Novel green technology for wastewater treatment: Geo-material/geopolymer applications for heavy metal removal from aquatic media

The aim of this paper is to show the concise chemico-physical adsorbent performance of water purification systems utilizing geo-(e.g., allophane, clinoptilolite, and smectite) and bio-polymer materials(e.g.,chitosan or cellulose nanocomposite materials) and to propose an optimal ground-water remediation technique. The performance of geo-materials is evaluated based on the individual sorption and immobilization capacities for various priority substances and pollutants(e.g., lead, zinc, cadmium, c...     

Adsorption of Zinc using Tea Factory Waste: Kinetics,Equilibrium and Thermodynamics

In India, the annual production of tea is ca. 857,000 tonnes, which is 27.4% of the total world production. The amount of tea factory waste (TFW) produced per annum after processing is ca. 190,400 tonnes. TFW can be used as a low cost adsorbent for the removal of toxic metals from the aqueous phase. An investigation was carried out to study the feasibility of the use of TFW as an adsorbent for the removal of the heavy metal, zinc. Equilibrium, kinetic and thermodynamic studies were reported. The straight line plot of log (q_e–q) versus time t for the adsorption of zinc shows the validity of the Lagergren equation. The various steps involved in adsorbate transport from the solution to the surface of the adsorbent particles were dealt with by using a Weber‐Morris plot, q_e versus t^0.5 for the TFW. The rate controlling parameters, k_id,1 and k_id,2, were determined and it was found that the macro‐pore diffusion rate was much larger than micro‐pore diffusion rate. A batch sorption model, which assumes the pseudo‐second‐order mechanism, was used to predict the rate constant of sorption, the equilibrium sorption capacity and the initial sorption rate with the effect of initial zinc (II) ion concentration. Equilibrium data obtained from the experiments were analyzed with various isotherms, i. e., Freundlich, Langmuir, Redlich‐Peterson and Tempkin. The adsorption equilibrium was reached in 30 min and the adsorption data fitted well to all models. The maximum adsorption capacity of TFW for zinc (II) ions was determined to be 14.2 mg/g. The capacity of adsorption on Zn(II) increased with increasing temperatures and pH. The maximum uptake level of zinc was observed at pH of 4.2. The various thermodynamic parameters, i. e., ΔG°, ΔH° and ΔS°, were estimated. The thermodynamics of the zinc ion/TFW system indicated a spontaneous, endothermic and random nature of the process. The results showed that the TFW, which has low economical value, is a suitable adsorbent for the removal of zinc (II) ions from aqueous solutions.     

Reuse of Drinking Water Treatment Waste for Remediation of Heavy Metal Contaminated Groundwater

Lime softening produces an estimated 10,000 metric tons of dry drinking water treatment wastes (DWTW) per year, costing an estimated one billion dollars annually for disposal worldwide. Lime softening wastes have been investigated for reuse as internal curing agents or supplementary cementitious materials in concrete as well as a high-capacity sorbent for heavy metal removal. Lead, cadmium, and zinc are common heavy metals in groundwater contaminated by mine tailings. Cement-based filter media (CBFM) are a novel material-class for heavy metal remediation in groundwater. This study investigated the incorporation of DWTW as a recycled, low-cost additive to CBFM for the removal of lead, cadmium, and zinc. Jar testing at three different metal concentrations and breakthrough column testing using synthetic groundwater were performed to measure removal capacity and reaction kinetics. Jar testing results show as DWTW content increases at low concentrations, removal approaches 100% but at high metal concentrations removal decreases due to saturation or exhaustion of the removal mechanisms. Removal occurs through the formation of metal carbonate precipitates, surface sorption, and ion exchange with calcium according to the preferential series Pb⁺² > Zn⁺² > Cd²⁺. Removal kinetics were also measured through column testing and exceeded estimated calculations derived from batch jar testing isotherms due to the large formation of oolitic metal carbonates. Lead, cadmium, and zinc was concentrated in the column precipitates from 0.29, 0.23, and 20.0 μg/g in the influent solution to approximately 200, 130, 14,000 μg/g in the reacted DWTW-CBFM. The control and DWTW-CBFM columns had statically similar removal for zinc and lead. In the DWTW-CBFM, cadmium had decreased removal of approximately 25% due to proportionately decreased hydroxide content from cement replacement with 25% DWTW. This study shows the potential for DWTW as an enhancement to CBFM, thereby valorizing an otherwise waste material. Furthermore, the concentrative abilities of CBFM through precipitate and oolitic mineral formation could provide a minable waste product and close the waste-product cycle for DWTW.     

Biopolymer-Based Nanocomposites for Removal of Cr(VI) from Aqueous Systems: A Review

Hexavalent chromium Cr(VI) has emerged as a contaminant of prime concern for the environmentalists because of its improper disposal by tannery, dye, and electroplating industries. Adsorption is the most exploited method for its removal from industrial wastewater because of its high removal efficiency even at low Cr(VI) concentration, minimal sludge, and ease of regeneration. In recent years, several adsorbents of biological origin such as plants, algae, fungi, and bacteria have been explored for Cr(VI) remediation. This review comprehends the recent studies involving usage of biopolymer-based nano-composites with respect to its adsorption mechanisms, adsorption capacities, isotherms, and kinetics. The conventional abiotic and biotic techniques for removal of Cr(VI) are also discussed with a comparative insight of their adsorption capacity and removal efficiency. Nano-biocomposites integrate the functional properties of both nanoparticles and biopolymers, which make them efficient biosorbents. Nano-biocomposites offer a large surface area, reduced particle loss, minimal particle agglomeration on the surface, and high stability. Common kinetic models among the nano-biocomposites,  and various equilibrium models are also analyzed to understand the mode of adsorption and associated factors. These materials are mostly found to follow monolayer adsorption with ion exchange, electrostatic interaction, and surface complexation as major players in the process.     

Remediation of Radionuclide Pollutants through Biosorption – an Overview

The development of nuclear science and technology has led to the increase of nuclear wastes containing radionuclides to be released and disposed in the environment. Pollution caused by radionuclides is a serious problem throughout the world. To solve the problem, substantial research efforts have been directed worldwide to adopt sustainable technologies for the treatment of radionuclide containing wastes. Biosorption represents a technological innovation as well as a cost effective excellent remediation technology for cleaning up radionuclides from aqueous environment. A variety of biomaterials viz. algae, fungi, bacteria, plant biomass, etc. have been reported for radionuclide remediation with encouraging results. This paper reviews the achievements and current status of radionuclide remediation through biosorption which will provide insights into this research frontier.     

Cd(II), Pb(II) and Zn(II) Removal from Contaminated Water by Biosorption Using Activated Sludge Biomass

Biosorption using activated sludge biomass (ASB) as a potentially sustainable technology for the treatment of wastewater containing different metal ions (Cd(II), Pb(II) and Zn(II)) was investigated. ASB metal uptake clearly competed with protons consumed by microbial biomass compared with control tests with non‐activated sludge biomass. Biosorption tests confirmed maximum exchange between metal ions and protons at pH 2.0–4.5. It was revealed by the study that the amount of metal ions released from the biomass increased with biomass sludge concentration. The result showed that maximum absorption of metal ions was observed for Cd(II) at pH 3.5, Pb(II) at pH 4.0, and pH 4.5 for Zn(II) ions. The maximum absorption capacities of ASB for Cd(II), Pb(II) and Zn(II) were determined to be 59.3, 68.5 and 86.5%, respectively. The biosorption of heavy metals was directly proportional to ASB stabilization corresponding to a reduction in heavy metals in the order of Cd < Pb < Zn. The order of increase of biosorption of metal ions in ASB was Zn(II) < Pb(II) < Cd(II), and this was opposite to that of non active sludge. The results indicate that ASB is a sustainable tools for the bioremediation of Cd(II), Pb(II) and Zn(II) ions from industrial sludge and wastewater treatment plants.     

Chromium Removal through Biosorption and Bioaccumulation by Bacteria from Tannery Effluents Contaminated Soil

Four bacterial isolates (two resistant and two sensitive to chromium) were isolated from soil contaminated with tannery effluents at Jajmau (Kanpur), India, and were identified by 16S rDNA gene sequencing as Stenotrophomonas maltophilia, Exiguobacterium sp., Pantoea sp., and Aeromonas sp. Biosorption of chromium by dried and living biomasses was determined in the resistant and sensitive isolates. The effect of pH, initial metal concentration, and contact time on biosorption was studied. At pH 2.5 the living biomass of chromium resistant isolate Exiguobacterium sp. ZM‐2 biosorbed maximum amount of Cr⁶⁺ (29.8 mg/g) whereas the dried biomass of this isolate biosorbed 20.1 mg/g at an initial concentration of 100 mg/L. In case of chromate sensitive isolates, much difference was not observed in biosorption capacities between their dried and living biomasses. The maximum biosorption of Cr³⁺ was observed at pH 4.5. However, biosorption was identical in resistant and sensitive isolates. The data on chromium biosorption were analyzed using Langmuir and Freundlich isotherm model. The biosorption data of Cr⁶⁺ and Cr³⁺ from aqueous solution were better fitted in Langmuir isotherm model compared to Freundlich isotherm model. Metal recovery through desorption was observed better with dried biomasses compared to the living biomasses for both types of chromium ions. Bioaccumulation of chromate was found higher in chromate resistant isolates compared to the chromate sensitive isolates. Transmission electron microscopy confirmed the accumulation of chromium in cytoplasm in the resistant isolates.     

Demobilization of Heavy Metals from Mine Waters

The present study elucidates the remediation of mine waters by means of geochemical barriers („active barriers“). Active barrier systems (ABS) are developed, which can prevent heavy metal dispersion by introducing the barrier into the mine. Therefore, low‐cost materials are investigated which can remove contaminants by chemical, and/or physical mechanisms from water. The materials investigated are industrial by‐products (e.g. fly ash, red mud, scale arrears), natural wastes (e.g. tree bark), and relatively cheap natural products (bentonite, zeolites). Red mud and fly ash show the best results for the removal of Zn, Cd, Ni, and Mn from model water. Cd seems to have the strongest binding of the investigated metals on the sorption sites. The main mechanisms of metal removal from solution in this case are sorption and precipitation. Both materials have very good sorption and acid neutralization capacities (ANC), but ANC seems to be the determining factor.     

A Study: Removal of Cu(II), Cd(II), and Pb(II) Ions from Real Industrial Water and Contaminated Water Using Activated Sludge Biomass

This study aims to remove of Cu²⁺, Cd²⁺, and Pb²⁺ ions from solution and to investigate the adsorption isotherms, adsorption kinetics, and ion‐exchange affinities of these metals using waste activated sludge (AS) biomass. The adsorptions of the metals on biomass were optimal at an acidic pH value of 6.0 based on its monolayer capacities. Maximum monolayer capacities of AS biomass (q_max) were calculated as 0.478, 0.358, and 0.280 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, and the adsorption equilibrium time was found as 60 min for each metal. The adsorbed amount of metal rose with increasing of initial metal ion concentration. The equilibrium adsorption capacity of AS for initial 0.25 mmol L^?1 metal concentration was determined as 0.200, 0.167, and 0.155 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺ ions, respectively. These relevant values were determined as 0.420, 0.305, and 0.282 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺ ions, respectively, when initial metal concentration was 0.50 mmol L^?1. In the multi‐metal sorption system, the adsorption capacity of AS biomass was observed in the order of Cu²⁺ > Cd²⁺ > Pb²⁺. In the presence of 100 mmol L^?1 H⁺ ion, the order of ion‐exchange affinity with H⁺ was found as Cu²⁺ > Cd²⁺ > Pb²⁺. The adsorption kinetics were also found to be well described by the pseudo‐second‐order and intraparticle diffusion models. Two different rate constants were obtained as k_i1 and k_i2 and k_i1 (first stage) was found to be higher than k_i2 (second stage).     

Kinetics,Mechanistic and Thermodynamics of Zn(II) Ion Sorption: A Modeling Approach

Biosorption potential of Cedrus deodara sawdust (CDS) in terms of sorption of Zn(II) ion across liquid phase has been evaluated in the present investigation. The surface of the CDS biomass before the sorption of Zn(II) ions seemed to be more porous, non‐crystalline and heterogeneous. The maximum uptake capacity of CDS was 97.39 mg g^?1. Sorption of Zn(II) ion on the surface of CDS sawdust was maximum at pH 5, temperature 45°C, initial concentration of Zn(II) ion 100 mg L^?1, biomass dose 1 g L^?1, contact time 150 min, and agitation rate 160 rpm. Pseudo second‐order kinetics with the highest linear regression coefficient (R² = 0.99), and lowest values of error functions, i.e., chi (χ²) and sum of square errors (SSE) against pseudo first‐order rate kinetics showed that the sorption of Zn(II) ion on the surface of CDS was mediated by chemosoprtive forces of attraction rather than physical adsorption. Mechanistically, relatively higher proportion of sorption of Zn(II) ion in early phase of contact time was profoundly explained by Bangham's equation and film diffusivity (D^f). Intraparticle or pore diffusion (D_p) of Zn(II) ion inside the pores of CDS was rate limiting step at the later stage of contact time. Furthermore, the thermodynamic study on sorption of metal ion delineated the fact that the Zn(II) sorption on the surface of CDS was spontaneous, endothermic together with increased entropy at solid liquid interface.     

Anreicherung von Metallionen durch Membranfiltration von Polyelektrolytkomplexen

The separation of heavy metals by complexation with macromolecular water-soluble agents and subsequent ultrafiltration is described. The method can be expected to join common techniques of metal separation like liquid-liquid extraction, adsorption, redox reaction or liquid membrane permeation. Reactions between metal ions and polymer phases are characterized as pH-dependent distribution equilibria illustrated at a propene-maleic acid copolymer as an example. The complexation behaviour of the substance under study is governed by isotherms of the saturation type. Attempts proved to be successful to calculate break-through constants as well as saturation capacities from batch-type studies and dynamic measurements by transferring the laws of adsorption and ion exchange, respectively, to the ultrafiltration process. The quantities of fixed metals amounting to about 2.5 mmol/g were found to be in the range of moderate adsorbents. A solution consisting of 3 solutes has been tested to get more detailed information on mixture behaviour as compared to single component systems. In the long run, the proposed method should provide an additional variant for the extraction and concentration of metal ions from diluted aqueous solutions.     

Treating Leather Tanning Wastewater with Stone Cutting Solid Waste

This paper presents a new environmental approach for reducing environmental impacts of two local Palestinian industries: It implements the principle of “treating waste by waste.” The technical feasibility of chromium removal from wastewater in leather making by its treatment with solid waste from stone cutting industry is demonstrated experimentally, and found to be an efficient approach. Nearly full removal of chromium is obtained at optimum operating conditions using sufficient mass of solid waste (limestone) and allowing enough contact time between the two wastes. This study investigated effects of various parameters on the percentage relative decrease in concentration by using ultra violet (UV)/Vis spectrophotometry. Kinetic curves showed that percentage relative decrease in concentration increased with time until approaching a plateau (adsorption capacity). The adsorption capacity increased with increasing limestone to liquid ratio (solid content), until nearly full removal of chromium was obtained when the solid content was 5 g/100 mL or higher. This was accomplished within few days when the particles were settled. The adsorption capacity was pH dependent; adsorption at pH < 5 was obtained, as a finding which was not reported by previous investigators for Cr(III) adsorption using other particles. The percentage removal was nearly doubled at higher pH values (>5). Further research work is proposed to distinguish between the contributions of the two removal mechanisms of precipitation and adsorption.     

Design and Development of Onsite Biofilter Unit for Effective Remediation of Contaminants from Wastewater

Agricultural biomass is proven ecofriendly and effective adsorbent for the remediation of contaminants from wastewater. Here, rice husk biochar (600 °C) prepared by a one-step pyrolysis method is used for the remediation of different contaminants in real samples. An onsite biofilter unit is fabricated with parallel trenches of different layers of coconut coir and biochar and is used as a biofiltration unit. The efficiency of the designed unit is assessed for the removal of different contaminants in pilot-scale experiments. Results show that removal efficiency varies from metal to metal and ranges from 5.52% to 90.76% using the biofilter unit. Fourier-transform infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray analysis, carbon, hydrogen, nitrogen, and Brunauer–Emmett–Teller analysis before and after the adsorption represent the changes in the morphology and surface functionalization of the biochar. Results indicate that the designed biofilter unit could also be used as a promising agent for the remediation of pharmaceutical and other emerging contaminants from wastewater.     

Removal of Cu2+ and Pb2+ Ions Using CMC Based Thermoresponsive Nanocomposite Hydrogel

In this study, carboxymethylcellulose (CMC) based thermoresponsive nanocomposite hydrogel was synthesized for the removal of Cu²⁺ and Pb²⁺ ions from aqueous solutions. To prepare nanocomposite hydrogel, graft copolymerization of N‐isopropyl acrylamide (NIPAm) and acrylic acid (AA) onto CMC was carried out in Na‐montmorillonite (MMT)/water suspension media and ammonium persulfate (APS) used as initiator. The chemical structures of hydrogels were characterized by Fourier transform infrared (FT‐IR) and X‐ray diffraction spectroscopy (XRD). Lower critical solution temperature (LCST), pH responsivity, swelling, and deswelling properties of the hydrogels were also examined. In addition competitive and non‐competitive removal of Cu²⁺ and Pb²⁺ studies were carried out. According to heavy metal sorption studies results, removal capacities of nanocomposite hydrogel for both metal ions were found to be higher than those of pure hydrogel. The analyzed adsorption data showed that the adsorption process of Cu²⁺ and Pb²⁺ could be explained by pseudo‐second order kinetic model. Moreover, according to competitive sorption studies, it is found to be that both hydrogels are more selective to Cu²⁺ ion rather than Pb²⁺.     

Adsorption of zinc onto bed sediments of the River Ganga: adsorption models and kinetics

Abstract

A laboratory study was performed to study the effects of various operating factors, viz. initial metal ion concentration, solution pH, amount of sediment, contact time, particle size and temperature on the adsorption of zinc ions onto the bed sediments of the River Ganga (India). The equilibrium time was found to be of the order of 60 min. The adsorption curves are smooth and continuous leading to saturation, suggesting the possible monolayer coverage of zinc ions on the surface of the adsorbent. The extent of adsorption increases with an increase of pH. Furthermore the adsorption of zinc increases with increasing amount of adsorbent and decreases with adsorbent particle size. The important geochemical phases, iron and manganese oxide act as the active support material for the adsorption of zinc ions. The adsorption data have been analysed with the help of Langmuir and Freundlich adsorption models to determine the mechanistic parameters associated with the adsorption process. An attempt has also been made to determine thermodynamic parameters of the process, viz. free energy change, enthalpy change and entropy change. The negative values of free energy change (ΔG°) indicated the spontaneous nature of the adsorption of zinc onto the bed sediments and positive values of enthalpy change (ΔH°) suggest the endothermic nature of the adsorption process. The intraparticle diffusion of zinc in the adsorbent was found to be the main rate-limiting step.     

Synthesis,Mechanism, and Performance Assessment of Zero‐Valent Iron for Metal‐Contaminated Water Remediation: A Review

Recently, increased industrial and agriculture activities have resulted in toxic metal ions, which has increased public concern about the quality of surface and groundwater. Various types of physical, biological, and chemical approaches have been developed to remove surface and groundwater metal ions contaminants. Among these practices, zero‐valent iron (ZVI) is the most studied reactive material for environmental clean‐up over the last two decade and so. Although ZVI can remove the contaminants even more efficiently than any other reactive materials. However, low reactivity due to its intrinsic passive layer, narrow working pH, and the loss of hydraulic conductivity due to the precipitation of metal hydroxides and metal carbonates limits its wide‐scale application. The aim of this work is to document properties, synthesis, and reaction mechanism of ZVI for the treatment of metal ions from the surface and groundwater in recent 10 years (2008–2018). So far, different modified techniques such as conjugation with support, bimetal alloying, weak magnetic field, and ZVI/oxidant coupling system have been developed to facilitate the use of ZVI in various environmental remediation scenarios. However, some challenges still remain to be addressed. Therefore, development and research in this field are needed to overcome or mitigate these limitations.     

Rhizofiltration of a Heavy Metal (Lead) Containing Wastewater Using the Wetland Plant Carex pendula

Rhizofiltration is a subset technique of phytoremediation which refers to the approach of using plant biomass for removing contaminants, primarily toxic metals, from polluted water. The effective implementation of this in situ remediation technology requires experimental as well as conceptual insight of plant–water interactions that control the extraction of targeted metal from polluted water resources. Therefore, pot and simulation experiments are used in this study to investigate the rhizofiltration of a lead containing wastewater using plants of Carex pendula, a common wetland plant found in Europe. The metal contaminant extraction along with plant growth and water uptake rates from a wastewater having varying Pb concentration is studied experimentally for 2 wk. The temporal distribution of the metal concentration in the wastewater and the accumulated metal in different compartments of C. pendula at the end are analyzed using atomic absorption spectrometry. Parameters of the metal uptake kinetics are deduced experimentally for predicting the metal removal by root biomass. Further, mass balance equations coupled with the characterized metal uptake kinetics are used for simulating the metal partitioning from the wastewater to its accumulation in the plant biomass. The simulated metal content in wastewater and plant biomass is compared with the observed data showing a good agreement with the later. Results show that C. pendula accumulates considerable amounts of lead, particularly in root biomass, and can be considered for the cleanup of lead contaminated wastewaters in combination with proper biomass disposal alternatives. Also, the findings can be used for performing further non‐hydroponics experiment to mimic the real wetland conditions more closely.     

Copper Biosorption by Spent Coffee Ground: Equilibrium,Kinetics, and Mechanism

The potential use of spent coffee ground (SCG) for the removal of copper has been investigated as a low‐cost adsorbent for the biosorption of heavy metals. Adsorption batch experiments were conducted to determine isotherms and kinetics. The biosorption equilibrium data were found to fit well the Freundlich model and an experimental maximum biosorption capacity of copper ions 0.214 mmol/g was achieved. The biosorption kinetics of SCG was studied at different adsorbate concentrations (0.1–1.0 mM) and stirring speeds (100–400/min). The results showed an increase in the copper ion uptake with raising the initial metal concentration and the kinetic data followed the pseudo‐second order rate expression. The effect of stirring speed was a significant factor for the external mass transfer resistance at 100/min and coefficients were estimated by the Mathews and Weber model. Biosorption of copper ions onto SCG was observed to be related mainly with the release of calcium and hydrogen ions suggesting that biosorption performance by SCG can be attributed to ion‐exchange mechanism with calcium and hydrogen ions neutralizing the carboxyl and hydroxyl groups of the biomass.     

Adsorption of Chromium(III), Nickel(II), and Copper(II) from Aqueous Solution by Activated Alumina

The possible use of activated alumina powder (AAP) as adsorbent for Cr(III), Ni(II), and Cu(II) from synthetic solutions was investigated. The effect of various parameters on batch adsorption process such as pH, contact time, adsorbent dosage, particle size, temperature, and initial metal ions concentration were studied to optimize the conditions for maximum metal ion removal. Both higher (molar) and lower (ppm) initial metal ion concentration sets were subjected to adsorption on AAP. Adsorption process revealed that equilibrium was established in 50 min for Cr(III) at pH 4.70, 80 min for Ni(II) at pH 7.00, and 40 min for Cu(II) at pH 3.02. Percentage removal was found to be highest at 55°C for Cr(III) and Ni(II) with 420 µm and 45°C for Cu(II) with 250‐µm particle size AAP. A dosage of 2 g for Cr(III), 8 g for Ni(II), and 10 g Cu(II) gave promising data in the metal ion removal. The adsorption process followed Langmuir as well as Freundlich models. The thermodynamics of adsorption of these metal ions on activated aluminum indicated that the adsorption was spontaneous and endothermic in nature. Present study indicates that AAP can act as a promising adsorbent for industrial wastewater treatment.     

Removal of Chromium from Synthetic Effluent using Nymphaea rubra

In the present work, biosorption of Cr(VI) by Nymphaea rubra was investigated in batch studies. Batch experiments were conducted to study the effect of initial sorbent dosage, solution pH and initial Cr(VI) concentration. The results showed that the equilibrium uptake capacity was increased with decrease in biomass dosage. The Cr(VI) removal was influenced by the initial chromium compound concentration. Langmuir and Freundlich adsorption isotherm models were used to represent the equilibrium data. The Freundlich isotherm model was fitted very well with the equilibrium data when compared to Langmuir isotherm model. The sorption results were analyzed for pseudo‐first order and pseudo‐second order kinetic model. It was observed that the kinetic data fitted very well with the pseudo‐second order rate equation when compared to the pseudo‐first order rate equation. Fourier transform infrared spectrum showed the presence of different functional groups in the biomass. The surface morphology of the sorbent was exemplified by SEM analysis. Aquatic weeds seem to be a promising biosorbent for the removal of chromium ions from water environment. This paper reports the research findings of a laboratory‐based study on the removal of Cr(VI) from the synthetic solution using the dried stem of N. rubra as a biosorbent.