Biosorbent derived from coffee husk for efficient removal of toxic heavy metals from wastewater

A Comprehensive Bibliometric Study in the Context of Chemical Hazards in Coffee

The research aimed to carefully review the chemical hazards linked to the coffee production chain to analyse the risks and opportunities for consumers and the environment, as well as identify potential knowledge gaps. The Scopus database was consulted from 1949 to April 2024 to conduct a bibliometric analysis. As a result, 680 articles were analysed. Results indicated a significant increase in research activity since 2015. China, Brazil, and the USA were the leading countries in scientific production and collaborations. The most prolific journals in this field were Chemosphere, Science of the Total Environment, Food Chemistry, Journal of Agricultural and Food Chemistry, and Journal of Environmental Management, all of which are in the first quartile. The word analysis revealed two main themes: the first focuses on the chemical hazards of coffee and their impact on health, while the second explores the waste generated during coffee production and its potential for reuse. The topics covered in the research include the composition of coffee, associated chemical hazards, possible health risks, and ways to reuse waste for environmental protection. Future research should concentrate on optimising techniques and processes to ensure quality, safety, and sustainability.

Preparation of basic magnesium carbonate nanosheets modified pumice and its adsorption of heavy metals

Heavy metal pollution in wastewater poses a grave danger to the environment and the human body. Pumice is a mineral with abundant reserves and low prices, and its prospect of heavy metal adsorbent is very broad. In this work, we modified pumice with basic magnesium carbonate nanosheets by a convenient hydrothermal synthesis. The adsorption capacity of heavy metals is greatly improved. The effects of different pH and adsorption dosages are investigated. All the optimum pH values for Cu2+, Pb2+, and Cd2+ are 5. The adsorption of three kinds of ions conforms to the quasi-second-order adsorption kinetics model. The theoretical adsorption capacities of Cu2+, Pb2+, and Cd2+, which are calculated by the Langmuir model, are 235.29 mg/L, 595.24 mg/L, and 370.34 mg/L, respectively. The adsorption of Cu2+ and Cd2+ fit the Langmuir model better. The Freundlich model is fitted well with the adsorption of Pb2+. In the experiment simulating real wastewater, the adsorption capacity of heavy metals is not affected. It also shows good reusability in three regeneration cycles. And Mg5(CO3)4(OH)2·4H2O@pumice adsorption column showed the good removal efficiency of three heavy metals at different concentrations and different spatial velocities in the column experiment. Thus, it is believed that the Mg5(CO3)4(OH)2·4H2O@pumice is a promising adsorbent for the efficient removal of heavy metals.

State-of-the-art adsorption and adsorptive filtration based technologies for the removal of trace elements: A critical review

Water and wastewater are contaminated with various types of trace elements that are released from industrial activities. Their presence, at concentrations above the permissible limit, will cause severe negative impacts on human health and the environment. Due to their cost-effectiveness, simple design, high efficiency, and selectivity, adsorption, and adsorptive filtration are techniques that have received lots of attention as compared to other water treatment techniques. Adsorption isotherms and kinetic studies help to understand the mechanisms of adsorption and adsorption rates, which can be used to develop and optimize different adsorbents. This state-of-the-art review provides and combines the advancements in different conventional and advanced adsorbents, biosorbents, and adsorptive membranes for the removal of trace elements from water streams. Herein, this review discusses the sources of different trace elements and their impact on human health. The review also covers the adsorption technique with a focus on various advanced adsorbents, their adsorption capacities, and adsorption isotherm modeling in detail. In addition, biosorption is critically discussed together with its mechanisms and biosorption isotherms. In the end, the application of various advanced adsorptive membranes is discussed and their comparison with adsorbents and biosorbents is systematically presented.

Magnesium oxide nanoparticles modified biochar derived from tea wastes for enhanced adsorption of o-chlorophenol from industrial wastewater

In this work, magnesium oxide nanoparticles supported biochar derived from tea wastes (MgO@TBC) was prepared as an effective adsorbent for removing hazardous o-chlorophenol (o-CP) from industrial wastewater. The surface area, porous structure, surface functional groups and surface charge of tea waste biochar (TBC) significantly enhanced after the modification process. The best uptake performance of o-CP was found at pH = 6.5 and 0.1 g of MgO@TBC adsorbent. According to the adsorption isotherm, the adsorption of o-CP onto MgO@TBC followed the Langmuir model with a maximum uptake capacity of 128.7 mg/g, which was 26.5% higher than TBC (94.6 mg/g). MgO@TBC could be reused for eight cycles with a high o-CP uptake performance (over 60%). Besides, it also exhibited good removal performance of o-CP from industrial wastewater with a removal rate of 81.7%. The adsorption behaviors of o-CP onto MgO@TBC are discussed based on the experimental results. This work may provide information to prepare an effective adsorbent for removing hazardous organic contaminants in wastewater.

Valorization of Fibrous Plant-Based Food Waste as Biosorbents for Remediation of Heavy Metals from Wastewater-A Review

Mobilization of heavy metals in the environment has been a matter of concern for several decades due to their toxicity for humans, environments, and other living organisms. In recent years, use of inexpensive and abundantly available biosorbents generated from fibrous plant-based food-waste materials to remove heavy metals has garnered considerable research attention. The aim of this review is to investigate the applicability of using fibrous plant-based food waste, which comprises different components such as pectin, hemicellulose, cellulose, and lignin, to remove heavy metals from wastewater. This contribution confirms that plant-fiber-based food waste has the potential to bind heavy metals from wastewater and aqueous solutions. The binding capacities of these biosorbents vary depending on the source, chemical structure, type of metal, modification technology applied, and process conditions used to improve functionalities. This review concludes with a discussion of arguments and prospects, as well as future research directions, to support valorization of fibrous plant-based food waste as an efficient and promising strategy for water purification.

Biorefining of rapeseed meal: A new and sustainable strategy for improving Cr(VI) biosorption on residual wastes from agricultural byproducts after phenolic extraction

Phenolic recovery from agricultural byproducts has been highlighted due to their health-promoting bioactivities. However, uncontrolled discard of residues after extraction process would induce environmental pollution and bioresource waste. In this study, biorefining of phenolic-rich rapeseed meal (RSM) and its defatted sample (dRSM) was attempted by holistic utilization of phenolic extract and residue separately. Phenolic removal could significantly improve residues' Cr(VI) adsorption capacities by about 21%, which presented extended physical surface and more released functional groups. Moreover, simulating raw material by remixing 3% separated phenolic extracts or main component sinapic acid therein with corresponding residues further improved about 12% adsorption efficiencies. These indicated that the different present forms of phenolics had opposite effects on Cr(VI) removal. While natural conjugational form inhibited hosts' biosorption, free form had enhanced functions for either extract or residue. Four optimal adsorption parameters (pH, adsorbent dosage, contact time and initial Cr(VI) concentration), three kinetic (pseudo-first order, pseudo-second order and intra-particle diffusion) models and two isotherms (Langmuir and Freundlich) were used to reveal the adsorption process. The maximum Cr(VI) adsorption capacity on residues could reach about 100 mg/g, which was superior to that of most biosorbents derived from agricultural byproducts, even some biochar. Together with the residues' advantages with everlasting capacity after 3 adsorption-desorption cycles and excellent abilities for adsorbing multiple co-existed metal ions (Cr(VI), Cd(II), Cu(II), Pb(II), Ni(II) and Zn(II)), phenolic recovery was first proved to be a new and sustainable strategy for modifying biosorbents from agricultural byproducts with zero waste.

Preparation of manganese-oxides-coated magnetic microcrystalline cellulose via KMnO4 modification: Improving the counts of the acid groups and adsorption efficiency for Pb(II)

Herein, the manganese-oxides-coated magnetic microcrystalline cellulose (MnOx@Fe₃O₄@MCC) was prepared by coprecipitation and subsequently modified with KMnO₄ solution at room temperature, which was in turn applied for the removal of Pb(II) from wastewater. The adsorption properties of Pb(II) on MnOx@Fe₃O₄@MCC were investigated. The kinetics and isothermal data of Pb(II) were described well by the Pseudo-second-order model and the Langmuir isotherm model, respectively. At pH = 5, 318 K, the Langmuir maximum Pb(II) adsorption capacity of MnOx@Fe₃O₄@MCC was 446.43 mg/g, which is higher than many documented bio-based adsorbents. The results of Fourier transform infra-red and X-ray photoelectron spectroscopy indicated that the adsorption mechanisms for Pb(II) mainly involved surface complexation, ion exchange, electrostatic interaction and precipitation. Interestingly, the increased amount of carboxyl group on the surface of microcrystalline cellulose modified by KMnO₄ was one of the important reasons for the high Pb(II) adsorption performance of MnOx@Fe₃O₄@MCC. Furthermore, MnOx@Fe₃O₄@MCC exhibited excellent activity (70.6 %) after five consecutive regeneration cycles, indicating its high stability and reusability. Endorsing to the cost-effectiveness, environmentally friendliness, and reusable nature, MnOx@Fe₃O₄@MCC can be counted as a great alternative contender for the remediation of Pb(II) from industrial wastewater.

Improved Cr (VI) adsorption performance in wastewater and groundwater by synthesized magnetic adsorbent derived from Fe3O4 loaded corn straw biochar

This work developed an easy method to utilize corn straw (CS) waste for sustainable development and reduce the volume of waste volume as well as bring value-added. The magnetic adsorbent was prepared by loading Fe₃O₄ onto biochar derived from corn straw (Fe@CSBC), then used for capturing Cr (VI) in groundwater and wastewater samples. The characterization of adsorbents showed that Fe3O4 was successfully loaded on corn straw biochar (CSBC) and contributed to the improvement of the surface area, and surface functional groups like Fe-O, Fe-OOH, CO, and O-H. The presence of iron oxide was further confirmed by XPS and XRD analysis and a magnetization value of 35.6 emu/g was obtained for Fe@CSBC. The highest uptake capacity of Cr (VI) onto Fe@CSBC and CSBC by monolayer were 138.8 and 90.6 mg/g, respectively. By applying magnetic adsorbent Fe@CSBC for the treatment of groundwater and wastewater samples, the chromium could be removed up to 90.3 and 72.6%, respectively. The remaining efficiency of Cr (VI) was found to be 84.5% after four times reused Fe@CSBC, demonstrating the great recyclable ability of the adsorbent. In addition, several interactions between Cr (VI) and Fe@CSBC like ion exchange, complexation, and reduction reaction were discussed in the proposed adsorption mechanism. This study brings an efficient method to turn corn straw biomass into an effective magnetic adsorbent with high adsorption performance and good reusability of Cr (VI) in groundwater as well as in wastewater.

Cobalt Biosorption in Fixed-Bed Column Using Greenhouse Crop Residue as Natural Sorbent

Intensive greenhouse agriculture annually produces large amounts of residues. The present work focused on the study of the dynamic adsorption of cobalt from aqueous solutions over a vegetal residue from intensive greenhouse cultivation. The influence of three operating variables, feed-flow rate, inlet concentration of cobalt and bed height, was analyzed. According to the results, the variable that particularly affected the percentage of cobalt adsorbed was the feed-flow rate. The results were also fitted to an adaptive neuro fuzzy system (ANFIS) model to predict cobalt adsorption from aqueous solutions and choose the most favorable operating conditions. Results were evaluated using root mean squared error (RMSE), coefficient of determination (R2) and other typical statistic factors as performance parameters. The experimental and model outputs displayed acceptable result for ANFIS, providing R2 values higher than 0.999 for both cobalt removal (%) and biosorption capacity (mg/g). In addition, the results showed that the best operating conditions to maximize the removal of cobalt were 4 mL/min of feed-flow rate, 25 mg/L of inlet concentration and 11.5 cm of bed-height.

Visible-light photocatalysis of Ag-doped graphitic carbon nitride for photodegradation of micropollutants in wastewater

This work reports on graphitic carbon nitride (C₃N₄) modified with silver to investigate its visible-light-driven photocatalysis for decomposition of micropollutants in wastewater. Various characterization methods were conducted to examine the physico-chemical properties of Ag-doped C₃N₄ (Ag-C₃N₄) photocatalyst. The results from structural, morphological, and surface chemical analysis indicated that C₃N₄ was successfully doped with Ag. Photoluminescence and transient photocurrent density studies revealed that the recombination rate of electron-hole pairs was reduced, leading to the enhancement of photocatalytic activities of the photocatalyst. Ag-C₃N₄ showed high photocatalytic performance for photodegradation of our target micropollutant, bisphenol A (BA). It could completely remove BA in 1 h with kinetic constant 6.2 times higher than that of the undoped C₃N₄ photocatalyst. Recycling test and the assessment of the photocatalyst in wastewater further confirmed the excellent stability and applicability of the Ag-C₃N₄ photocatalyst. This work could provide a new solution to the practical application of photocatalyts for the degradation of micropollutants in wastewater.

An insight on Vietnamese bio-waste materials as activated carbon precursors for multiple applications in environmental protection

Vietnam is known as an agricultural country with a variety of agricultural crops. In addition to agricultural by-products, bio-waste is the by-product from livestock waste, forestry, industry, and daily life. They affect the soil, water, and air environment by self-degradation processes in the environment. Therefore, researchers have come up with ideas for the usage of the by-products to decrease the amount of waste and minimize the environmental effects. In Vietnam, the by-products were used by researchers to produce bio-ethanol, fertilizers, composites, and activated carbon (AC). AC is one of the materials used to rapidly reduce the number of agricultural by-products by researchers. The synthesis process is optimized for the highest yield, while the physicochemical properties are also clearly analyzed through the X-ray diffraction, Fourier transform infrared, and Bacterial endotoxin testing assays. The average recorded specific surface area was about 300 m2 g−1. The functional groups and surface structure showed that the material has an amorphous structure with –OH, –CH, –CC, –C═C, –C═O groups. The AC from agricultural waste had been studied and applied to treat pollutants present in water.

Biochar can mitigate co-selection and control antibiotic resistant genes (ARGs) in compost and soil

Heavy metals (HMs) contamination raises the expression of antibiotic resistance (AR) in bacteria through co-selection. Biochar application in composting improves the effectiveness of composting and the quality of compost. This improvement includes the elimination and reduction of antibiotic resistant genes (ARGs). The use of biochar in contaminated soils reduces the bioaccessibility and bioavailability of the contaminants hence reducing the biological and environmental toxicity. This decrease in contaminant bioavailability reduces contaminants induced co-selection pressure. Conditions which favour reduction in HMs bioavailable fraction (BF) appear to favour reduction in ARGs in compost and soil. Biochar can prevent horizontal gene transfer (HGT) and can eliminate ARGs carried by mobile genetic elements (MGEs). This effect reduces maintenance and propagation of ARGs. Firmicutes, Proteobacteria, and Actinobacteria are the major bacteria phyla identified to be responsible for dissipation, maintenance, and propagation of ARGs. Biochar application rate at 2-10% is the best for the elimination of ARGs. This review provides insight into the usefulness of biochar in the prevention of co-selection and reduction of AR, including challenges of biochar application and future research prospects.

Cadmium-Tolerant Plant Growth-Promoting Bacteria Curtobacterium oceanosedimentum Improves Growth Attributes and Strengthens Antioxidant System in Chili (Capsicum frutescens)

The remediation of potentially toxic element-polluted soils can be accomplished through the use of microbial and plant-assisted bioremediation. A total of 32 bacteria were isolated from soil samples contaminated with potentially toxic elements. The isolated bacterial strain DG-20 showed high tolerance to cadmium (up to 18 mM) and also showed bioaccumulative Cd removal properties, as demonstrated by atomic absorption spectroscopy studies. By sequencing the 16S rRNA gene, this strain was identified as Curtobacterium oceanosedimentum. Under stress and normal conditions, isolate DG-20 also produced a wide range of plant growth promoting traits, including ammonia production (51–73 µg/mL) and IAA production (116–183 µg/mL), alongside siderophore production and phosphate solubilization. Additionally, pot experiments were conducted to determine whether the strain could promote Chili growth when Cd salts are present. Over the control, bacterial colonization increased root and shoot lengths significantly up to 58% and 60%, respectively. Following inoculation with the Cd-tolerant strain, the plants also increased in both fresh and dry weight. In both the control and inoculated plants, Cd was accumulated more in roots than in shoots, indicating that Chili was phytostabilizing Cd levels. Besides improving the plant attributes, Cd-tolerant bacteria were also found to increase the amount of total chlorophyll, proline, total phenol, and ascorbic acid in the soil when added to the soil. These results suggest that the inoculant provides protection to plants from negative effects. The results of the present study predict that the combined properties of the tested strain in terms of Cd tolerance and plant growth promotion can be exploited for the purpose of the bioremediation of Cd, and for the improvement of Chili cultivation in soils contaminated with Cd.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Mechanistic insight into the removal of aqueous Cd using an immobilized ZIF-8 and microflora cooperative composite

Biotechnology and metal-organic-frameworks (MOFs) materials have been investigated intensively for the removal of heavy metal from wastewater. However, the cooperative effect of bacteria and MOFs on heavy metal adsorption was less reported. Considering this, this study has screened out microflora with cadmium (Cd) adsorption ability. Furthermore, it was combined with zeolitic imidazolate framework-8 (ZIF-8) to form a ZIF-8 and microflora complex (ZMC). Moreover, ZMC was further immobilized to improve its Cd adsorption effect and reusability. Results revealed that the immobilized ZMC exhibited 99.91% and 78.83% Cd adsorption rate for 20 mg L^-1 and 300 mg L^-1 Cd, respectively. Meanwhile, the immobilized ZMC maintained a relatively stable adsorption effect under varied external pH. The reaction mechanism was summarized as covalent binding accompanied with a small amount of electrostatic attraction. Microflora could enhance the surface electronegativity of ZIF-8. ZIF-8 could strengthen the response of antioxidant activity of microflora and augmented the affinity of microflora secretions for Cd. This proposed method may provide a new insight for the removal of heavy metal contaminants in water.

Modeling the Biosorption Process of Heavy Metal Ions on Soybean-Based Low-Cost Biosorbents Using Artificial Neural Networks

Pollution of the environment with heavy metals requires finding solutions to eliminate them from aqueous flows. The current trends aim at exploiting the advantages of the adsorption operation, by using some low-cost sorbents from agricultural waste biomass, and with good retention capacity of some heavy metal ions. In this context, it is important to provide tools that allow the modeling and optimization of the process, in order to transpose the process to a higher operating scale of the biosorption process. This paper capitalizes on the results of previous research on the biosorption of heavy metal ions, namely Pb(II), Cd(II), and Zn(II) on soybean biomass and soybean waste biomass resulting from biofuels extraction process. The data were processed by applying a methodology based on artificial neural networks (ANNs) and evolutionary algorithms (EAs) capable of evolving ANN parameters. EAs are represented in this paper by the differential evolution (DE) algorithm, and a simultaneous training and determination of the topology is performed. The resulting hybrid algorithm, hSADE-NN was applied to obtain optimal models for the biosorption process. The expected response of the system addresses biosorption capacity of the biosorbent (q, mg/g), the biosorption efficiency (E, %), as functions of input parameters: pH, biosorbent dose (DS, mg/g), the initial concentration of metal in the solution (c0, mg/L), contact time (tc, h), and temperature (T, °C). Models were developed for the two output variables, for each metal ion, finding a high degree of accuracy. Furthermore, the combinations of input parameters were found which can lead to an optimal output in terms of biosorption capacity and biosorption efficiency.

A review on recent advances in electrodeionization for various environmental applications

The growing contamination of ecosystems necessitates the development of long-term pollution-removal technologies. Electrodeionization, in notably, has newly proven as an efficient method for removing ionic chemicals from polluted waterways. The fact that continuous electrodeionization is a greener technique is most probably the biggest cause for its success. It replaces the toxic chemicals typically required to replenish resins with electric power, therefore eliminating the wastewater involved with resin renewal. In water treatment, electrodeionization solves some of the drawbacks of ion exchange resin beds, particularly ion dumping as beds expire. This comprehensive review explores the theory, principles, and mechanisms of ion movement and separation in an electrodeionization unit. Also, it investigated the construction and usage, notably in removing heavy metal and its current developments in electrodeionization unit. Recent advances in Electrodeionization like polarity reversal, Resin wafer Electrodeionization, membrane free Electrodeionization, and electrostatic shielding with novel materials and hybrid process along with Electrodeionization were addressed. Further advancements are expected in electrodeionization systems that exhibit better efficacy while running at lower costs due to decreased energy usage, rendering them appealing for industrial scale up across a wide range of applications across the world.

Investigation of mechanism of heavy metals (Cr6+, Pb2+& Zn2+) adsorption from aqueous medium using rice husk ash: Kinetic and thermodynamic approach

In this work, we examined the possibility on the application of rice husk as biosorbent for the elimination of heavy metal ions (chromium, lead, and zinc) existing in the aqueous solutions. The biosorbent was prepared from rice husk powder and modified with 0.1 N of HCl for creating the functional groups and increase specific surface area. The FT-IR spectra, SEM& EDX studies of rice hulls powder were examined for the pristine adsorbent and after the adsorption of heavy metal ions. The batch adsorption technique was adopted for this work and adsorption parameters were optimized. The maximum efficiency of adsorption is obtained at 6.0 pH, 1 h of contact duration, the rice husk dosage is 2.5 g/L, and temperature of 30°C for 25 mg/L of Cr, Pb & Zn metal ion solutions. The Cr, Pb & Zn metal ions are removed up to 87.12 %, 88.63 % & 99.28 %, respectively, using the rice husk powder. The adsorption process follows the Temkin & D-R isotherm model. Elovich model was fitted against the kinetic data of metal ion adsorption. Based on the experimental observations, the rice husk powder can be considered as a low cost adsorbent for heavy metal ion removal from the industrial effluent.