Ali Asghar Neshat - Department of Environmental Health Engineering, Esfarayen Faculty of Medical Sciences, Esfarayen, Iran.
Abdomajid Gholizadeh - Department of Environmental Health Engineering, Esfarayen Faculty of Medical Sciences, Esfarayen, Iran.
Babak Jahed - Department of Public Health, School of Nursing and Midwifery, Iranshahr University of Medical Sciences, Iranshahr, Iran.
Pouria Nikvand - Department of Public Health, School of Nursing and Midwifery, Iranshahr University of Medical Sciences, Iranshahr, Iran.

Introduction: The biological denitrification process is an interesting costeffective technique to remove nitrate from water supplies. Acetic acid can be used as a carbon source in this process, but its consumption rate is a critical issue and, in some cases, it is quite different from stoichiometric constants. The current study aimed to investigate the nitrate removal in an up-flow packed bed bioreactor. Furthermore, various parameters affecting this process were investigated and optimized. In this study, the autotrophic bacteria were used for the heterotrophic process. Materials and Methods: Initially, the autotrophic bacteria were cultured and used for the following heterotrophic conditions in distinct reactors. A pilotscale anoxic up flow bioreactor packed was constructed using the polyethylene media and applied to remove nitrate from the aqueous environment. Consequently, the effects of hydraulic retention times (HRT) and different acetic acid concentrations as carbon source were evaluated. During the study, the amounts of alkalinity, pH, temperature, and nitrate were checked.Results: The designed bioreactor removed an average of over 88% of nitrate, while the acetic acid consumption was 2 mg/mg NO3-N, which was lower than the stoichiometric constant for heterotrophic process. Moreover, in the three studied HRTs (1.5, 3, and 5 h), the Alkalinity increased from 14.2 to 19.8 %. Conclusion: The results of this study showed high efficiency in nitrate removal via heterotrophic denitrification using acetic acid as carbon source for autotrophic bacteria.

Nitrate Removal, Heterotrophic Denitrification , Acetic acid