Oxygen-Assisted Supercapacitive Swing Adsorption of Carbon Dioxide.

We report on the supercapacitive swing adsorption (SSA) of carbon dioxide at different voltage windows in the presence of oxygen using activated carbon electrodes, and deliquescent, aqueous electrolytes. The presence of O2 in the CO2/N2 gas mixture results in an up to 11 times higher CO2 adsorption capacity with 3M MgBr2 (at 0.6V) and up to 4-5 times higher adsorption capacity with 3M MgCl2 (at 1V). A tradeoff between high CO2 adsorption capacities and lower coulombic efficiencies was observed at voltages above 0.6V. The energetic and adsorptive performance of the electrodes in the presence of oxygen below 0.5V was similar to the performance with a CO2/N2 mixture without oxygen at 1V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the electrodes demonstrate that the specific capacitance increases while the diffusion resistance decreases in the presence of oxygen. Oxygen concentrations ranging between 5-20% give similar energetic and adsorptive performance. The electrodes exhibit stable performance for up to 100 cycles of operation.

Enhancing the adsorption capacity of organic and inorganic pollutants onto impregnated olive stone derived activated carbon.

This study presents a sustainable approach to activated carbon production from olive stones in comparison to commercial ones, using various activating agents such as H3PO4, KOH, and ZnCl2, for enhancing the adsorption properties and versatile adsorption capability to remove a range of pollutants including copper ion, methylene blue, and 2,4-Dichlorophenoxyacetic acid from aqueous solutions. The performances of activated carbons across varying conditions such as pollutant concentrations, temperatures, pH levels, and adsorbent amounts were tested. Increased initial pollutant concentrations correlated with higher adsorption capacities. Maximum adsorption capacities were achieved at pH levels of 5, 10, and 2 for Cu, MB, and 2,4-D, respectively. For KOSAC, Cu removal rose from 27 % to 52 %, for ZOSAC, MB removal increased from 39 % to 65 %, and for ZOSAC, 2,4-D removal surged from 33 % to 99 % at varying adsorbent amounts. Model validation was carried out utilizing the kinetic models (PFO, PSO) and isotherm models (Langmuir, Redlich-Peterson). The PFO kinetic model and Langmuir isotherm model proved more suitability for Cu adsorption, whereas PFO and PSO kinetic models, along with Redlich-Peterson isotherm models, were more prominent for MB and 2,4-D adsorption. Thermodynamic analysis revealed that the adsorption of Cu and 2,4-D was exothermic, while MB adsorption was endothermic. By optimization of experimental conditions, the maximum adsorption capacities were attained at 30.34 °C and 297.65 mg L-1 for KOSAC-Cu, 48.62 °C and 269.37 mg L-1 for ZOSAC-MB, and 30.31 °C and 299.02 mg L-1 for ZOSAC-2,4-D sorption. This research highlights ZOSAC's potential as a cost-effective, eco-friendly solution for water treatment, contributing to environmental sustainability and economical feasibility.

Assessment of carbonized himalayan chir pine biomass as an eco-friendly adsorbent for effective removal of industrial dyes.

This study investigates the use of carbonized Himalayan Chir Pine Biomass, known as Chir Pine Activated Carbon (CPAC), as an eco-friendly and cost-effective adsorbent for efficient industrial dye removal, with a focus on environmental sustainability. By applying different additive treatments, four adsorbents (C1, C2, C3, and C4) were formulated. CPAC was synthesized through pyrolysis and characterized using various analytical techniques including FE-SEM, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The adsorption capacity of CPAC was evaluated using Malachite Green (MG) dye as a model contaminant. FE-SEM images revealed high porosity (~ 10 µm) and a high surface area (119.886 m2/g) as confirmed by BET testing. CPAC effectively removed MG dye within 30 min at a solution pH of 7. Langmuir and Freundlich isotherm models indicated both monolayer and multilayer adsorption, while kinetic models suggested chemisorption. The regeneration efficiency was assessed using 0.1 N HCl over five consecutive cycles, with C4 demonstrating a high regeneration tendency of 85% and only a 9% reduction in adsorption ability after the fifth cycle. The developed CPAC shows excellent potential for use in the textile, paper, and leather industries for industrial dye adsorption, contributing to the protection of aquatic ecosystems. Additionally, CPAC can be utilized in other water and air purification applications.

Valorization of residual lignocellulosic biomass in South America: a review.

Residual lignocellulosic biomass (RLB) is a valuable resource that can help address environmental issues by serving as an alternative to fossil fuels and as a raw material for producing various value-added molecules. To gain a comprehensive understanding of the use of lignocellulosic waste in South America, a review was conducted over the last 4 years. The review focused on energy generation, biofuel production, obtaining platform molecules (such as ethanol, hydroxymethylfurfural, furfural, and levulinic acid), and other materials of interest. The review found that Brazil, Colombia, and Ecuador had the most RLB sources, with sugarcane, oil palm, and rice crop residues being the most prominent. In South America, RLB is used to produce biogas, syngas, hydrogen, bio-oil, biodiesel, torrefied biomass, pellets, and biomass briquettes. The most studied and produced value-added molecule was ethanol, followed by furfural, hydroxymethylfurfural, and levulinic acid. Other applications of interest that have been developed with RLB include obtaining activated carbon and nanomaterials. Significant progress has been made in South America in utilizing RLB, and some countries have been more proactive in regulating its use. However, there is still much to learn about the potential of RLB in each country. This review provides an updated perspective on the typification and valorization of residual biomass in South America and discusses the level of research and technology being applied in the region. This information can be helpful for future research on RLB in South America.

Nitrogen-doped mesoporous activated carbon from Lentinus edodes residue: an optimized adsorbent for pharmaceuticals in aqueous solutions.

In this study, phosphoric acid activation was employed to synthesize nitrogen-doped mesoporous activated carbon (designated as MR1) from Lentinus edodes (shiitake mushroom) residue, while aiming to efficiently remove acetaminophen (APAP), carbamazepine (CBZ), and metronidazole (MNZ) from aqueous solutions. We characterized the physicochemical properties of the produced adsorbents using scanning electron microscopy (SEM), nitrogen adsorption isotherms, and X-ray photoelectron spectroscopy (XPS). MR1, MR2, and MR3 were prepared using phosphoric acid impregnation ratios of 1, 2, and 3 mL/g, respectively. Notably, MR1 exhibited a significant mesoporous structure with a volume of 0.825 cm3/g and a quaternary nitrogen content of 2.6%. This endowed MR1 with a high adsorption capacity for APAP, CBZ, and MNZ, positioning it as a promising candidate for water purification applications. The adsorption behavior of the contaminants followed the Freundlich isotherm model, suggesting a multilayer adsorption process. Notably, MR1 showed excellent durability and recyclability, maintaining 95% of its initial adsorption efficiency after five regeneration cycles and indicating its potential for sustainable use in water treatment processes.

Fluoride removal from coal mining water using novel polymeric aluminum modified activated carbon prepared through mechanochemical process.

Defluoridation of coal mining water is of great significance for sustainable development of coal industry in western China. A novel one-step mechanochemical method was developed to prepare polymeric aluminum modified powder activated carbon (PAC) for effective fluoride removal from coal mining water. Aluminum was stably loaded on the PAC through facile solid-phase reaction between polymeric aluminum (polyaluminum chloride (PACl) or polyaluminum ferric chloride (PAFC)) and PAC (1:15 W/W). Fluoride adsorption on PACl and PAFC modified PAC (C-PACl and C-PAFC) all reached equilibrium within 5 min, at rate of 2.56 g mg-1 sec-1 and 1.31 g mg-1 sec-1 respectively. Larger increase of binding energy of Al on C-PACl (AlF bond: 76.64 eV and AlFOH bond: 77.70 eV) relative to that of Al on C-PAFC (AlF bond: 76.52 eV) explained higher fluoride uptake capacity of C-PACl. Less chloride was released from C-PACl than that from C-PAFC due to its higher proportion of covalent chlorine and lower proportion of ionic chlorine. The elements mapping and atomic composition proved the stability of Al loaded on the PAC as well as the enrichment of fluoride on both C-PACl and C-PAFC. The Bader charge, formation energy and bond length obtained from DFT computational results explained the fluoride adsorption mechanism further. The carbon emission was 7.73 kg CO2-eq/kg adsorbent prepared through mechanochemical process, which was as low as 1:82.3 to 1:8.07 × 104 compared with the ones prepared by conventional hydrothermal methods.

ZIF-67 and Biomass-Derived N, S-Codoped Activated Carbon Composite Derivative for High-Effective Removal of Hydroquinone from Water.

Hydroquinone (HQ) in wastewater is of great concern, as it is harmful to human health and threatens the ecological environment. However, the existing adsorbents have low adsorption capacity for HQ. To improve the removal of HQ, N,S-codoped activated carbon-ZIF-67 (NSAC-ZIF-67@C) was synthesized in this study by in situ growth of ZIF-67 on N,S-codoped activated carbon (NSAC) and carbonization. The influence of pH, contact time, and initial concentration on the adsorption behaviors of NSAC-ZIF-67@C on HQ were investigated. Owing to the synergistic effect of abundant active sites and well-developed pore structure, the NSAC-ZIF-67@C achieved a prominent adsorption capacity of 962 mg·g-1 and can still retain high adsorption performance after 5 cycles for HQ, which is superior to that of reported other adsorbents. HQ adsorption follows the pseudo-second-order kinetics model (R2 = 0.99999) and the Freundlich isotherm model. X-ray photoelectron spectroscopy (XPS) analysis before and after adsorption as well as density functional theory (DFT) calculation results showed that pyridinic-N-termini were conducive to the π-π interactions and hydrogen-bonding interactions. Therefore, the adsorption mechanisms of NSAC-ZIF-67@C on HQ involve pore filling, electrostatic attraction, π-π interaction, and hydrogen bonding. This study is expected to provide a reference for designing highly effective adsorbents for wastewater treatment.

Evaluation of three granular activated carbon filters for the treatment of collections foul air entering a water resource recovery facility.

The treatment of raw foul air that could escape to the atmosphere from the head space of the incoming wastewater sewer lines into a Southern California Water Resource Recovery Facility was evaluated by using a 1/20th scale pilot unit consisting of three different granular activated carbon filter technologies, operating side by side, under similar operating conditions, each having an average 3.8-s contact time. The three activated carbon filters contained each 0.07 m3 of coconut, coal, and coconut mixed with permanganate media. The foul air entering the granular activated carbon filters contained 82% to 83% relative humidity. No moisture removal mechanism was used prior to treatment. The removal of six different odor characters from eight chemical odorants present in the foul air were assessed. These were rotten egg (hydrogen sulfide), rotten vegetables (methyl mercaptan), canned corn (dimethyl sulfide), rotten garlic (dimethyl disulfide), earthy/musty (2-methyl isoborneol and 2-isopropyl 3-methoxy pyrazine), and fecal (skatole and indole). This is the first time a study evaluates the removal of specific odors by simultaneously employing sensory analyses using the odor profile method, which defines the different odor characters and intensities, together with chemical analyses of the odorants causing these odors. The results show that the three granular activated carbon filters, before hydrogen sulfide breakthrough, provided significant improvement in odor intensity and odorant removal. Breakthrough was reached after 57 days for the coconut mixed with permanganate, 107 days for the coconut, and 129 days for the coal granular activated carbon filter. Breakthrough (the critical saturation point of the activated carbon media) was considered reached when the hydrogen sulfide percentage removal diminished to 90% and continued downward. The coconut mixed with permanganate granular activated carbon filter provided the best treatment among the media tested, achieving very good reduction of odorants, as measured by chemical analyses, and reasonable removal of odor intensities, as measured by the odor profile method. The coconut mixed with permanganate granular activated carbon is recommended for short-term odor control systems at sewer networks or emergency plant maintenance situations given its shorter time to breakthrough compared with the other granular activated carbons. The coal and coconut granular activated carbon filters are generally used as the last stage of an odor treatment system. Because of the observed poor to average performance in removing odorants other than hydrogen sulfide, the treatment stage(s) prior to the use of these granulated activated carbons should provide a good methyl mercaptan removal of at least 90% in order to avoid the formation of dimethyl disulfide, which, in the presence of moisture in the carbon filter, emit the characteristic rotten garlic odor. The differences observed between the performances based on odorant removal by chemical analysis compared with those based on sensorial analyses by the odor profile method indicate that both analyses are required to understand more fully the odor dynamics. PRACTITIONER POINTS: Three virgin granulated activated carbon media were evaluated in a field pilot unit using raw collections foul air. Coal, coconut, and coconut mixed with permanganate were tested until breakthrough. Samples were analyzed both chemically (odorants) and sensorially (odors). Coconut mixed with permanganate proved to be the media that better reduced odorants and odors.

Adsorption of arsenic and fluoride: Modeling of single and competitive adsorption systems.

The elevated co-occurrence of arsenic and fluoride in surface and groundwater poses risks to human health in many parts of the world. Using single and competitive batch equilibrium adsorption studies, this research focuses on As(V) and F adsorption by activated carbon and its modeling. BET, XRD, FESEM, EDS, and FTIR analysis were used to discern the structural characteristics of activated carbon. The influence of dosage, pH, and contact time were also investigated in single and simultaneous adsorption systems. The maximum adsorption capacity of activated carbon for arsenic and fluoride were found to be 3.58 mg/g and 2.32 mg/g, respectively. Kinetics studies indicated that pseudo-second-order kinetic model fit better than pseudo-first-order, Elovich, and intraparticle diffusion kinetic models. The non-linear regression analysis of Langmuir, Freundlich, Toth, Redlich Petersons, and Modified Langmuir Freundlich models was used to determine single-component asorption model parameters. Additionally, the simultaneous adsorption was rigorously modeled and compared using the Extended Langmuir (EL), Extended Langmuir Freundlich (ELF), Modified Competitive Langmuir (MCL), and Jeppu Amrutha Manipal Multicomponent (JAMM) isotherm models, and competitive mechanisms were interpreted for the simultaneous adsorption system. Further, the model performances were evaluated by statistical error analysis using the normalized average percentage error (NAPE), root mean square errors (RMSE), and the correlation coefficient (R2). According to the modeling results, single equilibrium data fitted better with the Modified Langmuir Freundlich isotherm model, with a higher R2 of 0.99 and lower NAPE values of 3.8 % and 1.28 % for As(V) and F, than other models. For the binary adsorption, the Extended Langmuir Freundlich isotherm model demonstrated excellent fit with lowest errors. All the competitive isotherm models fit the As(V) and F simultaneous sorption systems reasonably well. Furthermore, the research unveiled a nuanced hierarchy of isotherm fitting, with ELF > EL > MCL > JAMM in varying arsenic at a constant fluoride concentration, and ELF > JAMM > EL > MCL in varying fluoride at a constant arsenic concentrations. In addition, competitive studies divulged crucial insights into selective adsorption, as As(V) exhibits a pronounced adsorption selectivity over F on activated carbon. In essence, As(V) showed a more pronounced antagonistic behavior over F, whereas F exhibited a much lesser competitive behavior in the adsorption of arsenic.

Perfluoroalkyl acid adsorption by styrenic ß-cyclodextrin polymers, anion-exchange resins, and activated carbon is inhibited by matrix constituents in different ways.

Perfluoroalkyl acids (PFAAs) are ubiquitous environmental contaminants of global concern, and adsorption processes are the most widely used technologies to remove PFAAs from water. However, there remains little data on the ways that specific water matrix constituents inhibit the adsorption of PFAAs on different adsorbents. In this study, we evaluated the adsorption of 13 PFAAs on two styrene-functionalized ß-cyclodextrin (StyDex) polymers, an activated carbon (AC), and an anion-exchange resin (AER) in the absence and presence of specific water matrix constituents (16 unique water matrices) in batch experiments. All four adsorbents exhibited some extent of adsorption inhibition in the presence of inorganic ions and/or humic acid (HA) added as a surrogate for natural organic matter. Two PFAAs (C5-C6 perfluorocarboxylic acids (PFCAs)) were found to exhibit relatively weak adsorption and five PFAAs (C6-C8 perfluorosulfonic acids (PFSAs) and C9-C10 PFCAs) were found to exhibit relatively strong adsorption on all four adsorbents across all matrices. Adsorption inhibition was the greatest in the presence of Ca2+ (direct site competition) and HA (direct site competition and pore blockage) for AC, NO3- (direct site competition) and Ca2+ (chemical complexation) for the AER, and SO42- (compression of the double layer) for the StyDex polymers. The pattern of adsorption inhibition of both StyDex polymers were similar to each other but different from AC and AER, which demonstrates the distinctive PFAA adsorption mechanism on StyDex polymers. The unique performance of each type of adsorbent confirms unique adsorption mechanisms that result in unique patterns of adsorption inhibition in the presence of matrix constituents. These insights could be used to develop models to predict the performance of these adsorbents in real water matrices and afford rational selection of adsorbents based on water chemistry for specific applications.

Hydrolysis of Casein by Pepsin Immobilized on Heterofunctional Supports to Produce Antioxidant Peptides.

A study was carried out on the immobilization of pepsin in activated carbon functionalized by different techniques (glutaraldehyde, genipin, and metallization) aiming at its application in obtaining bioactive peptides through casein hydrolysis. Studies of the immobilized derivatives were carried out in addition to the evaluation of the antioxidant potential of the peptides. Among the pH range studied, pH 3.0 was selected due to the higher activity of the derivatives at this pH. The support modification by metallization was the method with the best results, providing a 121% increase in enzymatic activity compared to other immobilization methods. In addition, this derivative provided activity closer to the soluble enzyme activity (3.30 U) and better storage stability, and allows reuse for more than 8 cycles. In turn, the peptides from casein hydrolysis showed potential as antioxidant agents, with a DPPH radical scavenging activity higher than 70%, maximum protection against ß-carotene oxidation close to 70%, and a maximum reducing power of Fe(III) into Fe(II) of 400 uM by the FRAP assay. The results showed that the new techniques for modification of activated carbon can be a promising approach for pepsin immobilization.

Implications of the operation of continuous granular activated carbon filters on the effluent quality.

Granular activated carbon (GAC) filtration is a commonly used method for advanced wastewater treatment. Filters can be operated continuously or discontinuously, with continuous operation not requiring feed flow interruption for backwashing and circulation (B/C). This study investigated the influence of B/C on the effluent quality of continuous filters. Two continuous GAC filters were operated for 1.5 years, with analysis of dissolved substances and particulate matter in the influent and effluent. The results indicated that various B/C modes had no impact on the removal of dissolved organic carbon and organic micropollutants (OMP), achieving an OMP removal of over 70% after 5,600 treated bed volumes (m3 treated wastewater per m3 GAC). However, it was evident that continuous B/C over 2-4 h resulted in increased turbidity, total suspended solids over 30 mg/L and total phosphorus concentrations of 1.3 mg/L in the filter effluent. Additionally, the study demonstrated that longer and more intensive B/C processes resulted in GAC size degradation with AC concentrations of up to 6.9 mg/L in the filter effluent, along with a change in GAC particle size. Furthermore, the importance of pre-filtration in reducing particulate matter in the filter influent and decreasing hydraulic head loss could be demonstrated.

Effective degradation of tetracycline in aqueous solution by an electro-Fenton process using chemically modified carbon/α-FeOOH as catalyst.

This study applied an electro-Fenton process using chemically modified activated carbon derived from rubber seed shells loaded with α-FeOOH (RSCF) as catalyst to remove tetracycline residues from aquatic environment. Catalyst characteristics were evaluated using SEM, EDS, XRD, and XPS, showing successful insertion of iron onto the activated carbon. The effects of the parameters were investigated, and the highest treatment efficiency was achieved at pH of 3, Fe: H2O2 ratio (w/w) of 500:1, catalyst dose of 1 g/L, initial TCH concentration of 100 mg/L, and electric current of 150 mA, with more than 90% of TCH being eliminated within 30 min. Furthermore, even after five cycles of use, the treatment efficiency remains above 90%. The rate constant is calculated to be 0.218 min-1, with high regression coefficients (R 2 = 0.93). The activation energy (Ea) was found to be 32.2 kJ/mol, indicating that the degradation of TCH was a simple reaction with a low activation energy. These findings showed that the RSCF is a highly efficient and cost-effective catalyst for TCH degradation. Moreover, the use of e-Fenton process has the advantage of high efficiency, low cost thanks to the recyclability of the catalyst, and environmental friendliness thanks to less use of H2O2.

Preparation of composites with MgAl-LDH-modified commercial activated carbon for the quick removal of Cr(VI) from aqueous solutions.

The problem of soil and water contamination caused by Cr(VI) discharged from the dyeing, electroplating, and metallurgical industries is becoming increasingly serious, posing a potentially great threat to the environment and public health. Therefore, it is crucial to develop a fast, efficient, and cost-effective adsorbent for remediating Cr-contaminated wastewater. In this work, MgAl-LDH/commercial-activated carbon nanocomposites (LDH-CACs) are prepared with hydrothermal. The effects of preparation and reaction conditions on the composite properties are first investigated, and then its adsorption behavior is thoroughly explored. Finally, a potential adsorption mechanism is proposed by several characterizations like SEM-EDS, XRD, FTIR, and XPS. The removal of Cr(VI) reaches 72.47% at optimal conditions, and the adsorption study demonstrates that LDH-CAC@1 has an extremely rapid adsorption rate and a maximum adsorption capacity of 116.7 mg/g. The primary removal mechanisms include adsorption-coupled reduction, ion exchange, surface precipitation, and electrostatic attraction. The reusability experiment illustrates that LDH-CAC@1 exhibits promising reusability. This study provides an effective adsorbent with a remarkably fast reaction, which has positive environmental significance for the treatment of Cr(VI) wastewater.

Equilibrium, Kinetic, and Diffusion Mechanism of lead(II) and cadmium(II) Adsorption onto Commercial Activated Carbons.

The adsorption of Pb(II) and Cd(II) on three commercial microporous activated carbons was analysed. Adsorption kinetics and statistics were investigated, and the results were described with different models. The highest values of the correlation coefficient R2 were obtained for the pseudo-second-order kinetics model for all ions tested and all sorbents used. The adsorption process was found to be determined by both diffusion in the liquid layer and intraparticle diffusion. The adsorption equilibrium is very well described by Langmuir, Temkin, Thoth or Jovanovic isotherm models. Based on the values of n from the Freundlich isotherm and KL from the Langmuir isotherm, the adsorption of cadmium and lead ions was found to be favourable. The highest monolayer capacities were obtained during the adsorption of lead ions (162.19 mg/g) and for cadmium (126.34 mg/g) for activated carbon WG-12. This carbon is characterised by the highest amount of acid functional groups and the largest specific surface area. The adsorption efficiency of the tested ions from natural water is lower than that from a model solution made from deionised water. The lowest efficiencies are obtained when the process occurs from highly mineralised water.

Adsorption of Pb, Cu, and Ni Ions on Activated Carbon Prepared from Oak Cupules: Kinetics and Thermodynamics Studies.

Agricultural residue-activated carbon and biochar, inexpensive and environmentally friendly adsorbent materials, have recently received significant research attention. This study investigated the potential use of oak cupules in activated carbon form to remove widespread heavy metals (Pb2+, Cu2+, and Ni2+) from wastewater. The oak-activated carbon was prepared from oak cupules and activated with phosphoric acid. Oak-activated carbon was characterized using FTIR, BET analysis, energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Freundlich, Langmuir, and Temkin isotherm models were used to assess the equilibrium data. The impact of various parameters, including pH effect, temperature, adsorbent dose, and contact time, was estimated. The Freundlich model was the most agreeable with Pb2+ adsorption by oak-based activated carbon, and Langmuir was more compatible with Cu2+ and Ni2+. Under optimum conditions, the average maximum removal was 63% Pb2+, 60% Cu2+, and 54% Ni2+ when every ion was alone in the aqueous solution. The removal was enhanced to 98% Pb2+, 72% Cu2+, and 60% Ni2+ when found as a mixture. The thermodynamic model revealed that the adsorption of ions by oak-based activated carbon is endothermic. The pseudo-second-order kinetic best describes the adsorption mechanism in this study; it verifies chemical sorption as the rate-limiting step in adsorption mechanisms. The oak-activated carbon was effective in removing Pb2+, Cu2+, and Ni2+ from wastewater and aqueous solutions.

Effects of low frequency ultrasound treatment on dissolved organic nitrogen removal by biological activated carbon: Critical insights into molecular characteristics, microbial traits, and metabolism.

Drinking water treatment plants (DWTPs) in China that pioneered the biological activated carbon (BAC) process have reached 10 years of operation. There has been a renewed focus on biofiltration and the performance of old BAC filters for dissolved organic nitrogen (DON) has been poor, requiring replacement and regeneration of the BAC. Therefore, it is necessary to explore a cost-effective way to improve the water quality of the old BAC filters. To address this, low frequency ultrasound is proposed to enhance DON removal efficiency by BAC. In this study, bench and pilot tests were conducted to investigate the effect of low frequency ultrasound on DON removal by 10-year BAC. The results indicated that low frequency ultrasound significantly improved the DON removal rate increased from 15.83 % to 85.87 % and considerably inhibited the nitrogenous disinfection by-products (N-DBPs) formation potential, which was attributed to a decrease in the production of lipid-like, carbohydrate-like, and protein/amino sugar-like DON. The biomass on the BAC was significantly reduced after ultrasound treatment, and it decreased from 349.56∼388.98 nmol P/gBAC to 310.12∼377.63 nmol P/gBAC, enabling the biofilm thickness to decrease and the surface to become sparse and porous, which was conducive to oxygen and nutrients transfer. The Rhizobials associated with microbe-derived DON were stripped away during ultrasound treatment, which reduced microbe-derived DON associated with amino acids. Additionally, ultrasound regulated metabolic pathways, including amino acids, tricarboxylic acid (TCA) cycle, and nucleotide metabolism, to improve the osmotic pressure of the biofilm. In short, low frequency ultrasound treatment can enhance BAC biological properties and effectively remove DON and N-DBPs formation potentials, which provides a viable and promising strategy for improving the safety of drinking water in practice.

Water residence time is an important predictor of dissolved organic matter composition and drinking water treatability.

Freshwater ecosystems are critical resources for drinking water. In recent decades, dissolved organic matter (DOM) inputs into aquatic systems have increased significantly, particularly in central and northern Europe, due to climatic and anthropogenic drivers. The associated increase in dissolved organic carbon (DOC) concentration can change lake ecosystem services and adversely affect drinking water treatment processes. In this study, we examined spatial and temporal patterns of DOM treatability with granular activated carbon (GAC) and biological reactivity based on 14-day bacterial respiration incubations at 11 sites across Mälaren during six-time points between July 2019 and February 2021. Mälaren is the third largest lake in Sweden and provides drinking water for over 2 million people including the capital city Stockholm. In our spatio-temporal analysis, we assessed the influence of phytoplankton abundance, water chemistry, runoff, and climate on DOM composition, GAC removal efficiency, and biological reactivity. Variations in DOM composition were characterized using optical measurements and Orbitrap mass spectrometry. Multivariate statistical analyses indicated that DOM produced during warmer months was easier to remove by GAC. Removal efficiency of GAC varied from 41 to 87 %, and the best predictor of treatability using mass spectrometry was double bond equivalents (DBE), while the best optical predictors were specific UV absorbance (SUVA), and freshness index. The oxygen consumption rate (k) from the bacterial respiration incubations ranged from 0.04 to 0.71 d-1 and higher in warmer months and at deeper basins and was associated with more aliphatic and fresh DOM. The three deepest lake basins with the longest water residence time (WRT) were temporally the most stable in terms of DOM composition and had the highest DOC removal efficiency and k rates. DOM composition in these three lake basins was optically clearer than in basins located closer to terrestrial inputs and had a signature suggesting it was derived from in-lake processes including phytoplankton production and bacterial processing of terrestrial DOM. This means that with increasing WRT, DOM derived from terrestrial sources shifts to more aquatically produced DOM and becomes easier to remove with GAC. These findings indicate WRT can be highly relevant in shaping DOM composition and thereby likely to affect its ease of treatability for drinking water purposes.

Comparison of perfluoroalkyl substance adsorption performance by inorganic and organic silicon modified activated carbon.

Owing to the persistence and increasingly stringent regulations of perfluoroalkyl substances (PFAS), it is necessary to improve their adsorption capacities using activated carbon (AC). However, their adsorption capacities are suppressed by dissolved organic matter (DOM). In this study, two ACs modified with organic silicon (C-OS) and inorganic silicon (C-IS) were synthesized and used for the adsorption of PFAS in raw water (RW). The results showed that the PFAS adsorption capacity of C-IS was much less influenced by DOM than that of the original AC (C-virgin). In RW, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) adsorption capacities on C-IS were 15.08 and 3.65 times higher than those on C-virgin, respectively. DOM had less influence on the PFOA and PFOS adsorption kinetics of C-IS than C-OS and C-virgin. Under multi-PFAS condition, C-IS also exhibited slower desorption of short-chain PFAS and breakthrough in batch and column tests, respectively. Characterization of the ACs before and after adsorption and independent gradient modelling indicated that hydrogen bond interactions between the O-Si of C-IS and the -COOH or -CSO3H groups of PFAS contributed to PFAS adsorption. Density functional theory calculations demonstrated that the adsorption energy of C-IS was much lower than that of C-OS and C-virgin. The arrangement of PFAS molecules on C-OS was chaotic owing to the hydrophobic siloxane chain, whereas the arrangement of PFAS on C-IS was orderly in multi-layer or semi-micelle status and more favorable to PFAS adsorption. This study provides a new strategy for avoiding adverse effects of DOM on PFAS adsorption.

Mitigation of drought stress in chili plants (Capsicum annuum L.) using mango fruit waste biochar, fulvic acid and cobalt.

Drought stress can have negative impacts on crop productivity. It triggers the accumulation of reactive oxygen species, which causes oxidative stress. Limited water and nutrient uptake under drought stress also decreases plant growth. Using cobalt and fulvic acid with biochar in such scenarios can effectively promote plant growth. Cobalt (Co) is a component of various enzymes and co-enzymes. It can increase the concentration of flavonoids, total phenols, antioxidant enzymes (peroxidase, catalase, and polyphenol oxidase) and proline. Fulvic acid (FA), a constituent of soil organic matter, increases the accessibility of nutrients to plants. Biochar (BC) can enhance soil moisture retention, nutrient uptake, and plant productivity during drought stress. That's why the current study explored the influence of Co, FA and BC on chili plants under drought stress. This study involved 8 treatments, i.e., control, 4 g/L fulvic acid (4FA), 20 mg/L cobalt sulfate (20CoSO4), 4FA + 20CoSO4, 0.50%MFWBC (0.50 MFWBC), 4FA + 0.50MFWBC, 20CoSO4 + 0.50MFWBC, 4FA + 20CoSO4 + 0.50MFWBC. Results showed that 4 g/L FA + 20CoSO4 with 0.50MFWBC caused an increase in chili plant height (23.29%), plant dry weight (28.85%), fruit length (20.17%), fruit girth (21.41%) and fruit yield (25.13%) compared to control. The effectiveness of 4 g/L FA + 20CoSO4 with 0.50MFWBC was also confirmed by a significant increase in total chlorophyll contents, as well as nitrogen (N), phosphorus (P), and potassium (K) in leaves over control. In conclusion4g/L, FA + 20CoSO4 with 0.50MFWBC can potentially improve the growth of chili cultivated in drought stress. It is suggested that 4 g/L FA + 20CoSO4 with 0.50MFWBC be used to alleviate drought stress in chili plants.