Results in Materials (Dec 2022)
Sustainable usage and the positive environmental impact of wastewater dry sludge-based concrete
Abstract
The paper examined the application of dry sludge in lightweight concrete and the associated environmental risk. Population growth has led to an increase in residential and commercial wastewater sludge production. The sludge is deposited to a designated landfill, rendering the area useless and posing a significant environmental concern. The need for lightweight materials in the construction sector has resulted in the replacement of dry sludge for the basic components of concrete. The dry sludge came from the WWTPs in Polokwane, Limpopo Province, was used as a partial replacement for sand (0, 2.5, 5, 7.5, 10, and 12.5%) in concrete. The samples prepared were cured in wastewater and potable water. The results showed that the partial substitution of sand with 7.5% dry sludge in the concrete mixture reached the desired strength of 25 MPa and can be employed in lightweight structural applications. Concrete cube unit weight reduced by 0.8, 2.3, 2.6, 3.9, and 4.6% compared to the control sample when 2.5, 5.0, 7.5, 10, and 12.5% of the sand was substituted with sludge. Concrete samples were submerged in iodine water for 28, 90, and 140 days to test the leaching of soluble metals. The levels of heavy metals in leachate were far lower than what the US Environmental Protection Agency (EPA) considers to be safe, under their Toxicity Characteristics Leaching Procedure (TCLP) standards. EDX examination of sludge-based concrete showed a considerable reduction in metal weight percentage, the concentration of calcium increased by 69% due to the cement content; and the blending aggregates lowered silicon, aluminium, iron, and potassium by 33.3, 66.9, 34.2, and 77.8%. Therefore, wastewater may be utilized as a concrete curing medium, and sludge-based concrete can be used for simple structural repairs at WWTPs.
