| 摘要: | 隨著近年來台灣都市開發與公共建設工程的快速成長，營建剩餘土石方的產量持續攀升，導致大量B7類土方(即連續壁所產出之皂土)的產生。然而，目前國內對於此類土方之再利用技術與管理機制仍相對不足，使其多被堆置於土石方資源堆置處理場(以下簡稱土資場)中，造成土地資源閒置與環境負擔。另一方面，台灣部分地區長期受酸雨與農業過度施肥影響，導致土壤酸化問題日益嚴重；沿海地區亦因地下水超抽與海水入侵而出現鹽化現象；同時，工業活動與農業累積造成重金屬污染問題，進一步影響土地利用與生態安全。
因此，本研究旨在探討B7類土方作為土壤改良劑之再利用可行性，評估其於酸化土壤、重金屬污染土壤及鹽化土壤環境中的潛在應用效益與環境安全性。首先，四間土資場之B7類土方之毒性特性溶出程序(Toxicity Characteristic Leaching Procedure, TCLP) 檢測結果顯示，其pH值介於8.6~9.7，屬強鹼性範圍，且溶出液中重金屬濃度均低於《有害事業廢棄物認定標準》，顯示其具環境安全再利用潛力。酸鹼中和試驗結果指出，B7類土方可有效且快速提升酸性土壤之pH值，顯示其在酸化土壤改良上具顯著成效，並可依植物生長需求調整添加比例(5~25%)。重金屬固定試驗結果顯示，B7類土方對鎘固定效果不佳，隨時間及有機質分解，鎘由有機物鍵結態逐漸轉化為碳酸鹽態，導致其生物可利用性上升；相較之下，對鉛固定效果良好，鉛在有機物鍵結態與殘留態比例增加，酸可溶態比例降低，使其整體生物可利用性顯著下降。鹽化土壤改良試驗則顯示，雖初期因淋洗作用導致鹽分向下移動，但隨時間延長，蒸發作用使鹽分重新上移，最終形成鹽度再分布現象，顯示單獨添加B7類土方不足以有效降低土壤鹽度。
此外，為評估B7類土方中聚丙烯醯胺(Polyacrylamide, 簡稱PAM)的環境穩定性，本研究進行光降解模擬試驗，結果顯示所有樣品皆未檢測出丙烯醯胺(Acrylamide, 簡稱AMD)的釋出，推論在為期三個月的模擬光照條件(該模擬照射條件等同於自然陽光照射三年之條件)下，B7類土方中PAM具有良好穩定性，對環境不致造成顯著風險。
綜上所述，本研究結果證實B7類土方兼具強鹼性與低重金屬溶出特性，具作為酸化及重金屬污染土壤改良劑之潛力，並具環境安全再利用之可行性。然而，其對鎘固定及鹽分降低效果有限，未來仍需結合其他改良材料與長期穩定性評估，以確保其在多重污染環境下的持續效益與生態安全。
;In recent years, the rapid expansion of urban development and public construction projects in Taiwan has led to a continuous increase in the generation of construction surplus soils, resulting in a large amount of B7-type soil being produced. However, current reuse technologies and management strategies for B7-type soils remain insufficient, causing these materials to be stockpiled in disposal sites and contributing to land resource inefficiency and environmental burden. Meanwhile, Taiwan faces multiple soil-related environmental issues, including soil acidification caused by acid rain and excessive fertilizer application, soil salinization due to seawater intrusion and groundwater overextraction, and heavy metal contamination originating from industrial and agricultural activities. To address these problems, this study aimed to explore the feasibility of reusing B7-type soil as a soil amendment for improving acidic, heavy-metal-contaminated, and saline soils, while also assessing its environmental safety.
The Toxicity Characteristic Leaching Procedure (TCLP) results of B7-type soils collected from four soil resource treatment plants showed that their pH values ranged between 8.6 and 9.7, indicating strong alkalinity, and the concentrations of leached heavy metals were below the regulatory limits defined in Taiwan’s “Hazardous Industrial Waste Identification Standards.” These results demonstrate that B7-type soils possess low environmental risk and potential for safe reuse. The soil neutralization experiments revealed that B7-type soil effectively and rapidly increased the pH of acidic soils. Depending on plant requirements, the addition ratio can be adjusted between 5% and 25% to achieve the optimal pH range (5.5~7.0) for most crops.
The heavy metal stabilization tests indicated that the addition of B7-type soil showed limited effectiveness in Cd immobilization. Over time, with the decomposition of organic matter, Cd gradually transformed from the organic-bound fraction (F4) to the carbonate-bound fraction (F2), resulting in higher bioavailability. In contrast, B7-type soil exhibited strong Pb immobilization ability, as the proportions of Pb in the organic-bound and residual fractions increased while the acid-soluble fraction decreased, effectively reducing Pb bioavailability. In the saline soil remediation test, initial salt leaching caused downward salt migration; however, as time progressed, evaporation led to upward salt redistribution, resulting in a new equilibrium of salt concentration between surface and subsurface layers. These findings suggest that B7-type soil alone is insufficient to significantly reduce soil salinity.
To further assess environmental safety, a photodegradation experiment was conducted to evaluate the stability of polyacrylamide (PAM) in B7-type soil. The results showed that no acrylamide (AMD) release was detected in any of the samples, indicating that PAM remains stable under natural sunlight exposure and does not pose a significant environmental risk.
In summary, B7-type soil is characterized by strong alkalinity, low heavy metal leachability, and good environmental stability, making it a promising material for soil improvement and resource reuse. It can effectively ameliorate soil acidity and stabilize Pb contamination; however, its Cd fixation and salt reduction performance remain limited. Future research should focus on combining B7-type soil with other amendments and evaluating its long-term stability to ensure sustainable application and environmental safety in various contaminated soil systems. |
