Effect of polymer and fiber usage on dewatering and compressibility behavior of fly ash slurries

Coal ash producing is an increasing trend because of its high energy demand worldwide. For transportation, disposal, and reuse of the industrial waste materials, geotextile tube’s dewatering technology has been widely used over the last three decades, which helps to decrease the volume of the dewatered slurry. In this study, effect of usage of polymer and fibers on dewatering characteristic of fly ash slurries was investigated. For the experimental investigation, an anionic polymer and short nylon fibers were used. As a new concept, centrifuge test is introduced as an alternative for the widely used pressure filtration test (PFT). Centrifuge test was used to evaluate final solid content of the retained sediments and change in slurry volume of fly ash. Tests were conducted on unconditioned and anionic polyacrylamide and/or fiber conditioned fly ash slurries. Centrifuge test results were compared with PFT results with respect to final solid content. It was found that fiber and/or polymer usage has remarkable effect on the dewatering rate of fly ash slurry. It was also found that final solid content of fly ash slurries was decreased by inclusion of fibers and polymer, which indicates that fiber and/or polymer usage can create more permeable soil body.     

δ13C variation of soil organic matter as an indicator of vegetation change during the Holocene in central Cameroon

In order to better understand the dynamics of the forest–savanna mosaic from central Cameroon, we analyzed ¹³C and ¹⁴C profiles of six oxisols: two under forests and four under savannas. The δ¹³C soil profiles collected in the forests indicate that these environments are stable at least since the mid-Holocene, whereas the areas currently covered by savannas were formerly occupied by more forested vegetations. The ¹⁴C dating of organic matter indicate that the late extension of the savannas in central Cameroon date from the Late Holocene, starting from 4000–3500 ¹⁴C yr BP.     

An environmental geomorphologic approach to site selection for hazardous wastes

Geomorphological features are essential parts of the environment and they represent an important conditioning factor for the development and distribution of certain biological assemblages, as well as for a variety of human activities. However, environmental geomorphology usually receives very limited or no attention at all in the process of environmental impact assessment (EIA). Nevertheless, the site selection process for hazardous wastes in environmental impact studies for individual projects plays an essential role. In order to determine the most suitable site in a region for municipal/hazardous wastes, several criteria are used, including geology, groundwater condition, climate, and land use. The present work describes a methodology taking advantage of environmental geomorphological features, and reducing these criteria in the site selection procedure in land disposal of waste; in addition, a case study is presented to demonstrate the applicability of the proposed methodology. The validity of the adopted site screening method is explained. This methodology comprises the use of a single geomorphological map to locate suitable landfilling sites for hazardous waste, instead of using separate maps for geological features, climatic features (temperature, precipitation, and speed and direction of the prevailing wind), slope and erosion. Furthermore, the present study is compared with a previous study performed in the GAP region, where the use of land resources is crucial for agricultural and water management purposes. The application of the described selection process and the verified method in this region shows that the adopted method and detailed criteria are valid.     

Comparative evaluation of freeze and thaw effect on strength of BEICP-stabilized silty sands and cement- and fly ash-stabilized soils

Acta Geotechnica - This paper addresses a soil bio-stabilization technique using bacterial enzyme-induced calcium carbonate precipitation (BEICP) as an alternative to previous conventional methods...     

A satellite based assessment of the impact of urban expansion around a lagoon

This paper examines the coastal regional trends in urbanization processes using remotely sensed images around the Kucukcekmece Lagoon as a case study, located in the western part of Istanbul, Turkey. Throughout the examination process, the coastline changes are determined for a long-term period. To achieve this goal, post-classification comparison method is applied to the CORONA and LANDSAT TM satellite images of 1963, 1987 and 2005. In order to identify the land use changes, common landscape structures in the region were distinguished as water, green and open land, urban and industrial areas. Due to the mix up of land-cover types between urban and industrial areas, the classified images are integrated with geographic information system data obtained from visual interpretation of the enhanced images and auxiliary data sets. The results of the change analyses in coastal region showed that important alterations are taking place in the area due to the unplanned urban and industrial expansions that has irreversibly changed the physical features of the Kucukcekmece Lagoon. According to image classification results, the urban land use area increased from 2 % oftotal area in 1963 to 38 % in 1987 and 46 % in 2005, most of which converted from agricultural and greenlands. At the same time, the ecological impact of the loss of specific land covers is highlighted based on the results of the land use changes and the previous scientific applications. Furthermore, some recommendations are given to planners, decision makers and politicians to maintain the sustainable coastal ecosystem management.     

Oceanic conditions in the eastern equatorial Pacific during the onset of ENSO in the Holocene

Records from South America show that modern ENSO (El Nino-Southern Oscillation) did not exist 7000 cal yr B.P. and has developed progressively since then. There has been little information available on oceanic conditions in the eastern equatorial Pacific (EEP) to constrain explanations for ENSO onset. We report quantitative observations on thermocline and mixed-layer conditions in the EEP during ENSO start up. We found important changes in both the thermocline and the mixed layer, indicating increased upwelling of cooler waters since 7000 cal yr B.P. This resulted from change in the source and/or properties of waters supplying the Equatorial Undercurrent, which feeds upwelling along the equator and the Peru margin. Modeling shows that ENSO is sensitive to subsurface conditions in the eastern equatorial Pacific and that the changes in the thermocline we observed were driven by extratropical processes, giving these a role in conditioning the development of ENSO. This is in contrast to models that call for control of equatorial Pacific oceanography by tropical processes only. These infer stronger upwelling and cooler surface waters for the EEP during the mid-Holocene, which is not supported by our results.