Green activated carbons from different waste materials for the removal of iron from real wastewater samples of Nag River, India

Ultrasound-assisted adsorption on porous ceramic for removal of iron in water

This study proposes the use of an ultrasound-assisted adsorption system coupled to porous ceramic fragments to improve the removal of iron from FeSO₄ aqueous solution. Ultrasound was applied using an ultrasound bath at a low frequency (37 kHz, 330 W). The optimized conditions for Fe removal were achieved by 7 g of adsorbent, 40 min of sonication, 20 mg L^-1 of initial Fe concentration, and 30 °C of reaction temperature. After optimizing the conditions, the method was applied for the removal of iron in groundwater. A central composite design and response surface methodology were used to evaluate the degree to which different variables had a significant effect on iron removal. The efficiency of iron removal using the selected conditions for FeSO₄ solution was near to 100%. However, for groundwater samples, the maximum iron removal efficiencies of the system with and without ultrasound were 80.7% and 51.1%, respectively, indicating that the adsorption with ultrasound was significantly higher than that without ultrasound. It was shown that the proposed ultrasound-assisted adsorption system can be used to enhance the removal of inorganic iron from groundwater.

Sustainable utilization of water treatment residue as a porous geopolymer for iron and manganese removals from groundwater

Raw water is a significant resource for industrial water usage, but this water is not directly suitable for use due to the presence of contaminants. Therefore, pre-treatment is essential. The treatment generates water treatment residue (WTR) which consists of silt, clay and undesirable components. Most WTR is conventionally disposed of in landfill. In addition, the presence of iron (Fe) and manganese (Mn) in groundwater can result in a reddish-brown color and undesirable taste and odour. A number of expensive and complex technologies are being used for the removal of such iron and manganese. Due to the high Al₂O₃ and SiO₂ content in WTR, therefore, this research proposes the use of WTR as the source material for geopolymer production for Fe/Mn removal. With the availability of free alkali in the geopolymer framework, the OH^--releasing behavior of the WTR-based geopolymer was investigated by the precipitation of Fe(II) ion. The WTR-based geopolymer was calcined at 400 °C and 600 °C to obtain a strong geopolymer matrix with the ability to remove Fe/Mn ions. The results show that the WTR-based geopolymer has the potential to remove Fe from Fe-contaminated water. Hydroxide ions are released from the geopolymer and form an Fe(OH)₃ precipitate. Geopolymer with a calcination temperature of 400 °C provides total removal of the Fe after 24 h of immersion. In addition, the existence of Fe(OH)₃ helps to coprecipitate the Mn(OH)₂ in the Fe/Mn solution leading to a significant reduction of Mn from the solution. The pH value and retention time play an important role in the final metal concentration. The final pH of the solution is close to 8.5, which is the recommended value for boiler water. This method offers an alternative use of WTR in making a porous geopolymer for groundwater Fe/Mn removal using a simple method.

Removal of anti-inflammatory drugs using activated carbon from agro-industrial origin: current advances in kinetics, isotherms, and thermodynamic studies

Nonsteroidal anti-inflammatory drugs (NSAIDs) are highly consumed around the world and consequently found as emerging pollutants in water; they are found in concentrations up to µg L−1 making their removal a priority. In this matter, adsorption is an efficient alternative for drug removal, so using activated carbon (AC) as an adsorbent is a highly explored subject. The current interest is to obtain AC from waste, for example, those of agro-industrial origin, reducing this way the overall costs of the process. Although information regarding the use of AC from agro-industrial origin in the removal of NSAIDs is limited, an exclusive compilation is required to understand the state of the art to date. This work aims to update information related to the adsorption of ibuprofen, diclofenac, and naproxen on agro-industrial AC, and it is focused on the period 2016–2021. It highlights the characteristics of agro-industrial AC responsible for efficient adsorption. Recent adsorption studies, including kinetics, isotherms, and thermodynamics, are analyzed and compared. Progress on removing NSAIDs from real wastewater is also presented and finally proposed adsorption mechanisms and costs related to these removal processes.

Novel luminescent Schiff's base derivative with an azo moiety for ultraselective and sensitive chemosensor of Fe3+ ions

Chemosensors with ultrasensing capabilities for detection of metal ions have received particular attention when using luminescent organic compounds. Even though hundreds of chemosensor agents have been reported for Fe³⁺ ion sensing, the designs of those molecules have been complicated and time consuming, in addition to having limited application for aquatic samples due to their poor hydrophilicity. Here, we synthesized a novel azo-imine derivative (L2) that showed ultrasensitive and selective sensing for Fe³⁺ ions. L2 exhibited ultraselective detection of Fe³⁺ ions with a turn-off of its emission intensity at 341 nm in H₂ O:MeOH (4:1 v/v) aqueous medium. This quenching phenomenon was in good agreement with its colour change from orange-yellowish to colourless. Its capability was shown due to its very low limit of detection and limit of quantification values of 0.31 and 1.04 μM, respectively. The interference study showed that L2 is ultraselective for the detection of Fe³⁺ ions without a significant reduction in its sensing capability even in competitive metal mixtures. Furthermore, direct Fe³⁺ quantification of tap and drinking water showed that L2 gave good recovery percentages. These findings demonstrated that the Schiff's base with an azo fluorophore derivative is a potential chemosensor agent for Fe³⁺ ions sensing applications in aqueous media.

Valorization of agro-industry residues in the building and environmental sector: A review

Environmental pollution has become a relevant issue as the population rises and resources decrease. Reuse and recycling still have the greatest potential as they turn the waste into a new resource, representing the 'closed-loop' step of a circular economy (CE). Looking for new applications for agro-industry waste represents both an environmental issue, as its incorrect disposal is a cause of pollution, and a chance to exploit zero-cost natural wastes. The present review, with around 200 articles examined, focuses on possible reuses of these residues in (a) building construction, as additives to produce thermal and acoustic insulation panels, and (b) in water treatments, exploited for removal of pollutants. The selected materials (coconut, coffee, corn, cotton and rice) have industry production wastes with suitable applications in both sectors and huge worldwide availability; their reuse may thus represent a new resource, with an impact based on the production rate and the possible replacement of current inorganic materials. Along with possible implementation of the selected materials in the building industry and environmental engineering, a brief description of the production and supply chain are provided.

Optimization of the integral valorization process for orange peel waste using a design of experiments approach: Production of high-quality pectin and activated carbon

The aim of this study was to optimize the integral valorization of orange peel waste by obtaining activated carbon after a process of pectin recovery in recycling of orange peel by transformation to value-added products of pectin extraction and activated carbon preparation. The study was supported by statistical analysis, and the significant factors and optimal conditions were obtained from the statistical analysis. Using a representative sample of orange peel waste, a yield of 29.37% pectin was recovered at the optimal operating conditions (phosphoric acid as the extraction agent, 95 °C as the impregnation temperature and a 2-hour extraction time). Activated carbon (AC) was prepared from the remaining solid residue. The conditions that improve the resulting material quality were H₃PO₄ [0.6 M] used as the activating agent, an impregnation temperature of 95 °C, a carbonization temperature of 400 °C and 1 h of carbonization time. The obtained AC showed a sorption capacity of 2342.91 mg g^-1, a value higher than that reported for commercial activated carbon. Using a model dye chemical, the sorption kinetics and thermodynamics of AC were found to follow a pseudo-second-order rate and the Freundlich models, respectively. Using the process conditions obtained in this study, it was possible to optimize the yield and also obtain good-quality products from valorization of orange peel.