Publications by authors named "Ivar Zekker"

22 Publications

  • Page 1 of 1

New Insight Into the Interspecies Shift of Anammox Bacteria "Brocadia" and "Jettenia" in Reactors Fed With Formate and Folate.

Front Microbiol 2021 3;12:802201. Epub 2022 Feb 3.

Research Center of Biotechnology, Russian Academy of Sciences, Moscow, Russia.

The sensitivity of anaerobic ammonium-oxidizing (anammox) bacteria to environmental fluctuations is a frequent cause of reactor malfunctions. It was hypothesized that the addition of formate and folate would have a stimulating effect on anammox bacteria, which in turn would lead to the stability of the anammox process under conditions of a sharp increase in ammonium load, i.e., it helps overcome a stress factor. The effect of formate and folate was investigated using a setup consisting of three parallel sequencing batch reactors equipped with a carrier. Two runs of the reactors were performed. The composition of the microbial community was studied by the 16S rRNA gene profiling and metagenomic analysis. Among anammox bacteria, "Brocadia" spp. dominated during the first run. A stimulatory effect of folate on the daily nitrogen removal rate (dN) was identified. The addition of formate led to progress in dissimilatory nitrate reduction and stimulated the growth of "Jettenia" spp. The spatial separation of two anammox species was observed in the formate reactor: "Brocadia" occupied the carrier and "Jettenia"-the walls of the reactors. Biomass storage at low temperature without feeding led to an interspecies shift in anammox bacteria in favor of "Jettenia." During the second run, a domination of "Jettenia" spp. was recorded along with a stimulating effect of formate, and there was no effect of folate on dN. A comparative genome analysis revealed the patterns suggesting different strategies used by "Brocadia" and "Jettenia" spp. to cope with environmental changes.
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http://dx.doi.org/10.3389/fmicb.2021.802201DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8851195PMC
February 2022

Cholinesterase activity as a potential biomarker for neurotoxicity induced by pesticides exposed (Nile tilapia): assessment tool for organophosphates and synthetic pyrethroids.

Environ Technol 2022 Jan 12:1-9. Epub 2022 Jan 12.

Department of Chemistry, Abdul Wali Khan University, Mardan, Pakistan.

Organophosphates (OPs) and synthetic pyrethroids (SPs) are the most popular broad spectrum pesticides, used in agriculture as they have a strong pesticidal activity while also being biodegradable in the environment. The present study aimed to demonstrate the effects of these pesticides on the Acetylcholinesterase (AChE) activity in brain, gills and body muscles of - an important enzyme for the assessment and biomonitoring pollution caused by neurotoxins in the environment. The fish were exposed for 24 and 48 h to the LC concentrations of the malathion (1.425 mg/L), the chlorpyrifos (0.125 mg/L) and the λ-cyhalothrin (0.0039 mg/L), respectively. The activity of the AChE was significantly increased ( < 0.05) at 24 h and decreased at 48 h (except for the chlorpyrifos-treated brain and gills while tissues had shown no activity at 48 h's exposure) in all pesticides-treated tissues. The maximum increase in the activity and inhibition in the AChE activity were recorded as +92% and -52% in the chlorpyrifos and the lambda-cyhalothrin exposed brain tissues, respectively. Thus, the alterations in the AChE activities indicated that the applied pesticides are highly neurotoxic to fish and the enzyme (AChE) could be used as a useful biomarker for estimation of water pollution.
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http://dx.doi.org/10.1080/09593330.2021.2024276DOI Listing
January 2022

Evaluating groundwater nitrate and other physicochemical parameters of the arid and semi-arid district of DI Khan by multivariate statistical analysis.

Environ Technol 2021 Oct 16:1-10. Epub 2021 Oct 16.

Government Post Graduate College for Boys Lund Khwar, Mardan, Pakistan.

Nitrate as an important water pollutant, causing eutrophication was analyzed in Pakistan at different water sources (hand pump (HP), bore hole (BH) and tube well (TW)) to assess the contamination level caused by NO. NO concentrations in the HP water samples were 31 mg L to 59 mg L, in BH 20 mg L to 79 mg L while in TW water samples it was between 29 to 55 mg L. The association of NO with other selected parameter in groundwater can be determined by using statistical approaches. Different physicochemical parameters (pH, electrical conductivity (EC), temperature and dissolved oxygen (DO)) were studied in groundwater samples of the research district. The Pearson correlation coefficient (r) for groundwater characteristics were calculated. Hierarchical Cluster Analysis (HCA) was used to categorize samples based on their groundwater quality similarities and to find links between groundwater quality factors. The key relationship of the groundwater for HP samples on EC and TDS ( = 1) had a great correlation, while all other parameters correlations were lower ( = 0.40), BH's parameters on WT and WSD ( = 0.57), WT and pH ( = 0.57), EC and DO ( = 0.50), DO and TDS (0.50), EC and TDS ( = 1) had a quite high correlation, while all other parameters correlations were less than ( = 0.40), on the other hand, tube well parameters on TDS and EC ( = 1) had a perfect correlation, DO and pH ( = 0.75) parameters correlations were less than ( = 0.40).
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http://dx.doi.org/10.1080/09593330.2021.1987532DOI Listing
October 2021

Ameliorating effect of nitrate on nitrite inhibition for denitrifying P-accumulating organisms.

Sci Total Environ 2021 Nov 20;797:149133. Epub 2021 Jul 20.

Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia.

Lowered air supply and organic carbon need are the key factors to reduce wastewater treatment costs and thereby, avoid eutrophication. Denitrifying PO- removal (DPR) process using nitrate instead of oxygen for PO uptake was started up in the sequencing batch reactor (SBR) at a nitrate dosing rate of 20-25 mg N L d. Operation with a real municipal wastewater supplied with CHCOONa, KHPO and KNO succeeded in the cultivation of biomass containing denitrifying polyphosphate accumulating organisms (DPAOs). The durations of SBR process anaerobic/anoxic/oxic cycles were 1.5 h, 3.5 h and 1 h, respectively. SBR operation resulted in a maximum PO-P uptake of 17 mg PO-P g MLSS. The highest TN and PO removal efficiencies were observed during the first half of reactor operation at 77 (±10) % and 71 (±5) %, respectively. An average COD removal rate of 172 (±98) mg g MLSS and a high average removal efficiency of 89 (±4) % were achieved. Nitrite effect with/without nitrate as DPR electron acceptor was investigated in batch-scale to show possibilities to use high nitrite and nitrate contents simultaneously as electron acceptors for the anoxic phosphate uptake. Nitrate attenuation against nitrite toxicity can be economically justified in full-scale treatment applications in which wastewater has a high nitrogen content. Nitrate attenuated nitrite toxicity (caused by nitrite content at 5-100 mg NO-N L) when using supplemental additions of nitrate (at concentrations of 45-200 mg NO-N L) in batch tests. Illumina sequencing emphasized that during biomass adaption microbial community changed by lowered aerobic cycle length and by lowered nitrate dosing towards representation of key DPAO/PAO- organisms, such as Candidatus Accumulibacter, Xanthomonadaceae, Comomonadaceae, Saprospiraceae and Rhodocyclaceae. This study showed that DPAO biomass adaption to nitrate maintained an efficient COD, nitrogen and phosphorus removal and the biomass can be applied for treatment of wastewater containing high nitrite and nitrate content.
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http://dx.doi.org/10.1016/j.scitotenv.2021.149133DOI Listing
November 2021

Synthesis and Characterizations of PdNi Carbon Supported Nanomaterials: Studies of Electrocatalytic Activity for Oxygen Reduction in Alkaline Medium.

Molecules 2021 Jun 5;26(11). Epub 2021 Jun 5.

Department of Pharmacology and Therapeutics, Faculty of Veterinary Medicine, Damanhour University, Damanhour 22511, Egypt.

Electrocatalytic materials offer numerous benefits due to their wide range of applications. In this study, a polyol technique was used to synthesize PdNi nanoparticles (NPs) with different percent atomic compositions (Pd = 50 to 90%) to explore their catalytic efficiency. The produced nanoparticles were characterized using X-ray diffraction (XRD) and electrochemical investigations. According to XRD measurements, the synthesized NPs were crystalline in nature, with crystallite sizes of about 2 nm. The electrochemical properties of the synthesized NPs were studied in alkaline solution through a rotating ring-disk electrode (RRDE) technique of cyclic voltammetry. The PdNi nanoparticles supported on carbon (PdNi/C) were used as electrocatalysts and their activity and stability were compared with the homemade Pd/C and Pt/C. In alkaline solution, PdNi/C electrocatalysts showed improved oxygen reduction catalytic activity over benchmark Pd/C and Pt/C electrocatalysts in all composition ratios. Furthermore, stability experiments revealed that PdNi 50:50 is more stable in alkaline solution than pure Pd and other PdNi compositions.
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http://dx.doi.org/10.3390/molecules26113440DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8201116PMC
June 2021

ANAMMOX-denitrification biomass in microbial fuel cell to enhance the electricity generation and nitrogen removal efficiency.

Biodegradation 2020 12 3;31(4-6):249-264. Epub 2020 Sep 3.

Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India.

The inoculum biomass was collected from a pilot-scale (3 m process tank) nitritation-anaerobic ammonium oxidation (ANAMMOX) (deammonification moving bed biofilm (DeaMBBR)) reactor demonstrating the highest total nitrogen removal rate (TNRR) of 0.33 kg N m day. This biomass was used for inoculating the anodic chamber of a microbial fuel cell (MFC) to investigate the capacity of DeaMBBR biomass to act as an exo-electrogenic consortia. Performance of MFCs inoculated with ANAMMOX-specific consortia collected from DeaMBBR (MFC-ANA) and another MFC-CON inoculated with a septic tank mixed anaerobic consortium as a control was investigated for electrochemical performance and wastewater treatment efficiency. These MFCs were operated for the total duration of 419 days during which regular feed was given and performance was monitored for first 30 cycles and last 30 cycles, with each cycle of 3 day duration. The MFC-ANA continuously generated bio-energy with higher volumetric power density (9.5 W m and 6.0 W m) in comparison to MFC-CON (4.9 and 2.9 W m) during the first 30 and last 30 cycles of operational period, respectively. MFC-ANA also achieved 84 ± 2% and 80 ± 2% of COD removal efficiency and 89 ± 4% and 73 ± 2% of total nitrogen removal efficiency during first 30 and last 30 cycles of operational period, respectively. The improvement of nitrogen removal and power production in case of MFC-ANA over MFC-CON could be attributed to the ANAMMOX-denitrifiers populations and Trichococcus (14.92%) as denitrifying exo-electrogenic microbes (4.46%), respectively.
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http://dx.doi.org/10.1007/s10532-020-09907-wDOI Listing
December 2020

Mainstream-sidestream wastewater switching promotes anammox nitrogen removal rate in organic-rich, low-temperature streams.

Environ Technol 2021 Aug 9;42(19):3073-3082. Epub 2020 Feb 9.

Institute of Chemistry, University of Tartu, Tartu, Estonia.

The main issues with mainstream anammox application are loss of bacterial activity by low temperatures and by a high organic content of wastewater. We demonstrate a novel switching method between sidestream and mainstream wastewater. The wastewater flow was switched between sidestream (reject water at >22°C) and mainstream (municipal wastewater at 16.5°C), so that the anammox biomass activity and biomass growth could benefit from sidestream conditions. Real sidestream wastewater (biogas plant effluent) (≈1000 mg NH -N L) and synthetic mainstream (municipal wastewater-like source) (≈100 mg NH -N) wastewater were used for 20 L biofilm reactor feeding. The highest total nitrogen removal rate (TNRR) of 527 g N m d (average TNRR 180 (±140) g N m d) was achieved with sidestream wastewater at a low chemical oxygen demand (COD)/TN ratio of 1.1/1. For reactor feeding with mainstream, the highest TNRR achieved was 61 g N m d. Average TNRR for mainstream of 20 (±15) g N m d was low due to a higher COD/N ratio of 3.2/1. The highest TNRR in a batch test was achieved at the COD concentration of 480 mg L, reflecting a TNRR of ≈5 mg N g TSS h. With a high COD concentration of 2600 mg L (TOC/TN = 8/1), TNRR decreased similarly in both feeds to 1.6 mg N g TSS h. The anammox microorganism's genus enrichment in deammonification biofilm reactor was higher in the mainstream operation (7.6% of all bacteria) than in sidestream operation period (<0.7% of all bacteria).
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http://dx.doi.org/10.1080/09593330.2020.1721566DOI Listing
August 2021

Prokaryotic diversity and community composition in the Salar de Uyuni, a large scale, chaotropic salt flat.

Environ Microbiol 2017 09 24;19(9):3745-3754. Epub 2017 Aug 24.

Centro Nacional de Investigaciones Biotecnológicas, CNIB, Bolivia.

Salar de Uyuni (SdU), with a geological history that reflects 50 000 years of climate change, is the largest hypersaline salt flat on Earth and is estimated to be the biggest lithium reservoir in the world. Its salinity reaches saturation levels for NaCl, a kosmotropic salt, and high concentrations of MgCL and LiCl, both salts considered important chaotrophic stressors. In addition, extreme temperatures, anoxic conditions, high UV irradiance, high albedo and extremely low concentrations of phosphorous, make SdU a unique natural extreme environment in which to contrast hypotheses about limiting factors of life diversification. Geophysical studies of brines from different sampling stations show that water activity is rather constant along SdU. Geochemical measurements show significant differences in magnesium concentration, ranging from 0.2 to 2M. This work analyses the prokaryotic diversity and community structure at four SdU sampling stations, selected according to their location and ionic composition. Prokaryotic communities were composed of both Archaea (with members of the classes Halobacteria, Thermoplasmata and Nanohaloarchaea, from the Euryarchaeota and Nanohaloarcheota phyla respectively) and Bacteria (mainly belonging to Bacteroidetes and Proteobacteria phyla). The important differences in composition of microbial communities inversely correlate with Mg concentration, suggesting that prokaryotic diversity at SdU is chaotropic dependent.
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http://dx.doi.org/10.1111/1462-2920.13876DOI Listing
September 2017

Modeling Closed Equilibrium Systems of HO-Dissolved CO-Solid CaCO.

J Phys Chem A 2017 Apr 12;121(16):3094-3100. Epub 2017 Apr 12.

Institute of Chemistry, University of Tartu , 14a Ravila St., Tartu 50411, Estonia.

In many places in the world, including North Estonia, the bedrock is limestone, which consists mainly of CaCO. Equilibrium processes in water involving dissolved CO and solid CaCO play a vital role in many biological and technological systems. The solubility of CaCO in water is relatively low. Depending on the concentration of dissolved CO, the solubility of CaCO changes, which determines several important ground- and wastewater parameters, for example, Ca concentration and pH. The distribution of ions and molecules in the closed system solid HO-dissolved CO-solid CaCO is described in terms of a structural scheme. Mathematical models were developed for the calculation of pH and concentrations of ions and molecules (Ca, CO, HCO, HCO, CO, H, and OH) in the closed equilibrium system at different initial concentrations of CO in the water phase using an iteration method. The developed models were then experimentally validated.
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http://dx.doi.org/10.1021/acs.jpca.7b00237DOI Listing
April 2017

Nitrite inhibition and limitation - the effect of nitrite spiking on anammox biofilm, suspended and granular biomass.

Water Sci Technol 2017 Jan;75(2):313-321

Institute of Chemistry, University of Tartu, 14a Ravila St, 50411 Tartu, Estonia E-mail:

Anaerobic ammonium oxidation (anammox) has been studied extensively while no widely accepted optimum values for nitrite (both a substance and inhibitor) has been determined. In the current paper, nitrite spiking (abruptly increasing nitrite concentration in reactor over 20 mg NO-NL) effect on anammox process was studied on three systems: a moving bed biofilm reactor (MBBR), a sequencing batch reactor (SBR) and an upflow anaerobic sludge blanket (UASB). The inhibition thresholds and concentrations causing 50% of biomass activity decrease (IC) were determined in batch tests. The results showed spiked biomass to be less susceptible to nitrite inhibition. Although the values of inhibition threshold and IC concentrations were similar for non-spiked biomass (81 and 98 mg NO-NL, respectively, for SBR), nitrite spiking increased IC considerably (83 and 240 mg NO-NL, respectively, for UASB). As the highest total nitrogen removal rate was also measured at the aforementioned thresholds, there is basis to suggest stronger limiting effect of nitrite on anammox process than previously reported. The quantitative polymerase chain reaction analysis showed similar number of anammox 16S rRNA copies in all reactors, with the lowest quantity in SBR and the highest in MBBR (3.98 × 10 and 1.04 × 10 copies g TSS, respectively).
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http://dx.doi.org/10.2166/wst.2016.456DOI Listing
January 2017

Step-wise temperature decreasing cultivates a biofilm with high nitrogen removal rates at 9°C in short-term anammox biofilm tests.

Environ Technol 2016 Aug 16;37(15):1933-46. Epub 2016 Feb 16.

a Institute of Chemistry, University of Tartu , Ravila Str 14a, 50414 , Tartu , Estonia.

The anaerobic ammonium oxidation (anammox) and nitritation-anammox (deammonification) processes are widely used for N-rich wastewater treatment. When deammonification applications move towards low temperature applications (mainstream wastewater has low temperature), temperature effect has to be studied. In current research, in a deammonification moving bed biofilm reactor a maximum total nitrogen removal rate (TNRR) of 1.5 g N m(-2 )d(-1) (0.6 kg N m(-3 )d(-1)) was achieved. Temperature was gradually lowered by 0.5°C per week, and a similar TNRR was sustained at 15°C during biofilm cultivation. Statistical analysis confirmed that a temperature decrease from 20°C down to 15° did not cause instabilities. Instead, TNRR rose and treatment efficiency remained stable at lower temperatures as well. Quantitative polymerase chain reaction analyses showed an increase in Candidatus Brocadia quantities from 5 × 10(3) to 1 × 10(7) anammox gene copies g(-1) total suspended solids (TSS) despite temperature lowered to 15°C. Fluctuations in TNRR were rather related to changes in influent [Formula: see text] concentration. To study the short-term effect of temperature on the TNRR, a series of batch-scale experiments were performed which showed sufficient TNRRs even at 9-15°C (1.24-3.43 mg N g(-1 )TSS h(-1), respectively) with anammox temperature constants (Q10) ranging 1.3-1.6. Experiments showed that a biofilm adapted to 15°C can perform N-removal most sufficiently at temperatures down to 9°C as compared with biofilm adapted to higher temperature. After biomass was adapted to 15°C, the decrease in TNRR in batch tests at 9°C was lower (15-20%) than that for biomass adapted to 17-18°C.
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http://dx.doi.org/10.1080/09593330.2015.1135995DOI Listing
August 2016

Nitric oxide for anammox recovery in a nitrite-inhibited deammonification system.

Environ Technol 2015 27;36(19):2477-87. Epub 2015 Apr 27.

a Institute of Chemistry, University of Tartu , 14a Ravila St., 50411 Tartu , Estonia.

The anaerobic ammonium oxidation (anammox) process is widely used for N-rich wastewater treatment. In the current research the deammonification reactor in a reverse order (first anammox, then the nitrifying biofilm cultivation) was started up with a high maximum N removal rate (1.4 g N m(-2) d(-1)) in a moving bed biofilm reactor. Cultivated biofilm total nitrogen removal rates were accelerated the most by anammox intermediate - nitric oxide (optimum 58 mg NO-N L(-1)) addition. Furthermore, NO was added in order to eliminate inhibition caused by nitrite concentrations (>50 mg [Formula: see text]) increasing [Formula: see text] (2/1, respectively) along with a higher ratio of [Formula: see text] (0.6/1, respectively) than stoichiometrical for this optimal NO amount added during batch tests. Planctomycetales clone P4 sequences, which was the closest (98% and 99% similarity, respectively) relative to Candidatus Brocadia fulgida sequences quantities increase to 1 × 10(6) anammox gene copies g(-1) total suspended solids to till day 650 were determined by quantitative polymerase chain reaction.
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http://dx.doi.org/10.1080/09593330.2015.1034791DOI Listing
September 2016

Start-up of low-temperature anammox in UASB from mesophilic yeast factory anaerobic tank inoculum.

Environ Technol 2015 Jan-Feb;36(1-4):214-25. Epub 2014 Aug 20.

a Institute of Chemistry, University of Tartu , 14a Ravila Rd., Tartu 50411 , Estonia.

Robust start-up of the anaerobic ammonium oxidation (anammox) process from non-anammox-specific seeding material was achieved by using an inoculation with sludge-treating industrial [Formula: see text]-, organics- and N-rich yeast factory wastewater. N-rich reject water was treated at 20°C, which is significantly lower than optimum treatment temperature. Increasing the frequency of biomass fluidization (from 1-2 times per day to 4-5 times per day) through feeding the reactor with higher flow rate resulted in an improved total nitrogen removal rate (from 100 to 500 g m(-3)d(-1)) and increased anammox bacteria activity. As a result of polymerase chain reaction (PCR) tests, uncultured planctomycetes clone 07260064(4)-2-M13-_A01 (GenBank: JX852965) was identified from the biomass taken from the reactor. The presence of anammox bacteria after cultivation in the reactor was confirmed by quantitative PCR (qPCR); an increase in quantity up to ∼2×10(6) copies g VSS(-1) during operation could be seen in qPCR. Statistical modelling of chemical parameters revealed the roles of several optimized parameters needed for a stable process.
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http://dx.doi.org/10.1080/09593330.2014.941946DOI Listing
September 2015

Comparison of sulfate-reducing and conventional Anammox upflow anaerobic sludge blanket reactors.

J Biosci Bioeng 2014 Oct 23;118(4):426-33. Epub 2014 May 23.

Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia.

Autotrophic NH4(+) removal has been extensively researched, but few studies have investigated alternative electron acceptors (for example, SO4(2-)) in NH4(+) oxidation. In this study, sulfate-reducing anaerobic ammonium oxidation (SRAO) and conventional Anammox were started up in upflow anaerobic sludge blanket reactors (UASBRs) at 36 (±0.5)°C and 20 (±0.5)°C respectively, using reject water as a source of NH4(+). SO4(2-) or NO2(-), respectively, were applied as electron acceptors. It was assumed that higher temperature could promote the SRAO, partly compensating its thermodynamic disadvantage comparing with the conventional Anammox to achieve comparable total nitrogen (TN) removal rate. Average volumetric NH4(+)-N removal rate in the sulfate-reducing UASBR1 was however 5-6 times less (0.03 kg-N/(m(3) day)) than in the UASBR2 performing conventional nitrite-dependent autotrophic nitrogen removal (0.17 kg-N/(m(3) day)). However, the stoichiometric ratio of NH4(+) removal in UASBR1 was significantly higher than could be expected from the extent of SO4(2-) reduction, possibly due to interactions between the N- and S-compounds and organic matter of the reject water. Injections of N2H4 and NH2OH accelerated the SRAO. Similar effect was observed in batch tests with anthraquinone-2,6-disulfonate (AQDS). For detection of key microorganisms PCR-DGGE was used. From both UASBRs, uncultured bacterium clone ATB-KS-1929 belonging to the order Verrucomicrobiales, Anammox bacteria (uncultured Planctomycete clone Pla_PO55-9) and aerobic ammonium-oxidizing bacteria (uncultured sludge bacterium clone ASB08 "Nitrosomonas") were detected. Nevertheless the SRAO process was shown to be less effective for the treatment of reject water, compared to the conventional Anammox.
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http://dx.doi.org/10.1016/j.jbiosc.2014.03.012DOI Listing
October 2014

Arsenic thiolation and the role of sulfate-reducing bacteria from the human intestinal tract.

Environ Health Perspect 2014 Aug 9;122(8):817-22. Epub 2014 May 9.

Laboratorium voor Microbiële Ecologie en Technologie, Faculteit Bio-ingenieurswetenschappen, Universiteit Gent, Gent, Belgium.

Background: Arsenic (As) toxicity is primarily based on its chemical speciation. Although inorganic and methylated As species are well characterized in terms of metabolism and formation in the human body, the origin of thiolated methylarsenicals is still unclear.

Objectives: We sought to determine whether sulfate-reducing bacteria (SRB) from the human gut are actively involved in the thiolation of monomethylarsonic acid (MMAV).

Methods: We incubated human fecal and colon microbiota in a batch incubator and in a dynamic gut simulator with a dose of 0.5 mg MMAV in the absence or presence of sodium molybdate, an SRB inhibitor. We monitored the conversion of MMAV into monomethyl monothioarsonate (MMMTAV) and other As species by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry analysis. We monitored the sulfate-reducing activity of the SRB by measuring hydrogen sulfide (H2S) production. We used molecular analysis to determine the dominant species of SRB responsible for As thiolation.

Results: In the absence of sodium molybdate, the SRB activity-primarily derived from Desulfovibrio desulfuricans (piger)-was specifically and proportionally correlated (p < 0.01) to MMAV conversion into MMMTAV. Inactivating the SRB with molybdate did not result in MMAV thiolation; however, we observed that the microbiota from a dynamic gut simulator were capable of demethylating 4% of the incubated MMAV into arsenous acid (iAsIII), the trivalent and more toxic form of arsenic acid (iAsV).

Conclusion: We found that SRB of human gastrointestinal origin, through their ability to produce H2S, were necessary and sufficient to induce As thiolation. The toxicological consequences of this microbial As speciation change are not yet clear. However, given the efficient epithelial absorption of thiolated methylarsenicals, we conclude that the gut microbiome-and SRB activity in particular-should be incorporated into toxicokinetic analysis carried out after As exposure.
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http://dx.doi.org/10.1289/ehp.1307759DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4123032PMC
August 2014

Nitritating-anammox biomass tolerant to high dissolved oxygen concentration and C/N ratio in treatment of yeast factory wastewater.

Environ Technol 2014 May-Jun;35(9-12):1565-76

Maintaining stability of low concentration (< 1 g L(-1)) floccular biomass in the nitritation-anaerobic ammonium oxidation (anammox) process in the sequencing batch reactor (SBR) system for the treatment of high COD (> 15,000 mg O2 L(-1)) to N (1680 mg N L(-1)) ratio real wastewater streams coming from the food industry is challenging. The anammox process was suitable for the treatment of yeast factory wastewater containing relatively high and abruptly increased organic C/N ratio and dissolved oxygen (DO) concentrations. Maximum specific total inorganic nitrogen (TIN) loading and removal rates applied were 600 and 280 mg N g(-1) VSS d(-1), respectively. Average TIN removal efficiency over the operation period of 270 days was 70%. Prior to simultaneous reduction of high organics (total organic carbon > 600mg L(-1)) and N concentrations > 400 mg L(-1), hydraulic retention time of 15 h and DO concentrations of 3.18 (+/- 1.73) mg O2 L(-1) were applied. Surprisingly, higher DO concentrations did not inhibit the anammox process efficiency demonstrating a wider application of cultivated anammox biomass. The SBR was fed rapidly over 5% of the cycle time at 50% volumetric exchange ratio. It maintained high free ammonia concentration, suppressing growth of nitrite-oxidizing bacteria. Partial least squares and response surface modelling revealed two periods of SBR operation and the SBR performances change at different periods with different total nitrogen (TN) loadings. Anammox activity tests showed yeast factory-specific organic N compound-betaine and inorganic N simultaneous biodegradation. Among other microorganisms determined by pyrosequencing, anammox microorganism (uncultured Planctomycetales bacterium clone P4) was determined by polymerase chain reaction also after applying high TN loading rates.
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http://dx.doi.org/10.1080/09593330.2013.874492DOI Listing
May 2014

Deammonification process start-up after enrichment of anammox microorganisms from reject water in a moving-bed biofilm reactor.

Environ Technol 2013 Nov-Dec;34(21-24):3095-101

Deammonification via intermittent aeration in biofilm process for the treatment of sewage sludge digester supernatant (reject water) was started up using two opposite strategies. Two moving-bed biofilm reactors were operated for 2.5 years at 26 (+/- 0.5 degree C with spiked influent(and hence free ammonia (FA)) addition. In the first start-up strategy, an enrichment of anammox biomass was first established, followed by the development of nitrifying biomass in the system (R1). In contrast, the second strategy aimed at the enrichment of anammox organisms into a nitrifying biofilm (R2). The first strategy was most successful, reaching higher maximum total nitrogen (TN) removal rates over a shorter start-up period. For both reactors, increasing FA spiking frequency and increasing effluent concentrations of the anammox intermediate hydrazine correlated to decreasing aerobic nitrate production (nitritation). The bacterial consortium of aerobic and anaerobic ammonium oxidizing bacteria in the bioreactor was determined via denaturing gel gradient electrophoresis, polymerase chain reaction and pyrosequencing. In addition to a shorter start-up with a better TN removal rate, nitrite oxidizing bacteria (Nitrospira) were outcompeted by spiked ammonium feeding from R1.
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http://dx.doi.org/10.1080/09593330.2013.803134DOI Listing
April 2014

Effect of HCO3- concentration on anammox nitrogen removal rate in a moving bed biofilm reactor.

Environ Technol 2012 Oct-Nov;33(19-21):2263-71

Institute of Chemistry, University of Tartu, Tartu, Estonia.

Anammox biomass enriched in a moving bed biofilm reactor (MBBR) fed by actual sewage sludge reject water and synthetically added NO2- was used to study the total nitrogen (TN) removal rate of the anammox process depending on bicarbonate (HCO3-) concentration. MBBR performance resulted in the maximum TN removal rate of 1100 g N m(-3) d(-1) when the optimum HCO3- concentration (910 mg L(-1)) was used. The average reaction ratio of NO2- removal, NO3- production and NH4+ removal were 1.18/0.20/1. When the HCO3- concentration was increased to 1760mg L(-1) the TN removal rate diminished to 270 g N m(-3) d(-1). The process recovered from bicarbonate inhibition within 1 week. The batch tests performed with biomass taken from the MBBR showed that for the HCO3- concentration of 615 mg L(-1) the TN removal rate was 3.3 mg N L(-1) h(-1), whereas for both lower (120 mg L(-1)) and higher (5750 mg L(-1)) HCO3- concentrations the TN removal rates were 2.3 (+/- 0.15) and 1.6 (+/- 0.12) mg N L(-1) d(-1), respectively. PCR and DGGE analyses resulted in the detection of uncultured Planctomycetales bacterium clone P4 and, surprisingly, low-oxygen-tolerant aerobic ammonia oxidizers. The ability of anammox bacteria for mixotrophy was established by diminished amounts of nitrate produced when comparing the experiments with an organic carbon source and an inorganic carbon source.
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http://dx.doi.org/10.1080/09593330.2012.665487DOI Listing
March 2013

Accelerating effect of hydroxylamine and hydrazine on nitrogen removal rate in moving bed biofilm reactor.

Biodegradation 2012 Sep 8;23(5):739-49. Epub 2012 Apr 8.

Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia.

In biological nitrogen removal, application of the autotrophic anammox process is gaining ground worldwide. Although this field has been widely researched in last years, some aspects as the accelerating effect of putative intermediates (mainly N₂H₄ and NH₂OH) need more specific investigation. In the current study, experiments in a moving bed biofilm reactor (MBBR) and batch tests were performed to evaluate the optimum concentrations of anammox process intermediates that accelerate the autotrophic nitrogen removal and mitigate a decrease in the anammox bacteria activity using anammox (anaerobic ammonium oxidation) biomass enriched on ring-shaped biofilm carriers. Anammox biomass was previously grown on blank biofilm carriers for 450 days at moderate temperature 26.0 (±0.5) °C by using sludge reject water as seeding material. FISH analysis revealed that anammox microorganisms were located in clusters in the biofilm. With addition of 1.27 and 1.31 mg N L⁻¹ of each NH₂OH and N₂H₄, respectively, into the MBBR total nitrogen (TN) removal efficiency was rapidly restored after inhibitions by NO₂⁻. Various combinations of N₂H₄, NH₂OH, NH₄⁺, and NO₂⁻ were used as batch substrates. The highest total nitrogen (TN) removal rate with the optimum N₂H₄ concentration (4.38 mg N L⁻¹) present in these batches was 5.43 mg N g⁻¹ TSS h⁻¹, whereas equimolar concentrations of N₂H₄ and NH₂OH added together showed lower TN removal rates. Intermediates could be applied in practice to contribute to the recovery of inhibition-damaged wastewater treatment facilities using anammox technology.
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http://dx.doi.org/10.1007/s10532-012-9549-6DOI Listing
September 2012

Anammox enrichment from reject water on blank biofilm carriers and carriers containing nitrifying biomass: operation of two moving bed biofilm reactors (MBBR).

Biodegradation 2012 Jul 5;23(4):547-60. Epub 2012 Feb 5.

Institute of Chemistry, University of Tartu, 14a Ravila St., 50411, Tartu, Estonia.

The anammox bacteria were enriched from reject water of anaerobic digestion of municipal wastewater sludge onto moving bed biofilm reactor (MBBR) system carriers-the ones initially containing no biomass (MBBR1) as well as the ones containing nitrifying biomass (MBBR2). Duration of start-up periods of the both reactors was similar (about 100 days), but stable total nitrogen (TN) removal efficiency occurred earlier in the system containing nitrifying biomass. Anammox TN removal efficiency of 70% was achieved by 180 days in both 20 l volume reactors at moderate temperature of 26.0°C. During the steady state phase of operation of MBBRs the average TN removal efficiencies and maximum TN removal rates in MBBR1 were 80% (1,000 g-N/m(3)/day, achieved by 308 days) and in MBBR2 85% (1,100 g-N/m(3)/day, achieved by 266 days). In both reactors mixed bacterial cultures were detected. Uncultured Planctomycetales bacterium clone P4, Candidatus Nitrospira defluvii and uncultured Nitrospira sp. clone 53 were identified by PCR-DGGE from the system initially containing blank biofilm carriers as well as from the nitrifying biofilm system; from the latter in addition to these also uncultured ammonium oxidizing bacterium clone W1 and Nitrospira sp. clone S1-62 were detected. FISH analysis revealed that anammox microorganisms were located in clusters in the biofilm. Using previously grown nitrifying biofilm matrix for anammox enrichment has some benefits over starting up the process from zero, such as less time for enrichment and protection against severe inhibitions in case of high substrate loading rates.
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http://dx.doi.org/10.1007/s10532-011-9532-7DOI Listing
July 2012

Sulfate-reducing anaerobic ammonium oxidation as a potential treatment method for high nitrogen-content wastewater.

Biodegradation 2012 Jul 29;23(4):509-24. Epub 2011 Dec 29.

Institute of Chemistry, University of Tartu, 14a Ravila Street, 50411, Tartu, Estonia.

After sulfate-reducing ammonium oxidation (SRAO) was first assumed in 2001, several works have been published describing this process in laboratory-scale bioreactors or occurring in the nature. In this paper, the SRAO process was performed using reject water as a substrate for microorganisms and a source of NH(4) (+), with SO(4) (2-) being added as an electron acceptor. At a moderate temperature of 20°C in a moving bed biofilm reactor (MBBR) sulfate reduction along with ammonium oxidation were established. In an upflow anaerobic sludge blanket reactor (UASBR) the SRAO process took place at 36°C. Average volumetric TN removal rates of 0.03 kg-N/m³/day in the MBBR and 0.04 kg-N/m³/day in the UASBR were achieved, with long-term moderate average removal efficiencies, respectively. Uncultured bacteria clone P4 and uncultured planctomycete clone Amx-PAn30 were detected from the biofilm of the MBBR, from sludge of the UASBR uncultured Verrucomicrobiales bacterium clone De2102 and Uncultured bacterium clone ATB-KS-1929 were found also. The stoichiometrical ratio of NH(4) (+) removal was significantly higher than could be expected from the extent of SO(4) (2-) reduction. This phenomenon can primarily be attributed to complex interactions between nitrogen and sulfur compounds and organic matter present in the wastewater. The high NH(4) (+) removal ratio can be attributed to sulfur-utilizing denitrification/denitritation providing the evidence that SRAO is occurring independently and is not a result of sulfate reduction and anammox. HCO(3) (-) concentrations exceeding 1,000 mg/l were found to have an inhibiting effect on the SRAO process. Small amounts of hydrazine were naturally present in the reaction medium, indicating occurrence of the anammox process. Injections of anammox intermediates, hydrazine and hydroxylamine, had a positive effect on SRAO process performance, particularly in the case of the UASBR.
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http://dx.doi.org/10.1007/s10532-011-9529-2DOI Listing
July 2012

Modification of nitrifying biofilm into nitritating one by combination of increased free ammonia concentrations, lowered HRT and dissolved oxygen concentration.

J Environ Sci (China) 2011 ;23(7):1113-21

Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia.

Nitrifying biomass on ring-shaped carriers was modified to nitritating one in a relatively short period of time (37 days) by limiting the air supply, changing the aeration regime, shortening the hydraulic retention time and increasing free ammonia (FA) concentration in the moving-bed biofilm reactor (MBBR). The most efficient strategy for the development and maintenance of nitritating biofilm was found to be the inhibition of nitrifying activity by higher FA concentrations (up to 6.5 mg/L) in the process. Reject water from sludge treatment from the Tallinn Wastewater Treatment Plant was used as substrate in the MBBR. The performance of high-surfaced biocarriers taken from the nitritating activity MBBR was further studied in batch tests to investigate nitritation and nitrification kinetics with various FA concentrations and temperatures. The maximum nitrite accumulation ratio (96.6%) expressed as the percentage of NO2(-)-N/NOx(-)-N was achieved for FA concentration of 70 mg/L at 36 degrees C. Under the same conditions the specific nitrite oxidation rate achieved was 30 times lower than the specific nitrite formation rate. It was demonstrated that in the biofilm system, inhibition by FA combined with the optimization of the main control parameters is a good strategy to achieve nitritating activity and suppress nitrification.
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http://dx.doi.org/10.1016/s1001-0742(10)60523-2DOI Listing
December 2011
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