عنوان مقاله [English]
Background and objectives: Aqua solutions containing nitrogen as nitrate are considered to be one of the most important pollutants of surface water and underground water. Denitrification bioreactors would provide a carbon sourced environment. Passing drainage water through such bioreactors would result in an increase in denitrification level and also, an increase in nitrate elimination from the environment. Denitrification bioreactors provide a carbon sourced environment. Passing drainage water through such bioreactors results in an increase in denitrification level and nitrate elimination. In this study, biochar is used as carbon wall in bioreactors. At first, nitrate and ammonium elimination performance of biochar-filled bioreactors and wheat straw-filled bioreactors are compared to each other. Later, effect of height of bioreactor on concentration of output nitrate and ammonium is taken under study. Also, performance of bioreactors in nitrate and ammonium elimination is investigated in a four month time period.
Materials and methods: In order to perform this research, poly-ethylene bioreactors with height of 125 centimeters were used. Height factor is taken under study in four levels; H1= 32.5cm, H2=62.5cm, H3=92.5cm, and H4=125cm. Control bioreactors (B0) were filled with 30% wheat straw and sample bioreactors (B1) were filled with 30% Biochar of wheat straw.
Results: Results showed that output nitrate concentration of denitrification bioreactors significantly depends on biochar type. Output concentration of biochar-filled bioreactors (B1) were measured 18.16 mg/liter while the output nitrate concentration of wheat-straw filled bioreactors (B0) were 49.01 mg/liter. Also it has been shown that increasing bioreactor’s height would reduce output nitrate concentration in both bioreactors. After four month of sampling, output nitrate concentration from 160 mg/liter was reduced in different treatments; 20.91 mg/liter in H1B1, 12.85 in H1B2, 8.05 mg/liter in H3B1 and 5.23 in H4B1. Also in control treatments nitrate concentration was reduced to 42.17 mg/liter in H1B0, 36.36 mg/liter in H2B0, 28.99 mg/liter in H3B0 and 19.65 mg/liter in H4B0. Time also has a significant effect on nitrate elimination (P <0.01). after four month of experiment, average concentration of output nitrate in sample bioreactors reached the minimum 21.77 mg/liter, while it was measured 59.21 mg/liter on the first day of experiment. Concentration of output ammonium in both biochar-filled and wheat straw-filled bioreactors was increased comparing to concentration of input ammonium. It can be explained as some of the nitrate is dissimulate to ammonium by anaerobic bacteria. But this increase was less than 0.5 mg/liter, hence was negligible.
Conclusion: performance of nitrate elimination in biochar-filled bioreactors is more than wheat-straw bioreactors. Also height increase in bioreactors would result in more nitrate elimination.