Nitrifying Activity Research Articles

Salinity changes the nitrification activity and community composition of comammox Nitrospira in intertidal sediments of Yangtze River estuary.

The newly discovered complete ammonia-oxidizing (comammox) Nitrospira has been identified in different environments, including coastal environments, where salinity is one of the most important factors for the abundance and activity of nitrifiers. Here, we demonstrate the effect of salinity on comammox Nitrospira, canonical ammonia-oxidizing bacteria (AOB), and ammonia-oxidizing archaea (AOA) in the intertidal sediments of the Yangtze River estuary based on microcosm experiments, DNA stable-isotope probing (DNA-SIP), and potential ammonium-oxidation rate (PAR) tests for different groups of ammonia oxidizers with selective inhibitors. During microcosm incubations, the abundance of comammox Nitrospira was more sensitive to increased salinity than that of other ammonia oxidizers. The results obtained with DNA-SIP heavy fractions showed that the dominant phylotype in clade A.2 (containing genes involved in the adaptation to haloalkaline environments) had high proportions in comammox Nitrospira community under both freshwater (0.06% salinity) and highly saline water (3% salinity) conditions. In contrast, another phylotype of clade A.2 (which lacks these genes) was dominant only under freshwater conditions. The PARs confirmed that comammox Nitrospira presented greater contributions to nitrification under freshwater conditions with a PAR of 4.37 ± 0.53 mg N·day-1·kg soil-1 (54%) than under saline water conditions with a PAR of 0.60 ± 0.94 mg N·day-1·kg soil-1 (18%). Moreover, AOA were specific to saline water conditions, whereas AOB were common under both freshwater and saline water conditions (44% and 52%, respectively). The present study provided evidence that salinity markedly affects the activity of comammox Nitrospira, and that the salt sensitivity of different phylotypes varies. IMPORTANCE Complete ammonia oxidation (comammox) is a newly discovered type of nitrification through which ammonia is oxidized to nitrate in an organism. Comammox Nitrospira were abundantly found in coastal ecosystems and demonstrated high community diversity. Changes in salinity are considered one of the most important factors to comammox Nitrospira in coastal ecosystems; however, reports on the correlation between them remain inconsistent. Therefore, it is critical to experimentally determine the influence of salinity on comammox Nitrospira in the coastal ecosystem. This study demonstrated a clear effect of salinity on the abundance, activity, and relative contribution of different ammonia oxidizers, especially for comammox Nitrospira. To the best of our knowledge, this is the first study demonstrating comammox Nitrospira activity at seawater salinities, implying the existence of a salt-tolerant type comammox Nitrospira, despite its activity being much lower than in freshwater conditions. The indicated correlation between the activity of specific comammox Nitrospira and salinity is anticipated to provide insights into the distribution of comammox Nitrospira and their potential contributions in estuaries and coastal ecosystems.

Thickness of hydrogel for nitrifying biomass entrapment determines the free ammonia susceptibility differently in batch and continuous modes

Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O2/L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78–0.95 kg-N/m3 day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m3 day, while that of HG-1.13 was 0.0516 kg-FA/m3 day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.

Assessing the impact of increasing phenol loads on the performance and stability of an aerobic granular sludge system

This work evaluated the impact of phenol on the performance and stability of an aerobic granular sludge (AGS) sequencing batch reactor (SBR) operated under alternating anaerobic-aerobic conditions for simultaneous organic matter, nitrogen, and phosphorus removal. The reactor was fed with synthetic wastewater whose phenol concentration was gradually increased from 2 to 200 mg L−1, while the other carbon source (acetate) was reduced proportionally to keep the organic loading rate invariable. Up to 20 mg L−1 of phenol, the average COD removal was above 90%, while practically full ammonium, phosphorus, and phenol removal was achieved. However, at higher phenol concentrations, the activity of polyphosphate-accumulating organisms and nitrifiers was affected. Although the overall COD removal was only slightly affected by increasing phenol loads, replacing the main carbon source from acetate to phenol changed the organic matter removal profile over the cycle, with the latter being converted mainly within the aerated stage of the SBR. As a result, there was filamentous growth that deteriorated the settling properties of the granules. The establishment of an anaerobic feast-aerobic famine regime over the non-aerated and aerated phases of the AGS SBR and the presence of a readily biodegradable substrate (such as acetate) proved to be crucial for maintaining granules stability. Having phenol as the sole organic carbon source led to complete process failure regarding nutrient removal capability.

Municipal Sewage Treatment Technology: A2/O-VMBR Integrated Technology for Municipal Treatment and Improved Pollutant Removal

To modernize wastewater treatment plants, a pilot-scale anaerobic/anoxic/oxic-vibrating membrane bioreactor (A2/O-VMBR) was developed and successfully operated. Despite a low C/N ratio, the A2/O-VMBR achieved removal rates of 61.10%, 93.77%, 72.86%, and 54.75% for COD, TN, TP, and NH3-N, respectively. The maximum and extremity transmembrane pressures were 45 kPa, and 80 kPa, respectively, with no sludge bulking observed. The VMBR saved over 96–98% of energy compared to traditional MBR plants, making it a better option for municipal wastewater treatment. High-throughput sequencing analysis revealed identical bacterial population structures in samples obtained from the treatment units, with genera having nitrifying, denitrifying, hydrolyzing, and glycogen-accumulating activities, which allowed for nitrogen removal. The key functional microorganisms responsible for nitrification–denitrification were species belonging to the genera FCPU426, Fusobacteria, Planctomycetes, Verrucomicrobia, and Epsilonbacteraeota. The integrated experimental system produced favorable results in improving wastewater quality, highlighting the usability of the A2/O-VMBR technology. Therefore, this technique holds potential for further investigation into the context of wastewater treatment and recovery.

Understanding the role of sorption and biodegradation in the removal of organic micropollutants by membrane aerated biofilm reactor (MABR) with different biofilm thickness

The role of sorption and biodegradation in a membrane aerated biofilm reactor (MABR) were investigated for the removal of 10 organic micropollutants (OMPs) including endocrine disruptors and pharmaceutical active compounds. The influence of the biofilm thickness on the mechanisms of removal was analyzed via kinetic test at three different stages. At all biofilm stages, biodegradation was demonstrated to dominate the removal of selected OMPs. Higher OMPs rates of removal via biodegradation (Kbiol) were achieved when biofilm increased its thickness from (stage T1) 0.26 mm, to (stage T2) 0.58 mm and (stage T3) 1.03 mm. At stage T1 of biofilm, heterotrophs contribute predominantly to OMPs degradation. Hydrophilic compounds removal (i.e., acetaminophen) continue to be driven by heterotrophic bacteria at the next stages of biofilm thickness. However, for medium hydrophobic neutral and charged OMPs, the combined action of heterotrophic and enriched nitrifying activity at stages T2 and T3 enhanced the overall removal. A degradation pathway based on heterotrophic activity for acetaminophen and combined action of nitrifiers-heterotrophs for estrone was proposed based on identified metabolites. Although biodegradation dominated the removal of most OMPs, sorption was also observed to be essential in the removal of biologically recalcitrant and lipophilic compounds like triclosan. Furthermore, sorption capacity of apolar compound was enhanced as the biofilm thickness grew and increased in EPS protein fraction. Microbial analysis confirmed the higher abundance of nitrifying and denitrifying activity at stage T3 of biofilm, which not only facilitated near complete ammonium removal but also enhanced degradation of OMPs.

Effects of acidification on nitrification and associated nitrous oxide emission in estuarine and coastal waters

In the context of an increasing atmospheric carbon dioxide (CO2) level, acidification of estuarine and coastal waters is greatly exacerbated by land-derived nutrient inputs, coastal upwelling, and complex biogeochemical processes. A deeper understanding of how nitrifiers respond to intensifying acidification is thus crucial to predict the response of estuarine and coastal ecosystems and their contribution to global climate change. Here, we show that acidification can significantly decrease nitrification rate but stimulate generation of byproduct nitrous oxide (N2O) in estuarine and coastal waters. By varying CO2 concentration and pH independently, an expected beneficial effect of elevated CO2 on activity of nitrifiers (“CO2-fertilization” effect) is excluded under acidification. Metatranscriptome data further demonstrate that nitrifiers could significantly up-regulate gene expressions associated with intracellular pH homeostasis to cope with acidification stress. This study highlights the molecular underpinnings of acidification effects on nitrification and associated greenhouse gas N2O emission, and helps predict the response and evolution of estuarine and coastal ecosystems under climate change and human activities.

Impact of Chronic Crude Oil Pollution on Nitrification in Edaphic Systems

Nitrification plays a key role in regulating soil fertility, concentration of soil inorganic nitrogen and production of the highly potent greenhouse gas, nitrous oxide, from soil. This study investigated the effect of long-term crude oil pollution on the activity, abundance and diversity of autotrophic nitrifying bacteria in impacted soils from Bomu and Abonema in the Nigerian Niger Delta compared to unpolluted systems. Nitrifier activity was investigated by determining the soil oxidation potentials while the most probable number microtechnique using Winogradsky media was used to ascertain nitrifying bacteria abundance and soil DNA analysis alongside plate cultures defined nitrifying bacterial diversity. Nitrifier activity was found to be higher in the polluted soils than in the unpolluted soils while quantification of the nitrifying bacteria revealed that polluted samples had higher nitrifier counts. Statistically significant differences existed amongst nitrifier counts and activity (p≤0.05) between polluted and unpolluted systems with positive correlation between nitrifying bacteria counts and oxidation potential. The results highlighted the dominance of cultivable Nitrosomonas and Nitrobacter in both polluted and unpolluted soils while DNA analysis revealed that Nitrospira was the dominant nitrifier genus in unpolluted soils and Nitrobacter in polluted soils. Nitrospira was not detected the polluted ecosystems. No ammonia oxidisers were detected via metagenomics analysis. The ammonia oxidisers proved to be more sensitive to chronic crude oil pollution than the nitrite-oxidising bacteria. Long term crude oil exposure produced a 3 – 5 times increase in the activity of nitrifying bacteria in polluted soils with approximately twice the abundance when compared to the unpolluted systems.

Microbiome in soils of Mendoza: microbial resources for the development of agroecological management in viticulture

Rhizosphere microorganisms are considered an extension of plants, representing critical actors involved in the promotion of plant nutrient intake from the surrounding environment. Consequently, a great focus is being made on soil microorganisms since they are considered a promising source for crop resilience improvements under a global climate change scenario. To explore bacterial and fungal communities from arid soils in vineyards and their surroundings from two regions with very different climate and tillage histories, an amplicon sequencing analysis was performed. Specifically, Santa Rosa (SR) is in a region commonly known as the first zone, characterised by low altitude (607 m.a.s.l., Winkler V), while Gualtallary (G) is in the Uco Valley Zone, a region with high altitude (1245 m.a.s.l., Winkler III); both in the productive wine region of Mendoza. SR is characterised by its long cultivation history, while G is a recently cultivated region. Topsoil samples were collected and used for bacterial and fungal community profile characterisation. Ascomycota was the predominant phylum (38–97 %) in mycobiome composition, whereas Proteobacteria was the most abundant bacterial phylum (26–34 %) in both regions. Moreover, the main factor explaining microbiome differences between regions was the carbon-to-nitrogen ratio. Anaerolineae and Gammaproteobacteria were a distinctive bacterial class in SR-cultivated soils. Azospirillales were highly abundant in SR uncultivated soils, while Rhizobiales were differentially abundant in G uncultivated soils. Regarding functional analysis, soils from SR showed a higher denitrification activity of nitrifiers as well as glucose-related metabolism, while in G soils, bacterial photosynthesis activities were a differential trait. In addition, Actinobacteria abundance was lower in SR-cultivated soils, indicating a higher susceptibility of this phylum to grapevine crop practices. These results allow the development of hypothetical models of the local microbial resources and their contribution to grapevine nutrition, which is highly important to elaborate recommendations for grapevine management to preserve soil health in vine areas of Mendoza.

Potential roles of acyl homoserine lactones (AHLs) in nitrifying bacteria survival under certain adverse circumstances

Potential roles of quorum sensing (QS) in nitrifying bacteria activity and ecology, particularly under adverse circumstances have been rarely reported. Herein, eight lab-scale nitrification sequencing batch reactors, with or without adding acyl homoserine lactones (AHLs) were operated under adverse circumstances respectively. The results indicated that the introduction of AHLs significantly enhanced the nitrogen removal efficiency in the presence of nitrification inhibitors (dicyandiamide, DCD), accelerated the low temperature (10 °C) group into stable stage, and improved the utilization efficiency of AHLs in these two groups. Community analysis and qPCR further confirmed that AHLs significantly increased the abundance of nitrifying bacteria in low temperature group and DCD group, especially AOB. For normal condition (28 °C, pH = 8) or low pH level (5.5), however, the AHLs had no significant effect. Canonical correspondence analysis showed that nitrifying bacteria positively responded to AHLs, indicating that adding AHLs was an effective strategy to regulate nitrification process. However, under acid conditions, the effect of this regulatory mechanism was not significant, indicating that the influence of pH on the system was greater than that of AHLs. This study demonstrated that exogenous AHLs could enhance the competitiveness of nitrifying bacteria to utilize more resource and occupy space under some adverse environmental conditions.

Reactive and microbial inhibitory mechanisms depicting the panoramic view of pH stress effect on common biological nitrification

pH is a crucial factor of microbial nitrification, which often combines with high-strength ammonium to influence nitrogen removal pathway in wastewater treatment. However, the detailed inhibitory mechanisms of pH stress are not sufficiently disclosed yet. In this study, the pH stress effect on nitrification was comprehensively studied by a set of experiments which identified the reactivity of nitrification processes and activity of nitrifiers, the time dependence of inhibition effect and the hybrid pH stress effect with ammonium. The results revealed two distinct inhibitory mechanisms dominating in alkaline and acid ranges. In alkaline range (pH > 8), pH stress causes physiological damages on microorganisms which is named as microbial inhibition. It has the features of less recoverability of nitrifiers, time-dependent inhibition effect and low pH-tolerance of nitrite oxidation bacteria. Free ammonia enhanced microbial inhibition and greatly promoted nitrite accumulation. A novel reactive inhibition mechanism dominated in acid range (pH < 7) was disclosed. It only impedes ammonia oxidation process (AOP) but not impair microbial activity obviously and the effect is time-independent. The mechanism was clarified from H+ transport because AOP involved H+ production. The H+ transport was impeded under acid stress owing to the decrease of pH gradient across cell membrane. The two mechanisms formed a panoramic view of pH stress effect on nitrification advancing the understanding of nitrifier adaptability and nitritation regulation in wastewater treatment processes.

Meta-analysis of the effect of nitrification inhibitors on the abundance and community structure of N2O-related functional genes in agricultural soils

Application of nitrification inhibitors (NIs) in agricultural systems is an important strategy to enhance fertilizer nitrogen use efficiency and mitigate soil nitrous oxide (N2O) emissions. Here, we conducted a global meta-analysis of 88 published studies to assess the response of N2O-related functional gene and transcript abundances, and community structure to NIs application. Application of NIs significantly reduced the abundance of ammonia-oxidizing bacteria ammonia monooxygenase (AOB amoA) genes, AOB amoA transcript and nitrite reductase (nirS and nirK) genes. The effectiveness of NIs on reducing the AOB amoA abundance was influenced by N form, soil texture, soil pH and the experimental type (field vs. laboratory). Specifically, NIs were more effective when a mixed inorganic and organic N source was applied to a medium-textured soils. The NIs effectiveness increased with increasing soil pH. The response of AOB amoA abundance to NIs application was not affected by NI type, N rate, soil moisture, soil temperature and soil organic carbon (SOC). The inhibitory effect of NIs on nirS abundance increased with increasing soil temperature. NIs decreased soil nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) by 34.5 % and 27.0 %, respectively, leading to an overall 63.6 % reduction of N2O emissions. Soil NEA correlated positively with the abundance and community structure of AOB amoA but not with AOA amoA. Decrease in DEA with NIs application coincided with the decreasing nirS and nirK abundances. This global-scale assessment demonstrates that the effectiveness of NIs in reducing N2O emissions was attributed to the inhibiting effects on AOB amoA, nirS and nirK genes. Our findings highlight that NIs' inhibition effects on bacterial ammonia-oxidizing community and the encode enzymes in transformation of nitrite to nitric oxide are the main mechanisms for mitigation of N fertilizer-induced N2O emissions.

Long-term post-storage reactivation of a nitrifying sludge in a sequential batch reactor: physiological and kinetic evaluation.

Production, preservation and recovery of sludge with stabilized nitrifying activity over long time can be difficult. Information on the ability of nitrifying sludge to regain its nitrifying activity after long-term storage is still scarce. In this work, the physiological and kinetic changes during the reactivation and stabilization of a nitrifying sludge previously exposed to ampicillin (AMP) were evaluated in a sequential batch reactor (SBR) after its long-term storage (1year) at 4°C. After storage, both ammonium and nitrite oxidizing processes were slow, being nitrite oxidation the most affected step. During the reactivation stage (cycles 1-6), physiological and kinetic activity of the nitrifying sludge improved through the operating cycles, in both its ammonium oxidizing and nitrite oxidizing processes. At the end of the reactivation stage, complete nitrifying activity was achieved in 10h, reaching ammonium consumption efficiencies (ENH4 +) close to 100% and nitrate yields (YNO3 -) of 0.98mg NO3 --N/mg NH4 +-N consumed without nitrite accumulation. During the stabilization stage (cycles 7-17), results indicated that the sludge could maintain a steady-state respiratory process with restoration percentages of 100% for nitrifying specific rates (qNH4 + and qNO3 -) with respect to their values obtained before storage. Furthermore, during the addition of 15mg AMP/L (cycles 18-21), the sludge preserved its metabolic capacity to biodegrade 90% of AMP in 2h. Therefore, long-term storage of nitrifying sludge could be used to preserve nitrifying inocula as bioseeds for bioremediation and bioaugmentation strategies.

Selection of Active Microorganism Strains Isolated from a Naturally Salty Lake for the Investigation of Different Microbial Potentials

The biological variety of aquatic ecosystems is significantly impacted by the chemical and microbiological composition of water bodies, and there is strong reciprocal feedback between these two factors, especially for reservoirs, which can and do have a significant impact on neighboring ecosystems. Today there is an acute need to identify the most effective and economically feasible methods for cleaning and restoring water bodies. Therefore, the aim of the study was to find strains of microorganisms which are capable of biodegrading such problematic pollutants as insoluble phosphates and excess nitrogenous compounds and at the same time, are capable of suppressing the bacterial composition in reservoir waters. In the course of the research, a number of the most active strains of microorganisms were isolated from lake water samples. Five isolates were obtained from salt water and the isolates were then identified using morphological, and biochemical techniques, as well as the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition to the characterization and identification of the isolates, the species-specific levels of phosphate solubilizing, and nitrifying activities were also established. Thus, all isolated strains were studied and characterized, and their influence on the content of minerals such as phosphorus and nitrogen, which are important for living organisms in water, was studied. In summary, the Pseudomonas Extrem-Orientalis isolate was observed to be highly effective in solubilizing phosphates, nitrifying, and had the greatest antagonistic capacity among the investigated isolates. The information gleaned from the study’s findings helps raise more awareness in the field of microbiology and water treatment in general. The findings offer promise for the development of biopreparations with bioremediation capabilities for cleaning polluted water bodies of pollutants from various sources.

The nitrification inhibitor 1,9-decanediol from rice roots promotes root growth in Arabidopsis through involvement of ABA and PIN2-mediated auxin signaling

1,9-decanediol (1,9-D) is a biological nitrification inhibitor secreted in roots, which effectively inhibits soil nitrifier activity and reduces nitrogen loss from agricultural fields. However, the effects of 1,9-D on plant root growth and the involvement of signaling pathways in the plant response to 1,9-D have not been investigated. Here, we report that 1,9-D, in the 100–400 μM concentration range, promotes primary root length in Arabidopsis seedlings at 3d and 5d, by 10.1%–33.3% and 6.9%–32.6%, and, in a range of 50–200 μM, leads to an increase in the number of lateral roots. 150 μM 1,9-D was found optimum for the positive regulation of root growth. qRT-PCR analysis reveals that 1,9-D can significantly increase AtABA3 gene expression and that a mutation in ABA3 results in insensitivity of root growth to 1,9-D. Moreover, through pharmacological experiments, we show that exogenous addition of ABA (abscisic acid) with 1,9-D enhances primary root length by 23.5%–63.3%, and an exogenous supply of 1,9-D with the ABA inhibitor Flu reduces primary root length by 1.0%–14.3%. Primary root length of the pin2/eir1-1 is shown to be insensitive to both exogenous addition of 1,9-D and ABA, indicating that the auxin carrier PIN2/EIR1 is involved in promotion of root growth by 1,9-D. These results suggest a novel for 1,9-D in regulating plant root growth through ABA and auxin signaling.

Biological nitrification inhibitor-trait enhances nitrogen uptake by suppressing nitrifier activity and improves ammonium assimilation in two elite wheat varieties.

Synthetic nitrification inhibitors (SNI) and biological nitrification inhibitors (BNI) are promising tools to limit nitrogen (N) pollution derived from agriculture. Modern wheat cultivars lack sufficient capacity to exude BNIs, but, fortunately, the chromosome region (Lr#n-SA) controlling BNI production in Leymus racemosus, a wild relative of wheat, was introduced into two elite wheat cultivars, ROELFS and MUNAL. Using BNI-isogenic-lines could become a cost-effective, farmer-friendly, and globally scalable technology that incentivizes more sustainable and environmentally friendly agronomic practices. We studied how BNI-trait improves N-uptake, and N-use, both with ammonium and nitrate fertilization, analysing representative indicators of soil nitrification inhibition, and plant metabolism. Synthesizing BNI molecules did not mean a metabolic cost since Control and BNI-isogenic-lines from ROELFS and MUNAL presented similar agronomic performance and plant development. In the soil, ROELFS-BNI and MUNAL-BNI plants decreased ammonia-oxidizing bacteria (AOB) abundance by 60% and 45% respectively, delaying ammonium oxidation without reducing the total abundance of bacteria or archaea. Interestingly, BNI-trait presented a synergistic effect with SNIs since made it also possible to decrease the AOA abundance. ROELFS-BNI and MUNAL-BNI plants showed a reduced leaf nitrate reductase (NR) activity as a consequence of lower soil formation and a higher amino acid content compared to BNI-trait lacking lines, indicating that the transfer of Lr#-SA was able to induce a higher capacity to assimilate ammonium. Moreover, the impact of the BNI-trait in wheat cultivars was also noticeable for nitrate fertilization, with improved N absorption, and therefore, reducing soil nitrate content.

Wastewater treatment potential, light penetration profile and biomass settling performance of a photo‐sequencing batch reactor

AbstractBACKGROUNDThe performance of microalgal and bacterial systems devoted to wastewater treatment might be limited by the poor settling of microalgal biomass and the inhibition of nitrifying bacteria under high irradiance conditions. This work implemented a photo‐sequencing batch bioreactor (PSBR) treating medium‐ and low‐strength wastewaters. The impact of a short settling time on the formation of microalgal–bacterial aggregates (MABAs) was evaluated. Moreover, online photosynthetically active radiation (PAR) measurements at the bottom of the PSBR were used to identify potential nitrifying activity inhibition.RESULTSA chemical oxygen demand removal efficiency of up to 88% was obtained for the medium‐ and low‐strength wastewaters. Photoinhibition of the nitrifying activity was observed at PAR values from 73 to 480 μmol m−2 s−1, and it was confirmed under non‐limiting dissolved oxygen conditions. The PSBR operating conditions, including a short settling time (30 min) and treatment of medium‐strength wastewater, favored the rapid formation of MABAs in only 19 days, with a biomass settling velocity (vs) of 0.74 m h−1. The microalgal genera Acutudesmus, Desmodesmus, and Chlorella were predominant in the MABAs. Experimental estimation of the light extinction coefficient (λ = 0.056 m2 g−1 total suspended solids) allowed the simulation of light penetration profiles at different reactor liquid depths and biomass concentrations.CONCLUSIONA short settling time favors the rapid formation of MABAs in PSBR‐type reactors treating medium‐strength wastewater. Online monitoring and simulation of light penetration is a valuable tool to determine photoinhibition of the nitrifying activity in microalgal and bacterial systems. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).

Cold temperature drives the re-granulation of disintegrated partial nitritation granules in a continuous-flow reactor

To investigate the effect of temperature on the recovery of aerobic granule stability, two continuous-flow reactors inoculated with disintegrated partial nitritation granules were operated at different temperatures for organic-free wastewater treatment. Granules disintegration and partial nitritation deterioration further occurred in the reactor (R1) operating at 25–28 °C. However, successful sludge re-granulation with a decrease of sludge volume index (SVI5) from 73 mL/g to 35 mL/g was observed in the reactor (R2) operated with the decreasing temperature from 20 °C to 12 °C. The reduced temperatures decreased the activity and growth rate of nitrifiers (from 47.2 mg/g VSS/h to 21.3 mg/g VSS/h), and selected the extracellular polymeric substance (EPS) producing bacteria (e.g., Flavobacterium and Rhodobacteraceae sp.). Correspondingly, an enhanced secretion of tightly-bound EPS (200.3–224.6 mg/g VSS in R2 vs 166.8–152.5 mg/g VSS in R1), particularly proteins, and an increased expression of quorum sensing-related enzyme genes (2.98% in R2 vs 2.75% in R1) were obtained. All of this contributed to the cold temperature-driven sludge re-granulation. The recovery of granular structure promoted the stable maintenance of efficient partial nitritation at low temperatures. Overall, this study gives insights into the positive role of cold temperatures on the stability of partial nitritation granules.

The active functional microbes contribute differently to soil nitrification and denitrification potential under long-term fertilizer regimes in North-East China.

Nitrogen (N) cycling microorganisms mediate soil nitrogen transformation processes, thereby affecting agricultural production and environment quality. However, it is not fully understood how active N-cycling microbial community in soil respond to long-term fertilization, as well as which microorganisms regulate soil nitrogen cycling in agricultural ecosystem. Here, we collected the soils from different depths and seasons at a 29-year fertilization experimental field (organic/chemical fertilizer), and investigated the transcriptions of N-cycling functional genes and their contribution to potential nitrification and denitrification. We found that long-term fertilization exerted significant impacts on the transcript abundances of nitrifiers (AOA amoA, AOB amoA and hao) and denitrifiers (narG and nosZ), which was also notably influenced by season variation. The transcriptions of AOA amoA, hao, and narG genes were lowest in autumn, and AOB amoA and nosZ transcript abundances were highest in autumn. Compared to no fertilization, soil potential nitrification rate (PNR) was reduced in fertilization treatments, while soil potential denitrification rate (PDR) was significantly enhanced in organic combined chemical fertilizer treatment. Both PNR and PDR were highest in 0–20 cm among the tested soil depths. Path model indicated active nitrifiers and denitrifiers had significant impact on soil PNR and PDR, respectively. The transcriptions of AOA amoA and nxr genes were significantly correlated with soil PNR (Pearson correlation, r > 0.174, p < 0.05). Significant correlation of napA and nosZ transcriptions with soil PDR (Pearson correlation, r > 0.234, p < 0.05) was also revealed. Random forest analysis showed that SOC content and soil pH were the important factors explaining the total variance of active nitrifers and denitrifiers, respectively. Taken together, long-term fertilization regimes reduced soil PNR and enhanced PDR, which could be attributed to the different responses of active N-cycling microorganisms to soil environment variations. This work provides new insight into the nitrogen cycle, particularly microbial indicators in nitrification and denitrification of long-term fertilized agricultural ecosystems.

Cambios metabólicos y cinéticos de los lodos activados como consecuencia de las fallas en el sistema de aireación en una PTAR

The classic question from wastewater treatment plant (WWTP) operators is, how long can a secondary reactor be kept unaerated after an aeration system failure? Therefore, in the present research, samples of activated sludge (AS) were taken from a WWTP and left without aeration for 12, 18, 24, and 36 h; simulating an aeration failure. Subsequently, the activity of AS lacking aeration was evaluated in batch cultures. The results showed that the lack of AS oxygenation affected its metabolism. For example, the heterotrophic activity stopped completely when AS was not aerated for 24 h. The nitrifying activity, in the experiments from 12 to 24 h without aeration, the ammonium removal did not change, but there was an increase in nitrite concentration. In the 36-h experiment without aeration, the ammonium consumption rate and removal efficiency decreased by 56% and 43%, respectively, regarding the control. N2O was produced in the period when the AS was not aerated, which could be responsible for these metabolic and kinetic changes. Finally, this study suggested don't leave for more than 24 h the activated sludge without aeration for a quick recovery or to diminish the damage.

Estimation of nitrifying and heterotrophic bacterial activity in biofilm formed on RAS biofilter carriers by respirometry

Biofilm, the aggregates of microbial layers that are attached on the surface of biofilter carriers, plays a central role in the removal and conversion of nutrients in recirculating aquaculture systems (RAS). The bacterial activity in biofilm involves autotrophic and heterotrophic processes. These biological processes are crucial for the water quality in RAS but are difficult to monitor. In this study, we demonstrate a new method based on intermittent respirometry to selectively estimate bacterial activity in biofilm following a spike in substrate concentration. The method was tested with three different biofilter carriers (extruded polypropylene, injection molded polypropylene and polymeric foam) from moving bed biofilm reactors in a common freshwater RAS. Oxygen consumption rates of biofilm-associated bacteria were measured in closed metabolic chambers under standard conditions. The protocol included sequential flushes of either pure tap water, or tap water spiked with nitrite, ammonium or acetate. The results showed consistent carrier-specific metabolic activities of endogenous respiration, nitrite-oxidizing bacteria (NOB), ammonia-oxidizing bacteria (AOB) and heterotrophic bacteria (HB) in biofilm. The highest activities normalized to volumetric oxygen consumption rates, were found in polymeric foam with values of 677 ± 125, 764 ± 156 and 166 ± 36 g O2·m−3·d−1 for NOB, AOB and HB, respectively. The biofilter performance evaluation based on respirometric data showed satisfactory accordance with the values from substrate degradation batch kinetic tests for all three tested carriers, confirming the feasibility and robustness of the method as a means to assessing biofilter performance. Our study provides an on-site tool in biofilter performance tests and leads to a better understanding of dynamic and relationship between biofiltration and water quality.