Nitrate-contamination in groundwater sources has been globally taken as a crucial issue due to
the effects of nitrate on human health, e.g., methaemoglobinaemia. Various processes have been
applied for the treatment of contaminated groundwater with nitrate. Hydrogen-based autotrophic
denitrification (hydrogenotrophic denitrification) is an alternative process used for abatement of
the nitrate-contamination. Although high efficiency on nitrate removal was achieved by former
research, it is unclear whether the growth of true denitrifiers is affected by inorganic carbon in which
this is essential to comprehend the principal cause of nitrite accumulation. This study found that
inorganic carbon had no impact on the nitrate reduction rate whereas the nitrite reduction rate
was improved when a higher amount of inorganic carbon was supplied. Also, using bicarbonate as
an inorganic carbon source had a positive effect on the growth and adaptation of true denitrifiers
that can reduce the nitrite accumulation in hydrogen-based denitrification system.