Nutrient removal efficiency in a rice-straw denitrifying bioreactor

Rice straw was used as a carbon source in a denitrifying bioreactor, for the removal of nutrients from agricultural drainage. Nutrient removal efficiency was evaluated by: (a) nutrient loading rates (low, medium, and high); (b) hydraulic retention time, and (c) comparison with another carbon source (woodchip). The results show that concentrations of nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), total nitrogen (TN), and orthophosphate phosphorus (PO43−-P) in the rice-straw bioreactor effluents were reduced by 53%, 25%, 40%, and 35%, respectively, compared with influents at the medium nutrient loading rate (NO3−-N: 10-15 mg N L−1, NH4+-N: 10-15 mg N L−1, PO43−-P: 1.0-1.5 mg P L−1) and long hydraulic retention time (HRT, 24 h), with a corresponding denitrification rate (DR) of 0.40 mg N L−1 h−1. Moreover, the rice-straw bioreactor showed significantly higher (p < 0.05) nutrient removal efficiency than the woodchip bioreactor at the medium nutrient loading rate and 24 h HRT.