以連續式光催化反應系統還原水中硝酸鹽之研究

Removal of Nitrate in Aqueous Solution by Fluidized TiO2 Catalyst Bed Reactor

羅曉琪(Hsiao-Chi Lo)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00033

摘要

本研究擬以連續式光催化反應系統為主軸，並藉由有機物電洞捕捉劑之添加，利用二氧化鈦之同步氧化/還原作用以提升其對目標污染物之去除效率，且考量各項影響因子對硝酸鹽氮還原效能的影響。添加 5 mM 的各項電洞捕捉劑比較時，以甲酸效果明顯優於 EDTA、檸檬酸與水楊酸，主要是因為甲酸可產生具強還原力之 CO2．-，而最適添加的 HCOOH / NO3--N 莫耳比為 2.87，甲酸的濃度過與不及皆無益於硝酸鹽之還原。另於存在著硝酸鹽及甲酸之系統，直接光解與光觸媒之吸附現象對其影響不大，而除氧可促進硝酸鹽之還原，但對甲酸的去除卻有負面的效應。
在 pH 效應部分，降低 pH 有助於硝酸鹽及甲酸之去除，然而在使用低濃度甲酸於 pH 值為 1.5 時，硝酸鹽氮及甲酸之去除率各僅有 57、38%，主要是因為調整溶液 pH 值 所添加的氯離子會與目標污染物競爭吸附，進而降低處理效能。此外水力停留時間延長至 6.5 hr，硝酸鹽及甲酸之降解率皆可提高至 94%。另外硝酸鹽及甲酸之去除率皆與光照強度（1.0-2.5 W/m2）成線性關係。選擇甲酸濃度為 5 mM 時，或降低 pH 及減少甲酸的使用可提高氮氣之選擇性（94%），而水力停留時間與光照強度僅能改變系統之物理特性，故對選擇性不具影響力。另外在單位時間內的單位 TiO2 所能去除之硝酸鹽氮量以 HRT = 0.5 hr最多為10.5 mg，甲酸則以 40 mM 最多為 105 mg。最後經由多元迴歸分析得知本試驗之四項參數對硝酸鹽氮之去除效率確實有所影響，其中以甲酸被去除的濃度影響最大，其次 HRT 的增加及 pH的降低皆有助於提升硝酸鹽氮之去除效率，而光照強度的影響則相對較低。

關鍵字

光催化 ； 二氧化鈦 ； 連續式 ； 硝酸鹽 ； 甲酸 ； 氮氣 ； 飲用水

並列摘要

The purpose of this study is utilize TiO2 for simultaneous oxidization of hole scavenger / reduction of nitrate to enhance the removal efficiency of target pollutants by adding organic hole scavenger to the fluidized catalyst bed reactor, and consider the effectiveness of various parameters on the impact of nitrate reduction.
Direct photolysis and adsorption of photocatalyst had little influence on the presence of the system of nitrate and formic acid. Areation of N2 could promote the reduction of nitrate, but there was a negative effect on the removal of formic acid. In addition, formic acid was better than EDTA, citric acid and salicylic acid when comparing removal efficiency of nitrate between added various hole scavengers concentration of 5 mM. It was because mainly formic acid could generate a strong reducing species of the CO2. -. Moreover, the optimal value of added HCOOH / NO3--N molar ratio was 2.83. Too much or few concentration of formic acid were not conducive to the reduction of nitrate.
The removal of nitrate and formic acid increased with decreasing initial pH, however, the removal of nitrate and formic acid were only 57 and 38% respectively under low HCOOH concentration (5 mM), pH 1.5. It may be caused by competition for adsorption between target pollutants and chloride, and thereby decreased processing performance. Furthermore, the increasing of hydraulic retention time increased the efficiency for target pollutants removal. When HRT was extended to 6.5 hr, the degradation efficiency of nitrate and formic acid could be increased to 94%. Also, the removal efficiency of nitrate and formic acid was enhanced linearly with the increasing UV light intensity (from 1.0 W/m2 to 2.5 W/m2).
Selecting concentration of HCOOH was 2.83, decreasing the pH, and reducing the use of formic acid could enhance the selectivity of nitrogen (94%). And HRT and light intensity would not affect the selectivity of nitrogen which may be caused by the physical characteristics of the system only changed. Also, the capacity of TiO2 for NO3--N reduction was up to 10.5 mg when under 0.5 hr of HRT, and the capacity of TiO2 for formic acid oxidation was up to 105 mg when under 40 mM of formic acid concentration. Finally, the four factors of this experiment were all important parameters to determine the reduction of nitrate, all the results were regressed by multiple regression analysis. Among them, the removed formic acid had the greatest impact, longer HRT and lower pH were conducive to removal nitrate secondly, while the impact of light intensity was relatively low.

並列關鍵字

TiO2 ； fluidized catalyst bed reactor ； N-dope Nitrate ； Formic acid ； Nitrogen ； Drinking water

參考文獻

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