Long-term filtration performance of nonwoven geotextile-sludge systems

A study of the filtration behaviour of contaminated wastewater treatment sludges was conducted. The laboratory portion of the study included a series of filtration tests with different nonwoven geotextiles. Filtration performance of the sludge–nonwoven-geotextile systems was also observed in field test cells by exhuming geotextile samples from the cells after exposure followed by analysis. The results indicated that the sludges could be filtered with nonwoven geotextiles selected on the basis of geotextile permittivity. The standard gradient ratio test did not always reflect the filtration performance, and therefore other clogging ratios should be considered. Two commonly used geotextile constriction sizes, O95 and O50, could not be related to either clogging or piping. Additionally, ratios of geotextile constriction size to soil particle size in the existing filter criteria did not always predict the observed filtration performance.