Comparison of heterotrophic and autotrophic denitrification processes for treating nitrate-contaminated surface water.

Abstract

The goal of this study was to compare the nitrogen removal rate, effluent algal growth potential (AGP), nitrous oxide (N2O) emissions and global warming potential (GWP) between two laboratory-scale bioreactors: the autotrophic denitrification biofilter (ADBF) and heterotrophic denitrification biofilter (HDBF) for treating nitrate-contaminated surface water. The comparative study of nitrogen removal rate between ADBF and HDBF was conducted by a long-term experiment, and the comparative study of the effluent AGP, N2O emissions and GWP between ADBF and HDBF were carried out by the corresponding batch tests. The results show that the heterotrophic and autotrophic denitrification rates were close to each other. Besides, the AGP of the ADBF effluent was 2.08 times lower than that of the HDBF effluent, while the N2O concentration in off-gas emitted from HDBF was 6-8 times higher than that from ADBF. The higher N2O-N emission rate of HDBF was mainly responsible for the higher GWP of HDBF than that of ADBF. Furthermore, with a novel light-weight filtration media (NLWFM) for filtration, the autotrophic denitrification (ADN) process combined with biofilter process would be the optimal denitrification process for nitrogen removal from nitrate-contaminated surface water. The study also provided a systematic method for evaluation of biological nitrogen removal (BNR) process.