Miscibility and Biodegradability of Poly(Butylene Succinate)/Poly(Butylene Terephthalate) Blends

As one of the biodegradable polymers, the blend of poly(butylene succinate) and poly(butylene terephthalate) is dealt with in this study. In our previous work, it was demonstrated that PBS and PBT are immiscible not only from the changes of T _g but also from logG–log G plots. It is expected that the biodegradability of the blends could be improved by enhancing the miscibility. We tried to induce the transesterification reaction between two polyesters with various time intervals to enhance the miscibility of the blends. The extent of transesterification reaction was examined by ¹H-NMR. We utilized a dynamic mechanical thermal analyzer and a rotational rheometer to investigate the changes in miscibility. We also verified the biodegradability of PBS/PBT blends after the transesterification reaction by the composting method.     

Reliable evidences that the removal mechanism of hexavalent chromium by natural biomaterials is adsorption-coupled reduction

For the last few decades, over 200 papers have been published in the Cr(VI) biosorption research field. Most early studies have claimed that Cr(VI) was removed from aqueous phase through an anionic adsorption, but this approach has been lost old original position. It has been newly explained that these findings were misinterpreted due to errors in measuring the concentrations of different chromium species in the aqueous phase, insufficient contact time required for equilibrium and the lack of information about the oxidation state of the chromium bound to biomaterials. Although 'adsorption-coupled reduction' is now widely accepted as the mechanism of Cr(VI) biosorption by natural biomaterials, a number of researchers still believe that Cr(VI) is removed by anionic adsorption onto the biomaterials. Therefore, the objective of this study was to show reliable evidences that the removal mechanism of Cr(VI) by natural biomaterials is 'adsorption-coupled reduction'. Sixteen natural biomaterials were used to study the Cr(VI) biosorption. Not only Cr(VI) but also total Cr in the aqueous phase were analyzed. X-ray photoelectron spectroscope was also used to verify the oxidation state of the chromium bound to the biomaterials. Finally, the removal behavior of Cr(VI) by each biomaterial was described by a kinetic model based on a redox reaction.     

Calculation of environmental concentration and comparison of output for existing chemicals using regional multimedia modeling

The environmental fate of 40 existing chemicals is discussed using the EUSES multimedia distribution and risk assessment model with site-specific parameter setting in an urban area of Japan including a highly industrial region. There has been a strong need to assess the environmental fate of a huge number of existing chemicals. Data on the emission amounts of chemicals are essential for such prediction, and PRTR surveys may yield this data. The study delivered the following results: (1) Volatile compounds with large amounts of emission showed higher predicted concentrations in air, and the concentrations of several compounds agreed well with averaged monitoring data within an order of magnitude. (2) A close relationship was found between the concentration of water and that of sediment, suggesting that the fate of chemicals in sediment essentially depended on the water environment. (3) A group of volatile solvents had high mass distribution ratio to air. Some compounds having high solubility in water were also included in that group due to the high ratio of air emission. Highly hydrophobic compounds with logK(OW) larger than 6.0 showed a high distribution ratio to soil and sediment. (4) Volatile compounds were mostly taken through air. The exposure through fish is a dominant pathway for highly hydrophobic compounds. (5) Exposure ratio could be gathered from physicochemical properties. The exposure from fish intake was roughly estimated by logK(OW), whereas exposure from air and water intake was difficult to estimate simply by vapor pressure and solubility in water, respectively.     

Removal of ammonia by biofilters: a study with flow-modified system and kinetics

The characteristics of ammonia removal by two types of biofilter (a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow) were investigated. A mixture of organic materials such as compost, bark, and peat was used as the biofilter media based on the small-scale column test for media selection. Complete removal capacity, defined as the maximum inlet load of ammonia that was completely removed, was obtained. The modified biofilter showed complete removal up to 1.0 g N/kg dry material/day. However, the removal capacity of the standard biofilter started to deviate from complete removal around 0.4 g N/kg dry material/day, indicating that the modified biofilter system has higher removal efficiency than the standard upflow one. In kinetic analysis of the biological removal of ammonia in each biofilter system, the maximum removal rate, Vm, was 0.93 g N/kg dry material/day and the saturation constant, Ks, was 32.55 ppm in the standard biofilter. On the other hand, the values of Vm and Ks were 1.66 g N/kg dry material/day and 74.25 ppm, respectively, in the modified biofilter system.     

Seasonal variation in dissolved gaseous mercury and total mercury concentrations in Juam Reservoir, Korea

Dissolved gaseous mercury (DGM) and total mercury (TM) concentrations were measured in Juam Reservoir, Korea. DGM concentrations were higher in spring (64+/-13pgL(-1)) and summer (109+/-15pgL(-1)), and lower in fall (20+/-2pgL(-1)) and winter (23+/-6pgL(-1)). In contrast, TM concentrations were higher in fall (3.2+/-0.1ngL(-1)) and winter (3.3+/-0.1ngL(-1)) than in spring (2.3+/-0.1ngL(-1)) and summer (2.2+/-0.4ngL(-1)). DGM concentrations were correlated with water temperature (p<0.0001), ORP (p<0.0001), UV intensity (UV-A: p=0.008; UV-B: p=0.003), and DOC concentration (p=0.0107). DGM concentrations varied diurnally with UV intensity. The average summer DGM (109+/-15pgL(-1)) and TM (2.2+/-0.4ngL(-1)) concentrations in Juam Reservoir were higher than the averages for North American lakes (DGM=38+/-16pgL(-1); TM=1.0+/-1.2ngL(-1)), but lower than levels reported for Baihua Reservoir in China.     

Nationwide monitoring of atmospheric PCDD/Fs and dioxin-like PCBs in South Korea

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) were measured in ambient air samples collected from different parts of South Korea in 2008, and the measured levels were used for assessing the spatial and temporal distribution of atmospheric PCDDFs and DL-PCBs in South Korea. The average concentrations of atmospheric PCDD/Fs and DL-PCBs among the 37 sites were 28 fg I-TEQ m⁻³ (ND ∼ 617) and 1 fg WHO-TEQ m⁻³ (ND ∼ 0.016). Elevated atmospheric levels of PCDD/Fs and DL-PCBs observed at residential/industrial sites and in the north-west of Korea, indicated a potential contribution and impacts of anthropogenic sources of PCDD/Fs and DL-PCBs. These levels were similar or lower than those previously reported in other ambient air surveys. Average concentrations of PCDD/Fs showed small seasonal variations (ANOVA analysis, p = 0.144). The highest concentrations of PCDD/Fs were observed during winter, followed by spring, autumn and summer. Atmospheric PCDD/Fs and DL-PCBs in South Korea rapidly decreased during the last 10 years (1998-2008), demonstrating the efficiency of stricter regulations and the application of best available technologies/best environmental practices at emission sources. Comparison of the congener profiles and principal component analysis showed that current atmospheric PCDD/Fs are mostly influenced by industrial sources and PCBs from old commercial PCB uses. Nationwide POPs monitoring will continue and allows an effective evaluation of the implementation of the Stockholm Convention on POPs.     

Atmospheric bulk deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the vicinity of an iron and steel making plant

An IRA-743 resin bulk sampler was validated to monitor long-term bulk deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Six consecutive sampling campaigns (2008-2009) were conducted at four sites around steel complexes in Pohang, South Korea to investigate spatial and seasonal variations of PCDD/F bulk deposition. The bulk deposition within the steel complex showed the highest ∑_4-8PCDD/F (Tetra-Octa) fluxes, ranging from 204 to 608 (mean: 352) pg m⁻² d⁻¹, indicating steel complexes were major sources of PCDD/Fs. The homologue profiles were dominated with lower chlorinated PCDFs. Furthermore, the prevailing winds were confirmed to influence the spatial distribution of PCDD/F deposition. There were apparent seasonal variations of the bulk deposition at each site, and seasonal homologue patterns of PCDD/Fs were clearly observed. According to the passive air sampling, however, no significant seasonal change of ambient air concentrations of PCDD/Fs was observed. Therefore, it was concluded that the seasonal variations of deposition fluxes of PCDD/Fs probably resulted from temperature-dependent gas/particle partitioning.     

A study on the reaction characteristics of vanadium-impregnated natural manganese oxide in ammonia selective catalytic reduction

This study investigated the effect of adding vanadium (V) to natural manganese oxide (NMO) in ammonia (NH3) selective catalytic reduction (SCR). The addition of V to NMO decreased the catalytic activity at low temperatures by blocking the active site. However, the enhancement of catalytic activity was achieved by controlling NH3 oxidation at high temperatures. From the NH3 temperature programmed desorption and oxygen on/off test, it was confirmed that the amount of Lewis acid site and active lattice oxygen of the catalyst affects the catalytic performance at low temperature.     

The effect of emergent macrophytes on the dynamics of sulfur species and trace metals in wetland sediments

This study focuses on the effect of plants on the biogeochemistry of sulfur species and the mobility of heavy metals in wetland sediments. Results showed that, in the presence of plants, sediments had elevated sulfate concentrations in the rhizosphere during the growing season, ranging from 0.2 to 6.20 mmol L(-1), whereas only a small difference in the sulfate profiles between vegetated and non-vegetated sediments was observed during senescence. Based on the sulfate concentration increase, the oxygen release rate from the roots to achieve the corresponding oxidation of sulfide was estimated as 0.85 g m(-2) day(-1). Evapotranspiration-induced advection is a major contributor to the transport of sulfate from the water column into the sediments, and also allows dissolved trace metals (i.e. Cd, Pb, and Zn) to be transported into the sediments and react with the acid volatile sulfide pool, resulting in the immobilization of trace metals in these sediments.