Heavy Metal-contaminated Water Research Articles

Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar

Heavy metal contamination in water and soil has gradually become a concern with the development of industry in recent years and may pose a serious threat to human health if left untreated. Biochar is commonly used as an adsorbent/immobilizer of heavy metals from water and substrates because of its wide—ranging raw materials, low production cost, and good adsorption performance. Based on the adsorption mechanism of biochar, this paper analyzes different modification methods of biochar, aiming to provide an effective material for the treatment of heavy metals from water and sediment and provide a certain reference for its application to practical projects.

Assessment of water quality by analyzing heavy metals in the Levrier Bay (Nouadhibou, Mauritania)

In this study, variations in physicochemical parameters and heavy metal contamination in water of theBaie de Lévrier are instigated from 25 stations to assess the quality of water. The pH of the waters isrelatively basic and the temperatures are a little high compared to the temperatures of the Atlantic Ocean inDecember. The measured conductivity remains within the range of known conductivity quantities that is56 μS/cm for the oceans. The average concentration of the four heavy metals in water is therefore in theorder of 0.02. The comparison with the background (SE26) allows us to note that: - concentrations of Cu areeither low or similar to those of the stations SE5, SE8, SE10, SE12, SE13, SE24, SE25, - concentrations of Coare relatively high in most stations SE2, SE4, SE6, SE9, SE11, SE13, SE16, SE17, SE18, SE19, SE20, SE21,SE22, SE23, SE24, particularly in stations SE14 and SE16.; - As concentrations are the same except thestation SE1; - concentrations of Mo in the stations SE4, SE6, SE9, SE12, SE14, SE21, SE23, SE24 are relativelyhigher compared to that of the background, while in the other stations the concentrations are low. Calculatedpollution values (IPs) are less than1, suggesting the absence of pollution in the analyzed water.Igeo valuesare all very low (Igeo<<0) and attest to a very low level of contamination, the enrichment factor (EF)displayslarge values (>1) for arsenic, particularly at stations SE1 (EF=70), SE5 and SE22(EF=7). Such valueswould be related to the influence of external discrete sources like industrial activities and other anthropogenicorigins.

On As(III) Adsorption Characteristics of Innovative Magnetite Graphene Oxide Chitosan Microsphere.

A magnetite graphene oxide chitosan (MGOCS) composite microsphere was specifically prepared to efficiently adsorb As(III) from aqueous solutions. The characterization analysis of BET, XRD, VSM, TG, FTIR, XPS, and SEM-EDS was used to identify the characteristics and adsorption mechanism. Batch experiments were carried out to determine the effects of the operational parameters and to evaluate the adsorption kinetic and equilibrium isotherm. The results show that the MGOCS composite microsphere with a particle size of about 1.5 mm can be prepared by a straightforward method of dropping FeCl2, graphene oxide (GO), and chitosan (CS) mixtures into NaOH solutions and then drying the mixed solutions at 45 °C. The produced MGOCS had a strong thermal stability with a mass loss of <30% below 620 °C. The specific surface area and saturation magnetization of the produced MGOCS was 66.85 m2/g and 24.35 emu/g, respectively. The As(III) adsorption capacity (Qe) and removal efficiency (Re) was only 0.25 mg/g and 5.81% for GOCS, respectively. After 0.08 mol of Fe3O4 modification, more than 53% of As(III) was efficiently removed by the formed MGOCS from aqueous solutions over a wide pH range of 5–10, and this was almost unaffected by temperature. The coexisting ion of PO43− decreased Qe from 3.81 mg/g to 1.32 mg/g, but Mn2+ increased Qe from 3.50 mg/g to 4.19 mg/g. The As(III) adsorption fitted the best to the pseudo-second-order kinetic model, and the maximum Qe was 20.72 mg/g as fitted by the Sips model. After four times regeneration, the Re value of As(III) slightly decreased from 76.2% to 73.8%, and no secondary pollution of Fe happened. Chemisorption is the major mechanism for As(III) adsorption, and As(III) was adsorbed on the surface and interior of the MGOCS, while the adsorbed As(III) was partially oxidized to As(V) accompanied by the reduction of Fe(III) to Fe(II). The produced As(V) was further adsorbed through ligand exchange (by forming Fe–O–As complexes) and electrostatic attraction, enhancing the As(III) removal. As an easily prepared and environmental-friendly composite, MGOCS not only greatly adsorbs As(III) but also effectively removes Cr(VI) and As(V) (Re > 60%) and other metals, showing a great advantage in the treatment of heavy metal-contaminated water.

Optimization of coal fly ash-based porous geopolymer synthesis and application for zinc removal from water

Coal fly ash-based porous geopolymer (CFAPG) is a potential adsorbent for heavy metal-contaminated water remediation and can also mitigate the accumulation of coal fly ash from thermal power plants. Production parameters influence the physicochemical properties (e.g., adsorption capacity) of CFAPG. Ten potential factors involved in the CFAPG production process were examined using a Plackett-Burman design (PBD) and then an orthogonal experimental design (OED). The results show the alkali activator modulus (MS), alkali-ash mass ratio (AA), foaming agent-ash mass ratio (FAR), and sodium dodecyl sulfate-ash mass ratio (SDSA) were the most important factors influencing the Zn adsorption capacity of CFAPG. Ternary plots confirm the interaction between these four factors, with the role of FAR being easily masked by other factors and MS being the least influenced by other factors. Furthermore, Zn adsorption on the CFAPG created with optimal parameters was best described by the Bi_Langmuir model, indicating two different sorption site classes on the surface of CFAPG with a total maximum Zn adsorption capacity of 13.42 mg g−1. These results provide key parameters for the production of geopolymers as heavy metal adsorbents.

Modification of Glassy Carbon Electrode Using Microcrystalline Cellulose-Ethylenediaminetetraacetic Acid for the Detection of Lead and Cadmium Ions

There is a greater need for the identification and monitoring of metal contaminants as a result of the growing hazard that heavy metal contamination of water poses to the environment. In this work, microcrystalline cellulose was functionalised with ethylenediaminetetraacetic acid, and the product analysed using scanning electron microscopy and X-ray diffraction techniques. The functionalised microcrystalline cellulose-ethylenediaminetetraacetic acid was employed to modify the glassy carbon electrode. Detection for Pb2+ and Cd2+ ions was determined using square wave anodic stripping voltammetric analysis at square wave potential scan of -1.0 V to -0.2 V, and deposition potential of -1.0 V in 0.1M acetate buffer for 240 sec. Higher current response of Pb2+ was obtained at -0.6 V and that of Cd2+ at -0.8V. Limit of detection for Pb2+ was 1.8 ppb (MCC-EDTA GCE) and 5.0 ppb (MCC-GCE) , while that of Cd2+ was 7 ppb (MCC-EDTA GCE) and 10 ppb (MCC-GCE), these indicate MCC EDTA GCE has higher sensitivity towards detection of the metal ions and selectivity of modifiers for detection of Pd2+ and Cd2+ was achieved successfully.

Using Biochar and Nanobiochar of Water Hyacinth and Black Tea Waste in Metals Removal from Aqueous Solutions

The treatment of heavy metal-contaminated water is challenging. The use of nanomaterials from many environmental wastes is promising for removing metals and contaminants from aqueous solutions. This study is novel in using nanobiochar of water hyacinth (WH) and black tea waste (TW) as a promising approach to water decontamination owing to its unique properties that play an effective role in metal adsorption. The mono- and multi-adsorption systems of cadmium (Cd), chromium (Cr), and nickel (Ni) on biochar and nanobiochar of water hyacinths (BWH and NBWH) and black tea waste (BTW and NBTW) were investigated in this study as potential low-cost and environmentally friendly absorbents for the removal of previously mentioned heavy metals (HMs) from aqueous solutions. The WH and TW were collected from the locality, prepared, and kept until used in the experiment. Nanobiochar was prepared by grinding, characterizing, and storing in airtight containers until used. A batch experiment was designed in mono- and competitive systems to study the adsorption equilibrium behavior of HMs on biochar and nanobiochars. The Freundlich and Langmuir isotherm models were fitted to the mono- and competitive-adsorption equilibrium results. The Freundlich isotherm model provided a better fit. Furthermore, it was noticed that NBWH and NBWT efficiently removed the Cd in the mono-system by ≥99.8, especially in the smaller concentration, while NBWT and BTW removed ≥99.8 and 99.7% in the competitive system, respectively. In the mono- and competitive systems, the nanobiochars of NBTW removed more than 98.8 of Cr. The sorbents were less efficient in Ni removal compared to Cd and Cr. However, their effectiveness was very high also. The results revealed that Cd was the highest metal removed by sorbents, nanobiochars were better than biochars to remove the HMs, and the results also indicated that co-occurrence of multi-metals might fully occupy the adsorption sites on biochars and nanobiochars.

Assessment and source analysis of heavy metal contamination in water and surface sediment in Dongping Lake, China

Dongping Lake is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project, its water quality is of vital importance to the environmental protection and the security of water supply. To assess the heavy metal (HM) contamination in Dongping Lake, samples in water and surface sediment were taken from 59 sampling sites over the entire lake. The statistical characteristics, pollution conditions, and source identifications were analyzed using coupling methods of entropy water quality index (EWQI), modified pollution index (mCd), enrichment coefficient (EF), geo-accumulation index (Igeo), potential ecological risk index (PERI), and positive matrix factorization (PMF). In present study, the averaged concentrations of all studied HMs in water body of Dongping Lake were below the limit of drinking water quality standard recommended by WHO, and the EWQI and mCd of HM concentrations were identified to be in good and excellent conditions. The concentrations of almost all studied HMs in surface sediment of Dongping Lake exceeded the background values in the soil of Shandong Province, and Cd (cadmium) was the dominant pollutant. With EF > 2, Igeo > 1, and Er > 80, Cd in sediment was under moderate pollution. The outcomes of source analysis revealed that the HMs in surface sediment were mainly derived from the primary and secondary industries. Specifically, manufacturing industries contributed the most to the HM contaminations in sediment of Dongping Lake.

An eco-friendly removal of Cd(II) utilizing banana pseudo-fibre and Moringa bark as indigenous green adsorbent and modelling of adsorption by artificial neural network.

Heavy metal-contaminated water can be effectively treated using adsorbents made from abundantly available biomass. The present investigation was carried out to adsorb Cd(II) from synthetic solution by banana pseudo-stem(BP) and Moringa oleifera stem bark (MB). Adsorption efficiencies of both adsorbents were studied in the batch reactor by conducting experiments to determine the consequences of changes ofpH, adsorbent dosages, initial Cd(II) concentrations, incubation time, and temperature. The process parameters were tuned to attain the highest possible removal percentage. The characterization of the adsorbents was performed by utilizing Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) for the fresh and metal-loaded adsorbents. Atomic absorption spectroscopy (AAS) was employed to calculate the amount of Cd(II) in an aqueous solution. The experimental data were entirely consistent with the pseudo-second-order model for BP and MB. The findings of the study illustrated the better adsorption efficiency of BP-derived adsorbent (≈ 99%) at optimum conditions over the MB (≈ 97%), and the corresponding adsorption capacities were 11.98 and 7.04 mg/g, respectively. The 4 (four) well-known isotherm models were attempted both in linear and non-linear forms. BP (R2 =0.995) and MB (R2 =0.994) were found to be best described by the Freundlich isotherm, which was selected based on the highest R2 value. In thermodynamic studies, ΔH and ΔS were calculated for both the adsorbents. Cd(II) adsorption on BP and MB was endothermic, as evidenced by the positive ΔH. Finally, the prediction of the removal percentage was made by the artificial neural network (ANN) modelling. The present work developed regionally derived waste materials which are helpful for small-scale industrial units for their waste management in an economical and sustainable way.

A green approach to arsenic removal using ZnO nanoparticles synthesized from Acacia Catechu leaf extract

One of the world's most prevalent environmental challenges is heavy metal contamination in water. Because of uncontrolled discharge from numerous sectors, this issue is particularly dangerous in rising countries' large cities. Because of their carcinogenic effects on humans and harmful environmental effects, heavy metals are expected to require special attention. Heavy metals can enter the environment from both anthropogenic and natural sources. As a result, bioaccumulation and transmission to the ecological pyramid via the food chain are very likely. Heavy metal removal is a difficult issue that must be solved if harmful effects on individuals and the environment are to be avoided or mitigated. The current study focuses on using the Acacia Catechu tree to make zinc oxide nanoparticles in an environmentally friendly manner. The Acacia Catechu plant's leaves were chosen because they contain a substantial amount of Flavonoids and Phenols, which are principally responsible for decreasing the precursor without the need of conventional synthesis chemicals. The nanoparticles were characterised by UV–Vis Spectroscopy, XRD, FT-IR, SEM, DLS, and TEM imaging methods. When perfect conditions are maintained at a dose of 0.3 gm, pH of 7, and an optimum period of 40 min, the highest percentage removal of arsenic utilising ZnO nanoparticles is 90.3 percent.

Cost-effective microwave-assisted hydrothermal rapid synthesis of analcime-activated carbon composite from coal gangue used for Pb2+ adsorption.

Heavy metal contamination of water has brought about serious harm to the ecological environment and also threatens human health to a certain extent. In this study, a composite structure comprised of analcime-activated carbon (ANA-AC) was synthesized in situ via a microwave-assisted hydrothermal method using coal gangue (CG) for the potential treatment of Pb2+ from aqueous solution. The products were systematically characterized using XRD, SEM, BET, FTIR, and XPS. The results showed that activated carbon was successfully integrated with the structure of the analcime and the BET surface area of the ANA-AC (20.82 m2/g) was much greater than that of the CG (9.33 m2/g) and ANA (10.04 m2/g) independently. The relationship between Pb2+ adsorption capacity and the initial solution concentration, adsorbent dosages, contact time, pH, and temperature was studied. Under optimal conditions (Pb2+ = 100mg/L, dosage = 0.1g, contact time = 6h, pH = 5.4-6, temperature = 298K), the maximum adsorption capacity of ANA-AC can reach 100%, which was higher than that of CG and ANA. The Langmuir isotherm model was in good agreement with the data obtained for Pb2+ adsorption, and the pseudo-second-order kinetic model was more suitable for describing the experimental data, showing that chemical adsorption was the controlling step during the adsorption process. In summary, analcime-activated carbon composite prepared from coal gangue could be used as an appropriate adsorbent for Pb2+ adsorption from an aqueous solution.

Fluorescent hydrogels based on oxidized carboxymethyl cellulose with excellent adsorption and sensing abilities for Ag+

Heavy metal contamination in water and soil are harmful and destructive to the environment, it has always been regarded as a big problem. Herein, we developed a self-healing fluorescent hydrogel based on oxidized carboxymethyl cellulose with excellent sensing and adsorption abilities for Ag+. The detection and adsorption effects of hydrogels on heavy metal ions were studied. It turned out that the fluorescent hydrogel has sensitive detection and high adsorption capacity for Ag+, the detection limit was 3.798 μM, and the maximum adsorption capacity was 407 mg/g. The adsorption isotherm fitted the Langmuir model well, and the pseudo-secondary model for adsorption kinetics fitted well. The hydrogel could heal itself without external stimulus, it could be easily regenerated 7 times without loss of adsorption performance. In short, the prepared hydrogel has capability of self-healing, detecting and adsorbing heavy metal ions at the same time, good mechanical strength, these all made it a promising long-life adsorbent and provided a new way for wastewater treatment.

Heavy metals contamination in water, sediments and fish of freshwater ecosystems in Pakistan

Abstract Freshwater ecosystems are being contaminated by heavy metal pollution. The primary source of contamination is wastewater discharged from urban, industrial, and agricultural facilities. The contaminated water contains hazardous amounts of heavy metals mixed in the freshwater ecosystem, causing deleterious impacts on marine life and humans. This review paper highlights the contamination of the freshwater ecosystem of Pakistan with heavy metals. Heavy metals' concentration in sediments, water, and fish were assessed in the food chain, and their relationship with sites and sources was explored. It was observed that heavy metals present in freshwater and sediments bio-accumulate into fish organs. It was also found that some parts of freshwaters such as the rivers Ravi, Chenab, Kabul, and Indus were highly contaminated, and they imposed negative impacts on fish and human health. The River Ravi, receiving a huge amount of industrial and sewage wastewater from urban centers and industries of Central Punjab, was highly contaminated compared to other rivers of Pakistan. The ecosystem health of River Indus was the best among all the rivers of Pakistan due to the enormous volume of water flow and less number of industrial units along with it. Freshwater fish of the rivers Indus, Chenab, and Jhelum are consumable for humans. The presence of heavy metals also causes social, environmental, and economic problems. Therefore, the wastewater should be treated before discharge into freshwater streams and rivers to lessen the harmful impacts of heavy metals on marine life and human beings.

Silk fibroin: a promising bio-material for the treatment of heavy metal-contaminated water, adsorption isotherms, kinetics, and mechanism.

Silk is the strongest natural biopolymer produced by silk worms possessing superior adsorbent properties and thus extensively used in various applications. The present study involved the preparation of powder form of a silk fibroin materials and their application in adsorption of heavy metals, particularly, iron from aqueous solution. The morphological and structural characteristic properties of this promising materialswere examined by using different analytical techniques. Batch experiments were conducted within feasible parametric ranges to understand the effect of dose, time, concentration, pH, and reusability. Silk fibroin was effective for iron adsorption over a wide range of pH 6 to 10. The adsorption removal efficiency of 98% was attained for removal of iron from contaminated water at moderate dose of 0.25g and contact time of 60min, which is unprecedented by considering the environment benign nature of the material. The data was examined in different isotherm models wherein it fitted best in Langmuir adsorption model. Similarly, Langmuir isotherm model, with R2 value of 0.984 and KL 0.412 and maximum adsorption capacity as 12.82mgg-1, suggests monolayer adsorption. Kinetic study with better R2 value of 0.941 represented the pseudo-second order kinetics governed by the chemisorption reaction. To understand the practical applicability of silk fibroin, the repeatability study up to 5 cycles were performed. The findings are very encouraging which confirmed the usage of silk fibroin as adsorbent for multiple cycles with marginal decrease in adsorption efficiency. Eventually, the material was tested for iron removal in real contaminated water which revealed its potential and selectivity for removal of iron in different matrix.

ASSESSMENT OF HEAVY METALS UPTAKE BY SOME SELECTIVE BACTERIAL STRAINS ISOLATED FROM HAZARIBAGH TANNERY EFFLUENT IN DHAKA CITY, BANGLADESH: BIOSORPTION VIEWPOINT

Biosorption can be defined as a Physiochemical process that cleanses heavy metal-contaminated water and aids in environmental remediation. The present exploration was carried out to examine the metal biosorbent potentiality of five bacterial strains.Biosorption capacity was assessed using Atomic Absorption Spectrophotometer where Bacillus thuringiensis showed uptake of Pb 0.56mg/g that was around 34.74%, Cd 0.38mg/g (20.0%), Ni 0.30 mg/g (15.8%), Cr 0.76mg/g (39.58%), Cu 0.14mg/g (7.61%) and As 0.28mg/g (14.43%) respectively. Micrococcus sp. showed reduction of Pb 0.62mg/g (39.89%), Cd 0.40mg/g (21.10%), Ni 0.22mg/g (11.6%), Cr 0.46mg/g (23.96%), Cu 0.56mg/g (30.43%) and As 0.03mg/g (1.75%) respectively whereas Pseudomonas sp. exhibited reduction of As 0.56mg/g and 0.20mg/g (16% and 10%), Cu 0.26mg/g and 0.46mg/g (14% and 25%), Cr 0.74mg/g and0.56mg/g (39% and 29%), Ni 0.12mg/g and 0.38mg/g (6% and 20%), Pb 0.26mg/g and 0.68mg/g (19% and 41%) and Cd 0.46mg/g and 0.64mg/g (24% and 34%) respectively. The result displayed that the highest degradation of Pb and Cr were shown by Pseudomonas aeruginosa (41±0.01%) and Bacillus thuringiensis (39.58±0.05%) and lowest degradation of As was shown by Micrococcus sp. that was around 1.75±0.001%. By contrast, degradation of Pb in moderate condition was witnessed by Bacillus cereus (19.89±0.01%) and Ni by Bacillus thuringiensis (15.8±0.05%) respectively. Heavy metal’s biosorption is a quick process that might be an advantageous side for the removal of vast range of pollutants.

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

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

PREPARATION OF ACTIVATED CARBON ADSORBENT FROM COCONUT HUSK FOR THE ADSORPTION OF LEAD (II) IONS FROM AQUEOUS SOLUTION

Heavy metals contamination of water and wastewater is a common phenomenon. Industrial wastewaters are usually the cause of heavy metals pollution of the environment. In this work, the adsorptive removal of lead metal ions in aqueous solution is investigated using an activated carbon derived from coconut husk. The activated carbon was modified with NaOH and characterized for functional group, micro-structure and textural properties. The activated carbons have a surface area of 304.38 m 2 /g from 600 °C activation with NaOH modification and 281.19 m 2 /g (300 °C) without modification. FTIR demonstrated the different functional groups present and the SEM images showed the pores on the surface of the activated carbon due to the NaOH modification. The maximum adsorption capacity of 91.70 and 73.90 mg/g were obtained for the coconut husk modified and unmodified adsorbents respectively. The adsorption kinetics for lead metal ions onto both adsorbents can be described by a pseudo-second-order rate model and are well fitted to the Langmuir adsorption isotherm. The results indicated that coconut husk in modified and unmodified forms can be used for the efficient removal of lead (II) ions from water and wastewater.

Combined Effect of Zinc Oxide Nanoparticles and Bacteria on Osmolytes and Antioxidative Parameters of Rice (Oryza sativa L.) Plant Grown in Heavy Metal-Contaminated Water

With the advancement in nanotechnology, the use of nanoparticles has been enhanced dramatically in biomedical, agriculture, and industrial processes. However, the combined effect of nanoparticles and bacteria on plant growth in heavy metal (Cd, Cr, Cu, and Pb)-contaminated wastewater is greatly limited. Therefore, the recent work was designed to determine the synergistic impact of green synthesized zinc oxide nanoparticles (ZnO-NPs) (5-10 mg/L) and Bacillus spp. ( Bacillus cereus and Lysinibacillus macroides) on the physiological and biochemical activities of rice seedlings under heavy metal- (HM-) contaminated water. The results revealed that germination percentage (36%), root-shoot length (5.11 and 3.41 cm), fresh shoot-root weight (0.05 and 0.011 g), dry shoot-root weight (0.008 and 0.009 g), Chl a, Chl b, and carotenoid (5.4, 3.2 mg/g, and 4.3 μg/g), total soluble sugar (TSS) (26.44 mg/g), and total soluble protein (TSP) (21.99 mg/g) content considerably reduced in the plant tissues while combined impact of bacteria and ZnO NPs alleviates HM stress in contaminated water and improved seed germination (70%), root-shoot length (9.93 and 11.82 cm), fresh shoot-root weight (0.125 and 0.131 g), dry shoot-root weight (0.0532 and 0.042 g), Chl a, Chl b, and carotenoid (18.8, 13.9 mg/g, and 17.1 μg/g), TSS (57.651 mg/g), and TSP (47.990 mg/g) content. Lipid peroxidation induced by HM stress increased the amount of thiobarbituric acid reactive substances (TBRAS) (17.321 nM/mg) and hydrogen peroxide (H2O2) content (14.5 μM/g), stress markers such as glycine betaine (GB) (40.731 mg/g) and proline (Pro) (38.812 μmol/g) and antioxidant enzymes (SOD, POD, CAT, and APX) (180.87 U/mg, 450.677, 0.1066, and 0.631 μm/min/mg) under HM stress while the combined effect of ZnO NPs and bacteria reduced TBRAS (5.431 nM/mg), H2O2 content (2.25 μM/g), stress markers such as GB (24.731 mg/g) and Pro (18.811 μmol/g), and SOD, POD, CAT, and APX (187.53, 194.88, 0.061, and 0.271 μm/min/mg) contents. The present study suggested a potential role of combined impact of nanoparticles and bacteria in remediation of heavy metals from wastewater by improving plant growth.

Removal of Copper, Nickel, and Zinc Ions from an Aqueous Solution through Electrochemical and Nanofiltration Membrane Processes

Heavy metal contamination in water is a major health concern, directly related to rapid growth in industrialization, urbanization, and modernization in agriculture. Keeping this in view, the present study has attempted to develop models for the process optimization of nanofiltration (NF) membrane and electrocoagulation (EC) processes for the removal of copper, nickel, and zinc from an aqueous solution, employing the response surface methodology (RSM). The variable factors were feed concentration, temperature, pH, and pressure for the NF membrane process; and time, solution pH, feed concentration, and current for the EC process, respectively. The central composite design (CCD), the most commonly used fractional factorial design, was employed to plan the experiments. RSM models were statistically analyzed using analysis of variance (ANOVA). For the NF membrane, the rejection of Zn, Ni, and Cu was observed as 98.64%, 90.54%, and 99.79% respectively; while the removal of these through the EC process was observed as 99.81%, 99.99%, and 99.98%, respectively. The above findings and a comparison with the conventional precipitation and adsorption processes apparently indicate an advantage in employing the NF and EC processes. Further, between the two, the EC process emerged as more efficient than the NF process for the removal of the studied metals.

Fluorescence Quenching Probe Based on Graphene Quantum Dots for Detection of Copper Ion in Water

Heavy metal contamination in water is a serious issue causing adverse effects on health, ecosystem, and environment. To monitor this contamination, fluorescence quenching probe based on the graphene quantum dots (GQDs) was used for detection of metal compounds. The effect of metal compounds on the fluorescence quenching efficiency of the GQDs was investigated. A typical sample of metal compounds was selected from copper acetate, copper chloride, copper nitrate, copper sulfate, cobalt nitrate, cobalt chloride, and zinc nitrate. It was found that the GQDs exhibited high selectivity for copper acetate. The quantity of copper acetate was obtained using Stern-Volmer plot. It was found that the plot exhibited a linear behavior for the fluorescence quenching of the GQDs by copper acetate. This analytical method could be developed for the determination of copper acetate in the concentration range of 0–2.5 mM with the Stern-Volmer quenching constant of 2445 M−1. To understand an occurring interaction between metal compounds and the GQDs in the system, redox characteristics of the GQDs mixed metal compounds were investigated. Noticeably, electrochemical potential gap (ΔE) of the GQDs mixed copper acetate with UV irradiation seems higher than that of the GQDs mixed copper acetate without UV irradiation, implying better electron transfer behavior from the GQDs to copper acetate. This result was in good agreement with the fluorescence quenching of the GQDs by copper acetate. Accordingly, the nonradiative recombination of the GQDs could be explained in terms of the fluorescence quenching. The fluorescence quenching efficiency was proportional to the amount of the copper acetate. These results can be further explored for a novel graphene quantum dots-based fluorescent probe and this method could be more widely applied in water resources.

Ecological Risk Assessments of Heavy Metal Contamination in Water, Sediment and Biota of Otamiri and Imo Rivers, Nigeria

Heavy metals pollution of the environment is a serious concern because of the hazardous effects they pose to human health, ecosystems and other biological receptors. The aim of this study was to assess the ecological risk of exposure to heavy metals and physicochemical parameters around Otamiri and Imo rivers in Etche and Oyibo Local Government Areas of Rivers State. Water, sediment, arrow head plant (Sagittaria latifolia) and christmas bush Plant (Ceratopetalum gummiferum), tilapia fish samples (Oreochromis niloticus) and cat fish (Clarias gariepinus) were collected at different points from five sample stations for wet and dry seasons. These samples were analyzed quantitatively to assess the levels of contamination in the samples using the ecological risk assessment models associated with exposure to these contaminants. The results of the heavy metal analysis show that the Estimated Daily Intake (EDI) for biota samples ranged from 0.000 – 1.254 mg/kg/day while water ranged from 0.000 -0.322 mg/kg/day. The target hazard quotient (THQ) ranged from 0.000 – 69.228 for both biota and river water samples for Otamiri and Imo rivers The hazard index values indicated significant public health risk with values of 1.42 was recorded for Tilapia and 33.14 for Christmas bush plant. Cancer risk due to heavy metals exposure had a peak value of 1.04 x10-1 for wet season. The bioaccumulation of the metals showed that the pollution load index values ranged from 2.467- 5.822 in wet season and 9.708 – 99.853 in dry season. The presence of these heavy metals above threshold values suggest that the aquatic life that inhabit such rivers risk bioaccumulation which may affect the human population that depends on Otamiri/Imo rivers for fishing, drinking or irrigation. These poses a danger if bioaccumulation was to take place over a long period of time.