Life cycle assessment of the use of sewage sludge as Portland cement replacement

Abstract

In this paper, we proposed an alternative thermal treatment of sewage sludge, aimed at its application in blended cements, which can reduce the energy demands and requires less technologically sophisticated processing. The life cycle assessment (LCA) was performed to quantify the environmental impact of the sewage sludge used as a partial cement replacement. The LCA was focused on the CO₂ emission and energy consumption. The functional unit of 1 m³ of blended mortars composed of Portland cement CEM I 42.5, silica sand, and thermally treated sewage sludge, where the sludge was used as partial cement substitute in a dosage of 10, 20, and 30% by mass of cement, was analyzed. The positive effect of the use of sewage sludge as a partial cement replacement with respect to the energy consumption and GHG emission, considering the compressive strength of the analyzed composites, was quite apparent. The decrease of energy consumption necessary for the production of the analyzed blended binders was nearly 10% per each 10% of sewage sludge used as Portland cement replacement. The energy needed for the sludge thermal treatment at 700°C was 220 MJ/t. The emission of GHG related to the sludge thermal treatment was 40kg/t. The presented data were strongly affected by the applied distribution of electricity sources, with a high share of coal combustion plants.