Maximum Metal Removal Research Articles

Analysis on surface grinding of mild steel by varying grinding parameters

The most common method for smoothing the work piece is surface grinding in the manufacturing sector. It's like the process of termination. EN31AMsteel is machined by abrasive tools in the current study and assesses surface roughness (Ra) and the rate of material removal (MRR). Use the Design of Experiment (DoE) method to decide the optimized influenced input parameters of grinding speed, cut depth and feed rate. In this work, analytical models for surface roughness and metal removal rate were constructed by using response surface methodology to consider wheel speed, table speed and cutting depth as control factors. In this Response Surface Methodology (RSM), the optimal machining parameters that lead to minimum surface roughness and maximum metal removal rate in the surface grinding process have been used to detect.

Acid washing of incineration bottom ash of municipal solid waste: Effects of pH on removal and leaching of heavy metals

This study systematically investigated the acid washing of incineration bottom ash (IBA) of municipal solid waste, focusing on the removal and leaching of heavy metals (Pb, Zn, Cr, Cd, Cu, and Ni), as well as their pH-dependent behavior. A series of small-scale laboratory acid washing tests with different nitric acid concentrations and washing periods were conducted. The concentrations of metals in the washing water were measured to evaluate the metal removal efficiency. Then, one stage batch leaching test was conducted for washed IBA to evaluate the leaching reduction efficiency of washing. The results showed that the maximum metal removal efficiencies for Zn, Cu, and Ni (62–76%) were higher than those for Pb, Cr, and Cd (17–25%), which were reached at the highest acid addition for most of the metals. Increasing the washing period did not always increase the metal removal efficiency. The maximum leaching reduction efficiencies were higher for Zn, Cr, and Cu (93–98%) than those for Pb, Ni, and Cd (73–79%). Both washing and leaching processes showed a similar metal concentration-pH profile for each metal. For Pb, Zn, Cr, and Cd, the metal concentration-pH profile generally followed the metal hydroxide solubility versus pH curves. For Cu and Ni, the concentration of metal decreased with the increasing pH first and then kept at a stable concentration higher than the solubility of the hydroxide, indicating that Cu and Ni in the IBA washing water and leachates did not exist dominantly as their hydroxides.

Adsorption of selected metals from cassava processing wastewater using cow-bone ash

In this study, the efficiency of cow-bone ash (CBA) as an adsorbent for the removal of metals from real-time cassava wastewater was examined. Wastewater was characterized using atomic absorption spectrophotometry (AAS). The adsorbent was characterized using X-ray Fluorescence (XRF), Scanning electron microscopy (SEM), and Fourier transform infrared FTIR. The effect of adsorbent dose, contact time, and agitation speed was investigated by a batch experiment performed in triplicate, and the removal efficiency of the ions calculated. Characterization of the cassava wastewater revealed that the concentration of Fe2+, Zn2+, Pb2+, and Mn2+were above the USEPA permissible limit. The adsorbent's characterization showed that it possesses crystalline nature, porous and rough surface, and the presence of CH, C = O, and CO functional groups. The optimum adsorbent dose was 0.02 g/100 mL for Fe2+ and Zn2+, and 0.04 g/100 mL for Mn2+ and Pb2 at an optimum contact time of 60 min and agitation speed of 150 rpm. The maximum metal removal efficiency obtained were 99%, 97%, 93% and 98% for Fe2+, Zn2+, Pb2+, and Mn2, respectively. Cow-bone ash offers efficient and cost-effective removal of Fe2+, Zn2+, Pb2+, and Mn2+from cassava wastewater.

Enhancement of Mn-doped magnetite by mesoporous silica for technological application

Mn0.6Fe2.4O4 was synthesized by the co-precipitation method. A simple method was developed for preparing Mn0.6Fe2.4O4@SiO2 nanocomposite via few steps. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) images, BET surface area measurements were used to characterize the physical structures of the investigated samples. The crystallite size of the nanocomposite is greater than that of the parent sample. The dielectric constant (e/) of the Mn0.6Fe2.4O4 is greater than that of the sample Mn0.6Fe2.4O4@SiO2. The investigated samples have a semiconductor-like behavior with two different conduction mechanisms. M-H loops of the samples show ferrimagnetic properties. Mesoporous silica increased the coercive field and decreases the values of both Ms and Mr of Mn0.6Fe2.4O4. Mn0.6Fe2.4O4@SiO2 nanocomposite exhibits higher removal efficiency than Mn0.6Fe2.4O3. The maximum removal of the heavy metals is observed for Pb2+ and Cr6+.

Biosorption of Heavy Metals by the Bacterial Exopolysaccharide FucoPol

Despite the efforts for minimizing the usage of heavy metals, anthropogenic activities still generate high amounts of wastewater containing these contaminants that cause significant health and environmental problems. Given the drawbacks of the conventional physical and chemical methods currently used, natural biosorbents (microbial cells or their products) arise as promising environmentally friendly alternatives. In this study, the binding efficiency of the polysaccharide secreted by Enterobacter A47, FucoPol, towards lead (Pb2+), cobalt (Co2+), copper (Cu2+) and zinc (Zn2+) cations was demonstrated. FucoPol revealed a higher performance for the biosorption of Pb2+, with a maximum overall metal removal of 93.9 ± 5.3% and a specific metal uptake of 41.1 ± 2.3 mg/gEPS, from a Pb2+ solution with an initial concentration of 10 mg/L, by a 5 g/L FucoPol solution. The overall metal removal decreased considerably (≤31.3 ± 1.6%) for higher Pb2+ concentrations (48 and 100 mg/L) probably due to the saturation of FucoPol’s binding sites. Pb2+ removal was also less efficient (66.0 ± 8.2%) when a higher FucoPol concentration (10 g/L) was tested. Pb2+ removal efficiency of FucoPol was maximized at pH 4.3, however, it was affected by lower pH values (2.5–3.3). Moreover, the FucoPol’s sorption performance was unaffected (overall metal removal: 91.6–93.9%) in the temperature range of 5–40 °C. These findings demonstrate FucoPol’s great potential for utilization as a biodegradable and safe biosorbent for treating waters and wastewaters contaminated with Pb2+.

Investigation of cutting conditions on tool life in shoulder milling of Ti6Al4V using PVD coated micro-grain carbide insert based on design of experiments

Tool life prediction is generally of great importance in all metal cutting processes, including milling titanium. In this paper, tool life testing was performed based on full factorial design. The cutting speed and width varied between 100 and 120 m/min, and 10 and 70 percent of tool diameter, respectively. All cutting tests were performed in Ti6Al4V under wet conditions using Physical Vapor Deposition (PVD) coated milling inserts. The wear limit was set to 0.2 mm. The data were analyzed using multiple regression analyses, where the method of least squares was applied. A mathematical tool life model was established. Roughly, for each one percent increase in cutting width, tool life decreases on average by one percent, and an increase in cutting speed by a percent leads to a decrease in tool life by four percent. The adequacy of the model was verified using analysis of variance at 95% confidence level. Tool life contour in cutting width and speed was generated from the model. The results can be used for selecting optimum cutting parameters for providing a desired tool life or maximum metal removal rates for a favored tool life.

Continuous fixed-bed adsorption of Mo(VI) from aqueous solutions by Mo(VI)-IIP: Breakthrough curves analysis and mathematical modeling

In the search for cost-effective and highly selective adsorbents for the removal of Mo(VI) from aqueous systems, the Mo(VI)-imprinted polymer (Mo(VI)-IIP) has been identified as a potential candidate. In this study, we investigated the performance of Mo(VI)-IIP in the packed fixed-bed column, to assess its potential for industrial extension. In a laboratory-scale fixed-bed column, the effluent Mo(VI) concentration versus time span (i.e., breakthrough curves) were determined for various operational parameters, such as flow rate (5, 7 and 9 mL min−1), influent Mo(VI) concentrations (50, 70 and 90 mg L−1), bed depths (0.5, 1 and 1.5 cm) at pH 3. The breakthrough curve of various bed height demonstrated that the life span of the continuous fixed-bed column will be extended with a longer bed column. The maximum capacity and total metal removal reached 94.3 mg g−1 and 80.2% respectively, using 1.5 cm bed depth, 7 mL min−1 flow rate and 50 mg L−1 influent Mo(VI) concentration. The growth of influent Mo(VI) concentration and flow rate caused the earlier exhaustion time in the column. The experimental data were fitted with well-established mathematical models such as Yoon-Nelson, Thomas, and Adams-Bohart. The results were best-fitted with Thomas and Yoon-Nelson models (with correlation coefficient R2 ≥ 0.99) rather than the Adams-Bohart model for all conditions.

Polystyrene-based magnetic hydrogels for elimination of some toxic metal cations from aqueous solutions.

Three smart novel polystyrene-based hydrogel nanocomposites were introduced for recovery of some divalent heavy metals (Cu2+ ad Pb2+) from simulated solutions for industrial wastewater remediation. In this regard, magnetic nanoparticles were prepared then fabricated with polystyrene waste and a copolymer of acrylic acid and acrylamide in presence of an initiator/crosslinking system. The chemical amendment process was established by the IR spectroscopy and the prepared hydrogels were characterized by the AFM microscopy and XRD analysis. Moreover, the elimination efficacy of the prepared hydrogels was monitored for Cu2+ and Pb2+versus different temperatures and pH values in simulated solution. The data showed a direct relation between the contact time and the amount of the metal removed. Moreover, it was found that the removal efficiency decreases within the region between LCST of polyacrylamide and HCST of polystyrene. It was also proved that maximum metal removal was attained at neutral pH. The maximum removal was achieved by the hydrogel with minimum magnetite content with removal capacity of 128mg/g of Cu2+ and 122mg/g of Pb2+ in single removal experiments at optimum test conditions. In double removal experiments, the prepared hydrogels showed obvious selectivity towards Cu2+ ions. The reusability of the investigated hydrogels was examined at three swelling-deswelling cycles.

Biosorption of Chromium and Nickel from Aqueous Solution by Chicken Feather

Background & Aims of the StudyHeavy metals and its compounds are toxic pollutants that have priority in the studies due to their potential harm to human health.Materials and MethodsThis study evaluated the potential of a chicken feather for the removal of nickel and chromium from aqueous solutions. The chicken feather was prepared from aviculture for nickel and chromium removal from aqueous solutions. The effects of pH, contact time, adsorbent dosage, and initial metal concentration on Ni and Cr removal were also evaluated in this study. Freundlich and Langmuir isotherm models were used to characterize the biosorption of the mentioned metals onto the chicken feather.ResultsBased on the findings, the maximum removal of metals was found in a contact time of 3 h, 1 g/L of adsorbent, pH 5 (for Ni) and 6 (for Cr), and concentration of 1 mg/l of metals. According to the Langmuir isotherms, the maximum biosorption capacities (qm) of Cr and Ni were 22.3 and 119.05 mg/g, respectively.ConclusionThe results showed that chicken feathers can absorb chromium and nickel at low concentrations. However, the ability and possibility of the use of the chicken feather are limited for the treatment of contaminated wastewater at high concentrations.

Influence of Bioaugmentation on the Decontamination of Heavy Metal Impacted Landfill Soil

The research is aimed to decontaminate heavy metal polluted landfill soil using consortia of fungi as bioaugmentation agents. Two consortia namely highly metal tolerant fungi (HMTF) and moderately metal tolerant fungi (MMTF) were used for the bioaugmentation. The experiment was conducted at day 0, 20, 60, and 100. Soil physicochemical parameters (pH, conductivity, redox potentials, and metal concentrations) were found to decline along the duration of the experiment. The maximum metal removal (48%) was achieved in soil treated with HMTF. Both treatments were efficient than the control (P < 0.05). The bioremediation efficiency was significantly influenced by the bioaugmented fungi. Therefore, the technique can be utilized for future treatment of metal impacted soil.

Bioremediation of Heavy Metal Contaminated Soils Originated from Iron Ore Mine by Bio-augmentation with Native Cyanobacteria

The soil in the Sangan iron-mining region in the east of Iran is contaminated with a high concentration of heavy metals, especially iron. The release of these pollutants into environment results in the transfer and accumulation of iron through the food chains, hence a reasonable solution is required to restore it. Bioaugmentation is an environmental friendly option to reduce the hazard effects of heavy metal in the contaminated soil. In this study, the consortia of two indigenous cyanobacteria isolated from soil of Sangan iron mining and used to bioremediate soil contaminated with iron, chromium, copper, lead, and nickel. The experiments were carried out by three treatment methods, including control soil, surface soil sprayed with cyanobacteria, and soil mixed with cyanobacteria for six months under laboratory condition. The scanning electron microscope showed the development of a network of filaments of the inoculated cyanobacteria (Oscillatoria sp. and Leptolyngbya sp.) with soil particles in both treatments. Bio-augmentation of the soil increased initial nitrogen content from 406 mg/kg in control to 664 mg/kg in soil mixed with cyanobacteria and 710 mg/kg in soil sprayed with cyanobacteria. Cyanobacteria inoculation decreased the available concentration of lead and nickel. The non-available heavy metal of soil in sample sprayed with cyanobacteria was in decreasing order: Cr > Fe > Ni > As > Pb > Cu. The maximum metal removal efficiency was 32%. In soil mixed with cyanobacteria increased in the root and hypocotyl lengths of radish and lettuce was observed compared to that in the control soil, indicated in the improvement of soil quality after bioremediation.

Potential of Vetiver grass for the phytoremediation of a real multi-contaminated soil, assisted by electrokinetic.

Phytoremediation assisted by electrokinetic is a potential technology for remediation of contaminated soil, but little is known about its application on real contaminated soils. This study aims to evaluate the Vetiver grass application on the electro-phytoremediation of a real contaminated soil around a metal smelter factory. Different types of the electric field (AC-DC), voltage gradient (1-2V/cm), saturation and unsaturation condition, and Eh-pH variation were investigated for Vetiver electro-phytoremediation performance. Vetiver grass had been grown for 21 days. Then three different voltage gradients (1, 2DCV/cm and 2ACV/cm) were applied for 8h/d across the soil domain for the next 21 days in comparison with a control cell without electric field (PR). The results showed that despite the AC current application which induced small changes, the application of DC current significantly changed the Eh-pH values. The maximum accumulation of extractable metals in Vetiver grass occurred in 2DCV/cm that shows approximately 50% increase in comparison with the AC and PR cells. The presence of contaminants poisons the Vetiver in all cells and all plants under 2DCV/cm dried out at the end of the experiment. Despite the significant reduction of heavy metals, there was no noticeable phytoextraction due to the application of DC current. Therefore, DC current can be used for phytoremediation through phytostabilization. However, the overall metals uptake in plants shoots under AC treatment with BCF>1 was much higher than the PR and DC treatment. Considering the translocation rate and plants health, if the AC current is applied in a long treatment time, it could have better results in electro-phytoremediation of the Vetiver grass through phytoextraction process. However, the maximum removal of heavy metals was in the cathode part of the cell under 2DCV/cm that shows 65% improvement in comparison with the PR cell.

Novel insights into mechanism of biometal recovery from wastewater by sulfate reduction and its application in pollutant removal

Biological sulfate reduction is an emerging technique for both removal and recovery of heavy metals from wastewater. In this study, anaerobic biomass from three different sources were initially screened based on their metal removal and sulfate reduction efficiencies. The effect of metal loading on the removal of sulfate and chemical oxygen demand (COD) was further investigated to examine its toxic effect on sulfate reducing bacteria (SRB) present in the anaerobic biomass. At low metal loading conditions, biomass obtained from anaerobic rotating biological contactor (An-RBC) reactor treating metallic wastewater showed a maximum metal removal (95 ± 0.5%), sulfate reduction (90 ± 1.56%) and COD removal (80 ± 0.88%); the values decreased at a high metal concentration for all the biomass. Metals were then subsequently recovered from bioprecipitates in the form of nanopowder and the metal recovery efficiency was in the order Cu > Pb > Cd > Zn > Ni > Fe > Mn. Analysis of the bioprecipitates by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) confirmed that it was mainly composed of metal sulfide. Size, shape and crystallinity of the nanoparticles were determined by field emission transmission electron microscopy (FETEM) and X-ray diffractometer (XRD) which revealed its excellent potential for industrial reuse and application, particularly for treating toxic dye containing wastewater.

Potential of water fern (Azolla pinnata R.Br.) in phytoremediation of integrated industrial effluent of SIIDCUL, Haridwar, India: removal of physicochemical and heavy metal pollutants

Integrated industrial effluent (IIE) released from SIIDCUL causes serious environmental problems in the vicinity of Haridwar, India. Therefore, this study investigated the potential of water fern (Azolla pinnata R.Br.) for phyto-treatment of IIE. Laboratory experiments with six IIE concentrations (0 as control with bore well water, 20, 40, 60, 80 and 100%) were performed for bio-removal of selected physicochemical, microbiological and heavy metal parameters of IIE in pot type experiments. The overall results described maximum removal of physico-chemical (pH, EC, TDS, BOD, COD, TKN, Ca, Mg, Na, K), microbiological (MPN and SPC) and heavy metals (Cd, Cu, Cr, Fe, Pb, Mn, and Zn) parameters in 60% concentration of IIE, respectively. The stimulus effect of IIE concentration on pollutant removal process was confirmed using Kruskal–Wallis post hoc test, one way ANOVA (p < 0.05), and linear regression (R2 < 0.85) tools. Besides this, A. pinnata relative plant growth rate was also maximum in 60% IIE treatment. This is the first report on phytoremediation of IIE while findings of this study showed that A. pinnata was useful for the eco-friendly treatment of SIIDCUL IIE and could minimize potential wastewater management issues.

Enhanced Bioremediation of Heavy Metal Contaminated Landfill Soil Using Filamentous Fungi Consortia: a Demonstration of Bioaugmentation Potential

This study aimed to determine the mycoremediative capacity of filamentous fungi consortia in landfill heavy metal contaminated soil. Streak plate method was utilized for the isolation of fungi from the landfill soil. Isolates were identified using morphological and molecular techniques. Heavy metal tolerance of the fungi was determined using radial growth diameter technique. Twelve species of landfill indigenous fungi were used for the bioremediation process. Two categories of fungi consortia namely highly tolerant fungi (Perenniporia subtephropora, Daldinia starbaeckii, Phanerochaete concrescens, Cerrena aurantiopora, Fusarium equiseti, Polyporales sp., Aspergillus niger, Aspergillus fumigatus, and Trametes versicolor) and moderately tolerant fungi (Paecilomyces lilacinus, Antrodia serialis, and Penicillium cataractum) were used to amend the contaminated soil; meanwhile, the unamended soil served as control. Maximum tolerance index of 1.0 was reported in Cr-, Cu-, and Fe-amended PDA medium. Meanwhile, the maximum heavy metal bioremoval efficiencies were for highly tolerant fungal consortium treated soil and were recorded as As (62%) > Mn (59%) > Cu (49%) > Cr (42%) > Fe (38%). Likewise, the maximum metal removal rate constant (K) and the half-lives (t1/2) were 0.0097/day 71 days, 0.0088/day 79 days, 0.0067/day 103 days, 0.0054/day 128 days, and 0.0048/day 144 days for As, Mn, Cu, Cr, and Fe, respectively, which were all for soil treated with consortium of highly tolerant fungi (P. subtephropora, D. starbaeckii, P. concrescens, C. aurantiopora, F. equiseti, Polyporales sp., A. niger, A. fumigatus, and T. versicolor). Spectra analysis revealed a clear distinction in the functional groups between the fungal treated and the untreated soils. Peaks at 874 ± 2 cm−1 and 1425 ± 2 cm−1 were only found in fungi amended soil. Physicochemical parameters mainly pH and redox potential played a key role in the bioremediation process, and bioaccumulation was believed to be the favored mechanism for the metal bioremoval. The data are suitable for assessing the contribution of bioaugmentation with consortia of fungi. It is equally important for assessing the synergistic effect of fungi on the reduction of extractable heavy metals in contaminated soil.

An Investigation on Chemical Machining of NiTi SMA Prepared by Powder Metallurgy

Chemical machining is very important in solving problems constantly arising due to the requirement of high surface finish along with high productivity through machining of metals and alloys. Such requirement appears in machining of NiTi shape memory alloy (55wt%Ni and 45wt% Ti) which has widespread engineering applications. The present work aimed at utilizing of Taguchi design of experiments with the method of desirability function to optimize the chemical machining parameters (machining temperature and machining time) of NiTi alloy prepared by powder metallurgy technique. Taguchi experimental design concept, L25 (2×5) orthogonal array was used to determine the S/N ratio. Based on the analyses of multiple regression method, mathematical predictive models for the studied parameters had designed and validated. To achieve the objectives of the present work Datafit ver9, and Mini Tab14 softwares had employed. The powders with the required percentages were mixed for 5hours, compacted at pressure of 900MPa, and sintered in two stages, at 500°C for 2 hours and then at 950°C for 6hours under vacuum conditions (10-4 torr ). The X-ray diffraction test showed that the prepared sample are consisting of three phases (NiTi monoclinic phase, NiTi cubic phase, and Ni3Ti hexagonal phase). Machining temperature appears as the most significant factor, which controls both surface roughness and metal removal rate. Two mathematical models were developed to predict the metal removal rate and the surface roughness for any collection of machining temperature, and machining time. A minimum surface roughness of 0.666μm with a maximum metal removal rate of 0.0041g/min can be associated with machining temperature of 650C and machining time of 2min in solution consisting of 6%HCl, 19%HNO3, and 75%H2O.

In-vitro bio-mineralization of arsenic and lead from aqueous solution and soil by wood rot fungus, Trichoderma sp.

In the present study, we investigated the role of calcite, i.e., microbiologically-induced precipitate by ureolytic Trichoderma sp. MG, in remediation of soils contaminated with arsenic (As) and lead (Pb). The fungus tolerates high concentrations of As (500 mg/L) and Pb (650 mg/L). The effects of three factors, i.e., urea concentration, CaCl2 concentration and pH, on urease production and bio-mineralization of As and Pb were investigated using Box-Behnken design. The maximum urease production (920 U/mL) and metal removal efficiency (68% and 59% for Pb and AS, respectively) were observed in the medium containing urea of 300 mM and CaCl2 of 75 mM at pH 9.0. Fourier transform infrared spectroscopy result revealed the formation of metal carbonates by the isolate MG. Sequential extraction of metals revealed that the carbonate fractions of As and Pb were increased to 46.4% and 42.4% in bioremediated soil, whereas in control they were 35.5% and 32.5%, respectively. The X-ray powder diffraction result further confirmed the role of calcite precipitate in bioremediation of As- and Pb-contaminated soils. The results points out that the microbiologically-induced calcite precipitation is a feasible, eco-friendly technology for the bioremediation of As- and Pb-contaminated sites.

Efficacy of vermitechnology integration with Upflow Anaerobic Sludge Blanket (UASB) and activated sludge for metal stabilization: A compliance study on fractionation and biosorption

Efficacy of vermi-transformation for metal partitioning and transformation from Upflow Anaerobic Sludge Blanket (UASB) and Activated Sludge (AS) was investigated. Sludge samples were mixed with cow dung (CD) in two combinations (1:1 (UASB/AS:CD)) & (2:1(UASB/AS: CD)). Fractionation study revealed that Zn, Cd & Pb were associated with reducible fractions, and Cr, Cu with oxidizable fractions. Higher removal efficiency for 1:1 (UASB/AS: CD) combination over 2:1 (UASB/AS: CD) implies the non-significant contribution of cow dung during the metal stabilization process. After vermi-remediation, maximum metal removal was achieved at 1:1 ratio than 2:1 in AS. In UASB, 1:1 ratio worked better for Cr, Zn & Cd, whereas for Cu & Zn 2:1 ratio resulted in efficient removal. Overall for both AS and UASB, efficiency was found to be higher in 1:1 treatment ratio. The value of Kd (Bio sorption) was highest in Cu followed by Cr, which indicates the closer association with the metal bound organic matter (R2 ≥ 0.99). Based on the compliance study between two estimated sorption coefficients Kd (Biosorption & Fractions), vermi-remediation was found to be effective for AS than UASB. Therefore, the obtained results clearly validate the feasibility of integration of vermi-remediation as a potential promising ecological techniques for removing metal contaminant from the wastewater. Further research is required to study the decontamination of emerging contaminants with such integrated technology, which have physico-chemical properties different than metal ions.

Removal Methods of Heavy Metals from Laboratory Wastewater

The removal of heavy metals from the environment is the special concern due to their persistence without degradation. Methods for treating laboratory and industrial wastewater containing heavy metals often involve technologies for reduction of toxicity in order to meet technology-based treatment standards. Physico-chemical removal processes such as; adsorption on new adsorbents, ion exchange, membrane filtration, electrodialysis, reverse osmosis, and ultrafiltration were discussed. Their advantages and drawbacks in application were evaluated. In the processes of biological treatments microorganisms play a role of settling solids in the solution. Activated sludge, trickling filters, stabilization ponds are widely used for treating industrial wastewater. Bioadsorption is a new biological method and various low cost bioadsorbents (agricultural waste, forest waste, industrial waste, algae etc.) are used for maximum removal of heavy metals from wastewater. Bioadsorption techniques are eco friendly best solutions for removing heavy metals from wastewater rather than physic-chemical methods. But chemical methods are most suitable treatments for toxic inorganic compounds produced from various industries which cannot removed from any biological and physical techniques. Keywords: Heavy metals; removal techniques; Bioadsorption; physico-chemical treatments DOI : 10.7176/JNSR/9-2-04

Investigating metal removal potential of aquatic macrophytes at different harvest regimes to maximize remediation of metal contaminated wastewater in constructed wetland

In present study, the metal accumulation potential and growth dynamics of two aquatic macrophytes viz. Sagittaria sagittifolia and Colocasia esculenta were investigated at varying harvest time and frequency for maximum metal removal from mixed industrial wastewater employing horizontal flow constructed wetland (CW) technology. Both plant species were harvested five times i.e. 0, 30, 60, 90 and 120 days during experiment. S. sagittifolia attained maximum biomass (216.2 g dw m−1) and growth rate (1.25 g plant−1 day−1) at H3, whilst that of C. esculenta (204.3 g dw m−1 and 1.01 g plant−1 day−1 respectively) at H4. The plant species also differed in their metal uptake capability. With exception of Cr, other heavy metals viz. Zn, Cu and Cd accumulated more in S. sagittifolia than C. esculenta. In general, the metal uptake efficiency of S. sagittifolia was higher than that of C. esculenta, which increased up to H3 in former, whilst up to H4 in latter. The maximum Zn, Cu and Cd removal (115.55, 53.78 and 4.26 g/wetland respectively) was observed by S. sagittifolia in CW1, whilst Cr removal (12.79 g/wetland) by C.esculenta was recorded in CW2. Both plants showed metal tolerance ability in terms of reduced and oxidized glutathione content in their leaves. As such, the optimum harvesting regimes (time and frequency) in sequential manner accumulating maximum metals could enhance the metal removal efficiency of aquatic macrophytes.