利用畜牧廢水進行微藻養殖以提升微藻生物質及油脂產量

Abstract

微藻養殖需要大量水資源，利用廢水資源進行微藻養殖，不但能減少水資源消耗，亦可將廢水中所含氮、磷等物質作為微藻培養基使用，進而降低微藻養殖成本，移除廢水中污染物，達到水質淨化及水資源再利用之效用。畜牧廢水源自畜禽養殖場之糞尿排泄物經過沉降、厭氧及好氧處理程序後之放流水，而本研究目的為利用畜牧廢水進行淡水微藻株Chlorella sp.的養殖，促進微藻生物質生產，期能產製更多的微藻油脂以作為生質柴油之原料。 本研究首先利用不同稀釋比例之畜牧廢水進行Chlorella sp.之批次養殖，實驗結果顯示以100%廢水進行Chlorella sp.養殖，具有最佳的生長效率，其生物質產率可達0.681 g/L/day，約為控制組(即培養基養殖組)的1.5倍生長率；微藻油脂含量則是以25%廢水養殖時累積量最多，可達約30%的油脂含量；以廢水養殖之微藻，其適合用於生產生質柴油之脂肪酸含量高於65%；Chlorella sp.對於畜牧廢水中總氮與總磷的移除效率分別約為50%與100%。 為了更有效率且持續地生產微藻生物質，本研究利用畜牧廢水以半連續培養方式進行微藻養殖，即每兩天進行一半的微藻體回收和培養液置換。實驗結果顯示，Chlorella sp.利用100%廢水進行於半連續養殖時，微藻生長效率會隨著每次置換而逐漸降低，因此我們於100%廢水中添加額外微藻營養源，欲加強並穩定Chlorella sp. 於半連續養殖時的生長效率，並探討額外營養源的最適添加方式。實驗結果顯示，當100%廢水中添加10%額外營養源時，Chlorella sp.於半連續培養中有最佳且穩定的生長效率，其平均生物質產率可達1.18 g/L/day，油脂含量約為20%。於是，我們以含有10%額外營養源之100%廢水持續進行半連續Chlorella sp.之養殖策略，進行其對於微藻生物質產能之探討，實驗分別以每兩天、三天及四天的培養液置換方式進行之，在為期12天的半連續養殖結果中顯示，每兩天置換培養液的養殖方式，可得到最佳的微藻生物質產率為 1.09 g/L/day，12天的微藻生物質收成量可達12.2 g/L。 綜上所述，我們證實以畜牧廢水進行Chlorella sp.養殖可增進微藻生物質與油酯產量。此外，我們也建立了一套半連續養殖方式，可使微藻養殖有效率且穩定的生產微藻生物質與油脂，以利進行後續生質柴油料源生產之應用，並促進廢水資源的再利用。

Microalgae cultured with wastewater are benefit for minimizing the usage of freshwater, reducing the cost of nutrient addition, removing nitrogen and phosphorus from wastewater and producing microalgal biomass. Livestock wastewater derived from manure was treated by solid-liquid separation, anaerobic treatment and aerobic treatment. Recently, microalgal cultivation with wastewater is being a demand of water and nutrients in microalgal cultivation as a feedstock of biodiesel. The aims of this research are to develop the microalgal culture operation to efficiently produce microalgal biomass and oil for biodiesel production by using swine wastewater from a livestock farm. Growth rates and lipid contents of the microalga Chlorella sp. cultured with different ratios of the wastewater in a batch culture were firstly explored. The biomass productivity of the Chlorella sp. cultured with 100% wastewater was 0.681 g/L/day, which was approximately 1.5-fold higher than the culture with medium. The microalgal lipid content cultured with the 25% wastewater was approximate 30% (w/w). Over 65% of lipid of the Chlorella sp. cultured in wastewater is suitable as resources for biodiesel production. The wastewater bioremediation by the Chlorella sp. cultures was around 50% in removal efficiency of total nitrogen and almost 100% removal efficiency of total phosphorus in the livestock wastewater. In order to yield the microalgal biomass and lipid of microalgae efficiently and sustainably, the operation of semi-continuous cultures with half microalgal broth replacement was performed. Because of the gradually lower growth efficiency of the Chlorella sp. in semi-continuous cultures after each replacement, optimizing the components and concentration of extra nutrient added in the 100% wastewater was investigated. The maximum biomass productivity and lipid content of Chlorella sp. cultured with 100% wastewater added 10% of extra nutrients (culture medium) in the semi-continuous cultures were 1.18 g/L/day and 20.6%, respectively. The Chlorella sp. cultured in 100% wastewater with 10% extra nutrient addition by the operation of 2-day, 3-day and 4-day replacement and a period of 12-day culture was investigated. The results show that the biomass productivity per day and total biomass production in the 12-day period in 2-day replacement were 1.09 g/L/day and 12.2 g/L, respectively, which were higher than those in the other replacement operations. In summary, our experimental results mentioned above confirm that the Chlorella sp. cultured in livestock wastewater can produce microalgal biomass and accumulate lipid efficiently. In addition, the semi-continuous culture operation for microalgal culture using 100% livestock wastewater was established to produce microalgal biomass and oil for biodiesel production and wastewater utilization.