In this current study, sawdust and zero-valent iron (Fe-0) were used as co-electron donors to evaluate the effects of coexistent ions on the combined heterotrophic and autotrophic denitrification (HAD) processes. The results showed that HCO3- and SO42- drastically enhanced nitrate removal. The promotion effect derived from both biological and chemical process by HCO3- and chemical process by SO42-. However, Ca2+ ions would remarkably increase nitrate removal due to promoting the electron transfer and the metabolic activities of bacteria, whereas the Cu2+ ions inhibited the biological process due to the deleterious effect on bacteria. Meanwhile, Fe2+ and Fe3+ ions exhibited inhibition effect firstly because of their toxicity to bacteria and promotion subsequently due to their enhancement on Fe-0 chemical denitrification. Moreover, byproducts such as nitrite, ammonium, dissolved organic carbon (DOC), etc. were also influenced by common ions.