- 學位論文
零價鐵流體化床同步電化學循環再利用處理反應性染料(RB-19)之研究
Fluidized zero valent iron bed reactor for reactive dye (RB-19) removal with the ZVI recovering system by an electrochemical method
摘要
本研究利用零價鐵(ZVI)在低pH值及有氧條件下能產生強氧化能力之氫氧自由基的特性，並結合電化學還原法將反應過後造成污泥困擾之鐵離子還原成零價鐵金屬(ZVIR)，達到資源化再利用及污泥減量之效果。 零價鐵流體化床處理染料(RB-19)系統屬於連續式管柱床設備，研究結果顯示出，當系統無曝氣時，進流水pH值越低及零價鐵加藥量增加時，可增加染料處理效率，pH≦2.0及ZVI≧3.0g時染料去除效率及TOC去除效率皆可達到90 %及41 %之效果；於相同控制條件下，系統曝氣(O2 50 %)時可增加水中溶氧量，染料去除效率及TOC去除效率皆可達到96 %及52 %，有效提升去除效果；相同條件下系統控制不同氧氣濃度，曝氣時溶氧經由零價鐵反應過後水中溶氧量分別為1.3 mg/L、5.6 mg/L、7.5 mg/L，染料去除效率分別為45.6 %、84.9%、90.7%，顯示在高溶氧濃度有效提升零價鐵處理效率。 利用反應動力學評估本研究之流體化床為假一階反應，其控制最佳實驗參數pH=1.5、ZVI=3.0 g、O2 50 %條件下其反應速率常數15.076 min-1。反應性染料(RB-19)在無曝氣與曝氣條件下經過零價鐵處理後，利用GC/MS分析結果推估反應機制為ZVI與ZVI/O2(OH•)產生氧化能力達到去除效果，所生成中間產物為1-amino anthraquinone、Benzenamine, N-hydroxy、benzene、phenol、2-hydroxy 1,4-napthaquinoine。 本研究利用電化學還原法將反應過後鐵離子還原成零價鐵金屬(ZVIR)，系統屬於連續式電化學管柱床設備，利用管柱床完全混合優點增加電化學還原鐵離子之效果，結果顯示出增加電流密度(C.D.)時可有效提升還原效率(R.E.)及零價鐵金屬(ZVIR)產生量，但提高電流密度至2.0 mA/cm2無法有效提升還原效率而大幅降低電流效率(C.E.)，導致消耗大量電能，最佳操作電流密度控制在1.0 mA/cm2。將零價鐵流體化床同步電化學還原系統，控制參數pH=2.0、ZVI=1.0 g、U=1.0 mA/cm2，結果顯示出鐵還原效率及零價鐵金屬(ZVIR)產生量分別為99 %及9.69 g，且單一零價鐵粉(ZVI= 1.0 g)去除染料效率只能維持44 hr之後就穿透，結合零價鐵金屬(ZVIR= 9.69 g)可維持去除效率達74 hr，顯示出零價鐵金屬確實可達到循環再利用之成效。 評估系統經濟效益結果可知，操作電流密度1.0 mA/cm2時，所得到回收率為97 %，實際鐵金屬產生量為9.69 g，反應74 hr後所消耗電量為0.042624 kWh，估算得到本反應系統所使用電費為每度0.1602元，總電費為11.85元，估算本研究回收零價鐵金屬價值為29.1元，扣除電費後可得經濟收入為17.2元，系統符合經濟效益及高還原效率。
並列摘要
This research focused on the degradation of reactive dye (RB-19) by fluidized zero-valent iron (ZVI) bed reactor and the operating cost by recovering ZVI by electrochemistry reduction of ZVI (ZVIR). With the application of ZVI at the low pH under aeration condition, free radical of hydroxyl was generated and the sludge was reduced by utilization of ZVIR. The ZVI experiment was conducted in continuous fluidized bed system with and without aeration experiments for RB-19 removal, and the synthetic water containing RB-19 100 mg/L were treated at various pH, ZVI dosage and oxygen concentration. The results showed that the removal efficiencies of RB-19 and TOC after 180 min without aeration system was 90 % and 41 %, respectively, with the observed pseudo-first-order rate constants (kobs) for RB-19 removal of 5.207 min-1 when ZVI≧3.0g and pH≦2.0. Under the same experimental condition, the removals for ZVI fluidized bed aeration (50 % O2) system can increase to 96 % and 52 % with 15.076 min-1. Therefore, the high oxygen concentration could enhance the removal efficiency. The kinetic of RB-19 removal is pseudo-first order rate constant (kobs), and kobs was enhanced with increase of ZVI dosage, DO of water sample and decrease of pH. The greatest kobs was 15.076 min-1 when pH=1.5, ZVI=3.0 g and 50 % O2 in aeration system, due to that Fe2+ complexes can react with O2 which leads to the production of OH radical to oxidize RB-19. Finally, the analysis of the degraded products shows 1-amino anthraquinone, Benzenamine, N-hydroxy, benzene, phenol, and 2-hydroxy 1,4-napthaquinoine. With the application of electrochemical reductive system, the results showed the higher current density (C.D.) the higher reductive efficiency (R.E.) and lower current efficiency (C.E.). Moreover, the current density was higher than 2.0mA/cm2, the operating cost was increased. With the application of the synchronized electrochemical (ZVIR) recovering system under the same operating condition, the results showed that the reductive efficiency (R.E.) was 99 %, and ZVIR dosage was 9.69 g. The reaction time of RB-19 removal lasted 44 hr by ZVI for pH=2.0, and oxygen (50 % O2). Furthermore, the reaction time of RB-19 removal lasted 74 hr by ZVI/ZVIR under the same experimental conditions. The results of economic efficiency for electrochemical system showed, the recycling ZVIR was 9.69 g or 29.1 NT (according to the market iron metal price of 3.0 NT / g), and the consumption electricity was 0.0426 kWh or 11.8 NT (according to the electricity price of 3.76 NT / kWh). Therefore, this system has high recovering rate to reach the economic efficiency with the gain of 17.2 NT.