Factors affecting the spatial pattern of nitrate contamination in shallow groundwater

The elevated level of nitrate in groundwater is a serious problem in Korean agricultural areas. To control and manage groundwater quality, the characterization of groundwater contamination and identification of the factors affecting the nitrate concentration of groundwater are significant. The characterization of groundwater contamination at a hydrologically complex agricultural site in Yupori, Chuncheon (Korea) was undertaken by analyzing the hydrochemical data of groundwater within a statistical framework. Multivariate statistical tools such as cluster analyses and Tobit regression were applied to investigate the spatial variation of nitrate contamination and to analyze the factors affecting the NO3-N concentration in a shallow groundwater system. The groundwater groups from the cluster analysis were consistent with the land use pattern of the study area. The clustered group of a gentle-slope area with lower elevations showed higher NO3-N contamination of groundwater than groups on a hillside with higher elevations. Tobit regression results indicated that the agricultural activity in the vegetable fields and barns were the major factors affecting the elevated NO3-N concentration while the land slopes and elevations were negatively correlated with the NO3-N concentration. This shows that topographic characteristics such as land slopes and elevations should be considered to evaluate the land use impact on shallow groundwater quality.     

1H-NMR-based profiling of organic components in leachate from animal carcasses disposal site with time

Leachate, generated by the decomposition of animal carcasses, presents many environmental, sanitary, and food safety hazards. However, research on the characteristics of leachate is lacking. In this study, we performed biochemical profiling of leachate from two animal species (pig and cattle) in two soil types (sandy loam and sandy soil) using ¹H-NMR-based profiling, followed by multivariate data analysis. The leachate was collected from a well-controlled artificial burial site over a 31-week period. Principal components analysis (PCA) of the NMR data showed similar patterns between species and soil types. Organic components, including organic acids and phenols, predominated, and their levels increased with time. The methylamine level in leachate from pig carcasses 18 weeks following burial was significantly higher than that from cattle carcasses; leachate from cattle carcasses in sandy soil 1 week after burial contained unique components (specifically ethanol, formate, alanine, N-methylation, and taurine), in contrast with those from sandy loam soil. This study suggests that a NMR-based profiling approach is useful to characterize the organic components in leachate from animal carcasses over time.     

Phylogenetic relationship among several genera of Dictyotaceae (Dictyotales, Phaeophyceae) based on 18S rRNA and partial rbcL gene sequences

The partial sequences of the 18S rRNA gene and the rbcL gene, RuBisCo spacer region of representatives of the Dictyotaceae were determined and compared to resolve their phylogenetic relationships. A total of 1,861 base pairs of 18S rDNA sequences were aligned and examined. There was a high similarity of nucleotide sequences within the tribe Dictyoteae (99.4-99.6%) and the tribe Zonarieae (92.8-99.8%). The largest intergeneric divergence within the Dictyotaceae was 7.31%, between Dilophus and Zonaria. The aligned 422 bases of partial rbcL gene sequences gave a similar phylogenetic relationship among taxa to those of the 18S rDNA sequences, although our alignment covered less than 30% of the whole gene. All genera of Dictyotales consisted of several clades forming a polychotomy in MP trees based on partial rbcL gene sequences and on 18S rDNA sequences. The genera within the tribe Dictyoteae formed a clade, a Dictyota-Phacydictyon-Dilophus clade, while genera of the tribe Zonarieae formed four clades: Padina; Distromium-Lobophora-Zonaria; Spatoglossum-Lobospira; and Dictyopteris-Spatoglossum. All genera of the Dictyotaceae included in these sequence analyses are classified into five groups, which have little phylogenetic resolution among them. The genera classified in the tribe Zonarieae according to Womersley's criteria do not appear to be monophyletic, based on our analyses. Although not all genera of Dictyotaceae were analysed, our data suggest that the status of the meristem cells should not be a criterion for separating tribes within the family Dictyotaceae and that other hierarchical systems should be adopted to properly reflect phylogenetic relationships.     

Bioleaching of cadmium and nickel from synthetic sediments by Acidithiobacillus ferrooxidans

The microbial leaching process was evaluated for the treatment of synthetic sediments contaminated with cadmium and nickel sulfides. A series of batch leaching experiments was conducted to compare metal solubilization in sediment inoculated with Acidithiobacillus ferrooxidans -inoculated sediments to that in sterile control sediment. The rate and extent of metal solubilization were significantly higher in A. ferrooxidans -inoculated reactors than in acidified sterile reactors. The efficiency of cadmium (Cd) solubilization (80) in the bioleaching process was higher than that of nickel (Ni) solubilization (60). The performance of leaching reactors containing only culture supernatants was comparable to that of A. ferrooxidans -inoculated reactors, indicating that indirect non-contact leaching by the products of microbial metabolism is the predominant mechanism for metal solubilization rather than direct microbial sulfide oxidation. Moreover, the similar (60–75%) extents of Cd²⁺ leaching with A. ferrooxidans , cell-free filtrate, and Fe³⁺ suggest that abiotic oxidation of CdS by Fe³⁺ controls the overall leaching rate, and the role of A.␣ferrooxidans is most likely not to oxidize CdS mineral directly but to regenerate Fe³⁺ as an oxidant.     

An anaerobic continuous-flow fixed-bed reactor sustaining a 3-chlorobenzoate-degrading denitrifying population utilizing versatile electron donors and acceptors

An anaerobic continuous-flow fixed-bed column reactor capable of degrading 3-chlorobenzoate (3-CBA) under denitrifying conditions was established, and its rate reached 2.26 mM d(-1). The denitrifying population completely degraded 3-CBA when supplied at 0.1-0.54 mM, but its activity was partly suppressed when 3-CBA was supplied at 0.89 mM. Nitrate was concomitantly consumed throughout the operation of the reactor, the amount of which was similar to or up to 35% higher than the theoretical stoichiometric value that was calculated by assuming that 3-CBA degradation is coupled with denitrification. Batch incubation experiments proved that nitrate is strictly required for 3-CBA degradation in the absence of molecular oxygen. The population also degraded 3-CBA aerobically. Benzoate and 4-CBA were degraded under denitrifying conditions as well as 3-CBA, but 2-CBA was not. Considering that the previously reported denitrifying 3-CBA-degrading cultures do not exhibit 4-CBA degradation under denitrifying conditions, nor aerobic 3-CBA degradation [FEMS Microbiol. Lett. 144 (1996) 213, Appl. Environ. Microbiol. 66 (2000) 3446], the microbial population developed in this experiment was physiologically versatile with respect to the utilization of both electron donors and electron acceptors.     

Study on the initial velocity distribution of exhaled air from coughing and speaking

Increasing concerns about the spread of airborne pathogens such as severe acute respiratory syndrome (SARS) and novel swine-origin influenza A (H1N1) have attracted public attention to bioaerosols and protection against them. The airborne pathogens are likely to be expelled from coughing or speaking, so the physical data of the exhaled particles plays a key role in analyzing the pathway of airborne viruses. The objective of this study was to analyze the initial velocity and the angle of the exhaled airflow from coughing and speaking of 17 males and 9 females using Particle Image Velocimetry (PIV) and acrylic indoor chamber. The results showed that the average initial coughing velocity was 15.3 m/s for the males and 10.6 m/s for the females, while the average initial speaking velocity was 4.07 m/s and 2.31 m/s respectively. The angle of the exhaled air from coughing was around 38° for the males and 32° for the females, while that of the exhaled air from speaking was around 49° and 78° respectively. Also, the linear relation between the tested subject’s height and their coughing and speaking velocity was shown in this study.     

Absorption behavior of chlorine and sulfur by Ca(OH)<Subscript>2</Subscript> under simulated conditions with a fluidized bed combustor

This study was carried out to investigate the absorption reaction of chlorine and sulfur with Ca(OH)₂ under simulated conditions related to the co-combustion of refuse-derived fuel and sewage sludge in the fluidized bed combustor, such as high temperature, moisture and a mixing of samples. The combustion experiments were carried out in an electrical furnace with PVC and sulfur powders as the waste samples. High-purity slaked lime powder was used to capture the chlorine and sulfur. The experimental results showed that the removal efficiencies of both chlorine and sulfur were over 90% when the mole ratios of Ca on Cl and S were over 2.5. Furthermore, simultaneous absorption was helpful in improving the removal efficiency of chlorine and sulfur. The presence of chlorine markedly increased the removal efficiency of sulfur. The removal efficiency of chlorine was the highest at 700°C in both independent and simultaneous absorption. The removal efficiency of sulfur increased as the temperature increased, but the removal efficiency of chlorine sharply decreased from 95 to 83% when the moisture content in gases increased from 0 to 20 vol%. These results were confirmed by the combustion test of granular CaCl₂.     

Comparison between acetate and hydrogen as electron donors and implications for the reductive dehalogenation of PCE and TCE

Bioremediation by reductive dehalogenation of groundwater contaminated with tetrachloroethene (PCE) or trichloroethene (TCE) is generally carried out through the addition of a fermentable electron donor such as lactate, benzoate, carbohydrates or vegetable oil. These fermentable donors are converted by fermenting organisms into acetate and hydrogen, either of which might be used by dehalogenating microorganisms. Comparisons were made between H2 and acetate on the rate and extent of reductive dehalogenation of PCE. PCE dehalogenation with H2 alone was complete to ethene, but with acetate alone it generally proceeded only about half as fast and only to cis-1,2-dichloroethene (cDCE). Additionally, acetate was not used as an electron donor in the presence of H2. These findings suggest the fermentable electron donor requirement for PCE dehalogenation to ethene can be reduced up to 50% by separating PCE dehalogenation into two stages, the first of which uses acetate for the conversion of PCE to cDCE, and the second uses H2 for the conversion of cDCE to ethene. This can be implemented with a recycle system in which the fermentable substrate is added down-gradient, where the hydrogen being produced by fermentation effects cDCE conversion into ethene. The acetate produced is recycled up-gradient to achieve PCE conversion into cDCE. With the lower electron donor usage required, potential problems of aquifer clogging, excess methane production, and high groundwater chemical oxygen demand (COD) can be greatly reduced.     

Combustion kinetics of sewage sludge and combustible wastes

This study estimated the kinetics of the mono- and co-combustion of sewage sludge pellets and combustible wastes such as municipal solid waste (MSW) and refuse-derived fuel (RDF). Sewage sludge was manufactured into pellets with a diameter of 8, 12, or 16 mm and a length of 30 mm. The RDF was composed of paper and plastics and was formed into pellets with a diameter of 8 mm and a length of 30 mm. MSW samples were synthesized using combustible wastes such as garbage, paper, plastics, and wood. The MSW was adjusted to have a moisture content of around 40% after shredding to under 10 mm. A laboratory-scale batch type stoker incinerator was used for the combustion and the gas composition of the flue gas was measured. The activation energy was calculated using the experimental results, and then the relation of the decomposition rate and reaction time was evaluated using the shrinking core model. The decomposition rate of the sludge pellets decreased as their diameter and moisture content increased, and the co-combustion of sludge pellets and combustible waste was affected by the amount of combustible waste. The individual combustion rates of the cylindrical sludge pellets or RDF were mainly controlled by the chemical reaction, but in the case of shredded MSW it was mostly influenced by gas diffusion. The rate for the co-combustion of sludge pellets and combustible wastes was mainly determined by the combustion rate of the combustible waste. The activation energy of the 8-mm-diameter sludge pellets was between 6.70 and 10.0 kcal/mol, according to the moisture content, but it was lower for MSW and RDF. In the case of MSW co-combustion, the reaction rate accelerated as the moisture content of the sludge pellets decreased, but it was markedly increased by the addition of RDF, regardless of the sludge moisture content.     

Desiccation of contaminant barrier materials amended with aqueous carboxymethyl cellulose solution

The stabilization potential of negatively charged sodium carboxymethyl cellulose (CMC) solution was assessed through investigation of its retention on clays under environmental conditions that promote soil desiccation. Sodium montmorillonite and kaolinite, commonly used in clayey soils, were mixed with aqueous CMC solutions in concentrations ranging from 0 to 10 g/L. These samples were dried in a specially-designed desiccation chamber which was operated at a temperature of 25°C and relative humidity of 30%. The results show an inverse proportionality between liquid loss and CMC concentration. Liquid loss from clayey soil follows the first-order reaction with a rate constant in the range of 4.6–6.7 mg/h. CMC half-lives on sodium montmorillonite during desiccation ranged from 103 to 181 h for an aqueous concentration range of 0.5–10 g/L compared to 108 h for distilled water. For kaolinite, more liquid was retained at 10 g/L CMC concentration than at other concentrations, but liquid retention was generally insignificant. These conclusions are valid for a desiccation duration of 890 h, a time that is reasonably simulative of the duration of exposures of bare ground surfaces to weather elements. The experimental results are explained in terms of the role of CMC molecular interactions with clay minerals in controlling fluid flow to desiccating clay surfaces.