Environmental Friendly Operation Research Articles

Design and analysis methods for aerostatic bearings: The past, the present, and the future

Aerostatic bearings technology has been increasingly applied in the precision engineering and high-tech industries over the last decades, due to their considerable advantages including high motion accuracy, high speeds, low friction, and environment-friendly operations. This article presents a comprehensive and critical review with the historical progress on the state-of-the-art in research and development of design and analysis methods for aerostatic bearings and the associated products. The article also attempts to identify and discuss the scientific and technological challenges in air-bearing design and development, their future research development and trends, and their potential applications.

Toward an environmental friendly operation of the CBM-TOF system

The future fixed target high-rate compressed baryonic matter (CBM) experiment is one of the experimental pillars of the Facility for Antiproton and Ion Research (FAIR) located in Darmstadt/Germany. In order to provide an excellent particle identification (PID) of charged hadrons, the CBM-time-of-flight (TOF) group has developed a concept of a 120 m2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document} large TOF wall with a system time resolution below 80 ps based on multi-gap resistive plate chambers (MRPC). Currently, timing MRPC systems are operated with a gas mixture based on tetrafluoroethane (R134a, C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}F4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}) with additions of few vol% quencher gases, e.g., sulfur hexafluoride (SF6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_6$$\\end{document}) or/and isobutane (i-C4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}H10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_10$$\\end{document}). Unfortunately, these gas mixtures have a high global warming potential (GWP) in the order of 1500, and therefore, strategies to reduce the environmental impact have to be developed. The various possibilities, including studies on eco-friendly gases, and the considered strategy by the CBM-TOF group will be elaborated in this article.

Efficient algorithms for electric vehicles’ min-max routing problem

An increase in greenhouse gases emission from the transportation sector has led companies and the government to elevate and support the production of electric vehicles (EV). With recent developments in urbanization and e-commerce, transportation companies are replacing their conventional fleet with EVs to strengthen the efforts for sustainable and environment-friendly operations. However, deploying a fleet of EVs asks for efficient routing and recharging strategies to alleviate their limited range and mitigate the battery degradation rate. In this work, a fleet of electric vehicles is considered for transportation and logistic capabilities with limited battery capacity and scarce charging station availability. We introduce a min-max electric vehicle routing problem (MEVRP) where the maximum distance traveled by any EV is minimized while considering charging stations for recharging. We propose an efficient branch and cut framework and a three-phase hybrid heuristic algorithm that can efficiently solve a variety of instances. Extensive computational results and sensitivity analyses are performed to corroborate the efficiency of the proposed approach, both quantitatively and qualitatively. Finally a data-driven simulation implemented with the robot operating system (ROS) middleware are performed to corroborate the efficiency of the proposed approach, both quantitatively and qualitatively.

Understanding non-equilibrium [formula omitted]/[formula omitted] chemistry in plasma-assisted low-temperature [formula omitted] oxidation

Ammonia represents one of most promising zero-carbon energy solutions to address the increasingly urgent climate change problem. However, the existing utilization of ammonia faces significant challenges from low chemical reactivity and high N2O/NOx emissions, which cause severe inefficiency issues such as cold start and cycle variability of power generation, and detrimental effects on air quality, respectively. A sustainable and energy-efficient approach to tackle the above challenges is low temperature plasma which enables non-equilibrium energy and chemical utilization of ammonia such as oxidation using renewable electricity. As such, this work, for the first time, explores plasma assisted ammonia oxidation at room temperature with a focus on unveiling non-equilibrium NOx/N2O reaction pathways by combining in-situ laser diagnostics with plasma modeling. We found that the non-equilibrium plasma controls the NOx formation by supplying O/H/N atoms via electron-impact dissociation and collisional quenching of excited species. The N2O formation follows a two-step mechanism, where electron-impact reactions first provide amine radicals which further react with NOx to generate N2O. These pathways facilitate a high-efficiency and environment-friendly operation of plasma assisted ammonia oxidation with enhanced reactivity and reduced NOx/N2O emissions through manipulating mixture compositions and plasma discharge parameters.

Hydrogeochemical characterization and analysis of the relation between underground oil storage caverns construction and hydro-environment

Hydrogeochemical environment is of critical importance for the environment-friendly operation of underground oil storage caverns. The construction of underground oil storage caverns usually has an impact on the hydro-environment. The characterization and analysis of the hydrogeochemical environment can provide information on the relation between construction and hydro-environment. The quality of water samples was detected and analyzed to determine the chemical type in an underground oil storage cavern in China. The water samples are classified using principal component analysis and cluster analysis. The source and proportion of seepage water into the storage caverns are determined with end member mixing calculation. The results show that the chemical type of groundwater is mainly HCO3 + Cl − Na type, and the two dominant factors affecting the evolution of hydrogeochemical content are rock dissolution and groundwater seepage. All water samples can be catalogued as seepage water, water curtain water, X River water and background water. The water curtain water can fully penetrate into the ground to provide containment for the storage caverns, and the water curtain system has a good performance and can basically cover the project area. Most of the seepage water into the storage caverns comes from water curtain water and X River water, while the proportion of background water is relatively low. The construction of underground oil storage caverns affects the groundwater flow regime by changing the directions of groundwater flow around the caverns. This study showcases the use of hydrogeochemical analysis in depicting the interplay between surface water and groundwater for underground rock engineering.

A Bibliometric Analysis of Green Bonds and Sustainable Green Energy: Evidence from the Last Fifteen Years (2007–2022)

Organizations are shifting their focus towards utilizing green energy in the business process to enhance environmental sustainability. Similar to other business roles, the managerial team in the financial sector has also engaged in environment-friendly operations. A green bond is a new financial approach integrating the protection of the ecosystem into economic profits. This paper analyzes green bonds’ intellectual structure, publication, and networking. The bibliometric statistics utilized in the green bonds emerged from the Scopus database. The research examines published works from the most resourceful nations, institutions of higher learning, scholars, and high-profile publications on green bonds. Additionally, the study maps bibliographic coupling and co-citation to visualize the knowledge network.

Exploring the Antecedents of Employee Green Behaviors: A Conceptual Framework

The emergence of sustainable design has brought attention to the consideration of human behavior in creating environmentally-friendly operations. This study examines the role of the Theory of Planned Behavior (TPB) and the Value-Identity-Personal Norm (VIP) model in shaping employee green behavior (EGB) and explores how green human resource management (GHRM) practices impact EGB. Based on a review of 40 scholarly articles, the study proposes a conceptual model that integrates individual-level constructs from TPB and VIP, and highlights GHRM as an antecedent of EGB at the organizational level, with psychological capital and organizational identity as mediators. The study suggests a multilevel approach to examining EGB, incorporating person-environment interaction, job performance, and motivation theory. Ultimately, the study aims to provide a research agenda that encourages further investigation of the topic.
 Keywords: Employee Green Behavior; Green Human Resource Management; Sustainability; Theory of Planned Behavior; Value-Identity-Personal Norm Model.

Economic-environmental scheduling of microgrid considering V2G-enabled electric vehicles integration

As an important part of the Energy Internet, microgrid (MG) scheduling problem has always attracted great attention, especially under the background that large-scale penetration of electric vehicles (EVs) into buildings poses both opportunity and challenge to the MG energy management. This research presents a two-stage optimization strategy, for improving the economic and environment-friendly operation of MG considering EVs integration. In Stage 1, model of EVs under coordinate charging/discharging stimulated by time-of-use incentive mechanism is established, and the peak–valley hours are dynamically divided to obtain a load curve with minimized peak-to-valley difference (PVD). In Stage 2, aiming for the best tradeoff between the generation cost and pollutant emission, daily optimal scheduling of the MG generators is efficiently calculated according to the varying power demand. For enhancing the convergence, an advanced genetic algorithm with elite preservation strategy is employed. Two cases from a residential MG system is exploited to validate the proposed method, and the results show that firstly the power supply pressure could be obviously relieved owing to the load shifting effect of the coordinated vehicle-to-grid (V2G) service reflected by the decreased PVD (Case 1: from 76.16 to 54.35 kW, Case 2: from 76.25 to 46.19 kW); simultaneously, via applicable power planning of the MG components, cost saving and emission reduction can be both achieved (Case 1: ¥190.12 under V2G management compared to ¥281.66 under basic load, Case 2: ¥177.28 compared to ¥350.24), ensuring the feasibility of the control strategy, which promotes the economical-environmental and reliable operation of the MG system.

Enabling the Ambitious ZED Target Initiative of the Government of India Through CLAG Operations

The ZED (Zero Defect Zero Effect) programme introduced by the Indian government in 2014 aims to achieve defect-free and environment-friendly operations in MSMEs (medium, small and micro enterprises). It helps them derive benefits from the global markets. However, the ZED programme has not achieved its objectives despite the government’s effort to provide support in terms of education, training and guidance. There are just 304 ZED-certified MSMEs out of more than 60 million in India. This article advocates a blended approach that involves a combination of clean, lean and green (CLAG) operations, which has the potential to achieve the ZED target as demonstrated by many applications across the industries. Adopting the Six Sigma technique in manufacturing industries is discussed, which can deliver output with a defect rate close to zero. Usually, the CLAG approaches have been applied across different organizations individually. However, the proposed approach recommends a combination to seek superior benefits. The article provides evidence from secondary sources to justify the application of the proposed blended approach. The blended conceptual model will help enterprises achieve improved quality, reduce waste and lower environmental damage.

Micro-Siting of Wind Turbines in an Optimal Wind Farm Area Using Teaching–Learning-Based Optimization Technique

Nowadays, wind energy is receiving considerable attention due to its availability, low cost, and environment-friendly operation. Wind turbines are rarely placed individually but rather in the form of a wind farm with a group of several wind turbines. The purpose of this research is to perform studies on wind turbine farms in order to find the best distribution for wind turbines that maximizes the produced power, hence minimizing the wind farm area. Wind Farm Area Optimization (WFAO) is performed for optimal placement of wind turbines using elitist teaching–learning-based optimization (ETLBO) techniques. Three different scenarios of wind (first is fixed wind direction and constant speed, second is variable wind direction and constant speed, and third is variable wind direction and variable speed) are considered to find the optimal number of turbines and turbine positioning in a minimized squared land area that maximizes the power production while minimizing the total cost. Other research carried out in the past was to find the optimal placement of the wind turbines in a fixed squared land area of 2 km×2 km. In the present study, WFAO–ETLBO algorithm has been implemented to get the optimal land area for the placement of the same number of turbines used in the past research. For Case 1, there is a significant reduction in land area by approximately 30.75%, 45.25%, and 51.75% for each wind scenario, respectively. For Case 2, the reductions in land area for three different wind scenarios are respectively 30.75%, 7.2%, and 7.2%. For Case 3, there is a reduction of 7.2% in land area for each wind scenario. It has been observed that the results obtained by the WFAO–ETLBO algorithm with a significant reduction in the land area along with optimal placement of wind turbines are better than the results obtained from the wind turbines placement in the fixed land area of 2 km×2 km.

A detailed study on the rheological behavior of a novel cellulose-based hydrophobically-modified polymer

Hydrophobically-modified cellulose derivatives have been considered for improved oil recovery applications. However, the subsurface reservoir environment defined by combinations of brine salinity, temperature, and porous media-induced shear can pose an adverse challenge to the mobility control prospects of these materials. Previous studies have focused mostly on amphiphilic cellulose ethers. This study is based on a cellulose ester, herein, a novel polymeric surfactant derived from sodium cellulose sulfate is investigated. Rheological studies were carried out on the novel material under variable external reservoir conditions. From the results, the amphiphilic polymer was able to initiate associative behavior at a low concentration of 0.15 g/L. The biopolymeric surfactant exhibited tolerance to temperature and shear over the tested range of 35 °C to 75 °C, and 100 RPM to 250 RPM respectively by retaining its original rheological profile. The viscosity improved over a brine salinity range of 10,000ppm to 60,000ppm as it increased from 45.75 cp to 49.1 cp. From these findings, it can be inferred that the novel cellulose derivative is a good mobility control agent, and should be considered for oilfield applications that target cheap, cost-effective, and environmental-friendly operations.

High mechanical performance submicron-sized Cu2O-derived necklace-shaped PAN nanofiber composite membrane towards adsorption desulfurization application

The selective adsorption desulfurization technology is considered to be of energy conservation and environment-friendly operation. However, the ongoing development of adsorption desulfurization is greatly restricted by the adsorbents with preferable mechanical properties and sustainable separation efficiency. In this paper, a submicron-sized Cu2O necklace-shaped polyacrylonitrile (PAN) nanofiber composite membrane (Cu2O/PAN NFM) was prepared by electrospinning technology. The structure and mechanical properties of NFM were determined by a series of characterizations. The results showed that the resulting Cu2O/PAN-NFM has a larger total pore volume (0.0802 mL/g), higher tensile strength (5.65 MPa) and lower friction coefficient (0.2571) than those of PAN nanofiber membrane (PAN NFM). The static and dynamic adsorption performances of the Cu2O/PAN NFM were investigated with thiophene(TH) simulated oil. The results showed that the static and dynamic saturated adsorption capacities of the Cu2O/PAN NFM were up to 32.91 mg/g and 4.57 mg/g at 500 mg/L initial concentration, respectively. Besides, the adsorption kinetics and isotherms of TH on the Cu2O/PAN NFM indicated that the TH adsorption data are fitting to Avrami model and Liu isotherm. In addition, the exclusive notable merits of the Cu2O/PAN NFM expressed at the robust mechanical properties and outstanding separation efficiency while keeping the sustainable adsorption capacity after the repeated recycling, which exhibited a promising application towards adsorption desulfurization.

Environmental Mainstreaming in Greek TEN-T Ports

Along with recent fundamental changes in several aspects of the port industry, ports come up against formidable environmental challenges. It is thus important and often imperative to mainstream environmental concerns in their operation, planning, and development; improve their environmental performance; and make the transition to sustainable production and consumption patterns. The industry’s greening is largely underpinned by European Union (EU) transport and port policy, with major European initiatives such as the Trans-European Transport Network (TEN-T), the European Green Deal, and Blue Growth expected to give new impetus. This paper examines environmental mainstreaming in Greek TEN-T ports and their ability to cope with upcoming challenges based on questionnaire responses by 23 port authorities and taking into account the relevant progress made by ESPO port members. We argue that all respondents have gradually become aware of the need to move towards an environment-friendly operation and development, but progress is slow, and there is still a lot to be done. Performances vary and depend on different factors, while ports are faced with significant challenges and various constraints. Nevertheless, new environmental standards present a real opportunity for Greek ports to undertake deep structural changes, especially in view of current and future European port policy.

복합화력발전소 융합탈질설비에서 질소산화물 배출저감분석

Recently, the concern of the fine dust is increasing in our society and nitrogen oxides(NOx) has been considered as precursor of fine dust. Because, as well as the coal-fired power plants, the combined cycle power plants using LNG fuel also emit nitrogen oxides, our society strongly demands to lower the emission of NOx from the combined cycle power plants. In response of the public demand, Korean government set more stringent emission standard. Therefore, LNG power plants need to cope with it. The purpose of this paper is to study a reactive test that leads to Fast SCR by adjusting the mixing ratio of hydrocarbon reducing agent and NH3 reducing agent respectively. By so, it is expected to minimize the negative impact on the power plant operation and the power generation efficiency and contribute to the environment-friendly operation of power plant. Possessing a DeNOx system applicable to old combined cycle power plants and obtaining leading study results on the simultaneous removal of nitrogen oxides

Electrochemical analysis of electrolyte temperature and composition for all-iron redox flow battery

ABSTRACT At present, aqueous all-iron flow batteries have become one of the most potentials flow batteries system due to their low cost and environmental-friendly operation. However, the battery performance and cycle-life will to a great extent be limited by the electrolytes, which are mainly influenced by temperature, electrolyte concentration, and electrolyte additives. Herein, we repeatedly conducted the electrochemical tests on catholyte and anolyte in varied temperatures and electrolyte concentrations. Based on the analyses, it is proved that the electrolyte of an all-iron flow battery is suitable for high-temperature conditions. By comparing the electrochemical performance of anolyte and anolyte with citrate, the citrate is proved to be an effective additive in solving the problem of anolyte reversibility. This work can guide the conditional design of all-iron flow battery energy storage devices, and meanwhile, the solution is proposed to enhance the anolyte reversibility of the all-iron flow battery.

Thermal Simulation and Analysis of the Single LED Module

Light Emitting Diodes (LED) shows an important role in replacing traditional lamps due to their longevity, high efficiency, and environment-friendly operation. However, a large portion of the electricity applied on LED converts to heat, raising up the p-n junction working temperature, and lowering the output-light quality and the LED lifetime as well. Therefore, thermal management for LED is one of the key issues in LEDs lighting application. In order to investigate the impact of each component of the LED module on the junction temperature of the LED, we have performed thermal simulations of a typical single LED module by using the finite element method. Effects of thermal conductivity and thickness of each module’s components on junction temperature were analyzed systematically. The results provided a detailed understanding of thermal behavior of a single LED module and established a crucial insight into thermal management design for high-power white LED lamp. Thermal-interface-materials (TIM) and the dielectric layer are proposed to have thermal conductivity around 1 W/mK for system optimization. In addition, based on the thermal analysis of heat sink, we have proposed and investigated a new configuration of plastic heat sink embedded with aluminum-alloy. The thickness ratio between the embedded aluminum layer and the heatsink base is suggested to be around 0.1 to 0.15 for the optimal configuration.

An Artificial Intelligence Empowered Cyber Physical Ecosystem for Energy Efficiency and Occupation Health and Safety

Reducing energy waste is one of the primary concerns facing Remote Industrial Plants (RIP) and, in particular, the accommodations and operational plants located in remote areas. With the COVID-19 pandemic continuing to attack the health of workforce, managing the balance between energy efficiency and Occupation Health and Safety (OHS) in the workplace becomes another great challenge for the RIP. Maintaining this balance is difficult mainly because a full awareness of the OHS will generally consume more energy while reducing the energy cost may lead to a less effective OHS, and the existing literature has not seen a system that is designed for the RIPs to conserve energy usage and improve workforce OHS simultaneously. To bridge this gap, in this paper, we propose an AI Empowered Cyber Physical Ecosystem (AECPE) solution for the RIPs, which integrates Cyber-Physical Systems (CPS), artificial intelligence, and mobile networks. The preliminary results of lab experiments and field tests proved that the AECPE was able to help industries reduce the corporate annual energy cost that is worth millions of dollars, optimise the environmental conditions, and improve OHS for all workers and stakeholders. The implementation of the AECPE can result in efficient energy usage, reduced wastage and emissions, environment-friendly operations, and improved social reputation of the industries.

Permeability variation analysis using the superficial diameter correlation with porosity change

Permeability characterization is a major factor for ensuring more environment-friendly operations and economically viable industrial applications related to carbon capture sequestration, hydrocarbon recovery, nuclear waste disposal, and remediation in groundwater. Regardless, the permeability variation caused by changes in formation stress is simply defined as the power-law function of porosity. An alternative formula can be presented using the Kozeny–Carman equation based on hydraulic diameter and tortuosity. However, the hydraulic tortuosity and the Kozeny constant cannot be precisely measured because of the extremely complex and microscale pores. Accordingly, this study considers the Kozeny–Carman equation for presenting the other definable variables and more general correlations for performing permeability variation analyses. Herein, the effective tortuosity and effective and superficial diameters of porous media are deduced adopting the conventional viscous flow theory. Subsequently, the Kozeny–Carman equation is improved by replacing the immeasurable variables with the effective variables. The correlations of all the key geometric variables with permeability variation are investigated via pore-scale simulations based on two types of 20-series porous medium models with a wide range of porosity (13.4%–47.4%) and permeability (0.0073 –18.3 Darcy). Herein, several impressive functional aspects of the superficial diameter were discovered with porosity changes, such as quadratic functional correlations, parallel shifts for each flow path, and less sensitive variations in low porosity ranges. Consequently, this study proved that permeability variations can be more precisely and generally estimated using the quadratic correlations of the superficial diameter with porosity changes.

Multiscale Modelling and Analysis for Design and Development of a High-Precision Aerostatic Bearing Slideway and Its Digital Twin

Aerostatic bearing slideways have been increasingly applied in the precision engineering industry and other high-tech sectors over the last two decades or so, due to their considerable advantages over mechanical slideways in terms of high motion accuracy, high speeds, low friction, and environment-friendly operations. However, new challenges in air bearings design and analysis have been occurring and often imposed along the journeys. An industrial-feasible approach for the design and development of aerostatic bearing slideways as standard engineering products is essential and much needed particularly for addressing their rapid demands in diverse precision engineering sectors, and better applications and services in a continuous sustainable manner. This paper presents the multiscale modelling and analysis-based approach for design and development of the aerostatic bearing slideways and its digital twin. The multiscale modelling and analysis and the associated simulation development can be the kernel of the digital twin, which cover the mechanical design, direct drive and control, dynamics tuning of the slideway, and their entire mechatronic system integration. Using this approach and implementation, the performance of an aerostatic bearing slideway can be predicted and assessed in the process. The implementation perspectives for the sideway digital twin are presented and discussed in steps. The digital simulations and digital twin system can be fundamentally important for continuously improving the design and development of aerostatic bearing slideways, and their applications and services in the context of industry 4.0 and beyond.

Significant removal of ammonia nitrogen in low concentration from aqueous solution at low pH by advanced air stripping.

In recent years, the excess discharge of ammonia nitrogen from wastewater into surface water has been regulated by more stringent standard. The air stripping method is successfully used to treatment of high-concentration ammonia nitrogen; however, alkali will be added to keep pH more than 10, which is costly and not environment-friendly operation. In this study, an advanced air stripping (AAS) based on foam separation of removing ammonia nitrogen in low concentration from aqueous solution at low pH was proposed. The effect of conditions such as air flow rate, temperature, SDS dosage, coexisting ionic strength, pH, and initial ammonia nitrogen concentration on the removal efficiency was studied. The advanced air stripping exhibited favorable removal efficiency for NH4+-N in low concentration from aqueous solution (20 mg·L-1) with a broad range of low pH 3.0-9.0. Besides, for strongly alkaline (pH=11.0) solution, the advanced air stripping can alleviate the decrease of pH to some extent and keep ammonia nitrogen stripping out continuously based on equilibrium shift between NH4+ and NH3. A microcalorimeter was applied to demonstrate the interaction between the negatively charged hydrophilic groups of SDS and NH4+ ions, helping to understand the mechanisms more clearly. The simple operation and the satisfactory removal efficiency could imply that the advanced air stripping is a promising technology for minimizing low-concentration NH4+-N.