The Immobilisation of Heavy Metals from Sewage Sludge Ash in CO2-Cured Mortars

Sewage treatment processes are a serious environmental threat due to the difficulties involved in its waste management and disposal. Therefore, one developing trend in sewage sludge processing is its thermal treatment, which generates sewage sludge ash that may contain many environmental pollutants, such as heavy metals. Moreover, due to the European Union requirements that not only focus on the waste generation reduction but also on its reuse and final disposal, it is essential to pursue new applications of such resources, such as the waste-based material incorporation into alternative cementitious materials. Thus, this study evaluated the heavy metals leachability of CO2-cured mortars incorporating sewage sludge ash as filler. For this purpose, Portland cement, reactive magnesia, and electric arc furnace slag were used to produce three different CO2-cured mortars, which were cured though pressurised accelerated carbonation curing for 24h. These mortars presented up to 12.7 MPa as compressive strength and their carbonation was confirmed by TG-DTG and FT-IR analyses. Their leachability of heavy metals met the European requirements for all waste materials, including inert materials, and post-industrial wastewater. Therefore, the immobilisation of heavy metals in this binding technology may be considered an effective method to safely manage sewage sludge ash.

Automated summary

The study found that incorporating sewage sludge ash as filler in CO2-cured mortars can immobilize heavy metals, meeting European requirements for heavy metal leachability in all waste materials, demonstrating the potential effectiveness of this technology for safely managing sewage sludge ash.