The two-stage anaerobic-aerobic treatment is applied by preference for the purification of high-concentrated industrial wastewaters. With regard to the elimination of nitrogen compounds by denitrification the far-reaching reduction of organic carbon during the anaerobic pre-treatment is problematic. A new process of nitrification/denitrification via nitrite wais found to be available in half-technical experiences with high operation security. The carbon consumption amounts only to 60 % in comparison with denitrification via nitrate. The essential parameter for regulating the process is the concentration of free ammonia in the reactor. Concentrations of 1 to 5 mg NH3/l inhibit the nitratation but not the nitritation. The content of ammonia was controlled by means of continuous NH4− and pH-measuring. The inhibition limit for denitrification was found to be at 0.13 mg HN02/l.

In full scale wastewater treatment plants with at times considerable deficits in the nitrogen balances, it could hitherto not be sufficiently explained which reactions are the cause of the nitrogen losses and which micro-organisms participate in the process. The single stage conversion of ammonium into gaseous end-products--which is henceforth referred to as deammonification--occurs particularly frequently in biofilm systems. In the meantime, one has succeeded to establish the deammonification processes in a continuous flow moving-bed pilot plant. In batch tests with the biofilm covered carriers, it was possible for the first time to examine the nitrogen conversion at the intact biofilm. Depending on the dissolved oxygen (DO) concentration, two autotrophic nitrogen converting reactions in the biofilm could be proven: one nitritation process under aerobic conditions and one anaerobic ammonium oxidation. With the anaerobic ammonium oxidation, ammonium as electron donor was converted with nitrite as electron acceptor. The end-product of this reaction was N2. Ammonium and nitrite did react in a stoichiometrical ratio of 1:1.37, a ratio which has in the very same dimension been described for the ANAMMOX-process (1:1.31 +/- 0.06). Via the oxygen concentration in the surrounding medium, it was possible to control the ratio of nitritation and anaerobic ammonium oxidation in the nitrogen conversion of the biofilm. Both processes were evenly balanced at a DO concentration of 0.7 mg/l, so that it was possible to achieve a direct, almost complete elimination of ammonium without addition of nitrite. One part of the provided ammonium did participate in the nitritation, the other in the anaerobic ammonium oxidation. Through the aerobic ammonium oxidation into nitrite within the outer oxygen supplied layers of the biofilm, the reaction partner was produced for the anaerobic ammonium oxidation within the inner layers of the biofilm.

Several aspects of using ashes from sewage sludge incineration in the brick and tile industry have been examined. After discussing the item of ash production in Germany, the impact of different wastewater treatment methods is described; for instance, the use of precipitation agents containing iron will considerably influence the ash quality. Depending on their respective chemical composition, different ashes have different effects on the ceramic qualities of the bricks made of clay blended with ashes. These effects will be shown in regard to the major ceramic parameters. Similarly, the quality of the ashes also influences the elution behaviour and the mineral fixation of heavy metals.

The leachate treatment plant of the landfill in Mechernich including biological pretreatment, reverse osmosis and evaporation and drying of the concentrate has been in operation since the beginning of 1994. Balancing the nitrogen transformations in the biological contactor plant as the nitrification step in the biological pretreatment, a large amount of the ammonium can be eliminated under aerobic conditions by deammonification. It succeeded obviously under the special conditions to establish a non-negligible amount of denitrifying ammonia oxidants. Experiences concerning this effect were described several times in the past.

For the development of alternative concepts for the cost effective treatment of wastewaters with high ammonium content and low C/N-ratio, autotrophic consortia of micro-organisms with the ability to convert ammonium directly into N2 are of particular interest. Several full-scale industrial biofilm plants eliminating nitrogen without carbon source for years in a stable process, are suspected for some time to harbor active anaerobic ammonium oxidizers in deeper, oxygen-limited biofilm layers. In order to identify the processes of the single-stage nitrogen elimination (deammonification) in biofilm systems and to allocate them to the responsible micro-organisms, a deammonifying moving-bed pilot plant was investigated in detail. 15N-labelled tracer compounds were used as well as 16S rDNA libraries and in situ identification of dominant organisms. The usage of rRNA-targeted oligonucleotide probes (FISH) was particularly emphasized on the ammonium oxidizers of the beta-subclass of Proteobacteria and on the members of the order Planctomycetales. The combined application of these methods led to a deeper insight into the population structure and function of a deammonifying biofilm.