammonia from concentrated waste streams have become available. Here, we review those processes that make use of new concepts in microbiology: partial nitrification, nitrifier denitrification and anaerobic ammonia oxidation (the anammox process). These processes target the removal of ammonia from gases, and ammonium-bicarbonate from concentrated wastewaters (i.e. sludge liquor and landfill leachate). The review addresses the microbiology, its consequences for their application, the current status regarding application, and the future developments.

Aerobic and anaerobic ammonia oxidizing bacteria--competitors or natural partners?

The biological nitrogen cycle is a complex interplay between many microorganisms catalyzing different reactions. For a long time, ammonia and nitrite oxidation by chemolithoautotrophic nitrifiers were thought to be restricted to oxic environments and the metabolic flexibility of these organisms seemed to be limited. The discovery of a novel pathway for anaerobic ammonia oxidation by Planctomyces (anammox) and the finding of an anoxic metabolism by 'classical'Nitrosomonas-like organisms showed that this is no longer valid. The aim of this review is to summarize these novel findings in nitrogen conversion and to discuss the ecological importance of these processes.