Effects of heavy metals on denitrification processes in water treatment: A review

[Display omitted] •Heavy metals significantly affect denitrification processes in water treatment.•Effects of heavy metals vary greatly with their types, valence, and concentrations.•Influence mechanisms of heavy metals on denitrification processes were discussed.•Regulatory strategies to reduce the effects of heavy metals were summarized.•The challenges and perspectives were proposed for further works. Nitrate is a global contaminant in water bodies due to its high-water solubility, excess nitrate poses a significant threat to aquatic ecosystems and human health. Biological denitrification is considered as an environmentally friendly technology for nitrate pollution treatment, but it is sensitive to environmental conditions. Heavy metals are a common and important environmental factor for affecting biological denitrification. Its effects vary greatly with different types, valence, and concentrations. This article provides the first comprehensive review on the current research status of the effects of heavy metals on denitrification processes in water treatment, with emphasis on different denitrification processes and the corresponding denitrifying bacteria species, as well as the responding strategies. Finally, the challenges and perspectives are discussed for future studies on effects of heavy metals on different denitrification processes.