Enhanced ammonia recovery from wastewater by Nafion membrane with highly porous honeycomb nanostructure and its mechanism in membrane distillation

Bubble Turbulent Gas-Permeable Membrane for Ammonia Recovery from Swine Wastewater: Mass Transfer Enhancement and Antifouling Mechanisms

Recovering ammonium from swine wastewater employing a gas-permeable membrane (GM) has potential but suffers from the limitations of unattractive mass transfer and poor-tolerance antifouling properties. Turbulence is an effective approach to enhancing the release of volatile ammonia from wastewater while relying on interfacial disturbance to interfere with contaminant adhesion. Herein, we design an innovative gas-permeable membrane coupled with bubble turbulence (BT-GM) that enhances mass transfer while mitigating membrane fouling. Bubbles act as turbulence carriers to accelerate the release and migration of ammonia from the liquid phase, increasing the ammonia concentration gradient at the membrane-liquid interface. In comparison, the ammonium mass transfer rate of the BT-GM process applied to real swine wastewater is 38% higher than that of conventional GM (12 h). Through a computational fluid dynamics simulation, the turbulence kinetic energy of BT-GM system is 3 orders of magnitude higher than that of GM, and the effective mass transfer area is nearly 3 times that of GM. Seven batches of tests confirmed that the BT-GM system exhibits remarkable antifouling ability, broadens its adaptability to complex water quality, and practically promotes the development of sustainable resource recycling.

Bio-Inspired Functional Materials for Environmental Applications

With the global population expected to reach 9.7 billion by 2050, there is an urgent need for advanced materials that can address existing and developing environmental issues. Many current synthesis processes are environmentally unfriendly and often lack control over size, shape, and phase of resulting materials. Based on knowledge from biological synthesis and assembly processes, as well as their resulting functions (e.g., photosynthesis, self-healing, anti-fouling, etc.), researchers are now beginning to leverage these biological blueprints to advance bio-inspired pathways for functional materials for water treatment, air purification and sensing. The result has been the development of novel materials that demonstrate enhanced performance and address sustainability. Here, an overview of the progress and potential of bio-inspired methods toward functional materials for environmental applications is provided. The challenges and opportunities for this rapidly expanding field and aim to provide a valuable resource for researchers and engineers interested in developing sustainable and efficient processes and technologies is discussed.

Advancements in Nanoenabled Membrane Distillation for a Sustainable Water-Energy-Environment Nexus

The emergence of nano innovations in membrane distillation (MD) has garnered increasing scientific interest. This enables the exploration of state-of-the-art nano-enabled MD membranes with desirable properties, which significantly improve the efficiency and reliability of the MD process and open up opportunities for achieving a sustainable water-energy-environment (WEE) nexus. This comprehensive review provides broad coverage and in-depth analysis of recent innovations in nano-enabled MD membranes, focusing on their role in achieving desirable properties, such as strong liquid-repellence, high resistance to scaling, fouling, and wetting, as well as efficient self-heating and self-cleaning functionalities. The recent developments in nano-enhanced photothermal-catalytic applications for water-energy co-generation within a single MD system are also discussed. Furthermore, the bottlenecks are identified that impede the scale-up of nanoenhanced MD membranes and a future roadmap is proposed for their sustainable commercialiation. This holistic overview is expected to inspire future research and development efforts to fully harness the potential of nano-enabled MD membranes to achieve sustainable integration of water, energy, and the environment.

Evaluation of nitrous oxide emission during ammonia retention from simulated industrial wastewater by microaerobic activated sludge process

Considering the reciprocating processes of nitrogen gas (N2) fixation to ammonia (NH4-N) and NH4-N removal to N2 through nitrification and denitrification during wastewater treatment, a microaerobic activated sludge process (MAS) is proposed in this study as a pretreatment to retain NH4-N from high-strength nitrogenous wastewater for further NH4-N recovery through membrane technology, that is, inhibit nitrification, with sufficient removal of total organic carbon (TOC). With DO and pH control, the 3-reactor bench-scale MAS systems successfully realized an NH4-N retention rate of over 80 %, with TOC removal rates of over 90 %. In addition, the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) during MAS were evaluated. The total N2O emissions were 407 and 475 mg-N/day when pH was controlled at 6.2 (S1) and 6.8 (S2), respectively, with average emission factors to total nitrogen load over 2 % in both systems. Also, the global warming potential of N2O is one order of magnitude larger than that of CO2, indicating the significance of N2O in the MAS process. Therefore, the mechanisms of N2O emission from each reactor were investigated. The first reactor, where most of the TOC was adsorbed, emitted only 1.98 % (S1) and 2.43 % (S2) of the total N2O emissions through the denitrification of nitrite and nitrate (NOx) from the return sludge. The second reactor emitted 79.9 % (S1) and 69.0 % (S2) of the total N2O with the emission rates the same order of magnitude as the NOx production rates. Multiple pathways were considered to contribute to the high N2O emissions, and biotic NH2OH oxidation was one potential pathway at pH 6.2. Finally, the third reactor emitted 9.98 % (S1) and 16.8 % (S2) of the total N2O by nitrifier denitrification. Overall, this study showed that the large N2O emissions under nitrification-inhibiting conditions of the MAS process owed to the incomplete nitrification under acidic conditions and large abundances of denitrifiers. On the other hand, the lower N2O emissions at pH 6.2 evidenced the potential N2O mitigation under slightly more acidic conditions, underlining the necessity of further study on N2O mitigation when adapting to the trend of NH4-N recovery.

Membrane Technologies for Nitrogen Recovery from Waste Streams: Scientometrics and Technical Analysis

The concerns regarding the reactive nitrogen levels exceeding the planetary limits are well documented in the literature. A large portion of anthropogenic nitrogen ends in wastewater. Nitrogen removal in typical wastewater treatment processes consumes a considerable amount of energy. Nitrogen recovery can help in saving energy and meeting the regulatory discharge limits. This has motivated researchers and industry professionals alike to devise effective nitrogen recovery systems. Membrane technologies form a fundamental part of these systems. This work presents a thorough overview of the subject using scientometric analysis and presents an evaluation of membrane technologies guided by literature findings. The focus of nitrogen recovery research has shifted over time from nutrient concentration to the production of marketable products using improved membrane materials and designs. A practical approach for selecting hybrid systems based on the recovery goals has been proposed. A comparison between membrane technologies in terms of energy requirements, recovery efficiency, and process scale showed that gas permeable membrane (GPM) and its combination with other technologies are the most promising recovery techniques and they merit further industry attention and investment. Recommendations for potential future search trends based on industry and end users' needs have also been proposed.

Enhancing the Ammonia Selectivity by Using Nanofiber PVDF Composite Membranes Fabricated with Functionalized Carbon Nanotubes

Conventional hydrophobic membrane-based membrane distillation (MD) has been applied for ammonia recovery from an anaerobic digestion (AD) effluent. However, the typical hydrophobic membranes do not have selectivity for ammonia and water vapor, which results in high energy consumption from the water evaporation. To enhance the selectivity during the ammonia recovery process, the functionalized carbon nanotubes (CNTs)/polyvinylidene fluoride (PVDF) nanofiber membranes were fabricated by electrospinning, and the effects of different CNTs and their contents on the performance of nanofiber membranes were investigated. The results indicate that CNTs can be successfully incorporated into nanofibers by electrospinning. The contact angles of the composite membrane are all higher than those of commercial membrane, and the highest value 138° can be obtained. Most importantly, under the condition of no pH adjustment, the ammonia nitrogen transfer coefficient reaches the maximum value of 3.41 × 10^-6 m/s, which is about twice higher than that of commercial membranes. The ammonia separation factor of the carboxylated CNT (C-CNT) composite membrane is higher than that of the hydroxylated CNT(H-CNT) composite membrane. Compared with the application of the novel C-CNT composite membrane, the ammonia separation factor is 47% and 25% higher than that of commercial and neat PVDF membranes. This work gives a novel approach for enhancing ammonia and water selectivity during AD effluent treatment.

Enhancement of swine manure anaerobic digestion using membrane-based NH3 extraction

The influence of suspended solids and pH in anaerobically digested piggery wastewater on membrane-based NH₃ extraction was evaluated in batch tests. The increase in pH in the anaerobic broth from 8 to 9 resulted in an increase in NH₃ removal efficiencies from 15.8 % ± 0.1 % to 20.9 % ± 0.4 % regardless of the suspended solids. The influence of membrane based NH₃ extraction on piggery wastewater treatment was also assessed in a CSTR interconnected with PTFE membrane modules. The decrease in TKN concentrations mediated by membrane operation induced an increase in CH₄ yield from 380.4 ± 84.9 up to 566.1 ± 7.8 NmLCH₄ g VS fed^-1. Likewise, COD and VS removal efficiencies significantly increased from 33.0 % ± 2.0 % and 25.7 % ± 2.3 % up to 61.8 % ± 1.3 % and 37.9 % ± 1.8 %, respectively. Interestingly, the decrease in NH₃ concentration entailed a complete assimilation of VFA.

Study on treatment of wastewater with low concentration of ammonia-nitrogen by vacuum plate membrane distillation technology

The removal of low concentration ammonia-nitrogen in industrial wastewater is necessary before discharged into the environment. In this study, vacuum plate membrane distillation (VPMD) technology was utilized and operating parameters such as pH, feed temperature, vacuum degree, feed flow and time were investigated. Based on the experimental data, the heat and mass transfer mechanism and mathematic model were studied. The experimental results show that low solution pH was significantly beneficial to ammonia-nitrogen removal but permeate flux was nearly changeless. At pH = 4, a removal rate up to 93.33% was achieved. Ammonia-nitrogen mainly exists with NH₄⁺ ions in acidic solution, so only water molecules pass through the membrane to acquire the water product in the permeate side. Increasing the temperature of the solution was disadvantageous to the ammonia-nitrogen removal due to membrane pores expanding and the mass transfer coefficient of NH₃ molecules increasing; therefore a low temperature was chosen if possible. Because vapor pressure of the feed solution increases exponentially with temperature and results in membrane surface pressure difference increases, therefore increasing the temperature enhances the permeate flux. Raising the vacuum degree enhanced ammonia removal rate and permeate flux obviously, a vacuum degree of 0.09 MPa was chosen for the experiment. The effect of feed flow rate on ammonia-nitrogen removal instead of permeate flux is weak, the reason is that the boundary layer wears thin when the feed flow rate is increased, which is conducive to permeate flux increasing. In a two-parameter model of Knudsen diffusion, Poiseuille flow was chosen to demonstrate the heat and mass transfers in the process of VPMD in the study. Based on the experimental values of permeate flux, two parameters C_K and C_P in the model were calculated using a nonlinear fitting method software, which indicated that the Knudsen diffusion model more than the Poiseuille flow model was suitable. The maximum values of the relative average deviation (RAD) and root mean square difference (RMSD) of experimental and calculated values with model equations of the permeate flux at the different temperature, vacuum degree and feed flow rate were no more than 8.7% and 3.20 kg · (m² · h)^-1, respectively.

Influences of Permeate Solution and Feed pH on Enhancement of Ammonia Recovery from Wastewater by Negatively Charged PTFE Membranes in Direct Contact Membrane Distillation Operation

This research investigated the feasibility of enhancing ammonia recovery from wastewater using a negatively charged poly(tetrafluoroethylene) (PTFE) membrane in a direct contact membrane distillation (DCMD) system. The influences of phosphate solution types (as the permeate solutions) and feed pH on ammonia recovery were analyzed. Three types of permeate solutions-DI water and two types of phosphate solutions (H₃PO₄ and KH₂PO₄)-were investigated for recovery of ammonia gas on the permeate side. From the obtained results, the H₃PO₄ solution was found to be the most suitable permeate solution to recover ammonia gas in the DCMD operation with the highest overall ammonia mass transfer coefficient of 7.4 × 10^-5 m/s, compared to values of 1.2 × 10^-5 and 2.4 × 10^-5 m/s for DI water and KH₂PO₄ solution, respectively. Moreover, an increase in the H₃PO₄ concentration from 0.3 to 0.5 M in the permeate solution also could significantly enhance ammonia recovery. With an increase in the feed pH from 10.0 to 11.8, the ammonia recovery could be enhanced to 92.98% at a pH of 11.8. Liquid ammonium phosphate fertilizer could be produced by the DCMD system with the use of 0.5 M H₃PO₄ solution. Therefore, the DCMD process using a negatively charged PTFE membrane with an appropriate permeate solution is one of the challenging processes for ammonia recovery from wastewater to promote the circular economy concept.

Armor-Structured Interconnected-Porous Membranes for Corrosion-Resistant and Highly Permeable Waste Ammonium Resource Recycling

Ammonium recovery from wastewater by gas-permeable membranes is promising but suffers from the tradeoff between membrane stability and permeability under harsh operating conditions. Chemical-resistant membranes display modest permeability due to the poor solubility and processibility; chemically active membranes are easier to be endowed with better permeability however hinder by instability. To resolve such a problem, we cleverly design a novel membrane configuration via one-step solution-electrospinning, with the chemical-active component (low-strength fluorine polymer) as the inner skeleton to construct interconnected porous structures and the chemical-resistant component (high-strength fluorine polymer) as the outer armor to serve as a protective layer. Due to the significantly enhanced mass transfer coefficient, the interconnected-porous armor-structured membrane exhibited much higher permeability for NH₄⁺-N recovery, which was 1.4 and 5 times that of the traditional PTFE membrane and PP membrane, respectively. Through long-term intermittent and consecutive experiments, the reusability and durability of the armor-structured nanofibrous membrane were verified. When treating actual hoggery wastewater with complicated water quality, the armor-structured nanofibrous membrane also displayed robust stable performance with excellent antiwettability. The mechanisms of membrane formation, corrosion resistance, and mass transfer were discussed in detail.

Bio-membrane integrated systems for nitrogen recovery from wastewater in circular bioeconomy

Wastewater contains a significant amount of recoverable nitrogen. Hence, the recovery of nitrogen from wastewater can provide an option for generating some revenue by applying the captured nitrogen to producing bio-products, in order to minimize dangerous or environmental pollution consequences. The circular bio-economy can achieve greater environmental and economic sustainability through game-changing technological developments that will improve municipal wastewater management, where simultaneous nitrogen and energy recovery are required. Over the last decade, substantial efforts were undertaken concerning the recovery of nitrogen from wastewater. For example, bio-membrane integrated system (BMIS) which integrates biological process and membrane technology, has attracted considerable attention for recovering nitrogen from wastewater. In this review, current research on nitrogen recovery using the BMIS are compiled whilst the technologies are compared regarding their energy requirement, efficiencies, advantages and disadvantages. Moreover, the bio-products achieved in the nitrogen recovery system processes are summarized in this paper, and the directions for future research are suggested. Future research should consider the quality of recovered nitrogenous products, long-term performance of BMIS and economic feasibility of large-scale reactors. Nitrogen recovery should be addressed under the framework of a circular bio-economy.

A Systematic Study of Ammonia Recovery from Anaerobic Digestate Using Membrane-Based Separation

Ammonia recovery from synthetic and real anaerobic digestates was accomplished using hydrophobic flat sheet membranes operated with H₂SO₄ solutions to convert ammonia into ammonium sulphate. The influence of the membrane material, flow rate (0.007, 0.015, 0.030 and 0.045 m³ h⁻¹) and pH (7.6, 8.9, 10 and 11) of the digestate on ammonia recovery was investigated. The process was carried out with a flat sheet configuration at a temperature of 35 °C and with a 1 M, or 0.005 M, H₂SO₄ solution on the other side of the membrane. Polytetrafluoroethylene membranes with a nominal pore radius of 0.22 µm provided ammonia recoveries from synthetic and real digestates of 84.6% ± 1.0% and 71.6% ± 0.3%, respectively, for a membrane area of 8.6 × 10⁻⁴ m² and a reservoir volume of 0.5 L, in 3.5 h with a 1 M H₂SO₄ solution and a recirculation flow on the feed side of the membrane of 0.030 m³ h⁻¹. NH₃ recovery followed first order kinetics and was faster at higher pHs of the H₂SO₄ solution and recirculation flow rate on the membrane feed side. Fouling resulted in changes in membrane surface morphology and pore size, which were confirmed by Atomic Force Microscopy and Air Displacement Porometry.

From pollutant removal to resource recovery: A bibliometric analysis of municipal wastewater research in Europe

Municipal wastewaters are abundant low-strength streams that require adequate treatment and disposal to ensure public and environmental health. This study aims to provide a comprehensive summary of municipal wastewater research in Europe in the 2010s in the form of bibliometric analysis. The work was based on the Science Citation Index Expanded (Web of Science) and carried out using the R-package bibliometrix for bibliometric data analysis and the software VOSviewer for science mapping. Analysing a dataset of 5645 publications, we identified the most influential journals, countries, authors, institutions, and publications, and mapped the co-authorship and keyword co-occurrence networks. Spain had produced the most publications while Switzerland had the highest average citations per publication. China was the most collaborative country from outside of Europe. Analysis of the most cited articles revealed the popularity of micropollutant removal in European municipal wastewater research. The keyword analysis visualized a paradigm shift from pollutant removal towards resource recovery and circular economy. We found that current challenges of resource recovery from municipal wastewater come from both technical and non-technical (e.g., environmental, economic, and social) aspects. We also discussed future research opportunities that can tackle these challenges.

A Study on the Hydrolysis of Urea Contained in Wastewater and Continuous Recovery of Ammonia by an Enzymatic Membrane Reactor

1. Background: Urea is the main product of the nitrogenous breakdown of protein metabolism in mammals. In this study, process intensification for enzymatic hydrolysis of urea by urease enzyme (jack bean urease) was examined in a membrane reactor. 2. Methods: Batch and continuous enzymatic hydrolysis reactions were performed at different substrate concentrations to determine the digestibility and affinity of the substrate with that of the enzyme. The hydrolysate samples were obtained by an optimized continuous enzyme membrane reactor (EMR) coupled with an ultra-filtration membrane (250 kDa). Feed concentration varied from 100 to 500 mg/L. Laboratory experiments were conducted at room temperature (20 ± 1 °C), with a flow rate of 20 mL/min, urease concentration of 0.067 g/L, ionic strength (I = 0, 0.01, 0.05), and ammonium nitrogen addition of (0, 100 mg/L, 200 mg/L, 500 mg/L). Moreover, the effect of ionic strength, ammonium nitrogen concentration, feed concentration, and enzyme concentration on urea hydrolysis was examined. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX) analysis were used to identify the physicochemical properties as well as the elemental composition of the Ultra-Filtration membrane used in this study. 3. Results: The study revealed that higher ionic strength and higher concentrations of NH4SO2 and ammonium nitrogen (NH3-N) inhibithydrolysis of urea by reducing the urease enzyme activity in the system over time. 4. Conclusions: Herein, a sustainable alternative for the conversion of urea to ammonia by utilizing urease in an EMR was demonstrated.

A New Process for the Recovery of Ammonia from Ammoniated High-Salinity Brine

This paper describes a new method for the recovery of high-concentration ammonia from water in the form of ammonium chloride, ammonium hydroxide and ammonium carbonate. The method was applied to the Solvay process, in which sodium bicarbonate is produced through the reaction of ammoniated brine and CO2 gas. The Solvay effluent contains ammonia in the form of soluble ammonium chloride. The proposed method is based on the recovery of ammonia using a high-alkalinity reactant, calcium oxide (CaO), in a closed electrocoagulation cell operating at a specific current density. The recovered ammonia is collected as a gas within a closed cell containing deionized (DI) water at room temperature. Afterwards, the collected solution (DI water–NH3 gas) is concentrated through a separate process, and is then reused in the Solvay process and other applications. The electrocoagulation process is applied to the treatment cell using aluminum electrodes and a current density of 5–15 mA/cm2. After 7 h of treatment using the electrocoagulation cell, a high reduction of the ammonia concentration—99%—was realized after ~9 h of the electrochemical treatment. The initial ammonia concentration in a Solvay effluent of 13,700 mg/L N was decreased to 190 mg/L N. Furthermore, an ammonia recovery of 77.1% in the form of ammonium hydroxide was achieved. Generally, this process, which starts at room temperature, can result in an energy reduction of 80%—from 7.8 to 2.3 kWh/kg NH3—compared to conventional processes, which entail heating the Solvay effluents to 160 °C. The proposed system and method were found to be suitable for the recovery of ammonia from ammoniated water, and can be utilized for the treatment of landfill leachate, and municipal and industrial wastewater.

Ammonia recovery from simulated anaerobic digestate using a two-stage direct contact membrane distillation process

Ammonia is a key inorganic contaminant in wastewater and an important nutrient element for agriculture. Herein, a two-stage direct contact membrane distillation (DCMD) system was developed and investigated for ammonia recovery from a synthetic anaerobic digestate. In the 1st stage DCMD (DCMD-1), both ammonia and water moved across MD membrane to realize ammonia separation, while in the 2nd stage (DCMD-2), only water migrated and as a result ammonia was concentrated. It was found that increasing the initial feed solution pH could enhance ammonia removal in the DCMD-1 from 16.0 ± 2.0% (no pH adjustment) to 84.2 ± 1.9% (pH 12). A higher feed solution temperature increased both ammonia flux and water flux. The optimal condition was determined as an initial feed pH of 12, a feed temperature of 60°C, and the 0.6 M H₂ SO₄ adsorption solution. With the addition of the DCMD-2, the ammonia concentration was improved from 3 g L^-1 to 7.8 ± 0.2 g L^-1 , which was further enhanced to 26.3 ± 3.0 g L^-1 after five batches of operation. These results have demonstrated the feasibility of a two-stage DCMD system for ammonia recovery from anaerobic digestate and warrant further investigation of several key issues that may advance this technology. PRACTITIONER POINTS: A two-stage membrane distillation system is developed to remove and recover ammonia from anaerobic digester effluents. The system uses ammonia/ammonium equilibrium to separate ammonia in the 1st stage and then concentrate it in the 2nd stage. A high initial pH of the feed solution plays a key role in achieving high ammonia removal. Minimizing the volume of permeate solution can increase the ammonia concentration.

In Situ Three-Dimensional Welded Nanofibrous Membranes for Robust Membrane Distillation of Concentrated Seawater

Membrane distillation (MD) is a promising technology for treating the concentrated seawater discharged from the desalination process. Interconnected porous membranes, fabricated by additive manufacturing, have received significant attention for MD technology because of their excellent permeability. However, their poor hydrophobic durability induced by the deformation of pores constrains their water desalination performance. Herein, an in situ three-dimensional (3D) welding approach involving emulsion electrospinning is reported for fabricating robust nanofibrous membranes. The reported method is simple and effective for welding nanofibers at their intersections, and the reinforced membrane pores are uniform in the 3D space. The results show that the in situ 3D welded nanofibrous membrane, with a stability of 170 h and water recovery of 76.9%, exhibits better desalination performance than the nonwelded (superhydrophobic) nanofibrous membrane and the postwelded (superhydrophobic) nanofibrous membrane. Furthermore, the stability mechanism of the in situ 3D welded nanofibrous membrane and the two different wetting mechanisms of the nonwelded and postwelded nanofibrous membranes were investigated in the current work. More significantly, the in situ 3D welded nanofibrous membrane can further concentrate the actual concentrated seawater (121°E, 37°N) to crystallization, demonstrating its potential applications for the desalination of challenging concentrated seawater.

Visible light-conducting polymer nanocomposites as efficient photocatalysts for the treatment of organic pollutants in wastewater

This review compiles recent advances and challenges on photocatalytic treatment of wastewater using nanoparticles, nanocomposites, and polymer nanocomposites as photocatalyst. The review provides an overview of the fundamental principles of photocatalytic treatment along the recent advances on photocatalytic treatment, especially on the modification strategies and operational conditions to enhance treatment efficiency and removal of recalcitrant organic contaminants. The different types of photocatalysts along the key factors influencing their performance are also critically discussed and recommendations for future research are provided.

Development of a label free electrochemical sensor based on a sensitive monoclonal antibody for the detection of tiamulin

Based on a murine monoclonal antibody (mAb) against tiamulin (TML), an electrochemical immunosensor was proposed using silver-graphene oxide (Ag-GO) nanocomposites and gold nanocomposites (AuNPs) to detect tiamulin (TML). Due to the synergetic properties of Ag-GO nanocomposites and AuNPs, the conductivity of the immunosensor was significantly enhanced. On account of the specific mAb and conductive nanocomposites, the proposed electrochemical immunosensor exhibited a low LOD of 0.003 ng mL^-1 for the detection of TML in a wide linear range of 0.01 to 1000 ng mL^-1. In addition, the immunosensor did not involve additional redox species. Furthermore, the efficient and simple electrochemical immunosensor was employed to detect TML in real samples with high accuracy, suggesting a potential detection platform for other veterinary antibiotics in animal derived foods.