| Design of capping for contaminated sludges typically involves use of a geotextile and requires evaluation of filtration performance. The objective of this study was to investigate the filtration performance of wastewater sludge with a variety of geotextiles and develop geotextile filter criteria based on a rational and quantitative approach. Laboratory filtration tests were performed to characterize the filtration performance of geotextile-sludge systems. Performance was also observed in ten different field test cells where sludge was capped using variety of geotextiles. The pore structure parameters of woven geotextiles (i.e., percent open area and pore size distribution) were determined with a new image analysis method. The constriction pore size distribution of nonwoven geotextiles, on the other hand, was determined using a model, named CONS, based on Markov processes and image analysis. A probabilistic filter model, named RETAIN, was developed for woven geotextiles based on the pore structures determined using the image analysis method. The results obtained from the probabilistic model were used to propose a semi-analytical method for developing filtration criteria for woven geotextiles. The filtration criteria for woven geotextiles based on this method and the existing empirical criteria from the literature were evaluated against the actual performance of the geotextiles observed in the laboratory filtration tests.; Results of the study show that: (1) filtration behavior of wastewater treatment sludge is different than that of a regular soil (e.g., silty sand), (2) woven geotextiles can be used effectively in filtering sludges, (3) for woven geotextiles, percent open area, and for nonwoven geotextiles, permittivity are the main parameters affecting the filtration performance, (4) the improved image analysis method and the Markov process-based model can determine the pore structure parameters of geotextiles at a reasonable level of accuracy, (5) the methodology based on the probabilistic filter model provides rational and quantitative filter criteria for selection of woven geotextiles, and (6) the proposed filter criteria successfully predict the filtration performance of sludge-woven geotextile systems. |
