建構一新穎光生物養殖模組結合廢水和廢氣再利用於二氧化碳減量和生產生物質能

Establishing a novel microalgae-cultivated system reutilizated wastewater and flue gas for CO2 reduction and biomass production

郭秋媚(Chiu-Mei Kuo)

指導教授 ： 林志生 ； 賴進此

國立交通大學/生物科技學院/生物科技學系暨研究所/博士(2018年)

摘要

利用廢水和廢氣進行微藻養殖可同時達到二氧化碳(CO2)減量和廢水淨化之效益，所生產的微藻生物質還可作為生物燃料的料源使用。本研究中，利用豬場廢水、魚塭廢水和鍋爐廢氣整合再利用於微藻Chlorella sp. GD養殖，此微藻能有效地於廢水中生長，所產製的微藻生物質進一步萃取其藻油後評估其轉化為生質柴油之潛力。接著，我們也利用化學突變篩選耐鹼微藻Chlorella sp. AT1和建構一Photobioreactors (PBRs)/Raceway微藻循環養殖系統，以增加微藻總固碳量和CO2利用效率，並藉由半連續培養策略建立微藻穩定且長期生長之養殖程序。
首先，Chlorella sp. GD培養於0、25、50、75及100%豬場廢水(以培養基稀釋)，結果以培養於100%豬場廢水(無稀釋)可獲得最大微藻比生長速率和微藻生物質產率分別為0.839 d−1和0.681 g/L/d，但當使用25%豬場廢水可獲得最大的油脂含量和油脂產率分別為29%和0.155 g/L/d。以25−75%豬場廢水進行半連續培養時，微藻生物質產率和油脂產率分別為0.852 g/L/d和0.128 g/L/d以上，結果顯示Chlorella sp. GD可直接利用豬場廢水進行養殖且有效地生長，且可藉由半連續培養策略建立長期且穩定生長之微藻養殖程序。接著，我們也研究魚塭廢水和鍋爐廢氣(約含8% CO2)整合再利用於Chlorella sp. GD養殖，使用石斑魚塭廢水並添加額外的營養源，培養7天的微藻生物質產率為0.794 g/L/d。將添加營養源的魚塭廢水和鍋爐廢氣進行微藻半連續養殖每2、3及4天置換一半培養液，微藻生物質產率分別為1.296、0.985及0.944 g/L/d，CO2固碳效率分別為2.333、1.773及1.699 g/L/d。本研究顯示利用魚塭廢水和鍋爐廢氣再利用於Chlorella sp. GD養殖可有效達到水資源再利用、CO2減量及產製可作為生質燃料料源使用的微藻生物質。
為了提升CO2利用效率，我們將Chlorella sp. GD進行N-methyl-N'-nitro-N-nitrosoguanidine (NTG)突變處理後，篩選出一株可於pH 6−11培養基中生長良好，以及生長最適化pH為10的耐鹼藻株Chlorella sp. AT1。當每3小時間歇通入10、20及30分鐘的10% CO2於pH 11鹼性培養基中，Chlorella sp. AT1的CO2利用效率分別約為80、42及30%。同樣於鹼性pH 11培養基中，每3、6及12小時間隔通入30分鐘10% CO2，培養液中的pH會逐漸上升至10，Chlorella sp. AT1生物質產率分別為0.987、0.848及0.711 g/L/d。當每3小時間隔通入30分鐘10% CO2進行Chlorella sp. AT1養殖，每3天置換一半培養液共為期21天養殖，平均微藻生物質濃度和生物質產率分別為4.35 g/L和0.726 g/L/d。研究顯示耐鹼藻Chlorella sp. AT1培養於鹼性培養基中，可利用間歇通入CO2和鹼性培養液吸附多量CO2以供微藻生長之操作策略，此明顯地提升微藻的CO2利用效率。
最後，本研究建構一高生長效率和固碳效率的PBRs/Raceway微藻循環養殖 (PsRC)系統，本系統包含數支高生長效率的PBR和可大規模養殖的Raceway相互串聯組成，並整合鹼性培養液吸附多量CO2之操作策略，以增加微藻養殖的總CO2固碳量。在一室內模擬的1噸規模PsRC系統中，Chlorella sp. AT1養殖於pH 11培養基以PBRs與Raceway間循環流速為2 L/min培養下，相較於pH 6培養基的培養，平均微藻生物質可增加約2倍，達0.346 g/L/d；室內PsRC系統中PBRs和Raceway的養殖體積比為1:10時，具有相對最大的總CO2固碳量和CO2利用效率。本研究也建構了10噸規模的戶外實場PsRC系統，於20 L/min循環條件與PBRs和Raceway養殖體積比1:10操作下，我們可利用半連續養殖策略穩定且長期地進行微藻的養殖，其CO2利用效率可達50%，總CO2固碳量為1.2 kg/d。

關鍵字

鹼性培養液 ； 小球藻 ； 二氧化碳吸附 ； 二氧化碳利用效率 ； 鍋爐廢氣 ； Photobioreactors/Raceway微藻循環養殖系統 ； 廢水

並列摘要

Integration with wastewater and flue gas in microalgal cultivation can be used for CO2 reduction, wastewater purification and the resulting microalgal biomass can be a feedstock of biofuels. In this study, Chlorella sp. GD cultured in piggery wastewater (PW) and aquaculture wastewater (AW) aerated with boiler flue gas to efficiently produce biomass and lipid for biodiesel production was investigated. After that, to increase the CO2 utilization efficiency and total amount of CO2 fixation, the alkali-tolerant Chlorella sp. AT1 was screened by chemical mutagenesis and a Photobioreactors (PBRs)/Raceway circulating (PsRC) system was established. The stable growth performance of microalgae was achieved for long-term microalgal cultivation in a semi-continuous culture.
First, Chlorella sp. GD was cultivated with 0, 25, 50, 75 and 100% PW (diluted by medium) in batch cultures, the maximum specific growth rate and biomass productivity of the microalga obtained in 100% PW were 0.839 d−1 and 0.681 g/L/d, respectively. The highest lipid content and lipid productivity were 29% and 0.155 g/L/d at 25% PW, respectively. In semi-continuous cultures, the biomass and lipid productivities with 25−75% PW ratios were greater than 0.852 g/L/d and 0.128 g/L/d, respectively. These results show that Chlorella sp. GD grows efficiently in PW, and that a stable growth performance was achieved for long-term microalgal cultivation in a semi-continuous culture. Second, Chlorella sp. GD was also cultivated in AW aerated with boiler flue gas. When AW from a grouper fish farm was supplemented with additional nutrients, the microalgal biomass productivity was 0.794 g/L/d. When the microalgal strain was cultured with boiler flue gas in nutrient-added AW, biomass productivity increased to 0.892 g/L/d. In semi-continuous cultures, average biomass productivities and CO2 fixation efficiencies of the microalgal strain in 2-day, 3-day and 4-day replacement cultures were 1.296, 0.985 and 0.944 g/L/d, and 2.333, 1.773 and 1.699 g/L/d respectively. These results demonstrate the potential of using Chlorella sp. GD cultivations in AW aerated with boiler flue gas for reusing water resources, reducing CO2 emission, and producing microalgal biomass.
To enhance the CO2 utilization efficiency, an alkali-tolerant Chlorella sp. AT1 mutant strain was screened by N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagenesis. The strain grew well in pH 6–11 media and the optimal pH for growth was 10. The CO2 utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO2 aeration for 10, 20 and 30 min at 3-h interval in alkaline medium (pH = 11) were approximately 80, 42 and 30%, respectively. In pH 11 medium with intermittent 10% CO2 aeration for 30 min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.711 g/L/d, respectively. When Chlorella sp. AT1 was aerated with 10% CO2 intermittently for 30 min at 3-h interval in semi-continuous cultivation for 21 days, the biomass concentration and biomass productivity were 4.35 g/L and 0.726 g/L/d, respectively. Our results show that CO2 utilization efficiency can be markedly increased by intermittent CO2 aeration and alkaline media as a CO2-capturing strategy for alkali-tolerant microalga cultivation.
Finally, a high efficiency of microalgal growth and CO2 fixation in a PsRC system combined with alkaline-CO2 capturing medium and operation was established and investigated. The PsRC system was composed of PBRs in series, a Raceway and circulation pump. In 1-ton indoor-simulated PsRC system, compared with a pH 6 medium, the average biomass productivity of Chlorella sp. AT1 cultured in a pH 11 medium at 2 L/min circulation rate between PBRs and Raceway was increased by about 2-fold to 0.346 g/L/d. The maximum amount of CO2 fixation and CO2 utilization efficiency of Chlorella sp. AT1 could be obtained at PBRs to Raceway ratio of 1:10 in an indoor PsRC system. An outdoor PsRC system with a 10-ton pilot scale for microalgal cultivation was also established. Under 20 L/min circulation rate and PBRs to Raceway ratio of 1:10 in an outdoor PsRC system, the stable growth performance of Chlorella sp. AT1 cultured by long-term semi-continuous operation was observed, and the total amount of CO2 fixation was around 1.2 kg/d with 50% CO2 utilization efficiency.

並列關鍵字

Alkaline ； Chlorella ； CO2 capture ； CO2 utilization efficiency ； boiler flue gas ； Photobioreactors/Raceway circulating system ； wastewater

參考文獻

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