Abstract
Biosolids/sewage sludge materials are the residue by-products of municipal wastewater treatment. Drainage of biosolids storage facilities is a critical aspect of their design. Laboratory permeability tests are widely performed for economical and practical reasons. Reported laboratory coefficient of permeability (k) values for these materials suggests very/extremely low permeability. However, limited field data reported for sewage sludge material would tend to suggest significantly greater k values. This briefing article explores issues related to the water permeability (filter size) of the porous media (discs) in contact with the specimen drainage boundaries during laboratory consolidation and permeability testing of biosolids/sewage sludge materials. These include clogging of their pores by fine soil particles and biogenic gas bubbles, bio-clogging, and the increase in viscosity of the pore liquid remaining within the test specimen due to filtering action. In applications where rates of flow (and consolidation) are measured, their effect can be to produce misleading results, potentially by many orders of magnitude. Recommendations on laboratory consolidation and permeability testing, including selection and verification of appropriate porous media, are presented. Issues relating to the analysis and interpretation of experimental consolidation data are discussed, with caution urged on the use of classical consolidation theory for these difficult and unconventional geomaterials.
Published Version
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