황을 이용한 독립영양탈질에서 FNA농도에 의한 탈질 효율 저해 특성

Abstract

국 문 요 지

고농도의 암모니아성 질소를 처리하기 위해 단축질소제거와 황탈질을 연계하여 적용할 경우 단축질소제거공정의 유출수를 황탈질의 유입수로 사용하게 된다. 생물학적 단축질소제거 공정에 따라 pH는 낮아지고(7.5-8.0) 아질산성 질소의 축적으로 인해 발생하는 FNA(free nitrous acid)는 황탈질 공정에서 탈질 미생물에 영향을 주어 탈질속도를 저하 시킬 수 있는 문제가 있다. 따라서 본 연구는 황을 이용한 독립영양 탈질에서 FNA의 저해영향을 파악하기 위해 실시하였다. FNA는 pH에 따라 값이 크게 변하기 때문에 우선, 황산화 미생물의 탈질속도에 영향을 주지 않는 적절한 pH 범위를 찾고자 하였다. 그 결과 탈질속도에 저해를 주지 않는 pH 범위는 7.5~8.0으로 관찰되었다. pH 7.5~8.0 범위를 넘지 않는 조건에서 FNA의 농도에 따라 탈질 효율을 평가하였다. pH를 7.5와 8.0을 고정으로 하고, 아질산성 질소의 농도를 높여 FNA에 변화를 주어 탈질속도를 비교하였다. 그 결과 아질산성 질소의 농도가 높아질수록 FNA가 증가하여 탈질속도는 감소하는 것으로 나타났으며, FNA 약 25 μg/L 이상부터 탈질속도에 영향을 주는 것으로 관찰되었다. pH변화에 따른 탈질 효율 평가와 FNA 농도 변화에 따른 탈질 효율 평가는 모두 하나의 동일한 황-CaCO3 복합담체 충진 반응기를 이용하였으며, 회분식으로 진행되었다. 이후에 도출된 FNA 범위를 위와 동일한 황탈질 반응기를 회분식에서 연속식으로 바꾸어 실험하였다. FNA 농도에 따라 제거효율의 변화를 평가한 결과, FNA 약 20 μg/L에서는 탈질에 대한 영향을 주지 않는 관찰됐으며, FNA 약 40 μg/L로 증가시켰을 경우 제거효율이 약 95%에서 56%로 감소하였다. 또한, FNA를 70 μg/L로 증가시켰을 경우 제거효율이 약 17%로 감소하는 것으로 나타났다.|ABSTRACT

Inhibition effect of Free Nitrous Acid (FNA) for autotrophic denitrification using sulfur by Wooram Lee

Master of Science Degree in Envitonmental Engineering The Graduate School, Hanyang University, 2013

Advisor : Professor Wookeun Bae, Ph.D.

For the treatment of wastewater containing high concentration of ammonia nitrogen, shortcut biological nitrogen in conjunction with autotrophic sulfur denitrification was investigated in this study. Biological nitrogen removal process is lowered due to FNA at pH (7.5-8.0) and high concentration of nitrite which can ultimately have an effect on sulfur denitrification. This study determines the inhibitory effects of FNA on autotrophic sulfur denitrification. Since FNA is also function of pH, so appropriate pH range was determined on which speed of reaction is not hampered. pH in the range of 7.5-8.0 was determined to be the most appropriate range which has no inhibitory effect on reaction rate. It was observed that between 7.5-8.0 pH, denitrification does not hamper. Denitrification rate was also evaluated under conditions that exceeds the pH range 7.5-8.0 depending upon the FNA concentration. Since increase in nitrite concentration increases FNA concentration, so it was observed that approximately 25 µg-FNA/L or above was more affecting concentration to decrease the denitrification rate. By using Sulfur-CaCO3 composite carrierfilled reactor, denitrification efficiency was evaluated by the evaluation of pH changes and FNA concentration. FNA range was also derived for the sulfur denitrification in continuous reactor same as in batch mode. As a result, approximately 20 µg-FNA/L does not affect the denitrification rate, but when this concentration was increased to 40 µg-FNA/L , removal efficiency decreased from 95% to 56%. Further, when FNA concentration was increased to 70 µg/L, the removal efficiency decreased to 17%.; ABSTRACT

Inhibition effect of Free Nitrous Acid (FNA) for autotrophic denitrification using sulfur by Wooram Lee

Master of Science Degree in Envitonmental Engineering The Graduate School, Hanyang University, 2013

Advisor : Professor Wookeun Bae, Ph.D.

For the treatment of wastewater containing high concentration of ammonia nitrogen, shortcut biological nitrogen in conjunction with autotrophic sulfur denitrification was investigated in this study. Biological nitrogen removal process is lowered due to FNA at pH (7.5-8.0) and high concentration of nitrite which can ultimately have an effect on sulfur denitrification. This study determines the inhibitory effects of FNA on autotrophic sulfur denitrification. Since FNA is also function of pH, so appropriate pH range was determined on which speed of reaction is not hampered. pH in the range of 7.5-8.0 was determined to be the most appropriate range which has no inhibitory effect on reaction rate. It was observed that between 7.5-8.0 pH, denitrification does not hamper. Denitrification rate was also evaluated under conditions that exceeds the pH range 7.5-8.0 depending upon the FNA concentration. Since increase in nitrite concentration increases FNA concentration, so it was observed that approximately 25 µg-FNA/L or above was more affecting concentration to decrease the denitrification rate. By using Sulfur-CaCO3 composite carrierfilled reactor, denitrification efficiency was evaluated by the evaluation of pH changes and FNA concentration. FNA range was also derived for the sulfur denitrification in continuous reactor same as in batch mode. As a result, approximately 20 µg-FNA/L does not affect the denitrification rate, but when this concentration was increased to 40 µg-FNA/L , removal efficiency decreased from 95% to 56%. Further, when FNA concentration was increased to 70 µg/L, the removal efficiency decreased to 17%.