Nitrate Removal from Drinking Water by Autotrophic Denitrification

• Main Authors: Chih Cheng Chang, 張志誠
• Other Authors: Szu Kung Tseng
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/37107958120976173498

博士 === 國立臺灣大學 === 環境工程學研究所 === 87 === Two pure cultures of hydrogen oxidation bacteria were tested to determine the optimal denitrification conditions and thereby choose the better strain to immobilize for continuous flow reactor study. A novel cell immobilization technique is reported, and the operational results are compared with three other immobilization methods. In this paper, the operational factors and kinetic parameters were studied and a kinetic model was established to predict and to prove the operational data. The results show that this autotrophic denitrification system is a practical technique for nitrate removal in drinking water. Nitrate removal efficiency was found to be higher than 90% when nitrate concentration was below 45 mg-N/L at HRT = 1 hour. The microorganism was very stable. Alcaligenes eutrophus was the main microorganism in this system and could sustain superiority for a long time. The TOC concentrations in the effluent water were all below 4.0 mg/L, which can conform the drinking water intake standard. Four cell immobilization methods (alginate, PAA-alginate, PU sponges and PVA-alginate) were compared in this study. Among these methods, PVA-alginate is the best choice for cell immobilization; The second-best method is PU sponger. PAA-alginate is also a practical method although the gel structure is weaker, and alginate is not suitable for use in this system. The dissolved hydrogen concentration is the most important factor of denitrification. The dissolved hydrogen concentration needed for this system increased with increasing nitrate concentration. Nitrite reductase is more sensitive than nitrate reductase to dissolved hydrogen concentration. Nitrite reductase was inhibited at dissolved hydrogen concentrations below 0.2 mg/L, whereas nitrate reductase was inhibited at dissolved hydrogen concentrations below 0.1 mg/L when the influent nitrate concentration was 25 mg-N/L. The hydrogen gas, which was first dissolved in a pressurized tank, can provide a higher dissolved hydrogen concentration and a high hydrogen utility efficiency. Phosphate can improve the activity of nitrite reductase and help to reduced the nitrite concentration in the reactor. The economical phosphate concentration for the continuous flow reactor is 0.5 mg-P/L. A kinetic model, using carrier volume to replace the biomass of microorganism, was established in this study. The kinetic parameters obtained in this study were apparent parameters which include biomass effects, diffusion effects and so on. The results show that the model can successfully prove the experimental data and can be used to predict the affection of dissolved hydrogen concentration.