以奈米生物操控法去除優養化水體中微囊藻及其藻毒之研究

Abstract

我國因水文及地形的因素導致飲用水水源相當仰賴湖泊及水庫，近年來由於集水區的農牧業發展及人為活動增加，造成水庫中氮與磷濃度上升而形成優養化現象，尤以離島小型湖泊水庫最為嚴重。依環保署卡爾森指標（Carlson trophic stateindex）界定優養化情形可知，民國 102 年台灣離島水庫優養化比例高達 91.2 %以上，已知湖庫優養化衍生許多問題，其中以釋放微囊藻毒素之微囊藻最受矚目，微囊藻毒素對脊椎動物具有強烈肝毒性，會引起魚群暴斃或家畜死亡；目前的淨水程序上並無法有效去除微囊藻毒素，大幅增加飲用水的安全顧慮，故如何將微囊藻及其毒素在淨水程序前有效去除是非常重要的課題。全世界優養化情形大多好發於淺型湖泊，本研究目的在於利用奈米材料及生物操控技術解決淺型湖泊優養化，從水體中總磷控制、藻華去除以及直接改善水下光照三個分向來著手，其中以奈米過氧化鈣為材料去除水體中的微囊藻及藻毒，同時進行總磷的削減，並以導光設備刺激水下植物生長，達到降低微囊藻及藻毒危害之目的。

本研究自行製備之奈米過氧化鈣，純度可達 80%以上，顆粒大小可達 37.0±4.5nm，具有均一度佳、結晶形狀完整等優點。在微囊藻生長抑制實驗中，較低藻類細胞濃度下（1.45×106 cells/ml）使用低劑量的奈米過氧化鈣即能達到抑制效果，可知 CPNP 應用於優養化的水體之中可行性相當高，較佳之加藥時機為中低微囊藻密度，也就是微囊藻尚未大量繁殖之前，且加量應至少高於 10 ppm。於濁度去除實驗中，發現奈米過氧化鈣相較起傳統的混凝劑及奈米矽片（NSP）去除濁度的效果較差，故奈米過氧化鈣並不適合當成混凝劑使用。微囊藻毒素分解實驗中，以劑量 100 ppm 的奈米過氧化鈣去除微囊藻毒素 MC-LR 效果最好，實驗可以看出奈米過氧化鈣對於 MC-LR 的去除效果較去除 MC-RR 優異。整體而言，使用奈米過氧化鈣整治微囊藻可同時具有抑制其生長與其分解毒素的效果。單純在水相中除磷的實驗結果顯示加入低劑量的奈米過氧化鈣除磷效果不佳，應加量至 100 ppm較為保險。過氧化鈣添加進實際底泥湖水的批次實驗結果顯示奈米過氧化鈣的確有將水中總磷沉降至底泥中的效果，且劑量為 500 ppm 的奈米過氧化鈣使底泥總磷增加的幅度最大。在改善水下光照的實驗，光纖最佳照度測試結果可知，將光纖兩端均修飾可以讓光纖照度有明顯提升，而聚光罩的確對光纖的導光強度有再提升的能力，在 90 公分光纖下測出的平均照度為 371.4 lux。最後的管柱實驗中，發現有添加 100 ppm 之奈米過氧化鈣又有放光纖導光的管柱降低水中總磷的效果最明顯，也有效提升台灣水韭葉子部分的總磷濃度，顯示提升水下光纖照度並添加奈米過氧化鈣對於沉水植物生長有正面影響。

Lake eutrophication is an imperative environmental problem around the world. In recent years, algal bloom has become a serious threat to drinking water safety. Especially cyanobacteria in eutrophic water bodies produce not only odorous compounds but also lethal toxins. Microcystis aeruginosa is a common species of cyanobacteria which releases toxins named microcystin. In Taiwan, there are 35 major water reservoirs on isolated islands, in which 91.2 % of them have been identified as eutrophic. Methods of water treatment plant to removing Microcystis aeruginosa and microcystins include chemical methods and prechlorination in Taiwan. However, these methods easily result in harmful by-products, such as trihalogenated carbons. This study is aimed to reduce the impact of ertrophication by using nanomaterials for growth inhibition of Microcystis aeruginosa, decomposition of microcystin, and removal of phosphate in water, light guiding device to improve the light climate in the eutrophic water body, and growing submerged plants for removing nutrients in water, especially phosphorus.

The material used in this study is calcium peroxide nanoparticle (CPNP), and the particle size is as small as 37.0 ± 4.5 nm. In Microcystis aeruginosa growth inhibition test, dosage more than 10 ppm yielded good effects. The results showed that at 100 ppm and 500 ppn doses, the removal is 87.7 % and 93.0 % respectively. However, the efficacy of turbidity removal of CPNP is not significant. A toxin decomposition test showed that CPNP can remove microcystin-RR and microcystin-LR at as low as a 10 ppm dosage, and the effect on removing microcystin-LR is better than that on microcystin-RR. In phosphorus removal test, the calcium ion from CPNP dissociation precipitated with phosphorus in aqueous solution. The results showed that dosages of 100 ppm and 500 ppm have excellent removal efficiency. In the other hand, in the light climate improvement experiments, Taiwanese isoetes was chosen as submerged plant to conduct experiments with optical fiber assembled equipment. The results showed that adding 100 ppm CPNP and directing light to bottom water is effective to stimulate the growth of Taiwanese isoetes.