Biosolids as Fill Material in Road Embankment

Abstract

Biosolids are organic solid residues produced through the wastewater treatment process and contain many of the constituents removed from the influent wastewater. Currently, sewage treatment plant is experiencing a massive increase in the amount and composition of waste water and final component from these facilities i.e. biosolids, are constantly increasing and have made the disposal of solids waste a major problem around the world. The unutilized huge quantity of biosolids has drawn the attention of researchers to explore new strategies for bulk utilization. Thus, on account of this reality; reuse of biosolids as construction material for use in engineered fills can significantly reduce the demand for scarce virgin natural resources. Proper analysis on biosolids has pushed the boundaries of geotechnical engineering practice, in terms of identification and assessment of strength and deformation characteristics of biosolids. The engineering properties of biosolids with regards to moisture characteristics and geotechnical stability are of utmost importance. This thesis deals with an extensive suite of geotechnical and chemical laboratory tests which were undertaken on wastewater biosolids collected from the Kankhal Sewage Treatment Plant in India to evaluate their sustainable usage as a fill material in road embankments. As in India current scenario of utilization of biosolids in roads and embankment is relatively unknown. The laboratory tests include particle size distribution, specific gravity, Atterberg limits, compaction, hydraulic conductivity, California bearing ratio, consolidation and direct shear test. The results of an experimental study indicates that biosolids are classified as organic silt-sized particles of medium to high plasticity with high moisture content and liquid limit values. Compacted biosolids indicates very low particle density and high moisture content. CBR test results satisfy the local road authority specification for fill material. With regards to chemical test, the results of heavy metals were within acceptable limits for usage in geotechnical applications. This thesis therefore presents the innovative research study undertaken to analyze the biodegradation settlement characteristics of fresh biosolids by applying an analytical method when used as fill material in road embankment applications. The adopted model shows the effect of changing pH, temperature and moisture content on biodegradation settlement of biosolids layer in road embankment.