Hosein Asgari - Graduate, MSc Irrigation and Drainage Engineering, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran.
Javanshir Mobaser - Associate Professor. Department of Water Engineering, University of Mohaghegh Ardabili, Ardabil, Iran.
Ali Rasoulzadeh - Associate Professor. Department of Water Engineering, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran.
Javad Ramezani Moghadam - Assistant Professor. Department of Water Engineering, University of Mohaghegh Ardabili, Ardabil, Iran.

Denitrification bioreactors for nitrate removal from agricultural water effluents have improved in recent years due to their low cost and ease of use. Scientific results and local experience are required for the optimal use of bioreactors. This study aimed to study nitrate removal efficiency and the effectiveness of each of these factors. Thus, ۲۷ pilot bioreactors had the same volume and depth with different cross-sections in a randomized statistical design. Three geometric shapes of the trapezoid, rectangle, and triangle for the cross-section bioreactors and three organic matters including wood chips, corn stem chips, and wheat straw in ۳ replications were used. Nitrate concentration at the inlet of the reactor and their outlet was measured at hydraulic retention times of ۳, ۶, ۱۲, ۱۶, and ۲۴ hours. According to the average nitrate removal from the effluent, wood chips, wheat straw, and corn stem chips with ۳۱.۳, ۲۸.۶, and ۲۷%, respectively, were prioritized during the ۲۴-hour hydraulic retention time. Therefore, wood chips are the most suitable organic matter for nitrate removal from drainage water in actual biological reactors compared to other organic materials used in this study. The results demonstrated nitrate removal the ۲۵.۶, ۳۰.۱, and ۳۵.۳% for triangular, rectangular, and trapezoidal geometric shapes, respectively, for wood chips organic matters. Also, reactors with trapezoidal cross-sections have higher efficiency. In sum, this study showed that where there is a limit to the supply of wood chips, wheat straw and corn stalk chips can be used in bioreactors to remove nitrate.

Denitrification, Water reuse, Hydraulic retention time, Wood chip