Byong-Hun Jeon

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.

Reactions of ferrous iron with hematite

Abstract The adsorption of Fe(II) onto hematite was measured as a function of pH, surface area, and time. The effects of anions (chloride, sulfate, or nitrate) and of Zn(II) were also determined. All experiments were conducted under strict anoxic conditions with 5 or 30 days for equilibration. Results showed that immobilization of Fe(II) on hematite consists of a fast sorption process and one or more slow processes, which probably include both sorption and formation of new phases. Sorption occurred at pH values as low as 4, which has not been reported in existing literature. Some Fe(II) could not be extracted after 20 h with 0.5 N HCl. In the presence of 0.01 M NaCl, all of the added Fe(II) was recovered when pH was below 6, but either 100% or less than 25% of added Fe(II) was recovered when pH was greater than 6. These results are consistent with auto-catalytic formation of magnetite, which was stable relative to hematite for pH above 5.9. However, when sulfate was greater than 1 mM, unextracted Fe(II) was observed at pH above 5 where only approximately 15% of added Fe(II) was recovered by a 0.5 N HCl extraction; these results could not be explained by precipitation of magnetite nor of known sulfate phases. Based on these results, existing models for adsorption of Fe(II) onto ferric oxides (based on experiments of several hours to a day) are not accurate for prediction of environmentally significant Fe(II) reactions with ferric oxides, when much longer times are available for reaction. There was no competition between Zn(II) and Fe(II) for 0.25 mM or less and 90 m 2 l −1 hematite. Zn(II) was completely recovered using 0.5 N HCl for every condition that was tested.

Bromate removal from water by granular ferric hydroxide (GFH)

The feasibility of granular ferric hydroxide (GFH) for bromate removal from water has been studied. Batch experiments were performed to study the influence of various experimental parameters such as effect of contact time, initial bromate concentration, temperature, pH and effect of competing anions on bromate removal by GFH. The adsorption kinetics indicates that uptake rate of bromate was rapid at the beginning and 75% adsorption was completed in 5 min and equilibrium was achieved within 20 min. The sorption process was well described by pseudo-second-order kinetics. The maximum adsorption potential of GFH for bromate removal was 16.5 mg g(-1) at 25 degrees C. The adsorption data fitted well to the Langmuir model. The increase in OH peak and absence of Br-O bonding in FTIR spectra indicate that ion-exchange was the main mechanism during bromate sorption on GFH. The effects of competing anions and solution pHs (3-9) were negligible. Results of the present study suggest that GFH can be effectively utilized for bromate removal from drinking water.

Sorption kinetics of Fe(II), Zn(II), Co(II), Ni(II), Cd(II), and Fe(II)/Me(II) onto hematite.

The reactions of Fe(II) and other divalent metal ions including Zn, Co, Ni, and Cd on hematite were studied in single and competitive binary systems with high sorbate/sorbent ratios in 10 mM PIPES (pH 6.8) solution under strict anoxic conditions. Adsorbed Me(II) was defined as extractable by 0.5 N HCl within 20 h, and fixed Me(II) was defined as the additional amount that was extracted by 3.0 N HCl within 7 days. Binary systems contained Fe(II) plus a second metal ion. The extent of uptake of divalent metal ions by hematite was in order of Fe> or =Zn>Co> or =Ni>Cd. For all metals tested, there was an instantaneous adsorption followed by a relatively slow stage that continued for the next 1-5 days. This sequence occurred in both single and binary systems, and could have been due to a variety of sorption site types or due to slow conversion from outer- to inner-sphere surface complexes due to increasing surface charge. Sorption competition was observed between Fe(II) and the other metal ions. The displacement of Fe(II) by Me(II) was in order of Ni approximately Zn>Cd, and the displacement of Me(II) by Fe(II) was in order of Cd>Zn approximately Ni>Co. Fixed Fe(II) was in order of Fe+Co (20%)>Fe+Cd (6%)>Fe approximately Zn (4%)>Fe approximately Ni (4%) after 30 days. There was no fixation for the other metals in single or binary systems.

Enhancement of microalgae growth and fatty acid content under the influence of phytohormones.

The growth of Scenedesmus obliquus improved with increase in phytohormones concentrations (10(-8)-10(-)(5)M). Indole-3-acetic acid (IAA) supported the maximum growth at 10(-5)M with 17.7×10(6)cells/mL and total fatty acid of 97.9mg/g-DCW, enhancing the growth by 1.9-fold compared to control (9.5×10(6)cells/mL). While 10(-5)M of a newly discovered phytohormone Diethyl aminoethyl hexanoate (DAH) demonstrated a 2.5-fold higher growth with 23.5×10(6)cells/mL and a total fatty acid content of 100mg/g-DCW. Poly-unsaturated fatty acid content increased up to 56% and 59% at 10(-)(5)M of IAA and DAH, respectively. The highest carbohydrate content (33% and 34%) achieved at 10(-8)M and 10(-5)M of IAA and DAH, respectively. While, the highest protein content (34% and 35%) obtained at 10(-8)M of IAA and DAH, respectively. The current investigation demonstrates that phytohormones accelerate microalgal growth and induce the quality and quantity of fatty acid content for biodiesel production.

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.

Enhancement of fermentative bioenergy (ethanol/hydrogen) production using ultrasonication of Scenedesmus obliquusYSW15 cultivated in swine wastewater effluent

The influence of ultrasonication pretreatment on fermentative bioenergy [ethanol/hydrogen (H2)] production from a newly isolated microalgae biomass (Scenedesmus obliquusYSW15) was investigated. S. obliquusYSW15 biomass was sonicated for 0 min (control), 5 min (short-term treatment), 15 and 60 min (long-term treatment), which caused different states of cell lysis for microbial fermentation. Long-term sonication significantly damaged the microalgal cell integrity, which subsequently enhanced the bioenergy production. The accumulative bioenergy (ethanol/hydrogen) production after long-term sonication was almost 7 times higher than that after short-term treatment or the control. The optimal ratio of microalgal biomass to anaerobic inoculum for higher bioenergy production was 1:1. Microscopic analyses with an energy-filtering transmission electron microscope (EF-TEM) and an atomic force microscope (AFM) collectively indicated that cells were significantly damaged during sonication and that the carbohydrates diffused out of the microalgae interiors and accumulated on the microalgae surfaces and/or within the periplasm, which led to enhanced bioaccessibility and bioavailability of the biomass. These results demonstrate that ultrasonication is an effective pretreatment method for enhancing the fermentative bioenergy production from microalgal biomass.

Ferrous oxidation chemistry in passive abiotic systems for the treatment of mine drainage

The rates of chemical oxidation and gas transfer were determined for two passive abiotic systems for the treatment of mine drainage. One system (HB) is a series of ponds whose discharge was net acidic. The second treatment system (CK) has shallow channels and net alkaline discharge. The O2 mass transfer coefficient was 2 cm h−1 for HB Pond #2 and ranged from 4 to 40 cm h−1 for the CK channels, depending on channel velocity and depth. The CO2 mass transfer coefficient was 1.3 cm h−1 for HB Pond #2 and ranged from 1.4 to 15 cm h−1 for the CK channels. Oxygen transfer appeared to be the rate-limiting step for oxidation of Fe(II) at HB Pond #2. The oxidation rate for Fe(II) adsorbed to already-formed ferric oxides (heterogeneous oxidation) appeared to control the rate of oxidation of Fe(II) at the CK channels. Based on field data, the heterogeneous rate constant for oxidation of Fe(II) was 6.0×10−9 mg l−1 s−1 at 17°C or k2 of 5.5×10−8 mg l−1 s−1 at 25°C. This value was consistent with previously reported values for k2 based on laboratory experiments. The annual-averaged iron removal rates were 18 g d−1 m−2 for HB and 42 g d−1 m−2 for CK, compared to empirical design expectations of 10 to 20 g d−1 m−2. Heterogeneous oxidation accounted for >80 of the oxidation of Fe(II) at HB and >90% of the oxidation of Fe(II) at CK.

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.

Removal of Anionic Dyes from Water using Citrus limonum (Lemon) Peel: Equilibrium Studies and Kinetic Modeling

Abstract The present study was undertaken to evaluate the adsorption potential of Citrus limonum (lemon) peel as an adsorbent for the removal of two anionic dyes, Methyl orange (MO) and Congo red (CR) from aqueous solutions. The adsorption was studied as a function of contact time, initial concentration, and temperature by batch method. The adsorption capacities of lemon peel adsorbent for dyes were found 50.3 and 34.5 mg/g for MO and CR, respectively. The equilibrium adsorption data was well described by the Langmuir model. Three simplified kinetic models viz. pseudo-first-order, pseudo-second-order, and Weber and Morris intraparticle diffusion model were tested to describe the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities, and related correlation coefficients for each kinetic model were determined. It was found that the present system of dyes adsorption on lemon peel adsorbent could be described more favorably by the pseudo-first-order kinetic model. The results of the present study reveal that lemon peel adsorbent can be fruitfully utilized as an inexpensive adsorbent for dyes removal from effluents.