A novel derivative synchronous fluorescence method for the rapid, non-destructive and intuitive differentiation of denitrifying bacteria

It is challenging to differentiate bacteria residing in the same habitat by direct observation. This difficulty impedes the harvest, application and manipulation of functional bacteria in environmental engineering. In this study, we developed a novel method for rapid differentiation of living denitrifying bacteria based on derivative synchronous fluorescence spectroscopy, as exemplified by three heterotrophic nitrification-aerobic denitrification bacteria having the maximum nitrogen removal efficiencies greater than 90%. The intact bacteria and their living surroundings can be analyzed as an integrated target, which eliminates the need for the complex pre-processing of samples. Under the optimal synchronous scanning parameter (Δλ = 40 nm), each bacterium possesses a unique fluorescence spectral structure and the derivative synchronous fluorescence technique can significantly improve the spectral resolution compared to other conventional fluorescence methods, which enables the rapid differentiation of different bacteria through derivative synchronous fluorescence spectra as fast as 2 min per spectrum. Additionally, the derivative synchronous fluorescence technique can extract the spectral signals contributed by bacterial extracellular substances produced in the biological nitrogen removal process. Moreover, the results obtained from our method can reflect the real-time denitrification properties of bacteria in the biological nitrogen removal process of wastewater. All these merits highlight derivative synchronous fluorescence spectroscopy as a promising analytic method in the environmental field.

Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

Heterotrophic nitrification and aerobic denitrification characteristics of the psychrotolerant Pseudomonas peli NR-5 at low temperatures

The nitrogen removal efficiency of heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria can be seriously inhibited at low temperatures (< 15 °C). A novel psychrotolerant bacterium, Pseudomonas peli NR-5 (P. peli NR-5), with efficient HN-AD capability was isolated and screened from river sediments in cold areas. When P. peli NR-5 was aerobically cultivated for 60 h at 10 °C with NH₄⁺-N, NO₃^--N, and NO₂^--N as the sole nitrogen sources (N 105 mg/L), the nitrogen removal efficiencies were 97.3, 95.3, and 87.8%, respectively, without nitrite accumulation, and the corresponding average nitrogen removal rates were 1.71, 1.67, and 1.55 mg/L/h, respectively. Meanwhile, P. peli NR-5 exhibited excellent simultaneous nitrification and denitrification capabilities at 10 °C. Sodium succinate was the most favorable carbon substrate for bacterial growth and ammonia removal by strain NR-5. The optimal culture conditions determined by the response surface methodology model were a carbon to nitrogen ratio of 5.9, temperature of 11.5 °C, pH of 7.0, and shaking speed of 144 rpm. Under these conditions, 99.1% of the total nitrogen was removed in the verification experiments, which was not significantly different from the predicted maximum removal in the model (99.6%). Six functional genes participating in the HN-AD process were successfully obtained by polymerase chain reaction amplification, which further confirmed the HN-AD capability of P. peli NR-5 and proposed the metabolic pathway of HN-AD. The above results provide a theoretical background of psychrotolerant HN-AD bacteria in wastewater purification under low-temperature conditions.

Performance of Paracoccus pantotrophus MA3 in heterotrophic nitrification-anaerobic denitrification using formic acid as a carbon source

Excess amount of nitrogen in wastewater has caused serious concerns, such as water eutrophication. Paracoccus pantotrophus MA3, a novel isolated strain of heterotrophic nitrification-anaerobic denitrification bacteria, was evaluated for nitrogen removal using formic acid as the sole carbon source. The results showed that the maximum ammonium removal efficiency was observed under the optimum conditions of 26.25 carbon to nitrogen ratio, 3.39% (v/v) inoculation amount, 34.64 °C temperature, and at 180 rpm shaking speed, respectively. In addition, quantitative real-time PCR technique analysis assured that the gene expression level of formate dehydrogenase, formate tetrahydrofolate ligase, 5,10-methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, respiratory nitrate reductase beta subunit, L-glutamine synthetase, glutamate dehydrogenase, and glutamate synthase were up-regulated compared to the control group, and combined with nitrogen mass balance analysis to conclude that most of the ammonium was removed by assimilation. A small amount of nitrate and nearly no nitrite were accumulated during heterotrophic nitrification. MA3 exhibited significant denitrification potential under anaerobic conditions with a maximum nitrate removal rate of 4.39 mg/L/h, and the only gas produced was N₂. Additionally, 11.50 ± 0.06 mg/L/h of NH₄⁺-N removal rate from biogas slurry was achieved.

New insight into the nitrogen removal capacity and mechanism of Streptomyces mediolani EM-B2

The utilization of actinomycetes as the bioresources for heterotrophic nitrification and aerobic denitrification is rarely reported due to the lack of work to explore their nitrogen biodegradation capabilities. Streptomyces mediolani EM-B2 belonging to actinomycetes could effectively remove high concentration of multiple nitrogen forms, and the maximum removal rates of ammonium, nitrate and nitrite reached 3.46 mg/(L·h), 1.71 mg/(L·h) and 1.73 mg/(L·h), respectively. Nitrite was preferentially consumed from the simultaneous nitrification and denitrification reaction system. Nitrogen balance analysis uncovered that more than 37% of the initial total nitrogen was converted to nitrogenous gas by aerobic denitrification. Experiments with specific inhibitors of nitrification and denitrification revealed that strain EM-B2 contained ammonia monooxygenase, hydroxylamine oxidoreductase, nitrate reductase and nitrite oxidoreductase, which were successfully expressed and detected as 0.43, 0.59, 0.12 and 0.005 U/mg proteins, respectively. These findings may provide new insights into the actinomycetes for bioremediation of nitrogen pollution wastewater.

Biodegradation of p-xylene-a comparison of three psychrophilic Pseudomonas strains through the lens of gene expression

p-Xylene is considered a recalcitrant compound despite showing a similar aromatic structure to other BTEXs (benzene, toluene, ethylbenzene, xylene isomers). This study evaluated the p-xylene biodegradation potential of three psychrophilic Pseudomonas strains (Pseudomonas putida S2TR-01, Pseudomonas synxantha S2TR-20, and Pseudomonas azotoformans S2TR-09). The p-xylene metabolism-related catabolic genes (xylM, xylA, and xylE) and the corresponding regulatory genes (xylR and xylS) of the selected strains were investigated. The biodegradation results showed that the P. azotoformans S2TR-09 strain was the only strain that was able to degrade 200 mg/L p-xylene after 60 h at 15 °C. The gene expression study indicated that the xylE (encoding catechol 2,3-dioxygenase) gene represents the bottleneck in p-xylene biodegradation. A lack of xylE expression leads to the accumulation of intermediates and the inhibition of biomass production and complete carbon recovery. The activity of xylene monooxygenase and catechol 2,3-dioxygenase was significantly increased in P. azotoformans S2TR-09 (0.5 and 0.08 U/mg, respectively) in the presence of p-xylene. The expression of the ring cleavage enzyme and its encoding gene (xylE) and activator (xylS) explained the differences in the p-xylene metabolism of the isolated bacteria and can be used as a novel biomarker of efficient p-xylene biodegradation at contaminated sites.

Characterization of a new heterotrophic nitrification bacterium Pseudomonas sp. strain JQ170 and functional identification of nap gene in nitrite production

Heterotrophic nitrification bacteria play a critical role in nitrogen cycling and pollution removal. However, the underlying nitrification mechanisms are diverse and have rarely been investigated at the genetic level. In this study, the new heterotrophic nitrifier Pseudomonas sp. strain JQ170 was isolated. Strain JQ170 can utilize ammonia (NH₄⁺-N), nitrite (NO₂^--N), or nitrate (NO₃^--N) as sole nitrogen sources, preferring NH₄⁺-N. A ratio of 96.4% of 1.0 mM NH₄⁺-N was removed in 24 h. The optimum pH, temperature, and carbon source for NH₄⁺-N removal were pH 7.0, 30 °C, and citrate, at a C/N ratio of 9-18, respectively. During the NH₄⁺-N removal process, only NO₂^--N but neither hydroxylamine, NO₃^--N, nor gaseous nitrogen were detected. A random transposon insertion mutagenesis library of strain JQ170 was constructed. Two NO₂^--N-production deficient mutants were screened and transposon insertion sites were located in nap genes (which encode periplasmic NO₃^--N reductase Nap). Further gene knockout and complementation of the napA gene confirmed nap as essential for NO₂^--N production. The following nitrification processes in strain JQ170 is proposed: NH₄⁺-N to NO₃^--N in the cytoplasm; then NO₃^--N to NO₂^--N in the periplasmic space by Nap; finally, NO₂^--N secreted out of cells. Overall, this paper provides new insight towards understanding heterotrophic nitrification at the genetic level.

Heterotrophic nitrification and aerobic denitrification process: Promising but a long way to go in the wastewater treatment

The traditional biological nitrogen removal (BNR) follows the conventional scheme of sequential nitrification and denitrification. In recent years, novel processes such as anaerobic ammonia oxidation (anammox), complete oxidation of ammonia to nitrate in one organism (comammox), heterotrophic nitrification and aerobic denitrification (HN-AD), and dissimilatory nitrate reduction to ammonium (DNRA) are gaining tremendous attention after the discovery of metabolically versatile bacteria. Among them, HN-AD offers several advantages because individual bacteria could achieve one-stage nitrogen removal under aerobic conditions in the presence of organic carbon. In this review, besides classical BNR processes, we summarized the existing literature on HN-AD bacteria which have been isolated from diverse habitats. A particular focus was given on the diversity and physiology of HN-AD bacteria, influences of physiological and biochemical factors on their growth, nitrogen removal performances, as well as limitations and strategies in unraveling HN-AD metabolic pathways. We also presented case studies of HN-AD application in wastewater treatment facilities, pointed out forthcoming challenges of HN-AD in these systems, and presented modulation strategies for HN-AD application in engineering. This review may help improve the existing design of wastewater treatment plants by harnessing HN-AD bacteria for effective nitrogen removal.

Effect of bacteria-to-algae volume ratio on treatment performance and microbial community of a novel heterotrophic nitrification-aerobic denitrification bacteria-chlorella symbiotic system

A novel symbiotic system combined by heterotrophic nitrification-aerobic denitrification (HN-AD) mixed bacteria and Chlorella pyrenoidosa was firstly proposed to resolve the poor tolerance and nitrogen removal performance of traditional symbiotic system for treating high ammonia biogas slurry. Results showed that the volume ratio of bacteria to algae had significant effects on nitrogen removal efficiency, microbial community structure, functional bacteria and genes. The optimal ratio was 1/3, and the average removal efficiency of TN and TP increased by 28.9% and 67.6% respectively, compared to those of HN-AD bacteria. High-throughput sequencing indicated nitrogen removal was jointly completed by HN-AD and heterotrophic denitrification. HN-AD bacteria Halomonas and Pseudomonas played a key role in nitrogen removal, and Rhodocyclaceae and Paracoccus took an important part in phosphorus removal. According to the functional gene prediction, the total relative abundance of nitrogen removal genes (0.0127%) and narG, narH and narL genes (0.0054%) were highest in 1/3 system.

Hydroxylamine and nitrite are removed effectively by Streptomyces mediolani strain EM-B2

Biological nitrogen removal is primarily conducted by bacteria and fungi rather than actinomycetes. However, accumulations of nitrite and hydroxylamine could significantly impair the biological nitrogen removal process. A strain of Streptomyces mediolani, termed EM-B2, was isolated from a cow dung fermentation biogas digester. The strain removed more than 99% of ammonium and 78% of total nitrogen in the presence of glucose and under environmental conditions of 30 °C, a carbon/nitrogen ratio of 15, 7.4 mg/L dissolved oxygen and a pH range of 7.5-9.0. Maximal removal rates were 2.29 mg/L/h for ammonium, 1.90 mg/L/h for nitrate and 2.01 mg/L/h for nitrite. The removal efficiencies of hydroxylamine and total nitrogen peaked at 81.48% and 60.38%, respectively. Notably, hydroxylamine and nitrite were never detected during the heterotrophic nitrification and aerobic denitrification. Nitrate rather than nitrite was accumulated from the process of hydroxylamine oxidation. These findings indicate that S. mediolani strain EM-B2 performs heterotrophic nitrification and aerobic denitrification, and can be used to remove hydroxylamine and nitrite from wastewater.

Nitrogen removal characteristics of a novel heterotrophic nitrification and aerobic denitrification bacteria, Alcaligenes faecalis strain WT14

Alcaligenes faecalis strain WT14 is heterotrophic nitrification and aerobic denitrification bacterium, newly isolated from a constructed wetland, and its feasibility in nitrogen removal was investigated. The result showed sodium citrate was more readily utilized by WT14 as a carbon source. The response surface methodology model revealed the highest total nitrogen removal by WT14 occurred at 20.3 °C, 113.5 r·min^-1, C/N 10.8, and pH 8.4. Under adapted environmental conditions, up to 55.9 mg·L^-1·h^-1 of ammonium nitrogen (NH₄⁺-N) was removed by WT14, and its NH₄⁺-N tolerance ability reached 2000 mg·L^-1. In addition to the reported high NH₄⁺-resistance of Alcaligenes faecalis, WT14 multiplied fast and had strong nitrate or nitrite removal capacity when high strength nitrate or nitrite was provided as the single nitrogen source; which differed from other Alcaligenes faecalis species. These results show WT14 is a novel strain of Alcaligenes faecalis and its nitrogen removal pathway will be carried out in the further study.

Changes in the fluorescence intensity, degradability, and aromaticity of organic carbon in ammonium and phenanthrene-polluted aquatic ecosystems

Mixed cultures were established by a sediment to investigate the changes in organic carbon (C) in a combined ammonium and phenanthrene biotransformation process in aquatic ecosystems. The microorganisms in the sediment demonstrated significant ammonium-N and phenanthrene biotransformation capacity with removal efficiencies of 99.96% and 99.99%, respectively. The changes in the organic C characteristics were evaluated by the fluorescence intensity, degradability (humification index (HIX) and UV absorbance at 254 nm (A₂₅₄)), aromaticity (specific UV absorbance at 254 nm (SUVA₂₅₄) and fluorescence index (FI)). Compared with C2 (the second control), the lower values of fluorescence intensity (after the 15^th d), HIX (after the 8^th d), A₂₅₄ (after the 11^th d), and SUVA₂₅₄ (after the 8^th d) and the higher FI value (after the 8^th d) in ammonium and phenanthrene-fed mixed cultures (N_PHE) suggest that aromatic structures and some condensed molecules were easier to break down in N_PHE. Similar results were obtained from Fourier transformation infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR) spectra. Changes in organic C characteristics may be due to two key organisms Massilia and Azohydromonas. The biodiversity also suggested that the selective pressure of ammonium and phenanthrene is the decisive factor for changes in organic C characteristics. This study will shed light on theoretical insights into the interaction of N and aromatic compounds in aquatic ecosystems.

Mixed cultures were established by a sediment to investigate the changes in organic carbon (C) in a combined ammonium and phenanthrene biotransformation process in aquatic ecosystems.

Characteristics and metabolic pathway of the bacteria for heterotrophic nitrification and aerobic denitrification in aquatic ecosystems

The present study investigated the nitrogen removal characteristics and metabolic pathway of bacteria in aquatic ecosystem, with a focus on heterotrophic nitrification and aerobic denitrification. The bacteria demonstrated significant heterotrophic nitrification and aerobic denitrification capacity. The highest ammonium-N, nitrate-N, and nitrite-N removal efficiencies were 95.31 ± 0.11%, 98.91 ± 0.05%, and 98.79 ± 0.09%, respectively. The Monod model was used to estimate the maximum rate of substrate utilization (R_mo) and the half-saturation concentration (K_s) for the two substrates, i.e., ammonium and nitrate. The kinetic coefficients were 3.34 mg/L/d (R_mo) and 30.59 mg/L (K_s) for ammonium-N, respectively, and 14.23 mg/L/d (R_mo) and 215.24 mg/L (K_s) for nitrate-N, respectively. The effects of initial nitrogen (ammonium-N or nitrate-N) concentration, temperature, and dissolved oxygen (DO) on nitrogen removal rate were investigated using response surface methodology (RSM), and the optimal conditions for nitrogen removal were determined. The principal nitrogen removal pathway of the bacteria was proposed as complete heterotrophic nitrification and aerobic denitrification, which was performed by six key genera: Arthrobacter, Pseudomonas, Rhodococcus, Bacillus, Massilia, and Rhizobium. Chryseobacterium and other denitrifying species may also reduce nitrification products (NO_X^-) via aerobic denitrification.

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.

Nitrogen removal characteristics of a versatile heterotrophic nitrifying-aerobic denitrifying bacterium, Pseudomonas bauzanensis DN13-1, isolated from deep-sea sediment

A heterotrophic nitrifying-aerobic denitrifying bacterium isolated from deep-sea sediment was identified as Pseudomonas bauzanensis DN13-1. Nitrogen (N) removal capability and relative expression of nitrification and denitrification genes of this strain were investigated. The NO2--N, NO3--N and NH4+-N removal efficiencies were 98.82%, 65.87% and 98.89%, respectively, and strain DN13-1 could efficiently remove mixed N. Meanwhile, other inorganic N was not accumulated during these N removal processes. Genomic analysis indicated that genes nirS, norB, nosZ, nasA and putative amo were identified. The relative expression of functional genes by real-time PCR (qPCR) further confirmed nitrite, nitrate and ammonium removal pathways of strain DN13-1 under aerobic condition. Especially, the ammonium removal pathway of this strain was achieved through heterotrophic ammonium nitrification coupled with fast nitrite denitrification directly. Taken together, strain DN13-1 possesses particularity to efficiently remove N, which guarantees its promising application in aquaculture wastewater treatment.

Utilization and re-use of solid and liquid waste generated from the natural indigo dye production process - A zero waste approach

The main aim of this work is focused towards possible reuse of both solid and liquid waste generated from the natural indigo dye production process. The solid waste (C/N:15.01) was utilized to produce stable compost with possible re-use in Indigofera cultivation. Among seven compost combinations (C1-C7) using jeevamrutha (JA) and cow-dung (CD) as inoculum, C4 with 8% JA showed higher biomass degradation (51%) and plant growth potential (GI > 125%). Whereas the undiluted liquid waste was treated using algal consortia, bacteria, and indigenous microbial population, achieved a maximum removal of 90% ammonia, 82% nitrate, and 88% phosphorus for its re-use in the dye production process. Hence, incorporation of suitable waste management strategies in natural indigo dye production could help to achieve a zero waste sustainable process.

Aerobic denitrification performance and nitrate removal pathway analysis of a novel fungus Fusarium solani RADF-77

Increasing nitrogenous contaminants have caused immense challenges to the environment and human health. As compared to physical and chemical methods, biological denitrification is considered to be an effective solution due to its environmental friendliness, high efficiency, and low cost. In the present work, a novel fungal strain identified as Fusarium solani (RADF-77) was isolated from cellulose material-supported denitrification reactor; this strain is capable of removing nitrogen under aerobic conditions. The average NO₃^--N removal rate for RADF-77 were 4.43 mg/(L·h) and 4.50 mg/(L·d), when using glucose and tea residue as carbon source, respectively. The nitrogen balance revealed that 53.66% of N vanished via gaseous products. Transcriptional results revealed that respiratory and assimilative nitrate reductases may work together for nitrate removal. Our results indicate that RADF-77 could be used as a potential means of enhancing nitrate-removal performance, as well as recycling tea residue, which is the main byproduct of the manufacture of tea extracts.

Role of heterotrophic aerobic denitrifying bacteria in nitrate removal from wastewater

With the increase in industrial and agricultural activities, a large amount of nitrogenous compounds are released into the environment, leading to nitrate pollution. The perilous effects of nitrate present in the environment pose a major threat to human and animal health. Bioremediation provides a cost-effective and environmental friendly method to deal with this problem. The process of aerobic denitrification can reduce nitrate compounds to harmless dinitrogen gas. This review provides a brief view of the exhaustive role played by aerobic denitrifiers for tackling nitrate pollution under different ecological niches and their dependency on various environmental parameters. It also provides an understanding of the enzymes involved in aerobic denitrification. The role of aerobic denitrification to solve the issues faced by the conventional method (aerobic nitrification-anaerobic denitrification) in treating nitrogen-polluted wastewaters is elaborated.

Identification and Characterization of Janthinobacterium svalbardensis F19, a Novel Low-C/N-Tolerant Denitrifying Bacterium

Herein, we isolated Janthinobacterium svalbardensis F19 from sludge sediment. Strain F19 can simultaneously execute heterotrophic nitrification and aerobic denitrification under aerobic conditions. The organism exhibited efficient nitrogen removal at a C/N ratio of 2:1, with an average removal rate of 0.88 mg/L/h, without nitrite accumulation. At a C/N ratio of 2, an initial pH of 10.0, a culturing temperature of 25 °C, and sodium acetate as the carbon source, the removal efficiencies of ammonium, nitrate, nitrite, and hydroxylamine were 96.44%, 92.32%, 97.46%, and 96.69%, respectively. The maximum removal rates for domestic wastewater treatment for ammonia and total nitrogen were 98.22% and 92.49%, respectively. Gene-specific PCR amplification further confirmed the presence of napA, hao, and nirS genes, which may contribute to the heterotrophic nitrification and aerobic denitrification capacity of strain F19. These results indicate that this bacterium has potential for efficient nitrogen removal at low C/N ratios from domestic wastewater.

Enhanced simultaneous nitrification and denitrification in treating low carbon-to-nitrogen ratio wastewater: Treatment performance and nitrogen removal pathway

Simultaneous nitrification and denitrification (SND) is an energy-saving wastewater treatment process, however, the nitrogen removal pathways are not clear. An enhanced SND sequencing batch biofilm reactor with a SND ratio above 97.3% was built to treat low carbon to nitrogen ratio wastewater. When traditional nitrification was inhibited, ammonia removal efficiency still reached 45% in 8 h while the NO₃^- and NO₂^- concentration was less than 3 mg/L and 0.01 mg/L during the complete process, respectively. The pathways that could not be suppressed by the inhibitors (ATU and ClO₃^-) were stimulated by heterotrophic nitrifiers and aerobic denitrifiers with periplasmic nitrate reductase and contributed 55% of the total removed NH₄⁺ and produced 51% of the emitted N₂O. The contributions of different nitrogen removal pathways indicate that the unconventional pathways are important in wastewater treatment system and inhibitors should be carefully used in nitrogen removal pathway assays.

Nitrogen cycling during wastewater treatment

Many wastewater treatment plants in the world do not remove reactive nitrogen from wastewater prior to release into the environment. Excess reactive nitrogen not only has a negative impact on human health, it also contributes to air and water pollution, and can cause complex ecosystems to collapse. In order to avoid the deleterious effects of excess reactive nitrogen in the environment, tertiary wastewater treatment practices that ensure the removal of reactive nitrogen species need to be implemented. Many wastewater treatment facilities rely on chemicals for tertiary treatment, however, biological nitrogen removal practices are much more environmentally friendly and cost effective. Therefore, interest in biological treatment is increasing. Biological approaches take advantage of specific groups of microorganisms involved in nitrogen cycling to remove reactive nitrogen from reactor systems by converting ammonia to nitrogen gas. Organisms known to be involved in this process include autotrophic ammonia-oxidizing bacteria, heterotrophic ammonia-oxidizing bacteria, ammonia-oxidizing archaea, anaerobic ammonia oxidizing bacteria (anammox), nitrite-oxidizing bacteria, complete ammonia oxidizers, and dissimilatory nitrate reducing microorganisms. For example, in nitrifying-denitrifying reactors, ammonia- and nitrite-oxidizing bacteria convert ammonia to nitrate and then denitrifying microorganisms reduce nitrate to nonreactive dinitrogen gas. Other nitrogen removal systems (anammox reactors) take advantage of anammox bacteria to convert ammonia to nitrogen gas using NO as an oxidant. A number of promising new biological treatment technologies are emerging and it is hoped that as the cost of these practices goes down more wastewater treatment plants will start to include a tertiary treatment step.

Biological nitrogen removal and metabolic characteristics of a novel aerobic denitrifying fungus Hanseniaspora uvarum strain KPL108

A novel aerobic denitrifying fungal strain KPL108 was isolated from the sediment of Jinpen drinking water reservoir and identified as Hanseniaspora uvarum. Strain KPL108 removed 99% of nitrate without nitrite accumulation under aerobic conditions, while the total organic carbon removal efficiency was 93%. KPL108 expressed fungal specific denitrifying gene p450nor. Nitrogen balance exhibited that approximately 92% of the initial nitrate was removed as gaseous products. Based on ¹³C-isotope labeling tracer, pentose phosphate pathway and tricarboxylic acid cycle were highly active in intracellular central carbon metabolism of strain KPL108. Response surface methodology revealed that the maximum total nitrogen removal efficiency occurred with the optimized parameters: C/N ratio of 6.4, pH of 8.2, 28.5 °C and 109.7 rpm. Collectively, the results from the present study indicate that strain KPL108 has aerobic denitrification ability, which has a great potential application for nitrogenous wastewater treatment.

Denitrification-Potential Evaluation and Nitrate-Removal-Pathway Analysis of Aerobic Denitrifier Strain Marinobacter hydrocarbonoclasticus RAD-2

An aerobic denitrifier was isolated from a long-term poly (3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV-supported denitrification reactor that operated under alternate aerobic/anoxic conditions. The strain was identified as Marinobacter hydrocarbonoclasticus RAD-2 based on 16S rRNA-sequence phylogenetic analysis. Morphology was observed by scanning electron microscopy (SEM), and phylogenetic characteristics were analyzed with the API 20NE test. Strain RAD-2 showed efficient aerobic denitrification ability when using NO3−-N or NO2−-N as its only nitrogen source, while heterotrophic nitrification was not detected. The average NO3−-N and NO2−-N removal rates were 6.47 mg/(L·h)and 6.32 mg/(L·h), respectively. Single-factor experiments indicated that a 5:10 C/N ratio, 25–40 °C temperature, and 100–150 rpm rotation speed were the optimal conditions for aerobic denitrification. Furthermore, the denitrifying gene napA had the highest expression on a transcriptional level, followed by the denitrifying genes nirS and nosZ. The norB gene was found to have significantly low expression during the experiment. Overall, great aerobic denitrification ability makes the RAD-2 strain a potential alternative in enhancing nitrate management for marine recirculating aquaculture system (RAS) practices.

Substrates removal and growth kinetic characteristics of a heterotrophic nitrifying-aerobic denitrifying bacterium, Acinetobacter harbinensis HITLi7T at 2 °C

In order to investigate the heterotrophic nitrification and aerobic denitrification ability of Acinetobacter harbinensis HITLi7^T at 2 °C, both the growth parameters and substrates utilization characteristics were tested and appropriated kinetic models were obtained in this study. Under the initial concentration of 5 mg/L, the maximum NH₄⁺-N and NO₃^--N degradation rates were 0.076 mg NH₄⁺-N/L/h and 0.029 mg NO₃^--N/L/h, respectively. At the simultaneous presence of 2.5 mg/L NH₄⁺-N and NO₃^--N, the maximum nitrate removal rate increased to 0.054 mg NO₃^--N/L/h (1.86 folds), while a slight decrease was observed in NH₄⁺-N removal. Two double-substrate models, Contois-Contois (1) for NH₄⁺-N and TOC, Monod-Contois (2) for NO₃^--N and TOC matched well with the experimental data. The kinetic parameters were determined as μ_max1 = 0.095 h^-1, B_A1 = 0.012 mg/L, B_T1 = 0.784 g TOC/g biomass (R₁² = 0.9997), and μ_max2 = 0.032 h^-1, K_N2 = 0.375 mg/L, B_T2 = 1.108 g TOC/g biomass (R₂² = 0.9731) by multiple regression equation.

GIS-based evaluation of groundwater geochemistry and statistical determination of the fate of contaminants in shallow aquifers from different functional areas of Agra city, India: levels and spatial distributions

The quality of groundwater is very important in Agra because groundwater is the main source of water for drinking, domestic, agricultural and industrial uses. A groundwater geochemistry study was conducted in Agra where 28 samples were collected from shallow aquifers in May 2016 from different sites. The aim of this research was to assess the quality of groundwater for drinking purposes in the study area. Arc-GIS has been used to prepare geographic information system-based spatial distribution maps of different major elements. The groundwater quality was analyzed for various physico-chemical parameters, major cations and anions and some trace metals. The observed values were compared with BIS and WHO standards. Statistical parameters such as the mean, median, standard deviation, skewness and kurtosis were used to analyze the hydrogeochemical characteristics of the groundwater. Correlation coefficient analysis and principal component analysis (PCA) were performed to identify the sources of the water constituents. Our results showed that most of the samples exceeded the acceptable limit for drinking water standards. The sequence of abundance of the main cations was generally Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, while the anions in order of abundance were HCO₃⁻ > Cl⁻ > SO₄²⁻ and NO₃⁻ > F⁻. All of the trace metals were within the permissible limit except for iron and manganese. The hazard index value of 5.7 × 10⁻² indicated that there was no potential health risk in the study area. Ca²⁺, Mg²⁺, Cl⁻ and SO₄²⁻ were the dominant hydrogeochemical facies in the majority of the groundwater samples. Most of the parameters such as TDS, Cl⁻, HCO₃⁻, SO₄²⁻, NO₃⁻, Ca²⁺, Mg²⁺, Na⁺, K⁺ and TH showed strong correlations with each other, which were due to natural processes such as weathering, exchangeable ions and reduction/oxidation, as well as anthropogenic activity around the study area. The water quality index indicated that the water quality was poor at 46.43% of the sampling sites, very poor at 28.57% of the sites and unsuitable for drinking purposes at 25% of the sampling sites. Gibbs diagrams suggested rock weathering as a major driving force for controlling the groundwater chemistry in the study area, along with evaporation as a minor influence.

A groundwater geochemistry study was conducted in Agra where 28 samples were collected from shallow aquifers in May 2016 from different sites. The aim of this research was to assess the quality of groundwater for drinking purposes in the study area.

Simultaneous removal of nitrogen and phosphorous from domestic wastewater using Bacillus cereus GS-5 strain exhibiting heterotrophic nitrification, aerobic denitrification and denitrifying phosphorous removal

A newly isolated GS-5 strain exhibiting heterotrophic nitrification, aerobic denitrification and denitrifying phosphorous removal was identified as Bacillus cereus GS-5 based on its phenotypic and phylogenetic characteristics. The isolate had exhibited efficient NH₄⁺-N, NO₃^--N, NO₂^--N and PO₄^3--P removal from nutrient spiked real domestic wastewater with average rates of 2.62, 2.69, 1.16 and 0.42mgL^-1h^-1, respectively under aerobic condition. Metabolic inhibitor based mass balance analysis indicated that dinitrogen gas (41%), intracellular nitrogen (29%) and intracellular phosphorous (60%) were the major fates of the initial NH₄⁺-N and PO₄^3--P. The successfully expression of hydroxylamine oxidase (hao), nitrate reductase (nar), nitrite reductase (nir) and poly phosphate kinase (ppk) enzyme in the cell free extracts and PCR amplification of nar, nir and ppk genes in the isolated strain provided further evidences for the nutrient removal possibility. A possible pathway of for nitrogen removal by GS-5 is suggested.

Ammonium stimulates nitrate reduction during simultaneous nitrification and denitrification process by Arthrobacter arilaitensis Y-10

The ability of Arthrobacter arilaitensis Y-10 for nitrogen removal from simulated wastewater was studied. Results showed that ammonium was the best inorganic nitrogen for strain Y-10's cell growth, which could also promote nitrate reduction. Approximately 100.0% of ammonium was removed in the nitrogen removal experiments. The nitrate removal efficiency was 73.3% with nitrate as sole nitrogen source, and then the nitrate efficiency was increased to 85.3% and 100.0% with ammonium and nitrate (both about 5 or 100mg/L) as the mixed nitrogen sources. Nitrite accumulation was observed in presence of ammonium and nitrate. When the concentration of sole nitrite nitrogen was 10.31mg/L, the nitrite removal efficiency was 100.0%. Neither ammonium nor nitrate was accumulated during the whole experimental process. All experimental results indicated that A. arilaitensis Y-10 could remove ammonium, nitrate and nitrite at 15°C from wastewater, and could also perform simultaneous nitrification and denitrification under aerobic condition.

Aerobic denitrification and biomineralization by a novel heterotrophic bacterium, Acinetobacter sp. H36

A novel aerobic denitrification and biomineralization strain H36 was isolated from the Qu Jiang artificial lake. Based on phylogenetic characteristics, the isolated strain was identified as Acinetobacter species. Strain H36 was confirmed to have the ability to perform simultaneous denitrification and biomineralization. Results showed the strain H36 had the capability to completely reduce 96.29% of NO₃^--N and 78.59% of Ca²⁺ over 112h under aerobic condition. Response surface methodology (RSM) analysis demonstrated the highest removal ratio of Ca²⁺ was 74.24% with hardness concentration of 350mg/L, pH of 8.5, organic concentration of 0.75g/L and inoculum size of 15%. The highest removal ratio of nitrate was 77.00% with hardness concentration of 350mg/L, pH of 7.5, organic concentration of 0.75g/L and inoculum size of 10%. Besides, X-ray diffraction (XRD) analysis showed calcium carbonate could be formed in the process of biomineralization.

Nitrogen Removal Characteristics of Pseudomonas putida Y-9 Capable of Heterotrophic Nitrification and Aerobic Denitrification at Low Temperature

The cold-adapted bacterium Pseudomonas putida Y-9 was investigated and exhibited excellent capability for nitrogen removal at 15°C. The strain capable of heterotrophic nitrification and aerobic denitrification could efficiently remove ammonium, nitrate, and nitrite at an average removal rate of 2.85 mg, 1.60 mg, and 1.83 mg NL^-1h^-1, respectively. Strain Y-9 performed nitrification in preference to denitrification when ammonium and nitrate or ammonium and nitrite coexisted in the solution. Meantime, the presence of nitrate had no effect on the ammonium removal rate of strain Y-9, and yet the presence of high concentration of nitrite would inhibit the cell growth and decrease the nitrification rate. The experimental results indicate that P. putida Y-9 has potential application for the treatment of wastewater containing high concentrations of ammonium along with its oxidation products at low temperature.

Coupled Nitrification-Denitrification Caused by Suspended Sediment (SPS) in Rivers: Importance of SPS Size and Composition

Suspended sediment (SPS) is ubiquitous in rivers, and SPS with different particle sizes and compositions may affect coupled nitrification-denitrification (CND) occurring on SPS significantly. However, there is no related research report. In this work, ¹⁵N isotope tracer technique was adopted to explore the CND in systems containing SPS (8 g L^-1 and 1 g L^-1) collected from the Yellow River with various particle sizes, including <2, 2-20, 20-50, 50-100, and 100-200 μm. The results showed that the CND occurred on SPS and the CND rate was negatively related to particle size; both nitrification and denitrification rate constants increased with decreasing SPS particle size. For instance, SPS (8 g L^-1) with a particle size below 2 μm had the highest ¹⁵N₂ emission rate of 1.15 mg-N/(m³·d), which was 2.9 times that of 100-200 μm. This is because SPS with a smaller particle size had a larger specific surface area and a higher organic carbon content, which is beneficial for bacteria growth. Both the nitrifying and denitrifying bacteria population were positively correlated with CND rate (p < 0.05). Different from the ¹⁵N₂ production, ¹⁵N₂O emission rate did not decrease with increasing SPS particle size. For the system containing 8 g L^-1 SPS, ¹⁵N₂O emission rate reached the highest of 1.05 μg-N/(m³·d) in the 50-100 μm SPS system, which was 17.5 times that of 100-200 μm. Similar results could be found from the system with 1 g L^-1 SPS. This is due to the fact that the oxygen concentration at the SPS-water interface increased with SPS particle size, and the oxygen conditions might be most suitable for the production of N₂O in the 50-100 μm system. This study suggests that SPS size and composition play an important role in nitrogen cycle of river systems, especially for the production of N₂O.

BTEX biodegradation and its nitrogen removal potential by a newly isolatedPseudomonasthivervalensisMAH1

Benzene, toluene, ethylbenzene, and xylene (BTEX) are of great environmental concern because of their widespread occurrence in groundwater and soil, posing an increasing threat to human health. The aerobic denitrifying BTEX-degrading bacterium Pseudomonas thivervalensis MAH1 was isolated from BTEX-contaminated sediment under nitrate-reducing conditions. The degradation rates of benzene, toluene, ethylbenzene, and xylene by strain MAH1 were 4.71, 6.59, 5.64, and 2.59 mg·L−1·day−1, respectively. The effects of sodium citrate, nitrate, and NaH2PO4on improving BTEX biodegradation were investigated, and their optimum concentrations were 0.5 g·L−1, 100 mg·L−1, and 0.8 mmol·L−1, respectively. Moreover, MAH1, which has nirS and nosZ genes, removed ammonium, nitrate, and nitrite at 2.49 mg NH4+-N·L−1·h−1, 1.50 mg NO3−-N·L−1·h−1, and 0.83 mg NO2−-N·L−1·h−1, respectively. MAH1 could help in mitigating the pollution caused by nitrogen amendments for biostimulation. This study highlighted the feasibility of using MAH1 for the bioremediation of BTEX-contaminated sites.

Effect of temperature, salinity, heavy metals, ammonium concentration, pH and dissolved oxygen on ammonium removal by an aerobic nitrifier

An aerobic nitrifier WY-01 was identified asAlcaligenes faecalisby its 16S rRNA gene sequence analysis. It could remove ammonium effectively in varying physico-chemical conditions, such as low temperature, high salinity and high ammonium loads.