Nutrient recovery from pig manure digestate using electrodialysis reversal: Membrane fouling and feasibility of long-term operation

Integration of anaerobic digestion and electrodialysis for methane yield promotion and in-situ ammonium recovery

Ammonia inhibition is a common issue encountered in anaerobic digestion (AD) when treating nitrogen-rich substrates. This study proposed a novel approach, the electrodialysis-integrated AD (ADED) system, for in-situ recovery of ammonium (NH4+) while simultaneously enhancing AD performance. The ADED reactor was operated at two different NH4+-N concentrations (5,000 mg/L and 10,000 mg/L) to evaluate its performance against a conventional AD reactor. The results indicate that the ADED technology effectively reduced the NH4+-N concentration to below 2,000 mg/L, achieving this with a competitive energy consumption. Moreover, the ADED reactor demonstrated a 1.43-fold improvement in methane production when the influent NH4+-N was 5,000 mg/L, and it effectively prevented complete inhibition of methane production at the influent NH4+-N of 10,000 mg/L. The life cycle impact assessment reveals that ADED technology offers a more environmentally friendly alternative by recovering valuable fertilizer from the AD system.

17β-estradiol (E2) removal in anode-electrodialysis (anode-ED) during nutrient recovery from pig manure digestate

Nutrient recovery from anaerobic digestate through electrodialysis technology (ED) has been investigated and shown high promise, but the removal of 17β-estradiol (E2), which is a natural estrogen and widely found in manure digestate, is not clear. This study examined the mechanism of membrane adsorption and anodic oxidation of E2 during recovering nutrient from manure digestate, and further investigated the performance of Anode-ED in E2 removal. The results showed that the removal of E2 in conventional ED was primarily attributed to membrane adsorption, resulting in no detectable E2 in the product solution. The adsorption capacity of the anion exchange membrane for E2 was significantly higher compared to that of the cation exchange membrane. During Anode-ED operation, E2 was efficiently removed by electrochemical oxidation, in which the chlorination played a primary role. Moreover, the oxidation intermediates of E2 were further removed after 40 min. Even though the carbonate, volatile fatty acid (VFA), and humic acid in the real wastewater have a negative impact on E2 oxidation, the E2 was completely removed from digestate during nutrient recovery in the anode-ED. This study indicates that anode-ED is a promising technology for the removal of E2 during nutrient recovery from digestate.

Emerging electro-driven technologies for phosphorus enrichment and recovery from wastewater: A review

The recovery of phosphorus from wastewater is a critical step in addressing the scarcity of phosphorus resources. Electro-driven technologies for phosphorus enrichment have gathered significant attention due to their inherent advantages, such as mild operating conditions, absence of secondary pollution, and potential integration with other technologies. This study presents a comprehensive review of recent advancements in the field of phosphorus enrichment, with a specific focus on capacitive deionization and electrodialysis technologies. It highlights the underlying principles and effectiveness of electro-driven techniques for phosphorus enrichment while systematically comparing energy consumption, enrichment rate, and concentration factor among different technologies. Furthermore, the study provides a thorough analysis of the capacity of various technologies to selectively enrich phosphorus and proposes several methods and strategies to enhance selectivity. These insights offer valuable guidance for advancing the future development of electrochemical techniques with enhanced efficiency and effectiveness in phosphorus enrichment from wastewater.

Feasibility of electrodeionization for phosphate removal

In this study, electrodeionization (EDI) in bath mode was tested regarding its capability to remove phosphate (PO4 3- ) ions from aqueous solutions. Various parameters affecting the phosphate removal rate via EDI were determined. The results showed that the phosphate removal rate depends on the applied voltage and that the optimum potential was 15 V, corresponding to a phosphate removal rate of 97%. Changing the stream rate of the phosphate-containing solution also affected the phosphate removal rate. Changing the pH of the phosphate-containing solution from 2 to 6 enhanced the phosphate removal rate from 80% to 97%. The presence of Cl- , NO3 - , and SO4 2- ions did not affect the phosphate removal rate. The highest mass transfer coefficient (k) of phosphate was calculated to be 7.85 × 10-4  m/s, and the flux was calculated to be 3.72 × 10-4  mol/m2  s1 at a flow velocity of 3 L/h. Thus, the study results showed the feasibility of EDI as an alternative membrane process for removing phosphate from aqueous solutions. PRACTITIONER POINTS: Electrodeionization was employed for the removal of phosphate. The removal of phosphate exhibited dependence on applied potential. EDI demonstrated a remarkable 97% efficiency in phosphate removal. The pH of the solution was found to influence the removal rate.

Nutrient recovery and valorisation from pig slurry liquid fraction with membrane technologies

Livestock slurry has been reported to be a potential secondary raw material as it contains macronutrients ‑nitrogen, phosphorus and potassium-, which could be valorised as high-quality fertilizers if proper separation and concentration of valuable compounds is performed. In this work, pig slurry liquid fraction was assessed for nutrient recovery and valorisation as fertilizer. Some indicators were used to evaluate the performance of proposed train of technologies within the framework of circular economy. As ammonium and potassium species are highly soluble at the whole pH range, a study based on phosphate speciation at pH from 4 to 8 was assessed to improve the macronutrients recovery from the slurry, resulting in two different treatment trains at acidic and alkaline conditions. The acidic treatment system based on centrifugation, microfiltration and forward osmosis was applied to obtain a nutrient-rich liquid organic fertilizer containing 1.3 % N, 1.3 % P₂O₅ and 1.5 % K₂O. The alkaline path of valorisation was composed by centrifugation and stripping by using membrane contactors to produce an organic solid fertilizer -7.7 % N, 8,0 % P₂O₅ and 2.3 % K₂O-, ammonium sulphate solution -1.4 % N- and irrigation water. In terms of circularity indicators, 45.8 % of the initial water content and <50 % of contained nutrients were recovered - 28.3 % N, 43.5 % P₂O₅ and 46.6 % K₂O - in the acidic treatment resulting in 68.68 g fertilizer per kg of treated slurry. 75.1 % of water was recovered as irrigation water and 80.6 % N, 99.9 % P₂O₅, 83.4 % K₂O was valorised in the alkaline treatment, as 219.60 g fertilizer per kg of treated slurry. Treatment paths at acidic and alkaline conditions yield promising results for nutrients recovery and valorisation as the obtained products (nutrient rich organic fertilizer, solid soil amendment and ammonium sulphate solution) fulfil the European Regulation for fertilizers to be potentially used in crop fields.

Cadmium-treatment efficiency and membrane fouling during electrodialysis of wastewater discharged from zinc smelting

Zinc smelting wastewater contains high concentrations of Cd. Here, the treatment efficiency of Cd using electrodialysis was evaluated. In addition, scale accumulation of ion-exchange membrane (IEM) was analyzed, and fouling control was studied. The results showed that spacers effectively improved the limiting current density but accelerated foulant accumulation. The Cd-treatment efficiency improved to 85.4% without a spacer. Dissolved organic carbon (DOC) and hydrophobic DOC levels in diluted water decreased by 0.65 mg L^-1 and 2.1 mg L^-1, respectively; in contrast, hydrophilic DOC level increased by 1.45 mg L^-1. Some of the hydrophobic DOC in the diluted water was converted to hydrophilic DOC and subsequently to low-molecular-weight (LMW) DOC. DOC level in the concentrated water did not change substantially, but the LMW fraction of the hydrophilic DOC increased. In the cation-exchange membrane, a material composed of calcium sulfate accumulated in the bottom layer, and hydroxides of divalent and trivalent ions accumulated on top of it. In contrast, the anion-exchange membrane was fouled by humic substances. In terms of fouling control, physical and acid cleaning of IEMs was more effective than the reversal operation.

Research on Membranes and Their Associated Processes at the Université Paris-Est Créteil: Progress Report, Perspectives, and National and International Collaborations

Research on membranes and their associated processes was initiated in 1970 at the University of Paris XII/IUT de Créteil, which became in 2010 the University Paris-Est Créteil (UPEC). This research initially focused on the development and applications of pervaporation membranes, then concerned the metrology of ion-exchange membranes, then expanded to dialysis processes using these membranes, and recently opened to composite membranes and their applications in production or purification processes. Both experimental and fundamental aspects have been developed in parallel. This evolution has been reinforced by an opening to the French and European industries, and to the international scene, especially to the Krasnodar Membrane Institute (Kuban State University-Russia) and to the Department of Chemistry, (Qassim University-Saudi Arabia). Here, we first presented the history of this research activity, then developed the main research axes carried out at UPEC over the 2012-2022 period; then, we gave the main results obtained, and finally, showed the cross contribution of the developed collaborations. We avoided a chronological presentation of these activities and grouped them by theme: composite membranes and ion-exchange membranes. For composite membranes, we have detailed three applications: highly selective lithium-ion extraction, bleach production, and water and industrial effluent treatments. For ion-exchange membranes, we focused on their characterization methods, their use in Neutralization Dialysis for brackish water demineralization, and their fouling and antifouling processes. It appears that the research activities on membranes within UPEC are very dynamic and fruitful, and benefit from scientific exchanges with our Russian partners, which contributed to the development of strong membrane activity on water treatment within Qassim University. Finally, four main perspectives of this research activity were given: the design of autonomous and energy self-sufficient processes, refinement of characterization by Electrochemical Scanning Microscopy, functional membrane separators, and green membrane preparation and use.

Macro-nutrients recovery from liquid waste as a sustainable resource for production of recovered mineral fertilizer: Uncovering alternative options to sustain global food security cost-effectively

Global food security, which has emerged as one of the sustainability challenges, impacts every country. As food cannot be generated without involving nutrients, research has intensified recently to recover unused nutrients from waste streams. As a finite resource, phosphorus (P) is largely wasted. This work critically reviews the technical applicability of various water technologies to recover macro-nutrients such as P, N, and K from wastewater. Struvite precipitation, adsorption, ion exchange, and membrane filtration are applied for nutrient recovery. Technological strengths and drawbacks in their applications are evaluated and compared. Their operational conditions such as pH, dose required, initial nutrient concentration, and treatment performance are presented. Cost-effectiveness of the technologies for P or N recovery is also elaborated. It is evident from a literature survey of 310 published studies (1985-2022) that no single technique can effectively and universally recover target macro-nutrients from liquid waste. Struvite precipitation is commonly used to recover over 95 % of P from sludge digestate with its concentration ranging from 200 to 4000 mg/L. The recovered precipitate can be reused as a fertilizer due to its high content of P and N. Phosphate removal of higher than 80 % can be achieved by struvite precipitation when the molar ratio of Mg²⁺/PO₄^3- ranges between 1.1 and 1.3. The applications of artificial intelligence (AI) to collect data on critical parameters control optimization, improve treatment effectiveness, and facilitate water utilities to upscale water treatment plants. Such infrastructure in the plants could enable the recovered materials to be reused to sustain food security. As nutrient recovery is crucial in wastewater treatment, water treatment plant operators need to consider (1) the costs of nutrient recovery techniques; (2) their applicability; (3) their benefits and implications. It is essential to note that the treatment cost of P and/or N-laden wastewater depends on the process applied and local conditions.

Electrodialysis Tartrate Stabilization of Wine Materials: Fouling and a New Approach to the Cleaning of Aliphatic Anion-Exchange Membranes

Electrodialysis (ED) is an attractive method of tartrate stabilization of wine due to its rapidity and reagentlessness. At the same time, fouling of ion-exchange membranes by the components of wine materials is still an unsolved problem. The effect of ethanol, polyphenols (mainly anthocyanins and proanthocyanidins) and saccharides (fructose) on the fouling of aliphatic ion-exchange membranes CJMA-6 and CJMC-5 (manufactured by Hefei Chemjoy Polymer Materials Co. Ltd., Hefei, China) was analyzed using model solutions. It was shown that the mechanism and consequences of fouling are different in the absence of an electric field and during electrodialysis. In particular, a layer of colloidal particles is deposited on the surface of the CJMA-6 anion-exchange membrane in underlimiting current modes. Its thickness increases with increasing current density, apparently due to the implementation of a trap mechanism involving tartaric acid anions, as well as protons, which are products of water splitting and "acid dissociation". A successful attempt was made to clean CJMA-6 in operando by pumping a water-alcohol solution of KCl through the desalination compartment and changing electric field direction. It has been established that such a cleaning process suppresses the subsequent biofouling of ion-exchange membranes. In addition, selective recovery of polyphenols with high antioxidant activity is possible.

Effect of Pulsed Electric Field on the Electrodialysis Performance of Phosphate-Containing Solutions

A comparative analysis of mass transfer characteristics and energy consumption was carried out for the electrodialysis recovery of P^V from of NaH₂PO₄ solutions and multicomponent (0.045 M Na_xH_(3-x)PO₄, 0.02 M KCl, 0.045 M KOH, 0.028 M CaCl₂, and 0.012 M MgCl₂, pH 6.0 ± 0.1) solution in conventional continuous current (CC) and pulsed electric field (PEF) modes. The advantages of using PEF in comparison with CC mode are shown to increase the current efficiency and reduce energy consumption, as well as reduce scaling on heterogeneous anion-exchange membranes. It has been shown that PEF contributes to the suppression of the "acid dissociation" phenomenon, which is specific for anion-exchange membranes in phosphate-containing solutions. Pulse and pause lapse 0.1 s-0.1 s and duty cycle 1/2 were found to be optimal among the studied PEF parameters.

Application and Visualization of Fluorescent-Tagged Antiscalants in Electrodialysis Processing of Aqueous Solutions Prone to Gypsum Scale Deposition

Membrane scaling is a serious problem in electrodialysis. A widely used technique for controlling scale deposition in water treatment technologies is the application of antiscalants (AS). The present study reports on gypsum scale inhibition in electrodialysis cell by the two novel ASs: fluorescent-tagged bisphosphonate 1-hydroxy-7-(6-methoxy-1,3-dioxo-1Hbenzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyl-bis(phosphonic acid), HEDP-F and fluorescein-tagged polyacrylate, PAA-F2 (molecular mass 4000 Da) monitored by chronopotentiometry and fluorescent microscopy. It was found that cation-exchange membrane MK-40 scaling is sufficiently reduced by both ASs, used in 10^-6 mol·dm^-3 concentrations. PAA-F2 at these concentrations was found to be more efficient than HEDP-F. At the same time, PAA-F2 reveals gypsum crystals' habit modification, while HEDP-F does not noticeably affect the crystal form of the deposit. The strong auto-luminescence of MK-40 hampers visualization of both PAA-F2 and HEDP-F on the membrane surface. Nevertheless, PAA-F2 is proved to localize partly on the surface of gypsum crystals as a molecular adsorption layer, and to change their crystal habit. Crystal surface coverage by PAA-F2 appears to be nonuniform. Alternatively, HEDP-F localizes on the surface of a deposit tentatively in the form of [Ca-HEDP-F]. The proposed mechanisms of action are formulated and discussed. The application of antiscalants in electrodialysis for membrane scaling mitigation is demonstrated to be very promising.

Anaerobic swine digestate valorization via energy-efficient electrodialysis for nutrient recovery and water reclamation

The development of cost-effective and energy-efficient technologies to recover nutrients from digestate is important. Anaerobic digestate can be concentrated into bio-nutrient products through an electrodialysis (ED) process in an energy-efficient manner. Despite recent advances, the operation modes of ED for nutrient recovery from swine digestate are yet to be systematically evaluated from the perspective of energy-water efficiencies, and the determination of optimal operations in ED units is still ambiguous. In this study, two different operating modes of electrodialysis, i.e., constant voltage and constant current, are designed to evaluate the energy efficiency and effectiveness of nutrient recovery from anaerobic swine digestate. The ion removal ratio and current efficiency of the different modes and their associated electromigration performance (e.g., rate constants) are evaluated. The results indicate that the maximum removal efficiency (in terms of electrical conductivity) is 92.8% at a cell voltage of 2.4 V/cell using the constant voltage operation. The current efficiencies of NH₄⁺ (43‒65%) are higher than that of other ions, such as K⁺ (12‒19%), Cl^- (4‒7%), and PO₄^3- (0.1‒1.5%). For nitrogen recovery, the required energy consumption was about 0.24‒15.2 kWh/kg-N (0.86‒54.7 kJ/g-N), corresponding to a removal ratio of ammonium from 70.8% to 99.1%. Based on the experimental data, the optimal operating conditions are identified using response surface models by considering process energy consumption and productivity to deliver energy-efficient nutrient separation. One candidate of the ideal conditions to achieve the total ion removal of ∼93% should be operated at a constant cell voltage of 1.15 V, corresponding to a productivity of 5.24 gal/hr/m² at an energy consumption of 0.44 kWh/m³. Last, a conceptual design of cascading separation processes is proposed for digestate valorization as biofertilizers, nutrients, organic acids, and reclaimed water. A preliminary benefit-cost evaluation is then performed to evaluate the engineering and economic performance of the developed process for nutrient recovery from swine digestate. This article provides insight into practical large-scale applications of digestate valorization through energy-efficient separation, thereby realizing a circular economy system and a decarbonizing supply chain of bio-nutrients.

Electrochemical phosphorus leaching from digested anaerobic sludge and subsequent nutrient recovery

With the rising concern over the depletion of phosphorus rock, phosphorus recovery from wastewater has become a key step for sustainable economy. Herein, simultaneous phosphorus leaching and nutrient recovery were accomplished in an electrochemical nutrient recovery cell (ENRC) treating digested anaerobic sludge. The anode reaction of water electrolysis lowered the sludge pH from 8.0 to 2.0 at a current density of 25 A m^-2, elevating the PO₄^3--P concentration from 27.72 to 253.47 mg L^-1, comparable to that from direct acid leaching. The released PO₄^3--P was transferred to the cathode chamber for recovery, where PO₄^3--P recovery efficiency was enhanced from 42.0% to 90.3% by 0.26 M HCl catholyte acidification. The ENRC recovered 90-98% of the coexisting NH₄⁺-N in the sludge. Increasing current density accelerated both phosphorus leaching and PO₄^3--P & NH₄⁺-N recovery, but at the expense of a higher energy consumption. After five consecutive cycles of operation, the PO₄^3--P and NH₄⁺-N concentrations reached 404.56 and 3493.56 mg L^-1, respectively, at a normalized energy consumption of 229.20 ± 30.13 kWh kg^-1 P or 25.67 ± 3.07 kWh kg ^-1 N. At pH 8.5, 99% of the recovered aqueous PO₄^3--P in the recovery solution precipitated, mainly as calcium phosphate that can have a good soil phosphorus availability. The results of this study have provided a foundation for further exploration of electrochemically leaching P from waste sludge with simultaneous nutrient recovery.

Recovery of Nutrients from Residual Streams Using Ion-Exchange Membranes: Current State, Bottlenecks, Fundamentals and Innovations

The review describes the place of membrane methods in solving the problem of the recovery and re-use of biogenic elements (nutrients), primarily trivalent nitrogen N^III and pentavalent phosphorus P^V, to provide the sustainable development of mankind. Methods for the recovery of NH₄⁺ − NH₃ and phosphates from natural sources and waste products of humans and animals, as well as industrial streams, are classified. Particular attention is paid to the possibilities of using membrane processes for the transition to a circular economy in the field of nutrients. The possibilities of different methods, already developed or under development, are evaluated, primarily those that use ion-exchange membranes. Electromembrane methods take a special place including capacitive deionization and electrodialysis applied for recovery, separation, concentration, and reagent-free pH shift of solutions. This review is distinguished by the fact that it summarizes not only the successes, but also the “bottlenecks” of ion-exchange membrane-based processes. Modern views on the mechanisms of NH₄⁺ − NH₃ and phosphate transport in ion-exchange membranes in the presence and in the absence of an electric field are discussed. The innovations to enhance the performance of electromembrane separation processes for phosphate and ammonium recovery are considered.

Recovery of nitrogen and phosphorus from livestock slurry with treatment technologies: A meta-analysis

The livestock industry has developed rapidly in recent decades, but the improper treatment of livestock manure, especially slurry, causes environmental pollution. Treatment technologies are considered to be effective in alleviating nitrogen (N) and phosphorus (P) losses from livestock slurry. Here, we used published research data to conduct a meta-analysis of the recovery efficiencies of N and P of five mainstream treatment technologies, including ammonia stripping, air scrubbing, membrane filtration, microalgae cultivation and struvite crystallization. Additionally, the agronomic effects of the recovered products of these treatment technologies were evaluated. The results showed that all technologies exhibited clear recovery effects on N and P. The N recovery efficiencies ranged from 57% to 86%, and those of P ranged from 64% to 87%. Struvite crystallization was the most efficient treatment technology for both N and P recovery; moreover, the ammonia stripping and microalgae cultivation technologies were less efficient. The pH levels and temperatures are the main factors that influence ammonia stripping, struvite crystallization and microalgae cultivation, while membrane filtration and air scrubbing are mainly affected by the membrane types and properties. When the equal amount of N or P input to fields, the recovered products (ammonium sulfate and struvite crystals) may achieve a similar crop yield, relative to commercial N or P fertilizers. Our findings can provide deep suggestions and parameters for designing proper treatment technologies to reduce nutrient discharge from livestock slurry in regions with high livestock density and also for identifying the research gaps that should be paid more attention in the future.

Phosphorus recovery from wastewater and bio-based waste: an overview

Phosphorus is one of the most important macronutrients needed for the growth of plants. The fertilizer production market uses 80% of natural, non-renewable phosphorus resources in the form of phosphate rock. The depletion of those deposits forces a search for other alternatives, including biological waste. This review aims to indicate the most important ways to recover phosphorus from biowaste, with particular emphasis on wastewater, sewage sludge, manure, slaughter or food waste. A comparison of utilized methods and directions for future research based on the latest research is presented. Combining biological, chemical, and physical methods with thermal treatment appears to be the most effective way for the treatment of wastewater sludge in terms of phosphorus recovery. Hydrothermal, thermochemical, and adsorption on thermally treated adsorbents are characterized by a high phosphorus recovery rate (over 95%). For animal by-products and other biological waste, chemical methods seems to be the most optimal solution with a recovery rate over 96%. Due to its large volume and relatively low phosphorus content, wastewater is a resource that requires additional treatment to recover the highest possible amount of phosphorus. Pretreatment of wastewater with combined methods seems to be a possible way to improve phosphorus recovery. A compressive evaluation of combined methods is crucial for future research in this area.

Emerging electrochemistry-based process for sludge treatment and resources recovery: A review

The electrochemical process is gaining widespread interest as an emerging alternative for sludge treatment. Its potentials for sludge stabilization and resources recovery have been well proven to date. Despite the high effectiveness of the electrochemical process having been highlighted in several studies, concerns about the electrochemical sludge treatment, including energy consumption, scale-up feasibility, and electrode stability, have not yet been addressed. The present paper critically reviews the versatile uses of the electrochemical processes for sludge treatment and resource recovery, from the fundamentals to the practical applications. Particularly considered are the enhancement of the digestion of the anaerobic sludge and dewaterability, removal of pathogens and heavy metals, and control of sludge malodor. In addition, the opportunities and challenges of the sludge-based resource recovery (i.e., nitrogen, phosphorus, and volatile fatty acids) are discussed. Insights into the working mechanisms (e.g., electroporation, electrokinetics and electrooxidation) of electrochemical processes are reviewed, and perspectives and future research directions are proposed. This work is expected to provide an in-depth understanding and broaden the potential applications of electrochemical processes for sludge treatment and resource recovery.

A Review on Ion-Exchange Membranes Fouling during Electrodialysis Process in Food Industry, Part 2: Influence on Transport Properties and Electrochemical Characteristics, Cleaning and Its Consequences

Ion-exchange membranes (IEMs) are increasingly used in dialysis and electrodialysis processes for the extraction, fractionation and concentration of valuable components, as well as reagent-free control of liquid media pH in the food industry. Fouling of IEMs is specific compared to that observed in the case of reverse or direct osmosis, ultrafiltration, microfiltration, and other membrane processes. This specificity is determined by the high concentration of fixed groups in IEMs, as well as by the phenomena inherent only in electromembrane processes, i.e., induced by an electric field. This review analyzes modern scientific publications on the effect of foulants (mainly typical for the dairy, wine and fruit juice industries) on the structural, transport, mass transfer, and electrochemical characteristics of cation-exchange and anion-exchange membranes. The relationship between the nature of the foulant and the structure, physicochemical, transport properties and behavior of ion-exchange membranes in an electric field is analyzed using experimental data (ion exchange capacity, water content, conductivity, diffusion permeability, limiting current density, water splitting, electroconvection, etc.) and modern mathematical models. The implications of traditional chemical cleaning are taken into account in this analysis and modern non-destructive membrane cleaning methods are discussed. Finally, challenges for the near future were identified.

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs' lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated.

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.

The Application of Cation Exchange Membranes in Electrochemical Systems for Ammonia Recovery from Wastewater

Electrochemical processes are considered promising technologies for ammonia recovery from wastewater. In electrochemical processes, cation exchange membrane (CEM), which is applied to separate compartments, plays a crucial role in the separation of ammonium nitrogen from wastewater. Here we provide a comprehensive review on the application of CEM in electrochemical systems for ammonia recovery from wastewater. Four kinds of electrochemical systems, including bioelectrochemical systems, electrochemical stripping, membrane electrosorption, and electrodialysis, are introduced. Then we discuss the role CEM plays in these processes for ammonia recovery from wastewater. In addition, we highlight the key performance metrics related to ammonia recovery and properties of CEM membrane. The limitations and key challenges of using CEM for ammonia recovery are also identified and discussed.

Application of membrane separation processes in phosphorus recovery: A review

The depletion of phosphorus resources and the excess discharge of phosphorus into waste streams are contrasting problems. The key to solving both problems is to recover phosphorus from the waste streams. Current phosphorus recovery technologies require high phosphorus concentrations and lack the ability to separate toxic substances from recovered phosphorus products. Membrane separation processes such as nanofiltration, forward osmosis, and electrodialysis are examples of effective methods for solving some of these issues. In this paper, the mechanisms, performance, and influential factors affect phosphorus recovery from membrane separation are reviewed. Membrane fouling, energy consumption, and the selectivity of toxic substances in membrane separation processes were evaluated. This work will serve as a basis for future research and development of phosphorus recovery by membrane separation processes and as a response to the increasingly pressing issues of eutrophication and the growing depletion of phosphorus resources.

Quantitative recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate via industrial strategy for sustainable biomass processing

Quantitative recovery is necessary for scale-up application of acidic ionic liquids (AILs). Ultrafiltration and bipolar membrane electrodialysis (BMED) was employed for the recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate (Bmim[HSO₄]) after biomass pretreatment. Ultrafiltration was designed for the purification of BMED feed solution. During BMED treatment, Bmim⁺ retention with OH^- generation occurred in mixing section and SO₄^2- immigration with H⁺ generation occurred in aciding section. Resulting aqueous Bmim[OH] in mixing section and H₂SO₄ in aciding section could be utilized for quantitative synthesis of Bmim[HSO₄]. Influence of BMED operating mode and major parameters including BMED feed concentration and current density of BMED module were studied in detail. The highest recovery ratio for Bmim⁺ and SO₄^2- reached 96.2% and 96.0%. And the lowest energy consumption of specific Bmim[HSO₄] recovery approached 9.0 kw∙h/kg. Insight gained from this study suggested a sustainable biomass processing methodology using AILs.

Treatment of Manure and Digestate Liquid Fractions Using Membranes: Opportunities and Challenges

Manure and digestate liquid fractions are nutrient-rich effluents that can be fractionated and concentrated using membranes. However, these membranes tend to foul due to organic matter, solids, colloids, and inorganic compounds including calcium, ammonium, sodium, sulfur, potassium, phosphorus, and magnesium contained in the feed. This review paper is intended as a theoretical and practical tool for the decision-making process during design of membrane-based systems aiming at processing manure liquid fractions. Firstly, this review paper gives an overview of the main physico-chemical characteristics of manure and digestates. Furthermore, solid-liquid separation technologies are described and the complexity of the physico-chemical variables affecting the separation process is discussed. The main factors influencing membrane fouling mechanisms, morphology and characteristics are described, as well as techniques covering membrane inspection and foulant analysis. Secondly, the effects of the feed characteristics, membrane operating conditions (pressure, cross-flow velocity, temperature), pH, flocculation-coagulation and membrane cleaning on fouling and membrane performance are presented. Finally, a summary of techniques for specific recovery of ammonia-nitrogen, phosphorus and removal of heavy metals for farm effluents is also presented.

Transport Characteristics of CJMAED™ Homogeneous Anion Exchange Membranes in Sodium Chloride and Sodium Sulfate Solutions

The interplay between the ion exchange capacity, water content and concentration dependences of conductivity, diffusion permeability, and counterion transport numbers (counterion permselectivity) of CJMA-3, CJMA-6 and CJMA-7 (Hefei Chemjoy Polymer Materials Co. Ltd., China) anion-exchange membranes (AEMs) is analyzed using the application of the microheterogeneous model to experimental data. The structure-properties relationship for these membranes is examined when they are bathed by NaCl and Na2SO4 solutions. These results are compared with the characteristics of the well-studied homogenous Neosepta AMX (ASTOM Corporation, Japan) and heterogeneous AMH-PES (Mega a.s., Czech Republic) anion-exchange membranes. It is found that the CJMA-6 membrane has the highest counterion permselectivity (chlorides, sulfates) among the CJMAED series membranes, very close to that of the AMX membrane. The CJMA-3 membrane has the transport characteristics close to the AMH-PES membrane. The CJMA-7 membrane has the lowest exchange capacity and the highest volume fraction of the intergel spaces filled with an equilibrium electroneutral solution. These properties predetermine the lowest counterion transport number in CJMA-7 among other investigated AEMs, which nevertheless does not fall below 0.87 even in 1.0 eq L-1 solutions of NaCl or Na2SO4. One of the reasons for the decrease in the permselectivity of CJMAED membranes is the extended macropores, which are localized at the ion-exchange material/reinforcing cloth boundaries. In relatively concentrated solutions, the electric current prefers to pass through these well-conductive but nonselective macropores rather than the highly selective but low-conductive elements of the gel phase. It is shown that the counterion permselectivity of the CJMA-7 membrane can be significantly improved by coating its surface with a dense homogeneous ion-exchange film.

Fouling of ion exchange membranes used in the electrodialysis reversal advanced water treatment: A review

Electrodialysis self-reversal (EDR) technology has attracted in the treatment of water for domestic and industrial uses. The self-reversal consists of a frequent reversal of the direction of current between the EDR-cell electrodes to combat fouling of ion exchange membranes (IEMs). Irrespective of the EDR self-cleaning processes, the role of natural organic matter and their complexing ability with metal ions on IEMs fouling is partially understood. The objective of this review is to identify the research gaps present in the elucidation of IEM fouling routes. The common IEMs' foulants are identified, and several fouling mechanisms are briefly discussed. The effectiveness of self-cleaning mechanisms to reduce IEMs fouling is also be discussed. Dissolved organic carbon (DOC) possesses high chelation which forms metal complexes with di and trivalent cations found in water. The role of ternary complexes, e.g. M^2+/3+-DOC and membrane surface, on membrane fouling via surface bridging, are also addressed. Finally, mitigation methods of IEMs membrane fouling are also discussed.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Effect of Pretreatment on Hydraulic Performance of the Integrated Membrane Process for Concentrating Nutrient in Biogas Digestate from Swine Manure

Nanofiltration (NF) or reverse osmosis (RO) process has been widely applied for concentrating nutrient in biogas digestate. However, efficient pretreatment is key to the sustainable operation of NF or RO. In this study, the combination of NF and RO for concentrating biogas digestate was compared using different pretreatments of hollow fiber ultrafiltration membrane (HFUFM) and ceramic membrane (CUFM). Pilot-scale batch tests were conducted (500 L). CUFM showed a higher membrane flux than HFUFM (100 ~ 180 L·(m²·h)⁻¹ vs. 17 ~ 35 L·(m²·h)⁻¹), but they showed little impact on the NF + RO process. Membrane fluxes of NF and RO were 20 ~ 48 L·(m²·h)⁻¹ and 16 ~ 40 L·(m²·h)⁻¹, respectively. In the RO permeates, the removal rates of total suspended solids (TSS), total solids (TS), chemical oxygen demand (COD), total nitrogen (TN), NH₄⁺-N, and Cl⁻ were above 91%. In the concentrates, TN and total potassium (TK) were concentrated by 1.60 and 2.00 folds in the NF stage, and by 2.10 and 2.30 folds in the RO stage. Further attention should be paid to the antibiotics risks in the concentrates before they are utilized as plant fertilizers.

Nutrient Capture from Aqueous Waste and Photocontrolled Fertilizer Delivery to Tomato Plants Using Fe(III)-Polysaccharide Hydrogels

Inexpensive and sustainable methods are needed to reclaim nutrients from agricultural waste solutions for use as a fertilizer while decreasing nutrient runoff. Fe(III)-polysaccharide hydrogels are able to flocculate solids and absorb nutrients in liquid animal waste from Confined Animal Feeding Operations (CAFOs). Fe(III)-alginate beads absorbed 0.05 mg g-1 NH4 + and NO3 - from 100 ppm solutions at pH = 7, with > 80% phosphate uptake and ∼30% uptake of ammonium and nitrate. Ammonium uptake from a raw manure solution (1420 ppm NH4 +) showed a significant 0.7 mg g-1 uptake. Tomato plant trials carried out with Fe(III)-alginate hydrogel beads in greenhouse conditions showed controlled nutrient delivery for the plants compared to fertilizer solution with the same nutrient content. Plants showed an uptake of Fe from the gel beads, and Fe(III)-alginate hydrogel beads promoted root growth of the plants. The plants treated with nutrient-loaded Fe(III)-alginate hydrogels yielded comparable tomato harvest to plants treated with the conventional fertilizer solution.

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and other treatments with significant environmental benefits. ED technologies can be used in operations of concentration, dilution, desalination, regeneration, and valorisation to reclaim wastewater and recover water and/or other products, e.g., heavy metal ions, salts, acids/bases, nutrients, and organics, or electrical energy. Intense research activity has been directed towards developing enhanced or novel systems, showing that zero or minimal liquid discharge approaches can be techno-economically affordable and competitive. Despite few real plants having been installed, recent developments are opening new routes for the large-scale use of ED techniques in a plethora of treatment processes for wastewater.

The Development of Electroconvection at the Surface of a Heterogeneous Cation-Exchange Membrane Modified with Perfluorosulfonic Acid Polymer Film Containing Titanium Oxide

One way to enhance mass transfer and reduce fouling in wastewater electrodialysis is stimulation of electroconvective mixing of the solution adjoining membranes by modifying their surfaces. Several samples were prepared by casting the perfluorosulfonic acid (PFSA) polymer film doped with TiO₂ nanoparticles onto the surface of the heterogeneous cation-exchange membrane MK-40. It is found that changes in surface characteristics conditioned by such modification lead to an increase in the limiting current density due to the stimulation of electroconvection, which develops according to the mechanism of electroosmosis of the first kind. The greatest increase in the current compared to the pristine membrane can be obtained by modification with the film being 20 μm thick and containing 3 wt% of TiO₂. The sample containing 6 wt% of TiO₂ provides higher mass transfer in overlimiting current modes due to the development of nonequilibrium electroconvection. A 1.5-fold increase in the thickness of the modifying film reduces the positive effect of introducing TiO₂ nanoparticles due to (1) partial shielding of the nanoparticles on the surface of the modified membrane; (2) a decrease in the tangential component of the electric force, which affects the development of electroconvection.

Non-biological methods for phosphorus and nitrogen removal from wastewater: A gap analysis of reinvented-toilet technologies with respect to ISO 30500

The aims of the Reinvent the Toilet Challenge (RTTC) include creation of an off-the-grid sanitation system with operating costs of less than US$0.05 per user per day. Because of the small scale at which many reinvented toilets (RT) are intended to operate, non-biological treatment has been generally favored. The RTTC has already instigated notable technological advances in non-sewered sanitation systems (NSSS). However, increasingly stringent liquid effluent standards for N and P could limit the deployment of current RT in real-world scenarios, despite the urgent need for these systems. The newly adopted ISO 30500 standards for water reuse in NSSS dictate minimal use of chemical/biological additives, while at the same time requiring a 70% and 80% reduction in total nitrogen and phosphorus, respectively. This document provides a brief overview of the mature and emerging technologies for N and P (specifically ammonia/ammonium and orthophosphate) removal from wastewater. At present, the dearth of nutrient removal methods proven to be effective at small scales is a significant barrier to meeting ISO 30500 standards. Closing the gap between RTs and ISO 30500 will require significant investments in basic R&D of emerging technologies for non-biological N and P remediation and/or increased reliance on biological processes. Adaptation of existing nutrient-removal technologies to small-scale NSSS is a viable option that merits additional investigation.