Simultaneous nitrate and perchlorate reduction using sulfur-based autotrophic and heterotrophic denitrifying processes

BACKGROUND: This study aims at comparing the performances of sulfur-based autotrophic and methanol-based heterotrophic denitrification processes for simultaneous removal of perchlorate and nitrate. Influent nitrate concentration was kept at 25 mg L^-1 NO₃^--N throughout the study and perchlorate concentration was varied between 50 and 1000 μg L^-1. RESULTS: The heterotrophic process reduced nitrate and perchlorate completely in all tested conditions (i.e. various nitrate and perchlorate loadings). As for the autotrophic process, although high perchlorate removals were attained, perchlorate was always detected in the effluent with varying concentrations from 21.88-85 μg L^-1 depending on the perchlorate and nitrate loadings. Perchlorate was reduced from 1000 μg L^-1 to 53 ± 21.36 μg L^-1, corresponding to around 95% reduction in the autotrophic process at HRT of 2 h. The presence of perchlorate did not adversely affect the denitrification performance of autotrophic and heterotrophic processes under the conditions studied. The presence of nitrate inhibited autotrophic perchlorate reduction and prevented complete perchlorate reduction. CONCLUSION: An autotrophic process may be preferred over a heterotrophic one due to the elimination of organic supplementation and the risk of effluent contamination with organic substrate, but further polishing steps may also be required.