Component innovations for lower cost mechanical vapor compression.

Despite significant capital and operating costs, mechanical vapor compression (MVC) remains the preferred technology for challenging brine concentration applications. This work seeks to assess the dependence of MVC costs on feedwater salinity and desired water recovery and to quantify the value of improved component performance or reduced component costs for reducing the levelized cost of water (LCOW) of MVC. We built a cost optimization model coupling thermophysical, heat and mass transfer, and technoeconomic models to optimize and identify low cost MVC system designs as a function of feedwater salinity and water recovery. The LCOW ranges over 3.6 to 6.1 $/m3 for seawater feed salinities of 25-150 g/kg and water recoveries of 40-80 %. We then perform sensitivity analysis on parameter inputs to isolate irreducible costs and determine high value component innovation targets. The LCOW was most sensitive to evaporator material costs and performance, including the overall heat transfer coefficient in the evaporator. Process and material innovations such as polymer-composite evaporator tubes that reduce evaporator costs by 25 % without reducing heat transfer performance by more than 10 % would result in MVC cost reductions of 8 %.

Electricity and natural gas tariffs at United States wastewater treatment plants.

Wastewater treatment plants (WWTPs) are large electricity and natural gas consumers with untapped potential to recover carbon-neutral biogas and provide energy services for the grid. Techno-economic analysis of emerging energy recovery and management technologies is critical to understanding their commercial viability, but quantifying their energy cost savings potential is stymied by a lack of well curated, nationally representative electricity and natural gas tariff data. We present a dataset of electricity tariffs for the 100 largest WWTPs in the Clean Watershed Needs Survey (CWNS) and natural gas tariffs for the 54 of 100 WWTPs with on-site cogeneration. We manually collected tariffs from each utility's website and implemented data checks to ensure their validity. The dataset includes facility metadata, electricity tariffs, and natural gas tariffs (where cogeneration is present). Tariffs are current as of November 2021. We provide code for technical validation along with a sample simulation.

The Future of Municipal Wastewater Reuse Concentrate Management: Drivers, Challenges, and Opportunities.

Water reuse is rapidly becoming an integral feature of resilient water systems, where municipal wastewater undergoes advanced treatment, typically involving a sequence of ultrafiltration (UF), reverse osmosis (RO), and an advanced oxidation process (AOP). When RO is used, a concentrated waste stream is produced that is elevated in not only total dissolved solids but also metals, nutrients, and micropollutants that have passed through conventional wastewater treatment. Management of this RO concentrate─dubbed municipal wastewater reuse concentrate (MWRC)─will be critical to address, especially as water reuse practices become more widespread. Building on existing brine management practices, this review explores MWRC management options by identifying infrastructural needs and opportunities for multi-beneficial disposal. To safeguard environmental systems from the potential hazards of MWRC, disposal, monitoring, and regulatory techniques are discussed to promote the safety and affordability of implementing MWRC management. Furthermore, opportunities for resource recovery and valorization are differentiated, while economic techniques to revamp cost-benefit analysis for MWRC management are examined. The goal of this critical review is to create a common foundation for researchers, practitioners, and regulators by providing an interdisciplinary set of tools and frameworks to address the impending challenges and emerging opportunities of MWRC management.

Multicriteria Suitability Index for Prioritizing Early-Stage Deployments of Wastewater-Derived Fertilizers in Sub-Saharan Africa.

Recycling nutrients from wastewater could simultaneously decrease the carbon intensity of traditional ammonia supply chains and increase the accessibility of local fertilizer. Despite the theoretical potential, techno-economic viability of wastewater nutrient recovery in sub-Saharan Africa has been poorly characterized at subnational scales. This work proposes a multicriteria suitability index to describe techno-economic viability of wastewater-derived fertilizer technologies with district-scale resolution. This index, with a range from 0 to 1 (highest suitability), incorporates key drivers, including population density, soil conditions, sanitation levels, and fertilizer prices. We found that suitability varies widely within and across countries in sub-Saharan Africa and that the primary limiting factor is the absence of sanitation infrastructure. Regions with a minimum of 10% cropland area and a suitability index of at least 0.9 were identified as highly suitable target regions for initial deployment. While they comprise only 1% of the analyzed area, these regions are home to 39 million people and contain up to 3.7 million hectares of cropland. Wastewater-derived fertilizer technologies could deliver an average of 25 kg of nitrogen per hectare of cropland, generating additional food equivalent to the annual consumption of 6 million people. Screening for high suitability can inform selection of effective lighthouse demonstration sites that derisk technology deployment and promote the transition to a more circular nutrient economy.

Integrated Energy Flexibility Management at Wastewater Treatment Facilities.

On-site batteries, low-pressure biogas storage, and wastewater storage could position wastewater resource recovery facilities as a widespread source of industrial energy demand flexibility. This work introduces a digital twin method that simulates the coordinated operation of current and future energy flexibility resources. We combine process models and statistical learning on 15 min resolution sensor data to construct a facility's energy and water flows. We then value energy flexibility interventions and use an iterative search algorithm to optimize energy flexibility upgrades. Results from a California facility with anaerobic sludge digestion and biogas cogeneration predict a 17% reduction in electricity bills and an annualized 3% return on investment. A national analysis suggests substantial benefit from using existing flexibility resources, such as wet-weather storage, to reduce electricity bills but finds that new energy flexibility investments are much less profitable in electricity markets without time-of-use incentives and plants without existing cogeneration facilities. Profitability of a range of energy flexibility interventions may increase as a larger number of utilities place a premium on energy flexibility, and cogeneration is more widely adopted. Our findings suggest that policies are needed to incentivize the sector's energy flexibility and provide subsidized lending to finance it.

Microporous Polyethersulfone Membranes Grafted with Zwitterionic Polymer Brushes Showing Microfiltration Permeance and Ultrafiltration Bacteriophage Removal.

Virus removal from water using microfiltration (MF) membranes is of great interest but remains challenging owing to the membranes' mean pore sizes typically being significantly larger than most viruses. We present microporous membranes grafted with polyzwitterionic brushes (N-dimethylammonium betaine) that combine bacteriophage removal in the range of ultrafiltration (UF) membranes with the permeance of MF membranes. Brush structures were grafted in two steps: free-radical polymerization followed by atom transfer radical polymerization (ATRP). Attenuated total reflection Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) verified that grafting occurred at both sides of the membranes and that the grafting increased with increasing the zwitterion monomer concentration. The log reduction values (LRVs) of the pristine membrane increased from less than 0.5 LRV for T4 (∼100 nm) and NT1 (∼50 nm) bacteriophages to up to 4.5 LRV for the T4 and 3.1 LRV for the NT1 for the brush-grafted membranes with a permeance of about 1000 LMH/bar. The high permeance was attributed to a high-water fraction in the ultra-hydrophilic brush structure. The high measured LRVs of the brush-grafted membranes were attributed to enhanced bacteriophages exclusion from the membrane surface and entrapment of the ones that penetrated the pores due to the membranes' smaller mean pore-size and cross-section porosity than those of the pristine membrane, as seen by scanning electron microscopy (SEM) and measured using liquid-liquid porometry. Micro X-ray fluorescence (µ-XRF) spectrometry and nanoscale secondary ion mass spectrometry showed that 100 nm Si-coated gold nanospheres accumulated on the surface of the pristine membrane but not on the brush-coated membrane and that the nanospheres that penetrated the membranes were entrapped in the brush-grafted membrane but passed the pristine one. These results corroborate the LRVs obtained during filtration experiments and support the inference that the increased removal was due to a combined exclusion mechanism and entrapment. Overall, these microporous brush-grafted membranes show potential for use in advanced water treatment.

Fixing the desalination membrane pipeline.

Materials discovery alone has not translated into lower-cost water treatment.

Unraveling pH Effects on Ultrafiltration Membrane Fouling by Extracellular Polymeric Substances: Adsorption and Conformation Analyzed with Localized Surface Plasmon Resonance.

Extracellular polymeric substances (EPSs) can conform and orient on the surface according to the applied aquatic conditions. While pH elevation usually removes EPSs from membranes, small changes in pH can change the adsorbed EPS conformation and orientation, resulting in a decrease in membrane permeability. Accordingly, EPS layers were tested with localized surface plasmon resonance (LSPR) sensing and quartz crystal microbalance with dissipation monitoring (QCM-D) using a hybrid sensor. A novel membrane-mimetic hybrid QCM-D-LSPR sensor was designed to indicate both "dry" mass and mechanical load ("wet" mass) of the adsorbed EPS. The effect of pH on the EPS layer's viscoelastic properties and hydrated thickness analyzed by QCM-D corroborates with the shift in EPS areal concentration, ΓS, and the associated EPS conformation, analyzed by LSPR. As pH elevates, the processes of (i) elevation in EPS layer's thickness (QCM-D) and (ii) decrease in the EPS areal density, ΓS (LSPR), provide a clear indication for changes in EPS conformation, which decrease the effective ultrafiltration (UF) membrane pore diameter. This decrease in the pore diameter together with the increase in surface hydrophobicity elevates UF membrane hydraulic resistance.

Effects of meteorological and land surface modeling uncertainty on errors in winegrape ET calculated with SIMS.

Characterization of model errors is important when applying satellite-driven evapotranspiration (ET) models to water resource management problems. This study examines how uncertainty in meteorological forcing data and land surface modeling propagate through to errors in final ET data calculated using the Satellite Irrigation Management Support (SIMS) model, a computationally efficient ET model driven with satellite surface reflectance values. The model is applied to three instrumented winegrape vineyards over the 2017-2020 time period and the spatial and temporal variation in errors are analyzed. We illustrate how meteorological data inputs can introduce biases that vary in space and at seasonal timescales, but that can persist from year to year. We also observe that errors in SIMS estimates of land surface conductance can have a particularly strong dependence on time of year. Overall, meteorological inputs introduced RMSE of 0.33-0.65 mm/day (7-27%) across sites, while SIMS introduced RMSE of 0.55-0.83 mm/day (19-24%). The relative error contribution from meteorological inputs versus SIMS varied across sites; errors from SIMS were larger at one site, errors from meteorological inputs were larger at a second site, and the error contributions were of equal magnitude at the third site. The similar magnitude of error contributions is significant given that many satellite-driven ET models differ in their approaches to estimating land surface conductance, but often rely on similar or identical meteorological forcing data. The finding is particularly notable given that SIMS makes assumptions about the land surface (no soil evaporation or plant water stress) that do not always hold in practice. The results of this study show that improving SIMS by eliminating these assumptions would result in meteorological inputs dominating the error budget of the model on the whole. This finding underscores the need for further work on characterizing spatial uncertainty in the meteorological forcing of ET. Supplementary Information: The online version contains supplementary material available at 10.1007/s00271-022-00808-9.

High-Resolution Carbon Accounting Framework for Urban Water Supply Systems.

Decarbonization of urban infrastructure systems is imperative to meeting global climate goals. Urban water supply systems (UWSSs) account for 1-3% of urban electricity consumption in the U.S., a value expected to increase, as municipalities tap nontraditional water supplies that are either more distant or require more energy-intensive treatment. Reducing the carbon intensity of UWSSs will require a combination of infrastructure upgrades, operational modifications, and behavioral interventions, but urban water planners, water treatment system operators, and consumers lack transparent tools for quantifying the carbon emission implications of these decisions. We propose a high-resolution carbon accounting framework that allows for attribution of carbon emissions to individual water sources, water system components, or individual consumers in a UWSS. The high temporal resolution of this framework also enables rapid assessment of the potential for operational and behavioral interventions to reduce the carbon intensity of UWSSs. We demonstrate this carbon accounting framework on a real-world UWSS serving a city of roughly 100 000 residents. The high spatial and temporal resolution, coupled with the scalability of this approach, makes it a valuable tool for consulting engineers, operators, and consumers seeking to deliver Net Zero water supplies.

Energy-Optimal Siting of Decentralized Water Recycling Systems.

Decentralized water recycling systems (DWRS) have emerged as a viable option for incrementally augmenting water supply in water-stressed regions, but DWRS are generally more energy-intensive than traditional centralized water treatment systems. When DWRS are deployed incrementally in small batches, the marginal energy intensity (MEI) of water supply quantifies the location-specific energy footprint of centralized water supply and serves as a robust metric measuring the energy implications of replacing centralized supply with DWRS supply. This research develops and applies a MEI-based decision framework that identifies the energy-optimal siting of DWRS to minimize the overall system operational energy consumption given a target fraction of water demand to be met by newly deployed DWRS. In a small benchmark water supply system where the energy intensity of the intended DWRS is 5.3% higher than the current system average energy intensity of centralized supply, we demonstrate that the optimal siting of DWRS to offset 10% of the system-wide water demand reduces the overall system energy consumption by 0.77%. In contrast, the naive and worst-case siting of the same DWRS increases the energy consumption of the overall system by 0.65 and 2.0%, respectively. The proposed MEI-based decision framework is particularly valuable for application in large multi-source systems, where an optimization-based approach is computationally intractable. This study highlights the importance of accounting for both distribution and treatment energy intensity when evaluating new water sources and demonstrates the viability of DWRS as an energy-efficient tool for augmenting water supply.

Build back wiser.

The US Infrastructure Investment and Jobs Act (IIJA), which is winding its way through Congress, makes progress toward President Biden's campaign promise to "build back better" by investing $0.55 trillion to repair the nation's transportation, water, and energy systems. But this allocation is only a fraction of the American Society of Civil Engineers estimated $2.5 trillion infrastructure investment deficit. To bridge this value gap, the nation must build back "wiser" by investing IIJA dollars in digitized, versatile, distributed, and inclusive infrastructure systems.

High-impact innovations for high-salinity membrane desalination.

Reducing the cost of high-salinity (>75 g/L total dissolved solids) brine concentration technology would unlock the potential for vast inland water supplies and promote the safe management of concentrated aqueous waste streams. Impactful innovation will target component performance improvements and cost reductions that yield the highest impact on system costs, but the desalination community lacks methods for quantitatively evaluating the value of innovation or the robustness of technology platforms relative to competing technologies. This work proposes a suite of methods built on process-based cost optimization models that explicitly address the complexities of membrane-separation processes, namely that these processes comprise dozens of nonlinearly interacting components and that innovation can occur in more than one component at a time. We begin by demonstrating the merit of performing simple parametric sensitivity analysis on component performance and cost to guide the selection of materials and manufacturing methods that reduce system costs. A more rigorous implementation of this approach relates improvements in component performance to increases in component costs, helping to further discern high-impact innovation trajectories. The most advanced implementation includes a stochastic simulation of the value of innovation that accounts for both the expected impact of a component innovation on reducing system costs and the potential for improvements in other components. Finally, we apply these methods to identify innovations with the highest probability of substantially reducing the levelized cost of water from emerging membrane processes for high-salinity brine treatment.

Energy and CO2 Emissions Penalty Ranges for Geologic Carbon Storage Brine Management.

Safe and cost-effective geologic carbon storage will require active CO2 reservoir management, including brine extraction to minimize subsurface pressure accumulation. While past simulation and experimental efforts have estimated brine extraction volumes, carbon management policies must also assess the energy or emissions penalties of managing and disposing of this brine. We estimate energy and CO2 emission penalties of extracted brine management on a per tonne of CO2 stored basis by spatially integrating CO2 emissions from U.S. coal-fired electric generating units, CO2 storage reservoirs, and brine salinity data sets under several carbon and water management scenarios. We estimate a median energy penalty of 4.4-35 kWh/tonne CO2 stored, suggesting that brine management will be the largest post capture and compression energy sink in the carbon storage process. These estimates of energy demand for brine management are useful for evaluating end-uses for treated brine, assessing the cost of CO2 storage at the reservoir level, and optimizing national CO2 transport and storage infrastructure.

Performance Loss of Activated Carbon Electrodes in Capacitive Deionization: Mechanisms and Material Property Predictors.

Understanding the material property origins of performance decay in carbon electrodes is critical to maximizing the longevity of capacitive deionization (CDI) systems. This study investigates the cycling stability of electrodes fabricated from six commercial and two post-processed activated carbons. We find that the capacity decay rate of electrodes in half cells is positively correlated with the specific surface area and total surface acidity of the activated carbons. We also demonstrate that half-cell cycling stability is consistent with full cell desalination performance durability. Additionally, our results suggest that increase in internal resistance and physical pore blockage resulting from extensive cycling may be important mechanisms for the specific capacitance decay of activated carbon electrodes in this study. Our findings provide crucial guidelines for selecting activated carbon electrodes for stable CDI performance over long-term operation and insight into appropriate parameters for electrode performance and longevity in models assessing the techno-economic viability of CDI. Finally, our half-cell cycling protocol also offers a method for evaluating the stability of new electrode materials without preparing large, freestanding electrodes.

Magnetic Field-Induced Alignment of Nanofibrous Supramolecular Membranes: A Molecular Design Approach to Create Tissue-like Biomaterials.

A molecular design approach to fabricate nanofibrous membranes by self-assembly of aromatic cationic peptides with hyaluronic acid (HA) and nanofiber alignment under a magnetic field is reported. Peptides are designed to contain a block composed of four phenylalanine residues at the C-terminus, to drive their self-assembly by hydrophobic association and aromatic stacking, and have a positively charged domain of lysine residues for electrostatic interaction with HA. These two blocks are connected by a linker with a variable number of amino acids and the ability to adopt distinct conformations. Zeta potential measurements and circular dichroism confirm their positive charge and variable conformation (random coil, ß-sheet, or α-helix), which depend on the pH and sequence. Their self-assembly, examined by fluorescence spectroscopy, small-angle X-ray scattering, and transmission electron microscopy, show the formation of fiberlike nanostructures in the micromolar range. When the peptides are combined with HA, hydrogels or flat membranes are formed. The molecular structure tunes the mechanical behavior of the membranes and the nanofibers align in the direction of magnetic field due to the high diamagnetic anisotropy of phenylalanine residues. Mesenchymal stem cells cultured on magnetically aligned membranes elongate in direction of the nanofibers supporting their application for soft tissue engineering.

Flue Gas Desulfurization Wastewater Composition and Implications for Regulatory and Treatment Train Design.

The U.S. Environmental Protection Agency is currently revising its regulations on trace element discharges from flue gas desulfurization (FGD) wastewater. In this work, we expand a predictive model of trace element behavior at coal-fired power plants (CFPPs) to estimate the trace element concentration of FGD wastewater at the plant level. We demonstrate that variation in trace element concentrations in FGD wastewater can span several orders of magnitude and is a function of both coal rank and installed air pollution control devices. This conclusion suggests that the benefits and costs of FGD wastewater treatment for the median plant will poorly describe the actual benefits and costs over the full range of existing CFPPs. Our model can be used to identify different "classes" of CFPPs for future regulatory and technology development efforts and to evaluate the robustness of proposed treatment technologies in light of large intraplant variability. The model can also elucidate new compliance pathways that exploit empirical and mechanistic relationships between coal concentration, trace element partitioning, and FGD wastewater composition.

Trace Element Mass Flow Rates from U.S. Coal Fired Power Plants.

Trace elements (TEs) exit coal-fired power plants (CFPPs) via solid, liquid, and gaseous waste streams. Estimating the TE concentrations of these waste streams is essential to selecting pollution controls and estimating emission reduction benefits. This work introduces a generalizable mass balance model for estimating TE mass flow rates in CFPP waste streams and evaluates model accuracy for the U.S. coal fleet given current data constraints. We stochastically estimate, using a bootstrapping approach, the 2015 plant-level mass flow rates of Hg, Se, As, and Cl to solid, liquid, and gas phase waste streams by combining publicly available data for combusted coal TE concentrations with estimates of TE partitioning within installed air pollution control processes. When compared with measured and reported data on TE mass flow rates, this model generally overestimates masses by 30-50%, with larger errors for Hg. The partitioning estimates are consistent for Se, As, and Cl removal from flue gas, but tend to underestimate Hg removal. While our model is suitable for first-order estimates of TE mass flows, future work to improve model performance should focus on collecting and using new data on TE concentrations in the coal blend, where data quality is the weakest.

Cost Optimization of Osmotically Assisted Reverse Osmosis.

We develop a nonlinear optimization model to identify minimum cost designs for osmotically assisted reverse osmosis (OARO), a multistaged membrane-based process for desalinating high-salinity brines. The optimization model enables comprehensive evaluation of a complex process configuration and operational decision space that includes nonlinear process performance and implicit relationships among membrane stages, saline sweep cycles, and makeup, purge, and recycle streams. The objective function minimizes cost, rather than energy or capital expenditures, to accurately account for the trade-offs in capital and operational expenses inherent in multistaged membrane processes. Generally, we find that cost-optimal OARO processes minimize the number of stages, eliminate the use of saline makeup streams, purge from the first sweep cycle, and successively decrease stage membrane area and sweep flow rates. The optimal OARO configuration for treating feed salinities of 50-125 g/L total dissolved solids with water recoveries between 30-70% results in costs less than or equal to $6 per m3 of product water. Sensitivity analysis suggests that future research to minimize OARO costs should focus on minimizing the membrane structural parameter while maximizing the membrane burst pressure and reducing the membrane unit cost.

Mechanisms of Humic Acid Fouling on Capacitive and Insertion Electrodes for Electrochemical Desalination.

Though electrochemical deionization technologies have been widely explored for brackish water desalination and selective ion removal, their sustained performance in the presence of foulants common to environmental waters remains unclear. This study investigates the fundamental mechanisms by which carbonaceous electrodes used in capacitive deionization and insertion electrodes used for high-capacity selective ion removal are affected by the presence of humic acid (HA). We evaluate HA adsorption behavior and the resulting impact on the ion storage capacity and cycling stability of the electrode materials. We find that HA is primarily adsorbed to the mesopores of two carbonaceous electrodes with distinctly different pore structures, but that the ion storage and transport properties of the electrodes are not significantly impacted by HA adsorption. In contrast, HA adsorption resulted in sharp capacity decay for the insertion (Na4Mn9O18) electrode. We attribute this decay to both hindered Na+ ion diffusion to the insertion interface in the presence of adsorbed HA, as well as HA mediated electrode dissolution. These findings highlight the contrasting mechanisms for HA fouling of capacitive and insertion electrodes and suggest that insertion electrodes may be more susceptible to performance decline in electrochemical deionization of environmental waters.