Marivirga aurantiaca sp. nov., a halophilic nitrite-reducing bacterium, isolated from intertidal surface sediments.

A novel Gram-stain-negative strain, designated S37H4T, was isolated from an intertidal surface sediment sample collected from Zhanjiang City, Guangdong province, south PR China. Cells of the strain were aerobic, non-flagellated, long rod-shaped and motile by gliding. S37H4T could grow at 4-40 °C, pH 7.0-8.5 and in 2.0-15.0 % NaCl, with optimal growth at 25-30 °C, pH 7.5 and 9.0 % NaCl, respectively. S37H4T was capable of nitrite removal under high-salt conditions, and there were three denitrification genes, nirK, norB and nosZ, in its genome. The results of phylogenetic analyses based on the 16S rRNA gene and genome sequences indicated that S37H4T represented a member of the genus Marivirga and formed a subclade with Marivirga lumbricoides JLT2000T. S37H4T showed the highest 16S rRNA sequence similarity to M. lumbricoides JLT2000T (98.3 %) and less than 97.0 % similarity with other type strains of species of the genus Marivirga. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between S37H4T and the reference type strains of species of the genus Marivirga were 70.7-74.3 % and 18.2-19.2 %, respectively. The major fatty acids of S37H4T were iso-C15 : 0, iso-C15 : 1G, iso-C17 : 0 3-OH and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c). The major respiratory quinone of this novel strain was MK-7, and the predominant polar lipids were identified as phosphatidylethanolamine, an unidentified aminolipid, an unidentified phospholipid and three unidentified lipids. The results of analyses of phylogenetic, genomic, physiological and biochemical characteristics indicated that S37H4T represented a novel species of the genus Marivirga, for which the name Marivirga aurantiaca sp. nov. is proposed. The type strain is S37H4T (= GDMCC 1.1866T = KACC 21922T).

Application of Surface-Modified Nanoclay in a Hybrid Adsorption-Ultrafiltration Process for Enhanced Nitrite Ions Removal: Chemometric Approach vs. Machine Learning.

Herein, we report the results of a study on combining adsorption and ultrafiltration in a single-stage process to remove nitrite ions from contaminated water. As adsorbent, a surface-modified nanoclay was employed (i.e., Nanomer® I.28E, containing 25-30 wt. % trimethyl stearyl ammonium). Ultrafiltration experiments were conducted using porous polymeric membranes (Ultracel® 10 kDa). The hybrid process of adsorption-ultrafiltration was modeled and optimized using three computational tools: (1) response surface methodology (RSM), (2) artificial neural network (ANN), and (3) support vector machine (SVM). The optimal conditions provided by machine learning (SVM) were found to be the best, revealing a rejection efficiency of 86.3% and an initial flux of permeate of 185 LMH for a moderate dose of the nanoclay (0.674% w/v). Likewise, a new and more retentive membrane (based on PVDF-HFP copolymer and halloysite (HS) inorganic nanotubes) was produced by the phase-inversion method, characterized by SEM, EDX, AFM, and FTIR techniques, and then tested under optimal conditions. This new composite membrane (PVDF-HFP/HS) with a thickness of 112 µm and a porosity of 75.32% unveiled an enhanced rejection efficiency (95.0%) and a lower initial flux of permeate (28 LMH). Moreover, molecular docking simulations disclosed the intermolecular interactions between nitrite ions and the functional moiety of the organonanoclay.

Enhancement of iron-based nitrogen removal with an electric-magnetic field in an upflow microaerobic sludge reactor (UMSR).

Traditional denitrification often produces high operating costs and excessive sludge disposal expenses due to conventional carbon sources. A novel electric-magnetic field (MF) 48 mT with Fe0 and C-Fe0 powder in an upflow microaerobic sludge reactor (UMSR) improved nitrogen removal from wastewater without organic carbon resources and gave richness to the heterotrophic bacterial community. In the current study, the reactor was operated for 78 ± 2 days, divided into five stages (without Fe0, with Fe0, coupling with MF, without coupling with MF, and coupling with MF again), at a hydraulic retention time (HRT) of 2.5 h, with an influent loading of ammonium (NH4+-N) 50 ± 2 mg/L, at 25-27 °C, and less than 1.0 mg/L dissolved oxygen (DO). The results demonstrated nitrogen removal efficiency enhanced after coupling with MF on the levels of NO3--N by 76% with an effluent concentration of 8.7 mg/L, NH4+-N by 72% with an effluent concentration of 13.6 mg/L, and total nitrogen removal (TN) by 76%, respectively. After coupling the MF with the reactor, the microbial community data analysis showed the dominant abundance of ammonia-oxidizing bacteria, heterotrophic nitrifying bacteria, and denitrifying bacteria on the level of Anaerolineaceae_uncultured 2%, which is capable of denitrification that uses Fe2+ as an electron source, Gemmatimonadaceae_uncultured 4%, Hydrogenophaga 4% which is capable of catalyzing hydrogenotrophic denitrification and correlating to nitrate removal, denitrification and desulfurization bacteria SBR1031_norank 18%, anammox-bacteria Saccharimonadales_norank 2%, and (AOM) Limnobacter 3% in the sludge.

Nitrite reduction using a membrane biofilm reactor (MBfR) in a hypoxic environment with dilute methane under low pressures.

Methane-based membrane biofilm reactors (MBfRs) can be an effective solution for nitrogen control in wastewater, but there is limited information on nitrite reduction for dilute wastewater (e.g., municipal wastewater) in hypoxic MBfRs. This study assessed the impacts of dilute (20 %), low-pressure methane (0.35-2.41 kPa) applied to MBfRs at hydraulic retention times (HRTs) of 2-12 h on nitrite removals, dissolved methane concentrations, and the resulting changes in the microbial community. High nitrite flux along with rapid and virtually complete (>99 %) nitrite removals were observed at methane pressures of 1.03-2.41 kPa at HRTs above 4 h, despite the use of diluted methane gas for the MBfR. The lowest methane pressure (0.35 kPa) was also able to achieve up to 98 % nitrite removals but required HRTs of up to 12 h. All scenarios had low dissolved methane concentrations (<10 mg/L), indicating that dilute methane at low supply pressures can effectively remove nitrite while meeting dissolved methane guidelines in treated effluent. Methylococcus genus was the key bacterium in MBfR biofilm grown at different HRTs and methane pressures, along with Methylocystis and other heterotrophic denitrifiers (Terrimonas and Hyphomicrobium). This study indicates that methane-based denitrification MBfRs can be a valuable tool to meet nitrogen limits for dilute wastewater coupled to partial nitrification, while limiting the release of methane to the environment.

Nitrite removal by Acinetobacter sp.TX: a candidate of curbing N2O emission.

The nitrite removal pathway in Acinetobacter sp. TX5 was explored through the key gene identification and the corresponding enzyme purification, after which the capability to reduce nitrite by immobilized beads was investigated in a fixed-bed reactor. Results revealed that a nosZ gene encoding nitrous oxide reductase (N2OR) exists in TX5 cells, and a N2OR responsible for the reduction of N2O to N2 was purified successfully with a molecular weight of 70.05 kDa, a purification fold of 16.30 and a recovery rate of 5.17%. For TX5 immobilization, the optimal values of polyvinyl alcohol (PVA), spent mushroom substrate (SMS) and Aci (TX5) obtained by response surface methodology (RSM) were 6.32%, 2.92% and 4.57%, respectively. In a fixed-bed reactor packed with immobilized TX5, the removal efficiency (RE) achieved 90% (at 50 h) for NO2--N and 85% (at 96 h) for total nitrogen (TN). On the basis of these results, a nitrite removal pathway in TX5 was proposed. Overall, Acinetobacter sp. TX5 might be a promising candidate for nitrite removal with an ability to suppress N2O accumulation.

Response difference of simultaneous sulfide and nitrite removal process to different cooling modes.

The effects of various cooling modes (sudden cooling (25℃→10℃) and step cooling (25℃→20℃→15℃→10℃)) on the performance of simultaneous sulfide and nitrite removal process were reported. Regardless of cooling mode adopted, the process maintained good sulfide removal performance, and removal percentage was 100.00%. Considering nitrite removal percentage, the process was more sensitive to step cooling mode (k = 0.06707) in comparison to sudden cooling mode (k = 0.02760). Lowering temperature promoted the transformation from sulfate to elemental sulfur, and it was easier to increase the proportion of elemental sulfur (79.90%) by means of step cooling. The sulfide oxidation rate and nitrite reduction rate were 0.01540 mg /(L∙min) and 0.00354 mg /(L∙min), respectively, in the sudden cooling mode, and 0.01168 mg /(L∙min) and 0.00138 mg /(L∙min), respectively, in the step cooling mode. Low temperature reduced the diversity of microbial community, and Sulfurovum was still a dominant bacterial member in both cooling modes.

Microalgal-bacterial granular sludge process for non-aerated aquaculture wastewater treatment.

Microalgal-bacterial granular sludge (MBGS) process has become a focal point in treating municipal wastewater. However, it remains elusive whether the emerging process can be applied for the treatment of aquaculture wastewater, which contains considerable concentrations of nitrate and nitrite. This study evaluated the feasibility of MBGS process for aquaculture wastewater treatment. Result showed that the MBGS process was competent to remove respective 64.8%, 84.9%, 70.8%, 50.0% and 84.2% of chemical oxygen demand, ammonia-nitrogen, nitrate-nitrogen, nitrite-nitrogen and phosphate-phosphorus under non-aerated conditions within 8 h. The dominant microalgae and bacteria were identified to be Coelastrella and Rhodobacteraceae, respectively. Further metagenomics analysis implied that microbial assimilation was the main contributor in organics, nitrogen and phosphorus removal. Specifically, considerable nitrate and nitrite removals were also obtained with the synergy between microalgae and bacteria. Consequently, this work demonstrated that the MBGS process showed a prospect of becoming an environmentally friendly and efficient alternative in aquaculture wastewater treatment.

Fish pond water treatment using ultrasonic cavitation and advanced oxidation processes.

This investigation explores the efficacy of employing ultrasonic cavitation and coupling it with advanced oxidation processes (hydrogen peroxide and Fenton's reagent) for reducing the levels of total ammonia nitrogen in fish pond water containing Tilapia fishes. Ultrasonic cavitation is a phenomenon where the formation, growth and collapse of vaporous bubbles occur in a liquid medium producing highly reactive free radicals. Ultrasonic probe system (20 kHz with 750 W and 1000 W) was used to induce cavitation. Besides, to intensify the process, ultrasonic cavitation was coupled with hydrogen peroxide and Fenton's reagent. Using SERA colour indicator test kits, the levels of ammonium, nitrite and carbonate hardness were measured. The results obtained from this study clearly show that the advanced oxidation processes are more efficient in reducing the ammonium and nitrite levels in fish pond water than using ultrasound alone. The pH and carbonate hardness levels were not affected significantly by ultrasonic cavitation. The optimal treatment time and ultrasound power to treat the water samples were also established. Energy efficiency and cost analysis of this treatment have also been presented, indicating that ultrasonic cavitation coupled with hydrogen peroxide appears to be a promising technique for reducing total ammonia nitrogen levels in the fish pond water.

Combined electrocoagulation and electrochemical oxidation treatment for groundwater denitrification.

Electrocoagulation (EC) with an aluminum electrode arrangement as anode-cathode was applied to denitrify groundwater and electrooxidation (EO) was examined as a post-treatment step to remove the produced by-products. Initially, EC experiments were performed under batch operating mode using artificially-polluted tap water to investigate the effects of initial pH (5.5, 7.5, 8.5), initial NO3--N concentration (25, 35, 45, 55 mg L-1) and applied current density (10, 20 mA cm-2) on process efficiency. The effect of initial solution pH on ammonium cation concentration was also investigated as their generation (as a by-product) is the main drawback preventing wide-scale application of these treatment processes. Experimental results revealed high nitrate removal percentages (up to 96.3%) for initial pH 7.5 and all initial concentrations and current densities, while the final ammonium concentrations ranged between 5.3 and 9.2 mg NH4+-N L-1 (for initial NO3--N of 25 mg L-1). Therefore, EO was examined to oxidize the ammonium cations to nitrogen gas on iridium oxide coated titanium electrodes (IrO2/Ti) anode surface. The effects of cathode material (aluminum, stainless steel), total current density and anode surface area (3.3-30 mA cm-2 and 12-36 cm2, respectively) were investigated, and lead to NH4+-N percentage removals of between 25% (10 mA cm-2, 12 cm2) and 100% (30 mA cm-2, 24 cm2) for an initial NH4+-N concentration of 10 mg L-1. The optimum EC (20 mA cm-2, natural initial pH 7.5-7.8) and EO parameters (30 mA cm-2, 24 cm2 surface area anode, Al cathode) were combined into a hybrid system to treat two real nitrate-polluted groundwaters with initial NO3--N concentrations of 25 and 75 mg L-1. Results revealed that the proposed hybrid treatment system can be used to efficiently remove nitrate from groundwaters.

A study on the nitrogen removal efficacy of bacterium Acinetobacter tandoii MZ-5 from a contaminated river of Shenzhen, Guangdong Province, China.

Heterotrophic nitrification-aerobic denitrification (HN-AD) has advantages over the traditional nitrogen removal process when removing multiple types of nitrogen in wastewater treatment. Acinetobacter tandoii MZ-5, which is capable of HN-AD, was isolated from the sediment of a polluted river for the first time. It used NH4+-N, NO2--N and NO3--N as sole nitrogen sources with maximum removal rates of 2.28, 1.18 and 1.04 mg L-1h-1, respectively. Simultaneous nitrification and denitrification were observed when using mixed N sources and NH4+-N was preferentially utilized. High nitrogen removal efficiencies (>90%) were achieved under the following conditions: C/N ratio 11-18, pH 6-8, 25-30 °C and dissolved oxygen 7.35-7.66 mg L-1. Strain MZ-5 was effective at treating wastewater from landfill leachate treatment plants, with NH4+-N, NO3--N and total nitrogen (TN) removal efficiencies of 99.28%, 44.85% and 45.31%, respectively. Thus, strain MZ-5 may be a good candidate for wastewater treatment.

Cold-Resistant Heterotrophic Ammonium and Nitrite-Removing Bacteria Improve Aquaculture Conditions of Rainbow Trout (Oncorhynchus mykiss).

The aim of this study was isolation and characterization of heterotrophic bacteria capable of ammonium and nitrite removal at 15 °C (optimal temperature for growing rainbow trout Oncorhynchus mykiss). Environmental isolates were grown in liquid media containing ammonium or nitrite, and best strains in terms of growth and ammonium or nitrite removal were identified via 16S rRNA sequencing. Dyadobacter sp. (no. 68) and Janthinobacterium sp. (no. 100) were selected for optimal adaptation to growth at 15 °C and best ammonium and nitrite removal (P < 0.05), respectively. A heterotrophic ammonium and nitrite removal (HAN) microbial complex, containing selected strains, was prepared and applied in a trout culture system. After 10 days, the effect of microbial HAN complex was investigated in terms of ammonium and nitrite removal, as well as stress and immune indices present in the plasma of cultivated trout. Compared to a standard cultivation setup, addition of the HAN complex had a clear beneficial effect on keeping the un-ionized ammonia and nitrite level below prescribed standards (P < 0.05). This resulted in reduction of stress and immune reactions of cultivated fish (P < 0.05), leading to an augmentation of final weight and survival. Application of the selected microbial complex resulted in a significant improvement of the aquaculture ecosystem.

Effect of anolytic nitrite concentration on electricity generation and electron transfer in a dual-chamber microbial fuel cell.

This study reports the effect of anolytic nitrite concentration on electricity generation and electron transfer in microbial fuel cells (MFCs). Anolytic nitrite enhanced the electricity generation capability of the MFCs at relatively low concentrations (< 60 mg·L-1) but inhibited the activity of anodic electrogenic bacteria at high concentrations. In the anode chamber of the MFC, nitrite was converted to nitrate-releasing electrons before being quickly removed through denitrification. Nitrite alone (in the absence of organic matters) could not perform as an electricity production matrix but promoted electricity production as a co-matrix in the MFC. At an influent nitrite concentration of 60 mg·L-1, the coulombic efficiency of the MFC was minimized at approximately 5.4%, and the charge transfer resistance was also lowest, while the concentrations of extracellular polymeric substances (EPS) and cytochrome c were both maximized. Higher anolytic nitrite concentrations (> 60 mg·L-1) inhibited the production of cytochrome c and EPS and increased the charge transfer resistance, thereby reducing the efficiency of electron transfer in the anodic biofilm. The results provide valuable guidelines for MFC applications in wastewater treatment processes with nitrite-containing influents.

A Novel Nitrite-Base Aerobic Denitrifying Bacterium Acinetobacter sp. YT03 and Its Transcriptome Analysis.

Nitrite in a water environment is very harmful to humans and aquatic animals. A novel aerobic denitrifying bacterium able to utilize NO 2 - -N as the only nitrogen source was isolated for the purpose of removing nitrite from water, which was identified as Acinetobacter sp. and named as YT03. The growth and denitrification activity of strain YT03 was assessed comprehensively. Results showed that the nitrite in water with an initial concentration of 10 mg L-1 could be completely removed within 6 h by strain YT03, and the optimal conditions for strain YT03 to remove nitrite were as follows: sodium succinate as the carbon source, C/N ratio of 16, pH of 6.5, temperature of 30°C, and shaking speed of 250 rpm. An RNA-Seq transcriptome analysis was used to find genes associated with nitrite removal. Compared with the removal of ammonia nitrogen, 47 genes were significantly differentially expressed, including 20 up-regulated and 27 down-regulated genes, mainly involved in the transport process, biosynthetic process, and so on. And among the differentially expressed genes, C4-dicarboxylate transporter (DctA) and nitrate/nitrite transporter (Nrt) might be of importance for the efficient utilization of carbon and nitrogen sources in aerobic nitrite denitrification with sodium succinate by strain YT03.

Simultaneous removal of nitrate and nitrite using electrocoagulation/floatation (ECF): A new multi-response optimization approach.

This study aims to remove both nitrate and nitrite from wastewater as well as modeling and simultaneous optimizing the electrocoagulation/floatation (ECF) process with 3 responses, namely, the residual nitrate, the residual nitrite and the operating costs; so that all responses meet the standard limitations. For this purpose, 57 experiments designed by the response surface method (RSM) were carried out. The effect of selected variables, including initial pH, current intensity, initial nitrate concentration, number of electrodes, reaction time and their interactions were evaluated. The analysis of variance (ANOVA) confirmed that the predicted equations were in reasonable agreement with the experimental data for three responses. To reach a new multi-response optimization approach, a code was developed in MATLAB software, which was applied to optimize the responses all together. Eight optimized conditions were obtained in accordance with the residual nitrate and the residual nitrite of less than 50 mg/L and 10 mg/L, respectively, and the limited operating costs to 10 ±â€¯0.05 US$/(kg NO3-removed).

Biopotentiality of High Efficient Aerobic Denitrifier Bacillus megaterium S379 for Intensive Aquaculture Water Quality Management.

Excessive nitrite accumulation is a very tough issue for intensive aquaculture. A high efficient aerobic denitrifier Bacillus megaterium S379 with 91.71±0.17% of NO2--N (65 mg L-1) removal was successfully isolated for solving the problem. Denitrification of S379 showed excellent environment adaptation that it kept high nitrite removal ratio (more than 85%) when temperature ranged from 25°C to 40°C and pH varied between 7.0 and 9.0, and could endure as high as 560 mg L-1 of NO2--N. Immobilization of S379 could enhance denitrification even when NO2--N adding amount got to 340 mg L-1. Immobilized cells also showed well pollutants removal performance in aquaculture wastewater treatment. Moreover, S379 possessed positive hydrolase activities for starch, casein, cellulose and fat and bore more than 60 ppt of salinity. Totally, all the results revealed significant potentiality of immobilized S379 applied in aquaculture water quality management.

Potential for aerobic NO2- reduction and corresponding key enzyme genes involved in Alcaligenes faecalis strain NR.

The potential for aerobic NO2- removal by Alcaligenes faecalis strain NR was investigated. 35 mg/L of NO2--N was removed by strain NR under aerobic conditions in the presence of NH4+. 15N-labeling experiment demonstrated that N2O and N2 were possible products during the aerobic nitrite removal process by strain NR. The key enzyme genes of nirK, norB and nosZ, which regulate the aerobic nitrite denitrification process, were successfully amplified from strain NR. The gene sequence analysis indicates that copper-containing nitrite reductase (NIRK) and periplasmic nitrous oxide reductase (NOSZ) were both hydrophilic protein and the transmembrane structures were absent, while nitric oxide reductase large subunit (NORB) was a hydrophobic and transmembrane protein. According to the three-dimensional structure and binding site analysis, the bulky and hydrophobic methionine residue proximity to the nitrite binding sites of NIRK was speculated to be related to the oxygen tolerance of NIRK from strain NR.

Microbial mediated iron redox cycling in Fe (hydr)oxides for nitrite removal.

Nitrite, at an environmentally relevant concentration, was significantly reduced with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. The average nitrite removal rates of 1.28±0.08 and 0.65±0.02(mgL-1)h-1 were achieved with ferrihydrite and magnetite, respectively. The results showed that nitrite removal was able to undergo multiple redox cycles with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. During the bioreduction of the following cycles, biogenic Fe(II) was subsequently chemically oxidized to Fe(III), which is associated with nitrite reduction. There was 11.18±1.26mgL-1 of NH4+-N generated in the process of redox cycling of ferrihydrite. Additionally, results obtained by using X-ray diffraction showed that ferrihydrite and magnetite remained mainly stable in the system. This study indicated that redox cycling of Fe in iron (hydr)oxides was a potential process associated with NO2--N removal from solution, and reduced most nitrite abiotically to gaseous nitrogen species.

Nitrogen removal characteristics of a heterotrophic nitrifier Acinetobacter junii YB and its potential application for the treatment of high-strength nitrogenous wastewater.

Acinetobacter junii YB was found to exhibit efficient heterotrophic nitrification and aerobic denitrification ability, with the maximum ammonium, nitrite and nitrate removal rate of 8.82, 8.45 and 7.98 mg/L/h, respectively. Meanwhile, ammonium was found to be removed preferentially in the process of simultaneous nitrification and denitrification in mixed N-sources. The successful PCR amplification of hao, napA and nirS genes further provided additional evidence of heterotrophic nitrification and aerobic denitrification by strain YB. In addition, orthogonal test showed that dissolved oxygen was the most important determinant of nitrite removal, and the optimal conditions were C/N 15, pH 7.0, 37 °C and 200 rpm. Furthermore, stable nitrogen and organics removal were achieved by one-time dosing of enriched bacteria in a sequencing batch reactor. The inoculation of strain YB significantly improved the denitrification efficiency with minimal accumulation of nitrified products, which demonstrated high potential of the isolate for future practical applications.

Using Bacillus amyloliquefaciens for remediation of aquaculture water.

Remediation of aquaculture water using microorganisms like Bacillus species is a burgeoning trend for the sustainable development of aquaculture industries. In this work, a Bacillus amyloliquefaciens strain (namely B. amyloliquefaciens HN), isolated from activated sludge of a polluted river, was evaluated for its potential in water remediation using simulated aquaculture water. B. amyloliquefaciens HN exhibited high tolerance towards 80 mg l(-1) of nitrite-N and ammonia-N. It could effectively remove 20 mg l(-1) of nitrite-N, but was inefficient in eliminating ammonia-N when the ammonia-N concentration was below 20 mg l(-1). Further studies showed that the ammonia-N removal by B. amyloliquefaciens HN was more efficient at 30°C and 35°C than 25°C, and that maximum nitrite-N removal rate was achieved at pH 8.