The Removal of Strontium Ions from an Aqueous Solution Using Na-A Zeolites Synthesized from Kaolin.

Sr2+ ions in an aqueous solution were removed using Na-A zeolites synthesized from kaolin, a natural mineral. Na-A zeolites with high crystallinity were synthesized using NaOH/kaolin mass ratios of 0.6 (ZK06) and 0.9 (ZK09). The adsorption reached equilibrium within 120 min. The adsorption data obtained from experiments for Sr2+ using ZK06 and ZK09 were appropriately analyzed with pseudo-second-order kinetic and Langmuir isotherm models. Comparing the maximum adsorption capacities (qm) of ZK06 and ZK09 for Sr2+, the highest values were obtained at 1.90 and 2.42 mmol/g, respectively. Consequently, the Na-A zeolites synthesized from kaolin can be evaluated as adsorbents with high adsorption capacities for the removal of Sr2+, proportional to the degree of their crystallinity.

Characterizing land use effect on shallow groundwater contamination by using self-organizing map and buffer zone.

Nitrate-nitrogen (NO3-N) contamination in groundwater is a major problem of drinking and domestic waters in rural areas. This study revealed the influence of land use type on shallow alluvial groundwaters in a typical rural area in South Korea by applying a self-organizing map (SOM), principal component analysis (PCA), and hierarchical cluster analysis (HCA). The uncertainty of spatial information on land use was improved by using a buffer zone of the average influence radius of 32.65 m surrounding wells. Two major land-use types, forests (44.9%) and rice fields (28.8%), occupied a total of 73.7% of the rural area. The higher concentrations of NO3-N in public facilities and livestock areas were demonstrated to directly recharge groundwater pollutants. NO3-N contamination in rice paddies, which also contained chlorine (Cl) and sulfate (SO4), was assessed according to the nutrients and residual salt in the soil. In addition, different NO3-N concentrations for the same land use indicate various biochemical reactions and NO3-N recharge types into the groundwater system. The shallow groundwaters in the study area were classified into three clusters according to their chemical constituents and land-use properties, especially NO3-N concentration, including pH, Cl, and SO4, using a SOM, PCA, and HCA. Unlike existing studies, we applied a buffer zone based on the Cooper-Jacob equation to obtain an improved SOM model prediction accuracy approximately 10% greater than that using the original dataset.

Contribution of nitrate-nitrogen concentration in groundwater to stream water in an agricultural head watershed.

This study characterized nitrate-nitrogen (NO3-N) concentrations in groundwater and stream water in an agricultural head watershed in South Korea and identified the pollution load of NO3-N as a result of the groundwater entering streams using field surveys, analyses of chemical constituents, and numerical modeling. The mean NO3-N concentration in groundwater was 7.373 mg/L, which is approximately 1.9 times higher than concentrations found in stream water. The groundwater and stream water samples belonged to the Ca-HCO3 type. The concentration of NO3-N in groundwater tended to increase in the lowland areas downstream. There was seasonal variations of NO3-N in both the groundwater and stream water samples, with increases in concentration during the dry season (January-April) and decreases during the wet season (June-October). The NO3-N load in stream water to that in groundwater (R) was higher during the wet season (September) than the dry season (March), with R distinctly increasing in upstream areas relative to downstream areas, indicating that during the wet season, a large amount of NO3-N is introduced into stream water from groundwater. By analyzing the relationship between groundwater and stream water and through NO3-N transport modeling, it was revealed that in the watershed, the nitrate-N load in stream water is greatly augmented by inputs from groundwater, particularly in the middle and downstream areas.

Incidence and predictors of HBV relapse after cessation of nucleoside analogues in HBeAg-negative patients with HBsAg ≤ 200 IU/mL.

The predictors of hepatitis B virus (HBV) relapse and HBsAg loss after cessation of nucleos(t)ide analogues (NA) in HBeAg-negative patients with end-of-treatment HBsAg ≤ 200 IU/mL remains unclear. The study recruited 119 chronic hepatitis B (CHB) patients who achieved end-of-treatment HBsAg ≤ 200 IU/mL, were treated with lamivudine (n = 34) and entecavir (n = 85). The 5-year rates of post-treatment virological relapse, clinical relapse, and HBsAg loss at 60 months were 39.4%, 27.6%, and 45.9%, respectively. Cox regression analysis revealed that HBV DNA at entry and end-of-treatment HBsAg levels were independent predictors of virolgical and clinical relapse. HBV genotype C and end-of-treatment HBsAg were independent factors of HBsAg loss. Patients with a combination of end-of-treatment HBsAg < 50 IU/mL and HBV DNA < 2 × 105 IU/mL at entry experienced the lowest virological and clinical relapse rates (5% and 0% at 60 months, respectively). In contract, patients with a combination of end-of-treatment HBsAg ≥ 50 IU/mL and HBV DNA ≥ 2 × 105 IU/mL at entry experienced high virological and clinical relapse (80.7% and 71.5% at 60 months, respectively). No patients experienced hepatic decompensation when clinical relapse occurred after timely retreatment. A combination of HBV DNA levels at entry and end-of-treatment HBsAg levels was useful for predicting the post-treatment HBV relapse in HBeAg-negative patients with HBsAg ≤ 200 IU/mL.