Removal of highly elevated nitrate from drinking water by pH-heterogenized heterotrophic denitrification facilitated with ferrous sulfide-based autotrophic denitrification

► Heterotrophic denitrification occurred at acceptable rates in the acidic zone (pH 4.8-6.2) of the fixed bed. ► Acetic acid as substrate completely eliminated pH adjustment for denitrification. ► FeS-based denitrification at pH 7.8 reliably removed nitrate of low levels. ► Acetic acid-supported denitrification facilitated with FeS-supported denitrification reliably removed highly elevated nitrate.