ACS ES&T engineering最新文献

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.

Recovering ammonia from wastewater by membrane distillation (MD) is a sustainable approach to remediating environmental issues while simultaneously conserving energy both in wastewater treatment and in the Haber-Bosch process. MD leverages the volatility of ammonia to enhance ammonia transport, and hence its performance is impacted by the pH of the solution. We comprehensively investigated the effect of pH on ammonia transport and recovery efficiency using both experimental and simulation approaches. Our analyses provide new insights into how solution pH significantly impacts ammonia recovery through two primary mechanisms: it both governs the ammonia-ammonium equilibrium and influences the ammonia mass transfer coefficient. When changing MD feed solution pH from 9 to 10, ammonia flux is enhanced by 177% and ammonia mass transfer coefficient increases from 2.64 × 10^-6 m·s^-1 to 6.14 × 10^-6 m·s^-1. Notably, solution pH adjustment has a more significant effect than increasing solution temperature on enhancing the ammonia mass transfer coefficient and improving recovery efficiency, making it a more feasible and effective approach for improving ammonia transport and recovery. Additionally, our explicit simulations of ammonia recovery efficiency provide valuable insights for optimizing MD performance by adjusting solution pH values and operation time, and enable a maximum profit estimation of $598,000 for operating MD to recover ammonia in a dairy farm with 2000 cows.

Locally enhanced electric field treatment (LEEFT) is an emerging technology that employs electric fields to inactivate bacteria in water. Compared to traditional chlorine-based solutions, LEEFT allows for efficient water disinfection while preventing the formation of harmful disinfection byproducts. When combined with copper (Cu), a material recognized for its antimicrobial properties, LEEFT-Cu has demonstrated increased bacteria inactivation efficiency. In this study, LEEFT-Cu is tested for its disinfection performance against 8 different bacteria (4 Gram-negative (G-) and 4 Gram-positive (G+)), each grown in both stable and exponential phases. The primary focus is on the effectiveness of LEEFT-Cu against both gram structures. It is concluded that LEEFT-Cu can achieve >3 log removal for most bacteria species (7/8) using <0.7 mg/L Cu. Additionally, the calculated degree of improvement using LEEFT-Cu in comparison to Cu ions alone indicates >20 times increase in disinfection performance. The degree of improvement also leads to the conclusion that G+ bacteria are up to 3 times more vulnerable to the impacts of EFT (i.e., increased membrane permeability) than G-. Future work should focus on testing the current bench-scale prototype with more complex water matrices to further advance LEEFT-Cu for practical applications in water disinfection.