Anammox coupling with nitrate reduction under various electron donors was studied using sludge acclimatized to have anammox and denitrification activities. Due to a deficiency in electron donors for NO3- reduction, anammox activity in an inorganic medium containing NO3- and NH4+ was lower than that in NO2- and NH4+. Anammox could use NO2- competitively against denitrifiers under a very limited NO2- concentration, and additions of swine wastewater or acetate stimulated anammox activity in an inorganic medium containing NO3- and NH4+ with no inhibition effects. However, a high concentration of swine wastewater caused an exponential increase in denitrification activity. The addition of hydrogen and iron stimulated anammox activity in an inorganic medium containing NO3- and NH4+ but iron showed an inhibitory effect on anammox in a medium containing NO2- and NH4+. Hydrogen was shown to be advantageous since it did not increase denitrification even when its addition was increased. (C) 2012 Elsevier Ltd. All rights reserved.