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Several billion metric tons per year of durable carbon dioxide removal (CDR) will be needed by mid-century to prevent catastrophic climate warming, and many new approaches must be rapidly scaled to ensure this target is met. Geologically permanent sequestration of carbon dioxide (CO2) in carbonate minerals-carbon mineralization-requires two moles of alkalinity and one mole of a CO2-reactive metal such as calcium or magnesium per mole of CO2 captured. Chemical weathering of geological materials can supply both ingredients, but weathering reactions must be accelerated to achieve targets for durable CDR. Here, a scalable CDR and mineralization process is reported in which water electrolysis is used to produce sulfuric acid for accelerated weathering, while a base is used to permanently sequester CO2 from air into carbonate minerals. The process can be integrated into existing extractive processes by reacting produced sulfuric acid with critical element feedstocks that neutralize acidity (e.g., rock phosphorus or ultramafic rock mine tailings), with calcium- and magnesium-bearing sulfate wastes electrolytically upcycled. The highest reported efficiency of electrolytic sulfuric acid production is achieved by maintaining catholyte feed conditions that minimize Faradaic losses by hydroxide permeation of the membrane-separated electrochemical cell. The industrial implementation of this process provides a pathway to gigaton-scale CO2 removal and sequestration during the production of critical elements needed for decarbonizing global energy infrastructure and feeding the world.

We present the mass balances associated with carbon dioxide (CO2) removal (CDR) using seawater as both the source of reactants, and as the reaction medium via electrolysis following the “EquaticTM” (formerly known as “SeaChange”) process. The process involves the application of an overpotential that splits water to form H+ and OH– ions, producing acidity and alkalinity, i.e., in addition to gaseous co-products, at the anode and cathode, respectively. The alkalinity that results, i.e., via the “continuous electrolytic pH pump” results in the instantaneous precipitation of calcium carbonate (CaCO3), magnesium carbonates (Mg–CO3), and/or magnesium hydroxide (Mg(OH)2) depending on the CO32– activity in solution. This results in the trapping, and hence durable and permanent (at least ~10,000–100,000 years) immobilization of CO2 that was originally dissolved in water, and that is additionally drawn down from the atmosphere within: a) mineral carbonates, and/or b) as solvated bicarbonate (HCO3–) and carbonate (CO32–) ions (i.e., due to the absorption of atmospheric CO2 into seawater having enhanced alkalinity). Taken together, these actions result in the net removal of up to ≈4.6 kg of CO2 per m3 of seawater processed. Geochemical simulations quantify the extents of net CO2 removal including the dependencies on the process configuration. It is furthermore indicated that the efficiency of realkalinization of the acidic anolyte using alkaline solids depends on their H+ neutralization capacity and dissolution reactivity. We also assess changes in seawater chemistry resulting from Mg(OH)2 dissolution with emphasis on the change in its alkalinity and saturation state. Overall, this analysis provides direct quantifications of the ability of the EquaticTM process to serve as a means for technological CDR to mitigate the worst effects of accelerating climate change.

Surface-heated membrane distillation (MD) enhances the energy efficiency of desalination by mitigating temperature polarization (TP). However, systematic investigations of larger scale, multistage, surface-heated MD system with high water recovery and heat recycling are limited. Here, we explore the design and performance of a multistage surface-heated vacuum MD (SHVMD) with heat recovery through a comprehensive finite difference model. In this process, the latent heat of condensation is recovered through an internal heat exchanger (HX) using the retentate from one stage as the condensing fluid for the next stage and an external HX using the feed as the condensing fluid. Model results show that surface heating enhances the performance compared to conventional vacuum MD (VMD). Specifically, in a six-stage SHVMD process, 54.44% water recovery and a gained output ratio (GOR) of 3.28 are achieved with a surface heat density of 2000 W m

Nanotechnology-based approaches have demonstrated encouraging results for sustainable agriculture production, particularly in the field of fertilizers and pesticide innovation. It is essential to evaluate the economic and environmental benefits of these nanoformulations. Here we estimate the potential revenue gain/loss associated with nanofertilizer and/or nanopesticide use, calculate the greenhouse gas emissions change from the use of nanofertilizer and identify feasible applications and critical issues. The cost-benefit analysis demonstrates that, while current nanoformulations show promise in increasing the net revenue from crops and lowering the environmental impact, further improving the efficiency of nanoformulations is necessary for their widescale adoption. Innovating nanoformulation for targeted delivery, lowering the greenhouse gas emissions associated with nanomaterials and minimizing the content of nanomaterials in the derived nanofertilizers or pesticides can substantially improve both economic and environmental benefits.

Heavy metals (HMs), such as lead (Pb) and cadmium (Cd), in municipal wastewater (MWW) limit its use as an alternative water resource. Therefore, monitoring HM concentrations in MWW is critical to e...

This perspective proposes a potential pathway to diminish atmospheric CO2 accumulations which is distinct from traditional carbon capture and geological sequestration strategies and from existing n...

Membrane distillation (MD) has attracted significant attention owing to its unique advantages in desalination of hypersaline water. However, commercially available membranes used for MD desalination face fouling and wetting issues in treating wastewater containing low surface tension contaminants (e.g., oil and alcohol) and surface-active agents (e.g., surfactants). Herein, a superamphiphobic (i.e., superhydrophobic and near-superoleophobic) MD membrane was fabricated using the electrospinning technique followed by a simple surface modification step for treating challenging wastewater containing low surface tension substances. In order to fabricate a superamphiphobic membrane, a highly hydrophobic nanofibrous mat was first prepared by electrospinning a mixture of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP, also refers to PH) and reduced graphene oxide (rGO). Surface superamphiphobicity was then supplemented by a facile one-step grafting of low surface energy fluoroalkylsilane POTS. The influence of this one-step surface modification on the morphology and physicochemical properties of the membranes was investigated, revealing the altered elemental composition and enhanced hydrophobicity of the electrospun nanofiber mats. The resulting membranes demonstrated superamphiphobicity, confirmed by their wetting resistance evaluated with water and low surface tension liquids. The anti-wetting performance of the membrane was tested through desalinating 35 g L−1 sodium chloride solution in the presence of a surfactant (sodium dodecyl sulfate, SDS) in the direct contact membrane distillation (DCMD) unit. Membranes modified with fluoroalkylsilane (PH–rGO–POTS) exhibited enhanced stability and durability in terms of both permeation flux (∼27.94 kg m−2 h−1) and salt rejection (∼100%), while control membranes suffered from severe wetting problems.

The conversion of organic waste into value-added chemicals provides a sustainable pathway toward a circular economy, but anaerobic digestion (AD) as an established technology has faced great challe...

Although mineral dissolution and precipitation have been extensively studied, the role of electric stimulation on these processes remains unclear. We reveal the effects of subcritical electric pote...

Municipal water managers are intensifying efforts to reduce urban water use and increase the reliability of local water supplies to combat rising water scarcity and drought. Incentivizing increases in water-use efficiency and mandating conservation are two strategies to rein in demand. Concurrently, local water supplies are being augmented through investments in reclaiming and treating municipal wastewater. Although reducing urban water consumption is necessary to deal with population growth and a more variable climate, it does come at a cost. In particular, cutting back on indoor water consumption impacts the generation and quality of wastewater, which can have widespread and underappreciated consequences on human society and the environment. Here, to quantify these impacts, we tracked monthly effluent flow, salinity levels and the properties of 34 wastewater treatment plants throughout Southern California from 2013 to 2017—a period that included extreme drought and abundant precipitation. Our analysis demonstrates that conservation measures significantly reduced effluent flow and increased effluent salinity (P value ≤ 0.05). Our findings further highlight the need for policymakers to recognize the interdependencies and complexities within a water system. While many regions are striving to reduce water consumption, this Article examines the side effects and downstream impacts on wastewater quality for human and ecosystem health.

Nanotechnology and nanomaterials have attracted interest due to their potential in mitigating contemporary environmental challenges, such as the stressors imposed by increased industrial and agricultural activities, and the deterioration of air, soil and water quality. In particular, advanced technologies that harness carbon-based nanomaterials are poised to emerge as tools that provide new solutions for the global water crises. These tools include, electrically conductive membrane processes, which uniquely combine a separation process with a functional surface. In this respect, laser-induced graphene (LIG) and carbon nanotubes (CNTs) are electrically conductive carbon nanomaterials that hold great utility in a multitude of environmental applications, including the development of fouling-resistant systems for desalination and water treatment, enhanced separation methods, and innovative pollutant sensing and electrocatalytic platforms. Consequently, this review article describes and compares some important recent advances in LIG- and CNT-based electroactive surfaces. The discussion of LIG as an emerging carbon material set in context with CNTs is intended to shed light on future directions and development possibilities to meet the growing global challenges in terms of water treatment applications of both materials as well as other electrically conductive carbon-based nanomaterials exhibiting exceptional performance and versatility.

Recovery of nutrients, such as ammonia, from wastewater offers an attractive approach to increase the overall sustainability of waste management practices. Conventional wastewater treatment processes require significant energy input, and the useful form of nitrogen (ammonia), is usually lost. Ammonia, a major component of fertilizers, is conventionally manufactured using the Haber–Bosch process, which accounts for approximately 2% of worldwide energy demand. A better approach would efficiently capture ammonia directly from the wastewater. In this study, ammonia is recovered directly by using an electrically conducting gas-stripping membrane that is immersed into a wastewater reactor. Under cathodic potentials, these membranes were used to facilitate conversion of ammonium (NH4+) into ammonia (NH3), which was then extracted by either circulating an acid solution or by applying a vacuum on the back side of the membrane. The mechanism involves water electrolysis, which generates OH−, and transforms ammonium to ammonia that is stripped through the membrane. By engineering the surface and transport properties of the membrane 68.8 ± 8.0 g N per m2 d−1 of ammonia was recovered, with an energy consumption of 7.1 ± 1.1 kW h kg−1 N.

Nitrate removal from groundwater remains a challenge. Here, we report on the development of a flow-through, electrically charged, granular-activated carbon (GAC)-filled column, which effectively removes nitrate. In this system, the GAC functioned as an anode, while a titanium sheet acted as a cathode. The high removal rate of nitrate was achieved through a combination of electrosorption and electrochemical transformation to N

Specific-ion selectivity is a highly desirable feature for the next generation of membranes. However, existing membranes rely on differences in charge, size and hydration energy, which limits their ability to target individual ion species. Here we demonstrate a nanocomposite ion-exchange membrane material that enables a reverse-selective transport mechanism that can selectively pass a single ion species. We demonstrate this transport mechanism with phosphate ions selectively transporting across negatively charged cation exchange membranes. Selective transport is enabled by the in situ growth of hydrous manganese oxide nanoparticles throughout a cation exchange membrane that provide a diffusion pathway via phosphate-specific, reversible outer-sphere interactions. On incorporating the hydrous manganese oxide nanoparticles, the membrane's phosphate flux increased by a factor of 27 over an unmodified cation exchange membrane, and the selectivity of phosphorous over sulfate, nitrate and chloride reaches 47, 100 and 20, respectively. By pairing ion-specific outer-sphere interactions between the target ions and appropriate nanoparticles, these nanocomposite ion-exchange materials can, in principle, achieve selective transport for a range of ions.

Stimuli-responsive membranes that enable the smart control of membrane transport properties represent an interesting class of materials for a wide range of separation processes. In this work, surfa...

The widespread environmental occurrence of per- and polyfluoroalkyl substances (PFAS) has attracted significant regulatory, research, and media attention because of their toxicity, recalcitrance, and ability to bioaccumulate. Perfluorooctane sulfonate (PFOS) is a particularly troublesome member of the PFAS family due to its immunity to biological remediation and radical-based oxidation. In the present study, we present a heterogeneous reductive degradation process that couples direct electron transfer (ET) from surface-modified carbon nanotube electrodes (under low potential conditions) to sorbed PFOS molecules using UV-generated hydrated electrons without any further chemical addition. We demonstrate that the ET process dramatically increases the PFOS defluorination rate while yielding shorter chain (C3-C7) perfluorinated acids and present both experimental and ab initio evidence of the synergistic relationship between electron addition to sorbed molecules and their ability to react with reductive hydrated electrons. Because of the low energy consumption associated with the ET process, the use of standard medium-pressure UV lamps and no further chemical addition, this reductive degradation process is a promising method for the destruction of persistent organic pollutants, including PFAS and other recalcitrant halogenated organic compounds.

Fouling and wetting of membranes are significant concerns that can impede the widespread application of the membrane distillation (MD) process during high-salinity wastewater reclamation. Fouling, caused by the accumulation of undesirable materials on the membrane surface and pores, causes a decrease in permeate flux. Membrane wetting, the direct permeation of the feed solution through the membrane pores, results in reduced contaminant rejection and overall process failure. Lately, the application of MD for water recovery from various types of wastewaters has gained increased attention among researchers. In this review, we discuss fouling and wetting phenomena observed during the MD process, along with the effects of various mitigation strategies. In addition, we examine the interactions between contaminants and different types of MD membranes and the influence of different operating conditions on the occurrence of fouling and wetting. We also report on previously investigated feed pre-treatment options before MD, application of integrated MD processes, the performance of fabricated/modified MD membranes, and strategies for MD membrane maintenance during water reclamation. Energy consumption and economic aspects of MD for wastewater recovery is also discussed. Throughout the review, we engage in dialogues highlighting research needs for furthering the development of MD: the incorporation of MD in the overall wastewater treatment and recovery scheme (including selection of appropriate membrane material, suitable pre-treatment or integrated processes, and membrane maintenance strategies) and the application of MD in long-term pilot-scale studies using real wastewater.

The increasing demand for food coupled to various environmental pressures, is increasing the importance of sustainable agricultural practices. Based on results published across a wide range of disciplines, it is becoming evident that nanotechnology can play a crucial role in increasing the sustainability of agriculture, particularly in the area of fertilizer delivery, gene modification, and pest control. In this paper, we review critical plant morphological and physiological indices (pore size in xylem and phloem, xylem/phloem sap composition, xylem/phloem sap flow rate and flow conducting area) for nanoparticle (NP) transport, and examine the efficacy of various delivery methods for NPs (foliar application, root application, and feeding/injecting directly into plant tissue) with an emphasis on NP transport efficiency throughout the entire plant. While only few studies have explored the feeding/injection of NPs, these application pathways are the most efficient in terms of delivery, indicating their practical potential (e.g., for agrochemical delivery). In contrast, when applied via soil drenching or foliar spraying, the majority of the applied NPs are not taken up by the plants. However, those NPs that do penetrate the plant exhibit efficient transport from leaf to root, and vice versa. Of these two application methods, foliar application appears to be more effective in both NP delivery and transport than soil drenching. To further explain the data reported in the literature and to study the transport processes of NPs throughout the plant, we applied the Derjaguin–Landau–Verwey–Overbeek model to study the interactions of NPs with the surfaces of the plant vascular system (xylem and phloem), by which these NPs are transported throughout the plant structure. We found that the interaction energy between negatively charged NPs and plant tissue is positive, indicating that these NPs can effectively transport. We discuss future research needs regarding NP transport, which will enable effective utilization of NPs for different agricultural applications.

Membrane distillation (MD) is an emerging thermal desalination technology capable of desalinating waters of any salinity. During typical MD processes, the saline feedwater is heated and acts as the thermal energy carrier; however, temperature polarization (as well as thermal energy loss) contributes to low distillate fluxes, low single-pass water recovery and poor thermal efficiency. An alternative approach is to integrate an extra thermal energy carrier as part of the membrane and/or module assembly, which can channel externally provided heat directly to the membrane-feedwater interface and/or along the feed channel length. This direct-heat delivery has been demonstrated to increase single-pass water recovery and enhance the overall thermal efficiency. We developed a bench-scale direct-heated vacuum MD (DHVMD) process to desalinate pre-treated oil and gas "produced water" with an initial total dissolved solids of 115,500 ppm at a feed temperature ranging between 24 and 32 °C. We evaluated both water flux and specific energy consumption (SEC) as a function of water recovery. The system achieved a 50% water recovery without significant scaling, with an average flux6 kg m

As(III) species are the predominant form of arsenic found in groundwater. However, nanofiltration (NF) and reverse osmosis (RO) membranes are often unable to effectively reject As(III). In this study, we fabricate highly conducting ultrafiltration (UF) membranes for effective As(III) rejection. These membranes consist of a hydrophilic nickel-carbon nanotubes layer deposited on a UF support, and used as cathodes. Applying cathodic potentials significantly increased As(III) rejection in synthetic/real tap water, a result of locally elevated pH that is brought upon through water electrolysis at the membrane/water interface. The elevated pH conditions convert H3ASO3 to H2AsO3−/HAsO32− that are rejected by the negatively charged membranes. In addition, it was found that Mg(OH)2 that precipitates on the membrane can further trap arsenic. Importantly, almost all As(III) passing through the membranes is oxidized to As(V) by hydrogen peroxide produced on the cathode, which significantly decreased its overall toxicity and mobility. Although the high pH along the membrane surface led to mineral scaling, this scale could be partially removed by backwashing the membrane. To the best of our knowledge, this is the first report of effective As(III) removal using low-pressure membranes, with As(III) rejection higher than that achieved by NF and RO, and high water permeance.

Hydrothermal carbonization (HTC) of raw and anaerobically digested (AD) manure with either water or whey was studied, with the goal of recovering energy and nutrients. Specifically, the impacts of HTC reaction temperature (180–240 °C), solid feedstock, and type of liquid on hydrochar quality and aqueous phase properties were tested. Of the hydrochars produced, the calorific value of whey-based hydrochar was the highest, (19.4 and 16.0 MJ/kg for manure and digestate, respectively). Overall, the net energy gain was higher for HTC of manure with whey (7.4–8.3 MJ/kg dry feedstock) and water (4.4–5.1 MJ/kg) compared to the combined AD-HTC process with whey (4.4–5.3 MJ/kg) and water (2.3–2.9 MJ/kg). Digestate-derived hydrochar contained up to 1.8% P, higher than manure-derived hydrochar (≤1.5%). Using whey as a liquid for HTC increased the aqueous-phase N-P-K concentrations up to 3,200, 410, and 7,900 mg/L, respectively, suggesting its potential use as a liquid fertilizer.