Initial Heavy Metal Concentration Research Articles

Highly efficient removal of Cd(II) ions by composite of GO and layered double hydroxide composite

Herein, we report a novel nanocomposite (graphene oxide/Ni-Co LDH) via a simple and effective chemical precipitation route. First, the GO nanosheets were synthesized by Marcano method, and then, Ni-Co LDH sheets were deposited on the surface of GO by chemical precipitation. The synthesized nanocomposite was characterized by field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy and x-ray diffraction measurements. The prepared nanocomposite was investigated as an adsorbent for cadmium (II) ions removal from aqueous solutions. Batch studies have been done for obtaining optimal experimental conditions for maximizing metal sorption on the nanocomposite. The nanocomposite shows highest adsorption capacity toward Cd(II) in aqueous solution (126.58 mg g−1). The influence of experimental parameters like time of contact between adsorbent and adsorbate, pH, adsorbent dosage, initial heavy metal concentration and temperature on the removal efficiency of Cd(II) ions was extensively investigated. Kinetic and isotherm parameters of adsorption of Cd(II) were also evaluated. The pH = 7 was chosen as an optimal pH for study of the Cd(II) removal from aqueous solutions. Langmuir isotherm and pseudo-second-order kinetic models were fitted well with experimental data of Cd(II) removal. The reusability of nanocomposite exhibited reasonable values. However, the current nanocomposite could be used as a new adsorbate for adsorption of Cd(II) from contaminant water sources.

Effective removal of heavy metals by nanosized hydrous zirconia composite hydrogel and adsorption behavior study

A novel type of adsorbent, hydrous zirconium oxide (HZO) based on polymer hydrogel (HZO-P(TAA/HEA) hydrogel), was synthesized by irradiation polymerization and in situ precipitation methods to remove heavy metals from water efficiently. The composite hydrogel was characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), swelling kinetics, zeta potential, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The results indicated that HZO nanoparticles were stably loaded on the P(TAA/HEA) hydrogel, swelling properties, and thermal stability were also enhanced after the loading of HZO. Besides, the batch adsorption experiments revealed that adsorption time, pH, initial concentration of heavy metals, and coexisting ions influenced the adsorption process significantly. The adsorption capacities of HZO-P(TAA/HEA) hydrogel for Pb2+, Cu2+, Cd2+, and Ni2+ was 0.620mmolg-1, 0.615mmolg-1, 0.701mmolg-1, and 0.700mmolg-1, respectively. The adsorption isotherms fitted Langmuir equation well, and the adsorption kinetics followed second-order kinetics; it was manifested that the priority of competitive adsorption followed the order: Pb2+ > Cu2+ > Ni2+ > Cd2+. Furthermore, based on the analysis results of FTIR and XPS, the adsorption mechanism could mainly be the complexation between hydrous zirconia and heavy metals. The results indicate that nanocomposite HZO-P(TAA/HEA) hydrogel is a promising heavy metal adsorbent.

Adsorption of heavy metal tolerance strains to Pb2+ and Cd2+ in wastewater.

The functional strains with high tolerance to heavy metal Pb2+ and Cd2+ were screened from soil obtained in a heavy metal waste accumulation area. The immobilized biological adsorbent was made by embedding method and used for treatment of wastewater containing heavy metals. The effects of initial concentration of heavy metals, adsorption time, pH value of wastewater, and dosage of adsorbent on adsorption performance were investigated. The study showed (1) the strains tested were Brevibacterium and their maximum tolerable concentrations for Pb2+ and Cd2+ were 2200 and 700mg/L, respectively; (2) the maximum adsorption rate for Pb2+ and Cd2+ was 87.77% and 57.50% respectively when the dosage of adsorbent was 10g/L and the pH value of wastewater was 6; (3) Pb2+ and Cd2+ could be adsorbed in the equilibrium solution for 40min and the maximum adsorption capacity reached 114.36mg/g and 82.12mg/g, respectively; and (4) when the initial pH value of the wastewater was 5-7, the adsorption rate decreased with the increase of the concentration, and the initial concentration of Pb2+ had a greater effect on the adsorption rate than Cd2+. Langmuir and Freundlich equation showed that the adsorption of Pb2+ and Cd2+ was mainly on the surface of monolayer. And the pseudo-second-order kinetic equation indicates that Cd2+ has a relatively greater adsorption rate than Pb2+ does.

Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation

In this study, a comparative evaluation of floating and submerged macrophytes was performed. Azolla filiculoides (free floating) and Hydrilla verticillata (submerged) aquatic macrophytes were utilized for arsenic, copper, chromium and lead removal from the respective metallic ion solutions. Batch experiments were performed initially with optimization of different physical parameters viz., pH, initial heavy metal concentration, biosorbent dosage, contact time, temperature and agitation speed. Submerged (Hydrilla verticillata) had depicted better removal efficiency in comparison to the floating macrophyte (Azolla filiculoides). Field emission scanning electron microscopy equipped with energy dispersive spectroscopy and Fourier transform infrared spectroscopy analysis was performed for the characterization of the metal loaded biosorbents. Biosorption of the respective heavy metal was clearly depicted in the FESEM-EDX spectrum, although not much change in the morphology of the biosorbents were examined. FTIR spectra of the biosorbents obtained after the experiments confirmed the involvement of C–H bend, –CH2–(C=O), N–H, –C–O, R2–C= bending and –C–C=O on the biomass. Furthermore, the biosorbent regeneration followed by heavy metal biosorption confirmed the reusability of the prepared biosorbent for at least two consecutive cycles without much significant change in the heavy metal biosorption capacity.

Carboxyl functionalized Cinnamomum camphora for removal of heavy metals from synthetic wastewater-contribution to sustainability in agroforestry

Abstract Biosorption of heavy metals (HMs) using agricultural and forestry wastes (AFWs) attracts much attention due to numerous advantages, but more studies are necessary to develop effective biosorbent using locally available AFWs. Cinnamomum camphora leaves were used for HMs removal from synthetic wastewater. Carboxyl functionalized camphor leaf (CFCL) was prepared by a two-step modification including alkalization and carboxylation. Sorption of Cd(II), Cu(II) and Ni(II) was evaluated at different CFCL dose, pH, contact time and initial concentration of HMs. Experimental data were examined by sorption isotherms, kinetic models and thermodynamics equations. XPS, FTIR, XRD and SEM verify the introduction of carboxyl groups on CFCL and reveal sorption mechanism. CFCL is effective for fast removing metal ions with low concentration. The removal rate reaches 99%, and the maximum sorption capacity is 62.42 mg g−1 Cd(II), 49.96 mg g−1 Cu(II), and 26.42 mg g−1 Ni(II), respectively. Sorption of Cd(II), Cu(II) and Ni(II) onto CFCL is spontaneous and follows pseudo-second order and Langmuir model. CFCL also shows a good regeneration and cycling performance. This work suggests that the modified camphor leaf has remarkable potential as biosorbent for fast removal of HMs. Conversion of camphor leaf into value-added biosorbent reduces its negative effects and HMs pollution, providing a sustainable way to utilize agricultural and forestry wastes.

The removal of heavy metal ions from aqueous solutions by hydrogels based on N-isopropylacrylamide and acrylic acid

The temperature- and pH-sensitive poly(N-isopropylacrylamide-co-acrylic acid) hydrogels, poly(NIPAM-co-AA), were synthesized by radical polymerization. The characterizations of hydrogels based on N-isopropylacrylamide (NIPAM) and acrylic acid (AA) before and after adsorption of heavy metal ions was performed by Fourier transform infrared spectroscopy and scanning electron microscopy. Heavy metal ions (Cr, Mn, Pb) adsorbed onto poly(NIPAM-co-AA) hydrogels were identified using the energy-dispersive X-ray spectroscopy. The mechanism of the water transport within the matrix of synthesized poly(NIPAM-co-AA) hydrogels at pH 4.5 is Super Case II diffusion, and at pH 6.8 corresponds to the non-Fickian diffusion mechanism. The effect of pH, temperature, contact time, and the initial concentration of heavy metals on the adsorption process of Cr(VI), Mn(II), and Pb(II) ions from aqueous solutions onto poly(NIPAM-co-AA) hydrogels were investigated. The kinetic and equilibrium data were best fitted by the pseudo-second-order model and Langmuir adsorption isotherm. Thermodynamic results indicate that the removal process of heavy metal ions from aqueous solutions by poly(NIPAM-co-AA) hydrogels was spontaneous and exothermic in nature. Maximum adsorption capacities of poly(NIPAM-co-AA) hydrogels for heavy metal ions decrease in the following order: Pb(II) > Cr(VI) > Mn(II).

Adsorption Behavior of Manganese Dioxide Towards Heavy Metal Ions: Surface Zeta Potential Effect

The zeta potential of hydrous manganese dioxide (HMO) may significantly influence its adsorption towards heavy metals. The effect of zeta potential of HMO on adsorption efficiency of three heavy metal ions, Pb(II), Cd(II), and Ni(II), was investigated. The zeta potential values decreased with decreasing Mn2+/MnO 4 − ratio in the HMO synthesis. The larger adsorption capacity was observed for HMO with more negative zeta potentials, and its zeta potential values increased after the adsorption of Pb(II), Cd(II), and Ni(II). The adsorption equilibrium of HMO at 303.15 K could be well described by Langmuir isotherm equation with qmax value of 502.85 mg/g for Pb(II), 155.11 mg/g for Cd(II), and 87.52 mg/g for Ni(II), respectively. Higher initial heavy metal concentration and solution pH both favored the enhancement of adsorption capacity. The pseudo-second-order equation could best fit the adsorption process. Furthermore, the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that Pb(II), Cd(II), and Ni(II) may form inner-sphere complex on HMO surface. In addition, HMO adsorbent can be regenerated readily by treating with 50% KMnO4 solutions. After five rounds, the zeta potential value decreased to − 50.6 mV and the Pb(II) removal efficiency is 91% as compared to previous HMO removal efficiency of 93%. These findings revealed that the surface zeta potential of HMO adsorbent might be used as a parameter to determine its performance for the removal of heavy metals from contaminated water.

Preparation and characterization of the eco-friendly chitosan/vermiculite biocomposite with excellent removal capacity for cadmium and lead

The chitosan/vermiculite biocomposite (CTS-VMT) was synthesized successfully with epichlorohydrin (ECH) cross-linking agent and used to remove cadmium and lead from the aqueous solution. CTS-VMT was characterized by FTIR, SEM, BET, TG-DTG, zeta potential and XPS. The effects of critical parameters including solution pH, contact time, initial heavy-metal concentration and adsorbent regeneration were investigated. Besides, adsorption mechanisms were also researched. The results indicated that chitosan molecule cannot intercalate into the interlayer space but cross link on the external surface of VMT. The maximum adsorption capacities for Cd(II) and Pb(II) were 58.48 mg g− 1 and 166.67 mg g− 1 at pH 4, respectively. The adsorption process fitted well the pseudo-second-order model and the adsorption isotherms could be correctly simulated by the Langmuir isotherm model. The zeta potential analyses put forward that electrostatic attraction existed in the adsorption process between the metal cations and CTS-VMT. However, the principal mechanism for adsorption on CTS-VMT was chelation according to the kinetic study and XPS analyses. Moreover, the desorption experiments revealed the prepared adsorbent tended to be regenerated by using HCl and the removal rations for four cycles were all > 90%. Therefore, the synthesized CTS-VMT in this study has the potential to be utilized as an eco-friendly adsorbent for removing Cd(II) and Pb(II).

English

Indigenous bacteria and fungi were isolated from soil obtained from a metal scrap dumpsite in Ibadan, Nigeria. Soil sample analyses showed presence of calcium, iron, magnesium, zinc, manganese and copper. A selective isolation of microorganisms was done using heavy metal constituted growth media at concentration of 25 mg/L. Lactobacillus casei was isolated from cadmium and lead composed growth media, Corynebacterium xerosis and Corynebacterium kutsceri from nickel composed growth media. Aspergillus niger and Histoplasma capsulatum were isolated from growth media composed of nickel and lead respectively at a 25 mg/L concentration. Growths were observed for all isolates at 50mg/L, 100mg/L and 400mg/L composed growth media. A 7 day bio-treatment process with isolates for uptake of heavy metals from growth media solution at 50 mg/L concentration of heavy metal was done. Histoplasma capsulatum, Aspergillus fumigatus and Aspergillus niger reduced the heavy metal concentrations in lead, nickel and cadmium to 6, 18.12 and 12.45 mg/L respectively. Lactobacillus casei, and C. xerosis reduced the heavy metal concentration of cadmium, lead and nickel to 13.55, 33, 25, 22.38, 15.45 and 29.11 mg/L respectively. These microorganisms reduced the initial concentration of heavy metals and could thus be used for bioremediation processes. Key words: Bioremediation, biotreatment, bacteria, fungi.

Adsorptive Removal of Arsenic and Mercury from Aqueous Solutions by Eucalyptus Leaves

The study is a first-time investigation into the use of Eucalyptus leaves as a low-cost herbal adsorbent for the removal of arsenic (As) and mercury (Hg) from aqueous solutions. The adsorption capacity and efficiency were studied under various operating conditions within the framework of response surface methodology (RSM) by implementing a four-factor, five-level Box–Wilson central composite design (CCD). A pH range of 3–9, contact time (t) of 5–90 min, initial heavy metal (As or Hg) concentration (C 0) of 0.5–3.875 mg/L, and adsorbent dose (m) of 0.5–2.5 g/L were studied for the optimization and modeling of the process. The adsorption mechanism and the relevant characteristic parameters were investigated by four two-parameter (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) isotherm models and four kinetic models (Lagergren’s pseudo-first order (PFO), Ho and McKay’s pseudo-second order (PSO), Weber–Morris intraparticle diffusion, and modified Freundlich). The new nonlinear regression-based empirical equations, which were derived within the scope of the study, showed that it might be possible to obtain a removal efficiency for As and Hg above 94% at the optimum conditions of the present process-related variables (pH = 6.0, t = 47.5 min, C 0 = 2.75 mg/L, and m = 1.5 mg/L). Based on the Langmuir isotherm model, the maximum adsorption or uptake capacity of As and Hg was determined as 84.03 and 129.87 mg/g, respectively. The results of the kinetic modeling indicated that the adsorption kinetics of As and Hg were very well described by Lagergren’s PFO kinetic model (R 2 = 0.978) and the modified Freundlich kinetic model (R 2 = 0.984), respectively. The findings of this study clearly concluded that the Persian Eucalyptus leaves demonstrated a higher performance compared to several other reported adsorbents used for the removal of heavy metals from the aqueous environment.

Response Surface Methodology Optimization of Cobalt (II) and Lead (II) Removal from Aqueous Solution Using MWCNT-Fe3O4 Nanocomposite

The present investigation describes the evaluation of feasibility of MWCNT-Fe3O4 nanocomposite toward adsorptive removal of Co(II) and Pb(II) from aqueous solution in batch mode. The Fe3O4–MWCNT hybrid was prepared using a simple one-pot strategy via in situ growth of Fe3O4 magnetic nanoparticles onto the surface of the MWCNTs. The Fe3O4–MWCNT hybrid was characterized by X-ray diffractometry and Field Emission Scanning Electron Microscopy (FESEM). A Response Surface Methodology (RSM) with a Central Composite Design (CCD) was employed to evaluate the effects of solution pH, contact time, temperature, initial heavy metal concentration and adsorbent dosage on the removal efficiency of the heavy metals. Results of analysis of variance (ANOVA) showed that the initial metal concentration and absorbent dosage and their interaction effect were the most significant parameters for Co(II) ion removal. Adsorbent dosage, pH and initial metal concentration had significant influences on the removal efficiency of Pb(II) ions. The optimum pH, time, temperature, initial concentration of metals and adsorbent dosage were found to be 6.5,25 min, 40 °C, 35 mg/L, and 48.3 mg/50mL, respectively. Maximum removal of Pb(II) and Co(II) in optimum condition was 90.2 and 79.34% respectively. Results indicated that nanocomposite can be used as an effective adsorbent for effluent decontamination especially in Pb–Co bearing wastewaters. The equilibrium data were well fitted by the Langmuir model. The removal mechanism of metal ions followed adsorption and ion exchange processes.

Magnetically responsive gels based on crosslinked gelatin: An overview on the synthesis, properties, and their potential in water remediation

ABSTRACTEfficient adsorbent ferrogels based on gelatin and dextrose were synthetized using freeze-thawing technique. Two different methodologies of magnetic particles incorporation were developed. An exhaustive morphologic and thermal characterization of hydro and ferrogels was achieved. The performance of ferrogel in water remediation was tested using Cd(II) as model contaminant. The adsorption ability was evaluated as a function of pH, initial heavy metal concentration, and contact time. The maximum adsorption capacity was 35 mg of Cd(II)/g of adsorbent. Ferrogel was regenerated by washing with distilled water, maintaining efficiency of almost 30% after the fourth cycle.

Polyaspartate extraction of cadmium ions from contaminated soil: Evaluation and optimization using central composite design

The occurrences of heavy metal contaminated sites and soils and the need for devising environmentally friendly solutions have become global issues of serious concern. In this study, polyaspartate (a highly biodegradable agent) was synthesized using L-Aspartic acid via a new modified thermal procedure and employed for extraction of cadmium ions (Cd) from contaminated soil. Response surface methodology approach using 35 full faced centered central composite design was employed for modeling, evaluating and optimizing the influence of polyaspartate concentration (36–145mM), polyaspartate/soil ratio (5–25), initial heavy metal concentration (100–500mg/kg), initial pH (3–6) and extraction time (6–24h) on Cd ions extracted into the polyaspartate solution and its residual concentration in the treated soil. The Cd extraction efficacy obtained reached up to 98.8%. Increase in Cd extraction efficiency was associated with increase in the polyaspartate and Cd concentration coupled with lower polyaspertate/soil ratio and initial pH. Under the optimal conditions characterized with minimal utilization of the polyaspartate and high Cd ions removal, the extractible Cd in the polyaspartate solution reached up to 84.4mg/L which yielded 85% Cd extraction efficacy. This study demonstrates the suitability of using polyaspartate as an effective environmentally friendly chelating agent for Cd extraction from contaminated soils.

Removal of Pb(II) and Cr(VI) from aqueous solutions using the fly ash-based adsorbent material-supported zero-valent iron

In this study, a granular adsorbent material containing zero valent iron (ZVI-GAM) was made with fly ash as skeletal material, bentonite as binder and Enteromorpha prolifera as pore former. Zero-valent iron was synthesized by direct reduction of iron ore tailings with the coke as reductant at 900°C in the anoxic atmosphere. SEM/EDX, XRD, FTIR and BET analysis were used to characterize ZVI-GAM. SEM image showed that there were many different size pores in ZVI-GAM. XRD analysis indicated the presence of iron in zero-valent state. FTIR analysis revealed that the surface of ZVI-GAM owned the groups responsible for the heavy metals adsorption. The specific surface area of ZVI-GAM was 8.19m2/g. ZVI-GAM was used as reaction and adsorbent material for the removal of Pb(II) and Cr(VI) from aqueous solutions. The factors affecting Pb(II) and Cr(VI) ions removal by ZVI-GAM in a batch model were studied including initial heavy metal concentrations, contact time, adsorbent dosage, pH values and temperature. Maximum removal capacity for Pb(II) and Cr(VI) by ZVI-GAM was found to be 78.13mg/g and 15.70mg/g. ZVI-GAM had the best adsorption and reduction capacity for Cr(VI) and Pb(II) and could reduce Cr(VI) to Cr(III) and Pb(II) to Pb0. Therefore, ZVI-GAM was an effective, low-cost and recyclable material and had great potential to be a promising technique for heavy metal remediation.

Simultaneous removal of aqueous Zn2+, Cu2+, Cd2+, and Pb2+ by zeolites synthesized from low-calcium and high-calcium fly ash

In this study, zeolites were synthesized from low-calcium (LCZ) and high-calcium (HCZ) fly ash, respectively. Subsequently, the zeolites were tested for their removal effectiveness for four aqueous cations, namely, Zn2+, Cu2+, Cd2+, and Pb2+, as a function of contact time, pH value, adsorbent dosage, and initial concentration of heavy metals. Both zeolites were characterized by X-ray diffraction, X-ray fluorescence spectrometry, scanning electron microscopy, specific surface area, and cation exchange capacity. The results show that HCZ mainly consists of an unnamed zeolite (Na6[AlSiO4]6·4H2O), whereas LCZ mainly consists of faujasite-type zeolite. The optimum sorption conditions were pH = 6.0; adsorbent dosage = 1.0 g·L-1; temperature = 25 °C; contact time = 100 min; and initial heavy metal concentration = 100 mg·L-1. The sorption kinetics of the four aqueous cations on both LCZ and HCZ followed the pseudo-second-order kinetic model, and the sorption isotherm data fitted well with the Langmuir isotherm model. For LCZ, the maximum adsorption capacities of Zn2+, Cu2+, Cd2+, and Pb2+ were 155.76, 197.86, 123.76, and 186.22 mg·g-1, respectively. For HCZ, the values were 154.08, 183.15, 118.91, and 191.94 mg·g-1, respectively. The zeolites were regenerated by NaCl solution (1 mol·L-1) and showed high removal efficiency. In conclusion, zeolites produced by fly ash are promising materials for removing Zn2+, Cu2+, Cd2+, and Pb2+ from wastewater.

Synthesis and application of magnetic chlorapatite nanoparticles for zinc (II), cadmium (II) and lead (II) removal from water solutions

Magnetic chlorapatite nanoparticles (MNCLAP) was synthesized and used as adsorbent to remove Zn2+, Cd2+ and Pb2+ from aqueous solutions. The synthesized MNCLAP was characterized by scanning electron microscopy (SEM), energy dispersive analysis system of X-ray (EDAX), transmission electron microscopy (TEM) X-ray powder diffraction (XRD) and magnetization curves. Influence of different sorption parameters, such as equilibration time, initial heavy metal concentration, the amount of MNCLAP, pH values and competition adsorption were investigated in this study. Moreover, the desorption experiment was also carried out to explore the adsorption property of MNCLAP. The adsorption kinetic data has a very high correlation coefficient (R2=0.9999) with the pseudo-second-order kinetic model, and the Langmuir model was used in describing adsorption isotherms. The maximum adsorption capacities of MNCLAP adsorbent towards Zn2+, Cd2+ and Pb2+ were 1.1769, 1.1022 and 1.1546mmolg−1, respectively. EDTA solution was the best efficient eluant for heavy metal desorption with 25.94%, 22.95% and 32.84% released rate of Zn2+, Cd2+ and Pb2+, respectively. Experimental results revealed that the prepared MNCLAP combined both the properties of chlorapatite and magnetic material and it showed remarkable advantages in heavy metal removal from aqueous solutions.

Removal of Ni and Cd ions from aqueous solution using iron dust-zeolite composite: Analysis by thermodynamic, kinetic and isotherm studies

To examine the effectiveness of iron dust-zeolite composite as an adsorbent for the removal of heavy metal ions from aqueous solutions, the adsorption isotherms, the kinetic, thermodynamic and optimum conditions such as initial concentration, pH, contact time, adsorbent dosage and competitive adsorption conditions of heavy metals were investigated. The characterization of the composite was characterized via FTIR, SEM, XRF and XRD methods. Kinetic results on the removal of heavy metal ions from aqueous solutions have been well described by the pseudo-second-order model. The adsorption data for Cd and Ni ions were fitted well with the Langmuir and Freundlich isotherm models, respectively. The maximum adsorption capacities of iron dust-zeolite for Cd and Ni ions were equal to 78.125 and 76.33 mg/g, respectively. The thermodynamic parameters such as enthalpy, entropy and free energy of adsorption of metal ions were determined. It was found that the process is endothermic, favorable and spontaneous. The competitive adsorption ability of heavy metal ions in the binary system on the composite showed that Cd ions had a synergistic effect on the adsorption of Ni and Ni ions had the negative effect on Cd adsorption.

Influence of voltage input to heavy metal removal from electroplating wastewater using electrocoagulation process

In medium capacity, electroplating industry usually treats wastewater until 5 m3 per day. Heavy metal content becomes concern that should be reduced. Previous studies performed electrocoagulation method on laboratory scale, either batch or continuous. This study was aimed to compare the influence of voltage input variation into heavy metal removal in electroplating wastewater treatment using electrocoagulation process on laboratory-scale in order to determine the optimum condition for scaling up the reactor into pilot-scale. The laboratory study was performed in 1.5 L glass reactor in batch system using wastewater from electroplating industry, the voltage input varied at 20, 30 and 40 volt. The electrode consisted of aluminium 32 cm2 as sacrifice anode and copper 32 cm2 as cathode. During 120 min electrocoagulation process, the pH value was measured using pH meter, whereas the heavy metal of chromium, copper, iron, and zinc concentration were analysed using Atomic Absorption Spectrophotometer (AAS). Result showed that removal of heavy metals from wastewater increased due to the increasing of voltage input. Different initial concentration of heavy metals on wastewater, resulted the different detention time. At pilot-scale reactor with 30 V voltage input, chromium, iron, and zinc reached removal efficiency until 89-98%, when copper reached 79% efficiency. At 40V, removal efficiencies increased on same detention time, i.e. chromium, iron, and zinc reached 89-99%, whereas copper reached 85%. These removal efficiencies have complied the government standard except for copper that had higher initial concentration in wastewater. Kinetic rate also calculated in this study as the basic factor for scaling up the process.

Removal of cadmium and zinc from contaminated wastewater using Rhodobacter sphaeroides.

Rhodobacter sphaeroides was used for bioremediation of wastewater polluted with cadmium (Cd) and zinc (Zn). The tolerance of the microorganism to selected heavy metals (HMs), as well as the effects of pH, temperature and inoculum size on the removal rate, was investigated. The remediation effects of R. sphaeroides were analysed at different initial concentrations of HMs. Bioremediation mechanisms were thoroughly discussed based on the results from the cell characterisation analysis. Cd and Zn could inhibit the growth of R. sphaeroides. However, Cd was more toxic than Zn, with corresponding EC50 values of 5.34 and 69.79 mg L-1. Temperature and pH had greater influence on the removal rate of HMs than inoculum size. The optimal conditions for temperature and pH were 35 °C-40 °C and pH 7, respectively. Initial concentration of HMs and remediation time also affected the removal rate. Rhodobacter sphaeroides had a relatively higher remediation effect under the present experimental conditions. The removal rates for Cd and Zn reached 97.92% and 97.76%, respectively. Results showed that biosorption and HM precipitation were the main bioremediation mechanisms. This information is necessary to better understand the removal mechanism of R. sphaeroides, and is significant for its pilot test and future practical application.

Response Surface Modeling of Rate of Replenishing Processing Fluids During Hybrid Electrokinetics-Adsorption Treatment of Saline-Sodic Soil

Due to the inherent nature of saline-sodic soils, rapid decomposition of the processing fluids during electrokinetic remediation (EKR) renders the process unstable. This study investigated the influence of voltage gradient, polarity reversal, initial concentration of heavy metals on the frequency of replenishing processing fluids via refilling or replacing during hybrid electrokinetics-adsorption (HEKA) remediation of contaminated saline-sodic clay soil. Fifteen (15) EKR experiments were conducted according to Box–Behnken design. Each experiment was continuously ran for 21 days. As result of predominant electroosmosis flow toward the cathode, replenishing the anolyte was primarily by refilling rather than replacement following its complete degradation, while vice versa was in case of the catholyte. For the optimization and interpretation of results, mathematical models (\(R^{2}\) of 81.67–96.84 %) were developed based on response surface methodology with and insignificant lack of fit. Voltage gradient was found to be the most influential parameter for rapid degradation of the processing fluids with resulting increase in the frequency of replenishing and higher current flow and electrical conductivity. Numerical optimization in conjunction with desirability function analysis were employed for the optimization of five (5) different scenarios from which the most desirable scenario yielded a desirability value of 0.61 at an optimal voltage gradient of 0.34 V/cm. Under this condition, the rate of replacement of the anolyte is approximately 2 as against the maximum rate of 32 that was encountered during the tests. This study demonstrates that an optimal voltage gradient that will ensure stability must be chosen to ensure HEKA remediation of saline-sodic soil effectiveness.