農業濕地植物微生物燃料電池的產電研究

Abstract

植物微生物燃料電池(PMFC)是一種新型的整合了植物光合作用的微生物電化學系統，能通過植物根際的微生物發電。為了瞭解影響PMFC運行的關鍵因子所扮演的角色，本論文於第一部份研究深度探討了不同植物和土壤改良劑對PMFC性能的影響，實驗於受照明與溫度(27°C)及濕度(75%)控制的培養箱中進行為期200 天的試驗。植物方面，在PMFC系統中應用了兩種耐澇農業植物，水稻(Oryza sativa)和茭白筍(Zizania latifolia)；土壤改良劑方面，選擇了由食物廢棄物製成的堆肥和由廢棄木材生物質製成的生物炭作為土壤改良劑。結果顯示，不同的PMFC系統在運行期間觀察到不同的發電量。其中，帶有堆肥的水稻PMFC表現出相對更穩定的發電量(15.57 ± 8.15 mW/m2)和顯著更高電壓的產生，在所有PMFC中達到最高輸出電壓 894.39 ± 53.44 mV (34.78 mW/m2)。此外，具有植物的PMFC的輸出電壓顯著高於不具植物的土壤MFC，且水稻PMFC的輸出電壓顯著高於茭白筍PMFC，這意味著不同植物根系的根際沉積可能對發電性能具有重要意義。另一方面，具有生物炭的水稻PMFC的電壓產生明顯低於沒有生物炭的樣本，這可能是由於廢棄木材生物質製成的生物炭的抑製作用。陽極微生物群落的分類鑑定表明，變形桿菌門是最豐富的門，而伽瑪變形桿菌門和三角變形桿菌門是微生物群落中最主要的類別。進一步分析表明，具有生物炭的水稻PMFC具有最明顯的陽極微生物群落結構，以Gallionellaceae為主，而不是其他PMFC中的Geobacteraceae。Geobacter是所有樣品中微生物種群的主要屬，並且在帶有堆肥的水稻PMFC中顯示出最高的相對豐度，這表示該菌屬是PMFC系統中參與發電的主要貢獻者。本研究結果顯示，PMFC系統的功率輸出會受到不同農業植物和由廢棄生物質製成的土壤改良劑的影響，建議未來進一步了解陽極微生物群落、不同植物根系的根圈與電化學機制的關聯以邁向進一步的放大應用。 此外，提高農作物或濕地PMFC的發電量仍然受到關注。為了填補稻田等農業領域產電研究的空白，本論文於第二部份研究中，專注於提高稻田PMFC性能，探討水稻植物 (Oryza sativa) 在PMFC系統中使用化學肥料和不同PMFC串接放大方式長達150天的性能表現。結果顯示添加化肥的水稻PMFC最高輸出電壓為0.776 ± 0.33 V，而孔隙水的COD濃度為123.2 ± 11.3 mg/L。這表明在稻田中使用的化學施肥可能會影響陽極的電活性菌的活性並增加發電量。此外，串聯PMFC的平均電壓最高，為0.48 ± 0.17 V，其次是並聯水稻PMFC，為 0.40 ± 0.15 V。總體來看，具植物的PMFC的電壓輸出不僅明顯高於不具植物的土壤 MFC，而且串聯也比並聯有更高的功率輸出 (P < 0.05)。來自系統的溫室氣體通量顯示，串聯的PMFC的甲烷排放通量達到最高值，為3.82 ± 0.92 mg m-2 h-1，而並聯的土壤 MFC-的氧化亞氮平均排放通量最高，為106.48 ± 80.58 μg m-2 h-1。 16S rRNA 基因高通量測序表明，變形菌門是陽極微生物組中最豐富的門。Geobacter也是PMFC中產電相關菌群中的最豐富的菌屬。總體而言，這項研究探討了如何透過添加不同土壤肥料、串並聯方式來減少水稻PMFC溫室氣體的排放與產電量的增加。

Plant microbial fuel cell (PMFC) is a novel bioelectrochemical system that integrates the photosynthetic reaction from the living plants to generate electricity via microorganisms at the rhizosphere of the plant roots. To elucidate factors that are critical for PMFCs operation, this study investigated the effects of different plants and soil conditioners on PMFCs performance. The experiment was done in a controlled lighting incubator at 27 °C and 75% of humidity for 200 days. Two waterlogged agricultural plants, paddy (Oryza sativa) and water bamboo (Zizania latifolia), were applied in PMFC systems; besides, the compost made from food waste and biochar made from waste wood biomass were selected as soil conditioners. Results showed that varied electricity generation during the operation was observed for different PMFC systems, but the Paddy-PMFC with compost (PC-PMFC) demonstrated relatively more stable electricity generation for 200 days (15.57±8.15 mW/m2) and significantly higher voltage production, reaching the highest output voltage of 894.39±53.44 mV (34.78 mW/m2) among all PMFCs. It was observed that the output voltage of PMFCs was significantly higher than soil-MFC, and the output voltage of P-PMFC was significantly higher than water bamboo-PMFC, implying rhizodeposition of different plant roots could be important for the performance of electricity production in PMFCs. However, Paddy-PMFC with biochar (PB-PMFC) demonstrated significantly lower voltage production than those without biochar, likely due to the inhibitory effect of biochar made by waste wood biomass. The taxonomic identification of the microbial community at the anode showed that Proteobacteria was the most abundant phylum, and Gammaproteobacteria and Deltaproteobacteria were the most dominant classes of the microbial communities. Further analysis showed that the PB-PMFC had the most distinct anode microbial community structure, with the predominant family of Gallionellaceae, instead of Geobacteraceae as in other PMFCs. Geobacter was the major genus of the microbial population in all samples and showed the highest relative abundance in PC-PMFC, suggesting that it was the main exoelectrogen involved in electricity generation in our PMFC systems. To fulfill the gaps in bioelectrochemical systems, paddy PMFCs adding chemical fertilizer and the different paddy PMFC connections were investigated the performance through 150 days. Paddy PMFC adding chemical fertilizer (F-PMFC) showed the highest output voltage of 775.96 ± 230.21 mV while the COD concentration of pore water was 123.2 ± 11.3 mg/L. It indicated that chemical fertilization likely influenced the EAB acitivity at the anode and increased the power production. Besides, PMFC connected in series presented the highest average voltage of 474.97 ± 164.84 mV, followed by paddy PMFC-parallel at 396.89 ± 149.91 mV. By comparison, the voltage output of PMFCs was not only significantly higher than soil MFCs, but the series connection also has a higher power output than the parallel connection (P<0.05). The greenhouse gas (GHG) flux from the systems revealed that CH4 flux of PMFC-series reached the highest values at 3.82 ± 0.92 mg m-2 h-1 while soil MFC-in parallel showed the highest average N2O emission flux of 106.48 ± 80.58 µg m-2 h-1. The 16S rRNA gene high throughput sequencing showed that Proteobacteria were the most abundant phyla of the anodic microbiome. Geobacter is also the most abundant group that is associated with the bioelectricity generation in PMFCs. Overall, this study demonstrated the enhancement of the bioelectricity production from the paddy PMFCs with various soil additions, and electricity production and GHG emission from the serial and parallel connections of PMFCs, which will be beneficial for the future scale-up application of PMFCs.