本研究則擬以所產生的藻體以生物吸附的方式去除水體中有害之重金屬，取自南台灣水域所篩選分離之Scenedesmus obliquus CNW-N和 Chlorella vulgaris ESP-31為目標藻株，進行光自營培養。結果顯示，Scenedesmus obliquus CNW-N藻株之最高二氧化碳移除總量接近15 g，其生長量為319.3 g/l/d，而Chlorella vulgaris ESP-31 之二氧化碳移除量達9.5 g，而其平均每天生長量為214.2 g/l/d。接著，我們將藻體添加至含鎘、鎳、鋅等重金屬之水體中，進行不同重金屬吸附之可行性評估。結果顯示S. obliquus CNW-N在重金屬濃度50 mg/L下，對鎘(Cd) 、鎳(Ni)與鋅(Zn)吸附量分別為42.9、28.5與40.3 mg/ g，而Chlorella vulgaris ESP-31在相同情況下對對鎘(Cd) 、鎳(Ni)與鋅(Zn)吸附量分別為17.1、16.3與13.4 mg/ g。上述結果顯示S. obliquus CNW-N與C. vulgaris ESP-31除了對二氧化碳具有優異的移除效能外，且對水體中的重金屬鎘具有很好的吸附能力。
在重金屬鎘(Cd)生物吸附策略中，本研究探討接觸時間、pH、溫度、重金屬濃度與藻體添加量對生物吸附效率之影響，並在在最適化溫度與pH情況下，探討恆溫飽和吸附曲線與動力學機制。實驗結果顯示，S. obliquus CNW-N在pH 6與25oC與C. vulgaris ESP-31在pH 6與30oC有最佳吸附效果。且當藻重為0.8 g/L情況下進行吸附，在5分鐘內達到平衡，吸附過程符合Langmuir恆溫吸附曲線，可得到最大吸附量分別為68.6 mg/g和23.4mg/g。此結果指出S obliquus CNW-N有較佳的吸附效果。
因此，本研究選用S. obliquus CNW-N 為目標藻株進行固定化細胞連續式管柱進行鎘去除之生物吸附程序。此方法可提高藻體濃度，並方便微藻藻體利用及回收，且可利用供給營養源使藻體持續生長，使其附著在載體(luffa sponge)上之藻量增加，進而達到較佳的生物吸附效果。本研究分別探討流速(25、50、75 ml/min)、營養源置換次數(0次、1次、2次)、載體直徑(1cm、1.5cm、2cm3)對生物膜生長之影響。在最適化條件下(流速25 ml/min、營養源量置換1次、載體大小1cm3)，藻體濃度可達原本的3.5倍(約17.5 g/L)。再將固定化細胞在填充床反應器進行重金屬(Cd)吸附，並對重金屬(Cd)吸附量、吸附效率與貫穿曲線進行評估。結果發現在流速5 ml/min、鎘進料濃度濃度7.5 mg/L時，有最大吸附量為38.4 mg之總吸附量，穿透時間為15.5 h。此策略不但可同時兼具環保以及去除環境有害污染物等多重優勢，更具有未來開發與應用之潛力

In this study, microalgal cells were utilized for heavy metals removal via biosorption process, Efficient CO2-fixing microalgae Scenedesmus obliquus CNW-N and Chlorella vulgaris ESP-31 isolated from southern Taiwan were used as the biosorbents to remove cadmium from aqueous solution. The microalgae were grown by continuous feeding of atmospheric air enriched with 2.5% CO2, achieving a CO2 removal of around 15 g and a biomass production of 319.3 g/l/d for S. obliquus CNW-N for 8 days, and CO2 removal of 9.5g and a biomass production of 241.2 g/l/d for C. vulgaris ESP-31. The adsorption of Cd, Zn and Ni by Chlorella vulgaris ESP-31 and Scenedesmus obliquus CNW-N were investigated at various pH values. It was found that the adsorption capacities of Cd, Zn and Ni were 42.9, 40.3 and 28.5 mg/g, respectively for S. obliquus CNW-N and 17.1, 13.4 and 16.3 mg/g, respectively for C. vulgaris ESP-31. These results indicated that the two species had better ability to adsorb Cd, which became the target heavy metal ion for the later stage of this study.
The adsorption of Cd by the two microalgae species was further investigated with variations in contact time, temperature, pH, adsorbent concentrations and initial metal concentration. The effect of biosorbent dosage on biosorption performance was also investigated. Kinetic and isotherm adsorption experiments were carried out at the optimal pH and temperature. The biosorption of Cd by S. obliquus CNW-N was optimal at pH 6.0 and 30oC, while the C. vulgaris ESP-31 exhibited best biosorption efficiency at pH 6.0 and 25oC. A biosorbent dosage of 0.2 g was required for good Cd removal for both species. The biosorption reached equilibrium adsorption within 5 min of contact time and the adsorption equilibrium obeyed Langmuir isotherm with an estimated maximum biosorption capacity (Qmax) of 68.6 mg/g for Scenedesmus sp. and 23.4 mg/g for Chlorella sp..
As S obliquus CNW-N exhibits better adsorption ability for Cd, further experiments were carried out to establish a continuous fixed bed adsorption process for Cd removal by S obliquus CNW-N cells immobilized on loofa sponge. This immobilized-cell biosorption process allows better recovery and reusability of the microalgae biomass. The growth of microalgae on the support with proper nutrient supply could also enhance the overall metal removal activity. Operating parameters like feedstock flow rate, medium replacement, particle diameter of the sponge were varied and studied. The best cell growth on the sponge support was obtained with medium flow rate at 25 ml/min; using one-time medium replacement and adopting sponge particle diameter of 1 cm. The best performance on fixed-bed biosorption (38.4 mg, breakthrough time = 15.5 h) was achieved at a flow rate of 5 ml/min with the influent Cd concentration of 7.5 mg/L.

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