Impact of ultra-low emission technology retrofit on the mercury emissions and cross-media transfer in coal-fired power plants.

• Ultra-low emission (ULE) retrofit significantly improves the overall Hg removal efficiency of devices. • The improvement of overall Hg removal after ULE retrofit mainly comes from the effect of dust removal devices. • Hg contents of both fly ash and gypsum are significantly lower than 25 mg/kg. • Large amount of Hg embodied in fly ash and gypsum calls for policies to guide the disposal of these wastes. China has applied the ultra-low emission technology in coal-fired power plants to control traditional air pollutants and to reduce Hg emissions synergically. In this study, we applied field experiment, model calculation, and literature review to evaluate the Hg control effect of ultra-low emission technology and the potential cross-media effect comprehensively. The dominant ultra-low emission technology significantly improves the atmospheric Hg removal efficiency from 75% to 87%. Such improvement mainly comes from the effect of dust removal devices. Based on the calculated distribution characteristic of Hg content of wastes, we find out that the improvement of Hg control effect of air pollution control devices significantly increase the Hg content of fly ash, which rises from 0.16 mg/kg to 0.33 mg/kg. However, the Hg content of gypsum decreases from 0.75 mg/kg to 0.51 mg/kg. Whether or not to carry out ultra-low emission retrofits, Hg contents of wastes from coal-fired power plants are overall lower than the limit of 25 mg/kg which is intended to be set as the limit for Hg-containing wastes. However, the embodied more than two hundreds of tons Hg in these wastes still require policies to guide the disposal of these wastes. [ABSTRACT FROM AUTHOR]