| 摘要: | 隨著城市工業化及經濟產業蓬勃發展，伴隨而來的有害副產物更需被妥善處理。但近年屢屢發生工業重金屬廢水未經嚴格管末處理就任意排放到自然水體的案件，而這往往也是導致灌溉田地受到重金屬污染的根本原因。關於農地重金屬污染整治之策略，近年來許多學者主張以具環境友善性和低成本的土壤改良劑(例如：生物炭)來現地穩定稻田土壤中的重金屬，並且也已發展出許多種土壤改良劑。而當前需要思考的是，如何在已知的特定環境條件下，預先選擇出適合的土壤改良劑來進行土壤污染整治。因此，本研究將使用相關文獻所提及以等溫吸附研究為發想所建構的線性模型來預估不同生物炭對於現地穩定污染稻田土壤中鎘、銅、鋅之潛力，並且也會藉由土壤培養試驗觀察經施用不同生物炭後土壤孔隙水中重金屬的實際濃度變化。與此同時，將一併探討多重重金屬在生物炭表面的競爭吸附趨勢和吸附機制。而本研究總共合成出五種生物炭，分別為：稻殼生物炭300℃&600℃(RB300&RB600)、落葉生物炭300℃&600℃(LB300&LB600)以及鐵改質稻殼生物炭300℃(Fe-RB300)。首先經由水相吸附實驗結果發現，與高溫合成的生物炭(RB600、LB600)相比，反而是低溫合成的生物炭(RB300、LB300)對於鎘、銅、鋅有著更好的吸附能力，並且又以LB300對於此三種重金屬的吸附能力最佳。至於經鐵改質過的Fe-RB300對於鎘、銅、鋅的吸附效果反而比RB300還差。另外，由競爭等溫吸附實驗結果可觀察出絕大多數的生物炭對個別重金屬的吸附容量大小順序為：銅>鎘>鋅；但唯獨只有LB300對個別重金屬的吸附容量大小順序為：鎘>銅>鋅。接下來從土壤培養試驗之結果中發現，施用過不同生物炭的所有組別與控制組相比，其土壤孔隙水中鎘、銅、鋅的濃度皆有所下降，其中又以LB300對銅具有最好的穩定效果，並且以LB600對鎘、鋅的穩定效果最佳。至於經鐵改質過的Fe-RB300對於個別重金屬的穩定效果依然比RB300還差。最後，關於使用線性模型對土壤孔隙水中重金屬濃度的預測結果，可以發現鎘、銅、鋅於大部分組別之預測濃度值與實際濃度值相比還是有落差的，推測可能與等溫吸附實驗最初決定的重金屬濃度範圍不夠低以及土壤孔隙水中溶解性有機質(DOM)的介入有關，使得預測結果低估了各種生物炭對於個別重金屬的穩定效果。不過，在RB300、LB300組別中還是可發現，隨著重金屬的競爭數量增加，鎘的預測濃度值有更加貼近實際濃度值的趨勢，而這也進一步說明了還是有需將多重重金屬競爭吸附的因素納入考量之必要性。;The harmful by-products produced by urban industrialization and economic industries need to be treated properly. However, cases of industrial heavy metal wastewater arbitrarily discharged into natural waters without careful treatment have often occurred in recent years, and this is the main reason that irrigated fields are polluted by heavy metals. Regarding the strategies for remediation of heavy metal pollution in the agricultural field, scientists have mainly studied the use of eco-friendly and low-cost soil amendments (such as biochar) for in situ stabilize heavy metals in paddy soils in recent years, and many soil amendments have been developed. Therefore, it is necessary to consider how to pre-select the appropriate soil amendments for soil remediation on a site-specific basis. In view of this, this study will use the linear model maked based on the idea of isotherm adsorption as mentioned in the relevant literature to estimate the adsorption potential of cadmium, copper, and zinc for biochars in paddy soils. The soil incubation experiment was used to observe the actual concentration changes of heavy metals in pore waters after applying different biochars. Furthermore, we will also examine the competitive effect of co-existing other heavy metals on the adsorptive interaction between synthetic BC and the target metal, and discuss adsorption mechanism as well. Five biochars were used in this study. Biochars produced from rice husk and camphor tree leaf pyrolysed at either 300 or 600 °C (RB300, RB600, LB300 and LB600, respectively). The Fe-modified biochar was produced by immersing the rice husk into a FeCl3?6H2O solution, and then pyrolyzed at 300 °C (Fe-RB300). In the batch adsorption experiment, higher adsorption capacity of biochars synthesized at low temperature (RB300, LB300) for Cd(II), Cu(II) and Zn(II), compared to biochars synthesized at high temperature (RB600, LB600). LB300 showed a optimal adsorption capacity for these three heavy metals. As for the Fe-RB300, worse adsorption capacity for Cd(II), Cu(II) and Zn(II) compared to RB300. In addition, the adsorption capacity of most biochars toward heavy metals were in the order of Cu(II)>Cd(II)>Zn(II) for the multi-metal adsorption isotherm, whereas LB300 had the order of Cd(II)>Cu(II)>Zn(II). In the soil incubation experiment, concentrations of Cd(II), Cu(II) and Zn(II) in pore waters after different biochar treatments were all significantly lower than those in the control: LB300 was most effective for stabilizing Cu(II); LB600 was most effective for stabilizing Cd(II) and Zn(II); Biochar impregnated with iron oxides (Fe-RB300) had no apparent immobilization effect on heavy metals in comparison with the original biochar (RB300). Regarding the prediction results of heavy metal concentrations in pore waters using the linear model, most of the results showed that the linear model did not give reliable predictions in the reduction of Cd(II), Cu(II), and Zn(II) concentrations in pore waters, which might be due to the negligence of the dissolved organic matter (DOM) effect, or/and the lack of sufficiently low concentrations of heavy metals used in the aqueous adsorption experiments. Nonetheless, the modeled value was indeed closer to the observed value under RB300 and LB300 treatments when the metal competitive effect was taken into account for pore water Cd(II), and it still means that it is necessary to take the metal competitive effect into consideration. |
