Activity Of Ammonia-oxidizing Bacteria Research Articles

Effects of the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate on Nitrification and Nitrifiers in Two Contrasting Agricultural Soils

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N2O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a (15)N tracing and (13)CO2-DNA-stable-isotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N2O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The (15)N tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The (13)CO2-DNA-SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of (13)CO2 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter. The combination of the (15)N tracing model and (13)CO2-DNA-SIP technique provides important evidence that the nitrification inhibitor DMPP could effectively inhibit nitrification and nitrous oxide emission in an alkaline soil through influencing the abundance and metabolic activity of AOB. In contrast, DMPP amendment has no significant effect on nitrification or nitrifiers in an acidic soil, potentially owing to the low abundance of AOB and the possible adsorption of DMPP by organic matter. Our findings have direct implications for improved agricultural practices through utilizing the nitrification inhibitor DMPP in appropriate situations, and they emphasize the importance of microbial communities to the efficacy of DMPP.

Retraction Note to: Archaeal amoA Genes Outnumber Bacterial amoA Genes in Municipal Wastewater Treatment Plants in Bangkok.

The contribution of ammonia-oxidizing archaea (AOA) to nitrogen removal in wastewater treatment plants (WWTPs) remains unknown. This study investigated the abundance of archaeal (AOA) and bacterial (ammonia-oxidizing bacteria (AOB)) amoA genes in eight of Bangkok’s municipal WWTPs. AOA amoA genes (3.28 × 107 ± 1.74 × 107–2.23 × 1011 ± 1.92 × 1011 copies l−1 sludge) outnumbered AOB amoA genes in most of the WWTPs even though the plants’ treatment processes, influent and effluent characteristics, removal efficiencies, and operation varied. An estimation of the ammonia-oxidizing activity of AOA and AOB suggests that AOA involved in autotrophic ammonia oxidation in the WWTPs. Statistical analysis shows that the numbers of AOA amoA genes correlated negatively to the ammonium levels in effluent wastewater, while no correlation was found between the AOA amoA gene numbers and the oxygen concentrations in aeration tanks. An analysis of the AOB sequences shows that AOB found in the WWTPs limited to only two AOB clusters which exhibit high or moderate affinity to ammonia. In contrast to AOB, AOA sequences of various clusters were retrieved, and they were previously recovered from a variety of environments, such as thermal and marine environments.

Nitrogen mineralization as a result of phosphorus supplementation in long-term phosphate deficient soil

In red soil (with pH ≤6), high phosphorus deficiency hinders soil carbon and nitrogen cycling, and thus reduces plant nutrient use efficiency in terrestrial system. In this study, inorganic phosphate addition could accelerate litter nitrogen release and soil nitrogen mineralization through stimulating soil urease and dehydrogenase enzymatic activities. The abundance and composition of mineral N transforming genes with three levels of phosphate were assayed using quantitative real-time PCR and denaturing gradient gel electrophoresis. Soil ammonia-oxidizing bacteria (AOB) were sensitive to the inorganic phosphate supplementation level: P addition at levels lower than 25mgkg−1 accelerated soil nitrification via increased AOB activity. However, as the P level reached 50mgkg−1, higher levels of soil ammonium nitrogen from litter decomposition remained in the soil through a decrease in the activities of N-mineralization enzymes and the stabilization of the AOB community structure. Our results emphasize the importance of reasonable concentrations of P fertilization for accelerating litter N mineralization and avoiding N leaching in plant litter-amended soil where phosphate is deficient.

3,4-Dimethylpyrazole phosphate (DMPP) reduces activity of ammonia oxidizers without adverse effects on non-target soil microorganisms and functions

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is widely used within agriculture to reduce nitrate leaching and improve nitrogen use efficiency of fertilizers, but few studies examined effects on non-target soil functions and microorganisms, i.e. other than the intended delay of ammonia oxidation. We investigated effects of DMPP amendment equivalent to 0 (Control), 1 (regular dose, RD) or 10 (high dose, HD) kgha−1 in a sandy loam grassland soil at 50% water-filled pore space. Following incubation for 1, 7 or 14 d, soil was analyzed for fluorescein diacetate hydrolysis, dehydrogenase activity, phospholipid fatty acid composition and potential ammonia oxidation. DMPP showed no significant non-target effects (p>0.05), but a possible stress response in HD was indicated by a factor analysis of phospholipid fatty acid composition. There was a strong DMPP inhibition on potential ammonia oxidation which was still significant (p<0.05) in HD after 14 d. In separate treatments receiving 50mg NH4+-Nkg−1 dry soil in addition to DMPP, the inhibition of nitrate accumulation was similar in RD and HD at around 75%. Abundances of the gene amoA from ammonia oxidizing bacteria (AOB) and archaea (AOA) were quantified, and cell-specific nitrification rates were estimated. There was a general trend of increasing AOA and AOB abundance towards the end of incubation irrespective of DMPP treatment, whereas cell-specific activity of AOA and/or AOB was reduced in the presence of DMPP. Overall, this study indicated that DMPP effectively inhibited nitrification activity without effects on ammonia oxidizer populations, as well as non-target soil microorganisms or functions.

Production of nitrate-rich compost from the solid fraction of dairy manure by a lab-scale composting system

In the present study, we developed an efficient composting process for the solid fraction of dairy manure (SFDM) using lab-scale systems. We first evaluated the factors affecting the SFDM composting process using different thermophilic phase durations (TPD, 6 or 3days) and aeration rates (AR, 0.4 or 0.2 lmin−1kg−1-total solid (TS)). Results indicated that a similar volatile total solid (VTS) degradation efficiency (approximately 60%) was achieved with a TPD of 6 or 3days and an AR of 0.4 l min−1 kg−1-TS (hereafter called higher AR), and a TPD of 3days resulted in less N loss caused by ammonia stripping. N loss was least when AR was decreased to 0.2 l min−1 kg−1-TS (hereafter called lower AR) during the SFDM composting process. However, moisture content (MC) in the composting pile increased at the lower AR because of water production by VTS degradation and less water volatilization. Reduced oxygen availability caused by excess water led to lower VTS degradation efficiency and inhibition of nitrification. Adding sawdust to adjust the C/N ratio and decrease the MC improved nitrification during the composing processes; however, the addition of increasing amounts of sawdust decreased NO3− concentration in matured compost. When an improved composting reactor with a condensate removal and collection system was used for the SFDM composting process, the MC of the composting pile was significantly reduced, and nitrification was detected 10–14days earlier. This was attributed to the activity of ammonia-oxidizing bacteria (AOB). Highly matured compost could be generated within 40–50days. The VTS degradation efficiency reached 62.0% and the final N content, NO3− concentration, and germination index (GI) at the end of the composting process were 3.3%, 15.5×103mg kg−1-TS, and 112.1%, respectively.

Mainstream Deammonification

The objective of this research was to investigate the feasibility of applying the deammonification concept, which is already highly successful and proven in sidestream configurations, in the mainstream treatment process. The deammonification process for nitrogen removal provides a more efficient biological pathway compared to traditional nitrification/denitrification. The demonstrated advantages of applying deammonification to mainstream treatment include energy-neutral or even energy-positive wastewater treatment, reduction of aeration energy, and reduction in external carbon and alkalinity demands. Implementation of mainstream deammonification is compatible with existing wastewater infrastructure, often with minimal modifications. The successful application of full-plant deammonification could save wastewater utilities operations costs for aeration and external carbon costs in the life cycle. Through demonstration and conceptual application at collaborating utilities, this research develops an evaluation framework for implementing full-plant deammonification.Deammonification is a two-step biological process where ammonia-oxidizing bacteria (AOB) aerobically convert half of the ammonia present in the wastewater to nitrite. In the second step, anammox bacteria oxidize the ammonia using nitrite to produce nitrogen gas without the organic carbon substrate required for conventional heterotrophic denitrification. Deammonification requires significantly less oxygen and so less energy is needed for nitrogen removal. Deammonification requires no external carbon addition, eliminating chemical purchases such as methanol. Process configurations using mainstream deammonification maximize energy recovery by diverting more particulate organic carbon away from the nitrogen removal process and directing it toward anaerobic treatment from which methane can be captured. The implications of deammonification for sustainable, cost effective and energy positive wastewater treatment are extraordinary.The report discusses application of short-cut nitrogen removal which includes nitritation-denitritation, in which ammonia oxidation ends at the intermediate nitrite, with the mainstream deammonification pathway. Both short-cut nitrogen removal pathways result in savings in energy, carbon and alkalinity over conventional nitrification-denitrification. To be successful, short-cut nitrogen removal strategies require maximizing AOB activity, while preventing the establishment of the nitrite oxidizing bacteria (NOB) that oxidize nitrite to nitrate and this report introduces and develops concepts for NOB out-selection.To progress from nitritation-denitritation to deammonification, the AOB activity must be controlled to oxidize only half of the influent ammonia to nitrite, and a method of retaining the slow-growing anammox bacteria must be implemented. The report presents a progressive pathway from conventional nitrification-denitrification to short-cut nitrogen removal and discusses a framework of conditions and drivers for implementation.The research concludes that mainstream deammonification can be achieved. It is possible for wastewater treatment plants to retrofit to short-cut nitrogen removal utilizing existing infrastructure, often with minor modifications. The research revealed key site-specific drivers for applying short-cut nitrogen removal technology.This title belongs to WERF Research Report SeriesISBN: 9781780407852 (eBook)

Ammonia-oxidizing bacteria are more responsive than archaea to nitrogen source in an agricultural soil

In the majority of agricultural soils, ammonium (NH4+) is rapidly converted to nitrate (NO3−) in the biological ammonia and nitrite oxidation processes known as nitrification. The often rate-limiting step of ammonia oxidation to nitrite is mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4 N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kg N ha−1, and steer-waste compost (200 kg total N ha−1) over four seasons. DNA was extracted from the soil, and real-time PCR and 454-pyrosequencing were used to evaluate the quantity and diversity of the amoA gene which encodes subunit A of ammonia monooxygenase. Soil pH, nitrate pools, and nitrification potentials were influenced by ammonium and organic fertilizers after the first fertilization, while changes in AOB abundance and community structure were not apparent until after the second fertilization or later. The abundance of AOA was always greater than AOB but was unaffected by N treatments. In contrast, AOB abundance and community structure were changed significantly by ammonium fertilizers. Specific inhibitors of nitrification were used to evaluate the relative contribution of AOA and AOB to nitrification. We found that AOB dominantly contributed to potential nitrification activity determined at 1 mM ammonium in soil slurries and nitrification potential activity was higher in soils treated with ammonium fertilizers relative to control soils. However, AOA dominated gross nitrification activity in moist soils. Our result suggests that AOB activity and community are more responsive to ammonium fertilizers than AOA, but that in situ nitrification rate is controlled by ammonium availability in this agricultural soil. Understanding this response of AOA and AOB to N fertilizers may contribute to improving strategies for the management of nitrate production in agricultural soils.

Nitrification inhibition by hexavalent chromium Cr(VI) – Microbial ecology, gene expression and off-gas emissions

The goal of this study was to investigate the responses in the physiology, microbial ecology and gene expression of nitrifying bacteria to imposition of and recovery from Cr(VI) loading in a lab-scale nitrification bioreactor. Exposure to Cr(VI) in the reactor strongly inhibited nitrification performance resulting in a parallel decrease in nitrate production and ammonia consumption. Cr(VI) exposure also led to an overall decrease in total bacterial concentrations in the reactor. However, the fraction of ammonia oxidizing bacteria (AOB) decreased to a greater extent than the fraction of nitrite oxidizing bacteria (NOB). In terms of functional gene expression, a rapid decrease in the transcript concentrations of amoA gene coding for ammonia oxidation in AOB was observed in response to the Cr(VI) shock. In contrast, transcript concentrations of the nxrA gene coding for nitrite oxidation in NOB were relatively unchanged compared to Cr(VI) pre-exposure levels. Therefore, Cr(VI) exposure selectively and directly inhibited activity of AOB, which indirectly resulted in substrate (nitrite) limitation to NOB. Significantly, trends in amoA expression preceded performance trends both during imposition of and recovery from inhibition. During recovery from the Cr(VI) shock, the high ammonia concentrations in the bioreactor resulted in an irreversible shift towards AOB populations, which are expected to be more competitive in high ammonia environments. An inadvertent impact during recovery was increased emission of nitrous oxide (N2O) and nitric oxide (NO), consistent with recent findings linking AOB activity and the production of these gases. Therefore, Cr(VI) exposure elicited multiple responses on the microbial ecology, gene expression and both aqueous and gaseous nitrogenous conversion in a nitrification process. A complementary interrogation of these multiple responses facilitated an understanding of both direct and indirect inhibitory impacts on nitrification.

Nitritation via heat shock using immobilized active sludge aggregates

The nitritation process is considered to be one of the most energy-saving and efficient methods for treating polluted water. In this study, active sludge was immobilized with waterborne polyurethane (WPU), and a heat-shock method was employed to treat the immobilized aggregates. When environmental factors that adversely affect nitritation (pH, dissolved oxygen, temperature, etc.) were controlled, steady nitrite nitrogen accumulation was also successfully achieved. We investigated the effect of temperature and timing of the heat-shock method on the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Subsequently, temperatures of 60 and 70°C were selected to evaluate the nitritation stability of the heat-shocked immobilized aggregates, and continuous-flow experiments were conducted. The results of preliminary experiments indicated that NOB can be completely deactivated at temperatures above 60°C after 10 min, whereas AOB continued to exhibit some activity. In addition, the effect of temperature was more significant than the effect of heating time for NOB. The results of the nitritation stability assay indicated that the heat-shocked immobilized aggregates that formed at two temperatures remained in stable nitritation; however, the performance of the AOB was decreased at the highest temperature tested. A high temperature and long duration were required for stable nitritation. In the continuous-flow experiments, we discovered that nitrate nitrogen accumulation occurred after 65 d of operation. Therefore, the immobilized aggregates were heat shocked again, and nitrite nitrogen accumulation recurred in the reactor (results not shown). Heat shock is an effective method for stabilizing the nitritation of immobilized nitrifying sludge; this method also provides new ideas for a nitritation-based nitrogen removal process. Key innovations are: (1) a new nitration method based on heat shock has been proposed to generate steady nitritation using immobilized bacterial aggregates; (2) polymerase chain reaction (PCR) has been applied to analyze variations in the AOB and NOB populations of immobilized aggregates before and after heat shock; (3) optimal heat-shock conditions (including duration and temperature) have been identified.

Ammonium Oxidizing Bacteria Activity and Nitrification Rate in Oil Contaminated Wetland Soil under Remediation with Nutrient Supplements and Leguminous Plants

Previous investigation on the impact of crude oil on the growth of tropical legumes and its effect on nitrogen dynamics in wetland ultisol showed that oil contamination reduced N uptake by plants but increased N accumulation in soil microbial biomass. Moreover, the presence of hydrocarbons widened the C/N ratio in soil and led to more available N being immobilized by soil microorganisms. The present study was carried out to evaluate the activity of ammonium oxidizing bacteria (AOB) and their nitrification potential rate (NPR) in wetland soil under a remediation course. Mineralization studies showed that ammonium-N levels decreased while nitrate-N increased progressively in the uncontaminated soil (control) cultivated with leguminous plants (cover crops) during the 12 weeks remediation period. However, the remediated soils were affected in different ways. The experimented soil cultivated with Centrosema pubescens had higher mineral nitrogen (NH4-N, NO3-N, NO2-N, Total N and P) than soil cultivated with Calopogonium mucunoides and Pueraria phaseoloides. AOB counts recorded were in the ranged, 2.25 × 102 - 2.66 × 105, 2.31 × 102 - 2.11 × 104 and 4.25 × 102 - 2.98 × 104 respectively. The highest NPR was found in uncontaminated soil (11.68 - 60.92 nmol N/g dry weight soil (DWS)) followed by soil treated with poultry manure (9.65 - 24.86 nmol N/g DWS/h), NPK (7.88 - 39.45 nmol N/g DWS/h) and in the oil-contaminated soil (0.11 - 1.87 nmol N/g DWS/h). The relations between NH4-N concentration and NPR in soil cultivated with Centrosema (r = 0.852), Calopogonium (r = 0.745) and Pueraria (r = 0.722) were positively significant at 95% confidence limit. Similarly the relations between AOB density and NPR for Centrosema (r = 0.654; P = 0.05), Calopogonium (r = 0.588; P = 0.05) and Pueraria (r = 0.518; P = 0.05) were significant. The findings imply that nitrification potential of crude oil- contaminated soil differs significantly with the nutrient amendment/treatment technique adopted for remediation. Our research has shown that treatment of uncontaminated soil with cover crops increased AOB and nitrification rate. More so, contaminated soil treated with poultry manure and NPK-fertilizer, cultivated with covers crops resulted in remarkable reduction in hydrocarbons content and increased population of nitrifiers and nitrification potential rates of wetland soil over time. However, contaminated soil treated with poultry manure and cultivated with Centrosema pubescens is more effective in bioremediation of crude oil-contaminated soil.

NITROUS OXIDE EMISSION DURING NITRIFICATION OF INFLUENTS WITH DIFFERENT AMMONIUM CONCENTRATIONS

As the serious effect of climate change and global warming is recognized, nitrous oxide (N2O) emission during wastewater treatment is receiving lots of attention due to its high potential to greenhouse effect. In this study, nitrifiers were acclimated in sequencing batch reactors with influent ammonium nitrogen (NH4-N) concentrations of 60 mg/L (SBR60) and 180 mg/L (SBR180), respectively. Nitrous oxide emission during nitrification was examined in both typical cycles and batch experiments. The dominant ammonia oxidizing bacteria (AOB) of the enriched nitrifiers in both reactors were from Nitrosomonas oligotropha lineage. For the enriched nitrifiers, N2O emission during nitrification was mainly due to activities of AOB. Within typical cycles, the conversion ratio of the produced N2O to the removed NH4-N was 5.2% in SBR60 and 1.6% in SBR180.

A combined upflow anaerobic sludge bed, aerobic, and anoxic fixed-bed reactor system for removing tetramethylammonium hydroxide and nitrogen from light-emitting diode wastewater

ABSTRACTA laboratory study using a combined upflow anaerobic sludge bed (UASB) and aerobic and anoxic fixed-bed reactor system was undertaken to explore its capability for removing tetramethylammonium hydroxide (TMAH) and nitrogen from light-emitting diode wastewater. When the organic loading rate was maintained at 0.26–0.65 kg TMAH m−3 d−1, the UASB reactor removed 70–100% of TMAH through methanogenesis. When the -N loading rate was maintained at 0.73–1.4 kg -N m−3 d−1, the aerobic reactor oxidized 31–59% of -N to -N through nitritation. When the nitrogen loading rate was maintained at 0.42–0.75 kg N m−3 d−1, the anoxic reactor removed 27–63% of nitrogen through anammox. The performance data of the combined reactor system agreed well with the stoichiometric relationships of methanogenesis, nitritation, and anammox. The batch studies showed that a higher initial TMAH concentration of up to 2520 mg L−1 gave a higher methanogenic activity of up to 16 mL CH4 g−1 VSS d−1. An increase in the initial TMAH concentration of up to 500 mg L−1 gradually decreased the activity of ammonia-oxidizing bacteria; whereas an increase in the initial TMAH concentration of up to 47 mg L−1 imposed a marked inhibiting effect on the activity of anammox bacteria.

Archaeal Ammonia Oxidizers Dominate in Numbers, but Bacteria Drive Gross Nitrification in N-amended Grassland Soil.

Both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) play an important role in nitrification in terrestrial environments. Most often AOA outnumber AOB, but the relative contribution of AOA and AOB to nitrification rates remains unclear. The aim of this experiment was to test the hypotheses that high nitrogen availability would favor AOB and result in high gross nitrification rates, while high carbon availability would result in low nitrogen concentrations that favor the activity of AOA. The hypotheses were tested in a microcosm experiment where sugars, ammonium, or amino acids were added regularly to a grassland soil for a period of 33 days. The abundance of amoA genes from AOB increased markedly in treatments that received nitrogen, suggesting that AOB were the main ammonia oxidizers here. However, AOB could not account for the entire ammonia oxidation activity observed in treatments where the soil was deficient in available nitrogen. The findings suggest that AOA are important drivers of nitrification under nitrogen-poor conditions, but that input of easily available nitrogen results in increased abundance, activity, and relative importance of AOB for gross nitrification in grassland soil.

Shifts in Abundance and Diversity of Soil Ammonia-Oxidizing Bacteria and Archaea Associated with Land Restoration in a Semi-Arid Ecosystem.

The Grain to Green Project (GGP) is an unprecedented land restoration action in China. The project converted large areas (ca 10 million ha) of steep-sloped/degraded farmland and barren land into forest and grassland resulting in ecological benefits such as a reduction in severe soil erosion. It may also affect soil microorganisms involved in ammonia oxidization, which is a key step in the global nitrogen cycle. The methods for restoration that are typically adopted in semi-arid regions include abandoning farmland and growing drought tolerant grass (Lolium perenne L.) or shrubs (Caragana korshinskii Kom.). In the present study, the effects of these methods on the abundance and diversity of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were evaluated via quantitative real-time PCR, terminal restriction fragment length polymorphism and clone library analysis of amoA genes. Comparisons were made between soil samples from three restored lands and the adjacent farmland in Inner Mongolia. Both the abundance and community composition of AOB were significantly different between the restored lands and the adjacent control. Significantly lower nitrification activity was observed for the restored land. Clone library analysis revealed that all AOB amoA gene sequences were affiliated with Nitrosospira. Abundance of the populations that were associated with Nitrosospira sp. Nv6 which had possibly adapted to high concentrations of inorganic nitrogen, decreased on the restored land. Only a slight difference in the AOB communities was observed between the restored land with and without the shrub (Caragana korshinskii Kom.). A minor effect of land restoration on AOA was observed. In summary, land restoration negatively affected the abundance of AOB and soil nitrification activities, suggesting the potential role of GGP in the leaching of nitrates, and in the emission of N2O in related terrestrial ecosystems.

Modeling the low pH limit of Nitrosomonas eutropha in high-strength nitrogen wastewaters

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH3) limitation, inhibition by nitrous acid (HNO2), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH3 limitation and non-competitive HNO2 inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH3 limitation and HNO2 inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.

Resistance and resilience of nitrifying bacteria in aerobic granules to pH shock

To investigate the response difference between flocculent sludge and granular sludge in unfavourable environmental conditions, 1-h pH shock was exerted to both granular sludge and flocculent sludge with the same biomass concentration and the same population sizes of nitrifying bacteria. It was found that nitrite-oxidizing bacteria (NOB) were more sensitive to pH than ammonia-oxidizing bacteria (AOB). In addition, the deviation of 3 pH units to alkaline from the optimal pH was much more detrimental to AOB and NOB in both flocculent sludge and granular sludge compared with the deviation of 3 pH units to acidic. However, respirometric activities of both AOB and NOB in granular sludge after pH shock at 5 and 11 were much higher than those in the flocculent sludge. The recovery of nitrifying activities by only one batch culture indicated that nitrifying bacteria in granular sludge experienced a much less irreversible loss compared with flocculent sludge. The results in this study showed that compact structure and the big size of granules could play a buffering role to unfavourable conditions which resulted in a much higher resistance and resilience to shock. This study aims to provide some guidance to the application of aerobic granular sludge to real wastewater which might experience fluctuated pH. The findings in this study indicate that resistance and resilience of nitrifying bacteria in mature granules to pH shock at steady state is much better than flocculent sludge, suggesting more robust and flexible operation of granular sludge compared with traditional flocculent sludge. In addition, the results in this study underlined a more serious inhibition from free ammonia at high pH than free nitrous acid at low pH as well as the inaccuracy of reported bell-shaped modelling of pH effect on nitrification.

Sewage treatment by an UAFB–EGSB biosystem with energy recovery and autotrophic nitrogen removal under different temperatures

A system combined an upflow anaerobic fixed bed (UAFB) and an expanded granular sludge bed (EGSB) was designed and verified as a success for treating real sewage with simultaneous energy recovery and autotrophic nitrogen removal. The impact of temperature (stepwise decreased from 30°C to 20°C and 10°C) was a primary focus, aiming to reveal the response of the anaerobic digestion (AD) and anammox efficiency to the temperature variation. As the temperature decreases, the soluble chemical oxygen demand (sCOD) removal rate was 90.6%, 90.0% and 84.7%, respectively; total nitrogen (TN) removal was 69.4%, 48.8%, 38.4%, respectively; NH4+-N removal was 91.3%, 74.9%, 65.1%, respectively. Methanogenic activity of UAFB was significantly influenced by low temperatures, while the unavoidable growth of heterotrophic organisms in EGSB also contributed to the sCOD removal, even at 10°C. Lower working temperature (10/20°C) limited the growth and activity of ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidation bacteria (AnAOB), but improved the nitrite-oxidizing bacteria (NOB) activity.

Effects of constant pH and unsteady pH at different free ammonia concentrations on shortcut nitrification for landfill leachate treatment.

On the basis of achieving shortcut nitrification in a lab-scale SBR, the effects of constant pH and unsteady pH at different free ammonia concentrations on shortcut nitrification for landfill leachate treatment was investigated. The results indicate that under the condition of DO of 0.5 ± 0.2 mg/L and temperature of 30 ± 2 °C, the absolute value of nitrite accumulation increased significantly with the increase in free ammonia (FA) concentration from 5.30 to 48.67 mg/L; however, the nitrite accumulation rate remained almost constant at a constant pH of 8.0 ± 0.1. Ammonia oxidation and the nitrite accumulation become slow with the pH decreased from 8.0 ± 0.1 to 7.5 ± 0.2, and the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were severely inhibited when the pH further decreased to 6.5. More importantly, this study confirmed that the pH decrease from 8.0 to 6.5 within a short time exhibited significant negative effect on the ammonia oxidation rather than the FA concentration.

Hydroxylamine addition impact to Nitrosomonas europaea activity in the presence of monochloramine

In drinking water, monochloramine may promote ammonia–oxidizing bacteria (AOB) growth because of concurrent ammonia presence. AOB use (i) ammonia monooxygenase for biological ammonia oxidation to hydroxylamine and (ii) hydroxylamine oxidoreductase for biological hydroxylamine oxidation to nitrite. In addition, monochloramine and hydroxylamine abiotically react, providing AOB a potential benefit by removing the disinfectant (monochloramine) and releasing growth substrate (ammonia). Alternatively and because biological hydroxylamine oxidation supplies the electrons (reductant) required for biological ammonia oxidation, the monochloramine/hydroxylamine abiotic reaction represents a possible inactivation mechanism by consuming hydroxylamine and inhibiting reductant generation. To investigate the abiotic monochloramine and hydroxylamine reaction's impact on AOB activity, the current study used batch experiments with Nitrosomonas europaea (AOB pure culture), ammonia, monochloramine, and hydroxylamine addition. To decipher whether hydroxylamine addition benefitted N. europaea activity by (i) removing monochloramine and releasing free ammonia or (ii) providing an additional effect (possibly the aforementioned reductant source), a previously developed cometabolism model was coupled with an abiotic monochloramine and hydroxylamine model for data interpretation. N. europaea maintained ammonia oxidizing activity when hydroxylamine was added before complete ammonia oxidation cessation. The impact could not be accounted for by monochloramine removal and free ammonia release alone and was concentration dependent for both monochloramine and hydroxylamine. In addition, a preferential negative impact occurred for ammonia versus hydroxylamine oxidation. These results suggest an additional benefit of exogenous hydroxylamine addition beyond monochloramine removal and free ammonia release, possibly providing reductant generation.

AmoA Gene abundances and nitrification potential rates suggest that benthic ammonia-oxidizing bacteria and not Archaea dominate N cycling in the Colne Estuary, United Kingdom.

Nitrification, mediated by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), is important in global nitrogen cycling. In estuaries where gradients of salinity and ammonia concentrations occur, there may be differential selections for ammonia-oxidizer populations. The aim of this study was to examine the activity, abundance, and diversity of AOA and AOB in surface oxic sediments of a highly nutrified estuary that exhibits gradients of salinity and ammonium. AOB and AOA communities were investigated by measuring ammonia monooxygenase (amoA) gene abundance and nitrification potentials both spatially and temporally. Nitrification potentials differed along the estuary and over time, with the greatest nitrification potentials occurring mid-estuary (8.2 μmol N grams dry weight [gdw](-1) day(-1) in June, increasing to 37.4 μmol N gdw(-1) day(-1) in January). At the estuary head, the nitrification potential was 4.3 μmol N gdw(-1) day(-1) in June, increasing to 11.7 μmol N gdw(-1) day(-1) in January. At the estuary head and mouth, nitrification potentials fluctuated throughout the year. AOB amoA gene abundances were significantly greater (by 100-fold) than those of AOA both spatially and temporally. Nitrosomonas spp. were detected along the estuary by denaturing gradient gel electrophoresis (DGGE) band sequence analysis. In conclusion, AOB dominated over AOA in the estuarine sediments, with the ratio of AOB/AOA amoA gene abundance increasing from the upper (freshwater) to lower (marine) regions of the Colne estuary. These findings suggest that in this nutrified estuary, AOB (possibly Nitrosomonas spp.) were of major significance in nitrification.