Removal Of Nitrogen Compounds Research Articles

Biological removal of nitrogenous waste compounds in the biofloc aquaculture system: a review

Abstract Aquaculture has experienced significant global expansion and is considered one of the fastest-growing sectors in food production. However, there exist additional challenges that restrict the capacity to achieve maximum efficiency in aquaculture systems, such as issues over water quality and shortages of appropriate live feeds. Intensive aquaculture systems involve the use of protein-rich prepared feed for feeding the cultured animals. This may give rise to the discharge of nitrogenous compounds into the water, which can pose a risk to the environment when present in excessive quantities beyond the acceptable levels. In recent years, an innovative method called biofloc technology (BFT) has become a practical solution to this issue. Undoubtedly, BFT offers a groundbreaking method for nutrient disposal that eradicates the requirement for excessive water use or equipment maintenance. Three primary types of microorganisms are crucial in alleviating the adverse impacts of nitrogen compounds in this technique. Photoautotrophs participate in the processes of removal and absorption, whereas chemoautotrophs promote nitrification and conversion. Heterotrophs contribute to the absorption process. Biofloc predominantly consists of heterotrophic bacteria, alongside algae, protozoa, rotifers, and nematodes. While there have been reviews carried out on multiple aspects of biofloc technology, there exists a lack of literature that tackles this particular field of research progress. This article discusses every aspect and techniques of biological management used for removing nitrogenous waste compounds in biofloc aquaculture systems.

REACTOR SECTION PRESSURE CONTROL AT DIESEL HYDROTREATING UNIT

Diesel Hydrotreating Units (DHUs) are essential components within petroleum refineries, playing a critical role in the production of clean and high-quality diesel fuel. This abstract provides a comprehensive overview of the mechanisms, necessity, and operational significance of DHUs in the refining process. Firstly, the abstract discusses the fundamental principles underlying the operation of DHUs. The catalytic hydrotreating process is elucidated, highlighting the role of hydrogenation reactions in the removal of sulfur, nitrogen, and aromatic compounds from diesel feedstocks. The synergy between catalysts and hydrogen gas in promoting desulfurization, denitrification, and hydrodenitrogenation reactions is examined, emphasizing the pivotal role of DHUs in enhancing the environmental and performance attributes of diesel fuel. Furthermore, the abstract addresses the imperative need for Diesel Hydrotreating Units. The detrimental impacts of sulfur-containing compounds, such as sulfur oxides (SOx), on air quality and human health are discussed, underscoring the regulatory mandates aimed at reducing sulfur emissions from diesel fuel. DHUs emerge as indispensable tools for compliance with stringent environmental regulations, ensuring the production of low-sulfur diesel fuel that meets or exceeds regulatory standards. Moreover, the abstract emphasizes the operational significance of DHUs within petroleum refineries. Through the integration of advanced reactor designs, catalyst technologies, and process optimization strategies, DHUs enable refineries to achieve efficient desulfurization and meet production targets while minimizing energy consumption and operational costs. The adaptability of DHUs to varying feedstock compositions and processing conditions further underscores their versatility and importance in the refining industry. In conclusion, this abstract provides a comprehensive overview of Diesel Hydrotreating Units, elucidating their mechanisms, necessity, and operational significance in the production of clean and high-quality diesel fuel. By facilitating the removal of sulfur and other impurities from diesel feedstocks. Keywords: Diesel Hydrotreatment Unit, Control Systems, Petrochemical Industry, Efficiency, Safety.

Production of ammonium bicarbonate from the condensate of the upgrading biogas-pipelines

Developing a suite of biofuels for different applications relies heavily on upgrading technologies to remove nitrogen compounds and carbon dioxide. Particularly in the upgrading of biogas to biomethane, simple water scrubbing is the most widely used technology for biogas upgrading. This technology can be synergistically implemented without the need for additional equipment for processing steps, although this design has not been conceived yet. Samples of biogas-pipeline condensates were collected from 3 different anaerobic digestion plants processing 3 different feedstocks (i.e., food waste, agrowaste, and manure) at 3 different locations in each plant (i.e., biodigester and postdigester condensate pits, digestate pasteurizer, and biogas booster and chiller). The methodology for the analysis of the 5-mL biogas-pipeline condensates was acid-base titration with 0.06 M hydrochloric acid and 0.13 M sodium hydroxide solutions as titrants, and induction of crystallization by cooling at 3 °C, adding up to 40 mL of acetone as antisolvent, and settling for 12 h. The results showed that the concentration of ammonium bicarbonate in the condensates ranged from 0.75 to 50 g/L. The most suitable location to enhance the upgradation of biogas, formation of condensate, and precipitation of ammonium bicarbonate was the pit after the anaerobic digester and before the biogas storage. The most concentrated condensate was retrieved from the biogas-pipeline coming out of the pasteurization tank, but the operation at 70.5 °C also led to volatilization of organic compounds that negatively affected the biogas quality. Future work aims to investigate coating and granulation of ammonium bicarbonate crystals to improve their stability and commercialization.

Phosphorus Removal Rate and Efficiency in an Electrochemical Sequencing Reactor for the Treatment of Wastewater with Low Organic Carbon Content

Energy is essential for the operation of wastewater treatment systems. Simultaneously, it can be a factor facilitating the electrochemical purification processes. Previous studies have shown that under specific conditions, there is no technological justification for using bio-electrochemical reactors designed for the simultaneous removal of both phosphorus and nitrogen compounds. This is because similar dephosphatation process effects can be achieved in an electrochemical reactor. Additionally, in a bio-electrochemical reactor, a portion of the organic substrate introduced for biological treatment is lost due to the electrocoagulation process. The aim of the research was to determine the influence of low direct current densities (0.4–2.0 A/m2) on the rate and efficiency of phosphorus and other compound removal in a sequencing electrochemical reactor treating real wastewater from a greenhouse with low organic compound content. In the conducted studies, an increase in electric current density resulted in an increase in the removal rates of phosphorus from 26.45 to 34.79 mg/L·h, nitrogen from 2.07 to 6.58 mg/L·h, and organic compounds from 0.44 to 1.50 mg/L·h. This corresponded to maximum removal efficiencies of 88.6 ± 2.5% for phosphorus, 7.4 ± 2.5% for nitrogen, and 51.1 ± 8.3% for organic compounds. As a result of electrocoagulation, sludge rich in phosphorus was obtained, ranging from 347 ± 38 mg/L (18.1% P) to 665 ± 36 mg/L (11.7% P). The obtained results can be utilized in the future for the development of two-stage systems for wastewater treatment with a low content of organic compounds, aiming at the removal of phosphorus and nitrogen.

Bio-chemical treatment of landfill leachates with high load of organic and nitrogen compounds

This research encompassed an 8-month investigation to evaluate the biological treatment of complex landfill leachates. The primary objectives were the removal of organic and nitrogen compounds, as well as the mitigation of H2S and VOC emissions. Biological treatment was conducted within a sequencing batch reactor (SBR), incorporating aerobic, anaerobic, and anoxic stages. The results indicate that biological treatment is indeed effective in eliminating biodegradable organic matter, with an average removal rate of 84.5% for BOD5, 42.7% for COD, and 40.9% for TOC. Nonetheless, it is imperative to integrate supplementary processes to enhance organic removal. It is worth noting that biological nitrification proved inadequate for sufficiently reducing elevated ammonia concentrations, achieving only a 23.2% reduction. In controlled laboratory conditions, the utilization of chemical precipitation, employing either MgO+H3PO4 or MgCl2.6 H2O+Na2HPO4.7 H2O in an equimolar ratio of Mg:NH4:PO4, exhibited substantial ammonia removal rates of 76.8 ± 6.4% and 80.7 ± 4.5%, respectively. Additionally, the incorporation of an anoxic stage in reactor operation demonstrated its effectiveness in achieving proficient denitrification, with an 80% removal rate for nitrates present in the raw leachates. These findings underscore the potential for optimizing the efficiency of biological leachate treatment processes through strategic modifications and the integration of additional treatment steps.

The influence of seasonality on the technological parameters of biological wastewater treatment at existing wastewater treatment plants

The work carried out monitoring of the process of biological treatment of municipal and industrial wastewater at operating wastewater treatment plants in months that differ in temperature and flow rate of process influent. The analysis of wastewater pollution indicators was carried out at three main points of the process line (receiving chamber, settling tank and Venturi tray) with a sampling frequency of 1 every 5 days. It was found that in March and April, the flow rate of process influent and the concentration of suspended solids significantly exceed the specified parameters in February and May. At volley of sewage on wastewater treatment plants in March, the concentration of BOD5 is more than 600 mg l-1. It is shown that overestimated indicators of wastewater pollution at the entrance in the spring period significantly reduce the effectiveness of biological removal of nitrogen and phosphorus compounds.

Liquid-phase adsorption of nitrogen compounds from model diesel fuel on activated carbons

One of the great challenges in deep hydrodesulfurization (HDS) to produce ultra-low-sulfur diesel (ULSD) is the coexisting heterocyclic nitrogen-containing compounds in middle distillates, which significantly inhibit the HDS reactions. This study investigates various activated carbon (AC) samples for selectively removing nitrogen compounds from a model diesel fuel through adsorption. The physical and chemical properties of the AC samples were characterized using low-temperature N2 adsorption–desorption, SEM–EDS, and FT-IR to explore their impact on the adsorption performance. The results indicate that the adsorption performance is influenced not only by the surface area and by the number of oxygen-containing functional groups on the surface but also by the pore diameter distribution. Among all AC samples tested, AC-W exhibited the highest adsorption capacity, achieving a nitrogen removal rate of 97.8% with the addition of 10 wt.% of AC-W. The adsorption capacity was approximately 24.0 mg-N/g-A at a nitrogen equilibrium concentration of 200 ppmw. The adsorption isotherms for total nitrogen and individual nitrogen compounds in the fuel over AC can be described well by the Freundlich isotherm model. An approach for improving the ADN performance of AC is discussed based on the findings in this study.

Extraction of Pyrrole from Its Mixture with n-Hexadecane Using Ionic Liquids and Their Binary Mixtures.

The conventional hydrodenitrogenation method is expensive and involves the use of catalysts and harsh procedures. In the last few years, ionic liquids (ILs) have gained attention as a promising alternative solvent for fuel oil extractive denitrogenation. In this work, the Conductor-like Screening Model for Real Solvents (COSMO-RS) was used to screen 173 potential ILs as solvents for fuel oil. Two ILs (1-ethyl-3-methylimidazolium dicyanamide ([EMIM][N(CN)2]) and 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO3])) were selected for experimental investigation. The experimental liquid-liquid extraction of pyrrole (taken as the model nitrogen compound) from n-hexadecane (the model fuel) was conducted at 298 K and 1 atm with feed concentrations of pyrrole ranging from 10 to 50 wt%, using either the two pure ILs or their mixtures with dimethylformamide or ethylene glycol. Moreover, the NRTL model was effectively used to correlate the experimental tie lines. This work shows that the use of a binary mixture of ILs with a conventional solvent results in good selectivity, but has a low capacity for extracting pyrrole compounds. On the other hand, using an IL-IL mixture exhibits good results for both capacity and selectivity. All the ternary systems tested showed positive slopes, indicating that the nitrogen compounds had a higher affinity for the IL and binary mixture extract phase. In fact, the extraction efficiency for all the systems shows promising results. This characteristic is advantageous, as it requires less solvent to remove nitrogen compounds.

Nitrogen compounds removal from brackish water by electrodialysis at fixed electric potential and dynamic current density operations

Nitrogen (N) compounds can occur in water resources from natural and anthropogenic activities. It is ideal that these contaminants be removed before water consumption. As water quality has been affected by increased salinity and pH variation, more advanced and robust technologies such as electrodialysis (ED) can be considered for simultaneous desalination and pollutant removal. In this context, the removal of N-species (NO3−, NO2−, NH4+, and CH4N2O) from brackish water by ED was investigated for different feed water quality, considering increased salinity (0 – 10g/L NaCl) and pH variation (3 – 11), under limit current density (LCD) at fixed electric potential condition. The applied electric potential (5 – 25V) under, at, and over the LCD at fixed electric potential and dynamic current density (DCD), as a percentage of LCD (0.4 - 1.2), were analyzed to improve the process. In addition, energy efficiency in the form of specific energy consumption (SEC) and current efficiency (CE) were assessed for ED at fixed electric potential and DCD. The results showed that, at extreme pH of the feed water, the removal of NO2− and NH4+ can be affected, while NO3−was the most stable compound with pH variation. An increase in feed water salinity just slightly impacted the removal of N-compounds, due to the similar characteristics of the ions in the water. The increase in electric potential at fixed electric potential or DCD increased the removal and molar flux of N-compounds. However, operating over the LCD increased the SEC of the ED process while changes in removal were not significant. DCD procedures resulted in higher CE and shorter run time of the experiments. Therefore, ED proved to be a suitable treatment technique to produce fresh water due to the selective removal of the studied ions, especially at 15V (fixed electrical potential) and 0.8 LCD (DCD) related to removal, molar flux, and run time to achieve guidelines.

Multi-anode enhanced the bioelectricity generation in air-cathode microbial fuel cells towards energy self-sustaining wastewater treatment

Microbial fuel cells (MFCs) hold considerable promise for harnessing the substantial energy resources present in wastewater. However, their practical application in wastewater treatment is limited by inadequate removal of organic matter and inefficient power recovery. Previous studies have investigated aeration as a method to enhance the removal of organic matter, but this method is energy-intensive. To address this issue, this study proposed using MFC-recovered bioelectricity for aeration, thereby mitigating the associated expenses. An air-cathode MFC with multi-anode was constructed and optimized to maximize electricity supply for aeration. Carbon-felt anodes were chosen as the most effective anode configuration, due to the high abundance of electroactive bacteria and genes observed in the biofilm generated on their surface. By incorporating six carbon felt anodes, the MFC achieved a 1.7 and 1.1 fold enhancement in the maximum power and current density, respectively. The optimized MFC unit achieved a stable current density of 0.32 A/m2 and achieved COD removal of 60% in the long-term operation of 140 days in a 50 L reactor. In a reactor scaled up to 1600 L, 72 MFCs successfully powered a mini air pump work for 10 s after an 81-s charging period. The intermittent aeration resulted in partial increases in DO concentrations to 0.03–3.5 mg/L, which is expected to promote the removal of nitrogen compounds by the nitrification-anammox process. These groundbreaking results lay the foundation for self-sustaining wastewater treatment technologies.

Development and implementation of industrial wastewater treatment technologies

The results of the Igor Sikorsky Kyiv Polytechnic Institute the Department of Bioenergetics, Bioinformatics and Ecobiotechnology researches in two directions: 1 - research into the processes of physical and chemical purification of industrial wastewater of a number of industrial enterprises from antibiotics, heavy metal ions, synthetic surfactants, etc. pollutants, and the development of local cleaning technologies before discharging pre-treated wastewater into the city's drainage network; 2 – study of processes of biological wastewater treatment of industrial enterprises with deep removal of nitrogen and phosphorus compounds using immobilized microorganisms. The greatest decrease in the COD index was observed in the processes of coagulation and settling of wastewater of a pharmaceutical enterprise. The effects of purification according to the COD indicator in the case of using ferrous sulfate III were 76.0% and 72.2% for the initial values of COD of untreated wastewater, respectively, 90 and 120 mg/dm3. For biological purification, microorganisms immobilized on VIA carriers were used in oxygen conditions created in model bioreactors - anaerobic, anoxic, aerobic. To increase the biomass, we used nylon textured thread according to TU 6-06-S116-87 with a fiber diameter of 1.5-2.5 mm and a microfiber diameter of 100 μm. The specific surface area was 4000-5000 m2/m3. The average concentration of biomass in bioreactors by dry matter, g/dm3, was: in anaerobic I – 30; in anaerobic II – 24; in anoxic I - 16.8; in anoxic II - 5.4; in aerobic - 3.2. Biological treatment of industrial wastewater using immobilized microorganisms made it possible to obtain high pollutant removal effects. The indicators of purified wastewater were: COD - 50-80 mg/dm3; BODfull - 15-20 mg/dm3; suspended substances - up to 15 mg/dm3; compounds of nitrogen and phosphorus - within the norm for discharge into natural water bodies. The developed technologies were implemented at industrial enterprises, the savings in energy costs amounted to 40-45%, the high quality of purified water was ensured in accordance with the current standards for discharge into the city drainage system and into natural reservoirs.

The Importance of the Mineral Substrate of the Biofilm in the Process of Low-Temperature Removal of Nitrogen Compounds from Wastewater

This study researched the use of biofilms to remove nitrogen compounds from municipal sewages at low temperatures, especially in winter. An aluminosilicate substrate was used to create a biofilm, which has an affinity for ammonium ions. The selection of biofilm-forming microorganisms has been shown to occur on aluminosilicate. This substrate is mainly inhabited by microorganisms that remove nitrogen compounds. As a result, microorganisms protected against external factors in the biofilm effectively remove nitrogen compounds. The TN content in sewage treated at a temperature of 10 °C was of a 4 mg/L order and was 3–5 times lower than in the reference system (classical conditions). This process involves shortened nitrification/denitrification such as Anammox. As a result of a given process, CO2 emissions were reduced and much smaller amounts of NOx were produced, positively impacting the ongoing climate changes. Microbiological DNA/RNA tests have shown that the biofilm is primarily composed of archaea and bacteria that remove nitrogen compounds, including those that oxidize ammonia.

Central composite design approach for concurrent desulfurization and denitrogenation of model liquid fuel over Mo‐AAC

AbstractThe primary objective of this work was to investigate the simultaneous removal of refractory sulfur (dibenzothiophene, DBT) and nitrogen compounds (indole, IND) from model gasoline. This research aimed to develop an efficient adsorption process to mitigate the emission of sulfur oxide and nitrogen oxides, which pose direct threats to human health and the environment. Additionally, the study focused on addressing technical challenges encountered in the refinery process, particularly the poisoning of catalysts due to the presence of these compounds. To achieve the study's goals, granular activated carbon (GAC) was subjected to acid treatment for modification. Molybdenum species were then incorporated into the acid‐treated GAC using the wet impregnation technique. The composition and distribution of elements on the surface of the modified GAC (Mo‐AAC) were analyzed via X‐ray photoelectron spectroscopy (XPS). Various characterization techniques were employed to confirm the uniform dispersion of molybdenum species on the GAC surface. The specific surface area of the adsorbent was increased from 257 m2/g to 316 m2/g following the acid treatment and molybdenum modification. The study explored the impact of several key parameters on the removal of DBT and IND using central composite design (CCD). A regression model was derived using CCD through hybrid central composite design, and its adequacy was verified with the means of tests such as analysis of variance (ANOVA), a lack of fit test, and residuals distribution consideration. Experimental results match well with the results obtained by CCD model, justifying the accuracy of models. The results showed that all four parameters have a significant impact on removal of DBT and IND. Increasing temperature and the adsorbent dose positively affected the removal of both DBT and IND, indicating that higher temperatures and greater adsorbent dosages improved removal efficiency. On the other hand, the concentration of DBT and IND had a negative impact, signifying that higher initial contaminant concentrations hindered removal efficiency. The study determined the optimum initial contaminant concentrations for DBT and IND, temperature, and adsorbent dose to be 186 mg/L, 50 mg/L, 25.5°C, and 32 g/L, respectively. These conditions yielded the highest removal efficiency. The research demonstrated that Mo‐AAC has the capability to effectively reduce the sulfur and nitrogen content of model gasoline, making it a promising solution for addressing environmental and refinery challenges associated with these compounds.

Simultaneous selenite reduction and nitrogen removal using Paracoccus sp.: Reactor performance, microbial community, and mechanism

Selenium-containing wastewater has a high concentration of nitrogen compounds (ammonia nitrogen [NH4+-N]), leading to water pollution. Thus, the simultaneous reduction of selenium and removal of nitrogen compounds during wastewater treatment has become the top priority. However, the exogenous bacteria that can simultaneously reduce selenite and remove ammonia nitrogen and colonize in the wastewater treatment systems have not been reported. Additionally, the effects and the underlying mechanism of biofortification on the reduction and removal efficiency of the microorganisms remain unclear. In this study, we investigated the simultaneous selenite reduction and nitrogen removal efficiency of Paracoccus sp. (strain SSJ) isolated from selenium-contaminated soil and explored biofortification effects on the composition and structure of the microbial community. Using sequencing biofilm batch reactors (SBBRs), the structural and functional characteristics of the microbial community were systematically compared between the control (group A) and biofortified (group B) groups. Strain SSJ could simultaneously reduce 63.28% of selenite and remove 93.05% of NH4+-N within 24 h. Moreover, no accumulation of nitrate nitrogen (NO3−-N) and nitrite nitrogen (NO2−-N) was observed in the reaction process. The performance and stability of the SBBRs enhanced by strain SSJ were greatly improved. Illumina sequencing results showed that strain SSJ was surprisingly colonized, and Paracoccus was the predominant genus in group B (relative abundance: 13.93%). Moreover, PICRUSt2 analysis results suggested that the microbial community in group B demonstrated increased rates of ammonia nitrogen removal through ammonia assimilation and selenite reduction through sulfur metabolism and glutathione-mediated selenite reduction pathway. In summary, our findings shed light on the mechanism for simultaneous selenite reduction and nitrogen removal by biofortification and provide novel microbial resources for the treatment of selenite-containing wastewater.

Interconversion and Removal of Inorganic Nitrogen Compounds via UV Irradiation

Dissolved inorganic nitrogen (DIN) species are key components of the nitrogen cycle and are the main nitrogen pollutants in groundwater. This study investigated the interconversion and removal of the principal DIN compounds (NO3−, NO2− and NH4+) via UV light irradiation using a medium-pressure mercury lamp. The experiments were carried out systematically at relatively low nitrogen concentrations (1.5 mM) at varying pHs in the presence and absence of oxygen to compare the reaction rates and suggest the reaction mechanisms. NO3− was fully converted into NO2− at a pH > 3 in both oxic and anoxic conditions, and the reaction was faster when the pH was increased following a first-order kinetic at pH 11 (k = 0.12 min−1, R2 = 0.9995). NO2− was partially converted into NO3− only at pH 3 and in the presence of oxygen and was stable at an alkaline pH. This interconversion of NO3− and NO2− did not yield nitrogen loss in the solution. The addition of formic acid as an electron donor led to the reduction of NO3− to NH4+. Conversely, NH4+ was converted into NO2−, NO3− and to an unidentified subproduct in the presence of O2 at pH 10. Finally, it was demonstrated that NO2− and NH4+ react via UV irradiation with stoichiometry 1:1 at pH 10 with the total loss of nitrogen in the solution. With these results, a strategy to remove DIN compounds via UV irradiation was proposed with the eventual use of solar light.

Impact of Influent Composition and Operating Conditions on Carbon and Nitrogen Removal from Urban Wastewater in a Continuous-Upflow (Micro)Aerobic Granular Sludge Blanket Reactor

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system.

Evaluating the potential of nanofiltration membranes for removing ammonium, nitrate, and nitrite in drinking water sources

Advanced drinking water treatment process using nanofiltration (NF) membranes has gained attention recently because it removes many challenging constituents in contaminated surface waters, such as dissolved organics and heavy metals. However, much literature has reported high variations and uncertainties of NF membranes for removing nitrogen compounds in the contaminated water—ammonium (NH4+), nitrates (NO3−), and nitrites (NO2−). This study aimed to identify the ability of commercial NF membranes to remove NH4+, NO2−, and NO3− and clarify the mechanisms underlying their transport through NF membranes. This was examined by evaluating their rejection by three commercial NF membranes using artificial and actual river waters under various conditions (variable permeate flux, temperature, pH, and ionic strength). Ammonium commonly showed the highest removal among the three nitrogen compounds, followed by nitrites and nitrates. Interestingly, ammonium removal varied considerably from 6% to 86%, depending on the membrane type and operating conditions. The results indicated that the selected nitrogen compounds (NH4+, NO2−, and NO3−) could be highly rejected depending on the clearance between their hydrated radius and the membrane's pore walls. Further, the rejection of the lowest molecular-weight nitrogen compound (NH4+) could be higher than NO2− and NO3− due to its highest energy barrier and larger hydrated radius. This study suggests that compliance with the drinking water regulations of NH4+, NO2−, and NO3− can be reliably achieved by selecting appropriate membrane types and predicting the range of their removal under various feed water quality and operating conditions.

Green and low-cost deep eutectic solvents for efficient extraction of basic and non-basic nitrides in simulated oils

The removal of nitrogenous compounds from fuel oil is essential to reduce NOx emissions and improve the quality of the oil. In the present work, a new method of nitrogen removal using deep eutectic solvents (DESs) as extractants is reported. Seven green and low-cost quaternary ammonium acidic DESs were prepared and used for the extraction of basic N-compounds (quinoline) and non-basic N-compounds (indole) in model oil. The results indicated that the structure of DESs has a profound effect on denitrification performance. Under the same conditions, DES composed of tetrabutylammonium bromide and formic acid ([TBAB:2FA]) showed the best denitrification performance and could effectively remove both basic and non-basic nitrogen compounds. The main experimental parameters such as the mass ratio of DESs to model oil, extraction temperature, time, initial concentration of N-compounds and water content when [TBAB:2FA] were used as extractants were investigated. Under the optimal conditions (initial N-compounds concentration of 200 ppm, DESs-oil mass ratio of 1:5, 30 °C, and 60 min of extraction), the extraction efficiency of quinoline and indole were 99.60% and 98.42%, respectively. In addition, the DESs were regenerated with deionized water. When reused four times, the denitrification capacity remained high. Finally, the mechanism of the extraction process was investigated by FT-IR spectroscopy. This research is expected to provide a theoretical reference for the removal of nitrogen compounds from fuel oil.

Performance of a Series of Polishing Ponds in the Treatment of Sanitary Sewage

The main objective of this research was to evaluate the functioning of a system of polishing ponds on a pilot scale in the post-treatment of urban sewage discharged from an up-flow anaerobic sludge blanket reactor and followed by a submerged aerated filter. The following variables were analyzed: transparency, temperature, dissolved oxygen (DO), pH, alkalinity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), ammonia (NH3), organic nitrogen, nitrate (N-NO3), total phosphorus (TP), orthophosphate (PO43-), total suspended solids (TSS) and chlorophylla. In addition, the planktonic communities were also identified and quantified. During the study period, the pond system registered the following mean and standard deviation of the removal efficiencies: 32.9±31.7% of BOD, 26.5±33.9% of COD, and 29.0±49.6% of TSS; good performance was observed in the removal of nitrogen compounds, and the following results were obtained: 58.4±28.1%, 87.5±15.4%, 24.4±42.6%, and 9.4±51.8%, respectively for TKN, NH3, organic nitrogen, and N-NO3; and 26.9±25.8 of TP and 34.3±32.7% of PO4 3-. During the research period, the planktonic community was represented by the following classes: Chlorophyceae, Euglenophyceae, Cyanobacteria, Cryptophyceae, Zygnemaphyceae, Chrysophyceae, and Dinophyceae; concurrently, the zooplankton registered low densities and was represented by the Rotiferous, Copepod, and Cladocera groups. The results help us understand the performance of polishing ponds in treating sanitary effluents.

Changes of inorganic nitrogen compounds concentration in a mining enterprise wastewater by the microalgae Chlorella vulgaris

Wastewater contamination by nitrogen compounds is a serious problem for the mining, industrial and utility companies. Nitrogen can enter quarry effluent when explosives containing ammonium nitrate are used in blasting operations. This nitrogen pollution of water leads to environmental damage and human disease, companies that exceed the legal limits for nitrogen pollution are subject to fines. Nitrogen is removed from wastewater by biological methods, but their efficiency is low in the Northern regions of Russia due to climatic factors that hinder the vital activity of organisms. Therefore, it is essential to develop wastewater treatment technologies for the removal of nitrogen compounds. This study focuses on the ability of the microalgae Chlorella vulgaris to absorb and utilize various inorganic nitrogen compounds in mining effluents using the example of effluents from the "Karelsky Okatysh" mine and tailings dam (Kostomuksha, Republic of Karelia). Concentrations of ammonium, nitrate and nitrite in water and microalgal biomass in water samples have been investigated. A novelty of the study is the evaluation of pollutant concentrations in parallel experiments with different cultivation conditions. It has been found that when Chlorella vulgaris is cultivated at 26 °C, aeration and artificial light, the concentration of ammonium decreases. These results show the promising application of bioreactor technologies for the treatment of ammonium polluted wastewater.