Coconut coir as biosorbent for Cr(VI) removal from laboratory wastewater

Modified Ordered Mesoporous Carbons for Cr(VI) Removal from Wastewater

The pristine CMK-3 carbon was ozonized and then chemically modified by the Zr and Fe compounds. The synthesized carbonaceous materials were characterized with physicochemical methods. The obtained carbons had a high specific surface area (ca. 800 m2 g-1) and an acidic surface. The Cr(VI) adsorption properties of the oxidized and Zr/Fe-modified carbon were studied. The highest static adsorption capacity towards Cr(VI) ions was evaluated for Zr/Fe-modified carbon (50.1 mg g-1) at pHeq = 5.8 after 240 min. The Elovich and Freundlich theoretical models were well fitted to the Cr(VI) adsorption kinetic and isotherm data on the Zr/Fe-modified CMK-3-type carbon. The leading Cr(VI) adsorption mechanism acting on the Zr/Fe-modified carbon was probably based on the redox reactions between Cr(VI) and the carbonaceous surface. Electrostatic attraction and surface complexation processes could also occur during Cr(VI) adsorption in the studied system. The effect of the competitive anions on the concentration level, such as in the galvanic wastewater for Cr(VI) adsorption onto chemically modified carbon, was negligible. The HCl and HNO3 media were insufficient for the Zr/Fe-modified carbon regeneration after Cr(VI) adsorption. The Zr/Fe-modified carbon was successfully applied for the efficient (>90%) Cr(VI) removal from the model galvanic wastewater.

A comprehensive review of coconut-based porous materials for wastewater treatment and CO2 capture

For several decades, water pollution has become a major threat to aquatic and non-aquatic species, including humans. Different treatment techniques have already been proposed and implemented depending on wastewater characteristics. But many of these treatment techniques are expensive and inefficient. Adsorption-based techniques have shown impressive performances as an inexpensive treatment method previously. Coconut-based resources have been considered as adsorbents for wastewater treatment because of their abundance, low cost, and favorable surface properties. However, over the last decade, no comprehensive study has been published regarding biochar from coconut-based materials for wastewater treatment and CO2 capture. This review discusses biochar production technology for coconut-based materials, its modification and characterization, its utilization as an adsorbent for removing metals and organics from wastewater, and the associated removal mechanisms and the economic aspects of coconut-based biochar. Coconut-based materials are cheap and effective for removing various organic compounds such as pesticides, hormones, phenol, and phenolic compounds from solutions and capturing CO2 from air mainly through the pore-filling mechanism. Utilizing coconut-based biochars in a hybrid system that combines adsorption and other techniques, such as biotechnology or chemical coagulation is a promising way to increase their performance as an adsorbent in wastewater treatment.

Efficacious Sorption Capacities for Pb(II) from Contaminated Water: A Comparative Study Using Biowaste and Its Activated Carbon as Potential Adsorbents

Heavy-metal pollution is a persevering environmental menace, which demands the necessity of its removal by green and ecofriendly adsorbents. To combat this problem, discarded plant biomass can be used as an efficient substitute. Herein, a comparative study has been highlighted for the removal of Pb²⁺ ions using Euryale ferox Salisbury seed coat and its activated carbon, which is prepared by a first-time-reported activating agent that is a novel and non-hazardous bioresource. The batch investigation revealed a 99.9% removal efficiency of Pb(II) by the activated carbon compared to Euryale ferox Salisbury seed coat, which shows only an 89.5% removal efficiency at neutral pH. The adsorption mechanism is mainly a multilayered process, which involves electrostatic, van der Waals, and hydrogen bonding interactions. The adsorption equilibrium, kinetic, and thermodynamic studies were examined for the biosorbents, which revealed the adsorption process to be feasible, spontaneous, and exothermic with both physisorption and chemisorption adsorption mechanisms. The desorption study asserted the reusability of both the biosorbents to a maximum of three cycles.

A Comprehensive Review of the Current Progress of Chromium Removal Methods from Aqueous Solution

Chromium (Cr) exists in aqueous solution as trivalent (Cr³⁺) and hexavalent (Cr⁶⁺) forms. Cr³⁺ is an essential trace element while Cr⁶⁺ is a dangerous and carcinogenic element, which is of great concern globally due to its extensive applications in various industrial processes such as textiles, manufacturing of inks, dyes, paints, and pigments, electroplating, stainless steel, leather, tanning, and wood preservation, among others. Cr³⁺ in wastewater can be transformed into Cr⁶⁺ when it enters the environment. Therefore, research on Cr remediation from water has attracted much attention recently. A number of methods such as adsorption, electrochemical treatment, physico-chemical methods, biological removal, and membrane filtration have been devised for efficient Cr removal from water. This review comprehensively demonstrated the Cr removal technologies in the literature to date. The advantages and disadvantages of Cr removal methods were also described. Future research directions are suggested and provide the application of adsorbents for Cr removal from waters.

Removal of Cr(VI) from water by in natura and magnetic nanomodified hydroponic lettuce roots

Biosorption is a viable and environmentally friendly process to remove pollutants and species of commercial interest. Biological materials are employed as adsorbents for the retention, removal, or recovery of potentially toxic metals from aqueous matrices. Hexavalent chromium is a potential contaminant commonly used in galvanoplasty and exhibits concerning effects on humans and the environment. The present work used in natura lettuce root (LR) and nanomodified lettuce root (LR-NP) for Cr(VI) adsorption from water medium. The nanomodification was performed by coprecipitation of magnetite nanoparticles on LR. All materials were morphologically and chemically characterized. The conditions used in removing Cr(VI) were determined by evaluating the pH at the point of zero charge (pHPZC = 5.96 and 6.50 for LR and LR-NP, respectively), pH, kinetics, and sorption capacity in batch procedures. The maximum sorption capacity of these materials was reached at pH 1.0 and 30 min of adsorbent-adsorbate contact time. The pseudo-second-order kinetic equation provided the best adjustments with r2 0.9982 and 0.9812 for LR and LR-NP, respectively. Experimental sorption capacity (Qexp) results were 4.51 ± 0.04 mg/g, 2.48 ± 0.57 mg/g, and 3.84 ± 0.08 mg/g for LR, NP, and LR-NP, respectively, at a 10 g/L adsorbent dose. Six isothermal models (Langmuir, Freundlich, Sips, Temkin, DR, and Hill) fit the experimental data to describe the adsorption process. Freundlich best fit the experimental data suggesting physisorption. Despite showing slightly lower Qexp than LR, LR-NP provides a feasible manner to remove the Cr(VI)-containing biosorbent from the medium after sorption given its magnetic characteristic.

A global pollutant (PVC-polyvinyl chloride) applied as heavy metal binder from aqueous samples: green principles from synthesis to application

We have developed a clean route for the modification of polyvinylchloride surface (PVC) with 4-amino-5-hydrazino-1,2,4-triazole-3-thiol molecule. The modification reaction was investigated through Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analysis. According to our findings, S-H groups are responsible to the molecule attachment and nitrogen atoms are directly involved in metal ion coordination. These results are in agreement with the pseudo-second-order kinetic model, which infers that chemisorption is the main mechanism for metal removal. Adsorption isotherms of Cd(II), Cu(II) and Pb(II) follow the Langmuir model and the results indicated that N_s values are 0.39, 0.52 and 0.15 mmol g^-1, respectively. The calculated Ø^max values for Cu(II), Pb(II) and Cd(II) were 3.93, 2.95 and 1.13, respectively, indicating that three types of complex are formed depending on the adsorbed species. Therefore, it can be concluded that PVC use as adsorbent is feasible since it requires a simple modification reaction with nontoxic and low-cost solvents.

Bio-Stimulated Adsorption of Cr(VI) from Aqueous Solution by Groundnut Shell Activated Carbon@Al Embedded Material

In this study, a low-cost bioadsorbent aluminum metal blended with groundnut shell activated carbon material (Al-GNSC) was used for Cr(VI) adsorption from aqueous solutions. Al-GNSC was prepared and characterized using Fourier transform infrared spectrometer (FT-IR), scanning electron microscopic (SEM) and X-ray diffraction (XRD) to determine its surface morphology. Batch studies were performed and the optimum conditions for maximum Cr(VI) removal (of 94.2%) were found at pH 4.0, initial concentration 100 mg/L, adsorbent dosage 8 g/L of Cr(VI) solution, and time of contact 50 min. Moreover, the Langmuir isotherm model (maximum adsorption capacity of 13.458 mg/g) was the best fit and favored the mono-layered Cr(VI) adsorption. The kinetic studies reveal that the pseudo-second-order model was the best fit and favored chemisorption as the rate-limiting step. The desorption study revealed that Cr(VI) leached with sodium hydroxide solution acted as a regenerating agent. It is proved that Al-GNSC removes the Cr(VI) content in groundwater samples. The methodology developed using the Al-GNSC adsorbent as an alternative for the adsorption of Cr(VI) ions is remarkably successful in this study.

Biosorption of Cr(VI) using coconut fibers from agro-industrial waste magnetized using magnetite nanoparticles

Herein, the biosorption of Cr(VI) by magnetized coconut fibres obtained from agricultural waste has been described. Magnetization was achieved by incorporating magnetite nanoparticles into the fibres by a coprecipitation reaction in alkaline media. The biosorption capacity of the fibres was evaluated by two series of experiments. In the first series, 500 mg L^-1 of the biosorbent was added to a 50 mg L^-1 K₂Cr₂O₇ solution at 28 °C and stirred at 200 rpm and the pH was varied from 1 to 13 to determine the optimum pH value. The second series of experiments evaluated the sorption capacity of the fibres at the optimum pH, under the same agitation speed and temperature but with an adsorbate concentration of 100 mg L^-1. The biosorbents were characterized using Fourier transform-infrared spectroscopy, inductively coupled plasma-atomic emission spectroscopy, scanning electron microscopy, dispersive X-ray fluorescence, and X-ray powder diffraction. The biosorption experiments demonstrated that the magnetization process increased the biosorption capacity of the material. Optimum biosorption occurred at pH 2, and at optimal conditions, the best adsorptive efficiency exceeded 90%, reaching a biosorption capacity of 87.38 mg g^-1 for the magnetized fibre and 23.87 mg g^-1 for the natural fibre, with an equilibrium time of less than 20 min.

Hexavalent chromium removal from water: adsorption properties of in natura and magnetic nanomodified sugarcane bagasse

Biosorption has become a viable and ecological process in which biological materials are employed as adsorbents for the removal of potentially toxic metals, such as hexavalent chromium, from aqueous matrices. This work proposed the use of in natura (SB) and nanomodified sugarcane bagasse (SB-NP) with ferromagnetic nanoparticles (Fe₃O₄) to adsorb Cr(VI) from water. These materials were analyzed by X-ray Spectroscopy (XRD), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) to investigate their morphology and interaction with Cr(VI). It was observed the efficient impregnation of magnetite on the SB surface and the presence of functional groups such as O-H, C-H, C=O, C-O-C, C-O, and Fe-O (characteristic of magnetite). The best conditions for Cr(VI) removal in aqueous medium were determined by assessing the pH at the point of zero charge (pH_PZC = 6.1 and 5.8 for SB and SB-NP, respectively), adsorption pH and kinetics, and adsorption capacity. Batch procedures were performed using increasing concentrations of Cr(VI), 10-100 mg/L at pH 1.0, and 30 min of contact time. The adsorbent dose was 10 mg/L, and the experimental adsorption capacities (SC_exp) for SB, NP, and SB-NP were 1.49 ± 0.06 mg/g, 2.48 ± 0.57 mg/g, and 1.60 ± 0.08 mg/g, respectively. All Cr contents were determined by flame atomic absorption spectrometry (FAAS). The pseudo-2nd-order kinetic equation provided the best adjustments with r² 0.9966 and 0.9931 for SB and SB-NP, respectively. Six isotherm models (Langmuir, Freundlich, Sips, Temkin, Dubinin-Radushkevich, and Hill) were applied to the experimental data, and Freundlich, Dubinin-Radushkevich (D-R), and Temkin were the models that best described the experimental sorption process. The binding energy values (E) provided by the D-R model were 0.11 ± 0.25, 0.09 ± 0.20, and 0.08 ± 0.25 kJ/mol, for NP, SB-NP, and SB, respectively, and denote a physical interaction for the studied adsorbate-adsorbent system. The nanomodification of the biomass slightly improved the efficiency for the sorption of Cr(VI) and facilitated the removal of Cr(VI)-containing biosorbents from water medium.

Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074 mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R² and low χ² value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.

Returning to Nature for the Design of Sorptive Phases in Solid-Phase Microextraction

Green analytical chemistry principles aim to minimize the negative impact of analytical procedures in the environment, which can be considered both at close (to ensure the safety of the analysts) and global (to conserve our natural resources) levels. These principles suggest, among other guidelines, the reduction/minimization of the sample treatment and the use of renewable sources when possible. The first aspect is largely fulfilled by microextraction, which is considered to be among the greenest sample treatment techniques. The second consideration is attainable if natural products are used as raw materials for the preparation of new extraction phases. This strategy is in line with the change in our production system, which is being gradually moved from a linear model (take–make–dispose) to a circular one (including reusing and recycling as key terms). This article reviews the potential of natural products as sorbents in extraction and microextraction techniques from the synergic perspectives of two research groups working on the topic. The article covers the use of unmodified natural materials and the modified ones (although the latter has a less green character) to draw a general picture of the usefulness of the materials.

Oil spill cleanup employing magnetite nanoparticles and yeast-based magnetic bionanocomposite

Oil spill is a serious environmental concern, and alternatives to remove oils from water involving biosorbents associated to nanoparticles is an emerging subject. Magnetite nanoparticles (MNP) and yeast magnetic bionanocomposite (YB-MNP) composed by yeast biomass from the ethanol industry were produced, characterized, and tested to remove new motor oil (NMO), mixed used motor oil (MUMO) and Petroleum 28 °API (P28API) from water following the ASTM F726-12 method, which was adapted by insertion of a lyophilization step to ensure the accuracy of the gravimetric approach. Temperature, contact time, the type and the amount of the magnetic material were the parameters evaluated employing a fractional factorial design. It was observed the removal of 89.0 ± 2.6% or 3522 ± 118 g/kg (NMO) employing MNP; 69.1 ± 6.2% or 2841 ± 280 g/kg (MUMO) with YB-MNP; and 55.3 ± 8.2% or 2157 ± 281 g/kg (P28API) using MNP. The temperature was the most significant parameter in accordance with the Pareto's graphics (95% confidence) for all oil samples considered in this study as well as the two magnetic materials. Contact time and the interaction between the materials and temperature were also relevant. The D-Optimals designs showed that the NMO and P28API responded in a similar way for all evaluated parameters, while the uptake of MUMO was favored at higher temperatures. These behaviors demonstrate the influence of oil characteristics and the intermolecular forces between the oil molecules on the mechanism dragging process performed by the attraction between magnetite nanoparticles and a 0.7 T magnet. It was clear that this kind of experiment is predominantly a physic phenomenon which cannot be described as adsorption process.

Removal of chromium from laboratory wastewater using preparation–adsorption technology with a Mg/Al/Cr layered compound

A Mg/Al/Cr layered compound (Mg/Al/Cr(iii)–LDH) was prepared using laboratory wastewater containing Cr(iii), and the calcined Mg/Al/Cr(iii)–LDH compound (Mg/Al/Cr(iii)–CLDH) was applied to remove Cr(vi) from laboratory wastewater.

A preliminary investigation of the mechanism of hexavalent chromium removal by corn-bran residue and derived chars

Biochars were prepared from corn-bran residue (CBR) at 300–600 °C, which were utilized to removal Cr(vi) from aqueous solutions. The Cr(vi) removal capacity of CBR and CBR600 was attributed to the predominance of either reduction or adsorption.

Biosorption of hexavalent chromium from aqueous medium with Opuntia biomass

The biosorption of hexavalent chromium from aqueous solutions by Opuntia cladodes and ectodermis from cactus fruits was investigated. Both types of biomass are considered low-cost, natural, and ecofriendly biosorbents. Batch experiments were carried out to determine Cr(VI) biosorption capacity and the efficiency of the biosorption process under different pH, initial Cr(VI) concentration, and sorbent dosage. The biosorption of Cr(VI) by Opuntia biomass was highly pH dependent, favoring higher metal uptake at low pH. The higher biosorption capacity was exhibited at pH 2. The optimal conditions were obtained at a sorbent dosage of 1 g L(-1) and initial metal concentration of 10 mg L(-1). Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The rate constant, the initial biosorption rate, and the equilibrium biosorption capacity were determined. The experimental equilibrium data obtained were analyzed using two-parameter isotherm models (Langmuir, Freundlich, and Temkin). The Langmuir maximum monolayer biosorption capacity (q max) was 18.5 mg g(-1) for cladodes and 16.4 mg g(-1) for ectodermis. The results suggest that Opuntia biomass could be considered a promising low-cost biosorbent for the ecofriendly removal of Cr(VI) from aqueous systems.

Polymeric sorbents for removal of Cr(VI) from environmental samples

Chromium (Cr) is an important raw material in some chemical industries including paint, pigments, textiles, leather tanning, steel fabrication, electroplating, cement preservation, and canning industries. Once in the environment, Cr exists in various oxidation states depending on pH and concentration. Trivalent [Cr(III)] and hexavalent [Cr(VI)] forms are the most common with Cr(VI) being the most toxic to biota. The review discusses various types of polymeric sorbents that have been prepared for the extraction of Cr(VI) from environmental samples, mostly aqueous samples. Sorbents are categorized into biosorbents, hybrid sorbents, synthetic polymeric, and modified natural polymeric sorbents. Most of the emphasis will be on the advantages and disadvantages of different synthetic polymeric sorbents. Important parameters that define the performance of the sorbents, that is, binding capacity, equilibration time, optimum sample pH, and selectivity, are compared.

An Overview of Fruit Waste as Sustainable Adsorbent for Heavy Metal Removal

Biosorption is an environmental friendly method for metal removal as it can be used as a cost effective and efficient technique for heavy metal removal. A lot of biomass can be choosed as biosorbent such as waste material from food processing and agriculture.ent. This paper will review the potential used of local fruit rind as biosorbent for heavy metal removal in wastewater. Heavy metals have been in various industries and resulted to a toxic condition in aquatic ecosystem. Therefore, various techniques have been employed for the treatment of metal-bearing industrial wastewaters including biological treatment through biosorption. Biosorption offers the advantages of low cost, good efficiency and production of sludge with high metal content is possible to avoid by the existence of metal recovery method from metal loaded biosorbent. The successful application of local fruit waste in treating wastewater containing heavy metals requires a deeper understanding of how biosorbent material proceeds.

Removal of chromium (VI) from electroplating wastewater using an anion exchanger derived from rice straw

An anion exchanger from rice straw was used to remove Cr (VI) from synthetic wastewater and electroplating effluent. The exchanger was characterized using Fourier transform infrared (FTIR) spectrum and scanning electron microscopy (SEM), and it was found that the quaternary amino group and hydroxyl group are the main functional groups on the fibrous surface of the exchanger. The effect of contact time, initial concentration and pH on the removal of Cr (VI), and adsorption isotherms at different temperature, was investigated. The results showed that the removal of Cr (VI) was very rapid and was significantly affected by the initial pH of the solution. Although acidic conditions (pH = 2-6) facilitated Cr (VI) adsorption, the exchanger was effective in neutral solution and even under weak base conditions. The equilibrium data fitted well with Langmuir adsorption model, and the maximum Cr (VI) adsorption capacities at pH 6.4 were 0.35, 0.36 and 0.38 mmol/g for 15, 25 and 35 degrees C, respectively. The exchanger was finally tested with real electroplating wastewater, and at sorbent dosage of 10 g/L, the removal efficiencies for Cr (VI) and total Cr were 99.4% and 97.8%, respectively. In addition, the positive relationship between adsorbed Cr (VI) and desorbed Cl- suggested that Cr (VI) was mainly removed by ion exchange with chlorine.

Investigating the effectiveness of economically sustainable carrier material complexes for marine oil remediation

The application of bioremediation to marine oil spills is limited due to dilution of either nutrients or hydrocarbonoclastic organisms. This study investigated the effectiveness of three unique natural carrier materials (mussel shells, coir peat and mussel shell/agar complex) which allowed nutrients, hydrocarbonoclastic organisms and oil to be in contact, facilitating remediation. TPH analysis after 30 d showed that mussel shells exhibited the greatest capacity to degrade oil with a 55% reduction (123.3 mg l(-1) from 276 mg l(-1)) followed by mussel shell/agar complex (49%) and coir peat (36%). Both the mussel shells and mussel shell/agar complex carriers were significantly different to the control (P=0.008 and P=0.002, respectively). DGGE based cluster analysis of the seawater microbial community showed groupings based on time rather than carriers. This study demonstrated that inexpensive, accessible waste materials used as carriers of hydrocarbonoclastic bacteria led to significant degradation of hydrocarbon contaminants in seawater.

Removal of hexavalent Cr by coconut coir and derived chars--the effect of surface functionality

The Cr(VI) removal by coconut coir (CC) and chars obtained at various pyrolysis temperatures were evaluated. Increasing the pyrolysis temperature resulted in an increased surface area of the chars, while the corresponding content of oxygen-containing functional groups of the chars decreased. The Cr(VI) removal by CC and CC-derived chars was primarily attributed to the reduction of Cr(VI) to Cr(III) by the materials and the extent and rate of the Cr(VI) reduction were determined by the oxygen-containing functional groups in the materials. The contribution of pure Cr(VI) adsorption to the overall Cr(VI) removal became relatively significant for the chars obtained at higher temperatures. Accordingly, to develop a cost-effective method for removing Cr(VI) from water, the original CC is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application and CC has a higher content of functional groups for reducing Cr(VI) to less toxic Cr(III).

Highly active nanoscale zero-valent iron (nZVI)-Fe3O4 nanocomposites for the removal of chromium(VI) from aqueous solutions

For the first time, nanoscale zero-valent iron (nZVI)-Fe(3)O(4) nanocomposites, prepared by an in situ reduction method, are employed for chromium(VI) removal in aqueous environment. 96.4% Cr(VI) could be removed by these novel materials within 2h under pH of 8.0 and initial Cr concentration of 20 mg L(-1), compared with 48.8% by bare nFe(3)O(4) and 18.8% by bare nZVI. Effects of several factors, including mass composition of nZVI-Fe(3)O(4) nanocomposites, initial pH and Cr(VI) concentration, were evaluated. The optimal ratio of nFe(3)O(4) to nZVI mass lies at 12:1 with a fixed nZVI concentration of 0.05 g L(-1). Low pH and initial Cr(VI) concentration could increase both the Cr(VI) removal efficiency and reaction rate. Corresponding reaction kinetics fitted well with the pseudo second-order adsorption model. Free energy change (ΔG) of this reaction was calculated to be -4.6 kJ mol(-1) by thermodynamic study, which confirmed its spontaneous and endothermic characteristic. The experimental data could be well described by the Langmuir and Freundlich model, and the maximum capacity (q(max)) obtained from the Langmuir model was 100 and 29.43 mg g(-1) at pH 3.0 and 8.0, respectively. The reaction mechanism was discussed in terms of the mutual benefit brought by the electron transfer from Fe(0) to Fe(3)O(4).

Effectiveness and longevity of a green/food waste derived compost packed column to reduce Cr(VI) contamination in groundwater

PAS100 accredited compost derived from green and food waste sources was used to remediate groundwater containing Cr(VI) at a historically contaminated site in Falkirk, Scotland, UK. The compost was mixed with gravel at a ratio of 1:1 (v/v) to provide a reactive bedding material in an upflow column. The Cr(VI) concentration in the groundwater (inlet) ranged from 0.5 to 7.8 mg L(-1) during the 168 d trial period. After an acclimation period of 54 d, the flow rate was increased in the column from 5.8 to 8 mL min(-1). Cr(VI) in the outlet was less than 100 μg L(-1) up to 134 d, after which the concentration steadily increased till 168 d. Compost analysis following completion of the trial confirmed that Cr(VI) was captured within the column. Anaerobic microbial reduction of Cr(VI) to Cr(III) was thought to be a key mechanism responsible for the longevity of the system to remove Cr(VI) from the groundwater. Requiring no additional organic carbon or nitrogen during the trial period, this setup represents a cost-effective treatment approach for low flow-through systems.

Coconut-based biosorbents for water treatment--a review of the recent literature

Biosorption is an emerging technique for water treatment utilizing abundantly available biomaterials (especially agricultural wastes). Among several agricultural wastes studied as biosorbents for water treatment, coconut has been of great importance as various parts of this tree (e.g. coir, shell, etc.) have been extensively studied as biosorbents for the removal of diverse type of pollutants from water. Coconut-based agricultural wastes have gained wide attention as effective biosorbents due to low-cost and significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of coconut-based biosorbents from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. Available abundantly, high biosorption capacity, cost-effectiveness and renewability are the important factors making these materials as economical alternatives for water treatment and waste remediation. This paper presents a state of the art review of coconut-based biosorbents used for water pollution control, highlighting and discussing key advancement on the preparation of novel adsorbents utilizing coconut wastes, its major challenges together with the future prospective. It is evident from the literature survey that coconut-based biosorbents have shown good potential for the removal of various aquatic pollutants. However, still there is a need to find out the practical utility of such developed adsorbents on commercial scale, leading to the superior improvement of pollution control and environmental preservation.

Biosorption of Cr(VI) by coconut coir: spectroscopic investigation on the reaction mechanism of Cr(VI) with lignocellulosic material

In this study, the removal mechanism of Cr(VI) from water by coconut coir (CC) was investigated using X-ray photoelectron spectroscopy (XPS), Cr K-edge X-ray absorption near edge structure (XANES) and FTIR spectroscopy. The results showed that, upon reaction with CC at pH 3, Cr(VI) was reduced to Cr(III), which was either bound to CC or released back into solution. As revealed by the FTIR spectra of CC before and after reacting with Cr(VI), the phenolic methoxyl and hydroxyl groups of lignin in CC are the dominant drivers of Cr(VI) reduction, giving rise to carbonyl and carboxyl groups on CC. These functional groups can subsequently provide binding sites for Cr(III) resulting from Cr(VI) reduction. In conjunction with forming complexes with carbonyl and carboxyl groups, the formation of Cr(III) hydroxide precipitate could also readily occur as revealed by the linear combination fitting of the Cr K-edge XANES spectrum using a set of reference compounds. The phenolic groups in lignin are responsible for initiating Cr(VI) reduction, so lignocellulosic materials containing a higher amount of phenolic groups are expected to be more effective scavengers for removal of Cr(VI) from the environment.