Binding of cadmium to Strychnos potatorum seed proteins in aqueous solution: adsorption kinetics and relevance to water purification

Biosorption of Cadmium and Lead by Dry Biomass of Nostoc sp. MK-11: Kinetic and Isotherm Study

Cadmium (Cd) and lead (Pb) are global environmental pollutants. In this study, Nostoc sp. MK-11 was used as an environmentally safe, economical, and efficient biosorbent for the removal of Cd and Pb ions from synthetic aqueous solutions. Nostoc sp. MK-11 was identified on a morphological and molecular basis using light microscopic, 16S rRNA sequences and phylogenetic analysis. Batch experiments were performed to determine the most significant factors for the removal of Cd and Pb ions from the synthetic aqueous solutions using dry Nostoc sp. MK1 biomass. The results indicated that the maximum biosorption of Pb and Cd ions was found under the conditions of 1 g of dry Nostoc sp. MK-11 biomass, 100 mg/L of initial metal concentrations, and 60 min contact time at pH 4 and 5 for Pb and Cd, respectively. Dry Nostoc sp. MK-11 biomass samples before and after biosorption were characterized using FTIR and SEM. A kinetic study showed that a pseudo second order kinetic model was well fitted rather than the pseudo first order. Three isotherm models Freundlich, Langmuir, and Temkin were used to explain the biosorption isotherms of metal ions by Nostoc sp. MK-11 dry biomass. Langmuir isotherm, which explains the existence of monolayer adsorption, fitted well to the biosorption process. Considering the Langmuir isotherm model, the maximum biosorption capacity (q_max) of Nostoc sp. MK-11 dry biomass was calculated as 75.757 and 83.963 mg g^-1 for Cd and Pb, respectively, which showed agreement with the obtained experimental values. Desorption investigations were carried out to evaluate the reusability of the biomass and the recovery of the metal ions. It was found that the desorption of Cd and Pb was above 90%. The dry biomass of Nostoc sp. MK-11 was proven to be efficient and cost-effective for removing Cd and especially Pb metal ions from the aqueous solutions, and the process is eco-friendly, feasible, and reliable.

Difference in cadmium chemisorption on calcite and vaterite porous particles

Cadmium is adsorbed on calcium carbonate via chemisorption. All calcium carbonate polymorphs generate otavite (cadmium carbonate), indicating that the crystallographic differences in calcium carbonate should affect the chemisorption equilibrium and kinetics. This study investigates the influences of the polymorph and specific surface area on cadmium adsorption. Here, we synthesise two polymorphs of porous calcium carbonate: calcite and vaterite with a wide range of specific surface areas. Then the equilibrium of cadmium adsorption is evaluated using adsorption isotherm models. Based on the Langmuir model with linear regression analysis, the maximum adsorptions of porous calcite and vaterite particles are 287.8 mg/g and 883.5 mg/g, respectively. The kinetics of cadmium chemisorption show clear differences between polymorphs. The calculated rate constant of the porous calcite particles using a pseudo-second-order reaction and Elovich models are two orders larger than that of porous vaterite particles. Although the adsorbed amount is superior for porous vaterite particles, porous calcite particles exhibit a faster reaction and relatively high adsorbed capacity for cadmium ions.

Green synthesis of zinc oxide nanoparticles loaded on activated carbon prepared from walnut peel extract for the removal of Eosin Y and Erythrosine B dyes from aqueous solution: experimental approaches, kinetics models, and thermodynamic studies

Water contamination due to release of dye containing effluents is one of the environmental problems of serious concern today. The present study investigate the green synthesis of zinc oxide nanoparticles (ZnO-NPs) doped on activated carbon (AC) prepared from walnut peel extract and to estimate its efficiency in the removal of Eosin Y (Eo-Y) and Erythrosine B (Er-B) from its aqueous solution. The synthesized AC-ZnO was identified by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and the Brunauer-Emmett-Teller. The influence of various parameters such as pH, dosage of AC-ZnO, contact time, and concentrations of Eo-Y and Er-B was also studied. The pH 3 was observed as the optimum pH while the equilibrium was noticed to reach in 30 min at dosage of 1 g/L and initial concentration 100 mg/L for Eo-Y and Er-B adsorption onto AC-ZnO. The maximum adsorption capacity of Eo-Y and Er-B onto AC-ZnO was found to be 163.9 and 144.92 mg/g (and removal efficiencies of 95.11 and 98.31 %), respectively. The process of Eo-Y and Er-B adsorption on AC-ZnO was observed to be depended on the pseudo-second-order kinetic model which indicates chemisorption processes. Langmuir adsorption isotherm model test described the removal of Eo-Y and Er-B on AC-ZnO. The thermodynamic data indicated that the adsorption was endothermic process. Also, the values, S_BET and V_TOTAL, for the AC-ZnO were equal to 725.65 m²/g and 0.6004 cm³/g, respectively. The results of this study exhibited that AC-ZnO was a very effective method that can be used for the removal of Eo-Y and Er-B from aqueous solutions.

Recovery and recycle of wastewater contaminated with heavy metals using adsorbents incorporated from waste resources and nanomaterials-A review

Recovery and recycle of wastewater are essential because of the need of huge quantities of water everywhere in this world. Presence of heavy metals in wastewater such as iron (Fe), molybdenum (Mo), manganese (Mn), zinc (Zn), nickel (Ni), copper (Cu), vanadium (V), cobalt (Co), tungsten (W), chromium (Cr), arsenic (As), silver (Ag), antimony (Sb), cadmium (Cd), mercury (Hg), lead (Pd), uranium (U), etc is the serious environmental issues and risk for human and animal health. Adsorbents are simple and low-cost methods to treat the pollutants and heavy metals of wastewater. The adsorbents are capable to treat the wastewater prepared from different wastes such as domestic, agricultural, industrial, animal and marine waste etc. In recent years, novel nanomaterials are also used as adsorbents which enhance the treatment efficiency of wastewater. Adsorption is a mass transfer phenomenon revolving shift of elements from a fluid to a solid phase based on the concentration gradient. The mechanism which helps in separation of contaminants from the effluent and the factors governing the efficiency of adsorption are discussed elaborately.

A positive perspective during COVID-19 related to groundwater crisis

The months from March to June refer as water crisis months in many places of India, because in these months of summer generally, Indian people face shortage of water. In the summer season, groundwater level decreases due to high temperature and increased evaporation of water in most of the places. This present discussion is focused on one positive aspect during the COVID-19 pandemic, which is related to rainfall during this summer in India. It has been observed that the rainfall in India in the months of March to May (as of now, on May 18, 2020) is high as compared to previous years and it might increase the groundwater level and people of India would not face a water crisis during this summer.

Experimental modeling, optimization and comparison of coagulants for removal of metallic pollutants from wastewater

Wastewater treatment coagulation is one of the most important physicochemical operations used in industry. The adsorption capability of marigold leaf powder, tea waste and ferrous sulfate was investigated for domestic and tannery effluents. These adsorbents significantly affected the pH, electrical conductivity (EC) and turbidity of wastewater. Maximum decrease in all the attributes was observed for 10 g of adsorbents application. All the adsorbents significantly affected the physiochemical attributes of both wastewaters. Similarly, maximum adsorption potential was observed in case of tea waste powder. Maximum decrease in all physiochemical attributes such as pH (15%), EC (21%), turbidity (54%), total dissolved solids (TDS; 36%), total suspended solids (TSS; 43%), total hardness (TH; 52%), chloride contents (59%) and phosphate contents (60%) was observed with the application of 10 g of tea waste. Regarding the heavy metals, maximum decrease for cadmium (Cd; 47%), lead (Pb; 81%), arsenic (As; 44%), copper (Cu; 75%), iron (Fe; 49%), chromium (Cr; 68%) and zinc (Zn; 64%) was observed in same treatment. The decreasing order in terms of their adsorption potential for coagulants was tea waste > marigold leaf powder > ferrous sulfate. However, for the wastewater, the maximum effect of adsorbents was observed in case of domestic wastewater as compared to the tannery water. Based on these data, it is suggested that tea waste has maximum adsorption potential for the remediation of wastewater.

Transformation of Pb, Cd, and Zn Minerals Using Phosphates

Heavy metal contamination in soils has become one of the most critical environmental issues. The most efficient in-situ remediation technique is chemical immobilization that uses cost-effective soil amendments such as phosphate compounds to decrease Pb, Cd and Zn accessibility in the contaminated soils. The present study examined the effectiveness of KH2PO4 in immobilizing Pb, Cd and Zn in three samples of contaminated soils collected from ZGH “Bolesław” (Mining and Smelting Plant “Bolesław”). Effectiveness was evaluated using the following methods: a toxicity characteristic leaching procedure (TCLP)-based experiment, sequential extraction, X-ray diffraction analyses (XRD), and scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS). The most efficient percentage reduction of total leachable metal concentration assessed by TCLP was observed for lead (50%–80%), and the least reduction was observed for zinc (1%–17%). The most effective immobilization of stable compounds assessed by sequential extraction was noted for lead, while the weakest immobilization was noted for cadmium. New insoluble mineral phases were identified by SEM-EDS analysis. Cd, Zn, and Pb formed new stable mineral substances with phosphates. The predominant crystal forms were dripstones and groups of needles, which were easily formed by dissolved carbon rock surfaces containing zinc ions. The alkaline nature of the soil and a large number of carbonates mainly influenced the formation of new structures.

Hydrothermal synthesis of LaFeO3 nanoparticles adsorbent: Characterization and application of error functions for adsorption of fluoride

The adsorption of fluoride from aqueous solution by lanthanum ferrite nanoparticles (LaFeO₃ NPs) synthesized by the hydrothermal method has been investigated. This experimental study was conducted on a laboratory scale. The effects of various operating parameters such as pH (3-11), LaFeO₃ NPs dosage (0.1-1.0 g/L), contact time (15-120 min), temperature (303-318 K), and initial concentration of fluoride (15-40 mg/L) on fluoride adsorption were studied. The results showed that under optimal conditions of fluoride concentration of 20 mg/L, pH of 5, LaFeO₃ NPs dosage of 0.9 g/L, temperature of 308 K, and contact time of 60 min, maximum percentage removal of 94.75 % was obtained. The process of fluoride adsorption on LaFeO₃ NPs was found to depend on the Freundlich adsorption and Koble-Corrigan isotherm models. The monolayer adsorption capacity of LaFeO₃ NPs was 2.575 mg/g. The kinetic data fitted best into the pseudo-second-order model considering the values of the regression coefficients (r²) and error functions used. The thermodynamics study indicated that the adsorption process was exothermic (ΔH°< 0) and spontaneous (ΔG°< 0) in nature. It could be concluded that the synthesized LaFeO₃NPs can be used as an effective adsorbent for fluoride ions removal from aqueous solutions.

Isolation of active coagulant protein from the seeds of Strychnos potatorum - a potential water treatment agent

The application of natural coagulants for decentralized water treatment is gaining importance as a part of global sustainable initiative. This study focuses on the isolation of active coagulation components responsible for water clarification with respect to Strychnos potatorum seeds. The active coagulant components, protein and polysaccharide, were successfully isolated, dialysed and subjected to gel permeation chromatography. The polysaccharide was isolated with the saline extraction method and characterized using FTIR and NMR spectroscopy. Protein was precipitated with 80% ammonium sulphate solution combined with dialysis and gel permeation chromatography using Sephadex G-50. SDS-PAGE revealed that the isolated protein has a molecular weight of 12 kDa. The small-scale coagulation assay suggests that the protein fraction has superior coagulation activity than the isolated polysaccharide residue. The active coagulant fractions reported in this study would be helpful in deploying cheaper and simple methods in scaling up the coagulant fraction from these seeds acting as a potential water treatment agent.

Simultaneous removal of pollutants from water using nanoparticles: A shift from single pollutant control to multiple pollutant control

The steady increase in population, coupled with the rapid utilization of resources and continuous development of industry and agriculture has led to excess amounts of wastewater with changes in its composition, texture, complexity and toxicity due to the diverse range of pollutants being present in wastewater. The challenges faced by wastewater treatment today are mainly with the complexity of the wastewater as it complicates treatment processes by requiring a combination of technologies, thus resulting in longer treatment times and higher operational costs. Nanotechnology opens up a novel platform that is free from secondary pollution, inexpensive and an effective way to simultaneously remove multiple pollutants from wastewater. Currently, there are a number of studies that have presented a myriad of multi-purpose/multifunctional nanoparticles that simultaneously remove multiple pollutants in water. However, these studies have not been collated to review the direction that nanoparticle assisted wastewater treatment is heading towards. Hence, this critical review explores the feasibility and efficiency of simultaneous removal of co-existing/multiple pollutants in water using nanomaterials. The discussion begins with an introduction of different classes of pollutants and their toxicity followed by an overview and highlights of current research on multipollutant control in water using different nanomaterials as adsorbents, photocatalysts, disinfectants and microbicides. The analysis is concluded with a look at the current attempts being made towards commercialization of multipollutant control/multifunctional nanotechnology inventions. The review presents evidence of simultaneous removal of pathogenic microorganisms, inorganic and organic compound chemical pollutants using nanoparticles. Accordingly, not only is nanotechnology showcased as a promising and an environmentally-friendly way to solve the limitations of current and conventional centralised water and wastewater treatment facilities but is also presented as a good substitute or supplement in areas without those facilities.

Towards zero waste production in the paint industry wastewater using an agro-based material in the treatment train

An attempt has been made to evaluate the use of natural, agro-based material, Moringa oleifera as a coagulant in the treatment of recreated water-based paint effluent. The treatment train sequence comprising coagulation, flocculation, sedimentation, sand filtration, and membrane filtration was used. The efficiency was evaluated in terms of color and turbidity. The influence of experimental parameters such as eluent type, eluent concentration, coagulant dose, coagulant-eluate volume, initial effluent pH, and initial effluent concentration was examined. The recommended conditions to yield maximum removal efficiency are 80 mL of eluate prepared using 3 g of M. oleifera seed powder and 1 N NaCl, under actual pH, to treat a liter of effluent. The treated supernatant from coagulation unit was passed through a sand filtration setup and a membrane filtration, with a maximum removal of color above 95%. The results affirmed the positive coagulation properties of M. oleifera, which could serve as a better alternative for chemical coagulant. The optimized treatment conditions derived for the recreated paint effluent were applied in the real paint effluent treatment. An opportunity was identified for re-using treated wastewater, as a cooling fluid and a diluting agent for lower quality paints.The results affirmed the positive coagulation properties of M. oleifera, which could serve as a better alternative for chemical coagulant. Graphical abstract ᅟ.

Moringa oleifera (drumstick tree) seed coagulant protein (MoCP) binds cadmium - preparation and characterization of nanoparticles

Moringa oleifera is grown globally. It is a multipurpose tree and the seeds are rich in phytochemicals with antimicrobial activities. The crude powder of seeds clarify the turbid and metal contaminated water. M. oleifera (drumstick tree) seed coagulant protein (MoCP) was isolated to homogeneity from the crude extracts by carboxymethyl cellulose chromatography (CMC) and gel filtration. The molecular weight of the protein on gel filtration was 13 kDa and in SDS-PAGE it migrated as a single band under reducing conditions with molecular mass of 6.5 kDa (dimeric). Immobilized MoCP selectively binds cadmium from aqueous solutions (pH 2.0-7.0) with maximum binding at pH 6.0 in 180 min when tested at 10-600 minutes. It also bound the metal in the concentration range of 30-70mgL-1. The adsorption kinetics was better described by pseudo second order and the data better explained by freundlich isotherm model than Langmuir isotherm model as in Freundlich model the correlation coefficient (R2) is high and the calculated qmax is very close to the experimental qmax rather than Langmuir isotherm model. Furthermore, the nanoparticles of MoCP were prepared and characterized using transmission electron microscopy (TEM). The authenticity of the isolated protein and the nanopraticles prepared was confirmed by specific reactivity with the MoCP antibody raised earlier in our laboratory.

Cadmium in Chinese Postharvest Peanuts and Dietary Exposure Assessment in Associated Population

Cadmium (Cd) in 8698 peanut samples collected from China in 2009-2014 was studied to evaluate its contamination level, distribution, and health risk. The average Cd concentration was 0.1684 mg kg^-1; the range of 2.5-97.5% was 0.0191-0.4762 mg kg^-1, indicating the cadmium-contaminated peanut level was even lower. Some peanut strains for which protein contents had a significant correlation (Pearson correlation coefficient r = 0.86**) with the Cd concentration level should be of concern. Under the same soil Cd background, the difference in Cd contents in different peanut varieties is extremely significant. For example, the Cd concentration of Silihong is about 0.4522 mg kg^-1, being 7 times higher than that of Zhonghua 6. According to the exposure assessment using the probabilistic simulation method, the target hazard quotients (THQs) of all groups should be below 1. The THQ range in this study was from 0.0035 to 0.0202, suggesting that there were no potential noncinogenic effects in any group.

Kinetic and isotherm modeling of Cd (II) adsorption by L-cysteine functionalized multi-walled carbon nanotubes as adsorbent

In this study, multi-walled carbon nanotubes were functionalized by L-cysteine to show the kinetic and isotherm modeling of Cd (II) ions onto L-cysteine functionalized multi-walled carbon nanotubes. The adsorption behavior of Cd (II) ion was studied by varying parameters including dose of L-MWCNTs, contact time, and cadmium concentration. Equilibrium adsorption isotherms and kinetics were also investigated based on Cd (II) adsorption tests. The results showed that an increase in contact time and adsorbent dosage resulted in increase of the adsorption rate. The optimum condition of the Cd (II) removal process was found at pH=7.0, 15 mg/L L-MWCNTs dosage, 6 mg/L cadmium concentration, and contact time of 60 min. The removal percent was equal to 89.56 at optimum condition. Langmuir and Freundlich models were employed to analyze the experimental data. The data showed well fitting with the Langmuir model (R2=0.994) with q max of 43.47 mg/g. Analyzing the kinetic data by the pseudo-first-order and pseudo-second-order equations revealed that the adsorption of cadmium using L-MWSNTs following the pseudo-second-order kinetic model with correlation coefficients (R2) equals to 0.998, 0.992, and 0.998 for 3, 6, and 9 mg/L Cd (II) concentrations, respectively. The experimental data fitted very well with the pseudo-second-order. Overall, treatment of polluted solution to Cd (II) by adsorption process using L-MWCNT can be considered as an effective technology.

Adsorptive removal of cadmium ions by Spirulina platensis dry biomass

Cadmium is one of the most toxic substances found in aquatic ecosystems. This metal tends to accumulate in photosynthetic plants and fish and is transferred to humans causing many diseases. It has to be removed from our environment to reduce any health risks. Dry biomass of the microalga (cyanobacterium) Spirulina platensis was used as biosorbent for the removal of cadmium ions (Cd²⁺) from aqueous solutions. The effects of different levels of pH (3–9), biomass concentration (0.25–2 g), temperature (18–46 °C), metal concentration (40–200 mg/l) and contact time (30–120 min) were tested. Batch cultures were carried out in triplicate in an orbital shaker at 150 rpm. After centrifuging the biomass, the remaining levels of cadmium ions were measured in the supernatant by Atomic Absorption Spectrometer. Very high levels of removal, reaching up to 87.69% were obtained. The highest percentage of removal was reached at pH 8, 2 g of biosorbent, 26 °C, and 60 mg/l of cadmium concentration after 90 min of contact time. Langmuir and Freundlich isotherm models were applied to describe the adsorption isotherm of the metal ions by S. platensis. Langmuir model was found to be in better correlation with experimental data (R² = 0.92). Results of this study indicated that S. platensis is a very good candidate for the removal of heavy metals from aquatic environments. The process is feasible, reliable and eco-friendly.