Effects of salinity and empty bed contact time on simultaneous heterotrophic and sulfur based autotrophic denitrification

The effects of salinity and empty bed contact time (EBCT) on simultaneous heterotrophic and autotrophic denitrification of synthetic wastewater were evaluated in an up flow sulfur packed bed reactor. The reactor was filled with granular elemental sulfur particles with diameters of 2.8-5.6 mm and porosity of 40%. The initial culture was prepared from sludge of Shahrak-e-Ghods wastewater treatment plant. The influent nitrate concentration and EBCT were 600 mg NO3-N/lit and 16 h respectively. First the percent nitrate removal by heterotrophic denitrification (with methanol) supplied enough alkalinity to compensate the autotrophic alkalinity consumption, was determined 65%. Then salt concentration was gradually increased with NaCl from 0% in the feed. The Process kept high nitrate removal efficiency (99%) even at 3.5 % NaCl. During these changes the alkalinity variations were insignificant which showed the microbial population ratio of acclimated autotrophic to heterotrophic denitrifiers had no any significant change with NaCl concentrations up to 3.5% in the feed. At 4 and 5% NaCl, the efficiency drastically decreased to 78% and 48% respectively. Similar behavior was also observed for methanol removal efficiency, effluent turbidity and sulfate production. The effects of EBCT on denitrification of synthetic high saline wastewater under mixotrophic conditions were investigated at EBCT 20 to 2 h. Denitrification efficiency was close to 100% at EBCT of 20 to 8 h but decreased to 79% and 39% when the EBCT was 4 and 2 h respectively. The decrease in effluent sulfate concentration and the increase in effluent alkalinity and pH at EBCT of 4 and 2 h were considerable correspondingly. These results imply that the population ratio of autotrophic to heterotrophic denitrifiers depends on EBCT.

کلیدواژه ها:

Autotrophic Denitrification ، Heterotrophic Denitrification ، High Saline Wastewater ، Nitrate ، Sulfur ، Packed Bed Reactor