Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway and a cost-effective way to remove ammonium from wastewater. Anammox bacteria have been described as obligate chemolithoautotrophs. However, many chemolithoautotrophs (i.e., nitrifiers) can use organic compounds as a supplementary carbon source. In this study, the effect of organic compounds on anammox bacteria was investigated. It was shown that alcohols inhibited anammox bacteria, while organic acids were converted by them. Methanol was the most potent inhibitor, leading to complete and irreversible loss of activity at concentrations as low as 0.5 mM. Of the organic acids acetate and propionate, propionate was consumed at a higher rate (0.8 nmol min ؊1 mg of protein ؊1 ) by Percoll-purified anammox cells. Glucose, formate, and alanine had no effect on the anammox process. It was shown that propionate was oxidized mainly to CO 2 , with nitrate and/or nitrite as the electron acceptor. The anammox bacteria carried out propionate oxidation simultaneously with anaerobic ammonium oxidation. In an anammox enrichment culture fed with propionate for 150 days, the relative amounts of anammox cells and denitrifiers did not change significantly over time, indicating that anammox bacteria could compete successfully with heterotrophic denitrifiers for propionate. In conclusion, this study shows that anammox bacteria have a more versatile metabolism than previously assumed.Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway in the biological nitrogen cycle (9, 27) and a new cost-effective way to remove ammonia from wastewater (3, 6, 15, 16, 21, 22 34, 35). Anammox is carried out by the planctomycetes Candidatus "Brocadia anammoxidans" and Candidatus "Kuenenia stuttgartiensis" and several species of the genus Candidatus "Scalindua" (2,7,8,19,20). Nitrite is the electron acceptor for the anaerobic oxidation of ammonia to dinitrogen gas, and hydrazine is an important intermediate (32). Anammox bacteria have been described as strictly autotrophic, fixing CO 2 with nitrite as the electron donor, leading to the anaerobic production of nitrate (25, 33). The overall nitrogen balance showed a ratio of 1:1.32:0.26 for the conversion of ammonium and nitrite and the production of nitrate (26). The overall anammox reaction is presented in equation 1. Many other chemolithoautotrophs (i.e., nitrifiers) can grow mixotrophically; they can use organic compounds as a supplementory carbon source. This property is advantageous because mixotrophic growth can increase the growth rate and/or yield. In the case of anammox, this is especially advantageous, because both the growth rate (doubling time of 10 to 20 days) and yield (0.066 CO 2 fixed per mol of NH 4 ϩ ) are very low. Previously, it was found that some organic compounds inhibit anammox (32). In this study, the effects of organic compounds on the anammox bacteria and the potential for mixotrophic growth were investigated in detail. In experiments with anammox enrichment cultures an...

In the anaerobic ammonium oxidation (anammox) process, ammonia is oxidized with nitrite as primary electron acceptor under strictly anoxic conditions. The reaction is catalysed by a specialized group of planctomycete-like bacteria. These anammox bacteria use a complex reaction mechanism involving hydrazine as an intermediate. The reactions are assumed to be carried out in a unique prokaryotic organelle, the anammoxosome. This organelle is surrounded by ladderane lipids, which make the organelle nearly impermeable to hydrazine and protons. The localization of the major anammox protein, hydrazine oxidoreductase, was determined via immunogold labelling to be inside the anammoxosome. The anammox bacteria have been detected in many marine and freshwater ecosystems and were estimated to contribute up to 50% of oceanic nitrogen loss. Furthermore, the anammox process is currently implemented in water treatment for the low-cost removal of ammonia from high-strength waste streams. Recent findings suggested that the anammox bacteria may also use organic acids to convert nitrate and nitrite into dinitrogen gas when ammonia is in short supply.

Stringent standards for nitrogen discharge necessitate the implementation of new systems for the sustainable removal of ammonium from wastewater. One of such systems is based on the process of anaerobic ammonium oxidation (Anammox), which is a new powerful tool especially for strong nitrogenous wastewaters. In this study, the Anammox process performance was tested with synthetic wastewater in a completely stirred tank reactor (CSTR). The reactor was operated for 511 days and fed with increasing amounts of ammonium and nitrite. In this period, an increase of ammonium and nitrite utilization rates were observed as a result of the increase of nitrogen loads in the influent. After 272 days, about 60% of the biomass was removed from the reactor and the system was restarted. Throughout 511 days 90% of the ammonium and more than 99% of the nitrite were converted mainly to dinitrogen (N2) and nitrate. The microbial community in the reactor was characterized with Fluorescence in situ Hybridization (FISH). The study showed that the population in the reactor was dominated by the deep-branching planctomycete Candidatus "Brocadia anammoxidans" strain Dokhaven 2.

Ion exchange using clinoptilolite for the removal of peak concentrations of ammonia from domestic wastewater as a second stage, by itself and in combination with sand filters, is evaluated. It is observed that there is no significant loss of capacity of clinoptilolite when placed in sand filters. All three configurations studied are successful in the removal of peak concentrations of ammonia, and hence can be used as a polishing unit, to comply with the demands of stringent standards. Among those investigated, the combined scheme, with clinoptilolite and aerated sand filters where biological activity is enhanced, is found to be the most effective provided that sufficient time for the development of nitrifiers are allowed. The performance loss of the clinoptilolite was observed to be 10% after 10 cycles of regular operation and regeneration.

Stringent effluent limitations for nitrogen necessitate an accurate interpretation of the design and operation conditions of biological nitrogen removal systems. In this study, the effects of the nature of the organic substrate on biomass adaptation and response to different C/N ratios in terms of denitrification efficiency were investigated. A relatively high chemical oxygen demand (COD) utilized /NO x -N reduced ratio of 8.1 was obtained when an excess amount of readily biodegradable carbon was supplied, which is suggested as the conversion of substrate surplus into storage polymers. An anoxic yield of 0.64 g cell COD/g COD for a four-compound substrate mixture (acetate, propionate, ethanol and glucose), 0.63 g cell COD/g COD for a two-compound substrate mixture (acetate and propionate), and 0.5 g cell COD/g COD for methanol were calculated. Fluorescence in situ hybridization analysis showed that the b-subclass of proteobacteria was dominant in the seed and in cultures adapted to both the fourcompound and the two-compound substrate mixture, whereas in the methanoladapted culture significant amounts of b-proteobacteria were detected. The biocommunity composition, the type of organic compound and the COD/NO 3 -N ratio strongly influence the nitrate reduction and carbon utilization profiles. Methanol has been shown to select for a denitrifying population consisting of Paracoccus and Hyphomicrobium vulgare genera, when used as only external carbon source.

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