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Reducing carbon dioxide emissions is one of the critical challenges to mitigate global climate change, which is having detrimental impacts on society and the environment. Fossil fuel combustion in transportation, power generation, and industrial processes is the dominant contributor to carbon emissions. Over the past decades, sustainable solutions and strategies have been investigated and developed to enable decarbonization. Catalysis plays an essential role to address this global challenge by increasing energy efficiency, reducing carbon emissions, capturing carbon dioxide, and utilizing clean energy sources to displace fossil fuels. In this Review, the role of catalysis in reducing energy demand was discussed, enhancing process efficiency, displacing carbon-intensive feedstocks and products, and therefore, reducing carbon emissions. Recent advances in catalyst development were summarized, focusing on applications to enhance industrial processes efficiency and enable utilization of clean energy sources. Emerging approaches in catalysis were reviewed, including the manufacture of iron and steel, direct air capture of CO

Phosphodiesterase-5 inhibitors (PDE-5i, such as Sildenafil, Tadalafil and Vardenafil, mainly prescribed to treat erectile dysfunction) and their generic drug equivalents have been widely marketed and consumed in Korea. From the concentrations detected in wastewater, we could deduce that relatively large amounts of PDE-5i were consumed without a legal prescription. Thus, PDE-5i’s presence in the environment via sewage is unavoidable, and their environmental fate within a sewage treatment plant (STP) should be evaluated. In this study, we investigated the occurrence of three PDE-5i analogs in the influent and effluent of two STPs and the receiving water bodies. The PDE-5i concentration in total reached 62 ± 12 (STP#1) and 88 ± 37 ng L−1 (STP#2) in the sewage influent; about 70% of it was Sildenafil in both STPs. However, they were hardly removed by the STPs as the removal efficiency of the STPs was less than 10% ± 5%. Therefore, the pharmaceuticals were detected in the receiving water (lower than 7 ng L−1as a total amount) and the concentration slightly increased downstream of the STPs. A simple mass balance model applied for the compounds in the STP effluent and receiving water bodies also confirmed that the discharged PDE-5i were quite persistent. Lastly, we identified temporal and regional patterns in the consumption of the drugs from daily variations of PDE-5i in the influent to these two STPs. For instance, the levels of PDE-5i in the sewage significantly increased on weekends (from Friday to Saturday), and especially in the area where adult-entertainment businesses are common. We estimated that the amount of PDE-5i consumption in this area was 31% higher than that in the area with fewer nightlife spots. Considering that they are pharmaceutically active and resistant to treatment processes within an STP, it is advised that a regular monitoring and management program for PDE-5i should be developed to prevent the discharge of the pharmaceuticals into the water environment.

Thermoelectric power plants traditionally have required huge volumes of water to condense steam from the turbine exhaust. The complex interdependency between water and energy poses new challenges for policy makers to achieve a safe, secure and sustainable supply of water and energy in the future. Cooling systems are the most water-intensive part of the thermoelectric generation process, presenting significant opportunities to reduce the withdrawal and consumptive use of fresh water. Reuse of impaired water for cooling can reduce freshwater withdrawal and decrease water contamination and withdrawal-related impacts on aquatic life and the environment. Here we focus on challenges and opportunities for improving water efficiency in the cooling systems of thermoelectric power plants. First, we present the types of cooling systems in a thermoelectric power plant. Then, we illustrate the key criteria for feed water quality for cooling systems. We use this information to determine appropriate design and operation guidelines for cooling systems. In order to facilitate the use of impaired water in cooling systems, we suggest the key technical issues and available water technologies for brackish water desalination. Keywords: Water consumption, Water withdrawal, Energy-efficient technology, Zero liquid discharge, Fit-for-purpose use

A robust ion-exchange resin wafer electrodeionization technology was used to demonstrate the energy efficiency of impaired water desalination. The loose ion exchange resin beads used in conventional electrodeionization were immobilized and molded to form a porous resin wafer material. In this study, the energy efficiency of brackish water desalination using resin wafer electrodeionization was evaluated along with salt removal ratio, current efficiency and productivity. Several key operating factors, including treatment time, applied electrical energy and feed flow rate were selected through experimental design. In addition, the removal rate constant in resin wafer electrodeionization was determined via a pseudo first-order kinetic model, and then correlated with operation parameters. Furthermore, the prediction models of the productivity and energy consumption were established using response surface methodology. Results suggest that resin wafer electrodeionization can improve energy efficiency to greater than 35% in comparison to reverse osmosis (normally ∼12%) for impaired water desalination. The energy consumption of resin wafer electrodeionization was found to be 0.35–0.66 kWh/m3 with productivity of 20.1–44.7 L/hr/m2 (i.e., 5.3–11.8 gal/hr/m2) for brackish water desalination. Furthermore, a preliminary economic evaluation on impaired water desalination using resin wafer electrodeionization comparable to commercial reverse osmosis process was provided. It suggests that resin wafer electrodeionization offers the potential for an abundant source of fresh water from impaired water desalination at a cost-effective manner, which should be viewed as a crucial component in the portfolio of water supply options.

This review explores the current state-of-the-art in the removal of ions from water to treat brackish water using electrokinetic technologies, while identifying emerging technologies and potential advances in materials science, process engineering, and system integration. We first provide a definition of the class of electrokinetic desalination methods, and propose measurement and reporting standards to improve technology comparisons. The review focuses on two major types of electrochemical processes: electrodialysis (and electrodeionization) and capacitive deionization. We include hybrid systems that combine battery-based desalination, and capacitive neutralization deionization. Finally, we consider the interconnectivity between desalination and energy, and discuss the balance between energy efficiency, water throughput in the context of large-scale deployment of a desalination plant, and environmental impacts.

Use of groundwater, reclaimed water, and other impaired water sources is a critical strategy for fresh surface water conservation. Because impaired water desalination by reverse osmosis is energy-intensive, a robust ion-exchange resin wafer electrodeionization technology was developed to conserve energy during impaired water desalination. The loose ion-exchange resin beads were immobilized and molded to form a porous resin wafer material and utilized for impaired water desalination. In this study, the impaired water desalination using resin wafer electrodeionization was evaluated along with various key performance indicators, including current efficiency, energy efficiency, and productivity. Results suggest that resin wafer electrodeionization can improve energy efficiency to >35% in comparison to that of reverse osmosis (normally ∼12%) for impaired water desalination. The energy consumption of resin wafer electrodeionization was found to be 0.354–0.657 kWh/m3 with a productivity of 20.1–41.3 L h–1 m–2 (i...

In biorefinery procedures, pretreatment and conditioning of lignocellulose substrates are considered critical to enhance yields and rates of transformation. These processes use large volumes of water and chemicals, impacting the sustainability and economics of the biorefinery industry. In this study, we evaluate four pretreatment and conditioning process scenarios for removing acidic impurities from corn stover hydrolysate liquor, i.e., overliming, ammonia addition, two-stage treatment and membrane separations. The environmental impacts of these processes were determined using a life cycle assessment (LCA). Moreover, both the water and carbon footprints were estimated by considering energy and materials consumption. The results indicate that ammonia addition, two-stage treatment and membrane separations reduce environmental impacts in comparison to overliming. Integrated membrane separations exhibited the lowest water consumption (i.e., 2.5 L/kg-biomass) and carbon footprint (i.e., 6.2 g CO 2 /kg-biomass). In membrane separations, acidic impurities can be selectively recovered by electrodeionization as value-added products or reuse as process chemicals. Based on the LCA results, an integrated solution for hydrolysate pretreatment and conditioning is proposed as a cleaner and more sustainable process for the biorefinery industry.

Anaerobic digestion (AD) of sludge at wastewater treatment plants can benefit from addition of essential trace metals such as iron, nickel and cobalt to increase biogas production for utilization in combined heat and power systems, fed into natural gas pipelines or as a vehicle fuel. This study evaluated the impact and benefits of Ni/Co and olivine addition to the digester at mesophilic temperatures. These additions supplement previously reported research in which iron-rich olivine (MgSiO4) was added to sequester CO2 in-situ during batch AD of sludge. Trace element addition has been shown to stimulate and stabilize biogas production and have a synergistic effect on the mineral carbonation process. AD with 5% w/v olivine and 1.5 mg/L Ni/Co addition had a 17.3% increase in methane volume, a 6% increase in initial exponential methane production rate and a 56% increase in methane yield (mL CH4/g CODdegraded) compared to the control due to synergistic trace element and olivine addition while maintaining 17.7% CO2 sequestration from olivine addition. Both first-order kinetic modeling and response surface methodology modeling confirmed the combined benefit of the trace elements and olivine addition. These results were significantly higher than previously reported results with olivine addition alone [1] (Linville et al., 2016).

Biogas from anaerobic digestion of sludge at wastewater treatment plants consists of methane, carbon dioxide and trace contaminants which can be upgraded for utilization. Compared to current costly upgrading technologies, mineral carbonation has many benefits by using natural magnesium and calcium rich ores capable of sequestering CO2. The feasibility of olivine to sequester CO2 in-situ during batch anaerobic digestion of sludge was tested for (1) ambient versus mesophilic temperatures, (2) placement of olivine in the digester, and (3) olivine particle size and concentration. Increasing the temperature, increasing the olivine surface area via increased dose and decreased particle size, and elevating the olivine in the reactor increased mineral carbonation rates during anaerobic digestion. At mesophilic temperature, the elevated 5% w/v fine olivine digester had a 17.5% reduction in CO2 which equated to a 3.6% increase in methane content (%) and at ambient temperature, the same condition had a 21.7% CO2 sequestration resulting in an 8.8% increase in methane content compared to the control. Response surface methodology was applied for optimization of digestion time and olivine surface area at both temperatures.

Fluids that undergo endothermic reactions were evaluated as potential chemical energy carriers of heat from geothermal reservoirs for power generation. Their performance was compared with that of H2O and CO2. The results show that (a) chemical energy carriers can produce more power from geothermal reservoirs than water and CO2 and (b) working fluids should not be selected solely on the basis of their specific thermo-physical properties but rather on the basis of the rate of exergy (ideal power) they can deliver. This article discusses the results of the evaluation of two chemical energy carrier systems: ammonia and methanol/water mixtures.

This study presents a novel process for producing pipeline-quality biomethane by anaerobic digestion (AD) of sludge with in-situ biogas cleanup and upgrading using corn stover biochar. The biochar has high surface area (105 m2/g), high ash content (45.2% dry weight) and high concentrations of potassium, calcium and magnesium (14.2% K2O, 3.9% CaO and 4.2% MgO of the ash content, respectively). The biochar-amended digesters produced near pipeline-quality biomethane (>90% CH4 and

Green biotechnology related to biomass conversion for production of bio-based chemicals has drawn considerable attention because of the increasing costs of fossil fuels and their adverse effects on climate change, environmental pollution, and human health. In this study, the recent promises and issues of low-carbon-driven bio-product technology development using lignocellulosic substrates from agriculture were critically reviewed. First, the challenges in bio-based chemical production were addressed from the aspect of technology. After that, the lignocellulose feedstock and their building-block chemicals used in the literature were summarized. In addition, novel pretreatment, bio-conversion, and separations technologies for cleaner production of bio-based products were comprehensively reviewed. It suggests that the main challenge to deploying bio-based chemical technologies into commercialization is the high cost of product recovery from the bioreactor due to the relatively low product titers caused by the product inhibition and/or pH in conventional fermentation.

Recently the United States Environmental Protection Agency qualified biogas from landfills and anaerobic digesters as a cellulosic transportation biofuel under the expanded Renewable Fuel Standard (RFS2). Biogas is a renewable fuel that can generate Renewable Identification Number credits for the producer. The wastewater industry may not be able to keep pace with this opportunity. Less than 10% of WWTPs in the US have currently produced biogas for beneficial use. Supporting growth of the biogas industry requires implementation of new practices and policies. In this review, the barriers, gaps, and challenges in deploying biogas production technology are identified. Issues are classified as economic, technical, social or regulatory issues. Some of the critical challenges to the economics of digester operations are the slow rate of biogas generation, the low energy content of the biogas, and the costs to upgrade the biogas. Currently there is little biogas utilization at US WWTPs. Most biogas is flared while some is used for onsite process heat and power production. Case studies of co-digestion of biosolids with organic wastes at field-scale show the use of co-digestion could overcome significant economic challenges including higher methane yield, more efficient digester volume utilization and reduced biosolids production. These findings could provide guidance in retrofitting existing facilities or in designing new biogas production and utilization systems. The RFS2 ruling increases market certainty, hence reduces risk. The evaluation of applications of co-digestion at WWTP scales ranging from 1 million gallons per day (MGD) to 375 MGD determined its potential feasibility for different types of digester operation, organic waste and loading rate as well as effectiveness of providing energy self-sufficiency at the WWTPs. This work could improve economics of anaerobic digestion at WWTPs, enabling viable and sustainable biogas industry and offsetting costs for wastewater management.

This Feature examines significant challenges and opportunities to spur innovation and accelerate adoption of reliable technologies that enhance integrated resource recovery in the wastewater sector through the creation of a national testbed network. The network is a virtual entity that connects appropriate physical testing facilities, and other components needed for a testbed network, with researchers, investors, technology providers, utilities, regulators, and other stakeholders to accelerate the adoption of innovative technologies and processes that are needed for the water resource recovery facility of the future. Here we summarize and extract key issues and developments, to provide a strategy for the wastewater sector to accelerate a path forward that leads to new sustainable water infrastructures.

This article describes the key challenges and opportunities in modeling and optimization of biomass-to-bioenergy supply chains. It reviews the major energy pathways from terrestrial and aquatic biomass to bioenergy/biofuel products as well as power and heat with an emphasis on “drop-in” liquid hydrocarbon fuels. Key components of the bioenergy supply chains are then presented, along with a comprehensive overview and classification of the existing contributions on biofuel/bioenergy supply chain optimization. This paper identifies fertile avenues for future research that focuses on multi-scale modeling and optimization, which allows the integration across spatial scales from unit operations to biorefinery processes and to biofuel value chains, as well as across temporal scales from operational level to strategic level. Perspectives on future biofuel supply chains that integrate with petroleum refinery supply chains and/or carbon capture and sequestration systems are presented. Issues on modeling of sustainability and the treatment of uncertainties in bioenergy supply chain optimization are also discussed.

Energy-efficient capture of CO2 from power-plant flue gas is one of the grand challenges to reduce greenhouse gas (GHG) emissions. Current CO2-capture technologies are limited by parasitic energy loss, inefficient capture, and unfavorable process economics. We present a novel electrochemical method for CO2 capture from coal-fired power-plant flue gas. The method utilizes in-situ electrochemical pH control with a resin wafer electrodeionization (RW-EDI) device that continuously shifts the pH of the process fluid between basic and acidic in sequential chambers (pH swing). This pH swing enables capture of CO2 from flue gas in the basic chamber followed by release (recovery) of the captured CO2 (purified) in the acidic chamber of the same device. The approach is based on the sensitivity of the thermodynamic equilibrium of CO2 hydration/dehydration reactions over a narrow pH range. The method enables simultaneous absorption (capture) of CO2 from flue gas and desorption (release) at atmospheric pressure without...

Dilute acid (sulfuric acid) pretreatment of lignocellulosic biomass releases monomeric xylose, xylo-oligomers, and acetic acid by degradation of hemicellulose. Acids inhibit both the enzymatic hydrolysis of cellulose to monomeric sugars and downstream fermentation of sugars to biofuels. Removal of acetic acid and sulfuric acid, as well as the nonionic toxic impurities, from the hydrolysate liquor prior to enzymatic hydrolysis may improve biofuel yields. Development of an efficient acid separation technique is essential for enhanced process performance and cost-effective biofuel production. We evaluated the use of an electrically driven membrane separation technique, resin wafer based electrodeionization (RW-EDI), for the removal of ionic impurities (acetic acid and sulfuric acid) from corn stover hydrolysate liquor. RW-EDI provides the capability to control solution pH in situ by voltage adjustment. In situ pH control enables pKa-selective recovery of acids (or bases). The results indicate that RW-EDI is ...

This paper presents a concept for conducting commercial chemical reactions and production of power using geothermal heat. The high pressures (Ps) and temperatures (Ts) that fluids attain in deep reservoirs can be used to manufacture chemicals or decontaminate wastes. High P reactions which can be expensive and/or unsafe to conduct above ground can be conducted in geothermal reservoirs using closed designs. We present examples of reactions that could benefit from Enhanced Geothermal Systems (EGS) including production of ammonia (NH3), supercritical oxidation of wastewater contaminants, production of hydrogen (H2) by steam reforming of methanol (CH3OH) and partial oxidation of methane (CH4) to produce CH3OH.

To meet the stringent Great Lakes Initiative (GLI) wastewater discharge mercury (Hg) limit of 1.3 ppt (ng/L), mercury removal technologies need to be identified and investigated. The goals of this study were to (1) identify and assess available wastewater treatment technologies for mercury removal from an oil refinery wastewater; and (2) conduct bench-scale tests to provide comparable, transparent, and uniform results to assess their performance at low mercury concentrations. The study found that many tested technologies were able to achieve the GLI mercury target concentration at the bench-scale, albeit with different efficiencies and engineering implications. These results demonstrate that at this scale there is no fundamental physical or chemical barrier to achieving < 1.3 ng Hg/L in the tested wastewater. The study also found that some technologies were effective on particulate mercury whereas others were effective on dissolved mercury. One emerging treatment technology was found to be effective on both particulate and dissolved mercury. Three mercury-removal technologies--ultrafiltration (particulate mercury), adsorption (dissolved mercury), and an emerging reactive filtration technology (particulate and dissolved mercury)--are recommended for further study. This research offers treatment alternatives for different forms of mercury in an oil refinery wastewater, which might be applicable to other types of mercury-containing wastewater.

The applications of 1H and 13C nuclear magnetic resonance (NMR) and two-dimensional 1H/13C NMR spectroscopy have been shown to be useful techniques for the qualitative and quantitative characterization of hydrotreated recycled lube oils. The addition of hydrogen to aromatic and alkene hydrocarbons can be quantitatively and selectively measured. The decrease of oxygen/nitrogen/sulfur species can also be inferred from the reduction of specific resonances in the NMR spectra. Treated recycled lube oil was subsequently hydrotreated with Pd catalysts deposited by either atomic layer deposition (ALD) or incipient wetness impregnation (IWI) on a SiO2/Al2O3 support. In both cases, much lower hydrogenation temperatures were required than had been observed with typical NiMo or CoMo on Al2O3. In addition, the ALD-deposited catalyst was more effective for the reduction of aromatics and heteroatom components than the IWI catalyst. The lube oil fractions were of high purity (low aromaticity and low heteroatom content) e...

Understanding and restricting microbial surface attachment will enhance wastewater treatment with membranes. We report a maskless lithographic patterning technique for the generation of patterned polymer coatings on ultrafiltration membranes. Polyethylene glycol, zwitterionic, or negatively charged hydrophilic polymer compositions in parallel- or perpendicular-striped patterns with respect to feed flow were evaluated using wastewater. Membrane fouling was dependent on the orientation and chemical composition of the coatings. Modifications reduced alpha diversity in the attached microbial community (Shannon indices decreased from 2.63 to 1.89) which nevertheless increased with filtration time. Sphingomonas species, which condition membrane surfaces and facilitate cellular adhesion, were depleted in all modified membranes. Microbial community structure was significantly different between control, different patterns, and different chemistries. This study broadens the tools for surface modification of membranes with polymer coatings and for understanding and optimization of antifouling surfaces.

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for their ability to achieve the world's most stringent Hg discharge criterion (

This article addresses the optimal design and planning of cellulosic ethanol supply chains under economic, environmental, and social objectives. The economic objective is measured by the total annualized cost, the environmental objective is measured by the life cycle greenhouse gas emissions, and the social objective is measured by the number of accrued local jobs. A multiobjective mixed-integer linear programming (mo-MILP) model is developed that accounts for major characteristics of cellulosic ethanol supply chains, including supply seasonality and geographical diversity, biomass degradation, feedstock density, diverse conversion pathways and byproducts, infrastructure compatibility, demand distribution, regional economy, and government incentives. Aspen Plus models for biorefineries with different feedstocks and conversion pathways are built to provide detailed techno-economic and emission analysis results for the mo-MILP model, which simultaneously predicts the optimal network design, facility location, technology selection, capital investment, production planning, inventory control, and logistics management decisions. The mo-MILP problem is solved with an e-constraint method; and the resulting Pareto-optimal curves reveal the tradeoff between the economic, environmental, and social dimensions of the sustainable biofuel supply chains. The proposed approach is illustrated through two case studies for the state of Illinois. © 2011 American Institute of Chemical Engineers AIChE J, 2012

This article presents a summary of research issues and opportunities in alternative energy source research identified by panels of experts assembled by the Engineering Directorate of the US National Science Foundation. The objective was to identify transformative research issues and opportunities to make alternative energy sources viable. The article presents motivations for energy research, grand challenges, and specific challenges in the research areas covered. The grand challenges identified for the United States include supplying 30% of US electricity from photovoltaics by 2030, supplying 25% of US electricity from wind by 2025, displacing 30% of US hydrocarbon use by 2030 with bio-based products, and providing a practical 250–300 W h/kg energy storage system by 2025. Similar challenges could be outlined along the same lines for the remainder of the world. Examples of specific areas of research focus identified as promising include high performance p-type transparent conductors, multijunction thin-film photovoltaic devices, defects in chalcogenide semiconductors, experimental study and numerical modeling of the fluid mechanics of airflow as applied to wind turbines, improved materials for wind turbines, methods for creating high energy density transportable biological feedstocks, biorefinery processes yielding infrastructure-compatible biofuels and biochemicals directly, and improved electrodes and electrolytes for Li ion batteries. Arguments for each of these as research priorities are given.

The replacement of petrochemicals with biobased chemicals requires efficient bioprocesses, biocatalysis, and product recovery. Biocatalysis (e.g., enzyme conversion and fermentation) offers an attractive alternative to chemical processing because biocatalysis utilize renewable feedstocks under benign reaction conditions. One class of chemical products that could be produced in large volumes by biocatalysis is organic acids. However, biocatalytic reactions to produce organic acids typically result in only dilute concentrations of the product because of product inhibition and acidification that drives the reaction pH outside of the optimal range for the biocatalyst. Buffering or neutralization results in formation of the acid salt rather than the acid, which requires further processing to recover the free acid product. To address these barriers to biocatalytic organic acid production, we developed the “separative bioreactor” based on resin wafer electrodeionization, which is an electro-deionization platform that uses resin wafers fabricated from ion exchange resins. The separative bioreactor simultaneously separates the organic acid from the biocatalyst as it is produced, thus it avoids product inhibition enhancing reaction rates. In addition, the separative bioreactor recovers the product in its acid form to avoid neutralization. The instantaneous separation of acid upon formation in the separative bioreactor is one of the first truly one-step systems for producing organic acids. The separative bioreactor was demonstrated with two systems. In the first demonstration, the enzyme glucose fructose oxidoreductase (GFOR) was immobilized in the reactor and later regenerated in situ. GFOR produced gluconic acid (in its acid form) continuously for 7 days with production rates up to 1000 mg/L/hr at >99% product recovery and GFOR reactivity >30mg gluconic acid/mg GFOR/hour. In the second demonstration, the E. coli strain CSM1 produced lactic acid for up to 24 hours with a productivity of >200 mg/L/hr and almost 100% product recovery.