| 摘要: | 過去台灣傳統農村社會，人們常利用生活中所產生的水肥、農作有機廢棄物，或是畜牧產生的動物排泄物等，投入埤塘中做為肥料及營養來源，刺激水中浮游生物及水生植物的生長，經食物鏈關係進而提供埤塘中魚貝類養殖物的食物來源。此種利用物質循環及生態系統食性關係，將廢棄物中的營養物當成資源並轉換為漁獲提供食物來源的養殖方式，稱為生態養殖。生活污水中亦含豐富的有機質及氮磷營養物質，不僅可提供生態養殖的營養來源，亦可提供養殖物的水源，為生態養殖可利用的廢棄物資源。另一方面，以廢水處理的觀點，經生態養殖後污水中污染物（有機物及氮磷營養物）因循環轉換而削減，亦間接達到污水處理效能的目的，可視為一種廢棄物處理的生態工程技術。
本研究結合自然處理（人工濕地）系統預先淨化生活污水，再進一步回收處理後污水的營養物進行生態養殖。本研究以嘉南藥理科技大學人工濕地園區的人工濕地處理單元與景觀生態湖為實驗與養殖場所，於景觀生態湖（3,800 m2）中分別放養草魚、大頭鰱、鯽魚及吳郭魚，以不投餌料的養殖方式進行養殖。實驗結果發現，大頭鰱於養殖初期密度逐漸降低後維持穩定，並且大頭鰱的體長與體重略為增加，草魚放養60天後即無任何補獲之紀錄，鯽魚放養初期密度突然降低，但隨即維持穩定乃至逐漸增加密度，魚體體重與體長均持續增加。另外，本研究養殖初期並無放養吳郭魚，但於實驗過程中養殖池持續有捕獲吳郭魚之紀錄並且魚體密度、體重、體長均維持穩定增加，因此本研究於養殖期程60天後放養吳郭魚苗。比較養殖前與養殖後的人工濕地處理單元與景觀生態湖水質監測紀錄發現，進行生態養殖的景觀生態湖於進行養殖後，水中的SS濃度、濁度、葉綠素a、有機物與氮磷營養鹽均比養殖前濃度低，浮游動物的單位個體量於養殖過程也逐漸降低，但是浮游植物的數量在養殖過程中逐漸增加，顯示人工濕地處理單元放流水中含有的有機物與氮磷營養鹽物質，於景觀生態湖中成為浮游生物的營養來源，進而衍生為浮游生物，成為養殖魚種的食物來源。另外本研究也針對魚體的微量有毒物質含量進行評估，結果發現，養殖過程中捕獲吳郭魚的戴奧辛/呋喃當量濃度為0.033~0.033 pg-TEQ/g-(sample），與市售吳郭魚樣本濃度0.033 pg-TEQ/g-(sample）相當，並且均遠低於食品衛生標準的4pg-TEQ/g-(sample）；其養殖物（吳郭魚）的魚體重金屬含量分析也低於專業養殖池的重金屬含量。顯示本研究生態養殖的魚體有機毒物的風險是與一般市售魚類相當。
In the past agricultural society, people normally collected organic wastes, such as agricultural wastes and manure of livestock or human, which then were drained into fishponds acting as fertilizers to stimulate the growth of planktons or macrophytes, which in turn were fed by stocked fish and shellfish with various feeding and habit niches. Such aquaculture that follows principles of natural processes of nutrient recycling as well as food chains of aquatic ecosystem, and converting nutrients of wastes into useful food resource, is called ecological aquaculture. On the other hand, domestic wastewater contains sufficient organic matters and NP nutrients that may be feasible to provide nutrients and water sources for ecological aquaculture. From a viewpoint of wastewater treatment, ecological aquaculture with receiving domestic wastewater can also reduce a significant amount of organic and nutrient pollutants from the wastewater, achieving the goal of wastewater treatment efficiency, thereby being one of ecological approaches to water pollution control.
In this university-corporation collaboration project, ecological aquaculture was conducted by receiving treated domestic wastewater, which was purified by constructed wetlands, and recycling residual nutrients in wastewater. Freshwater polyculture experiment was initiated in an ecological pond (3,800 m2), which was a major component of the Wastewater Nature Treatment Park in Chia-Nan University of Pharmacy and Science. Various species of fish with different feeding habits, such as grass carp, bighead, silver crucian carp, and Tilapia, were stocked and cultivated in the pond without providing any external feed or fodder. Fish density together with length and weight of fish body were measured every 1~2 weeks. Results show that the density of bighead decreased initially and reached to a stable value, while its length and weight increased slightly. However, grass carp was not able to be captured and monitored after 60 days cultivation. Similar to bighead, population of silver crucian carp apparently decreased initially and reached to a stable number, but its body weight and length increased gradually. There was a number of existing Nile tilapia in the pond. They were observed having a significant increase in density, length and weight with experiment time, implying that tilapia was more adaptable to the culture environment and grew more efficiently than other fish species. Thus, we stocked more juvenile fish of tilapia into the pond after 60 days of experiment.
Water quality of the ecological pond and constructed wetlands was also investigated before and during the polyculture experiment. Results show that levels of suspended solids (SS), turbidity, chlorophyll a, 5-day biochemical oxygen demand (BOD5), total nitrogen, total phosphorous, and zooplanktons in pond water were all lower and phytoplankton concentration was higher in polyculture experiment period than those in pre-polyculture period. These findings suggest that polyculture or ecological aquaculture could enhance nutrient recycling in the pond ecosystem, thus improving water quality of the pond. We also measured the trace organic toxin cumulated in adult tilapia. Analytical data show that the Toxicity Equivalent (TEQ) of polychlorinated dibenzodioxins (PCDDs) plus polychlorinated dibenzofurans (PCDFs) for cultivated tilapia were 0.0327~0.0335 pg-TEQ/g-(sample), which was similar to 0.0327 pg-TEQ/g-(sample) for a market tilapia sample and much lower than 4 pg-TEQ/g-(sample) set as regulation limit for fish food. And the metal content of tilapia were also lower than professional cultifated. Thus, fish cultivated from ecological aquaculture could be concluded as a safe product with respect to dioxin content, which might have the same risk level as the market fish product. |
