Application of vacuum membrane distillation for ammonia removal

Nanofilament-Coated Superhydrophobic Membranes Show Enhanced Flux and Fouling Resistance in Membrane Distillation

Membrane distillation (MD) is an important technique for brine desalination and wastewater treatment that may utilize waste or solar heat. To increase the distillation rate and minimize membrane wetting and fouling, we deposit a layer of polysiloxane nanofilaments on microporous membranes. In this way, composite membranes with multiscale pore sizes are created. The performance of these membranes in the air gap and direct contact membrane distillation was investigated in the presence of salt solutions, solutions containing bovine serum albumin, and solutions containing the surfactant sodium dodecyl sulfate. In comparison to conventional hydrophobic membranes, our multiscale porous membranes exhibit superior fouling resistance while attaining a higher distillation flux without using fluorinated compounds. This study demonstrates a viable method for optimizing MD processes for wastewater and saltwater treatment.

Recovery of Ammonium from Biomass-Drying Condensate Via Ion Exchange and Its Valorization as a Fertilizer

In this study, an industrial biomass-drying wastewater condensate containing > 3200 mg/L NH4+ and >8900 mg/L CH3COO− was treated in ion-exchange columns for the recovery of NH4+. Two commercial resins (CS12GC and CS16GC) were studied on laboratory and pilot scales. CS16GC outperformed CS12GC by achieving better separation at the condensate temperature (60 °C), which was energy-efficient regarding NH4+ removal. K3PO4 was used for regeneration to produce a liquid compound fertilizer containing nutrient elements (N, K, and P) as a byproduct. The N/K ratio in the byproduct was found to be adjustable by varying the operating parameters. Regeneration with 2 mol/L K3PO4 gave a higher regeneration efficiency (97.67% at 3 BV and ~100% at 4 BV). The stability tests performed on a laboratory scale showed that the cyclic runs of the column separation process were steady and repeatable. Based on the outcomes of the laboratory-scale tests, the pilot-scale tests applied a loading volume of 7 BV. The pilot column purified the feed and achieved the target NH4+ level in the treated effluent within the seven tested cycles, revealing that the industrial application of the cation ion-exchange resin CS16GC is worth further study.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

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.

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.

Selective capture of ammonium ions from municipal wastewater treatment plant effluent with a nickel hexacyanoferrate electrode

Currently, intercalation materials such as Prussian blue analogs have attracted considerable attention in water treatment applications due to their excellent size-based selectivity toward cations. This study aimed to explore the feasibility of using a nickel hexacyanoferrate (NiHCF) electrode for selective NH₄⁺ capture from effluent from a municipal wastewater treatment plant. To assess the competitive intercalation between NH₄⁺ and other common cations (Na⁺, Ca²⁺), a NiHCF//activated carbon (AC) hybrid capacitive deionization (CDI) cell was established to treat mixed-salt solutions. The results of cyclic voltammetry (CV) analysis showed a higher current response of the NiHCF electrode toward NH₄⁺ ions than toward Na⁺ and Ca²⁺ ions. In a single-salt solution with NH₄⁺, the optimized operating voltage of the hybrid CDI cell was 0.8 V, with a higher salt adsorption capacity (51.2 mg/g) than those obtained at other voltages (0.1, 0.4, 1.2 V). In a multisalt solution containing NH₄⁺, Na⁺, and Ca²⁺ ions, the selectivity coefficients of NH₄⁺/Ca²⁺ and NH₄⁺/Na⁺ were 9.5 and 4.9, respectively. The feasibility of selective NH₄⁺ capture using the NiHCF electrode in a hybrid CDI cell was demonstrated by treating the effluent from a municipal wastewater treatment plant (WWTP). The intercalation preference of the NiHCF electrode with the WWTP effluent was NH₄⁺>K⁺>Na⁺>Ca²⁺>Mg²⁺, and NH₄⁺ showed the highest salt adsorption capacity among the cations during consecutive cycles. Our results revealed that cations with smaller hydrated radii and lower (de)hydration energies were more favorably intercalated by the NiHCF electrode. The results provide important knowledge regarding the use of intercalation-type electrodes for selective nutrient removal and recovery from wastewater.

High-Efficiency Water Recovery from Urine by Vacuum Membrane Distillation for Space Applications: Water Quality Improvement and Operation Stability

Water recovery by membrane distillation (MD) is an attractive alternative to existing urine treatment systems because it could improve the water recovery rate and reliability in space missions. However, there are few studies of urine MD, particularly on the removal of the remaining contaminants from distillate water and the assessment of its long-term performance. In this study, the influences of various operation parameters on distillate water quality and operation stability were investigated in batch mode. The low pH of feedstock reduced the conductivity and total ammonium nitrogen (TAN) in distillate water because the low pH promoted the ionization of ammonia to ammonium ions. However, the low pH also facilitated the formation of free chlorine hydride, which resulted in the minor deterioration of the conductivity in the distillate due to the increasing volatility of chlorine hydride in the feedstock. Thirty batches of vacuum membrane distillation (VMD) experiments demonstrated that the permeate flux and the distillate water quality slightly decreased due to the small range of membrane wetting but still maintained an over 94.2% and 95.8% removal efficiency of the total organic carbon (TOC) and TAN, and the conductivity was <125 μs cm−1 in the distillate water after 30 test batches. VMD is a feasible option for urine treatment in space missions.

Fouling, performance and cost analysis of membrane-based water desalination technologies: A critical review

While water is a key resource required to sustain life, freshwater sources and aquifers are being depleted at an alarming rate. As a mitigation strategy, saline water desalination is commonly used to supplement the available water resources beyond direct water supply. This is achieved through effective advanced water purification processes enabled to handle complex matrix of saline wastewater. Membrane technology has been extensively evaluated for water desalination. This includes the use of reverse osmosis (RO) (the most mature membrane technology for desalination), pervaporation (PV), electrodialysis (ED), membrane distillation (MD), and membrane crystallization (MCr). Though nanofiltration (NF) is not mainly applied for desalination purposes, it is included in the reviewed processes because of its ability to reach 90% salt rejection efficiency for water softening. However, its comparison with other technologies is not provided since NF cannot be used for removal of NaCl during desalination. Remarkably, membrane processes remain critically affected by several challenges including membrane fouling. Moreover, capital expenditure (CAPEX) and operating expenditure (OPEX) are the key factors influencing the establishment of water desalination processes. Therefore, this paper provides a concise and yet comprehensive review of the membrane processes used to desalt saline water. Furthermore, the successes and failures of each process are critically reviewed. Finally, the CAPEX and OPEX of these water desalination processes are reviewed and compared. Based on the findings of this review, MD is relatively comparable to RO in terms of process performance achieving 99% salt rejections. Also, high salt rejections are reported on ED and PV. The operation and maintenance (O&M) costs remain lower in ED. Notably, the small-scale MD OPEX falls below that of RO. However, the large-scale O&M in MD is rarely reported due to its slow industrial growth, thus making RO the most preferred in the current water desalination markets.

Challenges and opportunities for more efficient water use and circular wastewater management. The case of Campania Region, Italy

By 2050, global demand for water is expected to increase by some 55% due to population growth and urbanization. The utilization of large amounts of freshwater in the world, generate huge volumes of wastewater of which, globally, more than 80% is discharged without treatment, thus causing impacts on aquatic ecosystems, human health and economic productivity. More sustainable practices of wastewater management are expected as a way towards circular bioeconomy (CBE) processes, whose goal is to implement closed systems promoting the systematic use of recycling, reuse and recovery of bioproducts and by-products and the reduction of waste generation. This approach, if adopted in the water and wastewater sector, can ensure environmental, economic and social benefits. The reuse of wastewater, on the one hand, reduces the volume of wastewater and the pressure on water bodies; on the other hand, the recovery of nutrients (P or N) and/or other high value bioproducts (biogas, cellulose, biopolymers) from wastewater offers numerous advantages in terms of supplying new raw bio-based materials that can be refed back to supply chains (thus substituting fossil resources) and, at the same time, producing cleaner water to be reused. Nevertheless, while in Europe many industries have demonstrated the ability to recycle and reuse water, in many regions of Italy the sustainable management of water and wastewater is not yet consolidated. In this study we explore the available technological, economic and environmental options concerning water use and wastewater treatment and we apply them to design appropriate scenarios for improved use efficiency and circular management. A comprehensive literature review of the most promising wastewater treatment processes for resources and energy valorization was conducted. The recovery of PHAs, struvite, nitrogen and algal biomass, as potential substitutes for conventional PET, phosphate and nitrogen chemical fertilizers and electricity, respectively, in addition to reusable treated water, were hypothesized and carefully discussed. Resulting scenarios are tested against the present situation of Campania Region (situated in Southern Italy) based on population and demand statistics, in order to develop strategies and policies potentially applicable locally and elsewhere.

Recovery and applications of ammoniacal nitrogen from nitrogen-loaded residual streams: A review

Total ammoniacal nitrogen (TAN) is considered to be a pollutant, but is also a versatile resource. This review presents an overview of the TAN recovery potentials from nitrogen (N)-loaded residual streams by discussing the sources, recovery technologies and potential applications. The first section of the review addresses the fate of TAN after its production. The second section describes the identification and categorisation of N-loaded (≥0.5 g L^-1 of reduced N) residual streams based on total suspended solids (TSS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), TAN, and TAN/TKN ratio. Category 1 represents streams with a low TAN/TKN ratio (<0.5) that need conversion of organic-N to TAN prior to TAN recovery, for example by anaerobic digestion (AD). Category 2 represents streams with a high TAN/TKN ratio (≥0.5) and high TSS (>1 g L^-1) that require a decrease of the TSS prior to TAN recovery, whereas category 3 represents streams with a high TAN/TKN ratio (≥0.5) and low TSS (≤1 g L^-1) that are suitable for direct TAN recovery. The third section focuses on the key processes and limitations of AD, which is identified as a suitable technology to increase the TAN/TKN ratio by converting organic-N to TAN. In the fourth section, TAN recovery technologies are evaluated in terms of the feed composition tolerance, the required inputs (energy, chemicals, etc.) and obtained outputs of TAN (chemical form, concentration, etc.). Finally, in the fifth section, the use of recovered TAN for three major potential applications (fertilizer, fuel, and resource for chemical and biochemical processes) is discussed. This review presents an overview of possible TAN recovery strategies based on the available technologies, but the choice of the recovery strategy shall ultimately depend on the product characteristics required by the application. The major challenges identified in this review are the lack of information on enhancing the conversion of organic-N into TAN by AD, the difficulties in comparing the performance and required input of the recovery technologies, and the deficiency of information on the required concentration and quality of the final TAN products for reuse.

Azanone (HNO): generation, stabilization and detection

HNO (nitroxyl, azanone), joined the 'biologically relevant reactive nitrogen species' family in the 2000s. Azanone is impossible to store due to its high reactivity and inherent low stability. Consequently, its chemistry and effects are studied using donor compounds, which release this molecule in solution and in the gas phase upon stimulation. Researchers have also tried to stabilize this elusive species and its conjugate base by coordination to metal centers using several ligands, like metalloporphyrins and pincer ligands. Given HNO's high reactivity and short lifetime, several different strategies have been proposed for its detection in chemical and biological systems, such as colorimetric methods, EPR, HPLC, mass spectrometry, fluorescent probes, and electrochemical analysis. These approaches are described and critically compared. Finally, in the last ten years, several advances regarding the possibility of endogenous HNO generation were made; some of them are also revised in the present work.

Laboratory Scale Evaluation of Fertiliser Factory Wastewater Treatment through Membrane Distillation and Reverse Osmosis

The incumbent water stress scenario imposes wastewater valorisation to freshwater, promoting technology for its effective treatment. Wastewater from fertiliser factories is quite problematic because of its relevant acidity and solute content. Its treatment through vacuum membrane distillation (VMD) was evaluated through laboratory scale tests at 40 °C and 25 mbar vacuum pressure with polytetrafluoroethylene and polypropylene flat-sheet porous membranes. The wastewater from a partially disused Italian industrial site was considered. VMD distillate fluxes between 22 and 57.4 L m^-2 h^-1 (LMH), depending on the pore size of the membranes, along with very high retention (R > 99%) for anions (Cl^-, NO₃^-, SO₄^2-, PO₄^3-), NH₄⁺, and chemical oxygen demand (COD) were observed. Laboratory scale reverse osmosis (RO) tests at 25 °C and increasing of the operating pressure (from 20 bar to 40 bar) were carried out with a seawater desalination membrane for comparison purposes. Permeability values around 1.1 LMH/bar almost independently of the operating pressure were observed. Lower retentions than those measured from VMD tests were found. Finally, for any given RO operating pressure, the flux recovery ratio (FRR) calculated from permeate fluxes measured with pure water before and after wastewater treatment was always much lower that evaluated for VMD membranes.

Circular economy-driven ammonium recovery from municipal wastewater: State of the art, challenges and solutions forward

In current biological nitrogen removal (BNR) processes, most of ammonium in municipal wastewater is biologically transformed to nitrogen gas, making ammonium recovery impossible. Thus, this article aims to provide a holistic review with in-depth discussions on (i) current BNR processes for municipal wastewater treatment, (ii) environmental and economic costs behind ammonium in municipal wastewater, (iii) state of the art of ammonium recovery from municipal wastewater including anaerobic membrane bioreactor turning municipal wastewater to a liquid fertilizer, capturing ammonium in phototrophic biomass, waste activated sludge for land application, bioelectrochemical systems, biological conversion of ammonium to nitrous oxide as a fuel oxidizer, and adsorption, (iv) feasibility and challenge of adsorption for ammonium recovery from municipal wastewater and (v) innovative municipal wastewater reclamation processes coupled with ammonium recovery. Moving forward, municipal wastewater reclamation and resource recovery should be addressed under the framework of circular economy.

Solid-gas reactions for nitroxyl (HNO) generation in the gas phase

We present a novel nitroxyl (HNO) generation method, which avoids the need of using a liquid system or extreme experimental conditions. This method consists of the reaction between a gaseous base and an HNO donor (Piloty's acid) in the solid phase, allowing the formation of gaseous HNO in a fast and economical way. Detection of HNO was carried out indirectly, measuring the nitrous oxide (N₂O) byproduct of HNO dimerization using infrared spectroscopy, and directly, using mass spectrometry techniques and an electrochemical HNO sensor.

Membrane distillation of concentrated blackwater: Effect of temperature, solids concentration and membrane pore size

This study has elucidated the mechanisms governing water recovery from blackwater using membrane distillation, and has clarified the role of the organic particle fraction on membrane performance. Whilst fecal pathogen growth was initially observed at lower temperatures, pathogen inactivation was demonstrated over time, due to urea hydrolysis which liberated ammonia in excess of its toxic threshold. During the growth phase, membrane pore size <0.45 µm was sufficient to achieve high log reduction values for Escherichia coli, due to size exclusion complimented by the liquid-vapor interface which enhances selective transport for water. Higher feed temperatures benefitted rejection by promoting thermal inactivation and suppressing urea hydrolysis. Whilst the mechanism is not yet clear, suppression of hydrolysis reduced bicarbonate formation kinetics stabilizing the ammonia-ammonium equilibrium which improved ammonium rejection. Blackwater particle concentration was studied by increasing fecal content. Particle fouling improved selectivity for coarse pore membranes but increased mass transfer resistance which reduced flux. Particle fouling induced wetting as noted by an eventual breakthrough of feed into the permeate. We propose that by incorporating upstream solid-liquid separation for particle separation to limit wetting and mass transfer resistance, membrane distillation can be a reliable solution for the recovery of high-quality permeate from blackwater. PRACTITIONER POINTS: Membrane distillation demonstrated for concentrated blackwater. Multiple factors provide robust pathogen separation (pore size, vapor-liquid interface, temperature, free-ammonia). Excellent water quality produced for feed 40 times more concentrated than wastewater. Removing particle fraction will improve separation robustness and operating longevity.

Evaluating Critical Influencing Factors of Desalination by Membrane Distillation Process-Using Multi-Criteria Decision-Making

Water desalination by membrane distillation (MD) can be affected by a wide range of operating parameters. The present work uses combinational approach of Analytical Hierarch process (AHP) and Fuzzy Analytical Hierarchy process (Fuzzy-AHP) to identify the most important parameters in the MD desalination. Five process parameters and key-performance indicators, named derivable outputs (DOs), are considered, along with the critical factors affecting these DOs in the current study. The DOs and the critical influencing factors (CIFs) are selected based on their experimental feasibility. The investigation involves five DOs, which are liquid entry pressure, thermal power consumption, permeate quality, permeate flux, and pumping (feed circulation) power. A total of twenty-five critical influencing factor were associated with the DOs. The identification of the DOs and CIFs was based on the literature review, and further analyses were performed. Both methods, AHP and Fuzzy-AHP, determined six extremely important CIFs in the desalination MD, which are feed temperature, feed concentration, or feed salinity; feed flow rate; membrane hydrophobicity; pore size; and membrane material. Moderately important CIFs are found to be four by both methods. These common CIFs are feed solution properties, membrane thickness, feed channel geometry, and pressure difference along the feed channel. Finally, the least preferred CIFs are four common in both methods that are MD configuration, duration of test, specific heat of feed solution, and viscosity.

Hybrid forward osmosis/membrane distillation integrated with anaerobic fluidized bed bioreactor for advanced wastewater treatment

Forward osmosis (FO)-membrane distillation (MD) process was integrated with anaerobic fluidized bed bioreactor (AFBR) to advance wastewater treatment. Low removal efficiency of nutrients such as ammonia nitrogen was improved significantly by combining FO-MD process with AFBR. The MD membrane was applied to concentrate the draw solution (DS) which can be diluted by FO filtration. By using 1 M of NaCl as DS, about 80% of ammonia nitrogen was further removed by the FO membrane while the phosphorous was removed almost completely (99%). However, the accumulation of ammonia nitrogen in DS and the reverse salt flux through the FO membrane was unavoidable. Nevertheless, combining MD membrane produced excellent removal efficiency yielding only 4 and 5.6 mg/L of ammonia nitrogen and chemical oxygen demand (COD) in MD permeate, respectively at 15 ℃ of transmembrane temperature. Alternatively, there is the possibility that the FO-MD process can be superior to concentrate resources such as nitrogen and phosphorous present in AFBR. The reverse salt flux from DS into AFBR bulk suspension did not show adverse effects on the performances of bioreactor with respect to COD removal efficiency, conductivity and methane production during operational period. Deposit of the fouling layer on FO membrane was also observed, but the fouling on MD membrane was not severe probably because crystallization rate could be retarded by diluting the DS during FO filtration.

Role of Membrane Technology in Absorption Heat Pumps: A Comprehensive Review

The role of heat pumps is linked to the actions of human life. Even though the existing technologies perform well in general, they have still some problems, such as cost, installation area, components size, number of components, noise, etc. To address these issues, membrane technologies have been introduced in both heat and cooling devices. The present work proposes and studied the review of the role of membrane technology in the heat pumps. The study focuses on the advancement and replacement of membrane in the place of absorption and compression heat pump components. The detailed analysis and improvements are focused on the absorber, desorber, and heat and mass exchanger. The parameters conditions and operation of membrane technologies are given in detail. In addition to this, the innovation in the heat pumps using the membrane technology is given in detail.

Utilization of Bidirectional Cation Transport in a Thin Film Composite Membrane: Selective Removal and Reclamation of Ammonium from Synthetic Digested Sludge Centrate via an Osmosis-Distillation Hybrid Membrane Process

Selective removal and resource recovery of ammonium nitrogen (NH₄⁺-N) from high-strength ammonium waste streams is of practical importance for biological wastewater treatment and environmental protection. In this study, we demonstrate the simultaneous removal and reclamation of ammonium from synthetic digested sludge centrate via a novel osmosis-distillation hybrid membrane (ODHM) process. Using NaHCO₃ as the draw solute, ammonium diffuses from the synthetic centrate to the draw solution by utilizing the bidirectional cation transport nature of the thin film composite (TFC) membrane. Then, NH₄⁺ is converted to gaseous NH₃ at 60 °C and recovered by a sweeping gas membrane distillation (SGMD) process. Herein, the bidirectional transport of monovalent cations in the osmotic process, selectivity of TFC membranes for different cations, and recovery of the draw solution following the extraction of ammonia through the SGMD process were systematically investigated. The removal of NH₄⁺-N from the synthetic centrate achieved 21.34% during a 6-h continuous operation of the ODHM system, with ammonium fluxes through the TFC and SGMD membranes at 1.39 and 0.57 mol m^-2 h^-1, respectively. A secondary interfacial polymerization was proposed to further enhance ammonium transport through the TFC membrane. Results reported here highlight the potential of the ODHM process for the selective removal and reclamation of ammonium from ammonium-rich waste streams.

A hybrid catalytic hydrogenation/membrane distillation process for nitrogen resource recovery from nitrate-contaminated waste ion exchange brine

Ion exchange is widely used to treat nitrate-contaminated groundwater, but high salt usage for resin regeneration and management of waste brine residuals increase treatment costs and add environmental burdens. Development of palladium-based catalytic nitrate treatment systems for brine treatment and reuse has showed promising activity for nitrate reduction and selectivity towards the N₂ over the alternative product ammonia, but this strategy overlooks the potential value of nitrogen resources. Here, we evaluated a hybrid catalytic hydrogenation/membrane distillation process for nitrogen resource recovery during treatment and reuse of nitrate-contaminated waste ion exchange brines. In the first step of the hybrid process, a Ru/C catalyst with high selectivity towards ammonia was found to be effective for nitrate hydrogenation under conditions representative of waste brines, including expected salt buildup that would occur with repeated brine reuse cycles. The apparent rate constants normalized to metal mass (0.30 ± 0.03 mM min^-1 g_Ru^-1 under baseline condition) were comparable to the state-of-the-art bimetallic Pd catalyst. In the second stage of the hybrid process, membrane distillation was applied to recover the ammonia product from the brine matrix, capturing nitrogen as ammonium sulfate, a commercial fertilizer product. Solution pH significantly influenced the rate of ammonia mass transfer through the gas-permeable membrane by controlling the fraction of free ammonia species (NH₃) present in the solution. The rate of ammonia recovery was not affected by increasing salt levels in the brine, indicating the feasibility of membrane distillation for recovering ammonia over repeated reuse cycles. Finally, high rates of nitrate hydrogenation (apparent rate constant 1.80 ± 0.04 mM min^-1 g_Ru^-1) and ammonia recovery (overall mass transfer coefficient 0.20 m h^-1) with the hybrid treatment process were demonstrated when treating a real waste ion exchange brine obtained from a drinking water utility. These findings introduce an innovative strategy for recycling waste ion exchange brine while simultaneously recovering potentially valuable nitrogen resources when treating contaminated groundwater.

Permeate Flux and Rejection Behavior in Submerged Direct Contact Membrane Distillation Process Treating a Low-Strength Synthetic Wastewater

The effects of operational conditions such as permeate recirculation velocity, mixing intensity, and trans-membrane temperature on the performances of hydrophobic polyethylene (PE) hollow-fiber membrane were investigated by operating the submerged direct contact membrane distillation (SDCMD) process treating a synthetic low-strength wastewater. Permeate flux of the membrane increased with increasing a permeate recirculation velocity through the fiber lumen. However, the effectiveness was less pronounced as the velocity was higher than 0.5 m/s. Increasing rotational speed to 600 rpm, which can lead to mixing intensity from a bulk wastewater toward hollow-fiber membrane, enhanced permeate flux. Feed temperature played a more significant role in enhancing permeate flux rather than a permeate temperature under constant trans-membrane temperature. The SDCMD process treating a synthetic low-strength wastewater achieved an excellent rejection efficiency which is higher than 97.8% for both chemical oxygen demand (CODCr) and total phosphorus (T-P) due to the hydrophobic property of membrane material which can allow water vapor through membrane. However, the rejection efficiency of the ammonia nitrogen (NH3-N) was relatively low at about 87.5% because ammonia gas could be volatized easily through membrane pores in SDCMD operation. In a long-term operation of the SDCMD process, the permeate flux decreased significantly due to progressive formation of inorganic scaling on membrane.

Removal of fluoride in membrane-based water and wastewater treatment technologies: Performance review

The presence of excess fluoride in aqueous media above local environmental standards (e.g., the U.S. Environmental Protection Agency (EPA) standard of 4 mg/L) affects the health of aquatic life. Excess fluoride in drinking water above the maximum contaminant level (e.g., the World Health Organization (WHO) standard of 1.5 mg/L) also affects the skeletal and nervous systems of humans. Fluoride removal from aqueous solutions is difficult using conventional electrochemical, precipitation, and adsorption methods owing to its ionic size and reactivity. Thus, new technologies have been introduced to reduce the fluoride concentration in industrial wastewater effluents and various drinking water sources. Membrane technology is one of the newer technologies found to be very effective in significantly reducing fluoride to desired standards levels; however, it has received less attention than other technologies because it is perceived as a costly process. This study critically reviewed the performance of various membrane process and compared it with effluent and zero liquid discharge (ZLD) standards. The performance review has been conducted with the consideration of the theoretical background, rejection mechanisms, technical viability, and parameters affecting flux and rejection performance. This review includes membrane systems investigated for the defluoridation process but operated under pressure (i.e., reverse osmosis [RO] and nanofiltration [NF]), temperature gradients (i.e., membrane distillation [MD]), electrical potential gradients (i.e., electrodialysis [ED] and Donnan dialysis [DD]), and concentration differences (i.e., forward osmosis [FO]). Moreover, the study also addressed the advantages, limitations, & applicable conditions of each membrane based defluoridation process.

Toxicity alleviation for microalgae cultivation by cationic starch addition and ammonia stripping and study on the cost assessment

Aiming at promoting microalgae-based anaerobically digested swine manure (AD-SM) treatment, this work evaluated the feasibility of removing turbidity and ammonia in swine manure by cationic starch addition and air bubbling-driven ammonia stripping. It was observed that turbidity and ammonia toxicity were two main factors limiting algae growth. Addition of cationic starch effectively reduced turbidity of AD-SM by 77.10% in 40 min. 6 L min⁻¹ air flow rate and 5 h stripping time were regarded as good conditions for ammonia stripping. An economic analysis was conducted to assess the feasibility of this pretreatment strategy in a pilot scale system and results indicated that unit energy input and freshwater consumption were 0.036 kW h g⁻¹ dry biomass and 0.76 L g⁻¹ dry biomass, respectively, much lower than those of a high dilution strategy. So it is a more promising and feasible way to pretreat AD-SM with low dilution by turbidity removal and ammonia stripping.

Aiming at promoting microalgae-based anaerobically digested swine manure (AD-SM) treatment, this work evaluated the feasibility of removing turbidity and ammonia in swine manure by cationic starch addition and air bubbling-driven ammonia stripping.

Application of dynamic current density for increased concentration factors and reduced energy consumption for concentrating ammonium by electrodialysis

Ammonium (NH₄⁺) can be recovered from water for fertiliser production or even energy production purposes. Because NH₄⁺ recovery is more effective at increased concentrations, electrodialysis (ED) can be used to concentrate NH₄⁺ from side streams, such as sludge reject water, and simultaneously achieve high NH₄⁺ removal efficiencies. However, the effect of osmosis and back-diffusion increases when the NH₄⁺ concentration gradient between the diluate and the concentrate stream increases, resulting in a limitation of the concentration factor and an increase in energy consumption for NH₄⁺ removal. In this study, we showed that operation at dynamic current density (DCD) reduced the effect of osmosis and back-diffusion, due to a 75% decrease of the operational run time, compared to operation at a fixed current density (FCD). The concentration factor increased from 4.5 for an FCD to 6.7 for DCD, while the energy consumption of 90% NH₄⁺ removal from synthetic sludge reject water at DCD remained stable at 5.4 MJ·kg-N^-1.

Mainstream Ammonium Recovery to Advance Sustainable Urban Wastewater Management

Throughout the 20th century, the prevailing approach toward nitrogen management in municipal wastewater treatment was to remove ammonium by transforming it into dinitrogen (N₂) using biological processes such as conventional activated sludge. While this has been a very successful strategy for safeguarding human health and protecting aquatic ecosystems, the conversion of ammonium into its elemental form is incompatible with the developing circular economy of the 21st century. Equally important, the activated sludge process and other emerging ammonium removal pathways have several environmental and technological limitations. Here, we assess that the theoretical energy embedded in ammonium in domestic wastewater represents roughly 38-48% of the embedded chemical energy available in the whole of the discharged bodily waste. The current routes for ammonium removal not only neglect the energy embedded in ammonium, but they can also produce N₂O, a very strong greenhouse gas, with such emissions comprising the equivalent of 14-26% of the overall carbon footprint of wastewater treatment plants. N₂O emissions often exceed the carbon emissions related to the electricity consumption for the process requirements of WWTPs. Considering these limitations, there is a need to develop alternative ammonium management approaches that center around recovery of ammonium from domestic wastewater rather than deal with its "destruction" into elemental dinitrogen. Current ammonium recovery techniques are applicable only at orders of magnitude above domestic wastewater strength, and so new techniques based on physicochemical adsorption are of particular interest. A new pathway is proposed that allows for mainstream ammonium recovery from wastewater based on physicochemical adsorption through development of polymer-based adsorbents. Provided adequate adsorbents corresponding to characteristics outlined in this paper are designed and brought to industrial production, this adsorption-based approach opens perspectives for mainstream continuous adsorption coupled with side-stream recovery of ammonium with minimal chemical requirements. This proposed pathway can bring forward an effective resource-oriented approach to upgrade the fate of ammonium in urban water management without generating hidden externalized environmental costs.

Characterization and Assessment of a Novel Plate and Frame MD Module for Single Pass Wastewater Concentration-FEED Gap Air Gap Membrane Distillation

Membrane distillation (MD) is an up and coming technology for concentration and separation on the verge of reaching commercialization. One of the remaining boundaries is the lack of available full-scale MD modules and systems suitable to meet the requirements of potential industrial applications. In this work a new type of feed gap air gap MD (FGAGMD) plate and frame module is introduced, designed and characterized with tap water and NaCl–H₂O solution. The main feature of the new channel configuration is the separation of the heating and cooling channel from the feed channel, enabling a very high recovery ratio in a single pass. Key performance indicators (KPIs) such as flux, gained output ratio (GOR), recovery ratio and thermal efficiency are used to analyze the performance of the novel module concept within this work. A recovery rate of 93% was reached with tap water and between 32–53% with salt solutions ranging between 117 and 214 g NaCl/kg solution with this particular prototype module. Other than recovery ratio, the KPIs of the FGAGMD are similar to those of an air gap membrane distillation (AGMD) channel configuration. From the experimental results, furthermore, a new MD KPI was defined as the ratio of heating and cooling flow to feed flow. This R_F ratio can be used for optimization of the module design and efficiency.

The Influence of Alkalization and Temperature on Ammonia Recovery from Cow Manure and the Chemical Properties of the Effluents

Manure is a substantial source of ammonia volatilization into the atmosphere before and after soil application. The purpose of the study was to investigate the effects of temperature and alkalization treatments on the release of ammonia and ammonia recovery (AR) from cow manure and to characterize the chemical properties of the resultant effluents. In a closed glass reactor, 100 g of fresh cow manure was mixed with 100 mL of deionized water and the mixture was treated with various volume of KOH to increase the manure pH to 7, 9, and 12. Ammonia was distilled from the mixture at temperatures of 75, 85, 95, and 100 °C for a maximum of 5 h. Ammonia was received as diluted boric and sulfuric acids. Results indicated that the highest ammonia recovery was 86.3% and 90.2%, which were achieved at a pH of 12 and temperatures of 100 and 95 °C, respectively. The recovered ammonia in boric acid was higher than in sulfuric acid, except at a pH of 12 and temperatures of 95 and 100 °C. The effluents, after ammonia was removed, showed that the variation in pH ranged between 6.30 and 9.38. The electrical conductivity ranged between 4.5 and 9. (dS m−1) and total potassium ranged between 9.4 and 57.2 mg kg−1.

Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants

Ammonia recovery from urine avoids the need for nitrogen removal through nitrification/denitrification and re-synthesis of ammonia (NH₃) via the Haber-Bosch process. Previously, we coupled an alkalifying electrochemical cell to a stripping column, and achieved competitive nitrogen removal and energy efficiencies using only electricity as input, compared to other technologies such as conventional column stripping with air. Direct liquid-liquid extraction with a hydrophobic gas membrane could be an alternative to increase nitrogen recovery from urine into the absorbent while minimizing energy requirements, as well as ensuring microbial and micropollutant retention. Here we compared a column with a membrane stripping reactor, each coupled to an electrochemical cell, fed with source-separated urine and operated at 20 A m^-2. Both systems achieved similar nitrogen removal rates, 0.34 ± 0.21 and 0.35 ± 0.08 mol N L^-1 d^-1, and removal efficiencies, 45.1 ± 18.4 and 49.0 ± 9.3%, for the column and membrane reactor, respectively. The membrane reactor improved nitrogen recovery to 0.27 ± 0.09 mol N L^-1 d^-1 (38.7 ± 13.5%) while lowering the operational (electrochemical and pumping) energy to 6.5 kWh_e kg N^-1 recovered, compared to the column reactor, which reached 0.15 ± 0.06 mol N L^-1 d^-1 (17.2 ± 8.1%) at 13.8 kWh_e kg N^-1. Increased cell concentrations of an autofluorescent E. coli MG1655 + prpsM spiked in the urine influent were observed in the absorbent of the column stripping reactor after 24 h, but not for the membrane stripping reactor. None of six selected micropollutants spiked in the urine were found in the absorbent of both technologies. Overall, the membrane stripping reactor is preferred as it improved nitrogen recovery with less energy input and generated an E. coli- and micropollutant-free product for potential safe reuse. Nitrogen removal rate and efficiency can be further optimized by increasing the NH₃ vapor pressure gradient and/or membrane surface area.

Ammonia removal from chicken manure digestate through vapor pressure membrane contactor (VPMC) and phytoremediation

Ammonia removal from synthetic ammonia solutions and chicken manure digestate via vapor pressure membrane contactor through Polytetrafluoroethylene (PTFE) membrane was investigated. The highest ammonia mass flux, separation factor, and removal efficiencies of 28.6 ± 0.2 g N/m² h, 53.9 ± 10.7, and 97.6 ± 0.7% were observed for synthetic solutions, respectively. Ammonia removal efficiency of 93.6 ± 1.9% through membrane contactor was observed for chicken manure digestate decreasing the total ammonia concentration from 3643.5 ± 67.2 to 230.9 ± 46.2 mg N/L. Phytoremediation via Lemna minor species was used as a polishing step to remove remaining ammonia from the membrane contactor effluent. Total ammonia concentration was then decreased below 2 mg N/L through evaporation, nitrification, and plant uptake processes occurring in the phytoremediation containers. This study reveals that ammonia can be successfully removed via VPMC and phytoremediation systems and the process is implementable as it can be coupled to anaerobic digestion processes to recover ammonia and to prevent ammonia inhibition.