A regulatory strategy for the emission control of hexavalent Chromium from waste-to-energy plants

In the last decades, the considerable improvements made on the mitigation of the environmental impacts from waste-to-energy (WtE) plants have let heavy metals emerge as the most concerning pollutants emitted from this sector. Heavy metals include a broad spectrum of compounds with very different toxicological effects on human health. However, in the European Union (EU), the current legislation does not consider the specific health effects of each heavy metal. In fact, with the only exception of mercury, the legislation sets an aggregated emission limit value for cadmium and thallium and an aggregated emission limit value for eight metals including total chromium (Cr). This simplification becomes even more critical when considering that total Cr includes hexavalent Cr (Cr VI), whose cancer potency is higher than other metals by > 2 orders of magnitude. The aim of this paper is to highlight and solve this critical legislation gap, and propose an innovative way to manage the emissions of Cr VI at the stack of waste incinerators. By analyzing the case study of a waste gasifier, the paper demonstrates that Cr VI to total Cr ratios higher than 10% may contribute to more than 95% of the total cancer risk in the nearby territory. In the view of cleaner strategies for energy production and waste management, a Cr VI concentration limit value of 0.005 mg/Nm3 at the stack level could be assumed in a first discussion phase to reduce the potential impacts from WtE plants.