ACS ES&T engineering最新文献

Long-term anaerobic digestion (AD) of food waste often faces challenges, with volatile fatty acid inhibition being a common issue that hinders optimal performance. This research explores the effect of biochar supplementation on long-term AD of food waste characterized by volatile fatty acid inhibition. The findings demonstrate that adding a modest amount of biochar (0.055 g/L) effectively enhances AD under ambient conditions at 29 °C. This biochar supplementation reduced volatile fatty acids to a safe level of 1195 mg/L after 36 days, well within the generally accepted safe threshold of 1500 mg/L. This safe threshold is supported by other studies, which indicate that maintaining VFA concentrations below 1500 mg/L minimizes the risk of process inhibition and ensures stable AD operation. Additionally, the normalized specific biogas yield averaged 1.33 ± 0.45 m³/kg VS, representing a 47.4% improvement over the control AD conducted under identical conditions. After stabilization, the study assessed whether AD could maintain functionality and stability under mesophilic conditions (35 °C) without further biochar supplementation, simulating a real-world scenario to test long-term efficacy in industrial-like conditions. This mesophilic postbiochar AD resulted in an additional 31.8% increase in the normalized average specific biogas yield, reaching 1.95 ± 0.25 m³/kg VS. Biochar increased Methanosaeta methanogens by 30%, enhancing direct interspecies electron transfer and strengthening syntrophic interactions. This shift made aceticlastic methanogens 9 times more prominent, improving acetate oxidation, biogas yield, and overall AD stability. These findings highlight biochar’s potential to enhance decentralized biogas facilities, promote sustainable food waste management, and advance the bioeconomy by providing a replicable model for closing the food waste loop.

A tail end-of-life reverse osmosis (RO) element from the third stage of a three-stage train extensively fouled by silicon was investigated for the effects of repeated alkaline cleaning and their consequences on foulant reversal and membrane integrity. Detailed surface characterization revealed that after four years of operation in the world’s largest potable reuse facility, it was severely fouled by inorganic substances with lesser contributions from bioorganic materials that together had reduced its water permeance and salt rejection to only ∼20 and ∼80% of their initial values, respectively. Swatches of the heavily fouled membrane were exposed repeatedly (but separately) to two high-pH cleaning agents (NaOH or TPP/DBS, a mixture of sodium tripolyphosphate and sodium dodecylbenzesulfonate) simulating repetitive cleaning-in-place (CIP) protocols typical of real-world operations. Although five-to-ten cleaning cycles fully recovered the fouled membrane’s water permeance, salt rejection always remained below 90% confirming its end-of-life. X-ray photoelectron (XPS), energy-dispersive X-ray (EDS), and Fourier transform infrared (FTIR) spectroscopy of fouled membranes implicated silicon as the dominant foulant, which was only partially removed even after ten cleaning cycles, although water permeance was completely restored. Importantly, exposing a virgin membrane to identical “cleaning” regimens as the end-of-life membrane artificially increased water permeance without changing its salt rejection. FTIR and XPS scans of the virgin membrane following repetitive exposure to NaOH or TPP/DBS revealed no damage/degradation of its polyamide layer as demonstrated by the relatively constant amide I/amide II absorbance ratios and consistent oxygen/nitrogen atomic ratios, both symptomatic of maintaining membrane integrity. Hence, we phenomenologically invoked swelling and/or surface property modifications to mechanistically explain the quantitative increase of water permeance after repeatedly exposing the virgin membrane to CIP agents (while maintaining the active polyamide layer’s integrity). Similarly, we attributed a portion of the restored permeance of the fouled membrane upon progressive chemical cleaning to swelling and/or surface property modification that could be indirectly inferred. Therefore, it is paramount to comparatively characterize virgin and fouled membranes prior to and after exposure to CIP chemicals to distinguish foulant removal from other mechanisms potentially contributing to recovering water permeance.

A biofilm is a major contributor to microbiologically influenced corrosion (MIC) in cooling water systems, resulting in severe economical and environmental impacts. d-Amino acids offer a potential alternative for preventing biofilm formation in these systems, where salinity levels vary due to diverse water sources, such as freshwater and diluted seawater. However, the impact of d-amino acids on corrosion inhibition under saline conditions remains unexplored. In this study, we evaluated the effect of d-phenylalanine (d-Phe) on corrosion by Desulfovibrio vulgaris at three salinity levels. d-Phe (10 mg/L) played little role in corrosion inhibition at low salinity (5 g/L) but obviously decreased the corrosion by 40.6% and 59.6% at moderate salinity (15 g/L) and high salinity (20 g/L), respectively. It was attributed to that d-Phe reduced the secretion of extracellular protein from 292.5 μg/mg to 245.6 μg/mg and decreased the biofilm thickness from 25.46 μm to 20.87 μm on the coupon surface. Besides, d-Phe decreased the sessile cells from 15.1 × 10⁷ cells/cm² to 12.8 × 10⁷ cells/cm² at high salinity. Furthermore, transcriptome analysis found that indole, the signal molecule negatively regulating the biofilm formation, was increased by adding d-Phe at high salinity. Moreover, peptidoglycan reorganization was strengthened at high osmotic pressure via absorbing additional d-Phe, leading to weak bacterial adhesion. The work provides mechanistic insights into the application of d-Phe for biofilm inhibition and MIC mitigation in industries.

Nanoscale zerovalent iron (nZVI) is a promising remediation agent for the removal of heavy-metal wastewater. However, nZVI tends to agglomerate and be oxidatively deactivated during the reaction, which limits its application. To address the problem, this study develops a novel modification method to regulate the reaction interface of nZVI by introducing fulvic acid (FA), a naturally occurring environmental component, to the synthesis of nZVI. FA disrupts the circumferential-stress equilibrium of nZVI, enhances the Kirkendall effect, and establishes mass-transfer channels, facilitating the outward transfer of reducible Fe(II) and electrons and the inward transport of surface-adsorbed Cr(VI). The Cr(VI) removal is further enhanced by coupling FA-nZVI with Shewanella oneidensis MR-1, which reduces Fe(III) hydroxides to Fe(II) at the FA-nZVI interface, thereby preventing accumulation of the passivation layer that blocks the mass-transfer channels. The synergistic action of mass-transfer channels with MR-1 enhances the Cr(VI) removal rate by 4.7 times, ensuring a Cr(VI) removal rate of more than 60% under extreme conditions. By exploring the new functions of FA as an organic carbon component, this study provides a fresh perspective on carbon utilization in ecosystems. Leveraging environmental factors for the microstructural modulation of nZVI is an efficient and environmentally friendly approach for remediation of heavy-metal pollution.

The solubility of hydrophobic pollutants in the aqueous phase affects the degradation efficiency of the pollutants, and cosolvents are usually used to enhance the solubility of hydrophobic pollutants; however, the effect of cosolvents on the pollutant degradation process is not clear. This study constructed a sodium dodecylbenzenesulfonate (SDBS)/Fe@Fe₂O₃/PMS system for the efficient removal of tetrabromobisphenol A (TBBPA). SDBS increases the adsorption of oxygen species on the surface of Fe@Fe₂O₃, disrupts the dense oxide layer, and promotes the release of iron ions from the core. Kinetic results indicate that the degradation rate constant of TBBPA increases by 87.5 times in the presence of SDBS, and the system is minimally affected by environmental factors, making it broadly applicable. SDBS enhances the dissolved oxygen in the system, promotes the conversion of hydroxyl radicals (^•OH) into superoxide radical (O₂^•–) and singlet oxygen (¹O₂), and facilitates the transformation of TBBPA into TBBPA radical cations through electron transfer, which then undergoes debromination, hydroxylation, and demethylation to form small molecular degradation products. The dual role of SDBS enables the reutilization of aged ZVI, making it a promising technology for pollutant remediation.

The high level of sulfate in phosphogypsum (PG), a byproduct of phosphoric acid production, offers an option of recovering elemental sulfur (S⁰). The first step is reducing sulfate to soluble sulfide, which can then be partially oxidized to S⁰. We evaluated sulfate reduction to soluble sulfide using a hydrogen-based membrane biofilm reactor (H₂-MBfR) from PG leachate (PG water). The H₂-MBfR was initiated using synthetic sulfate medium prior to switching to PG water, and it achieved sulfate removal of 70–80% and ∼60% of influent S as soluble sulfide. Upon switching to PG water, sulfate removal flux increased due to higher sulfate surface loading, but soluble sulfide kept declining and precipitates began forming. Venting the fibers to release accumulated CO₂ increased the H₂ availability and improved flux. Batch operation increased the generation of soluble sulfide, as sulfate was reduced biologically instead of precipitating as CaSO₄ (as verified by X-ray diffraction and solubility calculations). Alkalinity analyses quantified the effects of precipitation, mainly CaSO₄, on the sulfide reduction performance. While H₂-MBfR demonstrated promise for reducing sulfate to sulfide in PG water, its long-term success will require that calcium be minimized to reduce abiotic sulfate removal, while H₂ delivery must slightly exceed the H₂ demand for biological sulfate reduction to sulfide.

Perfluorocarbons (PFCs) are synthetic industrial chemicals, which, once released into the atmosphere, exhibit strong greenhouse effects. They are also potential products of incomplete degradation of per- and polyfluoroalkyl substances in thermal processes. This study aims to fill a significant gap in the literature regarding the thermal stability of PFCs. Among the PFCs examined, perfluorohept-1-ene (C₇F₁₄) and perfluorooct-1-ene (C₈F₁₆) degraded at temperatures as low as 200 °C, achieving near-complete degradation at approximately 300 °C. The mineralization of these two unsaturated PFCs reached up to ∼40 mol % at temperatures between 300 °C and 500 °C. In contrast, their saturated counterparts required significantly higher temperatures (≥600 °C) for similar levels of degradation and yielded less than 10 mol % fluorine. This disparity is likely due to the hemolytic thermal cleavage of the relatively weak C3–C4 bonds in the unsaturated PFCs, initiating radical-chain reactions that release fluorine. The analysis indicates that the thermal degradation pathways of perfluoroalkenes predominantly involve chain scission and cyclization, leading to the formation of various linear and cyclic byproducts, particularly at temperatures below 500 °C. The addition of granular activated carbon enhanced the thermal mineralization of these PFCs, whereas common commercial catalysts were only moderately effective or ineffective.

Single-atom catalysts (SACs) such as iron (Fe) SACs have recently shown great promise for catalytic ozonation, but the major reactive species for pollutant degradation remain unclear. Here, a series of Fe SACs doped in porous nitrogen-doped graphitized carbon (Fe₁@NC, Fe₅@NC, Fe₁₀@NC) were prepared and used as model SACs for catalytic ozonation. It was found that the Fe₅@NC had much greater reactivity for catalytic ozonation than common catalysts, which was ascribed to the abundant catalytic sites including surface oxygen-containing groups and Fe–N₄ moieties. Pretreatment of Fe₅@NC by ozonation for 3 h did not deactivate the material. Accelerated formation of hydroxyl radicals in Fe SACs–O₃ oxidation was verified by electron spin resonance spectroscopy, but quenching tests showed conflicting results. Based on the experimental studies and density functional theory calculations, a pollutant-dependent degradation mechanism involving either free hydroxyl radicals or surface oxygen atoms as oxidizing species was proposed. Surface oxygen atom-dominated oxidation required the pre-adsorption of pollutants onto Fe₅@NC, otherwise, free hydroxyl radical-mediated oxidation occurred. This mechanism is expected to clarify the inconsistency regarding the formation of major reactive species in catalytic ozonation and could deepen our understanding of the catalytic behavior of SACs.

This study introduces a novel method for CO₂ capture and utilization by integrating chemically and physically dual-modified amino cellulose aerogels with microalgae-immobilized silk fibroin/sodium alginate (SF/SA) composite hydrogels. The modified cellulose aerogels, enhanced with 3-(2-aminoethylamino)propyl-dimethoxymethylsilane (AEAPMDS) and fumed silica-polyethyleneimine (SiO₂@PEI), exhibited significantly improved CO₂ adsorption capacity, mechanical strength, and thermal stability compared to microcrystalline cellulose (MCC) aerogels. This modification addresses the limitations of traditional physical and chemical adsorption methods. The captured CO₂ was effectively utilized by the microalgae embedded in the SF/SA hydrogel, leading to increased growth rates, improved carbon fixation efficiency, and reduced energy consumption during CO₂ capture and storage. Temperature regulation was applied to optimize CO₂ adsorption and desorption, demonstrating the system’s potential for air quality improvement and sustainable bioengineering applications, providing a new strategy to combat climate change.

Hypersaline produced water with >100,000 mg/L total dissolved solid concentration arising from unconventional oil and gas operations in the Permian Basin, Texas, was electrocoagulated with an aluminum anode and cathode. Anodic aluminum dissolution, formation of a (hydr)oxide passivation layer, and morphology and physicochemical properties of electrodes pre- and post-electrocoagulation were thoroughly characterized by microscopy, spectroscopy, and electrochemical techniques over a 10-fold variation in current density (2–20 mA/cm²) and a four-fold change in charge loading (CL) (∼270–1080 C/L). In addition to the anticipated oxidative anodic electrodissolution, both electrodes underwent chemical dissolution, leading to super-Faradaic aluminum dosing and lowering the bulk pH, contrary to the oft-cited advantage of electrocoagulation over conventional alum coagulation. The remarkably high concentration of chloride ions (∼68,000 mg/L) significantly influenced anodic dissolution behavior primarily by damaging the passive aluminum oxide layer leading to pitting corrosion. Importantly, organic compounds in the produced water negligibly impacted anodic aluminum (electro)dissolution. Not only the total CL but also the current affected pitting. Passing more current (and higher current densities) increased the chemical dissolution of aluminum, enhancing super-Faradaic behavior, and simultaneously increased the surface area and depth of pits (at constant CL) but had negligible effects on the floc size and morphology. The dependence of pitting and Faradaic efficiency on current constitutes a novel finding and is specific to hypersaline solutions as ohmic overpotentials were insufficient to trigger side reactions. Post-electrocoagulation, electrodes repassivated by consuming dissolved oxygen, resulting in a thicker and more conductive (hydr)oxide layer, characterized as an n-type semiconductor via Mott–Schottky analysis. Electrocoagulation effectively removed silicon (∼90%) by forming aluminosilicate flocs. Calcium and magnesium were removed by cathodic electrodeposition albeit to substantially smaller extents (∼20%) and strontium removal was negligible.