High-efficient nitrogen removal by coupling enriched autotrophic-nitrification and aerobic-denitrification consortiums at cold temperature

Subsurface wastewater infiltration systems for nitrogen pollution control

Subsurface wastewater infiltration systems (SWISs) are suggested to be a cost-effective and environmentally friendly method for sewage treatment. However, a comprehensive summary of the relevant mechanisms and optimization methods for nitrogen (N) removal in SWIS is currently lacking. In this review, we first summarize the N transformation mechanisms in SWIS. The impact of operational parameters on the N removal efficiency is then delineated. To enhance pollutant removal and minimize resource wastage, it is advisable to maintain a wet-dry ratio of 1:1 and a hydraulic loading rate of 8-10 cm/day. The organic load should be determined based on influent characteristics to optimize the balance between sewage treatment and nitrous oxide (N2O) emission. Finally, various strategies and modifications have been suggested to enhance pollutant removal efficiency and reduce N2O emissions in SWIS, such as artificial aeration, supply electron donors, and well-designed structures. Overall, greater emphasis should be placed on the design and management of SWIS to optimize their co-benefits while effectively controlling N pollution. PRACTITIONER POINTS: SWISs are often considered black boxes with their efficiency depending on hydraulic characteristics, biological characteristics, and substrate properties. Biological nitrification coupled with denitrification is considered to be the major N removal process. Increasing the reduction of N2O to the inert N2 form is a potential mechanism to mitigate global warming. Strategies such as artificial aeration, supply electron donors, and well-designed structures are suggested to improve N removal performance.

Enhanced heterotrophic nitrification and aerobic denitrification performance of Glutamicibacter arilaitensis EM-H8 with different carbon sources

Different carbon sources for Glutamicibacter arilaitensis EM-H8 were evaluated for ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) removal. Strain EM-H8 could rapidly remove NH₄⁺-N, NO₃^--N and NO₂^--N. The highest removal rates measured for different forms of nitrogen with different carbon sources were 5.94 mg/L/h for NH₄⁺-N with sodium citrate, 4.25 mg/L/h for NO₃^--N with sodium succinate, and 3.88 mg/L/h for NO₂^--N with sucrose. The Nitrogen balance showed that strain EM-H8 could convert 77.88% of the initial nitrogen into nitrogenous gas when NO₂^--N was selected as the sole nitrogen source. The presence of NH₄⁺-N increased the removal rate of NO₂^--N from 3.88 to 4.02 mg/L/h. In an enzyme assay, ammonia monooxygenase, nitrate reductase and nitrite oxidoreductase were detected at 0.209, 0.314, and 0.025 U/mg protein, respectively. These results demonstrate that strain EM-H8 performs well for nitrogen removal, and shows excellent potential for simple and efficient removal of NO₂^--N from wastewater.

Insight into the Cold Adaptation Mechanism of an Aerobic Denitrifying Bacterium: Bacillus simplex H-b

Psychrophilic bacteria with aerobic denitrification ability have promising potential for application in nitrogen-contaminated wastewater treatment, especially under cold conditions. A better understanding of the cold adaptation mechanism during aerobic denitrification would be beneficial for the practical application of this type of functional bacterium. In this study, Bacillus simplex H-b with good denitrification performance at 5°C was used to investigate the corresponding cold tolerance mechanism. Transcriptomics and nitrogen removal characterization experiments were conducted at different temperatures (5°C, 20°C, and 30°C). At low temperatures, more nitrogen was utilized for assimilation, accompanied by the accumulation of ATP and extracellular polymeric substances (EPS), rather than transforming inorganic nitrogen in the dissimilation pathway. In addition, the proportion of unsaturated fatty acids was higher in strains cultured at low temperatures. At the molecular level, the adjustment of membrane transport, synthesis of cofactors and vitamins, and transcriptional regulators might contribute to the survival of the strain under cold conditions. Moreover, nucleotide precursor synthesis, translation, and oxidative and temperature stress response mechanisms also enhanced the resistance of strain H-b to low temperatures. The results suggest that combining multiple regulatory mechanisms and synergistic adaptation to cold stress enabled the growth and relatively high nitrogen removal rate (27.22%) of strain H-b at 5°C. By clarifying the mechanism of regulation and cold resistance of strain H-b, a theoretical foundation for enhancing the application potential of this functional bacterium for nitrogen-contaminated wastewater treatment was provided. IMPORTANCE The newly isolated aerobic denitrifying bacterium Bacillus simplex H-b removed various forms of inorganic nitrogen (nitrate, nitrite, and ammonium) from wastewater, even when the temperature was as low as 5°C. Although this environmentally functional bacterium has been suggested as a promising candidate for nitrogen-contaminated water treatment at low temperatures, understanding its cold adaptation mechanism during aerobic denitrification is limited. In this study, the cold tolerance mechanism of this strain was comprehensively explained. Furthermore, a theoretical basis for the practical application of this type of functional bacterium for nitrogen removal in cold regions is provided. The study expands our understanding of the survival strategy of psychrophilic bacteria and hence supports their further utilization in wastewater treatment applications.

Six complex microbial inoculants for removing ammonia nitrogen from waters

To determine the effect of microbial inoculants on the removal of ammonia nitrogen (NH₄ ⁺ -N), six different complex microbial inoculants were studied. In this study, their effectiveness on NH₄ ⁺ -N removal was compared, and their microbial community composition was determined. High-throughput sequencing results showed that Proteobacteria and Firmicutes were the dominant phyla in six samples. Before the reaction, Bacillus, Cyanobacteria, and Mitochondria genera were the dominant genera. The dominant genera were significantly different after the reaction with the addition of bacterial agents. The six water samples were Massilia, Escherichia-Shigella, Brevibacillus, Mitsuaria, Bacillus, and Ralstonia. Among the six complex microbial inoculants, "Gandu nitrifying bacteria (NR₄ )" have the best removal effect on NH₄ ⁺ -N. In addition, the removal effect of six different bacterial agents on chemical oxygen demand (COD) was compared. The results showed that "Bilaiqing ammonia nitrogen removal bacteria agent (NR₅ )" has the best removal effect on COD. Single-factor experiments suggested that the optimal conditions for NR₄ bacteria were pH 7, 30°C, 1.0 g/L of bacterial agent dosage and a wide range of NH₄ ⁺ -N from 30 to 300 mg/L. PRACTITIONER POINTS: The nitrogen removal effects of six different microbial agents were compared. High-throughput sequencing provides important insights into the study of ammonia nitrogen removal by microbial communities. Analysis of six different complex bacterial agents by high-throughput sequencing. The relative abundance of microorganisms is not proportional to the ability to remove NH₄ ⁺ -N Good application effect in urban landscape water body.

Simultaneous Nitrification and Denitrification under Aerobic Atmosphere by Newly Isolated Pseudomona aeruginosa LS82

Discharge of wastewater contained high amount of nitrogen would cause eutrophication to water bodies. Simultaneous nitrification and denitrification (SND) has been confirmed as an effective process, the isolation of SND bacteria is crucial for its successful operation. In this study, an SND strain was isolated and identified as Pseudomona aeruginosa LS82, which exhibited a rapid growth rate (0.385 h−1) and good nitrogen removal performance (4.96 mg N·L−1·h−1). Response surface methodology was applied to optimize the TN removal conditions, at which nearly complete nitrogen (99.8 ± 0.9%) removal were obtained within 18 h at the condition: pH 8.47, 100 rpm and the C/N ratio of 19.7. The saddle-shaped contours confirmed that the interaction of pH and inoculum size would influence the removal of total nitrogen significantly. Kinetic analyses indicated that the reduction of nitrite was the rate-limiting step in the SND process. Our research suggested strain LS82 can serve as a promising candidate for the treatment of ammonium rich wastewater, and expended our understanding the nitrogen removal mechanism in the SND process.

Application of glucose for improving NH4+-N removal in micro-polluted source water by immobilized heterotrophic nitrifiers at low temperature

Bio-enhanced activated carbon (BEAC) filters have shown potential in source water purification. The key drawback of this system is the difficulty of the set-up at low temperature. Here, glucose was applied to help immobilize more functional heterotrophic nitrifiers and further improve NH₄⁺-N removal by BEAC. Results showed that pre-loading glucose on granular activated carbon could achieve better immobilization efficiency with 5.12 × 10⁸ CFU/g-DW C biomass and 3.77 mg TF/L/g-DW C dehydrogenase activity after artificial immobilization, which were separately 12.5 and 4.2 times of the control. 95-d running data at different conditions showed the superiority of both immobilization and NH₄⁺-N removal could last and defend environment changes during relatively long period. Even at the end of operating, the abundance of targeting genus (Acinetobacter) still occupied 9.59% of microbial communities on BEAC, while this value was only 1.24% without pre-loading glucose. Biolog-ECO plate analysis found pre-loading glucose improved organic nitrogen metabolism effectively, along with carbohydrate, amino, alcohol, amine and carboxylic acid metabolism on BEAC.

Nitrogen removal performance, quantitative detection and potential application of a novel aerobic denitrifying strain, Pseudomonas sp. GZWN4 isolated from aquaculture water

A novel Pseudomonas sp. GZWN4 with the aerobic nitrogen removal ability was isolated from aquaculture water, whose removal efficiency of NO₂^--N, NO₃^--N and NH₄⁺-N was 99.72%, 82.54% and 98.62%, respectively. The key genes involved in nitrogen removal, nxr, napA, narI, nirS, norB and nosZ, were successfully amplified and by combination with the results of nitrogen balance analysis, it was inferred that the denitrification pathway of strain GZWN4 was NO₃^--N → NO₂^--N → NO → N₂O → N₂. The strain GZWN4 had excellent nitrite removal performance at pH 7.0-8.5, temperature 25-30 ℃, C/N ratio 5-20, salinity 8-32‰ and dissolved oxygen concentration 2.52-5.73 mg L^-1. The receivable linear correlation (R² = 0.9809) was obtained with the range of quantification between l0³ and 10⁸ CFU mL^-1 of the strain by enzyme-linked immunosorbent assay. Strain GZWN4 could maintain high abundance in the actual water and wastewater of mariculture and the removal efficiency of TN were 52.57% and 63.64%, respectively. The safety evaluation experiment showed that the strain GZWN4 had no hemolysis and high biosecurity toward shrimp Litopenaeus vannamei. The excellent nitrogen removal ability and adaptability to aquaculture environment made strain GZWN4 a promising candidate for treatment of water and wastewater in aquaculture.

A review on performance of constructed wetlands in tropical and cold climate: Insights of mechanism, role of influencing factors, and system modification in low temperature

Constructed wetlands (CWs) are one of the most promising and sustainable alternatives for wastewater treatment that are being successfully implemented in several countries, especially in tropical and sub-tropical regions. The predominant mechanisms of removal of contaminants in CWs are microbial degradation, phytodegradation, phytoextraction, filtration, sedimentation, and adsorption, etc. Vertical flow subsurface CWs and hybrid CWs demonstrated promising results in terms of TN, BOD, and COD removal, while horizontal flow subsurface CWs were proficient in removal of TP. The performance of the CWs depends upon a various factors, such as hydraulic loading rate, pH, dissolved oxygen, temperature, etc. Among these, low temperature had the most antagonistic effect on the performance of the CWs because freezing ambient temperature lead to ice formation, hydraulic imperfections, malfunctioning of biotic and abiotic components, etc. Over the past three decades, thousands of studies have been conducted involving treatment of wastewater using CWs, among which only few have addressed the issues and concerns of cold climate representing a significant research gap in this field. Furthermore, the performance of CWs in terms of TN, TP, and COD removal was significantly lower in cold climates than that in tropical and sub-tropical climates. In order to find suitable remedies to overcome the challenges faced in cold climate various modifications, such as incorporating greenhouse structure, providing insulating materials, bio-augmentation, identification of suitable macrophytes, etc., in around 20 different scenarios have been studied. Greenhouse construction led to 20% increase in removal of TN and COD, while plant collocation accounted for up to 18% increase in the removal of COD. Artificial aeration, insulation and bio-augmentation also enhanced the performance of the CWs in low temperatures.

Simultaneous heterotrophic nitrification and aerobic denitrification by a novel isolated Pseudomonas mendocina X49

Six bacterial strains with simultaneous nitrification-denitrification abilities were isolated from a Beijing sewage treatment plant to improve nitrogen biodegradation efficiency. One of these strains, X49, was identified as Pseudomonas mendocina, and was characterized as the best strain with which to rapidly degrade a high concentration of inorganic nitrogen. X49 completely converted 5-100 mg.L^-1 of ammonia in 12 h, with no nitrite accumulation; the maximum removal rate of 26.39 mg (N).L^-1.h^-1 was achieved between 4 h and 6 h. In 16 h, the strain removed 100 mg.L^-1 nitrite and 72.61 mg.L^-1 nitrate under aerobic conditions, at degredation rates which reached 4.54 and 6.25 mg (N).L^-1.h^-1, respectively. Our results suggest that P. mendocina X49 achieved efficient and simultaneous nitrification and denitrification ability under heterotrophic aerobic conditions.

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.

Complete nitrogen removal via simultaneous nitrification and denitrification by a novel phosphate accumulating Thauera sp. strain SND5

Bacteria capable of simultaneous nitrification and denitrification (SND) and phosphate removal could eliminate the need for separate reactors to remove nutrients from wastewater and alleviate competition for carbon sources between different heterotrophs in wastewater treatment plants (WWTPs). Here we report a newly isolated Thauera sp. strain SND5, that removes nitrogen and phosphorus from wastewater via SND and denitrifying-phosphate accumulation, respectively, without accumulation of metabolic intermediates. Strain SND5 simultaneously removes ammonium, nitrite, and nitrate at an average rate of 2.85, 1.98, and 2.42 mg-N/L/h, respectively. Batch testing, detection of functional genes, nitrogenous gas detection and thermodynamic analysis suggested that nitrogen gas, with hydroxylamine produced as an intermediate, was the most likely end products of heterotrophic ammonium oxidation by strain SND5. The generated end products and intermediates suggest a novel nitrogen removal mechanism for heterotrophic ammonium oxidation in strain SND5 (NH₄⁺→NH₂OH→N₂). Strain SND5 was also found to be a denitrifying phosphate-accumulating organism, capable of accumulating phosphate, producing and storing polyhydroxybutyrate (PHB) as an intracellular source of carbon while using nitrate/nitrite or oxygen as an electron acceptor during PHB catabolism. This study identifies a novel pathway by which simultaneous nitrogen and phosphorus removal occurs in WWTPs via a single microbe.

The influence mechanism of bioclogging on pollution removal efficiency of vertical flow constructed wetland

The effect of change of hydraulic characteristic and microbial community on pollution removal efficiency of the infiltration systems in the bioclogging development process remain poorly understood. In this study, therefore, the pollutant removal as a response to hydraulic conductivity reduction and the change of diversity and structure of microbial communities in vertical flow constructed wetlands (VFCWs) was investigated. The results indicated that the richness and diversity of the bacterial communities in the columns at different depths were decreased, and the microbial communities of the genus level were changed in the process of bioclogging. However, the variation of microbial communities has a low impact on the purification performance of VFCWs because the abundance of function groups, respiratory activity, and degradation potentiality of microorganisms remain steady or even get improved in the columns after bioclogging. On the contrary, the hydraulic efficiency of VFCWs decreased greatly by 16.9%, 9.9%, and 57.1% for VFCWs filled with zeolite (Column I), gravel (Column II), and ceramsite (Column III), respectively. The existence of short-circuiting and dead zones in the filter media cause the poor pollution removal efficiency of VFCWs due to the short contact time and decrease of oxygenation renewal, as well as low activity in the dead zone.

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Heterotrophic nitrification and aerobic denitrification by a novel Acinetobacter sp. ND7 isolated from municipal activated sludge

A novel strain was isolated from municipal activated sludge and identified as Acinetobacter sp. ND7 based on its phenotypic and phylogenetic characteristics, which had efficient capability for heterotrophic nitrification and aerobic denitrification. Strain ND7 could remove approximately 99.8% of ammonium-N (51.0 mg/L), 96.2% of nitrite-N (51.8 mg/L) and 97.18% of nitrate-N (52.1 mg/L), with the maximum specific removal rate of 5.74, 4.17 and 3.63 mg/(L h), respectively. Ammonium was manifested to be utilized preferentially during simultaneous nitrification and denitrification. The functional genes hao, napA and nirS were successfully amplified by PCR, further evidencing the heterotrophic nitrification and aerobic denitrification capability of Acinetobacter sp. ND7. The optimal conditions for nitrogen removal were temperature of 35 °C, C/N ratio of 8. Acinetobacter sp. ND7 displays superior performance for nitrogen removal, with no nitrite accumulation under aerobic condition, and thus has significant potential for practical application for nitrogen removal from wastewater.

The role of a newly isolated strain Corynebacterium pollutisoli SPH6 in waste activated sludge alkaline fermentation

Alkaline fermentation has been considered as one of the efficient methods for waste activated sludge (WAS) treatment, but usually limited by microbial fermentation activities under extreme pH condition. One newly isolated alkali-tolerant strain Corynebacterium pollutisoli SPH6 was used to assess its potential role and effect on WAS alkaline fermentation process. Results from response surface method showed that the optimal organic nitrogen degradation rate by SPH6 was obtained under temperature of 35 °C, initial pH of 10, shaking speed of 80 rpm, inoculation ratio of 6.5%. Batch-scale experiments demonstrated that, compared with the control group, the inoculation of SPH6 finally achieved higher productions with 13.4% of carbohydrates, 27.1% of protein and 25.4% of total volatile fatty acids (VFAs), and more predominant functional bacteria characterized by high-throughput sequencing, such as genera Acinetobacter in phylum Proteobacteria, Tissierella and Acetoanaerobium in phylum Firmicutes. The strain SPH6 might play a vital role in maintaining and facilitating the growth and diversity of functional bacteria in WAS alkaline fermentation process. It has implied promising practical application of the present strain in enhancing WAS reduction and utilization.

Ozonation of ammonia at low temperature in the absence and presence of MgO

Ozone oxidation and ozonation catalyzed with MgO were applied to remove ammonia in water at low temperature (10℃). Results show that pH played a critical role in both ozonation and catalytic ozonation for ammonia removal, especially in the ozonation rate of ammonia and the types of oxidation products. For single ozonation, both O₃ and OH contributed to ammonia degradation. Lower pH is beneficial to high selectivity of gaseous products (N₂ or N₂O) in the presence of Cl^-. Significantly enhanced efficiency of ammonia removal was obtained under the catalysis of MgO, which worked as a solid alkali as well as a catalyst, facilitating ammonia oxidation both in the solution and on the MgO surface. Molecular O₃ dominated ammonia removal in the heterogeneous catalytic ozonation system, while the contribution of OH was not significant in quantity and a small part of ammonia was degraded by the reaction of ClO_x^- with NH₄⁺. A relatively high removal efficiency (77.53%˜80.17%) of ammonia could also be achieved in the temperature range of 0℃˜10℃, which indicates that catalytic ozonation over catalysts like MgO may be a potential method to control ammonia pollution during cold weather or under other conditions difficult for biological treatment.

Simultaneous nitrification, denitrification and phosphorus removal in a sequencing batch reactor (SBR) under low temperature

Simultaneous nitrogen and phosphorus removal in winter is one of the great challenges in wastewater treatment processes due to the poor bioactivity of microbial communities. In this study, excellent performance of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was achieved at low temperature of 10 ^°C and COD/N ratio of 6 in a lab-scale sequencing batch reactor. Total nitrogen (TN) and phosphorus (TP) removal efficiency reached 89.6% and 97.5%, respectively, accompanied with N₂O emission of 7.46% TN due to the primary contribution (70%) of nitrifier denitrification. It was further confirmed that polyphosphate accumulating organisms (PAOs) were dominant in microbial communities revealed by fluorescence in situ hybridization and 16S rRNA amplicon sequencing. Moreover, denitrifying phosphorus removal by PAOs through nitrite pathway was found to be the main reason for the high efficiency of this SNDPR process. Denitrifying PAOs, especially the subgroup PAOII capable of utilizing nitrite to take up phosphorus, played a significant role in highly efficient TN and TP removal at low temperature. Furthermore, genus Propionivibrio was enriched (48.9%) in the bacterial community based on the 16S rRNA analysis, which was proposed to be a crucial member involved in the nitrogen and phosphorus removal simultaneously at low temperature in this system.

A strategy of high-efficient nitrogen removal by an ammonia-oxidizing bacterium consortium

An ammonia-oxidizing bacterium consortium showed approximately 100% removal of NH₄⁺-N with an initial concentration of 262.28 ± 8.21 mg·L^-1 within 10 days, and only 16.54 ± 0.52% of NH₄⁺-N was converted to NO₂^--N in this study. The consortium removed ammonium by heterotrophic nitrification and aerobic denitrification (HNAD) without N₂O emission. The activity of AOB was not affected by low concentrations of FA or FNA, but completely inhibited by 0.04 mg HNO₂·L^-1. In a bioaugmentation treatment of eutrophic wastewater using the consortium, the removal efficiency of NH₄⁺-N reached 90.85 ± 0.8% and 77.88 ± 1.86% at initial concentrations of 1.80 ± 0.04 mg·L^-1 and 40.31 ± 0.57 mg·L^-1, respectively, and the dissolved oxygen level had a significant impact on the consortium activity. No significant changes in the bacterial community structure were observed after the consortium addition, and local functional bacteria were enriched by aeration and contributed to ammonium nitrogen removal with AOB.

Efficient nitrogen removal from synthetic domestic wastewater in a novel step-feed three-stage integrated anoxic/oxic biological aerated filter process through optimizing influent flow distribution ratio

In this study, a novel step-feed three-stage integrated anoxic/oxic biological aerated filter (STIAOBAF) process was developed to enhance nitrogen removal from the synthetic domestic wastewater through optimizing influent flow distribution ratio (IFDR) for three stage reactors (R1, R2, R3). Long-term operation demonstrated that the maximum nitrogen removal efficiency was achieved at the IFDR of 30%:50%:20%. The corresponding effluent total nitrogen (TN) was less than 10 mg/L, superior to the first A grade discharge standard of China (Effluent TN < 15 mg/L). The IFDR was further optimized to 32%:49%:19% by response surface methodology (RSM) model, thus obtaining the highest TN removal efficiency of 81.4%. Nitrogen profiles suggested the 2nd stage reactor was the greatest significant contributor for nitrogen removal of the whole system. Microbial community analysis revealed that Chloroflexi, Bacteroidetes, Firmicutes, and Acidobacteria were abundant in anoxic zones, while Planctomycetes, Bacteroidetes and Verrucomicrobia were rich in oxic zones. Nitrogen removal-associated functional bacterial groups (Nitrospira, Thauera, Azospira and Candidatus Kuenenia) were also identified, supporting high-rate nitrogen removal through the combination of anoxic denitrification with aerobic simultaneous nitrification and denitrification (SND). The STIAOBAF will offer a compact and robust alternative for advanced nitrogen removal from the sewage.

Simultaneous nitrification and denitrification without nitrite accumulation by a novel isolated Ochrobactrum anthropic LJ81

Nitrogen contaminants are widespread presence in municipal wastewater, heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria have advantages of dealing with multiple nitrogen. Strain LJ81 was isolated from domestic sludge, identified as Ochrobactrum anthropic, which was oxygen-dependent and could survive in a wide range of pH values. Results showed that strain LJ81 could achieve simultaneous nitrification and denitrification (SND) under aerobic condition, whilst more than 80% of initial nitrogen was converted into gaseous nitrogen. The removal rates of ammonia increased from 3.75 to 3.85 and 5.70 mg-N L^-1 h^-1 by adding nitrite and nitrate, respectively, while the nitrate denitrification was the rate-limiting step of SND process. Moreover, adding chlorate could inhibit not only the cell growth slightly but also denitrification of nitrate. All results indicated that O. anthropic strain LJ81 exhibited excellent performance on nitrogen removal without nitrite accumulation under aerobic condition.

How does iron facilitate the aerated biofilter for tertiary simultaneous nutrient and refractory organics removal from real dyeing wastewater?

Textile dyeing wastewater is characterized by low biodegradability and high nitrogen strength, which is difficult to meet the increasingly stringent discharge requirements. Therefore, the tertiary nutrient and refractory organics removal is considered and aerated biofilter is often adopted. However, the aerobic condition and carbon source shortage restrict tertiary biological nitrogen removal. In this study, iron scrap was introduced as the filter medium to enhance the pollutant removal capacity, and three aerobic biofilters were constructed. Biofilter Fe-CE was filled with iron scrap and ceramisite; biofilter Fe-AC was added with iron scrap and granular activated carbon, and biofilter CE only had ceramisite to pad as control system. After the biofilters were acclimatized by synthetic wastewater and actual dyeing wastewater, the optimal operation parameters based on nitrogen removal were determined as pH 7, gas-water ratio 5:1, hydraulic retention time 8 h and C/N ratio 8.5:1. The iron scraps improved total nitrogen (TN) removal significantly, with TN removal efficiency of 68.7% and 57.3% in biofilter Fe-AC and biofilter Fe-CE, comparing with biofilter CE of 29.9%. Additionally, phosphorus and COD had better removal performance as well when iron scrap existed. Further investigation interpreted the reason for iron's facilitating effect on tertiary nutrient and refractory organics removal. The introduction of iron scrap made the habitat conditions such as pH values, DO concentrations and biomass contents inside the biofilters change towards the direction beneficial for pollutant elimination especially for nitrogen removal. In iron containing biofilters, the majority of nitrogen, phosphorus and organic pollutants were removed in the iron scrap layers, and more pollutants types appeared, implying that iron triggered pollutants to go through more diverse degradation or transformation pathways. Moreover, the phylum Proteoabcteria dominated in samples of ceramisite-containing biofilters, with abundances more than 40%. The iron scrap existence increased the abundances of phyla Bacteroidetes and Firmicutes, and triggered higher abundance of denitrification bacteria.

Overview of strategies for enhanced treatment of municipal/domestic wastewater at low temperature

Biological wastewater treatment has been widely applied to municipal/domestic wastewater treatment systems. However, low temperature significantly decreases process performance. Furthermore, increasingly stringent effluent discharge standards are causing wastewater treatment facilities to have to improve and maintain contaminants removal under low temperature. Hence, this review aims to summarize strategies for enhanced treatment of municipal/domestic wastewater at low temperature. First, mechanisms of the effects of low temperature on wastewater treatment, including physiological characteristics, microbial growth rate, microbial activity, microbial community structure and sludge settleability, are analyzed. Strategies for performance intensifications at low temperature, mainly operational parameters regulation, bioaugmentation, biofilm technology, chemical phosphorus precipitation and application of novel process technologies, are then reviewed. Finally, future directions to address low temperature wastewater are highlighted. A special emphasis is given to the application of novel process/technology configurations to enhance process performance at low temperature in practical engineering.

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.

Iron Robustly Stimulates Simultaneous Nitrification and Denitrification Under Aerobic Conditions

Simultaneous nitrification and denitrification (SND) is a promising single-reactor biological nitrogen-removal method. Activated sludge with and without iron scrap supplementation (Sludge-Fe and Sludge-C, respectively) was acclimated under aerobic condition. The total nitrogen (TN) content of Sludge-Fe substantially decreased from 25.0 ± 1.0 to 11.2 ± 0.4 mg/L, but Sludge-C did not show the TN-removal capacity. Further investigations excluded a chemical reduction of NO₃^--N by iron and a decrease of NH₄⁺-N by microbial assimilation, and the contribution of SND was verified. Moreover, the amount of aerobic denitrifiers, such as bacteria belonging to the genera Thauera, Thermomonas, Rhodobacter, and Hyphomicrobium, was considerably enhanced, as observed through Miseq Illumina sequencing method. The activities of the key enzymes ammonia monooxygenase (AMO) and nitrite oxidoreductase (NXR), which are associated with nitrification, and periplasmic nitrate reductase (NAP) and nitrite reductase (NIR), which are related to denitrification, in Sludge-Fe were 1.23-, 1.53-, 3.60-, and 1.55-fold higher than those in Sludge-C, respectively. In Sludge-Fe, the quantity of the functional gene NapA encoding enzyme NAP, which is essential for aerobic denitrification, was significantly promoted. The findings indicate that SND is the primary mechanism underlying the removal of TN and that iron scrap can robustly stimulate SND under aerobic environment.

Nitrogen removal performance and microbial community changes in subsurface wastewater infiltration systems (SWISs) at low temperature with different bioaugmentation strategies

Poor nitrogen removal efficiency (mainly nitrate, NO₃^--N) at low temperatures strongly limits application of subsurface wastewater infiltration systems (SWISs). Seven psychrophilic strains (heterotrophic nitrifying bacteria and aerobic denitrifying bacteria) were isolated and added to SWISs to investigate the effect of embedding and direct-dosing bioaugmentation strategies on sewage treatment performance at low temperature. Both bioaugmentation strategies improved ammonium (NH₄⁺-N) removal efficiencies, and the embedding strategy also exhibited satisfactory NO₃^--N and total nitrogen (TN) removal efficiencies. Pyrosequencing results of the bacterial 16S rRNA gene indicated that the embedding strategy significantly decreased the indigenous soil microbial diversity (p < .05) and altered the bacterial community structure, significantly increasing the relative abundance of Clostridia, which have good nitrate-reducing activity.

Ammonium assimilation: An important accessory during aerobic denitrification of Pseudomonas stutzeri T13

The present study investigated effect of ammonium utilization on aerobic denitrification by Pseudomonas stutzeri T13. Per nitrogen balance calculation, all consumed ammonium was utilized as nitrogen source for cell propagation by assimilation rather than heterotrophic nitrification. Total organic carbon (TOC) and ammonium were necessary substrates to sustain heterotrophic propagation of P. stutzeri T13 at optimum proportion equal to seven. Under aerobic condition, nitrate was utilized as substitute nitrogen source when ammonium was completely exhausted. Biomass production effectively increased with increasing initial ammonium from 0mg/L to 100mg/L. Owing to enlarged biomass, average nitrate reduction rate increased from 7.36mgL^-1h^-1 to 11.95mgL^-1h^-1. Such process also successfully reduced nitrite accumulation from 121.8mg/L to 66.16mg/L during aerobic denitrification. As important accessory during aerobic denitrification, ammonium assimilation efficiently doubled total nitrogen (TN) removal from 54.97mg/L (no ammonium provided) to 113.1mg/L (100mg/L ammonium involved).

Optimizing external carbon source addition in domestics wastewater treatment based on online sensoring data and a numerical model

The removal of total nitrogen in wastewater treatment plants (WWTPs) is often unsatisfactory for a variety of reasons. One possible measure to improve nitrogen removal is the addition of external carbon. However, the amount of carbon addition is directly related to WWTP operation costs, highlighting the importance of accurately determining the amount of external carbon required. The objective of this study was to obtain a low nitrate concentration in the anoxic zone of WWTPs efficiently and economically by optimizing the external carbon source dosage. Experiments were conducted using a pilot-scale pre-denitrification reactor at a Nanjing WWTP in China. External carbon source addition based on online monitoring of influent wastewater quality and a developed nitrification-denitrification numerical model was investigated. Results showed that carbon addition was reduced by 47.7% and aeration costs were reduced by 8.0% compared with those using a fixed-dose addition mode in the pilot reactor. The obtained technology was applied to the full-scale Jiangxinzhou WWTP in Nanjing with promising results.

Enhancing wastewater reuse by forward osmosis with self-diluted commercial fertilizers as draw solutes

Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min(-1) did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m(-3). These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.

Microbial population dynamics in response to bioaugmentation in a constructed wetland system under 10°C

Compound microbial inocula were enriched and applied to a pilot-scale constructed wetland system to investigate their bioaugmentation effect on nitrogen removal under cold temperature (10°C). The results showed a 10% higher removal efficiency of ammonia and total nitrogen compared to a control (unbioaugmented) group. The microbial community structures before and after the bioaugmentation were analyzed through high throughput sequencing using Miseq Illumina platform. A variation of species richness and community equitability was observed in both systems. It is demonstrated that, based on the response of both the performance and microbial community, bioaugmentation using compound microbial inocula can fine tune the bacterial population and enhance the nitrogen removal efficiency of a constructed wetland system.

Heterotrophic nitrification and aerobic denitrification by Pseudomonas tolaasii Y-11 without nitrite accumulation during nitrogen conversion

A hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was found to display high removal capabilities for heterotrophic nitrification with ammonium and for aerobic denitrification with nitrate or nitrite nitrogen. When strain Y-11 was cultivated for 4days at 15°C with the initial ammonium, nitrate and nitrite nitrogen concentrations of 209.62, 204.61 and 204.33mg/L (pH 7.2), the ammonium, nitrate and nitrite removal efficiencies were 93.6%, 93.5% and 81.9% without nitrite accumulation, and the corresponding removal rates reached as high as 2.04, 1.99 and 1.74mg/L/h, respectively. Additionally, ammonium was removed mainly during the simultaneous nitrification and denitrification process. All results demonstrate that P. tolaasii strain Y-11 has the particularity to remove ammonium, nitrate and nitrite nitrogen at low temperatures, which guarantees it for future application in winter wastewater treatment.

Nitrifying bacterial biomass and nitrification activity evaluated by FISH and an automatic on-line instrument at full-scale Fusina (Venice, Italy) WWTP

In this study, monthly variations in biomass of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were analysed over a 1-year period by fluorescence in situ hybridization (FISH) at the full-scale Fusina WWTP. The nitrification capacity of the plant was also monitored using periodic respirometric batch tests and by an automated on-line titrimetric instrument (TITrimetric Automated ANalyser). The percentage of nitrifying bacteria in the plant was the highest in summer and was in the range of 10-15 % of the active biomass. The maximum nitrosation rate varied in the range 2.0-4.0 mg NH4 g(-1) VSS h(-1) (0.048-0.096 kg TKN kg(-1) VSS day(-1)): values obtained by laboratory measurements and the on-line instrument were similar and significantly correlated. The activity measurements provided a valuable tool for estimating the maximum total Kjeldahl nitrogen (TKN) loading possible at the plant and provided an early warning of whether the TKN was approaching its limiting value. The FISH analysis permitted determination of the nitrifying biomass present. The main operational parameter affecting both the population dynamics and the maximum nitrosation activity was mixed liquor volatile suspended solids (MLVSS) concentration and was negatively correlated with ammonia-oxidizing bacteria (AOB) (p = 0.029) and (NOB) (p = 0.01) abundances and positively correlated with maximum nitrosation rates (p = 0.035). Increases in concentrations led to decreases in nitrifying bacteria abundance, but their nitrosation activity was higher. These results demonstrate the importance of MLVSS concentration as key factor in the development and activity of nitrifying communities in wastewater treatment plants (WWTPs). Operational data on VSS and sludge volume index (SVI) values are also presented on 11-year basis observations.

Cold Temperature Effects on Long-Term Nitrogen Transformation Pathway in a Tidal Flow Constructed Wetland

The present study investigated long-term treatment performance and nitrogen transformation mechanisms in tidal flow constructed wetlands (TFCWs) under 4, 8, and 12 °C temperature regimes. High and stable ammonium (NH4(+)-N) removal efficiency (93-96%) was achieved in our TFCWs, whereas nitrate (NO3(-)-N) was accumulated at different levels under different temperatures. Quantitative response relationships showed anammox/amoA, (narG+napA)/amoA, and (narG+napA)/bacteria were the respective key functional gene groups determining 4, 8, and 12 °C NO3(-)-N reduction. Pathway analysis revealed the contribution of these functional gene groups along a depth gradient. In addition, denitrification process increased, while anammox process decreased consistent with a rise in temperature from 4 to 12 °C. Furthermore, cold temperatures exhibited different effects on anammox and denitrification and their long-term acclimatization capacities changed with temperature.