利用微波消化法高質化含有重金屬之微藻廢棄物以生成乙醯丙酸的生質轉換

Abstract

多年來，人為活動造成了許多環境問題，在許多工業行為中，重金屬為一種被廣泛應用的化學物，而其造成的污染對於生態環境是一項極大的問題。當今科學家開發了許多去除重金屬的方法，在眾多研究中，以微藻作為吸附劑去除重金屬污染已被證實具有良好的效果，為一項具備環境友善的重金屬處理方法。而近年來，利用生物質作為替代石油原料的研究日漸興盛，微藻體內所含的碳水化合物，使其成為一種可以獲得平台化合物的熱門生物質原料。因此除了能將微藻作為吸附劑外，將廢棄的微藻進行再利用，亦成為一項具有潛力的研究。 本研究以小球藻作為生物吸附劑，搭配沉浸式微藻膜生物反應槽系統對合成地下水中的重金屬鉻、鎳、銅進行吸附，並將吸附過重金屬的廢棄微藻進行資源化應用，利用微波消化與液態酸的催化，以產出平台化合物乙醯丙酸。考慮在不同溫度、反應時間與催化劑濃度下，找出可以得到乙醯丙酸最佳產率的反應條件。並探討經微波消化過後，原本存在於微藻中的重金屬在固相與液相中的分布。研究結果顯示，當反應溫度為180°C、反應時間為1小時、硫酸催化劑濃度為0.5 M，可以得到效益最大的乙醯丙酸產率，平均為5.49 % (¬± 0.179)；在相同反應溫度與催化劑濃度下，將反應時間延長至2小時則可得到最大的乙醯丙酸產率為6.44 %。分析三種重金屬鉻、鎳、銅經過微波消化完成後在生成固相與液相上的分布結果，就重金屬銅的分布情況而言，在最佳條件(反應溫度180°C、反應時間1小時、硫酸催化劑濃度為0.5 M) 下進行消化後所得到的液相中，幾乎沒有銅的存在，而固體殘餘物中所含銅的量為總重金屬銅的99.80 %，表明利用微藻吸附重金屬銅，並且將其進行資源化後，重金屬銅會殘留於固相生成物中，對於乙醯丙酸產物存在的液相產生的污染較少；而對於鎳與鉻而言，因大部分的重金屬溶於液相中，因此需要近一步純化以取得乙醯丙酸。

Over the years, human activities have caused many environmental issues. In many industrial activities, heavy metals are widely used, and the pollution from that is a serious problem for the ecological environment. Nowadays, scientists have developed many methods for removing heavy metals. In many studies, using microalgae as an adsorbent to remove heavy metal pollution has been proven to have a good effect. It is an environmentally friendly process for heavy metal treatment. Meanwhile, research on the use of biomass as a substitute for petroleum raw materials has flourished in recent years. The carbohydrates in microalgae turn them into a popular biomass raw material for obtaining platform compounds. Therefore, in addition to being able to use microalgae as an adsorbent, the reuse of discarded microalgae has also become a potential research. In this study, chlorella vulgaris was used as a biosorbent, combined with an immersed microalgae membrane bioreactor to adsorb chromium, nickel, and copper in synthetic groundwater. The waste microalgae that had adsorbed heavy metals were used for resource utilization, and microwave digestion with liquid acid is run to produce the platform compound levulinic acid. Conditions of temperature, reaction time and catalyst concentration were tested to obtain the optimal yield of levulinic acid. After microwave digestion, the distribution of heavy metals originally present in the waste microalgae was also discussed in solid residue and liquid phases products. The results of the study show that at 180°C, 1 hour, and the sulfuric acid catalyst concentration is 0.5 M, the efficient yield of levulinic acid can be obtained, with an average of 5.49% (± 0.179), and the maximum yield of levulinic acid can be achieved by extending the reaction time to 2 hours. Under the optimal conditions, there is almost no copper in the liquid phase after digestion, and the amount of copper remained in the solid residue is 99.80% of the total copper, causing less pollution to the liquid phase of the levulinic acid product. As for nickel and chromium, most of the them are soluble in the liquid phase, thus further purification is required to obtain levulinic acid.