ACS ES&T engineering最新文献

Despite the increasing number of studies on nitrogen (N) and phosphorus (P) removal in free water surface (FWS) wetland systems, there is still a gap in understanding the influence of design variables on the system performance. To address this, we conducted a global meta-analysis of 73 studies employing advanced statistical techniques, kinetic models, and machine learning along with variable importance analysis. The results indicated that random forest (R² = 0.55–0.77) and artificial neural network (R² = 0.5–0.85) were the best fitting models for TN and TP removal in pilot-scale and large-scale systems. Moreover, permutation importance results using different wetland design variables indicated that the inflow concentration, plant coverage, hydraulic loading rate, and system area are considered the most important variables for N and P removal under large-scale conditions, while the hydraulic retention time, inflow concentration, and water depth are deemed the most important variables under pilot-scale conditions. Furthermore, the removal of N and P was higher in pilot-scale (54.6% and 56.7%) systems compared to that in large-scale (29.0% and 41.9%) systems. Also, the interactions between design variables and the removal process of N and P were investigated to better understand the specific roles of these variables in improving the removal performance.

Palladium–indium (PdIn) is a well-established bimetallic composition for reductively degrading nitrate anions, one of the most ubiquitous contaminants in the groundwater. However, the scarcity and the variable price of these rare-earth and platinum group critical metals may hinder their use for water treatment. Nickel (Ni), a nonprecious metal in the same element group as Pd, could partially replace and lower Pd usage if the resulting trimetallic composition is sufficiently catalytically active. Herein, we report the synthesis and nitrate reduction catalysis of activated carbon-supported “In-on-Pd-on-Ni” catalysts (InPdNi/AC). While bimetallic InPd/AC (0.05 wt % In, 1.3 wt % Pd) was expectedly active, trimetallic InPdNi/AC containing the same In amount, much less Pd (0.1 wt %), and 1 wt % Ni was >17 more active (k_cat ≈ 20 vs 349 L min^–1 g_{surface metal}^–1). X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations showed that Pd gained electron density from Ni, correlating to the increased nitrate reduction activity. Ammonium byproduct selectivity for InPdNi/AC (18% at 50% nitrate conversion) was lower compared to that of InPd/AC (48%), suggestive of the higher surface coverage of NO or its greater reactivity with NO₂^–, which led to more N₂. Accounting for the catalyst precursor, manufacturing costs, and spent metal recovery, we calculated that Ni incorporation lowered the net catalyst cost significantly (from $1028/kg to $170/kg). The trimetallic composition lowered, by ∼26 times, the catalyst cost of a stirred tank reactor sized to the same treatment capacity as that for the bimetallic case. The results demonstrate that the partial replacement of the precious metal with an earth-abundant one leads to a higher efficiency and lower cost denitrification catalyst, via a material strategy that should be beneficial for other clean-water catalytic systems.

The efficient treatment and energy recovery from salvaged microalgae have been imperative considering both environmental and economic concerns. Herein, this study proposed a biotechnological platform for converting microalgae into medium-chain fatty acids (MCFAs) through anaerobic fermentation as well as exploring the roles of different electron donors (EDs). After exploring various ED combinations, the results suggested that a single ED, especially sole ethanol stimulation, exhibited more pronounced stimulation effects on MCFA production compared to those of the hybrid ED stimulations. Furthermore, ethanol and lactic acid served as the basis for the formation of longer-chain alcohols and odd-chain fatty acids in the liquid fermentation products, respectively. The dynamics and thermodynamics analyses confirmed the distinctions in the accumulation trends and saturated compositions of main products under different ED compositions. Moreover, mechanistic investigations revealed that differences in chain elongation efficiency of ethanol and lactic acid and in the genome-based metabolic potential for the microbial systems contributed to the intricate feedback regulations of biochemical reactions in different microalgae fermentation scenarios. Overall, this study provided valuable insights for sustainable energy conversion of microalgae by orienting toward the recovery of high-value biochemicals, serving as a theoretical basis for the selection and optimization of ED before industrial application.

Anaerobic sequencing batch reactors (ASBRs) treating wastewater rich in ciprofloxacin (CIP) were supplemented with an Fe/Zn@biochar catalyst to improve their performance. ASBR4, with 100 mg Fe/Zn@biochar/g_VS, showed substantial increased efficiencies in removing COD and CIP, reaching 86.9 ± 5.8 and 80.9 ± 8.6%, respectively, compared to no biochar addition (25.2% and 51.1% higher, respectively). Likewise, biogas yield augmented from 0.17 ± 0.06 to 0.34 ± 0.02 L/g COD_removed owing to the boosted abundance of acetolactic methanogens, i.e., Methanosaeta and Methanosarcina, which increased from 0.4 and 1.6% in the control ASBR1 to 1.6 and 2.2% in ASBR4, respectively. Microbial enzymatic activities, including dehydrogenase and extracellular polymeric substances (EPSs), highly increased by 38% and >100%, respectively, aiding in biochar adsorption and microbial biodegradation synergy. Fe/Zn@biochar contributed to both CIP adsorption and biodegradation with percentages of 59.5 ± 4.9 and 34.7 ± 2.6%, respectively. The synergistic effect between the biotic and abiotic impacts of Fe/Zn@biochar reached 94.2 ± 7.2%, suggesting that the addition of Fe/Zn@biochar is a promising approach to enhance the CIP-remediation process.

Algal organic matter (AOM), comprising intracellular organic matter (IOM) and extracellular organic matter (EOM), poses a significant challenge to drinking water safety. Coagulation serves as an effective method for removing algae, and investigating the binding sites of coagulant hydrolyzates is crucial for comprehending the coagulation mechanism. In this study, a novel polyferric titanium sulfate (PFTS) composite coagulant was prepared and used to remove AOM. Characterization techniques, including Fourier infrared (FTIR), X-ray photoelectron spectroscopy (XPS), hydrolysis polymerization curves, and chemical species analysis were utilized to identify the hydrolyzates of PFTS. The results revealed the formation of Fe–Ti copolymers through the interaction between Fe hydroxyl and Ti hydroxyl, facilitated by a Fe–O–Ti bond. Under optimal coagulation conditions (50 mg/L dosage at neutral pH), PFTS demonstrated superior performance in treating EOM and IOM compared to PFS and PTS, achieving significant DOC removal efficiencies of 46.69% and 56.8%, respectively. Furthermore, the removal characteristics of organics were investigated at the molecular level using Fourier transformation cyclotron resonance mass spectrometry (FT-ICR MS). It was found that organic compounds with unsaturated (H/C < 1.0) and oxidized (O/C > 0.5) substances containing carboxyl groups in AOM could be preferentially removed by PFTS for the carboxyl group demonstrate a higher affinity to Fe and Ti hydroxyl formed in PFTS coagulation. XPS and water contact angle analysis were conducted to gain deeper insights into the interaction between the hydrolyzates of PFTS and AOM. The findings demonstrated that Fe–Ti hydrolyzates could bind with EOM and IOM by forming coordination bonds and H–O···O and H–O···N hydrogen bonds with its −COOH, −NH₂, and −OH groups through bonding reactions. This study highlights the potential of composite coagulants as alternatives to conventional coagulants for the purification of algae-laden water.

This study explored the enhanced medium-chain fatty acids (MCFA) production by introducing a biocathode as a coelectron donor (ED) in the presence of different ethanol/acetate ratios (R_E/A). Results showed that the introduction of a biocathode effectively promoted MCFA production by 165%–749%. The highest promotion rate was achieved at R_E/A = 0:3, and the highest MCFA concentration of 305.1 mmol C/L was obtained at R_E/A = 2:1. Besides, the introduction of a biocathode also triggered the formation of longer-chain MCFA (i.e., caprylate), and caprylate production was increased with the increase of R_E/A. Electrochemical analyses exhibited a positive correlation between the electrochemical activity and R_E/A. Microbiological analyses showed that the introduction of a biocathode promoted MCFA production by enriching chain elongation functional microorganisms (unclassified_f_Neisseriaceae sp. and Clostridium_sensu_stricto_12 sp.) and electrochemically active bacteria (Alcaligenes sp.). Enzyme analyses indicated that promoted MCFA production was achieved by strengthening the acetyl Co-A formation and fatty acid biosynthesis pathway.

Electrocatalytic reduction of nitrate (NO₃^–) to ammonia (NH₃) (NO₃RR) coupled with NH₃ separation represents a sustainable approach to mitigate nitrate pollution and recycle nitrogen from contaminated water. Nevertheless, this process is deemed impractical for contaminated natural water bodies owing to the limited presence of NO₃^––N (<50 mg L^–1) and electrolytes and the relative abundance of scaling ions (Mg²⁺ and Ca²⁺). Furthermore, copper (Cu), as the primary NO₃RR catalyst, generally suffers from NO₂^– accumulation and a prevalence of side hydrogen evolution. Herein, we develop an integrated system comprising sections of NO₃^– enrichment and NO₃RR and NH₃ collection, alongside a single-atom Cu-bearing CeO₂ catalyst (Cu₁/CeO₂) for NO₃RR. With this system, diluted NO₃^– is extracted from contaminated water using anion-exchange resins and then released into a concentrated NaCl aqueous solution, providing a solution with ample NO₃^––N (∼822 mg L^–1) and electrolytes (∼1.7 M NaCl) while being free of scaling ions. Within this solution, the Cu₁/CeO₂ demonstrates an exceptional high and steady NH₃–N production rate of 7.8 g_NH3–N g_Cu^–1 h^–1, an NH₃–N selectivity of 90.1%, and a Faradaic efficiency of 91.3%, outperforming the Cu nanoparticles (1.8 g_NH3–N g_Cu^–1 h^–1, 46.3%, and 53.0%). In situ experiments and theoretical computations reveal a dual-site NO₃RR mechanism involving the electron-deficient Cu₁ site and adjacent oxygen vacancies, which collaborate to promote NO₃^– adsorption and lower conversion barrier while inhibiting hydrogen evolution. Finally, we implemented the integrated system along the Yangtze River, achieving nitrate elimination and nitrogen recycling with a competitive energy consumption of 1.36–1.54 kW h mol_N^–1.

The removal of gas environmental pollutants from their gaseous state using electrochemical methods is a futuristic technology. The effective migration of ions to the electrode without liquid electrolyte plays a key role in facilitating the removal from the gaseous state. In this study, a poly(vinyl alcohol)-sodium silicate gel membrane and a cobalt-modified graphitic carbon nitride (Co-GCN) electrode were developed for the mineralization of a common air pollutant, acetaldehyde (AA). Confocal laser microscopy, electrochemical impedance spectroscopy, and SEM-EDS analysis demonstrated that the as-prepared gel membrane stably conducts ions with lower resistance. The analysis of Co-GCN using XRD, FTIR, and cyclic voltammetry show a possible coordination of cobalt ions with GCN. At a given applied potential of 0.8 V, 82% removal of AA (80 ppm in 1 h) was achieved. The electron transfer kinetics follow pseudo-first-order kinetics, as the variation in the removal rate is less over a wide range of AA feed concentrations. For applied potentials above 1 V, the complete formation of CO₂ was equivalent to AA removal, with a formation capacity of 1.37 g cm^–2 h^–1. The seed of this first attempt at gaseous AA mineralization may open a new way to remove environmental gaseous pollutants.

Phototrophs with heterotrophic bacterial consortium as an electrode biocatalyst are an emerging concept for developing naturally sustained biophotovoltaic systems. Herein, Spirulina subsalsa-based mixed heterotrophic bacterial community as an anodic catalyst in a microbial fuel cell (MFC) setup with ferricyanide catholyte in 78 days light–dark (16–8 h) cycle-based operation was investigated. The biofilm developed with Spirulina inducted a recalcitrant bacterial community comprising Halomonas, Alcanivorax, Pelagibacterium, and Rhizobiales as the major genera. In an extended dark phase (9 days) within the cyclic operation, a sequential shift of the metabolism from photosynthesis to fermentative states and an increased heterotrophic population were observed. Under direct contact with the graphite anode, the biofilm initiated oscillating open-circuit potentials in the MFC in response to the light–dark circadian trend. The MFC delivered maxima of 587 μW m^–2 and 418 μW m^–2 (at 10 kΩ) under the corresponding circadian and extended dark phases, respectively. The anodic potential shifted to a more negative value, reaching −415.5 mV in the dark starvation period. Analyses of electrode reaction rates (extracted from Tafel plots), corrosion potential, corrosion current, polarization resistance, and residual redox charges (extracted from cyclic voltammograms) were performed to understand the redox processes. Two redox peaks corresponding to 0.6 V (irreversible, extracellular) and 0.26 V (reversible, cell-surface attached) were attributed to redox mediation in this process. Additionally, catholyte-diffused ferricyanide interacts with the biofilm, getting trapped in the matrix polymeric structures, thus preventing the sudden cytotoxic elimination of cells and promoting oxidative charge accumulation over its surface, improving the anodic potential. Rapid respiratory oxygen consumption, the biofilm’s structural reorganization, and ferricyanide’s chemical speciation inside the biofilm were the primary factors that govern the anodic performance of the biofuel cell during the prolonged dark phase operations. The critical findings unveiled through this study advance our understanding of the resilience of phototroph-based multispecies anodic catalysts for developing biophotovoltaic devices for long-term operations.

Microorganism-dominated nitrogen conversion in wastewater treatment is of great significance to the nitrogen cycle. Until now, Fe⁰ has been widely used in sludge dewaterability, sulfide control, and bioenergy recovery. However, there is limited information about the comprehensive assessment of Fe⁰ on multiple biological nitrogen removal processes. Here, the impact of Fe⁰ dosage on the activity of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, anammox bacteria, and denitrifiers was evaluated. The results revealed that anammox has a more sensitive response to iron dosages (5.34 mM), and improved intracellular iron (216%) is the key to stimulating microbial metabolism by accelerating electron transfer, enzymatic activity, and ATP biosynthesis. Moreover, the long-term operation confirmed that additional Fe⁰ increased the relative abundance of ammonia-oxidizing bacteria, anammox bacteria, and denitrifiers, and the enriched nitrogen removal pathways further improved the nitrogen removal to 93.3% from 79.2% in an oxygen-limited system. This study helps us deeply understand the underlying mechanism of microbial activity stimulated by iron.