碳化農業廢棄物改良水田重金屬污染之可行性研究

Abstract

Agricultural wastes in Taiwan are mass-produced and need befitting attention to avoid pollution. Some of agricultural wastes could be carbonized and activated to increase surface area and pore to adsorb more pollutants. The purpose of this study was to evaluate the feasibility of carbonized agricultural wastes as adsorbents of heavy metals to remedy heavy metals polluted paddy soil. The test soils were collected from six heavy metals polluted paddy field in Changhua. Rice hulls, peanut hulls and bagasse chosen as test agricultural wastes were carbonized and CO2 activated to be activated carbons. The ability of heavy metals adsorption of carbonized agriculture wastes were compared with market activated carbon and un-active rice hulls. The constant “K'' and the maximum adsorbed amounts of adsorbate “b” calculated from Langmuir adsorption isotherms indicate the order of adsorption efficiency of the heavy metals were Pb > Cu > Zn > Cd > Cr > Ni. The adsorbed amounts of heavy metals by carbonized agriculture wastes increased with increasing concentration of heavy metals. The adsorbed amounts of heavy metals by carbonized peanut hulls were the highest followed by carbonized bagasses. The adsorption abilities of carbonized agriculture wastes on EDTA-extracable heavy metals from soils were tested in batch and leaching experiments. The adsorption efficiency of carbonized bagasses was the best followed by carbonized peanut hulls and carbonized rice hulls. In general, the adsorbed amounts of heavy metals by market activated carbon and un-active rice hulls were less than carbonized agriculture wastes, because the un-active rice hulls were not activated to increase surface area. The low adsorption efficiency of both un-active rice hulls and market activated carbon was attributed to their small pore size resulting in more resistant to mass transport even the surface area was higher than the others, and to their low basic function groups on the surface.

台灣農業廢棄物產量非常大，需要適當處理方不致造成環境的污染 。某些農業廢棄物經碳化及活化製成活性碳後，可增加其比表面積及孔隙而能吸附污染物，故本研究之目的希望能利用碳化農業廢棄物作為重金屬污染的吸附劑，研究其在土壤重金屬污染改良上的可行性。 土樣採集自彰化縣六處受重金屬污染的水稻田。選擇稻殼、花生殼、蔗渣為測試農業廢棄物，經高溫碳化及CO2活化，並以市售活性碳及未活化稻殼作為比較，進行吸附水溶液重金屬試驗，測試其吸附重金屬能力。由Langmuir等溫吸附模式分析所得常數K和最大溶質吸附量b，評估碳化農業廢棄物對不同重金屬吸附效果依序為：鉛 > 銅 > 鋅 > 鎘 > 鉻 > 鎳。在不同濃度重金屬溶液中，碳化農業廢棄物吸附量會隨溶液濃度的提高而有增加的趨勢，且以碳化花生殼對水溶液重金屬的吸附量最大，碳化蔗渣吸附量次之。並利用EDTA震盪萃取土壤重金屬，以碳化農業廢棄物進行震盪吸附試驗及管柱淋洗吸附試驗測試其吸附土壤EDTA-重金屬能力，兩試驗結果顯示五種供試物中碳化蔗渣的吸附效果較佳，碳化花生殼、碳化稻殼之吸附效果次之。整體而言，市售活性碳及未活化稻殼為五種碳化農業廢棄物中吸附量較差者，原因可能為未活化稻殼因未受活化程序時得其比表面積小吸附量低，市售活性碳雖比表面積大但因其孔徑小質傳阻力大，且兩者的表面鹼性官能基都較少使得兩者的吸附能力較差。