Chromium-containing Wastewater Research Articles

Enhanced Removal of Cr (VI) by PEI/nFe3O4 Ultrafiltration Membranes Using Peristaltic Pump-Driven Dynamic Adsorption

In this study, Fe3O4 nanoparticles (nFe3O4) were loaded onto polyvinylidene fluoride ultrafiltration membranes and capped with polyethyleneimine in order to form PEI/nFe3O4 ultrafiltration membranes. We used a peristaltic pump as a driver for dynamic adsorption, and the PEI/nFe3O4 ultrafiltration membrane had a good ability to remove hexavalent chromium (Cr(VI)) from wastewater. The full permeate volume of the PEI/nFe3O4 ultrafiltration membrane was maximized at pH 3. Meanwhile, the removal of Cr(VI) from the wastewater reached 98% and reduced to trivalent chromium (Cr(III)). When the initial concentration of Cr(VI) increased, the active sites on the membrane would be filled and the removal efficiency of Cr(VI) would decrease. Meanwhile, the coexisting ions affect the removal efficiency of Cr(VI), and PO43- has a strong negative effect on the removal efficiency. PEI/nFe3O4 ultrafiltration membrane is an effective combination of multifunctional nanomagnetic materials and membrane materials, which can effectively remove hexavalent chromium from wastewater. The study provides a basis for future applications in the environmental remediation of low-concentration chromium-containing wastewater.

Study on the adsorption performance of fly ash loaded on nano-FeS for chromium-containing wastewater treatment

In view of the problems caused by chromium-containing wastewater, such as environmental pollution, biological toxicity, and human health risks. Based on fly ash adsorption and nano-FeS reduction characteristics, fly ash loaded nano-FeS composite (nFeS-FA) was synthesized using mineral supported modification technology and ultrasonic precipitation method. The effect of adsorbent dosage, initial pH, contact time, and initial concentration of the solution on the adsorption of Cr(VI) and total Cr by nFeS-FA was investigated. The characteristics of Cr(VI) and total Cr adsorption by nFeS-FA were studied using adsorption isotherms, adsorption kinetics principles, as well as XRD, TEM, SEM-EDS, and BET analysis. The results demonstrated that under the conditions of nFeS-FA of 8 g/L, initial pH of 4, contact time of 150 min, and initial concentration of the solution at 100 mg/L, nFeS-FA achieved removal efficiency of 87.85 % for Cr(VI) and 71.77 % for total Cr. The adsorption of Cr(VI) and total Cr by nFeS-FA followed the Langmuir model and pseudo-second-order kinetic model, indicating monolayer adsorption with chemical adsorption as the dominant mechanism. XRD, TEM, SEM-EDS, and BET revealed that the flaky nano-FeS was uniformly distributed on the surface of fly ash, exhibiting good dispersion and thereby increasing the specific surface area. During the adsorption experiments, nFeS-FA reacted with Cr(VI), and the generated Fe3+ mainly existed as FeOOH precipitation, while S2− reacted with Cr(III) to produce Cr2S3 precipitation. Therefore, nFeS-FA exhibited excellent adsorption performance towards Cr(VI) and total Cr. It can serve as a technological reference for the remediation of heavy metal chromium pollution in the field of water treatment.

Preparation and properties of electromagnetic shielding leather based on magnetic MgFeCr-LDHs

Leather, as a kind of renewable biomass, is naturally rich in dipoles as well as excellent 3D fiber structure, which provides the possibility for its application in electromagnetic shielding field. This study combined the utilization of chromium-containing wastewater with the intelligent development of leather. Nano zero-valent iron (NZVI) was innovatively used to prepare magnetic Mg/Fe/Cr layered double hydroxide (MgFeCr-LDHs) by co-precipitation method while treating chromium wastewater. And magnetic MgFeCr-LDHs was used for tanning leather, which prepared electromagnetic shield leather (MgFeCr-LDHs/L). Fe3+ and Cr3+ in MgFeCr-LDHs were closely bonded with the active groups on collagen fibers by chemical bonding, which give leather hygrothermal stability. The shrinkage temperature of MgFeCr-LDHs/L reached 89.1°C. Electromagnetic shielding efficiency of magnetic MgFeCr-LDHs/L reached 25 dB due to MgFeCr-LDHs had better dielectric and magnetic losses to electromagnetic waves. Magnetic MgFeCr-LDHs/L also had good softness and mechanical properties. In summary, we expect magnetic MgFeCr-LDHs/L to be used as a wearable material in the field of electromagnetic shielding.

Zr4+-modified chitosan coated nZVI enhance the removal of Cr(VI) by adsorption-reduction interaction

In order to solve the problems of poor mechanical properties and stability of chitosan and easy agglomeration and oxidation of nano zero-valent iron, Zr4+ crosslinked chitosan-coated nano zero-valent iron composites (CS-Zr@nZVI) were prepared for Cr(VI) removal from wastewater. The Zr-O, Zr-N and chitosan characteristic peaks in FTIR spectrum and the nZVI characteristic peaks in XRD pattern confirmed its successful synthesis. SEM and TEM showed that nZVI was dispersed on the surface of CS-Zr@nZVI, which solved the problem of easy agglomeration of nZVI. CS-Zr@nZVI has a wide operating pH range (pH= 2.0–10.0), high pHpzc, good stability and regeneration ability. The removal of Cr(VI) by CS-Zr@nZVI accords with pseudo-second-order kinetic model and Langmuir isotherm model, and it is a spontaneous, disordered and endothermic process. The maximum adsorption capacity was 344.82 mg g−1 at 318 K and pH = 2.0. At the dosage of 1.0 g L−1, CS-Zr@nZVI can treat 134.56 mg L−1 chromium-containing wastewater (pH = 3.5) to meet the discharge standard, which proves that CS-Zr@nZVI has the application prospect of removing Cr(VI). The main mechanisms of Cr(VI) removal by CS-Zr@nZVI are electrostatic interaction, ion exchange, reduction, complexation and co-precipitation. XPS analysis showed that 84.87 % of Cr(VI) was reduced to Cr(III). The above results provide a reference for the design of efficient Cr(VI) removal materials.

The hyper-crosslinked aniline polymer@MOFs hybrid materials reinforced with active ionic sites for efficient and fast Cr(VI) removal

The adsorption of toxic metal ions by composite materials of metal–organic frameworks (MOFs) has attracted significant attention in recent years. In this work, a series of hybrid materials HPAN@M−x consisting of protonated hyper-crosslinked aniline polymer (HPAN) and MOFs were synthesized via the Friedel-Crafts reaction between aniline and dimethoxymethane in the presence of MIL-101(Cr), followed by protonation with hydrogen bromide. These hybrid materials exhibited enhanced adsorption rate and capacity for Cr(VI) ions compared to both individual MIL-101(Cr) and HPAN. The effects of the ratio of aniline to MIL-101(Cr), solution pH, adsorption temperature, impurity ions on the removal of Cr(VI) ions were systematically investigated. Notably, HPAN@M−b not only achieved an adsorption capacity up to 290.9 mg·g−1 in 7 min but also exhibited excellent cycling stability by maintaining a high Cr(VI) removal efficiency of 95.6 % after five cycles. The enhanced adsorption performance is attributed to the synergistic effect between MIL-101(Cr) and HPAN. Mechanism studies indicated that the removal for Cr(VI) ions involved a combination of ion exchange and electrostatic adsorption processes. Additionally, the desorbed Cr(VI) ions were transformed into added-value barium chromate (BaCrO4) precipitates, allowing for resource utilization of Cr(VI) ions. This study represents a significant advancement towards developing MOFs-based hybrid materials for practical treatment of chromium-containing wastewater.

Integrated treatment of chromium-containing wastewater with application of the improved ferritization method

Integrated treatment of chromium-containing wastewater with application of the improved ferritization method

Green synthesis of iron nanoparticles using Pistacia-atlantica leaf extract for enhanced removal of Cr(VI) from aqueous solution

The discharge of chromium-containing wastewater from various industries into aqueous environments is regarded as an important and challengeable matter due to its high toxicity. The application of conventional methods for eliminating this pollutant are often very expensive and difficult. Therefore, the adsorption process has been introduced as a desirable and effective method for removing chromium ions from aqueous media. In this research, iron nanoparticles (Fe-NPs) were synthesized using Pistacia-atlantica leaf extract as a reducing agent, then they were characterized by DLS, XRD, FT-IR, FESEM/EDS, and TEM techniques and its effectiveness to eliminate hexavalent chromium (Cr (VI)) from aqueous solutions was carried out. The capability of the batch adsorption procedure was assessed under different operational factors, such as initial pH, adsorbent dose and initial Cr (VI) concentration. Optimum adsorption conditions were determined at initial pH of 2, Cr (VI) concentration of 25 mg L−1 and adsorbent dose of 0.24 g L−1. Based on the obtained results, the highest removal efficiency (99.9%) by the adsorption process was occurred at pH of 2, concentration of 5 mg L−1 and 30 min of operational time. On the other hand, the results showed that the percentage of the pollutant elevated by increasing the contact time and amount of adsorbent dose, whereas that of was declined by increasing the initial concentration of Cr (VI). Besides, the experimental equilibrium data was evaluated by Langmuir, Freundlich, and Temkin isotherm models, and the outcomes revealed conformity with the Langmuir isotherm model. The Cr (VI) adsorption utilizing Fe-NPs adhered to a pseudo-first-order kinetic model. Eventually, thermodynamic studies demonstrated that the adsorption of Cr (VI) onto the surface of the Fe-NPs is endothermic and spontaneous.

Increasing the Efficiency of Wastewater Treatment from Galvanic Production Using Titanium-containing Coagulants and Membrane Treatment

It has been stated that the use of complex titanium-containing agents can significantly increase the efficiency of wastewater treatment and achieve a reduction in residual concentrations of heavy metal compounds down to standard values. For further separation of coagulated sludge from purified water, it is proposed to use filtration methods with ceramic tubular filters. A significant increase in the filtration rate of titanium-containing coagulation sludge has been confirmed, leading to an increase in the productivity of treatment equipment by 20–30 %. It is recommended for purification of acid-base and chromium-containing wastewater to combine the process of coagulation of impurities by treating the wastewater with a complex titanium-containing coagulant, followed by filtering the resulting sludge using special ceramic tubular filters.

Efficient removal and transformation of Cr(VI) from alkaline wastewater to form a ferrochromium spinel multiphase via a modified ferrite process

Chromium-containing wastewater causes serious environmental pollution due to the harmfulness of Cr(VI). The ferrite process is typically used to treat chromium-containing wastewater and recycle the valuable chromium metal. However, the current ferrite process is unable to fully transform Cr(VI) into chromium ferrite under mild reaction conditions. This paper proposes a novel ferrite process to treat chromium-containing wastewater and recover valuable chromium metal. The process combines FeSO4 reduction and hydrothermal treatment to remove Cr(VI) and form chromium ferrite composites. The Cr(VI) concentration in the wastewater was reduced from 1040 mg L−1 to 0.035 mg L−1, and the Cr(VI) leaching toxicity of the precipitate was 0.21 mg L−1 under optimal hydrothermal conditions. The precipitate consisted of micron-sized ferrochromium spinel multiphase with polyhedral structure. The mechanism of Cr(VI) removal involved three steps: 1) partial oxidation of FeSO4 to Fe(III) hydroxide and oxy-hydroxide; 2) reduction of Cr(VI) by FeSO4 to Cr(III) and Fe(III) precipitates; 3) transformation and growth of the precipitates into chromium ferrite composites. This process meets the release standards of industrial wastewater and hazardous waste and can improve the efficiency of the ferrite process for toxic heavy metal removal.

Removal of hexavalent chromium using one-step synthesized metal-polyphenol composites epigallocatechin gallate/titanium: Performance, interference, and mechanisms

Chromium-containing wastewater intensifies the shortage of water resources, and how to solve the problem has become a research hotspot. In this study, epigallocatechin gallate and titanium salt were combined to prepare epigallocatechin gallate/titanium composites by one-step synthesis, and the effectiveness and mechanisms of removing hexavalent chromium from wastewater were studied. Based on the characterization results, the epigallocatechin gallate/titanium nanometer-scale materials were irregularly spherical, and their surface was rich in phenolic hydroxyl groups. The average particle size, average pore size, and BET surface area were 448 nm, 6.23 nm, and 15.40 m2/g, respectively. The Freundlich isothermal model for adsorption and pseudo-second-order adsorption kinetics were both applicable to the hexavalent chromium adsorption. The maximum adsorption capacity of hexavalent chromium was 105.8 mg/g, and the adsorption process was more inclined to endothermic reaction. The salinity resistance of epigallocatechin gallate/titanium materials to different salts was sodium chloride > magnesium sulfate heptahydrate. In the organic acid-coexisting system, the removal efficiency of epigallocatechin gallate/titanium materials for hexavalent chromium with 20 mg/L fulvic acid and citric acid was 82.7% and 81.5%, respectively. The epigallocatechin gallate/titanium materials also showed excellent removal ability for hexavalent chromium, lead(II), copper(II), and nickel(II), with removal efficiencies all above 95%. Hexavalent chromium was first adsorbed and then reduced to trivalent chromium with the help of phenol hydroxyl groups on the materials. The trivalent chromium was further immobilized through electrostatic attraction and complexation. This work aimed to provide a new idea for handling hexavalent chromium-contaminated wastewater by using green and versatile polyphenol nanomaterials.

Reparation of nano-FeS by ultrasonic precipitation for treatment of acidic chromium-containing wastewater

Nano-FeS is prone to agglomeration in the treatment of chromium-containing wastewater, and ultrasonic precipitation was used to synthesize nano-FeS to increase its dispersion. The optimization of the preparation method was carried out by single factor method (reaction temperature, Fe/S molar ratio and FeSO4 dropping flow rate) and response surface methodology. Dynamic experiments were constructed to investigate the long-term remediation effect and water column changes of nano-FeS and its solid particles. The changes of the remediation materials before and after the reaction were observed by SEM, and the mechanism of the remediation of chromium-containing wastewater by nano-FeS prepared by ultrasonication was revealed by XRD. The results showed that the reaction temperature of 12 °C, Fe/S molar ratio of 3.5 and FeSO4 dropping flow rate of 0.5 mL/s were the best parameters for the preparation of nano-FeS. The nano-FeS has efficient dispersion and well-defined mesoporous structure in the form of needles and whiskers of 40–80 nm. The dynamic experiments showed that the average removal of Cr(VI) and total chromium by nano-FeS and its immobilized particles were 94.97% and 63.51%, 94.93% and 45.76%, respectively. Fe2+ and S2− ionized by the FeS nanoparticles rapidly reduced Cr(VI) to Cr(III). Part of S2− may reduce Fe3+ to Fe2+, forming a small iron cycle that gradually decreases with the ion concentration. Cr(III) and Fe2+ form Cr(OH)3 and FeOOH, respectively, with the change of aqueous environment. Another part of S2− reacts with Cr(III) to form Cr2S3 precipitate or is oxidized to singlet sulfur. The FeS nanoparticles change from short rod-shaped to spherical shape. Compared with the conventional chemical precipitation method, the method used in this study is simple, low cost, small particle size and high removal rate per unit.

Biorreducción in vitro de cromo hexavalente utilizando consorcios microbianos

Constant industrial development has increased the chromium use, resulting in chromium discharge into wastewater. The implementation of microbial bioremediation has been proposed as an ecological, efficient and economical alternative for the implementation of microorganisms to reduce chromium to a less toxic form. Our objective was to evaluate the Cr (VI) removal capacity of microbial consortia at different concentrations. Accordingly, an activation and identification of microorganisms from chromium-containing wastewater was carried out. Seven microbial consortia were established and their synergy, individual and consortium growth curves were evaluated. Subsequently, a scaled adaptation of the consortia was carried out with eight concentrations of Cr (VI). Reciprocal regression models and growth curves were used to identify the consortium with the highest removal. Synergy was found in the consortia evaluated; growth curves of consortia showed higher absorbance than individually, with higher absorption in the Candida famata-Serratia sp. Consortium. However, in the scaled adaptation, greater Cr (VI) reduction capacity was demonstrated in Candida tropicalis-Serratia sp. with 79.20% at a concentration of 100 ppm with a total chromium reduction of 31.12%. At the same time, a greater adaptation of the consortia to high concentrations of Cr (VI) was identified. This is the first research to report C. tropicalis-Serratia sp. microbial consortium with a positive interaction and higher metabolic reduction capacity, which will have a positive impact on bioremediation of chromium-containing wastewater.

Synergistic purification of chromium-containing wastewater via adsorption-photocatalysis induced by multiple defect-containing CuS/Cv-CNNs

A defective CuS/Cv-CNNs heterojunction is proposed, which promotes its adsorption and photodegradation of Cr(vi) through the synergistic effect of multiple defects, thus accelerating the removal of high concentrations of Cr(vi).

Технологические решения и опыт промышленной переработки жидких хромсодержащих отходов

Analysis of the list of liquid wastes of hazard classes I and II in the Federal Classification Catalog of waste (FCCW) showed that one of the most common wastes is wastewater, waste technological solutions containing chromium ions(III, VI). This type of waste accounts for up to 15% of the total amount of liquid technogenic waste of hazard classes I and II, formed as a result of the activities of electroplating and chemical enterprises. Hexavalent chromium compounds belong to the class of toxic, extremely dangerous substances, the maximum permissible concentration (MPC) in the water of drinking water bodies for chromium (VI) is 0.05 mg/L. A feature of this type of waste is the increased salt background characteristic of electrolytes used in electroplating industries. The article presents experimental data, as well as basic technological solutions for the neutralization of chromium-containing wastewater and waste technological solutions. A technological scheme containing four main stages is proposed: reduction of hexavalent chromium, isolation of trivalent chromium from aqueous solutions, separation of accompanying compounds of heavy and non-ferrous metals, filtration post-treatment of the solution. Experimental studies have shown that, depending on the ionic composition of the medium, the efficiency of isolation of trivalent chromium compounds from aqueous solutions by electroflotation varies from 8 to 95%. The introduction of an anionic flocculant makes it possible to increase the degree of extraction to 99% or more.

Nitric Acid-Treated Blue Coke-Based Activated Carbon's Structural Characteristics and Its Application in Hexavalent Chromium-Containing Wastewater Treatment.

This study primarily focused on the efficient transformation of low-priced blue coke powder into a high-capacity adsorbent and aimed to address the pollution issue of hexavalent chromium (Cr (VI))-laden wastewater and to facilitate the effective utilization of blue coke powder. A two-step method was utilized to fabricate a blue coke-based nitric acid-modified material (LCN), and the impact of nitric acid modification on the material's structure and its efficacy in treating Cr (VI)-contaminated wastewater was evaluated. Our experimental results illustrated that, under identical conditions, LCN exhibited superior performance for Cr (VI) treatment compared to the method employing only potassium hydroxide (LCK). The specific surface area and pore volume of LCN were 1.39 and 1.36 times greater than those of LCK, respectively. Further chemical composition analysis revealed that the functional group structure on the LCN surface was more conducive to Cr (VI) adsorption. The highest amount of Cr (VI) that LCN could bind was measured at 181.962 mg/g at 318 K. This was mostly due to chemisorption, which is dominated by redox reactions. The Cr (VI) removal process by LCN was identified to be a spontaneous, exothermic, and entropy-increasing process. Several tests on recycling and reuse showed that LCN is a stable and effective chromium-containing wastewater adsorbent, showing that it could be used in many situations.

Adsorption of Chromium (VI) from Aqueous Solution Using Nano TiO2 Doped Strong Base Anion Exchange Resin

Background: The evolution of environmentally-safe methods for treating hazardous chemicals in wastewater, particularly urban and industrial wastewater, has increased interest over recent years. The chromium-containing wastewater is produced by industries from steel, metallurgical, electroplating, chemical, refractory, leather tanning, dye manufacturing, mining, cementing, textiles, etc. Consequently, advanced techniques are essential for treating chromium-polluted water. Objective: The prime objective of this effort was to assess the adsorption performance of nanoTiO2 (nanoparticles of average crystallite size 19.15 nm) doped strong base anion exchange resin (TDTulsion) for Cr(VI)to that of the host Tulsion A-62 (MP). Methods: The tests were carried out in batches in the temperature-controlled water bath shaking unit, with 30 ml of the aqueous solution containing Cr(VI) and a certain amount of resin being stirred for 6 hours at 303 K. Using a standard diphenylcarbazide (DPC) procedure at 540 nm, the solution was spectrophotometrically analyzed for Cr(VI). Results: The majority of the Cr(VI) ions are adsorbed by the anion exchange resins Tulsion A- 62(MP), and TD-Tulsion is in the pH range of 4.0 to 5.0. The maximal sorption capacity of Cr (VI) was established to be 181.5 and 204.8 mg/g for Tulsion A-62(MP) and TD-Tulsion, respectively. Conclusion: The TD-Tulsion has a substantially better adsorption capacity than Tulsion A-62(MP) under similar conditions. The outcomes show that modifying anion-exchange resin with nano titanium dioxide improves adsorption performance in Cr(VI) removal from drinking water and contaminated water.

Study on the performance of vertical flow constructed wetland microcosm with Canna sps. for treatment of high chromium-containing wastewater

Chromium (Cr (VI)) pollution has plagued the environment due to chromite mining and various industrial actions. Constructed wetlands (CW) have emerged as a potential wastewater management technique that utilizes physical, chemical, and biological processes. The present study investigates the use of vertical flow-constructed wetlands (CW) using manure-rich garden soil and sand as substrates in planted CW (CW–P) and unplanted CW (CW-UP) to remove Cr (VI) from simulated wastewater. The experiment was performed in two phases, i.e., Phase I and II, in the same system. In Phase I, initial Cr (VI) concentrations were varied between 5 and 200 mg/l at a fixed hydraulic retention time (HRT) of 48 h, while in Phase II, the effect of HRT (24 h, 48 h, and 96 h) was studied at a fixed Cr (VI) concentration of 200 mg/L in the influent. At 24 h, HRT removal efficiencies were 90.20% for CW-P and 86.41% for CW-UP. However, at 96 h of HRT, the system showed nearly the same removal efficiency. Scanning electron microscopy with energy dispersion X-Ray spectroscopy analysis suggested the conversion of Cr (VI) to Cr (III) in soil precipitate and the translocation of Cr (VI) in plant tissues (Canna sps.). Moreover, microbial diversity profiling indicated that microbial diversity involved in pollutant removal differed in both systems. The phytotoxicity test clearly showed the decrease in toxicity level in the treated effluent, concluding the reusability of treated water. This exploratory study suggested that the CW can potentially remove a higher concentration of hexavalent chromium at longer HRT.

Adsorption of Hexavalent Chromium Ions Using Pine Sawdust Cellulose Fibres

In developing countries, agriculture generates not only income but also waste. Therefore, it is essential to recycle this waste for different purposes. This study explored an affordable way to modify pine sawdust to treat chromium-containing wastewater, with successful outcomes. The biosorbent’s surface area was enhanced through pretreatment steps, including NaOH treatment, bleaching, and acid hydrolysis for cellulose fibre extraction. SEM–EDS, TEM, and XRD were used to study the chemical composition and morphology. XRD measurements also revealed a rise in the sizes of crystallites. FTIR results revealed shifts in bands (-OH), (-C-H), and (-COOH), suggesting their involvement in Cr (VI) ion adsorption. TGA/DTA indicated enhanced thermal stability for cellulose extracted from pine sawdust compared to untreated pine sawdust. The adsorption parameters for Cr (VI) ions were investigated through mass, pH, stirring time, and temperature studies. The optimal Cr (VI) adsorption conditions were 2.0 g mass, pH 6, 90 min stirring, 100 mg/L concentration, and 313 K temperature. The adsorption of Cr (VI) ions was best-fit to the Langmuir isotherm model (R2 = 0.9991, kL = 0.09). Pseudo-second-order kinetics (R2 = 0.9999) provided the best description for Cr (VI) biosorption on cellulose fibres (CF). The analysis results confirmed the isotherm and kinetics models. The negative thermodynamic parameters (ΔG° and ΔH°) indicated that the uptake of Cr (VI) ions on the adsorbent was exothermic and spontaneous.

Self-cross-linking of metal-organic framework (MOF-801) in nanocellulose aerogel for efficient adsorption of Cr (VI) in water

Chromium (Cr) poses significant hazards to both human health and the natural environment. Therefore, in this study, metal-organic framework (MOF-801) was compounded with nanocellulose aerogel for the first time. And a nanocellulose/metal-organic framework composite aerogel was developed for efficient chromium ion adsorption. The resulting aerogel has an ultra-low density (0.017 g/cm3) and high porosity (98.87%). The removal efficiency of this aerogel for Cr (VI) (93.86%) was measured to be higher than that of cellulose nanofiber aerogel (TCNF: 50.08%) and MOF-801 powder (59.86%). It was also higher than the cellulose nanocellulose aerogel prepared without MOF-801 (TMPA: 70.58%). This is because MOF-801 cross-linked with nanocellulose increased its porosity and provided a large number of adsorption sites. The maximum adsorption of Cr (VI) by this aerogel was 350.64 mg/g (5.96 mg/cm3). The adsorption mechanism was investigated by adsorption isotherms, adsorption kinetics, XPS, and FT-IR analysis. The aerogel has good reusability, with no significant loss of adsorption performance over 6 cycles. It is worth mentioning that 0.69 g (V: 7.363 cm3) of aerogel could effectively remediate 3710 mL of chromium-containing wastewater in a fixed-bed column adsorption experiment. In addition, the aerogel can effectively remove many metal ions from wastewater. As a result, the aerogel made in this study has the ability to be an effective adsorbent for metal ion removal.

Polydopamine and calcium functionalized fiber carrier for enhancing microbial attachment and Cr(VI) resistance

The formation of biofilm determines the performance and stability of biofilm system. Increasing the hydrophilicity of the carrier surface could efficiently accelerate the attachment and growth of microorganisms. Here, the surface of polypropylene (PP) fiber carrier was modified with polydopamine (PDA) and calcium (Ca(II)) to enhance microbial attachment and toxicity resistance. The results of surface characteristic confirmed the self-polymerization of PDA and the chelation mechanism of Ca(II). Subsequently, the biofilm formation experiments were conducted in sequencing batch biofilm reactors using both normal and chromium-containing wastewater. The biofilm on the surface of the modified carrier exhibited better nitrogen removal and Cr(VI) reduction ability. The biomass of the modified carrier was significantly increased, and the maximum microbial attachment amounts in normal wastewater and chrome-containing wastewater were 1153.34 and 511.78 mg/g carrier, respectively. Furthermore, the confocal laser scanning microscope (CLSM) indicated that the modified carrier coated with PDA and Ca(II) were both biocompatible, and the cell activity was significantly increased. 16S rRNA sequencing results showed that the modified carrier efficiently enriched both denitrification bacteria (Thauera and Flavobacterium) and chrome-reducing bacteria (Simplicispira and Arenimonas) to improve system stability and Cr(VI) resistance. Microbial phenotype prediction based on BugBase analysis further verified the enrichment effect of modified carriers on microorganisms responsible for biofilm formation and oxidative stress resistance. Overall, this work proposed a novel functional carrier that could provide references for advancing the application of biofilm systems in wastewater treatment.