autotrophic denitrification of synthetic nitrate-contaminated groundwater in up-flow fixed-bed bioreactor by pumice as porous media

Background: increasing nitrate concentrations in groundwater resources is considered a common environmental and public health problem worldwide. in this research, an autotrophic upflow bioreactor with pumice as media was used to study the effects of the sulfurtonitrogen (s/n) ratio and empty bed contact time (ebct) on nitrate removal efficiency and byproducts.methods: experiments were carried out in a 3.47 l upflow, fixedbed reactor with 3 sampling ports. to evaluate the overall impact of s/n ratio and ebct on the performance of the bioreactor, several phases with different s/n ratios and ebcts were applied.results: at a constant s/n ratio of 3.85 g/g, as ebct decreased from 24 hours to 2 hours, the nitrate removal efficiency decreased from 98% to 64%. on the other hand, at the desired ebct of 4 hr, as s/n ratio decreased from 3.85 to 1.51 g/g, nitrate removal efficiency was reduced from 85% to 32%. changing the ebct and s/n ratio also affected the effluent nitrite and sulfate concentrations as byproducts. at the s/n ratio of 3.85 g/gand ebct of 24 hours, effluent nitrite and sulfate concentrations were 0.1 mg no2n/l and 463 mg so4 2/l, respectively. decreasing the s/n ratio to 1.51 g/g and the ebct to 4 hours caused drastic changes in effluent nitrite and sulfate concentrations.conclusion: the results indicated that the autotrophic denitrification with thiosulfate as electron donor and pumice as media was feasible and applicable for nitrate contaminated groundwater.