Infection risk assessment of diarrhea-related pathogens in a tropical canal network

A quantitative microbial risk assessment (QMRA) of Cryptosporidium, Giardia and diarrhegenic Escherichia coli (DEC) infection was performed using Monte Carlo simulations to estimate the human health risks associated with the use of canal water for recreational purposes, unrestricted and restricted irrigation in a tropical peri-urban area. Three canals receiving municipal, agricultural, and, predominantly, industrial wastewater were investigated. Identification of pathogenic protozoans revealed the major presence of Cryptosporidium hominis and both assemblages A and B of Giardia lamblia. The highest individual infection risk estimate was found to be for Giardia in an exposure scenario involving the accidental ingestion of water when swimming during the rainy season, particularly in the most polluted section, downstream of a large wholesale market. The estimated annual risks of diarrheal disease due to infection by the protozoan parasites were up to 120-fold greater than the reported disease incidence in the vicinity of the studied district and the entire Thailand, suggesting a significant host resistance to disease beyond our model's assumptions. In contrast, annual disease risk estimates for DEC were in agreement with actual cases of diarrhea in the study area.     

Suitability of bentonite-paste tailings mixtures as engineering barrier material for mine waste containment facilities

This study investigates the feasibility of using bentonite-paste tailings (BPT) as a barrier (liner, cover) material for mine waste containment facilities. Improvements of the hydraulic properties are realized by using compaction to densify the paste tailings in the first stage and mixing an additive-like natural bentonite to paste tailings to further reduce the voids that control hydraulic conductivity in the second stage. A significant decrease in hydraulic conductivity is observed with these transformations. Values that are as low as 1 × 10^?9 and 4 × 10^?9 cm/s are obtained in 8% and 4% bentonite and BPT, respectively. Based on these satisfactory values, additional investigations are conducted to evaluate the freeze–thaw and wet–drying performance of BPT up to 5 and 6 cycles, respectively. The results show that negligible to acceptable changes in hydraulic conductivity occur. None of the changes reach one order of magnitude. As a final step, a cost analysis is undertaken to evaluate the economical benefits that can be obtained from such new material. When compared to conventional compacted clay–bentonite barrier or sand–bentonite with 12% bentonite concentration, it is found that the 4% BPT is less expensive by 66%. The results place this recycled BPT material as a promising candidate for barrier design while reducing the amount of waste to be managed and the cost of surface tailings management.     

The use of artificial neural networks to predict the effect of sulphate attack on the strength of cemented paste backfill

The growing use of cemented paste backfill (CPB) as a ground support method in mining and also as an environmentally friendly alternative for mine waste disposal demands a better understanding of the different processes that affect its strength. Due to its nature as cement based material, CPB is prone to the progressive loss of strength with sulphate attacks under certain conditions. The paper provides a background to sulphate attacks in CPB and artificial neural networks (ANN) and presents a model to predict the unconfined compressive strength of a CPB under sulphate attack, based on different water cement ratios, binder composition and binder content.     

Spectrometric characterization of effluent organic matter of a sequencing batch reactor operated at three sludge retention times

Effluent organic matter (EfOM) from activated sludge systems is composed primarily of influent refractory compounds, residual degradable substrate, intermediate products and soluble microbial products (SMPs). Depending on operational conditions (hydraulic and sludge retention time (SRT)), the quantity and quality of EfOM significantly changes. The main objective of this research was to quantify and characterize the EfOM of a lab-scale activated sludge sequencing batch reactor (SBR), which was operated at three SRTs and fed glucose, an easily biodegradable substrate. EfOM was followed with two direct-quantification methods (chemical oxygen demand (COD) and dissolved organic carbon (DOC)), three spectrometric methods (ultraviolet absorbance at 254 nm (UVA₂₅₄), excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC)) and three organic matter (OM) indices (specific UVA₂₅₄ (SUVA), SUVA-COD, COD/DOC ratio). The significant increment of UVA₂₅₄ and OM indices after treatment indicated an accumulation of refractory high-molecular-weight humic-like compounds in the EfOM, which demonstrated that EfOM was composed mainly by SMPs and not glucose. On the other hand, as the SRT increased, the amount of EfOM decreased, but SUVA, SUVA-COD and fluorescence intensity increased; these trends indicated the accumulation of SMPs of increased molecular weight and aromaticity. Increasing SRT in the SBRs reduced the amount of EfOM, but increased its aromaticity and reactivity. Visual analysis of EfOM EEMs showed two protein- and one humic-like peak, which were attributed to SMPs generated within the SBRs. PARAFAC determined that a two-component model best represented EfOM EEMs. The two-components from PARAFAC were mathematically correlated to the visually identified protein- and humic-like SMPs peaks.     

Effect of high temperature on strength and microstructural properties of cemented paste backfill

The main purpose of this research is to investigate the influence of high temperatures on the strength and microstructure (e.g. pore structure, porosity) of cemented paste backfill (CPB) through a series of experimental tests. A laboratory experimental setup allowing the simulation of various high-temperature conditions is developed. Different types of CPB specimens are exposed to different high temperatures (100, 200, 400 and 600 °C). The strength, porosity, pore size distribution and water absorption of these CPB specimens are then evaluated by laboratory tests. Thermogravimetric and differential thermal analyses are also performed to study the thermal behaviour of the CPBs exposed to high temperatures. The results show that high temperatures have a significant effect on the properties of CPBs. Generally, increasing temperatures up to 200 °C leads to higher strength in most types of CPB studied. The porosity and pore size distribution of the CPBs change only slightly. Above 200 °C, the temperature reduces the strength of the CPBs. The most notable strength decrease takes place at exposure temperatures exceeding 400 °C. The significant decrease of the strength of the CPB is accompanied by a significant change in the microstructure (porosity, pore size distribution, mineral phases). Moreover, the effect of high temperatures on the strength and microstructure of CPBs depends on the water/cement ratio (w/c ratio) and the tailings type.     

Comportement mécanique à l'appareil de cisaillement de casagrande de trois graveleux latéritiques compactés provenant du Sénégal Occidental

Compacted laterite soils are widely used as fills and road construction materials in tropical countries. The shear strength characteristics of these soils have been the subject of important studies and have produced slightly contrasting results. The results of the shear strength of three OMP compacted laterites from Western Senegal are examined in this paper. The shear strength parameter obtained using the big shear box (150 mm×150 mm, which can be extended to 300 mm) is a fonction of the level of stress and is also dependent on the state of the samples (soaked or not).     

Geotechnical characterization of expansive soils and their implications in ground movements in Dakar

To better understand the role of problematic soils in the instability phenomena observed in Dakar, investigations and laboratory tests have been undertaken including the clay mineralogy, physical properties, mechanical properties, shear strength and shrink/swell characteristics of the soils—fine/coarse-grained volcanic tuffs and residual (weathered) soil. The results were related to the slope instability and foundation failures observed in Dakar and recommendations made to mitigate the effects of these problematic soils in future developments.      

Knowledge Retrieval, Use and Storage for Efficiency

The Knowledge Retrieval, Use and Storage for Efficiency (KRUSE) symposiums aim at providing a forum for research related to efficient processing and management of complex information and knowledge. This special issue presents selected articles from the KURSE'97 symposium held in Vancouver, Canada. In this introductory article we describe the goals of KRUSE and present some background topics that are fundamental to the articles herein. In particular, we provide an overview of partial order theory, formal concept analysis and taxonomic encoding. We also outline the articles that follow.