ACS ES&T engineering最新文献

Selenium (Se) contamination in flue-gas desulfurization (FGD) wastewater from coal-fired power plants poses significant environmental and regulatory challenges. Here, we developed and optimized a three-dimensional electrochemical reactor (3DER) with carbon-based particle electrodes (PEs) to remove Se-(IV). Compared with conventional two-dimensional systems, the 3DER provides an enlarged electrode surface area, enabling faster removal kinetics and higher resilience without regeneration. Reactor performance was systematically evaluated as a function of PE geometry, recirculation rate, cell potential, and anode-to-cathode (A:C) chamber ratio. The optimized configuration (A:C = 1:2, E _cell = -2.1 V, recirculation rate 3.3 mL min^-1) balanced cathodic efficiency while minimizing anodic parasitic reactions. In synthetic wastewater containing 0.1 mM Se-(IV), the single-pass 3DER achieved steadily increasing performance, with hourly removal improving from 61.3% in the first hour to 68.1% by the 12th hour. Applied to real FGD wastewater, the system maintained an average hourly removal of 51.7% (4.2 mg of Se L^-1 h^-1) without regeneration and reached a specific energy consumption as low as 0.03 kWh g^-1 Se despite high chloride levels. Competing ions, including Mn and Si, further enhanced the Se reduction by forming oxide layers and rejecting Cl^- from the electrode surface. Enhanced kinetics under elevated Se-(IV) loadings yielded a peak removal of 74.4% (17.5 mg of Se L^-1 h^-1). These results demonstrate robust and efficient removal performance of the 3DER, supporting its promise for selenium-rich wastewater treatment and future scale-up.

Azelaic acid is a renewable monomer conventionally produced via the energy-intensive ozonolysis of oleic acid. Recent advancements have enabled the use of high-oleic vegetable oils (rather than tallow-derived oleic acid) and replaced ozonolysis with two-step oxidative cleavage using hydrogen and oxygen. Although this shift would improve process safety, the financial viability and environmental implications remain uncertain. In this study, we characterized the sustainability of azelaic acid production from high-oleic vegetable oil using two-step oxidative cleavage. Process design, simulation, technoeconomic analysis (TEA), and life cycle assessment (LCA) were executed under uncertainty using BioSTEAM. The modeled system produces azelaic acid at a market-competitive minimum selling price (MSP) of 8.32 [4.93-13.34] $ kg^-1 (median 5th-95th percentiles), below the minimum estimated market price of 9.93 $ kg^-1. Further, it has the potential to approach carbon neutrality (0.0 [-5.5 to 5.6] kg of CO₂-eq kg^-1) under displacement allocation. Improvements to dihydroxylation (86 to 99%) and oxidative cleavage conversions (93 to 99%) would reduce MSP to $5.24 kg^-1 and carbon intensity to -1.90 kg of CO₂-eq kg^-1 (displacement). Additionally, increasing the feedstock triolein content (75 to 85%) lowers MSP by $0.82 kg^-1. Overall, this research demonstrates the potential for financially viable production of azelaic acid from vegetable oils and the utility of agile TEA/LCA.

Locally enhanced electric field treatment (LEEFT) has emerged as a promising chlorine-free approach for water disinfection. However, its practical deployment has been limited by challenges in electrode durability and system scalability. Herein, we report a robust stainless-steel brush designed to enable long-term operation and scalability of LEEFT electrodes. A tubular reactor with coaxial electrodes featuring the brush as the center electrode was developed to combine both macroscale and microscale electric field enhancements. Operational parameters, including waveform, frequency, voltage, and flow rate, were systematically optimized to maximize microbial inactivation while minimizing metal release. Flow cytometry and control experiments revealed electroporation, assisted by reactive oxygen species, as the primary disinfection mechanism. Under optimal unipolar pulse conditions with high duty cycle and frequency, the system achieved efficient inactivation at voltages in the tens of volts range. Notably, the LEEFT system with the brush electrode has remained effective for about half a year with minimal metal release, representing a 10-fold increase in lifespan compared to previous LEEFT configurations. This work demonstrates a scalable, durable, and chemical-free solution for decentralized and sustainable water disinfection.

Nanofiltration (NF) membranes are increasingly being used to achieve precise solute-solute separation. These membranes are commonly synthesized using interfacial polymerization, offering great potential to separate lithium from magnesium. In this study, we have developed machine learning models that relate fabrication conditions, membrane properties, and operational conditions of NF membranes to predict water permeability and lithium/magnesium selectivity. Morgan fingerprints (MFs) and molecular descriptors (MDs) are used to represent the chemical and physical properties of the monomers. Explainable artificial intelligence tools such as Shapley additive explanations (SHAP) and partial dependence plots are used to evaluate the effects of the synthesis conditions and membrane properties on membrane performance. Based on the insights obtained from SHAP analysis, we developed a material screening approach to find promising monomers from a list of amines and cation-based ionic liquids. We construct a reference MF using the functional groups that positively contribute to membrane performance and compute a screening score that favors potential candidates with more desirable MDs. Finally, the synthesizability of these monomers is assessed using the synthetic accessibility score to find the most promising candidates. We compared the performance of screened monomers against traditional ones to validate the reliability of our approach. The results of this study provide critical insights into the relationships between synthesis conditions, membrane properties, and performance and establishes a novel, strategic framework for rational screening of monomers for NF membrane synthesis. This approach holds promise to accelerate the discovery of high-performance membranes tailored for specific separation challenges, thereby advancing the field of membrane technology.

Electrode behavior was elucidated during long-term galvanostatic electrocoagulation (aluminum anode and aluminum cathode) of a hypersaline oilfield produced water rich in divalent cations. Electrode potentials progressively increased (i.e., fouling) for most operational conditions due to surface accumulation of calcite and brucite. The interfacial resistance resulting from partial insulation by electrodeposited salts was quantified by using electrochemical impedance spectroscopy. The potential drop associated with this resistance correlated strongly and positively with the increased overpotential required to maintain the galvanostatic operation and was statistically indistinguishable from the calculated ohmic drop, confirming that electrode fouling could be fully attributed to ohmic effects. This also ruled out the occurrence of electrochemical side reactions at elevated potentials, despite their thermodynamic feasibility (note that H ₂(g) evolution is a non-Faradaic chemical reaction). We evaluated polarity reversal (PR) as a fouling mitigation strategy to restore electrode performance over a 4-fold variation in current density and a 100-fold variation in PR interval. The PR interval did not significantly influence performance, and fouling was effectively mitigated only at the highest applied current density (200 mA·cm^-2). Results indicated the existence of a threshold current density and associated hydrogen bubble generation rate necessary to effectively control electrode fouling under the experimental conditions investigated. Foulant deposition also hindered the migration of electrodissolved aluminum ions away from the anode, facilitating their supersaturation, nucleation, precipitation, and entrapment, thereby decreasing the apparent Faradaic efficiency of coagulant dosing.

This study investigates the impact of loosely bound (LB-) and tightly bound (TB-) polymeric substances (PS) on bioflocculation and organic matter harvesting in High Rate Activated Sludge (HRAS) systems, operated with primary effluent wastewater to specifically investigate the bioflocculation process. A pilot-scale HRAS system was operated at a contrasted solids residence time (SRT) of 0.2 and 0.8 d to assess the composition of polymeric substances extracted from the sludge (LB- vs TB-contents, biopolymers fraction), bioflocculation capacity, settleability, and the fate of organic matter. Results demonstrate that a low SRT (0.2 d) favors the accumulation of influent slowly biodegradable COD (more than 60% based on COD mass balance) and of LB-PS with a limited biopolymer content (<30%). The high LB-PS content observed at 0.2 d SRT (259 ± 15 mgCOD/gVSS) in turn hinders bioflocculation, resulting in the formation of small and loose flocs and a higher loss of effluent suspended solids. Conversely, sludge grown at 0.8 d SRT exhibited a lower LB-EPS (116 ± 9 mgCOD/gVSS) content with a better bioflocculation, resulting in the formation of larger, more structured and fluffier flocs. A poor bioflocculation at low SRT hampered particulate and colloidal organic matter removal, ultimately limiting the harvesting of organic matter despite an increased redirection. Overall, our results provide relevant insights into the role of sludge composition (influent slowly biodegradable COD, LB-PS, biopolymers content) in the bioflocculation and resulting harvesting of organics in HRAS systems. Our results also suggest that operation of HRAS systems at a very low SRT (e.g., 0.2 d) has the potential to increase the harvesting and valorisation of the organic matter of municipal wastewater but requires a better control of bioflocculation.

Photocatalytic antibacterial technologies, leveraging light-driven generation of reactive oxygen species (ROS), offer a promising, antibiotic-free alternative to combat the growing challenge of antibiotic-resistant bacteria. Graphitic carbon nitride (g-C₃N₄), a nonmetallic photocatalyst, is particularly appealing due to its abundant availability, ease of synthesis, and stability. However, challenges such as limited light absorption, rapid electron–hole recombination, and low surface area restrict its efficiency. This review highlights the synthesis, design strategies, and mechanisms behind g-C₃N₄’s photocatalytic antibacterial activity, focusing on ROS-induced bacterial inactivation. We discuss key engineering strategies─morphological optimization, chemical doping, heterojunction formation, and carrier confinement domain engineering─that enhance its photocatalytic properties. The review also addresses recent advancements in g-C₃N₄-based photocatalysis for environmental remediation, including water purification, fouling/corrosion prevention, and biological applications such as wound healing and bone regeneration. This work aims to provide insights into the rational design of g-C₃N₄ for sustainable, effective disinfection applications across various environmental and healthcare sectors.

Anthropogenic air pollution is one of the major threats to planetary and human health. In this view, nitrogen oxides (NO_x) and nitrous oxide (N₂O) are among the key responsible by contributing to photochemical smog, acid rain, eutrophication, and a variety of health issues. Effective after-treatment abatement technologies like selective catalytic reduction and decomposition routes exist, but the simultaneous conversion of NO_x and N₂O remains under-explored. This perspective addresses the challenges and opportunities in optimizing catalytic technologies for individual and simultaneous NO_x, N₂O, and NH₃ conversion. The integration of advanced catalytic systems in both established industrial processes and emerging technologies relying on the use of NH₃ as a fuel is crucial for achieving sustainable and environmentally friendly solutions. Addressing these challenges can significantly reduce greenhouse gas emissions and ensure ammonia’s promise as a low-impact carbon-free fuel. This publication emphasizes the importance of continuous innovation in the field of catalytic conversion strategies to meet stringent environmental regulations and mitigate the impacts of NO_x and N₂O emissions. Developing cost-effective, high-performance catalysts under real industrial conditions is essential for the widespread adoption of these technologies and the transition to a more sustainable future.

Plastic pollution has become a global environmental challenge, driving interest in enzymatic polyethylene terephthalate (PET) recycling by using polyester hydrolases. In this study, we produced the PET-degrading enzyme PHL7 and its variant PHL7mut3 in Escherichia coli and Pichia pastoris (syn. Komagataella phaffii) to investigate the impact of N-glycosylation on enzyme properties. While glycosylation upon expression in P. pastoris enhanced thermal stability, it reduced the catalytic activity of the enzymes, revealing a trade-off that adds complexity to the selection of the best-suited expression system. Additionally, we engineered P. pastoris to produce non-glycosylated enzyme variants by substituting the asparagine residues (N) at all three putative N-glycosylation sites with glutamine residues (Q). The non-glycosylated P. pastoris-produced enzymes showed a lower activity compared to those produced in E. coli, likely due to the differences in the amino acid sequence. The effects of glycosylation were less pronounced in PHL7mut3 than in PHL7, yet N-glycosylation strongly influenced the performance of both enzymes. We further demonstrate that the PET degradation performance of PHL7mut3 is less dependent on the buffer ionic strength than that of PHL7. The study emphasizes the need for the informed selection of a suitable expression host for polyester hydrolases to balance enzyme activity, thermostability, and production titer for applications in PET recycling.

Ozone, a strong oxidant, induces oxidative degradation in various materials and is known as an effective chemical for polymer modification. This study assesses ozone as an alternative to chlorine oxidation for converting end-of-life reverse osmosis membranes into nanofiltration- and ultrafiltration-like membranes across various new and used reverse osmosis and nanofiltration membranes. Membranes were characterized in terms of permeability and salt rejection, as well as surface characterization. Experiments were conducted at high ozone exposure (20 ppm) and low ozone exposure (3 ppm). At high exposure, ozone was found to degrade both the polyamide (PA) and polysulfone (PSf) layers, opening new possibilities for polyester (backing layer) recycling. At low exposure, degradation was limited to the PA layer; ozone converted membranes more effectively than chlorine, achieving similar performance in less time and at lower doses75 and 225 L·m^-2·h^-1·bar^-1 for SW and BW membranes after 30 min at 3 ppm ozone, comparable to 6000 ppm chlorine over 50 h. Ozone significantly impacted NF90, raising the permeability to 150 L·m^-2·h^-1·bar^-1 in 15 min at 3 ppm, while NF270 remained more resistant at 35 L·m^-2·h^-1·bar^-1. Ozone caused patchy degradation due to bubble interactions, while chlorine led to uniform attack. These findings highlight ozone's potential as a viable and more sustainable alternative to chlorine for polymeric membrane transformation.