利用廢水與碳捕獲再利用系統於微藻生長與生物 質產量最佳化之研究

Abstract

本論文第一部分的研究目的為利用魚塭廢水、生活廢水及工業廢水進行淡水微藻株Chlorella sp.的養殖，促進微藻生物質生產，期望能產製更多的微藻油脂以作為生質燃料之產物。研究首先利用不同來源的廢水進行Chlorella sp.之批次養殖進行生長速率探討，實驗結果顯示利用魚塭、生活及工業廢水進行Chlorella sp.養殖，其生物質產率分別可達0.309、0.291和0.194 g/L/day；Chlorella sp.對於這三種廢水中總氮與總磷的移除效率皆分別能達80%以上與幾乎100%的程度。但由於在工業廢水中，其氮磷濃度較低，且可能含有高毒化之化合物，故會造成微藻生長之限制。而為了能夠產製更多量的微藻生物質，我們於廢水中添加額外微藻營養源GA-03，實驗結果為添加GA-03營養基在魚塭及生活廢水中能達到最高的生物質產率分別為0.794和0.883 g/L/day，藻油產率分別為0.169和0.177 g/L/day。為了更有效率且持續地生產微藻生物質，本研究利用魚塭和生活廢水以半連續培養方式進行微藻養殖，實驗分別以每兩天、三天及四天的添加GA-03的廢水置換方式進行之。在為期12天的半連續養殖結果中顯示，以半置換魚塭和生活廢水的養殖方式可得到最佳的微藻生物質產率分別為1.216及1.029 g/L/day，12天的微藻生物質收成量則均大於12 g/L以上。 本論文第二部分研究則是建立一套室內微藻固碳再利用系統，並利用回歸曲面法(response surface methodology, RSM)探討微藻養殖之最佳化條件。系統是以複數可串聯之4-L光生物反應器(Photobioreactor, PBR)與一個240-L的養殖的跑道式養殖池(Raceway)相結合，PBR與Raceway間可循環養殖微藻液。RSM採4因子(factor)、12級別(level)進行之，其分別為PBR體積24、32及48 L，光照強度為300、335及370 µmol/m2/s，通入氣體中CO2濃度2、6及10 %，以及PBR與Raceway間微藻液循環流速為1、1.5及2 L/min。根據30組的實驗結果顯示，當PBR體積為48 L、光照強度為370 µmol/m2/s、CO2濃度為3%及循環流速為2 L/min時，預測能達到其最佳化生物質產率為0.316 g/L/day，而實際使用此組條件進行三重複可得到之生物質產率為0.311 ± 0.011 g/L/day (CV = 4.1%, p = 0.96) 綜上所述，本研究證實利用魚塭與生活廢水來進行Chlorella sp.養殖可有效地增進微藻生物質產量。此外，利用半連續養殖方式，於廢水中添加培養基可使微藻養殖有效率且穩定的生產微藻生物質與油脂，以利進行後續開發生質燃料之應用，並能促進廢水資源的再利用。本研究也建設了一套室內串聯PBR與Raceway之微藻固碳再利用系統，此可用於各項微藻養殖條件對微藻生物質產率影響之探討。

The first aims of this study is to develop the microalgal culture operation to efficiently produce microalgal biomass and oil for biofuels production by using different kinds of wastewater from aquaculture, industry and sewage. Growth rate of a microalga Chlorella sp. cultured with different wastewaters in a batch culture was explored. The biomass productivity of the Chlorella sp. cultured with wastewater of aquaculture, sewage and industry were 0.309, 0.291 and 0.194 g/L/day, respectively. There were more than 80% in removal efficiency of total nitrogen and almost 100% removal efficiency of total phosphorus by the microalgal cultures in both of aquaculture and municipal wastewaters. Due to low nitrogen and phosphorus concentrations, and high poison concentration, growth of Chlorella sp. was limited when the microlaga was cultured in industry wastewaters. To be able to produce a large amount of biomass production, we added GA-03 (culture medium) in wastewater for microalgal cultivation. The results showed that the maximum biomass productivity of Chlorella sp. cultured with aquaculture and municipal wastewaters added GA-03 in batch cultures were 0.794 and 0.883 g/L/day, and the oil productivity were 0.169 and 0.177 g/L/day, respectively. In order to obtain the microalgal biomass efficiently and sustainably, operation of semi-continuous cultures with half microalgal medium replacement was performed. The Chlorella sp. cultured in aquaculture and municipal wastewater with GA-03 addition by the operation of 2-day, 3-day and 4-day replacement and a period of 12-day culture was investigated. The results showed that the biomass productivity in aquaculture and municipal wastewater were 1.216 and 1.029 g/L/day, respectively. The biomass production of Chlorella sp. cultured in both wastewaters was greater than 12 g/L. The second aim of this study was to develop an in-door carbon capture and utilization system (CCU) of microalgae cultivation and to use the method of response surface methodology (RSM) to optimize microalgal culture conditions. The CCU system includes a 240-L Raceway, plurality of 4-L Photobioreactor (PBR), and a circulating apparatus between Raceway and PBRs. In the RSM test, 4 factors and 12 levels were designed and performed, including total volume of PBRs (24, 36 and 48 L); light intensity (300, 335 and 370 µmol/m2/s), aerated CO2 concentration (2, 6 and 10%) and circulation rate (1, 1.5 and 2 L/min). According to the results from 30 cultures, the maximum biomass productivity, 0.324 g/L/day in a 7-day culture, of Chlorella sp. could be predicted as the optimal culture conditions of 48 L of PBRs, 370 µmol/m2/s light intensity, 3% CO2 concentration and 2 L/min circulation rate. By these cultured conditions, the actual Chlorella sp. productivity was 0.311 ± 0.011 g/L/day by triplicated cultures (CV = 4.1%, p = 0.96). In summary, the present results confirm that the Chlorella sp. cultured in both of aquaculture and municipal wastewater could efficiently produce microalgal biomass. Additionally, the semi-continuous culture operation for microalgal culture using wastewater with medium addition could stably performed to produce microalgal biomass and oil for the further applications of biofuels generation, and could reuse waste resource. We have also developed an indoor Raceway and PBR circulating CCU system for microalgae cultivation to test the potential of microalgal biomass production for specific microalgal strains and culture conditions.