High Concentration Of Ammonia Nitrogen Research Articles

A Na+/H+-Exchanger Gene from Penaeus monodon: Molecular Characterization and Expression Analysis under Ammonia Nitrogen Stress

Na+/H+-exchanger (NHE) assumes a significant part in different particle transport in creatures. A clone of Penaeus monodon NHE cDNA was examined in this study (PmNHE), and its impact on high-concentration ammonia nitrogen stress was researched. The 877-amino acid (aa) protein was encoded by a full-length PmNHE cDNA that was 2788 base pairs (bp) long and had a 2643-bp open reading frame (ORF). The findings show that PmNHE was expressed in all of the P. monodon organs that were tested, including the intestine, muscle, hemolymph, heart, hepatopancreas, stomach, epidermis, gill, testis, and ovary, and the intestine and muscle were found to have the highest levels of PmNHE expression. The expression of PmNHE in the gill tissue of P. monodon was significantly up-regulated under high levels of ammonia nitrogen stress. The expression of PmNHE in the intestine of P. monodon under high-concentration ammonia nitrogen stress was significant. When exposed to high concentrations of ammonia nitrogen stress, P. monodon exhibited shorter survival times than the two control groups. Hence, it is suggested in the present study that PmNHE may have a significant impact on the environment with high levels of ammonia nitrogen.

A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 μs, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for ∙OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of ∙OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.

Efficient Removal of Ammonia Nitrogen by an Electrochemical Process for Spent Caustic Wastewater Treatment

Spent caustic wastewater produced in a soda plant has a high concentration of ammonia nitrogen (NH4+-N). As excessive NH4+-N discharging into water bodies would cause eutrophication as well as destruction to the ecology balance, developing an efficient technology for NH4+-N removal from the spent caustic wastewater is imperative in the current society. In this study, an electrochemical process with graphene electrodes was designed for the NH4+-N removal in the spent caustic wastewater. The removal efficiency of the NH4+-N during the electrochemical process could reach 98.7% at 4 A in a short treatment time (within 120 s) with an acceptable energy consumption (6.1 kWh/m3-order). NO3− and NO2− were not detected during the electrochemical process. An insignificant amount of NH2Cl, NHCl2, and NCl3 produced in the treatment suggested that little of the NH4+-N reacted with chlorine, that is, chlorination played a negligible role in the NH4+-N removal. By electron equilibrium and nitrogen conversion analysis, we think that NH4+-N was primarily converted to NH2(ads) on the surface of a graphene electrode by one-electron transfer during the direct oxidation of the electrochemical process. Due to the high calcium ion (Ca2+) in the spent caustic wastewater, the electrode scale significantly increased to 1.4 g after treatment of 240 s at 4 A. By X-ray diffraction (XRD) analysis, the composition of the electrode scale is portlandite Ca(OH)2. Although the electrode scale was obvious during the electrochemical treatment, it could be alleviated by alternating the electrode polarity. As a result, the life and efficiency of the graphene electrode for NH4+-N removal could remain stable for a long time. These results suggest that the electrochemical process with a graphene electrode may provide a competitive technology for NH4+-N removal in spent caustic wastewater treatment.

Comprehensive treatment of latex wastewater and resource utilization of concentrated liquid

Latex wastewater is a kind of refractory organic wastewater containing high concentrations of organics and ammonia nitrogen. In this work, the combined process of forward osmosis (FO) and reverse osmosis (RO) was designed to treat the latex wastewater in the whole process, achieving the water recovery rate of 99% and basically no waste discharge after the catalytic oxidation process. The turbidity of the latex wastewater was decreased to below 1 NTU by microfiltration pretreatment, and then using MgCl2 worked as the draw solution for FO process to treat the latex wastewater. Different operation conditions including adding acid or scale inhibitor as the pretreatment methods were conducted to improve the treatment performance of the combined process. After the treatment of the whole process, the concentration of COD was less than 20 mg⋅L−1, the concentration of NH3-N was less than 10 mg⋅L−1, and the concentration of TP was less than 0.5 mg⋅L−1 for the treated latex wastewater. The water quality met standards of industrial water reuse after the complete analysis of the treated latex wastewater, meanwhile, useful substances of L-Quebrachitol (L-Q) were successfully extracted from the concentrated solution. Therefore, the combined process of FO and RO could realize the efficient treatment and reuse of latex wastewater, which provided with some important guidance on the industrial application.

Chloride-Enhanced Removal of Ammonia Nitrogen and Organic Matter from Landfill Leachate by a Microwave/Peroxymonosulfate System

Landfill leachate contains not only high concentrations of refractory organic matter and ammonia nitrogen, but also high concentrations of chloride ions (Cl−). The modification of reactive species of the peroxymonosulfate (PMS) oxidation system by Cl− and its priority sequence for the removal of NH4+-N and organic matter from landfill leachate remain unclear. This study investigated the removal characteristics of NH4+-N and organic matter in the microwave (MW)/PMS system with high Cl− content. The results show that increasing Cl− concentration significantly improves the production of hypochlorous acid (HOCl) in the MW/PMS system under acidic conditions, and that the thermal and non-thermal effects of MW irradiation have an important influence on the HOCl produced by PMS activation. The maximum cumulative concentration of HOCl was 748.24 μM after a reaction time of 2 min. The formation paths of HOCl are (i) SO4•− formed by the MW/PMS system interacting with Cl− and HO•, and (ii) the nucleophilic addition reaction of PMS and Cl−. Moreover, the high concentration of HOCl produced by the system can not only remove NH4+-N in situ, but also interact with PMS to continuously generate Cl• as an oxidant to participate in the reaction with pollutants (e.g., NH4+-N and organic matter). Common aqueous substances (e.g., CO32−, HCO3−, NO3−, and humic acid) in landfill leachate will compete with NH4+-N for reactive species in the system, and will thereby inhibit its removal to a certain extent. It was found that when NH4+-N and leachate DOM co-exist in landfill leachates, they would compete for reactive species, and that humic acid-like matter was preferentially removed, leading to the retention of fulvic acid-like matter. It is hoped that this study will provide theoretical support for the design and optimization of methods for removing NH4+-N and organic matter from landfill leachate with high chloride ion content.

Effect of nano-Fe3O4 biochar on anaerobic digestion of chicken manure under high ammonia nitrogen concentration

In order to improve the stability and CH4 production efficiency of the anaerobic digestion (AD) system under high ammonia nitrogen (AN) concentration, this study investigated the effect of biochar loaded with nano-Fe3O4 particles to generate nano-Fe3O4 biochar on AD of chicken manure (CM). The results showed that biochar can be used as an excellent carrier for nano-Fe3O4 particles, solving the problem of easy agglomeration and loss. The inhibition of the AD system caused by high concentrations of AN was greatly mitigated after loading nano-Fe3O4 particles on biochar, and the CH4 yield was substantially increased. The highest CH4 yield was achieved when the amount of nano-Fe3O4 biochar was 15%, which was 62.61% higher compared to the control group. Microbial community analysis showed that the porous structure of biochar was capable of immobilizing and enriching microorganisms, and the relative abundance of Firmicutes and Methanobacterium increased by 28.67–54.44% and 52.62–87.70%, respectively. Firmicutes acted as an important acetate bacterium, contributing to syntrophic acetate oxidation (SAO) with hydrotropic methanogenesis. SAO was an effective alternative pathway for acetate degradation under ammonia stress involving the syntrophic activities of SAO bacteria and hydrogenotrophic archaea. The load of nano-Fe3O4 particles increased the relative abundance of Chloroflexi from 0.52% to 3.51% and the Methanosarcina from 27.50% to 49.30%. Chloroflexi and Methanosarcina could act as potential direct electron transfer (DIET) partners for facilitating methane production by promoting the SAO pathway.

Removal characteristics of ammonia nitrogen and refractory organic matter in waste leachate by Co2+/peroxymonosulfate process at high chloride ion concentration

Landfill leachate contains high concentrations of refractory organic matter (ROM), ammonia nitrogen (NH4+), and chlorine ion (Cl–). With efficient ROM removal being the focus of advanced oxidation processes, there is an urgent need to clarify the role of high Cl– concentration on reactive species and preferential reactivity towards coexistent ROM and NH4+. This study investigated the removal characteristics of ROM and NH4+ using a Co2+/peroxymonosulfate (Co2+/PMS) process with high Cl– concentration. The results showed that the system produced large amount of hypochlorous acid (HOCl), with a maximum accumulated HOCl concentration reaching 2.78 mM at Co2+, PMS, and Cl– concentrations of 105 μM, 10 mM, and 17 mM, respectively. The differences in Cl–-to-PMS molar ratios altered HOCl formation pathway, and both Co3+ and SO4•− played important roles in HOCl generation. Although the initial concentrations of PMS, Co2+, and Cl– were proportional to the cumulative HOCl concentration, increasing pH significantly inhibited HOCl formation. The coexisting anions commonly found in waste leachate (i.e., CO32−, HCO3−, and NO3−) promoted HOCl production to some extent, but both NH4+ and dissolved organic matter (humic acid and amino acid complex) severely depleted the formed HOCl. Analysis of the removal characteristics of NH4+ and ROM in co-occurrence in actual waste leachate at high Cl– concentrations revealed that NH4+ and ROM competed for HOCl, and preferential removal of humic-like substances led to retention of fulvic-like substances. These results provide theoretical support for the design and optimization of methods for NH4+ and ROM removal from waste leachate containing high Cl– content.

Metagenomics analysis of microbial community distribution in large-scale and step-by-step purification system of swine wastewater

Biological treatment is one of the most widely used methods to treat swine wastewater in wastewater treatment plants. The microbial community plays an important role in the swine slurry treatment system. However, limited information is available regarding the correlation between pollutant concentration and dominant microbial community in swine wastewater. This work aimed to study the profiling of microbial communities and their abundance in the 40 M3/day large-scale and step-by-step treatment pools of swine wastewater. Metagenome sequencing was applied to study the changes of microbial community structure in biochemical reaction pools. The results showed that in the heavily polluted pools, it was mainly Proteobacteria, Cyanobacteria, Chlorella and other strains that could tolerate high concentration of ammonia nitrogen to remove nitrogen and absorb chemical oxygen demand (COD). In the moderately polluted pools, Nitrospirae, Actinobacteria and other strains further cooperated to purify swine wastewater. In the later stage, the emergence of Brachionus indicated the reduction of water pollution. The dominant microbes and their abundance changed with the purification of swine wastewater in different stages. Moreover, the dominant microflora of swine wastewater treatment pools at all levels reflected little difference in phylum classification level, while in genus classification level, the dominant microflora manifested great difference. Findings demonstrated that the microorganisms maintained ecological balance and absorbed the nutrients in the swine wastewater treatment pools, so as to play the role of purifying sewage. Therefore, the stepwise purification of swine wastewater can be realized by adding bacteria and microalgae of different genera.

Enhanced removal of ammonia nitrogen from rare earth wastewater by NaCl modified vermiculite: Performance and mechanism.

Wastewater from rare earth mining (WREM) is very harmful to environment and human health due to its high concentration of ammonia nitrogen (NH3-N). It is therefore necessary and urgent to find a low-cost and convenient technique to remove high concentration of NH3-N from WREM. In this study, Natural powdered vermiculite (NV) was modified with seven sodium chloride (NaCl) solutions, and seven kinds of sodium chloride modified vermiculite (Na-V) were obtained. The NH3-N adsorption performance of Na-V is greatly improved compared with NV. Among them, vermiculite modified with 180g/L NaCl yielded the highest ammonium adsorption capacity (Qm, 11.569mg/g), which was 63.43% higher than NZ (Qm, 7.079mg/g). The characterizations of 180-Na-V confirmed the removal mechanism of NH3-N that the improved capacity of modified vermiculite was attributed to its higher mesoporous volume and ion-exchange capacity, which are the result of sodium-ion exchange and Interlayer effect from high concentration of NaCl. The adsorption isotherms and kinetics were respectively best consistent with Langmuir model and the pseudo-second-order (PSO) model. The adsorption capacity (3.808mg/g) of vermiculite after 5 cycles could still maintain 75.09% of the initial adsorption capacity (5.071mg/g). A large amount of Na-V had little effect on pH of water, which meet the requirements of practical application. Including pH, dosage, coexisting ions, the effects of other factors on ammonium adsorption were also determined. This study provides a new method for vermiculite to remove high concentration of NH3-N.

Effect of ozone pretreatment on biogranulation with partial nitritation - Anammox two stages for nitrogen removal from mature landfill leachate.

Due to the extremely low C/N ratio, high concentration of ammonia nitrogen and refractory organic matter of mature landfill leachate (MLL), appropriate processes should be selected to effectively remove nitrogen and reduce disposal costs. Partial nitritation (PN) and anaerobic ammonia oxidation (AMX) have been used as the main nitrogen removal processes for MLL, and the sludge granulation in PN and AMX processes could contribute to high biological activity, good sedimentation performance, and stable resistance to toxicity. In this study, the O3-PN-AMX biogranules process was selected to effectively remove nitrogen from MLL without carbon addition and pH adjustment. Without uneconomical NH4+-N oxidation and wasting the alkalinity of MLL, ozone pretreatment achieved color removal, decreased humic- and fulvic-like acid substances, and alleviated the MLL toxicity on ammonia oxidizers. In addition, the ozonation of MLL could shorten the start-up time and improve the treatment efficiency and biogranules stability of PN and AMX processes. Efficient and stable nitritation was achieved in PN reactor without strict dissolved oxygen (DO) control, which was attributed to the unique structure of granular sludge, ozone pretreatment, and alternating inhibition of free ammonia and free nitric acid on nitrite oxidizers. Through the application of ozone pretreatment and granular sludge, the nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) of the O3-PN-AMX biogranules process reached 0.39kg/m3/day and 85%, respectively, for the undiluted MLL treatment. This study might provide a novel and effective operation strategy of combined process for the efficient, economical, and stable nitrogen removal from MLL.

Influence of C/N ratios on treatment performance and biomass production during co-culture of microalgae and activated sludge.

Novel phycosphere associated bacteria processes are being regarded as a potential and cost-effective strategy for controlling anthropogenic contaminants in wastewater treatment. However, the underlying concern with the process is its vulnerability to improper organic or nutrient intake. This study established a synergistic interaction between microalgae and activated sludge in a three-photobioreactor system (without external aeration) to understand how pollutants could be mitigated whilst simultaneously yielding biomass under different C/N ratios of 1:1, 5:1 and 10:1. The result showed that the superior biomass productivity was facilitated at a C/N ratio of 5:1 (106 mg L-1 d-1), and the high degradation rate constants (kCOD = 0.25 d-1, kTN = 0.29 d-1, kTP = 0.35 d-1) was approximated using a first-order kinetic model. The removal of pollutants was remarkably high, exceeding 90% (COD), 93% (TN), and 96% (TP). Nevertheless, the C/N ratio of 1:1 resulted in a threefold drop in biomass-specific growth rate (μ = 0.07 d-1). Microalgal assimilation, followed by bacterial denitrification, is the major pathway of removing total nitrogen when the C/N ratio exceeds 5:1. Activated sludge plays an important role in improving microalgae tolerance to high concentration of ammonia nitrogen and boosting nitrification (light phase) and denitrification (dark phase). The use of phycosphere associated bacteria could be a promising strategy for controlling nutrients pollution and other environmental considerations in wastewater.

Physiological response and tolerance of Myriophyllum aquaticum to a wide range of ammonium concentrations.

Myriophyllum aquaticum (M. aquaticum) can be used in constructed wetlands (CWs) to effectively purify swine wastewater with high-ammonia nitrogen (NH3-N and NH4+-N) concentrations. However, the understanding of its tolerance mechanism to ammonia nitrogen is limited. The physiological response and tolerance mechanism of M. aquaticum to a wide range of NH4+ concentrations (0-35mM) were investigated in the present study. The results indicated that M. aquaticum can tolerate NH4+ concentrations of up to 30mM for 21 days and grow well with high nutrient (N, P) uptake. A suitable concentration of NH4+ for a better growth of M. aquaticum was 0.5-20mM. The free NH4+ content was no obviously increase at NH4+ concentration below 15mM, indicated there was no obviously ammonium accumulation. Exogenous NH4+ inhibited K+ absorption and improved Ca2+ absorption, indicating mineral cation could mediate NH4+ homeostasis under NH4+ stress. Moreover, comparison with those in the control group, the activities of glutamine synthetase (GS), glutamate synthetase (GOGAT) in M. aquaticum increased by 52.7%-115% at 1-20mM NH4+, and superoxide dismutase (SOD) increased by 29.2-143% at 1-35mM NH4+. This indicated that the high NH4+ tolerance of M. aquaticum was mainly due to the balance of free NH4+ content in tissues, as well as improved nitrogen metabolism and antioxidant system. This could be attributed to the role of the GS-GOGAT cycle and SOD. In conclusion, M. aquaticum, which tolerates high NH4+ concentration and has a high N uptake ability, can be used as a good candidate specie to help develop more efficient management strategies for treating high-NH4+ wastewater in CW systems.

Magnesium-modified biochar was used to adsorb phosphorus from wastewater and used as a phosphorus source to be recycled to reduce the ammonia nitrogen of piggery digestive wastewater

High concentrations of ammonia nitrogen in piggery digestive wastewater are toxic to the microorganisms in wastewater treatment systems. The ammonia nitrogen load can be decreased by struvite precipitation. The purpose of this paper was to take phosphate from magnesium-modified biochar adsorbed wastewater as a phosphorus source and add it to biogas slurry to reduce the ammonia nitrogen concentration . The effects of phosphorus source dosage, initial reaction pH value and reaction time on ammonia nitrogen removal from biogas slurry were investigated, and then the subsequent biogas slurry underwent sequencing batch reactor biochemical treatment. When the phosphorus source dosage was 20 g/L, initial reaction pH value was 10.0 and reaction time was 1 h, the NH 3 –N recovery was 62.98%. The subsequent biogas slurry met the discharge standards (DB44/613–2009) after biochemical treatment. An innovative process for the recycling of pig farm waste, nitrogen and phosphorus recovery and advanced treatment of biogas slurry is first proposed in this paper. • Mg@C was prepared by pyrolysis of pig manure and waste residue containing magnesium. • Mg@C adsorbed PO 4 3− from SBR effluent as a phosphorus source for MAP reaction. • After MAP reaction, the NH 3 –N concentration in biogas slurry was below 200 mg/L. • After MAP reaction, SBR effluent more easily met the discharge standard than CK.

The effect of activated sludge treatment and catalytic ozonation on high concentration of ammonia nitrogen removal from landfill leachate

This study adopted the combination of activated sludge treatment and catalytic ozonation technology to efficiently remove the high concentration of ammonia nitrogen from landfill leachate. Through optimizing the parameters continuously, the COD, NH4+-N, UV254 and colority respectively descended to 417.75 ± 6.72 mg/L, 9.77 mg/L, 1.98 ± 0.04 and 40 times, and 3D fluorescence also reduced significantly within 14 days. Target genes of AOB-amoA, nxrA, napA, nirS and nosZ analysis indicated that ammonia-oxidizing bacteria, nitrated bacteria, and denitrifying bacteria played a key role on nitrogen removal, aerobic denitrifying bacteria was dominated especially. The nitrogen removal process was as follows: catalytic ozonation converted nitrogen-containing organic matter into NH4+-N, then NH4+-N was converted into NO2–-N and NO3–-N with the action of ammonia oxidation, nitrification and catalytic ozonation. Finally, the denitrification microorganisms transformed NO3–-N or NO2–-N to N2. Therefore, this coupled process realized the nitrogen removal effectively from landfill leachate.

Complex network analysis of slaughterhouse waste anaerobic digestion: From failure to success of long-term operation

The study explored slaughterhouse waste (SHW) as prime feedstock associated with and without supplement of an external slowly degradable lignocellulosic carbon source to overcome the synergistic co-inhibitions of ammonia and fatty acids. Long-term solid-state digestion (SSD) and liquid-state digestion (LSD) were investigated using a mixture of pork liver and fat. At 2.0 g volatile solids (VS) L−1 d−1 of organic loading rate (OLR), the two reactors of SSD experienced operational instability due to ammonia inhibition and volatile fatty acid (VFA) accumulation while LSD successfully produced 0.725 CH4 L CH4 g−1VS during 197 d of working days under unfavorable condition with high total ammonia nitrogen (>4.7 g/L) and VFAs concentration (>1.9 g/L). The network analysis between complex microflora and operational parameters provided an insight for sustainable biogas production using SHW. Among all, hydrogenotrophic methanogens have shown better resistance than acetoclastic methanogens.

Role of spent coffee ground biochar in an anaerobic membrane bioreactor for treating synthetic swine wastewater

Using anaerobic membrane bioreactors (AnMBRs) to treat swine wastewater is an effective method to recover bioenergy. However, due to the inhibitory effect of high concentrations of organic matter and ammonia nitrogen on microbial activities in swine wastewater, some problems are evident such as low recovery efficiency and serious membrane fouling. In this study, biochar prepared from spent coffee grounds (SCG-BC) was added to AnMBR to investigate its effect on the operation process. Results reported that methane yield rose from 0.227 LCH4/g-CODremoved to 0.267 LCH4/g-CODremoved along with a reduction in CO2 being produced at 35.25 % after adding SCG-BC. It confirmed that in-situ biogas upgrading was achieved. As well, the total volatile fatty acids declined to a low concentration of 194.87 ± 51.82 mg/L while pH remained steadily at 7.70 ± 0.31. Adding SCG-BC reduced irreversible membrane fouling by 34.69 %. Microbial community analysis showed that SCG-BC increased the relative abundance of methanogenic archaea, especially Methanosarcina (from 1.47 % to 8.03 %). Also, Anaerolinea and Methanosaeta participating in direct interspecies electron transfer were enriched onto biochar. They acted together to enhance the biogas production. It can be concluded that AnMBR with SCG-BC addition has good application prospects in recovering bioenergy from wastewater.

Efficient treatment of aged landfill leachate containing high ammonia nitrogen concentration using dynamic wave stripping: Insights into influencing factors and kinetic mechanism

Aged landfill leachate is challenging to treat owing to its extremely high ammonia concentration and poor biodegradability. We constructed pilot-scale dynamic wave stripping equipment to separate ammonia from landfill leachate and achieved excellent results. To further expand the usage of pilot-scale equipment in actual water treatment process and implement it in a sewage plant, we established the mass transfer kinetic physics and mathematical model of the dynamic wave stripping process based on the surface renewal theory and the traditional stripping method. The surface renewal theory and the traditional stripping method are employed to analyze the mechanism of various experimental parameters affecting the stripping process, predict the stripping effect of the equipment under different conditions, and verify the calculation results of the model using the kinetic fitting results of the experimental data. These calculation results of the model indicate that the mass transfer kinetic coefficients of ammonia stripping at 20 °C, 25 °C, and 30 °C are 85.62 min, 75.34 min, and 65.88 min, respectively, when the gas–liquid ratio is 129. When the gas–liquid ratios are 62, 129, and 163 at 25 °C, the mass transfer kinetic coefficients of ammonia stripping are 102.61 min, 75.34 min, and 61.43 min, respectively. With increasing temperature and gas–liquid ratio, the particle size and number of bubbles in the wave tube of the stripping equipment gradually decrease and the mass transfer efficiency of free ammonia between the gas and liquid phases improves, enhancing the stripping efficiency of ammonia nitrogen.

Simultaneous removal of high concentrations of ammonia nitrogen and calcium by the novel strain Paracoccus denitrificans AC-3 with good environmental adaptability

The novel Paracoccus denitrificans AC-3 strain was isolated and displayed outstanding purification capability for high concentrations of ammonia nitrogen (NH4+-N) and calcium (Ca2+). Meanwhile, the strain exhibited excellent environmental adaptability within a wide pH range and high levels of NH4+-N and Ca2+. Nitrogen balance analysis demonstrated that the pathways of NH4+-N removal consisted of 80.12% assimilation and 16.60% heterotrophic nitrification aerobic denitrification (HNAD). In addition, Ca2+ was removed by forming calcium carbonate (CaCO3) with carbonate (CO32−) and bicarbonate (HCO3−). CO32−and HCO3− were obtained from carbon dioxide (CO2) hydration, which was catalyzed by carbonic anhydrase (CA) secreted by strain AC-3. The alkaline environment for carbonate precipitation was provided by CA and HNAD. The resulting CaCO3 existed in the form of calcite and exhibited a unique morphology and elemental composition.

Municipal wastewater discharge standards for ammonia nitrogen in Brazil: technical elements to guide decisions.

In Brazil, domestic effluents represent the primary source of pressure on water resources. Water pollution can be controlled by defining, applying, and enforcing the effluent standards for wastewater discharge. Discussions are ongoing in Minas Gerais State regarding the possibility of setting a discharge standard for ammonia nitrogen in municipal wastewater, which is currently not required. However, providing technical support for decision-making is challenging because of the difficulties in accessing monitoring data from sewage treatment plants. This study aimed to analyze the monitoring data from 49 sewage treatment plants operating in Minas Gerais to offer guidance for decision making. High concentrations of ammonia nitrogen in the effluents of the treatment plants were found, reinforcing the need for better control and the adoption of more advanced technologies. Furthermore, it was observed an increase in concentrations downstream of the discharges in the receiving water bodies. Adopting a progressive and adaptable discharge standard can be a solution for better control of treatment systems.

Comparative analysis of nitrogen removals and microbial communities in air and pure oxygen aeration systems during treatment of municipal solid waste incineration (MSWI) leachate

MSWI leachate contain high concentrations of ammonium nitrogen (NH4+-N). The conventional submerged air-diffusing (CSA) system are the dominant oxygen supply in the aerobic process for NH4+-N removal from leachate. However, it carries high energy consumption. In this study, Pure oxygen (PO), which is more environmentally friendly, was used as an alternative to air for solving this problem. For comprehensive analysis the effects of PO supersede air on nitrogen removals and microbial diversities in the aerobic process during treatment of MSWI leachate, two parallel full-scale anoxic-oxic systems were set with the floating Praxair's in situ oxygenation (I-SO™) system and the CSA system, respectively. Compared to the CAS system, the removal efficiency of total nitrogen (TN) increased by 9.79% with the I-SO™ system but COD and NH4+-N removals reduced by 6.83% and 1.19%, respectively. Metagenomic studies revealed that the bacterial richness, diversity, and evenness decreased with PO aeration, while the abundances of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB) increased, as well as the AOB/nitrite-oxidizing bacteria (NOB) ratios. In addition, the nitrite-denitrification functional genes (nirK and nirS) deposited from autotrophic and Heterotrophic bacteria were more predominant and accounted for the higher efficiency of TN removal in the PO aeration treatment, while complete nitrification and nitrate-denitrification were dominant in the air aeration anoxic-oxic system. Therefore, nitrogen removal from MSWI leachate by using PO aeration provided theoretical perspective for engineering applications.