Influence of Fe3+ Ions on Nitrate Removal by Autotrophic Denitrification Using Thiobacillus denitrificans

Abstract

The sulphur-based autotrophic denitrification process utilizing Thiobacillus denitrificans was studied experimentally as an alternative method of removing nitrates from industrial wastewater. The objective of the work was to examine the effect of ferric iron addition to the reaction mixture and determine optimal dosage for specific conditions. All experiments were carried out in anoxic batch bioreactor, and elemental sulphur was used as an electron donor. Compared to the control operation without ferric iron addition, significant increases in nitrates removal were demonstrated for the concentration of ferric iron equal to 0.1 mg L -1 . However, under these conditions, increased nitrite content was detected in the reaction mixture which exceeds the limits for drinking water.

Fabrication of a Sulfur/Steel Slag-Based Filter and Its Application in the Denitrification of Nitrate-Containing Wastewater

“…It was discovered that the SO 4 2− of the effluent of this system was slightly lower than the theoretical value; this may be due to the fact that the reactor simultaneously carries out the sulfur autotrophic denitrification and also due to the existence of a certain number of iron particles in the steel slag, which will also synchronize with the iron autotrophic denitrification and thus generate Fe 3+ [33,34]. Figure 3f shows the change of Fe 3+ in the system; the steel slag contained some iron particles, which partly enhance of the reactor's denitrification efficiency [29,35]. Usually, as the sulfur autotrophic denitrification is an acidproducing process, the pH of the system will gradually decrease as the reaction proceeds, while iron autotrophic denitrification is an alkaline-producing process, which can offset part of the acid produced by sulfur autotrophic denitrification to stabilize the pH of the whole system [36].…”

“…This may result from the fact that with the shortening of the hydraulic retention time, the system's treatment load increased, and the NO 3 − -N degradation also increased. Usually, the reaction rate of NO 3 − -N was faster than that of NO 2 − -N, which will result in the accumulation of some NO 2 − -N [28,29]. Figure 3d shows that the pH value of this system was always stabilized at 6.5-9 during the reactor operation, which was in the normal growth range of the microorganisms, indicating that steel slag could maintain the pH stabilization of this system [4,30].…”