Low-cost Sorbent Research Articles

Wastewater Purification from Permanganate Ions by Sorption on the Ocimum basilicum Leaves Powder Modified by Zinc Chloride

The powder of Ocimum Basilicum leaves was treated by zinc chloride (ZnCl2) and applied as a new and low-cost sorbent for extraction of permanganate anions (MnO4−) from liquid phase. The functional groups of the ring stretching vibration, –NH2 deformation, stretching of C-O, stretching of CH, and stretching of –NH were found in the sorbent of zinc chloride Ocimum basilicum leaves powder (ZCOBLP) at 1516.21, 1629.33, 1047.00, 2929.88, and 3294.93 cm−1, respectively. This adsorbent has 8.3 pHZPC, 117.27 m2·g−1 surface area, 0.00711 cc·g−1 pore volume and average pore diameter of 264.144 Å. The outcomes of sorption experiments designate the positive impact for temperature, time of agitation, and started concentration of MnO4− and negative impact for pH. The optimal conditions were 1300 mg·L−1 as started adsorbate concentration, 55°C as solution temperature, agitation time of 420 min, and pH of 1.5. The outcomes of the equilibrium and dynamic approve that this sorption is spontaneous and heat-absorbing process, and the obtained data were described well by isotherm model of Langmuir and 2nd-order dynamic model. The capacities of this sorption were 588.235, 625.000, 666.667, and 714.286 mg·g−1 at 25, 35, 45, and 55 (°C), respectively. The superior sorption capacities of the uncostly ZCOBLP will make it successfully used for MnO4− ions extraction from liquid phases.

Biosorption of Arsenic (III) by Using Lemon Peel Powder as Low Cost Effective Biosorbent

The use of lemon peel powder, a novel, low-cost, and sustainable biosorbent derived from food waste, to remove arsenic has largely gone unexplored. The feasibility and viability of the As (III) biosorption abilities of lemon peel powder are compared in this study. The parameters such as contact time, pH, the amount of lemon peels used, the initial arsenic concentration, and temperature all had an effect on the sorption process. Thermodynamic, kinetic, and equilibrium were all evaluated. The optimal pH was 6.0, and it lasted until pH 8 with 72.34% removal efficiency. Lemon peel (LP) has a pH PZC value of 7 and a surface pH of 7. The analysis of kinetics revealed that the biosorption was regulated by a second-order reaction, as well as the fact that the catalytic region of the biosorbent was heterogeneous; however, the biosorption process was better defined by the Freundlich and Temkin isotherms. Finally, it is possible to remove arsenic (III) using waste content. Thermodynamic and equilibrium analysis have shown that sorption is a natural process that is spontaneous, beneficial, and endothermic. In addition, Fourier Transfer Infrared Spectroscopy (FTIR) research shows that arsenic reacts with metal oxides and the -OH functional group in lemon peel. These findings indicate that this peel can be used to remove arsenic from a simulated aqueous solution as a valuable, low-cost sorbent. This research lays the groundwork for the potential production of an effective filtration device that uses citrus peel powder as a low-cost, innovative, and long-lasting biosorbent to treat water polluted with arsenic (III). Keywords: Arsenic, Equilibrium, FTIR, Isotherms, Kinetic, PZC, Thermodynami DOI: 10.7176/JNSR/12-14-01 Publication date: July 31 st 2021

Assessing phosphorus removal potential of laterite soil for water treatment and eco-technological application

The phosphorus (P) pollution and eutrophication in the aquatic environment are common and cause immensely adverse environmental health problems. In order to control the P pollution, the present study attempted to assess the phosphate-P removal capacity (PRC) of laterite soil (LS) and its application potentials in practical field. The physico-chemical characteristics of LS were analyzed using scanning electron microscopy coupled energy dispersive techniques, BET study and zeta potential. The PRC of LS was characterized by optimizing the sorption influencing parameters – contact time, solution pH, dosage of LS and concentration of phosphate-P as well as analyzing sorption isotherm and kinetics; and application potential of LS was evaluated by analyzing PRC in natural wastewater and by examining plant (Chick pea; Cicer arietinum) growth promoting properties of spent LS as phosphate fertilizer. The chemical characteristics revealed that LS is prevalently constituted by oxygen (48.52%), silicon (39.36%) and iron (10.57%) and aluminium (1.55%) and showed higher pore volume (1.678 cc/g), surface area (20.29 m2/g), particle density (2.25 g/cm3) and bulk density (1.94 g/cm3). LS demonstrated that contact time 390 min, pH 2.5, dosage 2.4 g/L and initial concentration 2 mg/L were optimum for highest phosphate-P sorption. Sorption data was well fitted by the Langmuir isotherm model and pseudo second order kinetic model. The phosphate-P sorption mechanism of LS is supposed to be governed by high porosity, surface area and specific chemical properties. LS showed excellent phosphate-P sorption (384.61 mg/g) and potential wastewater treatment properties. Phosphorous loaded spent LS also showed higher growth of Cicer arietinum (length of shoot, 38.21% and leaf number, 52.63%) than control. Therefore, the LS could ecofriendly be used as a low-cost sorbent for treating the polluted water and spent LS might be employed as a potentially fertile soil bed in yielding high amount of crop.

Removal of Heavy Metals during Primary Treatment of Municipal Wastewater and Possibilities of Enhanced Removal: A Review

Resource reuse has become an important aspect of wastewater management. At present, use of sludge in agriculture is one of the major reuse routes. Conventional municipal wastewater treatment does not involve any designated process for removal of heavy metals, and these distribute mainly between effluent and sludge. Enhanced removal of heavy metals during primary treatment may decrease the heavy metal concentrations in both effluent and sludge from secondary treatment and promote long-term reuse of secondary sludge. This review considers heavy metal occurrence and removal during primary settling, together with possible treatment technologies for heavy metal removal in primary settlers and their theoretical performance. The variation in total heavy metal concentrations and dissolved fraction in raw municipal wastewater points to a need for site-specific assessments of appropriate technologies for improved heavy metal removal. Studies examining the heavy metal speciation beyond dissolved/particulate are few. Missing or disparate information on process parameters such as hydraulic retention time, pH and composition of return flows makes it hard to generalize the findings from studies concerning heavy metal removal in primary settlers. Coagulation/flocculation and use of low-cost sorbents were identified as the most promising methods for enhancing heavy metal removal during primary settling. Based on the available data on heavy metal speciation and removal during primary settling, sorption technologies may be most effective for enhancing the removal of Cu and Ni, while coagulation may be efficient for Cd, Cr, Cu, Pb, Zn and Hg removal (but not as efficient for Ni removal).

Green and eco-friendly montmorillonite clay for the removal of Cr(III) metal ion from aqueous environment

Pollutants found in the wastewater streams of industrial processes such as heavy metals are a significant concern worldwide. Clays are low-cost sorbents that have attracted extensive research interest due to their potential applications in removing heavy metals from wastewater. In this work, montmorillonite clay was collected from the Bengurir region; Morocco was used as an eco-friendly adsorbent for the removal of chromium (III) at various operating conditions. The used adsorbent was characterized using X-ray diffraction, X-ray fluorescence spectrometry, Fourier Transform Infrared Spectroscopy, and scanning electron microscope coupled with X-ray energy dispersion spectrometer analysis. Effects of adsorbent dose, initial concentration, and pH were investigated to optimize the adsorption process. The controlling mechanism and the potential rate-limiting steps were analyzed using Lagergren’s pseudo-first-order and pseudo-second-order models, but the experimental data were better fitted to the pseudo-second-order equation. The equilibrium isotherm data were analyzed by applying Langmuir and Freundlich’s isotherm models, and Langmuir showed good fits with the experimental data. A maximum Cr(III) adsorption capacity of 7.5 mg g−1 was found in the studied conditions.

Low-Cost Organic Adsorbents for Elemental Mercury Removal from Lignite Flue Gas

The research presented by the authors in this paper focused on understanding the behavior of mercury during coal combustion and flue gas purification operations. The goal was to determine the flue gas temperature on the mercury emissions limits for the combustion of lignites in the energy sector. The authors examined the process of sorption of mercury from flue gases using fine-grained organic materials. The main objectives of this study were to recommend a low-cost organic adsorbent such as coke dust (CD), corn straw char (CS-400), brominated corn straw char (CS-400-Br), rubber char (RC-600) or granulated rubber char (GRC-600) to efficiently substitute expensive dust-sized activated carbon. The study covered combustion of lignite from a Polish field. The experiment was conducted at temperatures reflecting conditions inside a flue gas purification installation. One of the tested sorbents—tire-derived rubber char that was obtained by pyrolysis—exhibited good potential for Hg0 into Hg2+ oxidation, resulting in enhanced mercury removal from the flue. The char characterization increased elevated bromine content (mercury oxidizing agent) in comparison to the other selected adsorbents. This paper presents the results of laboratory tests of mercury sorption from the flue gases at temperatures of 95, 125, 155 and 185 °C. The average mercury content in Polish lignite was 465 μg·kg−1. The concentration of mercury in flue gases emitted into the atmosphere was 17.8 µg·m−3. The study analyzed five low-cost sorbents with the average achieved efficiency of mercury removal from 18.3% to 96.1% for lignite combustion depending on the flue gas temperature.

Equilibrium and Kinetic Study of Removal Copper(II) from Aqueous Solution Using Chicken Eggshells: Low Cost Sorbent

The research aims to investigate feasibility eggshells as potential adsorbent to remove copper(II) ions from aqueous solution. Eggshells powder was characterized using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Effect of copper(II) initial concentration, adsorbent dosage, and contact time have conducted. The optimum adsorption condition obtained when 0.7 g eggshells applied to 50 mg/L copper(II) solution for 50 minutes. The maximum percentage of copper(II) removal was exceeded more than 85%. Langmuir and Freundlich isotherm model were applied to describe the equilibrium adsorption. Copper(II) kinetics sorption process was fitted to pseudo-second order model with a rate constant equal to 0.516 g/mg.min. The results clearly exhibit that eggshells powder can be effectively used to remove copper(II) ions from aqueous solutions.

Immobilised Humic Substances as Low-Cost Sorbents for Emerging Contaminants

Environmental pollution with contaminants of emerging concern (CECs) is a worldwide problem that is receiving increasing attention. Although these substances have been released in the aquatic environment for a long time, wastewater treatment plants are still incapable of removing emerging contaminants completely. Consequently, trace metals, metalloids and pharmaceuticals, as well as surfactant leftovers, are often found in environmental samples. Environmentally friendly and cost-effective sorbents such as humic substances can be used for purification if their sorption properties are increased by immobilization. To our knowledge, immobilized humic substances have not been widely studied as sorbents up to now. In this study, humic substances were immobilized to obtain low-cost sorbents. The chosen methods for characterization of the obtained sorbents showed successful immobilization. Traditional pollutants, such as Cr(III) (a metal), As(V) (a metalloid) and chlorpromazine (a pharmaceutical), were used as representative contaminants. Sorption experiments were conducted using the batch system, and sorption was also studied based on the sorbent dosage, initial concentration of the studied element or substance, solution pH and sorption time. The results show that all the obtained immobilized humic substances in this study can be used as sorbents to remove contaminants from water. At the same time, from these humic substances, only those immobilized using iron compounds are suitable for the removal of arsenic.

Removal of Congo red dye from aqueous media using Litchi seeds powder: Equilibrium, kinetics and thermodynamics

The continuous quest for colouring materials has led to an increase in dyes production and use in recent times. Some of the dyes usually find their way into water sources which consequently leads to decrease in the aesthetic beauty of the water resource as well as its use potential. This study examined the potential of an agricultural waste (Litchi seed powder (LSP)) for the sequestration of a hazardous dye (Congo red (CR)) from aqueous media. The influence of several experimental drivers such as pH, sorption time, sorbent dosage, particle size and change in water chemistry were also examined. An optimum pH of 2 was established for best uptake of CR. The sorption process can be explained both by the Langmuir and Freundlich isotherm models. The pseudo second order kinetic model best describes the kinetics of the sorption. Scanning electron microscopy showed a significant change in the surface morphology of the spent sorbent. The sorption process was exothermic in nature (ΔH0=−0.45kJ/mol) and spontaneous (−ΔG0=11.52−12.25kJ/mol). Results from this study showed that LSP can be used as a potential low-cost sorbent for dyes decontamination from aqueous media.

Characterization and application of wood-ZrO2 sorbent for simultaneous removal of chromium (III) and chromium (VI) from binary mixture

Abstract A new woodchips-ZrO2 biosorbent (W-ZrO2) was synthesized using wood residue material generated from the oak tree (Quercus robur) during furniture manufacturing. Biosorbent was tested for the simultaneous removal of both chromium (Cr) ions: Cr(III) and Cr(VI), in the binary component solution. Biosorbent characterization was performed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). To define optimal process parameters for simultaneous removal of both Cr species, effects of pH, temperature, sorbent dosage and Cr ions concentration on the sorption process were investigated. Sorption of Cr ions onto W-ZrO2 was highly pH-dependent. Optimal pH for simultaneous removal of both Cr(III) and Cr(VI) ions is 4.0 with removal efficiency over 99.5 % in both cases. Equilibrium experimental results are the best fitted by the Langmuir sorption isotherm model. The maximal sorption capacities of the biosorbent for simultaneous removal of Cr(III) and Cr(VI) ions in binary-component system are 16.18 and 83.52 mg g−1, respectively. The present study shows that using wood residue material to produce a low-cost sorbent can effectively decrease the water pollution simultaneously removing both chromium species from water and also reduce wood waste and increase reuse/recycling options.

Advances in absorbents and techniques used in wet and dry FGD: a critical review

Abstract Sulfur dioxide is considered as an extremely harmful and toxic substance among the air pollutants emitted from the lignite- and other high-sulfur-coal based power plants, old tires processing units, smelters, and many other process industries. Various types of absorbents and desulfurization technologies have been developed and adopted by the industries to reduce the emission rate of SO2 gas. The present paper focuses on the ongoing advances in the development of varieties of regenerative and non-regenerative absorbents viz., Ca-based, Mg-based, Fe-based, Na-based, N2-based, and others along with various FGD technology, viz., wet, dry or semi-dry processes. Additionally, different types of contactors viz., packed column, jet column, spray tower, and slurry bubble columns along with their significant operational and design features have also been discussed. In the existing or newly installed limestone-based FGD plants, an increasing trend of the utilization of newly developed technologies such as limestone forced oxidation (LSFO) and magnesium-enhanced lime (MEL) are being used at an increasing rate. However, the development of low-cost sorbents, particularly suitable solid wastes, for the abatement of SO2 emission needs to be explored sincerely. Many such wastes cause air pollution by way of entrainment of fine particulate matter (PM), groundwater contamination by its leaching, or brings damage to crops due to its spreading onto the cultivation land. One such pollutant is marble waste and in this work, this has been suggested as a suitable substitute to limestone and cost-effective sorbent for the desulfurization of flue gases. The product of this process being sellable in the market or may be used as a raw material in several industries, it can also prove to be an important route of recycling and reuse of one of the air and water-polluting solid wastes.

Data-driven modeling and optimization of oil spill sorption by wool fibers: retention kinetics and recovery by centrifugation

Oil spills have provoked negative environmental impacts for decades. To combat such accidental pollutions, the exploiting of the low-cost sorbents is of real interest. We report herein the valorization of coarse grade wool fibers (biomass waste) as sorbents for the uptake of oily products. Response surface methodology was employed for modeling and optimization of the oil-uptake process. The optimal conditions were found to be (1) the sorbent dosage of 2.80 g/dm2; (2) the initial thickness of the oil layer of 3.0 mm (on the water surface), and (3) the dripping time equal to 10 s. The established optimal conditions yielded the maximum oil removal efficiency of 98.28%. In addition, the microscopy investigations revealed that the oil can be retained by the wool fibers as (1) adhered films, (2) ellipsoidal droplets, and (3) oil-bridges filling the voids between fibers. Kinetic data of liquids retention and dripping were modeled using the unsteady-state retention theory. According to the model parameters, the maximum sorption capacities of wool fibers were found to be 6.65, 17.86, and 22.54 g/g for the uptake of dodecane, motor oil 5 W, and 15 W, respectively. The desorption isotherm of cyclohexane disclosed the predominant role of the capillary phenomena in the retention of liquids. Ultimately, the used sorbents were centrifuged in order to recovery the oily liquids in an advanced mode (98.33 ± 0.42%—recovery efficiency).

Copper removal from water using carbonized sawdust

The occurrence of heavy metals in water sources is grave worldwide concerns for many reasons, firstly because the heavy metals could remain in the water for very long periods because they cannot be degraded by the microorganisms. Secondly, the heavy metals can be accumulated in the bodies of plants and other living cells to toxic levels and could affect humans through the food chain. Finally, the contaminated water by heavy metals causes severe health problems for consumers, such as kidney and brain diseases. Therefore, the development of effective water treatment methods for remediation of water from heavy metals is a vital concern for scientists nowadays. The present work uses sawdust as a chemically activated adsorbent to remove copper. The adsorption experiments were employed in a batch system to investigate the impact of different parameters such as contact time, solution pH, and adsorbent dose. The favorable pH for maximum copper removal was at neutral. After performing the batch experiments, an optimum contact time of 150 min was adopted. The findings indicated that the sawdust dosage of 2 g/L removed about 79% from the copper concentration in the aqueous solution. Sawdust has been successfully utilized as low-cost sorbents for copper removal.

Engineered biochar from wood apple shell waste for high-efficient removal of toxic phenolic compounds in wastewater

This study investigated a novel agricultural low-cost bio-waste biochar derived from wood apple fruit shell waste via the pyrolysis method, which is modified by ball milling and utilized to remove toxic phenol and chlorophenols (4-CPh and 2,4-DCPh) from contaminated aqueous media. The ball-milled wood apple fruit shell waste biochar (WAS-BC) sorbent was systematically analyzed by BET, CHN, and FTIR as well as particle size, SEM–EDS, XPS and TGA studies. The sorption equilibrium and kinetic studies exhibit that the sorption capacity was greater than 75% within the first 45 min of agitation at pH 6.0. The uptake capacity of 2,4-DCPh onto WAS-BC was greater than those of 4-CPh and phenol. Equilibrium results were consistent with the Langmuir isotherm model, while the kinetic data were best represented by the Elovich and pseudo-second-order model. The maximum uptake of phenol, 4-CPh, and 2,4-DCPh was 102.71, 172.24, and 226.55 mg/g, respectively, at 30 ± 1 °C. Thus, this study demonstrates that WAS-BC is an efficient, low-cost sorbent that can be used for the elimination of phenol and chlorophenol compounds from polluted wastewater.

Induced changes of pyrolysis temperature on the physicochemical traits of sewage sludge and on the potential ecological risks

Biochar from sewage sludge is a low-cost sorbent that may be used for several environmental functions. This study evaluates the induced effects of pyrolysis temperature on the physicochemical characteristics of sewage sludge (SS) biochar produced at 350 (SSB350), 450 (SSB450) and 600 (SSB600), based on the metal enrichment index, metal mobility index (MMI), and potential ecological risk index (PERI) of Cd, Cu, Pb, and Zn. Increased pyrolysis temperature reduced the biochar concentration of elements that are lost as volatile compounds (C, N, H, O, and S), while the concentration of stable aromatic carbon, ash, alkalinity, some macro (Ca, Mg, P2O5, and K2O) and micronutrients (Cu and Zn), and toxic elements such as Pb and Cd increased. Increasing the pyrolysis temperature is also important in the transformation of metals from toxic and available forms into more stable potentially available and non-available forms. Based on the individual potential ecological risk index, Cd in the SS and SSB450 were in the moderate and considerable contamination ranges, respectively. For all pyrolysis temperature biochar Cd was the highest metal contributor to the PERI. Despite this, the potential ecological risk index of the SS and SSBs was graded as low.

Decontamination of Anthraquinone Dyes Polluted Water Using Bioinspired Silica as a Sustainable Sorbent

The increased release of harmful dyes in water, along with the continuous reduction of the world’s freshwater supplies has placed the textile industry under greater pressure to safely and effectively treat wastewater effluents. Resistance of reactive dyes to breakdown naturally has highlighted the need for specialised removal methods. The growing need for low-cost, efficient sorbents has led to the exploration of bioinspired silicas (BIS) due to their green synthesis, proven scalability, and versatility for chemical functionalisation required for dye scavenging. Through a systematic approach, the removal of Reactive Blue 19 from water was studied using a range of BIS, and was compared to removal using a commercial sorbent. While 0% removal was denoted for the commercial sorbent, BIS showed up to 94% removal. The results obtained from a kinetic study suggested a pseudo-second-order reaction, indicating a chemisorption process via electrostatic interactions. Examination of the effects of various adsorption conditions (temperature, pH, sorbent and dye concentrations) using isotherm models (Langmuir and Freundlich) indicated that adsorption was of both chemical and physical nature. Examination of the adsorption mechanism suggest that dye adsorption on BIS was spontaneous. BIS showed higher adsorption capacity (334 mg g−1) compared to literature examples, with rapid adsorption under acidic conditions, excellent thermal stability and good reuse potential. These findings highlight the potential of BIS as a sustainable, efficient and low-cost sorbent that could be brought forward for future implementation.

Novel low cost nanoparticles for enhanced removal of chlorpyrifos from wastewater: Sorption kinetics, and mechanistic studies

Developing low cost sorbents for efficient elimination of organophosphorus pesticides from wastewater remains motivational. In this study, nanoparticles of water treatment residuals (nWTRs) derived from drinking water industry were produced and used for chlorpyrifos (CPF) removal from contaminated waste water. Batch sorption equilibrium study revealed that CPF sorption by nWTRs follow in order Langmuir > Temken > Kiselev adsorption models. The maximum adsorption capacity of nWTRs for CPF has shown 5 folds increase (50 mg g−1) compared to that of the conventional bulk WTRs and superior to most of the low cost adsorbents. Experimental parameters such as nWTR dosage, CPF concentration, and solution pH and exposure time were optimized. Remarkable CPF removal efficiency of 92% was achieved using nWTRs at pH 7 in contact time period of 30 min. The goodness-of-fit of the kinetic models tested showed that the power function model was successful in describing the kinetics of CPF adsorption with the lowest standard error (SE) of 0.0136. The thermodynamic parameters indicate the spontaneous and exothermic nature of CPF sorption on nWTRs sorbent. A possible mechanism of CPF removal by nWTRs includes formation of Al-CPF and Fe-CPF complexes and H-bonding. The novel nano-sorbent exhibits great potential as an efficient low cost sorbent for CPF removal from contaminated wastewater.

Safe disposal of deactivated commercial selective catalytic reduction catalyst (V2O5-MoO3/TiO2) as a low-cost and regenerable sorbent to recover gaseous elemental mercury in smelting flue gas

The reduction of Hg emissions from non-ferrous metal smelting was proposed in the Minamata Convention. Regenerable sulfureted MoO3/TiO2, which displayed excellent performance in capturing gaseous Hg0, was once developed by us to recover gaseous Hg0 in smelting flue gas (SFG) for centralized control. Recently, a large amount of spent commercial selective catalytic reduction catalysts (for example V2O5-MoO3/TiO2) mostly deactivated by CaSO4 was formed, creating a need for their safe disposal. As the main constituent of deactivated V2O5-MoO3/TiO2 is MoO3/TiO2, deactivated V2O5-MoO3/TiO2 was sulfureted to capture gaseous Hg0 from SFG for its safe disposal and the effects of V2O5 and CaSO4 on Hg0 adsorption onto sulfureted MoO3/TiO2 were investigated. Although the capturing capacity of sulfureted MoO3/TiO2 moderately decreased after the impregnation of V2O5 and CaSO4, sulfureted deactivated V2O5-MoO3/TiO2 still displayed excellent performance and reproducibility in gaseous Hg0 capture. Meanwhile, the cost performance of sulfureted deactivated V2O5-MoO3/TiO2 for Hg0 capture was outstanding as deactivated V2O5-MoO3/TiO2 needs to be safely disposed. Therefore, deactivated V2O5-MoO3/TiO2 can be sulfureted as a regenerable and low-cost sorbent that is effective in recovering gaseous Hg0 from SFG, as well as being a cost-effective and environmentally friendly method for the safe disposal of spent V2O5-MoO3/TiO2.

Removal of Dye Acid Red 1 from Aqueous Solutions Using Chitosan-iso-Vanillin Sorbent Material

Sorption of Acid Red 1 (AR1) from aqueous solutions utilizing low-cost sorbent material; (chitosan-iso-vanillin) is studied under batch conditions. The remaining concentrations of the azo dye are measured at λmax = 546 nm by UV spectrophotometric method. Langmuir data reveal that the maximum removal capacity was 555.556 mg/g at pH 3. Freundlich isotherm represents the best fitting model on the removal of AR1 using chemically modified chitosan verifying the sorption takes place on heterogeneous surfaces with multilayer adsorption. Kinetic studies of the sorption process revealed that intraparticle diffusion is not only the rate-determining step but also a chemical reaction takes place as well. The results indicate that high sorption rapidness with almost 90% achieved within 90 min. Thermodynamic investigations suggest that the process favours an exothermic nature. The polymer utilized in the present study is being considered as a feasible sorbent material for the removal of AR1 from waste effluent.

Heavy Metal Sorption by Sludge-Derived Biochar with Focus on Pb2+ Sorption Capacity at μg/L Concentrations

Municipal wastewater management causes metal exposure to humans and the environment. Targeted metal removal is suggested to reduce metal loads during sludge reuse and release of effluent to receiving waters. Biochar is considered a low-cost sorbent with high sorption capacity for heavy metals. In this study, heavy metal sorption to sludge-derived biochar (SDBC) was investigated through batch experiments and modeling and compared to that of wood-derived biochar (WDBC) and activated carbon (AC). The aim was to investigate the sorption efficiency at metal concentrations comparable to those in municipal wastewater (<1 mg/L), for which experimental data are lacking and isotherm models have not been verified in previous works. Pb2+ removal of up to 83% was demonstrated at concentrations comparable to those in municipal wastewater, at pH 2. SDBC showed superior Pb2+ sorption capacity (maximum ~2 mg/g at pH 2) compared to WDBC and AC (<0 and (3.5 ± 0.4) × 10−3 mg/g, respectively); however, at the lowest concentration investigated (0.005 mg/L), SDBC released Pb2+. The potential risk of release of other heavy metals (i.e., Ni, Cd, Cu, and Zn) needs to be further examined. The sorption capacity of SDBC over a metal concentration span of 0.005–150 mg Pb2+/L could be predicted with the Redlich–Peterson model. It was shown that experimental data at concentrations comparable to those in municipal wastewater are necessary to accurately model and predict the sorption capacity of SDBC at these concentrations.