The Application of Using Fluidized-Bed Crystallization to Treat Nickel-containing Wastewater
|關鍵字:||流體化床反應槽;結晶;含鎳廢水;擔體;連續操作;crystallization;fluidized bed reactor;nickel-containing wastewater;media;continuous operation||公開日期:||2004||摘要:||近年來，流體化床結晶技術已經廣泛的應用於含陰離子及陽離子廢水上，除了改善傳統混凝方式易產生大量污泥的缺點，同時生成的晶體可以回收再利用，使重金屬污染物資源化而不會有污泥的二次污染問題，並減少釵h處理的程序，在經濟上的效益更高，能讓處理的廢水降低至排放標準，而不需額外的處理設備。本研究以由三段反應槽串聯而成的流體化床設備來處理含鎳廢水，利用碳酸鈉作為結晶藥劑，使鎳離子形成碳酸鎳或氫氧化鎳的難溶性物質覆誚b擔體的表面。藉由改變不同的反應莫耳比、水力負荷、擔體量、廢水負荷等參數來進行試驗，以找出最佳的操作條件，此外，並以連續操作的方式對廢水進行處理，探討不同反應槽的擔體表面結晶結構及分析其中的結晶含量。
實驗結果顯示：在不同水力負荷與反應莫耳比操作下，越慢的水力負荷有越高的去除效果，以23 ~30 m/h為最適合，當總碳酸鹽與鎳離子之反應莫耳比達2.5時有最好的處理效率，總碳酸的量過低則系統的飽和度不足，不僅第一反應槽去除能力不佳，對於過濾後的出流水水質亦無法符合標準，而過高的加藥量則會造成過飽和度太高，雖然出流水過濾後皆能符合排放標準，但對初段反應槽來說則會使處理能力減少，且過多的加藥量亦造成浪費。就填充擔體量而言，增加其填充量雖能提高去除效果，但就實際操作上，考慮到擔體流體化時的膨脹程度，填充的量仍應以反應槽的1/4~1/3高度的擔體量為佳。
就整體的處理能力來說，在較佳的操作條件下，當進入反應槽的鎳離子負荷為3.61 kg/m2h時，第一段反應槽之去除率約90%，而處理後的出流水鎳離子濃度則可控制在2 mg/l以下；而當進流鎳離子負荷小於1.87 kg/m2h時，則排放水鎳離子濃度可控制在1 mg/l以下。當採迴流方式時，過低的反應莫耳比將造成放流水水質隨時間的增加而變差，過高的莫耳比亦有同樣的結果，最適的莫耳比為2左右。
In recent years, fluidized bed pellet reactors have been extensively applied in the removal of anions and cations from wastewater. It improved the disadvantage of producing a large number of sludge easily in traditional unseeded precipitation treatment, and produced reusable pellets as resources. This technology cut down many processors and let the contaminants of heavy metals resource, but no second pollution problems of sludge. On the processor of wastewater, it could fit the emission standard of wastewater easily, and it had even more economical benefit and had no additional treatment equipment. In this research, the crystallization process of a fluidized bed pellet reactor was studied in the treatment of nickel-containing wastewater .The crystallization reactor was connected by three same reactors. Sodium carbonate was added as the reagent solution to form nickel carbonate and nickel hydroxide on the surface of the pellets in fluidized bed reactor. This study investigated the effects of some important factors, including CT/Ni feeding ratio、upflow rate、quantity of pellet、Ni-loading etc. We made experiment by continuous worked for conferring the crystals structure of pellet’s surface in different reactors, and analyzed the coated quantity under optimum operation conditions finally. The results showed that operated with the different upflow rate and different CT/Ni feeding ratio ,the lower upflow rate increased removal efficiency ,especially on the condition of 23~30 m/h and CT/Ni feeding ratio was 2.5. The processor system would in low supersaturation when CT is not enough .On this condition the first reactor had bad removal efficiency and emission still couldn’t fit to the emission standard of wastewater. In the same way, overdosed of sodium carbonate would lead to high degree of supersaturation, the way would decrease removal efficiency of first reactor, but the filtrated wastewater could fit the emission standard .For the quantity of pellet, the increasing quantity could improve the removal efficiency. But in practical operation, we considered the expand level of pellet when it fluidized, the better amount of pellets should be 1/3~1/4 times of reactor’s height. For macrocosm treatment ability (under optimum operation conditions), the removal efficiency of the first reactor was about 90% when inflow Ni-loading was 3.61 kg/m2h.The concentration of nickel was less than 1 mg/l and could fit the emission standard as Ni-loading was smaller than 1.87 kg/m2h.On the condition of recirculation, the removal efficiency was more and more terrible with operation time increased as the too low or high CT/Ni feeding ratio. The optimum CT/Ni feeding ratio was 2. In the continuous process, we used as 35 mg/l of nickel inflowing in the fluidized bed, the results show that the removal efficiency would not decrease as operation time increased. The important factor was that the pellet’s size would more and larger and the interior’s free space of reactor decreased. We must change the pellet in fluidized bed reactors during a series processor. By the way, we observed the variation of pellet’s surface during the processor and discovered that some green crystal coated on pellet’s surface certainty. And then photographed the pellet’s surface by SEM, the images showed that the preceding reactor had the better strict structure. This result also showed that the majority mechanism of crystallization occurred in preceding reactor and sediment occurred in later reactor.
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