Hydrogenotrophic denitrification in an attached growth reactor under various operating conditions

To study the performance of an attached growth reactor on nitrate-nitrogen (NO₃-N) removal by a hydrogenotrophic denitrification process, the reactor was operated under various H₂ flow rates (30, 50 and 70 mL/min), hydraulic retention times (HRTs) (2.6, 3.1, 4.7 and 6.7 h) and inorganic carbon (IC) concentrations (excess and no IC addition). Synthetic NO₃-N water was prepared in accordance with the groundwater quality of the study area: Chyasal in Kathmandu Valley, Nepal. The results show an increase in denitrification efficiency with H₂ flow rate and HRT. Further, for effective denitrification, the dissolved hydrogen (DH) during operation should be maintained at greater than 0.1 mg/L. A sharp decrease in the denitrification efficiency from ∼96% (under excess IC) to 10–35% (under no IC) suggested occurrence of denitrification inside the attached growth reactor by a hydrogenotrophic process (using H₂) as well as heterotrophic process (using internal organic carbon). The good performance of the attached growth reactor in terms of high efficiency, low H₂ supply and short HRT requirement indicates the reactor's appropriateness for groundwater remediation through NO₃-N removal.