Woosik Jung

DEFLUORIDATION FROM AQUEOUS SOLUTIONS BY GRANULAR FERRIC HYDROXIDE (GFH)

This research was undertaken to evaluate the feasibility of granular ferric hydroxide (GFH) for fluoride removal from aqueous solutions. Batch experiments were performed to study the influence of various experimental parameters such as contact time (1 min-24h), initial fluoride concentration (1-100 mgL(-1)), temperature (10 and 25 degrees C), pH (3-12) and the presence of competing anions on the adsorption of fluoride on GFH. Kinetic data revealed that the uptake rate of fluoride was rapid in the beginning and 95% adsorption was completed within 10 min and equilibrium was achieved within 60 min. The sorption process was well explained with pseudo-first-order and pore diffusion models. The maximum adsorption capacity of GFH for fluoride removal was 7.0 mgg(-1). The adsorption was found to be an endothermic process and data conform to Langmuir model. The optimum fluoride removal was observed between pH ranges of 4-8. The fluoride adsorption was decreased in the presence of phosphate followed by carbonate and sulphate. Results from this study demonstrated potential utility of GFH that could be developed into a viable technology for fluoride removal from drinking water.

Removal of nitrate from water by adsorption onto zinc chloride treated activated carbon

Abstract Adsorption study with untreated and zinc chloride (ZnCl2) treated coconut granular activated carbon (GAC) for nitrate removal from water has been carried out. Untreated coconut GAC was treated with ZnCl2 and carbonized. The optimal conditions were selected by studying the influence of process variables such as chemical ratio and activation temperature. Experimental results reveal that chemical weight ratio of 200% and temperature of 500°C was found to be optimum for the maximum removal of nitrate from water. Both untreated and ZnCl2 treated coconut GACs were characterized by scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) N2‐gas adsorption, surface area and Energy Dispersive X‐Ray (EDX) analysis. The comparison between untreated and ZnCl2 treated GAC indicates that treatment with ZnCl2 has significantly improved the adsorption efficacy of untreated GAC. The adsorption capacity of untreated and ZnCl2 treated coconut GACs were found 1.7 and 10.2 mg/g, respectively. The adsorption of nitrate on ZnCl2 treated coconut GAC was studied as a function of contact time, initial concentration of nitrate anion, temperature, and pH by batch mode adsorption experiments. The kinetic study reveals that equilibrium was achieved within one hour. The adsorption data conform best fit to the Langmuir isotherm. Kinetic study results reveal that present adsorption system followed a pseudo‐second‐order kinetics with pore‐diffusion‐controlled. Results of the present study recommend that the adsorption process using ZnCl2 treated coconut GAC might be a promising innovative technology in future for nitrates removal from drinking water.

Photoautotrophic hydrogen production by eukaryotic microalgae under aerobic conditions

Eukaryotic algae and cyanobacteria produce hydrogen under anaerobic and limited aerobic conditions. Here we show that novel microalgal strains (Chlorella vulgaris YSL01 and YSL16) upregulate the expression of the hydrogenase gene (HYDA) and simultaneously produce hydrogen through photosynthesis, using CO2 as the sole source of carbon under aerobic conditions with continuous illumination. We employ dissolved oxygen regimes that represent natural aquatic conditions for microalgae. The experimental expression of HYDA and the specific activity of hydrogenase demonstrate that C. vulgaris YSL01 and YSL16 enzymatically produce hydrogen, even under atmospheric conditions, which was previously considered infeasible. Photoautotrophic H2 production has important implications for assessing ecological and algae-based photolysis.

ADSORPTION OF COBALT ONTO GRAPHITE NANOCARBON–IMPREGNATED ALGINATE BEADS: EQUILIBRIUM, KINETICS, AND THERMODYNAMICS STUDIES

A novel adsorbent was developed impregnating graphite nanocarbon (GNC) into alginate beads (AB) for efficient cobalt (Co(II)) removal from an aqueous solution. Physicochemical and spectroscopic properties of graphite nanocarbon–impregnated alginate beads (ABGNC) were characterized and compared with those of AB. Co(II) adsorption on ABGNC was quantitatively evaluated by determining kinetics and thermodynamics parameters. The Co(II) adsorption capacity onto ABGNC was highest at neutral pH condition. Increasing the temperature from 288 to 318 K resulted in a 2.5-fold higher Co(II) adsorption onto AB, while thermal dependence of Co(II) adsorption on ABGNC was not found. Kinetic studies showed an applicability of the pseudo-second-order kinetic model for both AB and ABGNC. Monolayer adsorption was the dominant mechanism of Co(II) adsorption on both AB and ABGNC. Thermodynamic studies revealed that Co(II) adsorption was an endothermic and spontaneous process. Positive values of entropy indicate randomness in solid/aqueous phases, and mean free energy (E a ) fits in the range of chemisorption.

Removal of arsenate and arsenite from aqueous solution by adsorption on clay minerals

Sorption of arsenic species [As(V) and As(III)] on different clay minerals including kaolinite (KGa-1), montmorillonite (SWy-1), and nontronites (NAU-1 and NAU-2) with respect to sorption kinetics, isotherms and pH was investigated. As(V) and As(III) sorption on clay minerals was significantly influenced by pH. Higher sorption of As(V) was observed at low pH that decreased above pH 5.0, while As(III) sorption was maximum around pH 7.0. The sorption kinetics was well described by the pseudo-second-order equation for both As(V) and As(III). Among the tested clay minerals, NAU-2 was most effective for the removal of arsenic with rate constants of 0.084 and 0.056 g mg− 1 min− 1 for As(V) and As(III), respectively. A good correlation was observed between adsorbing capacity (qe) and equilibrium mass concentration (Ce) using the isothermal Freundlich adsorption model for SWy-1, NAU-1, and NAU-2 minerals as indicated by the high values of R2 coefficient. Our results indicate that clay minerals can serve as effective sorbents for the removal of As from contaminated water streams.

Adsorption of Pb(II) and Ni(II) from aqueous solution by nanosized graphite carbon-impregnated calcium alginate bead

A composite adsorbent was prepared by immobilizing nanosized graphite carbon, obtained from an electrochemical process, in calcium alginate beads to remove Pb(II) and Ni(II) from aqueous solution. Potential of the adsorbent was evaluated by comparing adsorption kinetics and capacity of the nanosized graphite carbon-impregnated calcium alginate beads (NGCAB) with those of the pure calcium alginate beads (AB) in batch experimental reactors. Kinetic studies indicated that both ions onto AB and NGCAB reached adsorption equilibria at 16 and 12 h, respectively, and the experimental kinetic data were well described by a pseudo-second-order regression model. Relatively rapid uptake of both ions occurred within the first 2 h, followed by slower sorption process which was well explained by the intraparticle diffusion model of Weber and Morris. The maximum equilibrium uptake of Pb(II) and Ni(II) by NGCAB with the initial concentration range of 903 and 1023 mg/L were approximately 460.9 and 93.3 mg/g, respectively. Adsorption isotherm of Pb(II) onto AB was well fitted by Langmuir isotherm model, while that of NGCAB showed a good prediction using the Freundlich isotherm model. The Freundlich isotherm model was more suitable to describe Ni(II) adsorption by both adsorbents. The overall results demonstrated a potential applicability of NGCAB for Pb(II) and Ni(II) removal from aqueous solutions.

Enhanced iron oxidation to improve AMD treatment

Fe(II) and acidity are the most commonly encountered contaminants in acid mine drainage (AMD). Passive treatment for AMD involves addition of alkalinity, aerobic processes that result in oxidation of Fe(II) to Fe(III) oxides, and anoxic treatments in which sulfate is reduced to sulfide with consequent precipitation of Fe(II) sulfides. Alkalinity is usually provided by dissolution of limestone in passive treatments or by addition of lime or caustic in active systems. This paper focuses on the chemistry of AMD treatment, the mechanisms and the rates of oxidation of Fe(II) to produce Fe(III) oxides and strategies that can be used to manipulate the treatment chemistry in order to control the rate of oxidation and the quality of the residual Fe(III) oxides.