A study on torrefaction characteristics of waste sawdust in an auger type pyrolyzer

Torrefaction is thermo-chemical process which can improve solid fuel quality as well as grindability. In previous studies, torrefaction has been studied mainly for removal of moisture and for improving grindability. In this experiment, the characteristics of torrefied waste sawdust were studied especially for its energy yield. Hence, torrefaction was performed on varying reaction temperatures (200, 220, 240, 260, 280, 300 °C) and solid residence time (10, 30, 60 min). The results indicated that the yield of torrefaction decreases with increasing temperature and residence time. It was found that above 280 °C, the yield got remarkably decreased. The lowest yield was obtained at the residence time of 60 min. It was also noticed that the HHV of torrefied samples increases with increasing temperature. The highest HHV was found to be 26.09 MJ/kg which was obtained at 60 min and 300 °C. However, the highest energy yield was obtained to be 104.17 % which was noticed at 30 min and 260 °C.     

Diurnal vertical migration of Cochlodinium polykrikoides during the red tide in Korean coastal sea waters

The diurnal vertical migration of Cochlodinium polykrikoides (C. polykrikoides), which caused a red tide in the Korean coastal waters of the East Sea/Sea of Japan in September 2003, was examined by determining the time-dependent changes in the density of living cells in relation to the depth of the water column. The ascent of this species into the surface layer (depth of water 2 m) occurred during 1400-1500. The descent started at 1600 and a high distribution rate (86%) at 15-20 m was observed at 0300. During the ascent, the cells were widely distributed at each depth level from 0600 hr and at 0800-1100, the cells were primarily distributed in the middle layer (0-6 m). The concentration of dissolved inorganic nitrogen was generally < or = 2.86 micromol l(-1), but at 1400-1500, the concentration in the surface layer reduced to < or = 0.14 micromol l(-1). Moreover, the concentration gradually increased as the depth increased to > or = 5 m. These results showed that the nutrient-consumption rate associated with the proliferation of C. polykrikoides during a red tide is more influenced by the inorganic-nitrogen resources ratherthan the inorganic-phosphorus compounds.     

Sorption and biodegradation of vapor-phase organic compounds with wastewater sludge and food waste compost

To test the possible use of composted food waste and wastewater sludge as biofilters to treat gas-phase volatile organic compounds (VOCs), batch experiments were conducted with an isolated strain that could degrade aromatic compounds under aerobic conditions. A benzene and trichloroethylene (TCE) mixture was used as the gas-phase pollutant in experiments with composted food waste, sludge, and soil. Under aerobic conditions, benzene was degraded as a primary substrate and TCE was degraded cometabolically, with water contents varying from 6 to 60% (volume of water added/volume of solid). Optimal water content for VOC removal was 12% for the soil, 36% for the composted food waste, and 48% for the sludge. The extent of VOC sorption and biodegradation at the optimal water content was different for each material. With the same initial VOC concentration, more VOCs were removed by sorption onto the composted food waste and the sludge, while less VOCs were biodegraded in comparison with the results using soil. The reason the biodegradation in the soil was greater may be partly attributed to the fact that, due to less sorption, the aqueous-phase concentration of VOCs, which microorganisms could utilize as a carbon source or cometabolize, was higher. We also speculate that the distribution of microorganisms in each medium affects the rate of biodegradation. A large number of microorganisms were attached to the composted food waste and sludge. Mass transfer of VOCs and oxygen to these microorganisms, which appear to have been heterogeneously distributed in clusters, may have been limited, resulting in hindered biodegradation.     

Risk assessment for shallow land burial of low level radioactive waste

A composite model for the risk assessment is developed for the shallow-land burial of low-level radioactive waste. The composite model is composed of a source term, repository failure model, geosphere model, biosphere model, and finally, a dose-and-health-effects model. Uncertainty and sensitivity analyses are also carried out. In addition to the time-dependent annual release rate and dose rate for each nuclide, the ultimate risk in terms of cancer death rate is estimated.The results show that the highest value of the annual dose for the repository is less than the individual dose limit to the human body, and the calculated highest cancer death rate is much lower than other various risks. The highest value of the total annual dose appears at about 100 years after disposal, and at this time, dominant nuclides are Ni-63 and Cs-137.From the results of uncertainty and sensitivity analyses, it is found that the uncertainty associated with the public risk is strongly sensitive to the volume flow rate and irrigation rate of surface water and the retardation coefficient of geological structure.It is concluded that the methodology of simplified mathematical modeling for the risk assessment can be an effective tool for the decision making of the radioactive waste repository selection and the management of the repository system.     

Stochastic analysis of radioactive waste package performance using first-order reliability method

In order to license an underground radioactive waste repository, it is important to demonstrate regulatory compliance with authoritative regulations. Also it is evidence from NRC's criteria for waste package performance that a stochastic analysis is necessary to provide that these criteria can be met with confidence. The first-order reliability method is an attractive tool to the stochastic analysis and particularly useful when statistical information is incomplete, as is common for problems occurring in the subsurface environment. The method is based on using the first-order Taylor series expansion at a specific linearization point to calculate a measure of reliability. Results from a first-order reliability analysis include an estimate of the probability of exceeding a specified performance criteria and measures of the sensitivity of the stochastic solution to the changes in input random variables and their statistical moments. The method of stochastic analysis is illustrated by analyzing the canister corrosion in a radioactive waste package.     

The determination and distribution of Zn in surface water samples collected in the northeast Atlantic Ocean

Dissolved Zn concentrations were determined in surface water samples collected on-line along transects in the eastern North Atlantic in spring (March 1998). Two frontal zones could be identified in the research area by a change in salinity, temperature and nutrient concentrations. One zone was identified at 42 degrees N, separating the North Atlantic central water (NACW) and the Atlantic surface water (ASW) from each other, and another one crossing the continental slope at 12 degrees and 8 degrees E, respectively. Variability in Zn concentrations was observed near these zones, not only as a result of a change of water mass, but also due to external Zn sources. Surface Zn concentrations were 0.5-1 nM and 2 nM in the NACW and ASW, respectively, increasing to 4 nM over the continental shelf and finally 5-6 nM in the English Channel. Contributions of Zn derived from shelf sediments appear to be the major source for the enriched surface values in the continental zone.     

Determination of (mono-, di- and) tributyltin in sediments. Analytical methods

Methods for the reliable determination of butyltin compounds in sediments are required for both national and international marine monitoring programmes. This evaluation of current commonly used approaches to the analysis identifies critical aspects of extraction, derivatisation, clean-up, separation, standardisation and detection with the objective of improving the analytical capabilities both of experienced laboratories and of those addressing the problems for the first time.     

Methane and CO2 fluxes from an Indonesian peatland used for sago palm (Metroxylon sagu Rottb.) cultivation: Effects of fertilizer and groundwater level management

Tropical peatland is a vast potential land source for biological production, but peatland is a major natural source of greenhouse gases, especially methane (CH₄). It is important to evaluate the changes in greenhouse gas emissions induced by cultivation practices for sustainable agricultural use of tropical peatland. We investigated the effects of fertilizer application and the groundwater level on CH₄ and carbon dioxide (CO₂) fluxes in an Indonesian peat soil. The crop cultivated was sago palm (Metroxylon sagu Rottb.), which can grow on tropical peat soil without drainage and yield great amounts of starch. CH₄ emission through sago palm plants was first estimated by collecting gas samples immediately after cutting sago suckers using the closed chamber method. The CH₄ fluxes ranged from negative values to 1.0 mg C m⁻² h⁻¹. The mean CH₄ flux from treatment with macroelements (N, P, and K) and microelements (B, Cu, Fe, and Zn) applied at normal rates did not differ significantly from that of the No fertilizer treatment, although increasing the application rates of macroelements or microelements by 10-fold increased the CH₄ flux by a factor of two or three. The relationship between CH₄ flux and the groundwater table was regressed to a logarithmic equation, which indicated that to maintain a small CH₄ flux, the groundwater table should be maintained at <−45 cm. The CO₂ fluxes ranged between 24 and 150 mg C m⁻² h⁻¹, and were not significantly affected by either fertilizer treatments or the groundwater level. The inclusion of sago palm suckers in a chamber increased CH₄ emission from the peat soil significantly. Thus, gas emissions mediated by certain kinds of palm plants should not be disregarded.     

An examination of shared leadership configurations and their effectiveness in teams

A key challenge in the shared leadership literature has been a limited understanding of how multiple leadership activities are shared across team members and roles. We address this issue by conceptualizing and operationalizing shared leadership using both its content (i.e., what leadership roles are shared) and distribution (i.e., how leadership is shared across members and roles). In an exploratory study comprised of 129 work teams, we use latent profile analysis (LPA) to identify multiple shared leadership configurations that vary in the extent of sharing. Our second study of 103 MBA teams supports these findings and further (a) considers what shared leadership configurations have the greatest influence on team effectiveness, (b) examines the mediating role of teamwork processes, and (c) investigates the moderating role of temporal dispersion. We advance current research by demonstrating that shared leadership typically manifests in collective (i.e., members share all leadership roles) and distributed configurations (i.e., members hold one leadership role while other members hold other leadership roles), which has implications for team processes and effectiveness. Specifically, we show that collective configurations have higher team effectiveness (compared to distributed configurations) owing to improved teamwork processes and observe that these effects are more pronounced when temporal dispersion is high.     

Food web structure of a restored macroalgal bed in the eastern Korean peninsula determined by C and N stable isotope analyses

Loss of macroalgae habitats has been widespread on rocky marine coastlines of the eastern Korean peninsula, and efforts for restoration and creation of macroalgal beds have increasingly been made to mitigate these habitat losses. Deploying artificial reefs of concrete pyramids with kelps attached has been commonly used and applied in this study. As a part of an effort to evaluate structural and functional recovery of created and restored habitat, the macroalgal community and food web structure were studied about a year after the establishment of the artificial macroalgal bed, making comparisons with nearby natural counterparts and barren ground communities. Dominant species, total abundance, and community structure of macroalgal assemblage at the restored macroalgal bed recovered to the neighboring natural bed levels during the study period. The main primary producers (phytoplankton and macroalgae) were isotopically well separated. δ¹³C and δ¹⁵N values of consumers were very similar between restored and natural beds but varied greatly among functional feeding groups. The range of consumer δ¹³C was as wide as that of primary producers, indicating the trophic importance of both producers. There was a stepwise trophic enrichment in δ¹⁵N with increasing trophic level. A comparison of isotope signatures between primary producers and consumers showed that, while suspension feeders are highly dependent on pelagic sources, invertebrates of other feeding guilds and fishes mainly use macroalgae-derived organic matter as their ultimate nutritional sources in both macroalgal beds, emphasizing the high equivalency of trophic structure between both beds. Isotopic signatures of a few mollusks and sea urchins showed that they use different dietary items in macroalgal-barren grounds compared with macroalgal beds, probably reflecting their feeding plasticity according to the low macroalgal biomass. However, isotopic signatures of most of the consumers at the barren ground were consistent with those at the macroalgal beds, supporting the important trophic role of drifting algae. Our results revealed the recoveries of the macroalgal community and trophic structure at the restored habitat. Further studies on colonization of early settlers and the following succession progress are needed to better understand the process and recovery rate in the developing benthic community.