台灣養殖業逐年發達且每年用水需求大，為了減少養殖廢水的排放及換水所抽取大量的地下水，本研究以海水飼料類的微藻製作光生物反應器探討去除水中氮、磷的效果，並配合利用微藻吸收水中氮磷後會大量繁殖的特性，試驗是否可藉由去除營養鹽的過程而使得微藻大量繁殖，直接作為養殖池內生物的飼料來達到池內原水重複使用、減少抽取地下水及降低業者成本，以達到水資源永續利用的目的。本實驗所用的微藻為周氏扁藻，並培養至光生物反應器中，利用不同環境如光照強度、光源、溫度、硝酸鹽與磷酸鹽濃度及比例調整、曝氣、攪拌等條件，試驗何種條件下較利於本微藻去除水中氮、磷鹽及成長。 本研究結果顯示，周氏扁藻在本環境下最佳去除營養鹽效果及最適生長條件為照度為採用光模擬器且照度為12,000 Lux與12小時光照培養下，經由不同溫度條件培養本微藻也可得知最適合生長及去硝酸鹽溫度為攝氏24 ± 1度，從初始營養鹽比例調整後可明顯看出氮磷比調整至3:1下可有較佳的硝酸鹽去除量。而微藻在一般人工培養下會大量繁殖使得水體中碳源供不應求，在未施予曝氣下周氏扁藻對於硝酸鹽的去除效果不佳且會大量沉澱於反應器底部，而加入曝氣後本微藻不會沉澱於反應器底部，也可在短時間內去除硝酸鹽及快速成長。此外，藉由攪拌實驗可確定曝氣中的攪拌不助於周氏扁藻去除硝酸鹽及快速成長，而磷酸鹽則是在任何條件下，周氏扁藻都可快速且大量的去除。經由結果可得知周氏扁藻在適合的生長環境下可有效去除水中氮、磷，並降低養殖池中的營養鹽，若要做為水生生物的飼料則可額外補充磷源增加成長。 The nitrogen and phosphorus in aquaculture wastewater are difficult and expensive to be removed by traditional wastewater treatment process. Therefore aquaculture industry usually dilutes its wastewater by groundwater or direct outfall to natural water body that cause subsidence in coastal area or algal blooms. This study tries to test the feasibility of using microalgae, namely the Tetraselmis sp., to treat aquaculture wastewater and find the optimal conditions for the Tetraselmis sp. growth and the removal of nitrogen and phosphorus. The study concludes that Tetraselmis sp. growth in a 12,000 Lux light intensity and 12 hours light/dark period in a bio-photo reactor is better than that cultured under sun light and a 24 ± 1oC is best temperature setting for microalgae grow. An initial N/P ratio of 3/1 provides the best Tetraselmis sp. growth and nutrient removal. When artificial culture was used in growing microalgae, the cultured environment usually encounters limited carbon source and microalgae deposition problems. Aeration was applied to prevent microalgae settlement, to increase microalgae growth and to shorten nitrate removal time. A stirring only without aeration did not improve both microalgae growth and nitrate removal. Compared with nitrate removal, phosphate is always removed faster in all tested cases by Tetraselmis sp.. This study concludes that using Tetraselmis sp. in removing nitrate and phosphate in aquaculture wastewater with appropriate operations is feasible.
