Environmental potential assessment of MSWI bottom ash-based alkali-activated binders

Alkali-activated binders (AABs) stand out as a sustainable alternative to ordinary Portland cement (OPC) as they can be formulated using by-products or waste as raw materials. However, the presence of hazardous compounds in residues can lead to an increase in AABs' toxicity due to the highly alkaline media. Therefore, it is extremely important to evaluate their environmental risks to validate their use as building materials. This study environmentally assessed AABs prepared with two different fractions (0-30 mm and 8-30 mm) of weathered bottom ash (AA-WBA) from WtE plants. The potential leachate toxicity of AA-WBA was assessed using granular and monolithic leaching tests that simulated end-of-life and service life scenarios, respectively. Furthermore, an acute toxicity test with crustacean Daphnia magna as model organisms was conducted to determine the relationship between the leachate metal(loid) concentrations and the ecotoxicity of AA-WBA. The results showed higher metal(loid) concentrations in AA-WBA specimens prepared with the 0-30 mm fraction of WBA. The service life scenario revealed multiple metal(loid)-release mechanisms. The 48 h EC50 value (close to 10%; moderate toxicity) indicated that the use of the coarse fraction of WBA increased the immobilisation of the metal(loid)s. Finally, the correlation between the concentrations of some of the metal(loid)s and toxicity was demonstrated.The work is funded by the Spanish Government (BIA2017–83912- C2–1-R). The authors would like to thank the Catalan Government for the quality accreditation given to their research groups DIOPMA (2017 SGR 118), to SIRUSA and VECSA for supplying the MSWI Bottom Ash, and Befesa Company for supplying the PAVAL. Mr Alex Maldonado-Alameda is grateful to the Government of Catalonia for his research Grant (FI-DGR 2017). Dr Jessica Giro-Paloma is a Serra Húnter Fellow. Dr Araceli Rodríguez-Romero is supported by the Spanish grant Juan de la Cierva Incorporación referenced as IJC2018–037545-I