Jaeyoung Choi

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.

UV/TiO2 and UV/TiO2/chemical oxidant processes for the removal of humic acid, Cr and Cu in aqueous TiO2 suspensions

The objective of this study was to investigate the treatment efficiency of UV/TiO2 and UV/TiO2/chemical oxidant processes for the removal of humic acid and hazardous heavy metals in aqueous TiO2 suspensions. The reaction rate (k) of humic acid and hazardous heavy metals by UV/TiO2 was higher than that of UV illumination alone or TiO2 alone. The removal efficiency for humic acid and Cr(VI) at acid or neutral pH values was higher than that at basic pH values. However, the removal efficiency for Cu(II) at acid pH values was smaller compared with that at neutral or basic pH values. The reaction rate (k) of humic acid and hazardous heavy metals in the TiO2 concentration range of 0.1–0.3 g l−1 increased with increasing TiO2 dosage. However, amounts higher than a TiO2 dosage of 0.3 g l−1 reduced the removal efficiency for humic acid and hazardous heavy metals because of the shielding effect on the UV light penetration in the aqueous solution caused by the presence of excessive amounts of TiO2. The addition of oxidants to the UV/TiO2 system showed an increase in degradation efficiency for the treatment of humic acid and hazardous heavy metals. The optimal concentration of oxidants was: H2O2 50 mg l−1, O3 20 g m−3 and K2S2O8 50 mg l−1, respectively. The degradation efficiency of UV/TiO2/oxidant systems for the removal of humic acid and hazardous heavy metals was much greater when H2O2 was used as the oxidant.

Removal of nitrate and ammonium ions from livestock wastewater by hybrid systems composed of zero-valent iron and adsorbents

The feasibility of hybrid systems for simultaneous removal of nitrate (NO ) and ammonium ions (NH ) from livestock wastewater was examined in batch experiments. As a part of efforts to remove nitrate and ammonium simultaneously, Fe0 and adsorbents including coconut-based granular activated carbon (GAC), sepiolite and filtralite were used. Various parameters such as adsorbent dosages and temperature were studied. Removal of NO increased with increase in temperature. Maximum NO removal (85.3%) was observed for the Fe0–filtralite hybrid system at 45 °C for a 24 h reaction time. Increase in GAC and sepiolite dosages had significant (P<0.01) effect on the NH removal efficiency, which was primarily due to the net negative surface charge of the adsorbents. The efficiency of hybrid systems for the removal of NO was in the order of filtralite>sepiolite>GAC, and the order of the removal of NH was GAC>sepiolite>filtralite. The results of the present study suggest that the use of hybrid systems could be a promising innovative technology for achieving simultaneous removal of NO and NH from livestock wastewater.

Nitrate and ammonium ions removal from groundwater by a hybrid system of zero-valent iron combined with adsorbents

Nitrate (NO(3)(-)) is a commonly found contaminant in groundwater and surface water. It has created a major water quality problem worldwide. The laboratory batch experiments were conducted to investigate the feasibility of HCl-treated zero-valent iron (Fe(0)) combined with different adsorbents as hybrid systems for simultaneous removal of nitrate (NO(3)(-)) and ammonium (NH(4)(+)) ions from aqueous solution. The maximum NO(3)(-) removal in combined Fe(0)-granular activated carbon (GAC), Fe(0)-filtralite and Fe(0)-sepiolite systems was 86, 96 and 99%, respectively, at 45 °C for 24 h reaction time. The NO(3)(-) removal rate increased with the increase in initial NO(3)(-) concentration. The NO(3)(-) removal efficiency by hybrid systems was in the order of sepiolite > filtralite > GAC. The NH(4)(+) produced during the denitrification process by Fe(0) was successfully removed by the adsorbents, with the removal efficiency in the order of GAC > sepiolite > filtralite. Results of the present study suggest that the use of a hybrid system could be a promising technology for achieving simultaneous removal of NO(3)(-) and NH(4)(+) ions from aqueous solution.

Redox reaction of Fe(0) with As(V) sorbed onto goethite-coated sand under anoxic conditions

The objective of this study was to determine the applicability of reductive immobilization of As(V) by Fe(0) [zero valent iron (ZVI)] to the As contaminated soil. The experiments comprised reactions between ZVI and As(V) absorbed onto goethite-coated sand (GCS) simulating heterogeneous soil environment, and reactions between ZVI and dissolved As(V) simulating homogeneous environment. Arsenic(III+V) removal ratio in the heterogeneous system was lower than in the homogeneous system, which was due to the incomplete reduction of As(V) adsorbed onto GCS. Incomplete reduction might be caused by difficulty of desorption of As(V) or lower accessibility of ZVI to As(V) adsorbed onto GCS to react. Almost half of As(V) adsorbed onto GCS was instantly desorbed. Arsenic(III) produced by reaction between As(V) and ZVI was quickly removed by iron hydroxide including As(III). Effect of air injection for As removal in the heterogeneous system was smaller than in the homogeneous system because of difficulty in the oxidation of adsorbed Fe(II) on GCS in the heterogeneous system.