Using selectivity to evaluate aqueous- and resin-phase denitrification during biological ion exchange.

An increased fertilizer application for agricultural purposes has resulted in increased nitrate (NO3-) levels in surface water and groundwater around the globe, highlighting demand for a low-maintenance NO3- treatment technology that can be applied to nonpoint sources. Ion exchange (IEX) is an effective NO3- treatment technology and research has shown that bioregeneration of NO3- laden resins has the potential to minimize operational requirements and brine waste production that often prevents IEX application for decentralized treatment. In this work, batch denitrification experiments were conducted using solutions with low IEX selectivity capable of supporting the growth of denitrifying bacteria, while minimizing NO3- desorption from resins, encouraging resin-phase denitrification. Although only 15% of NO3- was desorbed by the low selectivity solution, this initial desorption started a cycle in which desorbed NO3- was biologically transformed to NO2-, which further desorbed NO3- that could be biotransformed. Denitrification experiments resulted in a 43% conversion rate of initially adsorbed NO3-, but biotransformations stopped at NO2- due to pH limitations. The balance between adsorption equilibria and biotransformation observed in this work was used to propose a continuous-flow reactor configuration where gradual NO3- desorption might allow for complete denitrification in the short retention times used for IEX systems.

Solar distillation of human urine to recover non-potable water and metal phosphate mineral.

Human urine is a readily available nutrient source that can complement commercial fertilizer production, which relies on finite mineral resources and global supply chains. This study evaluated the effectiveness of a simplified solar distillation process for urine to recover phosphorus (P) and nitrogen for agricultural use and water for non-potable purposes. Synthetic fresh, synthetic hydrolyzed, real fresh, and real hydrolyzed urine were exposed to direct sunlight for 6 h in a simple distillation apparatus, which produced distillation bottoms and distillate. Metal phosphate precipitation in the distillation bottoms was evaluated to recover P. The non-potable water was recovered as distillate. Hydrolyzed urine recovered more metal phosphate solid in the distillation bottoms and had a higher conductivity in the distillate than fresh urine. Hydrolyzed urine also achieved greater distillate volume recovery than fresh urine. Hydrolyzed urine had a greater presence of UV-absorbing organics in the distillate than fresh urine and therefore produced a lower-quality product water. There was no significant correlation between the daily high air temperature and the volume of distillate recovered. This study provides a comprehensive data set on simplified solar distillation of human urine considering the fate of nutrients and water for different types of urine.

A transition management framework to stimulate a circular phosphorus system.

As the global population is projected to increase by two billion people by 2050, so will the demand for phosphorus (P), an essential nutrient for all living organisms and a major driver of eutrophication. To sustainably meet these challenges, we apply the conceptual framework of transition management (TM) to demonstrate how the trajectory of the current linear P use system could be strategically shifted toward a more circular P system. We present US case studies to examine P transitions management in intensive agriculture, wastewater disposal, and food waste management. Our goal is twofold. By first understanding past transitions in P management in the USA, we can build upon these insights for future management. This can then be applied to other global regions such as developing countries to bypass stages of transition as they intensify agriculture, incorporate sewers into cities, and expand waste management, to avoid becoming entrenched in unsustainable P management. We suggest how spaces for experimentation and collaboration can be created, how and which actor networks can be mobilized, and what action strategies and policies can be recommended to accelerate their transition to P sustainability. Our case studies show that while substantial improvements have been made, the transition toward a circular economy of P is far from complete. Our findings point to the value of utilizing TM for future progress in the US Development of TM frameworks for managing P in other regions of the world may enable them to achieve sustainable P development faster and more effectively than the USA.

Removal of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) Using Ion-Exchange and Nonionic Resins.

Despite benefits to the firefighting industry, the release of per- and polyfluoroalkyl substances (PFASs) from aqueous film-forming foam (AFFF) into aquatic systems poses significant risks to human health and other organisms. While anion-exchange technologies have proven to be effective for removing perfluoroalkyl acids (PFAAs) from water, their effectiveness for removing the diverse PFAS structures discovered in AFFF remains unknown. Here, we report on the adsorption of 75 PFASs, including 63 polyfluorinated substances, in a diluted AFFF mixture using 14 commercially available ion-exchange (IX)/nonionic resins and granular activated carbon (GAC). Results showed that anion-exchange resins (AERs) exhibited significant adsorption of PFASs compared to cation-exchange resins (CERs), nonionic resins (NIRs), and GAC regardless of the PFAS's predicted charge. Isotherm data showed that macroporous AERs have a higher PFAS adsorption capacity compared to gel-type AERs. Cross-correlation comparison of PFAS/Cl- selectivity coefficients (Kex) for each PFAS-AER combination showed that the hydrophobicity of the AER functional group, and polymer matrix played a dominant role in determining resin affinity for PFASs. PFAS structural characteristics also significantly affected adsorption, with increasing chain length and a net negative charge increasing the extent of adsorption. Results from this study provide guidelines for the selection of resins to adsorb a wider range of PFASs and meaningful insights for the development of quantitative models for IX treatment of AFFF-impacted water.

Opportunities for Building-Scale Urine Diversion and Challenges for Implementation.

Urine diversion (i.e., urine source separation) has been proposed as a more sustainable solution for water conversation, nutrient removal and recovery, and pharmaceutical sequestration. As wastewater regulations become more stringent, wastewater treatment plants reach capacity, and water resources become more strained, the benefits of urine diversion become more appealing. By using nonwater urinals and urine-diverting toilets, urine diversion systems seek to collect undiluted human urine for nutrient recovery and pharmaceutical sequestration. Urine is a unique, nutrient-rich waste stream that constitutes an overall low volume of waste entering a wastewater treatment plant. If urine is separated at the building-scale, various technologies can be used to recover nutrients and sequester pharmaceuticals at their most concentrated location. However, the implementation of urine diversion requires a paradigm shift from conventional comingling of wastewater and centralized treatment to source separation and decentralized treatment. This Account proposes a vision for building-scale implementation of urine diversion with the goal of clarifying the opportunities and challenges in this context. The main components of urine, i.e., nitrogen, phosphorus, potassium, and pharmaceuticals, are major drivers for technology development and system implementation. Stepping back, the benefits from water conservation and effects on wastewater treatment are an extension of the system boundary that can impact the sustainability of adjacent systems. However, major challenges have been identified in the literature as hurdles for widespread implementation of urine diversion. Challenges include the comparison of recovering nutrients at the wastewater plant versus at the source, the collection and storage of urine, the ability to recover nutrients and sequester pharmaceuticals, and the overall environmental and economic impacts of urine diversion systems. While these challenges exist, studies have been conducted to address some of the underlying research questions. As more research is conducted, the vision of a seamless urine diversion system with building-wide plumbing and storage comes closer to reality. As such, the application of urine diversion systems will benefit from technology development and research to fill gaps that have been identified. It is important to classify urine diversion systems as a process and not a product. This has implications for the way these systems are evaluated, as their impact on peripheral systems can be of benefit to different stakeholders. In the same light, new research areas, such as cyber-physical systems, reverse logistics, and sustainability transitions, can be applied to urine diversion as approaches for ensuring a robust process for widespread implementation. However, established technologies should be constantly reassessed and enhanced by newer techniques. For example, membrane distillation, eutectic freeze concentration, and solar evaporation should be considered for nutrient recovery and volume reduction because they offer benefits over conventional technologies. Finally, the human behavior component of urine diversion cannot be ignored, as negative user acceptance and improper maintenance of these systems can have a detrimental impact on their future implementation.

Ammonia Recovery from Hydrolyzed Human Urine by Forward Osmosis with Acidified Draw Solution.

Forward osmosis (FO) is a low-pressure membrane process that can selectively separate low molecular weight neutral compounds such as ammonia from urine. However, an understanding of how un-ionized ammonia transfers is vital for maximizing ammonia recovery. Therefore, this research aimed to determine the transport behavior of low molecular weight neutral nitrogen compounds in order to maximize ammonia recovery from real hydrolyzed human urine by FO. Using urea as a model, batch FO experiments concluded that low molecular weight neutral compound transfer is dependent on concentration equilibrium between the feed and draw solutions due to its ability to freely move across the FO membrane. Therefore, 50% recovery is the theoretical maximum that could be achieved. However, novel strategic pH manipulation between the feed and the draw solution allowed for up to 86% recovery of ammonia by keeping the draw solution pH < 6.5 and the feed solution pH > 11, overcoming the 50% recovery barrier. An economic analysis showed that ammonia recovery by FO has the potential to be more economically favorable compared to ammonia air stripping or ion exchange if the proper draw solute is chosen.

Real-Time Monitoring and Control of Urea Hydrolysis in Cyber-Enabled Nonwater Urinal System.

This research used a cyber-physical system (CPS) to monitor and control the extent of urea hydrolysis in nonwater urinals. Real-time pH and conductivity data were used to control urea hydrolysis inhibition under realistic restroom conditions with acetic acid addition. Variable urination frequencies and urination volumes were used to compare three conditions that affect the progression of urea hydrolysis. Mechanistic and conceptual models were created to evaluate the factors that influence the progression of urea hydrolysis in nonwater urinals. It was found that low urination volumes at low frequencies created ideal conditions for urea hydrolysis to progress. Alternatively, high urination volumes at high frequencies created pseudo-inhibitory conditions because it did not allow for sufficient reaction time or mixing with older urine in the urinal trap. The CPS was used to control urea hydrolysis inhibition by two logics: (1) reactively responding to a pH threshold and (2) predictively responding to past measurements using four lasso regression models. Results from the control logic experiments showed that acid was added once per hour under low use conditions and once in a 4 h experiment for high use conditions. The CPS allowed for full control of urine chemistry in the nonwater urinal, reducing the conditions (i.e., clogging and malodor) that have led to the removal of nonwater urinals in the United States.

Managing Diffuse Phosphorus at the Source versus at the Sink.

Judicious phosphorus (P) management is a global grand challenge and critical to achieving and maintaining water quality objectives while maintaining food production. The management of point sources has been successful in lowering P inputs to aquatic environments, but more difficult is reducing P discharges associated with diffuse sources, such as nonpoint runoff from agriculture and urban landscapes, as well as P accumulated in soils and sediments. Strategies for effective diffuse-P management are imperative. Many options are currently available, and the most cost-effective and practical choice depends on the local situation. This critical review describes how the metrics of P quantity in kg ha-1 yr-1 and P form can influence decision-making and implementation of diffuse-P management strategies. Quantifying the total available pool of P, and its form, in a system is necessary to inform effective decision-making. The review draws upon a number of " current practice" case studies that span agriculture, cities, and aquatic sectors. These diverse examples from around the world highlight different diffuse-P management approaches, delivered at the source in the catchment watershed or at the aquatic sink. They underscore workable options for achieving water quality improvement and wider P sustainability. The diffuse-P management options discussed in this critical review are transferable to other jurisdictions at the global scale. We demonstrate that P quantity is typically highest and most concentrated at the source, particularly at farm scale. The most cost-effective and practically implementable diffuse-P management options are, therefore, to reduce P use, conserve P, and mitigate P loss at the source. Sequestering and removing P from aquatic sinks involves increasing cost, but is sometimes the most effective choice. Recovery of diffuse-P, while expensive, offers opportunity for the circular economy.

Fixed Bed Modeling of Nonsteroidal Anti-Inflammatory Drug Removal by Ion-Exchange in Synthetic Urine: Mass Removal or Toxicity Reduction?

Ion-exchange removal of nonsteroidal anti-inflammatory drugs (NSAIDs) in synthetic urine can selectively remove pharmaceuticals with minimal coremoval of nutrients to enhance nutrient recovery efforts. However, the effect of endogenous metabolites in urine on ion-exchange removal, and the corresponding reduction in ecotoxicity potential of pharmaceuticals in treated urine entering the environment, is unknown. To assess treatment efficacy, this work paired predicted breakthrough curves determined by the homogeneous surface diffusion model to an in vitro bioassay to evaluate COX-1 inhibition. The presence of endogenous metabolites in urine significantly impacted pharmaceutical removal, by competing for ion-exchange sites on the resin and reducing the resin capacity for pharmaceuticals. This indicates ion-exchange would be ineffective at removing NSAIDs and other negatively charged compounds in urine. Due to hydrolysis of pharmaceutical metabolites back to the parent compound, treatment systems should be designed based on the ultimate pharmaceutical concentration in ureolyzed urine. Mass removal and COX-1 inhibition followed a nonlinear correlation and mixture toxicity followed the generalized concentration addition model. This work demonstrates the importance of evaluating removal of contaminants of emerging concern, such as pharmaceuticals, using a risk-based approach to ecotoxicity end points in conjunction with mass removal.

Mimicking and Inhibiting Urea Hydrolysis in Nonwater Urinals.

Nonwater urinals are critical in the implementation of building-scale water conservation and urine diversion systems. However, because of the composition of urine and the prevalence of the urease enzyme that hydrolyzes urea, minerals readily precipitate in nonwater urinals and pipes. This leads to clogging, malodor, and possible replacement of nonwater urinals with flush urinals. Accordingly, the goal of this research was to provide an improved understanding of the urea hydrolysis process in nonwater urinals to benefit water conservation and phosphate recovery efforts. Acetic acid addition was used in nonwater urinals to inhibit the urea hydrolysis reaction by lowering the pH, thereby making the precipitation of calcium- and magnesium-containing minerals less favorable. Of the acids tested, 2.5 mL of 2500 mequiv/L acetic acid added after every urination event was able to inhibit urea hydrolysis in synthetic urine and real urine as indicated by the pH and conductivity of the effluent urine. Acid addition also allowed for 43% more phosphate recovery via struvite precipitation in the acetic acid addition synthetic urine than the synthetic urine with no acid addition.

Total Value of Phosphorus Recovery.

Phosphorus (P) is a critical, geographically concentrated, nonrenewable resource necessary to support global food production. In excess (e.g., due to runoff or wastewater discharges), P is also a primary cause of eutrophication. To reconcile the simultaneous shortage and overabundance of P, lost P flows must be recovered and reused, alongside improvements in P-use efficiency. While this motivation is increasingly being recognized, little P recovery is practiced today, as recovered P generally cannot compete with the relatively low cost of mined P. Therefore, P is often captured to prevent its release into the environment without beneficial recovery and reuse. However, additional incentives for P recovery emerge when accounting for the total value of P recovery. This article provides a comprehensive overview of the range of benefits of recovering P from waste streams, i.e., the total value of recovering P. This approach accounts for P products, as well as other assets that are associated with P and can be recovered in parallel, such as energy, nitrogen, metals and minerals, and water. Additionally, P recovery provides valuable services to society and the environment by protecting and improving environmental quality, enhancing efficiency of waste treatment facilities, and improving food security and social equity. The needs to make P recovery a reality are also discussed, including business models, bottlenecks, and policy and education strategies.

Degradation of pharmaceuticals and metabolite in synthetic human urine by UV, UV/H2O2, and UV/PDS.

To minimize environmental pharmaceutical micropollutants, treatment of human urine could be an efficient approach due to the high pharmaceutical concentration and toxic potential excreted in urine. This study investigated the degradation kinetics and mechanisms of sulfamethoxazole (SMX), trimethoprim (TMP) and N4-acetyl-sulfamethoxazole (acetyl-SMX) in synthetic fresh and hydrolyzed human urines by low-pressure UV, and UV combined with H2O2 and peroxydisulfate (PDS). The objective was to compare the two advanced oxidation processes (AOPs) and assess the impact of urine matrices. All three compounds reacted quickly in the AOPs, exhibiting rate constants of (6.09-8.53) × 10(9) M(-1)·s(-1) with hydroxyl radical, and (2.35-16.1) × 10(9) M(-1)·s(-1) with sulfate radical. In fresh urine matrix, the pharmaceuticals' indirect photolysis was significantly suppressed by the scavenging effect of urine citrate and urea. In hydrolyzed urine matrix, the indirect photolysis was strongly affected by inorganic urine constituents. Chloride had no apparent impact on UV/H2O2, but significantly raised the hydroxyl radical concentration in UV/PDS. Carbonate species reacted with hydroxyl or sulfate radical to generate carbonate radical, which degraded SMX and TMP, primarily due to the presence of aromatic amino group(s) (k = 2.68 × 10(8) and 3.45 × 10(7) M(-1)·s(-1)) but reacted slowly with acetyl-SMX. Ammonia reacted with hydroxyl or sulfate radical to generate reactive nitrogen species that could react appreciably only with SMX. Kinetic simulation of radical concentrations, along with products analysis, helped elucidate the major reactive species in the pharmaceuticals' degradation. Overall, the AOPs' performance was higher in the hydrolyzed urine than fresh urine matrix with UV/PDS better than UV/H2O2, and varied significantly depending on pharmaceutical's structure.

Predictive capability of chlorination disinfection byproducts models.

There are over 100 models that have been developed for predicting trihalomethanes (THMs), haloacetic acids (HAAs), bromate, and unregulated disinfection byproducts (DBPs). Until now no publication has evaluated the variability of previous THM and HAA models using a common data set. In this article, the standard error (SE), Marquardt's percent standard deviation (MPSD), and linear coefficient of determination (R(2)) were used to analyze the variability of 87 models from 23 different publications. The most robust models were capable of predicting THM4 with an SE of 48 µg L(-1) and HAA6 with an SE of 15 µg L(-1), both achieving R(2) > 0.90. The majority of models were formulated for THM4. There is a lack of published models evaluating total HAAs, individual THM and HAA species, bromate, and unregulated DBPs.

Removal of urea in ultrapure water system by urease-coated reverse osmosis membrane.

Among the various substances found in the feed source for the production of ultrapure water (UPW), urea is challenging to remove because it is a small molecular weight molecule that is not easily oxidized and does not carry a charge under neutral pH conditions. Urease enzyme, found in various organisms such as plants and bacteria, catalyze the hydrolysis of urea into carbon dioxide and ammonia. In this study, urease was immobilized on the polyamide layer of a reverse osmosis (RO) membrane to remove urea in UPW systems. The removal efficiency of urea by urease-coated RO membrane showed up to 27.9 % higher urea removal efficiency compared to the pristine membrane. This increase in urea removal can be attributed to both physical and biological effects from the urease coating on the membrane. Firstly, urease on the membrane surface can act as an additional physical barrier for urea to pass through. Secondly, urea can be hydrolyzed by the enzyme when it passes through the urease-coated RO membrane. In a two-pass RO system typical for UPW production, the removal of urea by a urease-coated membrane would be enhanced by twofold. This overall method can significantly increase the removal efficiency of urea in UPW systems, especially when considering the compounded removal by the urease coating, rejection by RO, and additional reactions by other treatment processes. Moreover, urea in UPW systems can be removed without the installment of additional processes by simply coating urease on the existing RO membranes.

Electrochemical degradation of acetaminophen in urine matrices: Unraveling complexity and implications for realistic treatment strategies.

Urine has an intricate composition with high concentrations of organic compounds like urea, creatinine, and uric acid. Urine poses a formidable challenge for advanced effluent treatment processes following urine diversion strategies. Urine matrix complexity is heightened when dealing with pharmaceutical residues like acetaminophen (ACT) and metabolized pharmaceuticals. This work explores ACT degradation in synthetic, fresh real, and hydrolyzed real urines using electrochemical oxidation with a dimensional stable anode (DSA). Analyzing drug concentration (2.5 - 40 mg L-1) over 180 min at various current densities in fresh synthetic effluent revealed a noteworthy 75% removal at 48 mA cm-2. ACT degradation kinetics and that of the other organic components followed a pseudo-first-order reaction. Uric acid degradation competed with ACT degradation, whereas urea and creatinine possessed higher oxidation resistance. Fresh real urine presented the most challenging scenario for the electrochemical process. Whereas, hydrolyzed real urine achieved higher ACT removal than fresh synthetic urine. Carboxylic acids like acetic, tartaric, maleic, and oxalic were detected as main by-products. Inorganic ionic species nitrate, nitrite, and ammonium ions were released to the medium from N-containing organic compounds. These findings underscore the importance of considering urine composition complexities and provide significant advancements in strategies for efficiently addressing trace pharmaceutical contamination.

Benchmarks for urine volume generation and phosphorus mass recovery in commercial and institutional buildings.

Phosphorus (P) is a finite resource and necessary nutrient for agriculture. Urine contains a higher concentration of P than domestic wastewater, which can be recovered by source separation and treatment (hereafter urine diversion). Commercial and institutional (CI) buildings are a logical location for urine diversion since restrooms account for a substantial fraction of water use and wastewater generation. This study estimated the potential for P recovery from human urine and water savings from reduced flushing in CI buildings, and proposed an approach to identify building types and community layouts that are amenable to implementing urine diversion. The results showed that urine diversion is most advantageous in CI buildings with either high daily occupancy counts or times, such as hospitals, schools, office buildings, and airports. Per occupant P recovery benchmarks were estimated to be between 0.04-0.68 g/cap·d. Per building P recovery rates were estimated to be between 0.002-5.1 kg/d, and per building water savings were estimated to be between 3 and 23 % by volume. Recovered P in the form of phosphate fertilizer and potable water savings could accrue profits and cost reductions that could offset the capital costs of new urine diversion systems within 5 y of operation. Finally, urine diversion systems can be implemented at different levels of decentralization based on community layout and organizational structure, which will require socioeconomic and policy acceptance for wider adoption.

Life cycle assessment and life cycle cost analysis of anion exchange and granular activated carbon systems for remediation of groundwater contaminated by per- and polyfluoroalkyl substances (PFASs).

Anion exchange resin (AER) and granular activated carbon (GAC) have emerged as prominent technologies for treatment of waters contaminated with per- and polyfluoroalkyl substances (PFASs). This study compares the life cycle environmental impacts and life cycle costs of remediating PFAS-contaminated groundwater with these competing technologies, using field pilot data to inform model inputs. Comparative analysis indicates that AER systems employing single-use "PFAS-selective" resins have lower environmental impacts and costs than systems using regenerable resins or GAC adsorbents, supporting its use in future remediation efforts. Use of GAC operated as a single-use adsorbent led to the highest emissions as well as the highest treatment costs, with thermally-reactivated GAC proving to be less impactful than regenerable AER treatment. Sensitivity analyses highlighted the dominance of media usage rate (MUR), which is highly dependent on the selected PFAS treatment goals, to determine environmental impacts and costs over a 30-year system life cycle. Selection of very stringent changeout criteria (e.g., detection of any PFASs in effluent) significantly reduces the advantages of single-use resins. For regenerable AER, environmental impacts were dominated by management of the PFAS-contaminated brine/co-solvent waste stream used to regenerate the adsorbent, as well as the cosolvent content of the regenerant mixture and the cosolvent recovery efficiency achieved via on-site distillation. High impacts estimated for GAC adsorption, the result of high MUR relative to ion exchange media, can be significantly reduced if spent adsorbents are reused after thermal reactivation, but impacts are still greater than those predicted for single-use ion exchange systems. Findings are expected to hold across a range of diverse sites, including drinking water systems treating more dilute sources of PFAS contamination, as PFAS breakthrough was not found to be highly sensitive to sourcewater PFAS concentrations.

Perspective: Phosphorus monitoring must be rooted in sustainability frameworks spanning material scale to human scale.

Phosphorus (P) is a finite resource, and its environmental fate and transport is complex. With fertilizer prices expected to remain high for years and disruption to supply chains, there is a pressing need to recover and reuse P (primarily as fertilizer). Whether recovery is to occur from urban systems (e.g., human urine), agricultural soil (e.g., legacy P), or from contaminated surface waters, quantification of P in various forms is vital. Monitoring systems with embedded near real time decision support, so called cyber physical systems, are likely to play a major role in the management of P throughout agro-ecosystems. Data on P flow(s) connects the environmental, economic, and social pillars of the triple bottom line (TBL) sustainabilty framework. Emerging monitoring systems must account for complex interactions in the sample, and interface with a dynamic decision support system that considers adaptive dynamics to societal needs. It is known from decades of study that P is ubiquitous, yet without quantitative tools for studying the dynamic nature of P in the environment, the details may remain elusive. If new monitoring systems (including CPS and mobile sensors) are informed by sustainability frameworks, data-informed decision making may foster resource recovery and environmental stewardship from technology users to policymakers.

Alkaline earth metal cation exchange: effect of mobile counterion and dissolved organic matter.

The goal of this research was to provide an improved understanding of the interactions between alkaline earth metals and DOM under conditions that are encountered during drinking water treatment with particular focus on cation exchange. Both magnetically enhanced and nonmagnetic cation exchange resins were converted to Na, Mg, Ca, Sr, and Ba mobile counterion forms as a novel approach to investigate the exchange behavior between the cations and the interactions between the cations and DOM. The results show that cation exchange is a robust process for removal of Ca(2+) and Mg(2+) considering competition with cations on the resin surface and presence of DOM. DOM was actively involved during the cation exchange process through complexation, adsorption, and coprecipitation reactions. In addition to advancing the understanding of ion exchange processes for water treatment, the results of this work are applicable to membrane pretreatment to minimize fouling, treatment of membrane concentrate, and precipitative softening.

Behavior of reoccurring PARAFAC components in fluorescent dissolved organic matter in natural and engineered systems: a critical review.

Fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) has been widely used to characterize dissolved organic matter (DOM). Characterization is based on the intensity and location of independent fluorescent components identified in models constructed from excitation-emission matrices (EEMs). Similar fluorescent components have been identified in PARAFAC studies across a wide range of systems; however, there is a lack of discussion regarding the consistency with which these similar components behave. The overall goal of this critical review is to compare results for PARAFAC studies published since the year 2000 which include one or more of three reoccurring humic-like components. Components are compared and characterized based on EEM location, characteristic ecosystems, and behavior in natural and engineered systems. This synthesis allows PARAFAC users to more confidently infer DOM characteristics based on identified components. Additionally, behavioral inconsistencies between similar components help elucidate DOM properties for which fluorescence spectroscopy with PARAFAC may be a weak predictive tool.