Yunchul Cho

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.

Transfer of antibiotic resistance plasmids in pure and activated sludge cultures in the presence of environmentally representative micro-contaminant concentrations

The presence of antibiotics in the natural environment has been a growing issue. This presence could also account for the influence that affects microorganisms in such a way that they develop resistance against these antibiotics. The aim of this study was to evaluate whether the antibiotic resistant gene (ARG) plasmid transfer can be facilitated by the impact of 1) environmentally representative micro-contaminant concentrations in ppb (part per billion) levels and 2) donor-recipient microbial complexity (pure vs. mixed). For this purpose, the multidrug resistant plasmid, pB10, and Escherichia coli DH5α were used as a model plasmid and a model donor, respectively. Based on conjugation experiments with pure (Pseudomonas aeruginosa PAKexoT) and mixed (activated sludge) cultures as recipients, increased relative plasmid transfer frequencies were observed at ppb (μg/L) levels of tetracycline and sulfamethoxazole micro-contaminant exposure. When sludge, a more complex community, was used as a recipient, the increases of the plasmid transfer rate were always statistically significant but not always in P. aeruginosa. The low concentration (10 ppb) of tetracycline exposure led to the pB10 transfer to enteric bacteria, which are clinically important pathogens.

Degradation of PCE, TCE and 1,1,1-TCA by nanosized FePd bimetallic particles under various experimental conditions.

The degradation of chlorinated organic compounds, such as PCE (tetrachloroethene), TCE (trichloroethene) and 1,1,1-TCA (1,1,1-trichloroethane), was conducted using nanosized FePd bimetallic particles. In order to enhance the reactivity of ZVI (zero valent iron) nanoparticles, surface modification of ZVI nanoparticles was performed using Pd and CMC (carboxymethyl cellulose). The surface modification was found to form CMC-stabilized FePd bimetallic nanoparticles (CMC-FePd). The average TCE removal efficiency by the CMC-FePd was significantly increased by ∼85% compared to employing conventional ZVI nanoparticles (∼15%). This increase in the TCE removal efficiency was most likely due to the increased amount of atomic hydrogen produced by the formation of CMC-FePd. For PCE and 1,1,1-TCA, the removal efficiencies by CMC-FePd were approximately 80% and 56%, respectively. For all three chlorinated organic compounds, the amount of Cl- ions in the aqueous phase during the degradation increased with increasing reaction time. This result suggests that the main degradation mechanism of the chlorinated compounds by CMC-FePd was reductive dechlorination.

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.

TOPOTACTIC CATION EXCHANGE IN TRANSFORMED MICAS UNDER HYDROTHERMAL CONDITIONS

The formation of hydroxylated phases was investigated using K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) under hydrothermal treatment with alkali (Li+, K+, NH4+, Rb+ and Cs+), alkaline earth (Mg2+, Ca2+, Sr2+ and Ba2+), and aluminum (Al3+) cations at 200°C for 1 and/or 3 days. The K-depleted biotite treated with alkali cations produced anhydrous hydroxylated phases, while the K-depleted muscovite did not significantly exchange alkali cations but dehydrated to form Na-muscovite in all cases. The alkaline earth cations, however, produced hydrous hydroxylated phases with both K-depleted micas. The degree of hydration energy of cations and the charge density of micas were found to influence the formation of anhydrous and hydrous phases from the K-depleted micas. This type of topotactic cation exchange potentially could be used for fixation and immobilization of radioactive species such as Cs, Sr, Ra, etc. in the transformed micas. The K-depleted biotite and muscovite treated with Al3+ were transformed to hydroxy-Al interlayered vermiculites (HIV) because of hydrolysis and polymerization of Al3+. These HIV phases could also serve as useful adsorbents for soil and groundwater contaminants.

Significance of metabolite extraction method for evaluating sulfamethazine toxicity in adult zebrafish using metabolomics.

Recently, environmental metabolomics has been introduced as a next generation environmental toxicity method which helps in evaluating toxicity of bioactive compounds to non-target organisms. In general, efficient metabolite extraction from target cells is one of the keys to success to better understand the effects of toxic substances to organisms. In this regard, the aim of this study is (1) to compare two sample extraction methods in terms of abundance and quality of metabolites and (2) investigate how this could lead to difference in data interpretation using pathway analysis. For this purpose, the antibiotic sulfamethazine and zebrafish (Danio rerio) were selected as model toxic substance and target organism, respectively. The zebrafish was exposed to four different sulfamethazine concentrations (0, 10, 30, and 50mg/L) for 72h. Metabolites were extracted using two different methods (Bligh and Dyer and solid-phase extraction). A total of 13,538 and 12,469 features were detected using quadrupole time-of-flight liquid chromatography mass spectrometry (QTOF LC-MS). Of these metabolites, 4278 (Bligh and Dyer) and 332 (solid phase extraction) were found to be significant after false discovery rate adjustment at a significance threshold of 0.01. Metlin and KEGG pathway analysis showed comprehensive information from fish samples extracted using Bligh and Dyer compared to solid phase extraction. This study shows that proper selection of sample extraction method is critically important for interpreting and analyzing the toxicity data of organisms when metabolomics is applied.

Sub-lethal pharmaceutical hazard tracking in adult zebrafish using untargeted LC-MS environmental metabolomics

Antibiotics in the aquatic environment are dispersed through anthropogenic activities at low concentrations. Despite their sub lethal concentration, these biologically active compounds may still have adverse effects to non-target species. This study examined the response of adult zebrafish to 0.1mg/L concentration of clarithromycin, florfenicol, sulfamethazine, and their mixture using environmental metabolomics. Embryo and larvae of the fish were also used to assess fish embryo acute toxicity and behavior tests respectively. The fish embryo toxicity test did not show any inhibition of growth and development of the embryos after 96h of exposure to the antibiotics. Changes in swimming activity were seen in 5-dpf larvae which is believed to be correlated with the length of exposure to the compounds. Meanwhile, environmental metabolomics revealed diverse metabolites and pathways that were affected after 72h of exposure of the adult fish to sub-lethal concentration of the compounds. We found that even at low concentration of the antibiotics, behavioral and metabolic effects were still observed despite the lack of visible morphological changes. Further studies involving other aquatic organisms and bioactive compounds are encouraged to strengthen the findings presented in this novel research.

Selectivity of Co and Ni by K-depleted micas.

Contamination of the environment with heavy metals, including cationic radionuclides, is a serious problem which has yet to be fully overcome. A class of potentially effective cation exchangers for sequestering heavy metals which has received little attention is K-depleted mica. The purpose of this study was to investigate the heavy-metal cation exchange properties of K-depleted phlogopite and biotite, which were prepared from a natural phlogopite and biotite, respectively, using sodium tetraphenylborate (NaTPB). The X-ray diffraction (XRD) patterns showed that interlayer K+ ions were completely replaced with exchangeable Na+ ions, resulting in the expansion of the d001 spacing of both K-depleted phlogopite and K-depleted biotite. In order to investigate the cation exchange selectivity of K-depleted phlogopite and biotite for Co2+ and Ni2+, cation exchange isotherms and Kielland plots were constructed. The isotherms and Kielland plots indicated that both K-depleted phlogopite and biotite are highly selective for Co2+ as well as Ni2+. The XRD patterns after both 2Na+ → Co2+ and Ni2+ exchange reactions suggest that double sheets of interlayer water are present in the interlayer. These K-depleted micas are potential cation exchange materials for removal of some heavy metals such as Ni and radioactive species such as 60Co from solution.

The Removal of Nutrients and Heavy Metals Using Household Rain garden

In Korea, most rainfall events occur during summer which then leads to an increasing concern regarding high influx of non-point source pollutants since the pollutant loadings from these non-point sources are very significant. In particular, the first flush of roof-harvested rainfall is said to contain the most highest concentration of nutrients and heavy metals. Accordingly, it is important to develope the possible water quality management options in treating the contaminants and considering reclaimed water reuse. The rain garden could be one of suitable alternatives in addressing this issue. In this study, the development of an effective adsorption media and its application to a lab-scale rain garden was tested to evaluate the removal rate of various nutrient and organic matter (TN, TP, CODcr), and heavy metals (Cu, Cd, Pb). Results showed that carbonized peatmoss produced at higher temperature have better adsorption capacity as compared to the one produced at a lower temperature. When the carbonized peatmoss was applied as rain garden media, the highest removal of TN, TP, and CODcr was observed compared to no carbonized peatmoss applied rain garden. Therefore, this study showed that the carbonized peatmoss would be effectively applied to the rain garden for removing nutrients and heavy metals from roof-harvested rainwater.