植物微生物燃料電池進行環境綠化、復育與資源化之研究

Abstract

植物微生物燃料電池是結合植物、微生物及電化學技術且能產生電力的一種永續性的技術。植物微生物燃料電池應用在環境工程領域以保護環境是一創新的科技。為減緩城市氣候與熱島效應，植物微生物燃料電池可結合綠屋頂可進行城市綠化。實驗結果顯示，狼尾草的實驗組在三月份的單日最大之平均輸出電壓達到了607.28 mV，水蠟燭也有215.17 mV，甚至有組樣品具有772.54 mV的輸出電壓。維持樓板溫度方面，高溫時段（11:00 to 15:00），系統模組下方的平均溫度較樓板低24.81oC。低溫時段（1:00 to 5:00）的情況，相較於無模組的樓板，植物微生物燃料電池能保持4.12oC的樓板恆溫。經過歸納，植物品種有不同的輸出電壓，可見植物的品種為影響輸出電壓的主要機制。環境溫度、淨太陽輻射、植物的生理構造以及植被覆蓋率皆影響系統的產電趨勢。其中狼尾草與水蠟燭之植物微生物燃料電池的產電趨勢分別受到淨太陽輻射與氣溫的影響。此外，經土壤熱通量(soil heat flux)分析儀得知，系統的溼地元素也能吸收源自於太陽的能量。 此研究中，試著建構植物微生物燃料電池技術復育受六價鉻污染土壤，提升對六價鉻的去除效果以及產生能源，再進行長時間的觀測探討系統運行的機制。此研究的植物微生物燃料電池使用狼尾草與蘆葦在溫室中進行實驗，分別處理不同濃度的六價鉻污染土壤，以求得最佳處理參數。實驗的結果顯示，土樣經過植物微生物燃料電池的運行，由酸性土壤提升至中性土，土壤導電度也下降。土壤六價鉻最大平均的去除率超過99%。土壤總鉻也是隨著系統的運行逐漸下降。運行過程中，使用石墨碳氈為電極的實驗組在外接1KΩ電阻下可在當日平均產生平均469.21 mV的輸出電壓。實驗結果顯示，植物微生物燃料電池可進行控制場址的污染土壤之復育，主要的去污機制為微生物電化學反應與植物吸收。 在植物微生物燃料電池超過10個月的運行，外源50 mg/kg Cr(VI)污染土壤中的化學與微生物的分佈有所不同。例如，狼尾草之植物微生物燃料電池在陰極土壤與陽極土壤的的pH值分別為7.03 ± 0.15 and 6.09 ± 0.05，顯示陰極土壤的pH高於陽極土壤。導電度分別是78.00 ± 5.61 與156.25 ± 7.89 μs/cm，表示陰極土壤的導電度低於陽極土壤。陰極土壤的總鉻濃度為65.75 ± 3.77 mg/kg，低於陽極土壤的總鉻濃度84.29 ± 2.87 mg/kg。經過16S rRNA基因世代定序結果的方差檢驗的置換多變量分析結果，陽極和陰極樣品的微生物群落有明顯的差異。陽極和陰極之間的分層化學與微生物特徵主要由植物微生物燃料電池內的生物電化學過程和電動勢趨動。 植物微生物燃料電池收割後，其生物質材料可被進行廢棄物資源化。我們可使用液體或固體酸為催化劑，搭配綠色溶劑，戊內酯溶液產生乙酰丙酸，以實現生物煉製。在微波消化爐的加熱至180度的條件下，硫酸水溶液在60分鐘的反應，使產率增加到15.20 mol %，高於使用固體酸催化劑。此外，在戊內酯溶液使用1M硫酸作為催化劑，60分鐘後的產率達到13.39 mol %，高於未使用硫酸為催化劑的戊內酯溶液。戊內酯溶液與水的比例會影響乙酰丙酸的產率。70/30與50/50的比例的條件有更高的乙酰丙酸之產率，因為此溶劑的水分子可提高五碳醣轉化至乙酰丙酸的效率。掃描式電子顯微鏡圖像證明，纖維素結構在固體酸的水溶液中是強韌的。但可用液體酸催化戊內酯水溶液改變纖維素結構。X-繞射儀提供了短時間內，纖維素溶解或水解的證據。根據衍射熱分析質譜的峰值，微波加熱後的固體殘留物的熱穩定性高於較低溫的反應條件。轉化反應後，總鉻與六價鉻皆留在固體殘留物中。 本博士論文研究將植物微生物燃料電池應用在城市綠化、重金屬土壤復育以及植物廢棄物資源化。整個研究流程對植物材料進行永續的循環使用。

The plant microbial fuel cell (PMFC) is considered as a sustainable technology in which plants, microbes, and electrochemical cells are the major components and has the synergistic effect on electricity generation. Applying PMFCs in the environmental engineering field for environmental protection is novelty technology. For relieving urban climate and the heat island effect, PMFCs with green roofs were used in urban greening. PMFCs with green roofs can generate higher output voltage than plant-free MFCs in March. Furthermore, the maximum daily average output voltage of Chinese pennisetum and Oriental Cat-tail systems were 607.28 and 215.17 mV in March, and one data point even showed high value of 772.54 mV. For temperature maintenance, cooling rate of PMFC systems was 24.81oC lower than no module slabs in hot periods but warming rate was 4.12oC in cold periods of the day. These results indicate different plant species of PMFC systems possess various efficiencies of electricity generation. The major mechanisms affecting electricity production are likely temperature, net solar radiation, physiological functions of plants and vegetation coverage. Electricity generation of Chinese pennisetum and Oriental Cat-tail PMFCs are affected by net solar radiation and air temperature, respectively. Moreover, wetland elements of PMFC systems help temperature maintenance of roof slabs. Furthermore, according to results of soil heat flux, PMFCs absorb and store solar thermal energy in liquid-solid phase. In this research, we intend to evaluate the used of PMFCs for bioremediation of Cr(VI)-contaminated soils and also produce energy at the same time, running mechanisms in long-term operation. PMFCs in this study used Chinese pennisetum and common reeds to treat different Cr(VI) concentrations samples in the greenhouse for evaluating the best treating performance. According to this experiment, PMFCs make acid soils to neutral soils and decrease electrical conductivity (EC) of soils. The maximum removal of Cr(VI) in soils was over 99% and total Cr decreased with time. The maximum average output voltage of PMFC systems with graphite carbon felt could achieve 469.21 mV. According to field contaminated soil experiment, major removing mechanisms of PMFCs are bioelectrochemical processes and plant uptake. PMFCs with spiking 50 mg/kg Cr(VI) were operated over 10 months and chemical and microbial characteristics of different locations of PMFC systems were investigated. For instance, pH values of soils around cathode and anode in PMFCs using Chinese pennisetum were 7.03 ± 0.15 and 6.09 ± 0.05 respectively, showing significantly higher pH values of soils of cathode parts than those of soils of anode parts. The EC of soils of cathode and anode parts in PMFCs using Chinese pennisetum was 78.00 ± 5.61 and 156.25 ± 7.89 μs/cm respectively, showing significantly lower ECs of soils around cathode parts than those of soils of anode parts. The total Cr of soils around cathode and anode parts in PMFCs using Chinese pennisetum was 65.75 ± 3.77 and 84.29 ± 2.87 mg/kg respectively, showing significantly lower total Cr of soils around cathode parts than that of soils of anode parts. The permutational multivariate analysis of variance test of results of 16S rRNA gene high-throughput sequencing revealed that microbial communities in anode and cathode samples had significant difference in compositions. The stratified chemical and microbial characteristics were primarily driven by the bioelectrochemical processes and electrokinetics effects within PMFCs. After PMFCs harvesting, PMFC waste could be converted into platform chemicals for waste valorization. We could use liquid and solid acid in aqueous solution with or without green solvent, gamma-Valerolactone (GVL) to produce levulinic acid (LA) for biorefinery. Under microwave heating, increasing temperature to 180oC increased the yield of LA to 15.20 mol % in 60 min in water with sulfuric acid, higher than using solid acid. Furthermore, using 1 M sulfuric acid as catalyst in GVL solvent increased the yield of LA to 13.39 mol % in 60 min, higher than using GVL solvent without sulfuric acid. GVL/H2O ratios of solvent could affect LA yields. 70/30 and 50/50 ratio could result in higher LA yields because H2O in GVL solvent could improve conversion of five carbon sugars to LA. Scanning electron microscope images proved the cellulose structure was recalcitrant in solid acid, Amberlyst acid with H2O. The cellulose structure changed under GVL/H2O with liquid acid catalyst. X-ray diffraction patterns provided spectroscopic evidence for the enhanced dissolution or hydrolysis of cellulose in short time. According to peaks on the diffraction thermo gravimetry spectra, thermal stability of the solid residues after microwave heating was higher than using lower temperature conditions. After conversion, total Cr and Cr(VI) stayed in solid residues. This Ph.D. thesis studies the application of plant microbial fuel cells in urban greening and heavy metal soil remediation, as well as the recycling of plant waste. The entire research process demonstrates the sustainable recycling of plant material.