| 摘要: | 表層下流動式(SSF，subsurface flow system)人工溼地為一種污染淨化效率頗高的廢水處理生態工法，可視為一個無須曝氣的生物濾床。雖然維護簡單且操作成本均較傳統生物率床為低，然而建造成本卻是另一種自由水層式(FWS，free water surface flow system)溼地的6.5 倍，其中礫石(gravel)基材所需費用便佔了SSF 溼地總設置成本的最主要項目(40~50%)。
本研究乃評估以海產廢棄物蚵殼取代礫石作為表層下流動式人工溼地基材之可行性。
初步將測量並比較兩種材料之物理性質包括：真密度、假密度、空隙率、比表面積、水流移動速率、抗壓強度等，及化學性質包括：pH、陽離子交換能力、元素組成等。另一方面，本研究另外建立了數個小型SSF 人工溼地(長0.7m、寬0.5m、高0.6m)，探討以蚵殼(Oyster
shell)與礫石(Gravel)作為介質之水質淨化效能比較。水質監測結果顯示，蚵殼介質之蘆葦溼地的啟動適應期比礫石介質之蘆葦溼地短。並且由於溼地基材的不同，使蚵殼介質溼地在出流水NO3-N 濃度均較礫石介質低。在相同水力負荷試驗中，蚵殼作為介質之蘆葦溼地其
NO3-N 去除速率均高於礫石作為介質之蘆葦溼地。在水力負荷為0.12 m d-1、NO3-N 污染負荷為2.71g N m-2 d-1 時，蚵殼作為介質之蘆葦溼地的去除速率為2.49 g Nm-2 d-1，礫石作為
介質之蘆葦溼地去除速率為2.35g N m-2 d-1。若進一步增加負荷，NO3-N 去除速率反而下降。
回收蚵殼廢棄物作為表層下流動式人工溼地之介質是技術可行，不僅在NO3-N 之去除效能的表現上，使用蚵殼介質的溼地比使用礫石介質還優越，並且可顯著降低SSF 溼地的建設成本。
Subsurface flow (SSF) constructed wetland is an efficient ecological technology for
wastewater treatment. This type of constructed wetland is similar to a biological biofilter process,
but with benefits of moderate low cost and easy operation because it never needs aeration.
Nevertheless, its capital cost is still 6.5 times higher than that of free water surface flow (FWS),
another type, constructed wetland. In an overall capital cost of a SSF wetland, gravel installation
is normally the most costly item (e.g., 40~50%) due to SSF wetland requires a large amount of
gravel using as the substrate for the growth of macrophyte and biofilm.
This project intends to evaluate the feasibility of recycling of wasted oyster shell to replace
the gravel as the substrate material using in the SSF constructed wetland. Physical properties
(including true density, bulk density, porosity, specific surface area, hydraulic conductivity,
compression strength etc.) and chemical properties (including pH, cation exchange capacity,
element composition etc.) of both oyster shell and gravel will be measured, and the results will be
used to make a comparison each other. On the other hand, Another essential goal of this study
was to investigate the feasibility of recycling the wasted oyster shell as substrates or media using
in an SSF constructed wetland, since the exploit of gravel, a normally used substrates, is
restrained by the local government and its price is becoming more and more expensive. Four
small-scale SSF wetland beds (each with dimensions of 0.6 m width and 0.7 m length), in which
two beds were packed with oyster shell and another two with gravel, were used for treating the
same nitrate-contaminated groundwater as abovementioned. One oyster shell bed and gravel bed
were planted with common reed, whereas another oyster shell bed and gravel bed were unplanted.
The oyster shell beds seemed to need shorter period to achieve a stable nitrate removal than
gravel bed. Oyster shell beds, both planted and unplanted, generally produced lower effluent
nitrate levels than gravel beds under the same hydraulic loading rate. Planted oyster shell bed and
gravel bed exhibited a nitrate removal rate of 2.49 and 2.35 g N m-2d-1, respectively, when
hydraulic loading rate retaining 0.12 m d-1and nitrate loading rate maintaining 2.71 g N m-2d-1.
Recycling the oyster shell as substrate for SSF constructed wetland was found economically and
technically feasible. |
