Nitrifying bacteria

Summary

Nitrifying bacteria are chemolithotrophic organisms that include species of genera such as Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira and Nitrococcus. These bacteria get their energy from the oxidation of inorganic nitrogen compounds. Types include ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Many species of nitrifying bacteria have complex internal membrane systems that are the location for key enzymes in nitrification: ammonia monooxygenase (which oxidizes ammonia to hydroxylamine), hydroxylamine oxidoreductase (which oxidizes hydroxylamine to nitric oxide - which is further oxidized to nitrite by a currently unidentified enzyme), and nitrite oxidoreductase (which oxidizes nitrite to nitrate). Ecology Nitrifying bacteria are present in distinct taxonomical groups and are found in highest numbers where considerable amounts of ammonia are present (such as areas with extensive protein decomposition, and sewage treatment plants)

Official source

https://en.wikipedia.org/wiki/Nitrifying_bacteria

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Optimization of Reactor Startup and Nitrogen Removal of Aerobic Granular Sludge Systems

Samuel Lochmatter

Aerobic granular sludge (AGS) in sequencing batch reactors (SBR) has recently made its proofs as full-scale technology for the biological treatment of urban wastewater. In contrast to conventional flocculent activated sludge, microorganisms aggregate to dense granular biofilm due to shear stress from aeration. Hence, AGS has much better settling characteristics and allows the construction of more compact wastewater treatment plants (WWTP) without secondary clarifiers. Due to diffusion limitations of oxygen through the biofilm, aerobic and anaerobic/anoxic zones coexist in AGS. Hence, AGS-SBR has the potential to treat organic matter (COD), nitrogen (N), and phosphorous (P) simultaneously in one single reactor. The focus of the present PhD thesis was on the startup of AGS-SBR and the optimization of biological nutrient removal (BNR). For the investigation of the optimal startup conditions, a study testing seven parameters in parallel was conducted. The main conditions identified for a rapid startup of AGS-SBRs with good nutrient removal performances were (i) the alternation of high and low dissolved oxygen (DO) phases during aeration, (ii) a settling strategy avoiding too high biomass washout, (iii) the adaptation of the pollution load in the early stage of the startup in order to ensure that all soluble COD was consumed before the aeration phase, (iv) higher temperature (20°C), and (v) a neutral pH. Under such conditions it took less than 30 days to produce granular sludge with high removal performances for COD, N and P. A control run of the best startup strategy led to very similar results, proving the reproducibility of the experimental approach. This control run was operated for 80 days without any problems concerning the stability of the granular sludge or the nutrient removal performances. Concerning the bacterial community composition during the startup phase, a general shift of the predominant populations from Intrasporangiaceae and Sphingobacteriales to Dechloromonas and Zoogloea was observed. This shift was mainly due to general conditions with lab-scale AGS-SBR, rather than the specific operation parameters tested in the different experimental runs. However, it has been observed that polyphosphate-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO) related populations were favored by the adaptation of the pollution load in the early stage of the startup in order to ensure that all soluble COD was consumed before the aeration phase. Besides the pollution load, the temperature and the pH had a significant impact on the global bacterial community structure. The predominant PAO were presumably Dechloromonas. In order to optimize BNR by AGS-SBR, different aeration strategies were tested. It has been concluded that the N-removal efficiency of COD-limited systems can be considerably enhanced with improved aeration strategies. Strategies promoting alternating nitrification and denitrification (AND) were significantly more efficient than simultaneous nitrification and denitrification (SND) strategies. The introduction of low DO phases or even anoxic phases in an early stage of the total aeration period probably enhanced denitrifying P-removal and led to COD savings. Intermittent aeration, which is a realistic AND strategy for full scale applications, led to the highest N-removal efficiency. The short mixing times implemented with this strategy were not problematic for the stability of the granules. Finally, to further optimize N-removal in COD-limited systems, the potential of aeration control for the achievement of N-removal over nitrite was investigated. It was shown that aeration phase length control combined with intermittent aeration or alternating high-low DO, is an efficient way to achieve N-removal over nitrite. N-removal efficiencies of up to 95% were achieved with this way of reactor operation. At 20°C, N-removal over nitrite was achieved within 20 – 60 days and it was possible to switch from N-removal over nitrite to N-removal over nitrate and back again. At 15°C, the nitrite-oxidizing bacteria population could be reduced, but nitrite oxidation could not be completely repressed. However, the combination of aeration phase length control and high-low DO was successful to maintain the nitrite pathway at 15°C where the maximum growth rate of nitrite-oxidizing bacteria is clearly higher than the one of ammonium-oxidizing bacteria. In conclusion, this thesis showed the potential of the optimization of operation conditions for the startup of AGS-SBR and BNR. An efficient strategy for the startup with flocculent inoculum sludge has been developed, maintaining high BNR. Moreover, it has been shown that N-removal under COD-limited conditions can be improved by aeration control, either by enhancing denitrifying P-removal or achieving N-removal over nitrite.

EPFL2013

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

• Goal The goal of the project was to produce biomolecular fingerprints in order to describe the structure of microbial community which develops during aerobic sludge granulation, initiated in sequencing batch wastewater treatment processes. Four SBR were run under different conditions of cultivation. Pulse and anaerobic feeding modes were applied, as well as mesophilic (20-30 ° C) and thermophilic (50 °C) conditions. Analytical methods of microscopy and molecular biology have been adapted to this purpose : optical microscopy, DNA extraction, polymerase chain reaction (PCR), gel electrophoresis, terminal restriction fragment length polymorphism (T¬RFLP), cloning and sequencing of fragments of Eubacteria 16S rRNA encoding genes. These analytical tools were applied to the characterization of the microbial architecture of the different states of the biomass present within the biosystems, such as dense and well settling granules, fluffy and non settling granules, suspended flocs and wall biofilms. • Results The inoculum of Morges municipal WWTP was containing a majority of heterotrophic bacteria, inducing a non optimal quality of aerobic granules and a low performance in the simultaneous removal of carbon, ammonium and phosphates. The optical microscopic analysis have shown that well settling granules possess a compact inner architecture, while fluffy granules, which are washed out of the SBRs, are mainly composed of filamentous bacteria. Yeast-like fungi were also detected by PCR/Gel electrophoresis in fluffy granules as well as in compact granules. Archaea bacteria were not present in the cultivated aerobic granules. The T-RFLP fingerprints of well settling granules and non settling consortiums include the same major terminal restriction fragment (TRF, in bases pairs) of Eubacteria 16S rDNA : after HaeIII digestion, TRF (74, 198, 211, 217 and 255 bp) were detected in pulse feeding mesophilic mode, and TRF (196, 198, 210, 214, 217, 245 and 321 bp) were detected in anaerobic feeding mesophilic mode. T-RFLP fingerprints were useful for the study of the temporal evolution of aerobic granules. Heterotrophic eubacterial species linked to TRF 198 bp are predominant in compact granules, while heterotrophic filamentous eubacterial species linked to TRF 210-211 bp are predominant in filamentous granules. The analysis of the presence of nitrifying bacteria is currently in progress, as well as cloning and sequencing of fragments of Eubacteria 16S rRNA encoding genes. • Conclusion The quality of the inoculum seems to be an operational key parameter. It should contain heterotrophic, nitrifying and phosphate-accumulating bacteria to allow their growth in multi-layered granules, competent for simultaneous C-, N- and P-removal. Analysis of scanning electron microscopy (SEM) and fluorescence in situ hybridization (FISH) coupled to confocal microscopy have to be pursued to localise the microbial layers and functions in the deepness of aerobic granules architecture. The development, the application and the use of biomolecular identity cards (fingerprinting) constitute an essential tool for following and anticipating the evolution of one aerobic granulation process, and to describe the relationship between the different microbial layers.

2006