活性碳與碳化料應用於水體遮光降低藻類生長之研究

Abstract

湖泊、水庫中因污染物累積，導致優養化情形時常發生，藻華為主要危害問題之一。水庫發生藻華，會增加淨水場成本，並造成許多環境問題。為確保淨水場單元之運作及用水安全，過去之研究發展出許多現地預處理工法(如氣體浮除法、超音波震盪法等)去除藻類，降低毒性物質釋放的方法。低光照與低溫等物理條件控制，亦可降低藻類光合作用，同樣能抑制藻華現象。目前已有一些遮光減藻之研究，例如利用黑色聚乙烯布做為遮光材料，顯示有效抑制藻類生長之效果。然而，水庫面積廣闊，不易全面佈設遮蔽措施。 本實驗考量活性碳與碳化料粉末為黑色且原料本身穩定不易釋放毒性物質，故選用為抑制藻類生長之遮光材料。本研究係利用研磨方法製備碳化料粉末及活性碳粉末製備懸浮液。透過沉降實驗探討兩種材料之懸浮效果，結果顯示碳化料粉末有較佳懸浮率，且吸光係數較高，吸光能力比活性碳懸浮液強。在遮光實驗中監測葉綠素a濃度、溶氧濃度與pH值變化，分別探討活性碳與碳化料粉末之遮光效果。遮光實驗之結果顯示兩種遮光材料(活性碳懸浮液與碳化料粉末)，皆使溶氧及pH值下降，表示兩者在水中皆有效阻擋陽光之效果，降低藻類行光合作用，使其生長受限制。然而，活性碳與碳化料吸附之干擾使得葉綠素a濃度無法正確檢測，後續仍需進一步實驗探討藻類生長情形，以確認藻類確實有受到活性碳或碳化料遮光抑制生長。 本研究結果與金門西湖水庫之遮光試驗比較，顯示施碳粉之成本低，操作上方便且彈性高，可免除建造工程與後期維護成本，黑色質地能吸收光線達到遮光效果，於現地控制藻類生長。同時碳化料為吸附劑，可吸收水中一些污染物質。使用碳化料作為遮光材料，不失為控制藻類生長之可行方法。

The accumulation of nutrients in reservoirs and lakes leads to eutrophication and frequent occurrence of algal blooms. During the periods of algal blooms in reservoirs, the cost of water purification and various environmental problems will increase. In order to ensure sound operation of the water purification unit and the safety of public water supply, many in situ treatment methods have been developed to remove algae and reduce the release of toxic substances. Reducing the intensity of irradiation through the water surface may be an approach to reduce photosynthesis and inhibit algal blooms. In this study we choose activated carbon and charcoal powders as shading materials for their black color and stable property. Charcoal was powdered by using ball mill, and activated carbon by ball mill and adding arabic gum. Results of the settlement experiments showed that charcoal powders had lower settling rate and higher extinction coefficient than activated carbon suspension. Chl-a, DO, and pH were monitored throughout the shading experiments. The results showed that these two kinds of materials were able to inhibit the photosynthesis and lower the algae growth. However, the strong adsorption of pigments on activated carbon and charcoal interfered the measurement of Chl-a. The reduction of algal growth after shading the light could only be suggested by the decrease of pH and dissolved oxygen as well. Comparing to the shading test by using plastic film in Jinmen Xihu Reservoir, the approach of applying carbon powder is easier to operate in-situ and having lower maintenance cost. As a sorbent, carbon can also absorb pollutants in the water. The results of this study have provided a feasible algal control measure.