Abstract
In this current study, sawdust and zero-valent iron (Fe0) 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 Fe0 chemical denitrification. Moreover, byproducts such as nitrite, ammonium, dissolved organic carbon (DOC), etc. were also influenced by common ions.
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