Effective adsorption of cadmium and nickel ions in mono and bicomponent systems using eco-friendly adsorbents prepared from peanut shells

The work investigates the potential of peanut shells, an abundant agro-industrial waste, to serve as an adsorbent precursor for the effective and simple treatment of effluents loaded with cadmium and nickel ions. Among the adsorbents prepared, carbonized peanut shell (CCarb), due to its higher adsorption capacity, proved to be the most effective compared to carbonized and activated peanut shell (CATQ). The carbonization process led to structural changes, which resulted in an increase in surface area (around 6 times more in CATQ) and pore volume (around 3 times more in CATQ). Even so, the amount of H+ acid sites due to acid activation produced unfavorable effects for adsorption. Hydroxyl, carboxyl and carbonyl groups were identified on the adsorbent surface which presented favorable charges for metal adsorption. This improvement propels the carbonized variant to the forefront, demonstrating the highest adsorption capacity and reaching equilibrium in less than 90 and 60 min for cadmium and nickel ions, respectively. In both monocomponent and bicomponent systems concentrations greater than 40 ppm signify an increase in adsorption capacity for Ni2+. The experimental data best fit the Freundlich model, showing maximum adsorption capacities of 17.04 mg g-1 for cadmium and 31.28 mg g-1 for nickel. Despite the antagonistic effect observed in the bicomponent system, this study concludes by underlining the promise of activated carbon from peanut shells to harmonize technical and environmental concerns.

Efficient microbial cellulose/Fe3O4 nanocomposite for photocatalytic degradation by advanced oxidation process of textile dyes

Fenton-type advanced oxidative processes (AOP) have been employed to treat textile dyes in aqueous solution and industrial effluent. The work focused on assisting the limitations still presented by the Fenton process regarding the use of suspended iron catalysts. Soon, a nanocomposite of bacterial cellulose (BC) and magnetite (Fe₃O₄) was developed. It has proven to be superior to those available in the literature, exhibiting purely catalytic properties and high reusability. Its successful production was verified through analytical characterization, while its catalytic potential was investigated in the treatment of different textile matrices. In initial tests, the photo-Fenton process irradiated and catalyzed by sunlight and BC/Fe₃O₄ discolored 92.19% of an aqueous mixture of four textile dyes. To improve the efficiency, the design of experiments technique evaluated the influence of the variables pH, [H₂O₂], and the number of BC/Fe₃O₄ membranes. 99.82% of degradation was obtained under optimized conditions using pH 5, 150 mg L^-1 of H₂O₂, and 11 composite membranes. Reaction kinetics followed a pseudo-first-order model, effectively reducing the organic matter (COD = 83.24% and BOD = 88.13%). The composite showed low iron leaching (1.60 ± 0.08 mg L^-1) and high stability. It was recovered and reused for 15 consecutive cycles, keeping the treatment efficiency at over 90%. As for the industrial wastewater, the photo-Fenton/sunlight/BC/Fe₃O₄ system showed better results when combined with the physical-chemical coagulation/flocculation process previously used in the industry's WWTP. Together they reduced COD by 77.77%, also meeting the color standards (DFZ scale) for the wavelengths of 476 nm (<3 m^-1), 525 nm (<5 m^-1), and 620 nm (<7 m^-1). Thus, the results obtained demonstrated that employing the BC/Fe₃O₄ composite as an iron catalyst is a suitable alternative to materials employed in suspension. This is mainly due to the high catalytic activity and power of reuse, which will reduce treatment costs.

Original nanostructured bacterial cellulose/pyrite composite: Photocatalytic application in advanced oxidation processes

The development of an original catalytic composite of bacterial cellulose (BC) and pyrite (FeS₂) for environmental application was the objective of this study. Nanoparticles of the FeS₂ were synthesized from the hydrothermal method and immobilized on the BC structure using ex situ methodology. In the BC, the FTIR and XRD analyzes showed the absorption band associated with the Fe-S bond and crystalline peaks attributed to the pyrite. Thus, the immobilization of the iron particles on the biopolymer was proven, producing the composite BC/FeS₂. The use of the SEM technique also ratifies the composite production by identifying the fibrillar structure morphology of the cellulose covered by FeS₂ particles. The total iron concentration was 54.76 ± 1.69 mg L^-1, determined by flame atomic absorption analysis. TG analysis and degradation tests showed respectively the thermal stability of the new material and its high catalytic potential. A multi-component solution of textile dyes was used as the matrix to be treated via advanced oxidative processes. The composite acted as the catalyst for the Fenton and photo-Fenton processes, with degradations of 52.87 and 96.82%, respectively. The material proved stability by showing low iron leaching (2.02 ± 0.09 and 2.11 ± 0.11 mg L^-1 for the respective processes). Thus, its high potential for reuse is presumed, given the remaining concentration of this metal in the BC. The results showed that the BC/FeS₂ composite is suitable to solve the problems associated with using catalysts in suspension form.

Presence Of Non-Steroidal Anti-Inflammatories In Brazilian Semiarid Waters

Non-steroidal anti-inflammatory drugs (NSAIDs) act as antipyretics, analgesics and anti-inflammatories. Among them, diclofenac and ibuprofen are the most consumed drugs worldwide. During the COVID-19 pandemic, some NSAIDs, such as dipyrone and paracetamol, have been used to alleviate the symptoms of the disease, causing an increase in the concentrations of these drugs in water. However, due to the low concentration of these compounds in drinking water and groundwater, few studies have been carried out on the subject, especially in Brazil. Thus, this study aimed to evaluate the contamination of the surface water, groundwater, and water treated with diclofenac, dipyrone, ibuprofen, and paracetamol at 3 cities (Orocó, Santa Maria da Boa Vista and Petrolândia) in the Brazilian semiarid region, in addition to analyzing the removal of these drugs by conventional water treatment (coagulation, flocculation, sedimentation, filtration and disinfection) in stations to each city. All drugs analyzed were detected in surface and treated waters. In groundwater, only dipyrone was not found. Dipyrone was seen in surface water with a maximum concentration of 1858.02 μg.L^-1, followed by ibuprofen (785.28 μg.L^-1), diclofenac (759.06 μg.L^-1) and paracetamol (533.64 μg.L^-1). The high concentrations derive from the increased consumption of these substances during the COVID-19 pandemic. During the conventional water treatment, the maximum removal of diclofenac, dipyrone, ibuprofen and paracetamol was 22.42%; 3.00%; 32.74%; and 1.58%, respectively, which confirms the inefficiency of this treatment in removing drugs. The variation in removal rate of the analyzed drugs is due to the difference in the hydrophobicity of the compounds.

Treatment of textile matrices using Fenton processes: influence of operational parameters on degradation kinetics, ecotoxicity evaluation and application in real wastewater

Since conventional processes for treating textile effluents have limitations, this work aimed to investigate the application of advanced oxidation technology in this type of matrix. Initially, for a textile dyes mixture in solution, the photo-Fenton/sunlight process proved to be the most efficient among other systems tested. During the tests it was found that the degradation kinetics depends of the pH and catalyst and oxidant concentrations. After 60 min under optimized conditions, the color was reduced by 98.19%, with 92.52% organic matter conversion. Ecotoxicity tests with the Lactuca Sativa vegetable indicated that the dyes were not totally oxidized to inert compounds, although the treated solution did not cause a significant toxic effect for this species. In the second stage of the research, the photodegradation in real samples of textile wastewater was evaluated. The efficiency of the photo-Fenton/sunlight process was lower than that obtained for the dyes solution, a fact attributed to the greater complexity of the real matrix. However, the data also indicated that the combination of coagulation/flocculation and advanced oxidation processes is the most suitable methodology to reduce the fraction of biodegradable compounds. In summary, research has revealed that photocatalytic degradation of dyes through advanced oxidation is an efficient treatment.

Degradation of the mixture of the ketoprofen, meloxicam and tenoxicam drugs using TiO2/metal photocatalysers supported in polystyrene packaging waste

The solution mixture of the non-steroidal anti-inflammatory drugs ketoprofen, meloxicam and tenoxicam was degraded through systems, composed of different photocatalysts based on TiO₂ (Fe and Cu) and the hydrogen peroxide oxidant. The monitoring was performed by UV-Vis spectroscopy. Under sunlight radiation, a reduction in peaks was observed with the use of impregnated photocatalysts. After 60 min, the sun/H₂O₂/Fe-TiO₂ system reached degradations of 46.5% and 93.2% at 260 and 367 nm, respectively, and was selected for further studies. The degradation kinetic reached 92 and 96% of degradation after 180 min, for the λ of 260 and 367 nm, respectively. The kinetic curve could be represented by the empirical model proposed by Nichela and co-authors, indicating that besides the heterogeneous photocatalysis that occurs at the surface of the TiO₂ there is also the joint effect of the photo-Fenton process. After the treatment, there was no toxicity to cress and lettuce seeds. However, a sensitivity of the thyme seeds to the compounds formed during the treatment was verified. After the fifth treatment cycle, the supported photocatalyst showed degradation higher than 82%. These results indicate that this system is suitable for the treatment of effluents containing pharmaceutical compounds.

Treatment of textile dyes using advanced oxidative and adsorptive processes individually and combined: study of the operational parameters, kinetic and adsorptive equilibrium

Advanced oxidative processes (AOP) have been consolidated as an efficient treatment technique to degrade persistent contaminants. In addition to them, biosorption also emerges as a technique capable of removing both pollutants and intermediate products generated by other treatments such as AOP. Thus, this work evaluated the degradation and removal of the mixture of dyes Direct Red 23 and Direct Red 227 in aqueous solution (50 mg·L^-1 of each). Preliminary tests showed that the photo-Fenton system under sunlight radiation was the most efficient, reaching a degradation ≥93%. For the adsorptive process using chicken eggshell, preliminary tests indicated that the ideal dosage of adsorbent was 8.0 g·L^-1. For this process, a factorial design indicated the best working conditions, which demonstrated from the system adjusted well to the Elovich (kinetic) model and to the Freundlich and Sips models (equilibrium). When associating the two processes, AOP followed by adsorption achieved a total degradation/removal of ≈98% (for all λ) in a time of 60 min. Thus, the feasibility of the combined treatment is indicated.

Investigation of paracetamol degradation using LED and UV-C photo-reactors

This work investigates the efficiency of LED and UV-C photo-reactors for paracetamol degradation using advanced oxidative processes. Among the evaluated processes, photo-Fenton was the most efficient for both radiations. Degradations greater than 81% (λ 197 nm) and 91% (λ 243 nm) were obtained in the kinetic study. These degradations were also observed by means of the reduction in the peaks in both spectral scanning and high-performance liquid chromatography analysis. The good fit of the Chan and Chu kinetic model shows that the degradation reaction has pseudo-first order behavior. Toxicity tests did not indicate the inhibition of growth of Lactuca sativa seeds and Escherichia coli bacterium. However, the growth of strains of the Salmonella enteritidis bacterium was inhibited in all the samples, demonstrating that only this bacterium was sensitive to solutions. The proposed empirical models obtained from the 2⁴ factorial designs were able to predict paracetamol degradation. These models could, at the same levels assessed, be used to predict the percentage of degradation in studies using other organic compounds. The LED and UV-C photo-reactors were, when employing the photo-Fenton process, able to degrade paracetamol, thus highlighting the efficiency of LED radiation when its power (three times smaller) is compared to that of UV-C radiation.

Application of the advanced oxidative process on the degradation of the green leaf and purple açaí food dyes with kinetic monitoring and artificial neural network modelling

The study evaluated the advanced oxidative processes concerning the degradation of green leaf and purple açaí dyes, as well as the prediction of data through artificial neural networks (ANNs). It was verified that percentage of degradation on the wavelengths (λ) of 215, 248, 523 and 627 nm was 5.95, 49.99, 98.17 and 95.99%, respectively, when UV/H₂O₂ action and UV-C radiation was applied. A non-linear kinetic model proposed by Chan and Chu presented a good fit to the experimental data, reaching an R² value between 0.978 and 0.999, for the studied λ. Within the ANN simulations through Statistica 6.0, the multilayer perceptron (MLP) (3-9-4) presented a better fit to the experimental data. However, higher values of R² were obtained when utilizing the sklearn package with Python language and an MLP (4-5-4) model. Assays with Staphylococcus aureus and Staphylococcus pyogenes bacteria isolates were performed and it was verified that after employing the UV/H₂O₂ process, there was a decrease in the toxicity of the solution of dyes. In evaluating S. aureus toxicity, normal growth was observed. However, for S. pyogenes bacteria, it was found that when using the UV/H₂O₂ process, toxicity was evidenced at post-treatment solution concentrations of 100, 70 and 50%.

Kinetic and ecotoxicological evaluation of the direct orange 26 dye degradation by Fenton and solar photo-Fenton processes

The presence of color in textile effluents has been studied because of the need for more effective treatments. Therefore, advanced oxidative processes (AOP) have been used in the degradation of dyes, as well as in the conversion of organic matter. This study evaluated the degradation of the direct orange 26 textile dye by Fenton and photo-Fenton processes (with natural solar radiation). A statistical analysis, based on factorial 23 indicated the best working conditions, being: [H2O2] = 100 mg·L-1 and pH 3-4, for both AOP in that the [Fe] =  1 e 5 mg·L-1, for photo-Fenton and Fenton, respectively. The results of the kinetic studies demonstrated a good fit to the nonlinear kinetic model proposed by Chan and Chu, with values of R2 > 0,996 (photo-fenton) and R2 > 0,939 (Fenton). The tests performed to evaluate the chemical oxygen demand indicated conversions of 62.05% (Fenton) and 66.41% (photo-Fenton). Finally, the ecotoxicity study indicated that the post-treatment samples were non-toxic to the bacteria Escherichia coli and Proteus mirabilis but showed growth inhibition for Lactuca sativa (Fenton and photo-Fenton) seeds and for Brassica juncea and Portulaca grandiflora (Fenton).

Performance verification of methodology for determination of nitrate ion in drinking water samples

Contaminated water is one of the main public health risks. One way to assess its quality is by quantifying nitrate through ultraviolet (UV) spectrophotometry. In this work, the performance of the UV spectrophotometric method for nitrate ion determination in water was studied, with linearity, precision, accuracy, limit of detection (LOD), limit of quantification (LOQ) and robustness being verified. In the working range studied (5.0-25.0 mgN·L-1), all validation parameters are in accordance with the acceptance criteria established by INMETRO. In linearity, the value of r (0.999) was higher than the criterion (0.995). In the study of precision and accuracy, the coefficients of variation for repeatability and intra-laboratory reproducibility were 1.79 and 2.34%, and 1.44 and 2.52%, respectively (<5%). The value of the relative error (15.8 and 8.1%) was also lower than the criterion (≤ 20%). The LOD and LOQ obtained were 0.56 and 1.70 mgN·L-1, respectively. In the evaluation of the robustness no factor had a significant effect on the final result. Analyzing real samples, the percentages of recovery were between 88.5 and 103.6%, according to the established criteria (80-110%). In this way, it can be said that the method presents reliability to the intended purpose.

Degradation of textile dyes Remazol Yellow Gold and reactive Turquoise: optimization, toxicity and modeling by artificial neural networks

In this work, the degradation of Remazol Yellow Gold RNL-150% and Reactive Turquoise Q-G125 were investigated using AOP: photolysis, UV/H2O2, Fenton and photo-Fenton. It was found that the photo-Fenton process employing sunlight radiation was the most efficient, obtaining percentages of degradation above 87%. The ideal conditions for the degradation of the dyes were determined from a factorial design 23 and study of the [H2O2] ([H2O2] equal to 100 mg·L-1); [Fe] equal to 1 mg·L-1 and pH between 3 and 4. In the kinetic study, a degradation of more than 97% was obtained after 150 min for the chromophoric groups and 91% for the aromatic compounds. The experimental data obtained presented a good fit to the nonlinear kinetic model. The model of artificial neural networks multilayer perceptron (MLP) (4-11-5) using the software Statistica 8.0 enabled the modeling of the degradation process and showed a better prediction of the data. The toxicity to the seeds of Lactuca sativa and the bacteria Escherichia coli and Salmonella enteritidis allowed to evaluate the effectiveness of the process. The results of this study suggest that the use of photo-Fenton process with sunlight radiation is an effective way to degrade the dyes under study.

Photodegradation applied to the treatment of phenol and derived substances catalyzed by TiO2/BiPO4 and biological toxicity analysis

For this work, a phenol solution model was treated by an advanced oxidation process (AOPs), using the heterogeneous catalyst TiO₂/BiPO₄ and hydrogen peroxide combined with UVA for 240 min. An annular reactor containing a UVA lamp (80 W) was employed. A central composite rotacional design was developed employing a TiO₂/BiPO₄ concentration of 87 mg L^-1 and a hydrogen peroxide concentration of 1800 mg L^-1, being evaluated by the degradation percentage and phenol mineralization percentage as responses; 94.30 and 67.00 % were obtained for the phenol degradation and total organic carbon (TOC) conversion, respectively. The lumped kinetic model (LKM) was applied and a satisfactory profile of the residual fractions of the organic compounds present in the liquid phase as a time function with a determination coefficient (R ² = 0.9945). The toxicity tests employing microbiological species indicated that the organisms tested for the evaluation of the toxic compounds present in the contaminated samples presented a practical low cost test, rapid execution, and high sensibility as an indicator of the presence of toxic substances in liquid effluents.