Characterization of residual sand removed from the grit chambers of a wastewater treatment plant and its use as fine aggregate in the preparation of non-structural concrete

This article demonstrates the potential use of residual sand removed from grit chambers, which are used in the primary treatment of Wastewater Treatment Plants (WWTPs), as an alternative material to commercial sand in the production of non-structural concrete in civil construction. The results indicated that the residual sand has a high percentage of total fixed solids (96.9%), high moisture content (14.8%) and significant total coliform [average of 3.84 × 10⁷(100 mL)⁻¹] and fecal coliform densities [average of 5.22 × 10⁵ (100 mL)⁻¹]. The sand cleaning and drying procedure used in the research was effective, since it achieved the following removal efficiencies: about 98.8% of moisture, 67.1% of total volatile solids and 4-log E. coli. After cleaning and drying the residual sand, different amounts of this material were used to prepare the test specimens, which underwent tensile tests. The results of this study confirmed the viable use of residual sand as fine aggregate in concrete for non-structural purposes, and the best performances were verified in tensile and compressive tests (f_ck) and tensile strength tests (f_ctk) using 30% (in mass) of the residual sand as fine aggregate (values of 16.6 and 1.60 MPa, respectively).