Nitrification | EPFL Graph Search

Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea. Microbiology Ammonia oxidation The oxidation of ammonia into nitrite (also known as nitritation) is performed by two groups of organisms, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). AOB AOB can be found among the Betaproteobacteria and Gammaproteobacteria. In soils the most studied AOB belong to the genera Nitrosomonas and Nitrococcus. AOA Since discovery of AOA in 2005, two isolates have been cultivated: Nitrosopumilus maritimus and Nitrososphaera vi

Inactivation of pathogens in urine nitrification reactors

Ariane Schertenleib

Through nutrient recovery by urine separation, the VUNA project aims to develop an effective sanitation system that simultaneously helps address important issues such as environmental pollution and water scarcity. Refinement of the nutrient recovery process presents several challenges: at a technical level, as nitrifying bacteria are sensitive to several parameters; and from a public health perspective, as nutrient recovery from urine implies exposure to pathogens. As part of this problematic, the present study focused on four main objectives: operating nitrification reactors, characterising both virus and bacteria inactivation, and evaluating different inactivation mechanisms. Indicator organisms (bacteriophages and bacteria) were used as surrogates for human pathogens. In a first set of experiments, the bacteriophage MS2 was spiked continuously over 60 days in a continuous flow nitrification reactor. Nitrification did not affect the bacteriophage concentration within the reactor. The second set of experiments consisted of the operation of small scale batch and semi-batch reactors to test in total three different bacteriophages (X147, MS2, Qbeta) and two bacteria (Salmonella typhimerium, Enterococcus spp.) under varying parameters. Pathogens can be inactivated or affected by different mechanisms. Four possible inactivation mechanisms were further evaluated: 1) effect of biological activity in a nitrification treatment system, 2) effect of the air-water interface in a buffer (PBS) and nitrified urine, 3) effect of the complexity of solution, 4) effect of ambient temperature. Results indicated that nitrification caused bacterial inactivation but did not influence the bacteriophages concentration. Air-water interface did not affect bacteria and showed mixed results for bacteriophages. Ambient temperature was not an inactivating parameter for neither of the groups studied. Finally, the bacteriophages presented signs of resistance, possibly due to a protective effect of the complex solution in the nitrification reactor.

2014

Technologies for the treatment of source-separated urine in the eThekwini Municipality

Bastian Etter, Tamar Kohn, Linda Strande, Kai Udert

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.

2015

Inactivation kinetics and mechanisms of viral and bacterial pathogen surrogates during urine nitrification

Tamar Kohn, Ariane Schertenleib, Kai Udert

This paper assesses the inactivation performance and mechanisms in urine nitrification reactors using bacteria and bacteriophages as surrogates for human pathogens. Two parallel continuous-flow moving bed biofilm reactors (MBBRs) were operated over a two-month period. One MBBR was used to conduct a continuous spike experiment with bacteriophage MS2. The second reactor provided the matrix for a series of batch experiments conducted to investigate the inactivation of Salmonella typhimurium, Enterococcus spp., MS2, Q beta, and Phi X174 during urine nitrification. The roles of aeration, biological activity, and solution composition in inactivation were evaluated. Whereas bacteriophages FX174 and MS2 remained infective following urine nitrification, partial inactivation of bacteriophage Q beta was observed. Q beta inactivation was attributed primarily to aeration with a potential additive effect of biological processes, i.e., processes that are attributable to the presence of other microorganisms such as sorption to biomass, predation or enzymatic activity. Tailing of Q beta inactivation to a plateau indicated a protective effect of the solution components in aerated nitrification reactors. In contrast to the bacteriophages, S. typhimurium and Enterococcus spp. were mainly affected by biological processes: they were inactivated in biologically active nitrification reactors while remaining stable in chemically equivalent filtered controls. The tested bacteria could, for example, be out-competed by other microbial communities or sorbed to biomass in the reactor. Microbial communities did not adapt to inactivate bacteriophage MS2 (e.g., via increased prevalence of virus predators) in the experimental time-scale evaluated, with no observed inactivation of MS2 during continuous input for 51 days in the flow-through MBBR. The compilation of these results suggests that biological nitrification as a fertilizer production process remains insufficient as a stand-alone technology for the sanitization of source-separated urine.

Royal Soc Chemistry2015