建立一般廢棄物焚化底渣再利用決策方法論之研究

Decision-Making Process for MSWI Bottom Ash Utilization

黃錦明(Chin-Ming Huang)

指導教授 ： 楊萬發

國立臺灣大學/工學院/環境工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.01436

摘要

焚化技術將垃圾中有機物分解，非有機成分及未完全燃燒的部分則轉化成焚化底渣與焚化飛灰，兩者混合不分類稱為灰渣。焚化灰渣產生率約為10~25%（以重量計），而飛灰與底渣之比例大約為1：5~1：10。臺灣地區大型垃圾焚化廠共有27座，處理量能為每日27,450公噸，預計每日將產生約6,500公噸的底渣與約1,500公噸的飛灰。
臺灣地區天然資源有限，土石資源屬不可再生資源，雖然焚化灰渣之處理或再利用技術如火如荼在進行，若沒有具科學基礎的法令規定，數量龐大之灰渣將無法達到有效妥善運用。本研究論文之主題，參酌先進國家建置資源回收再利用體制、環境管理稽核制度及生命週期評估等制度與作法，探討「建立一般廢棄物焚化底渣再利用決策方法論之研究」，建立科學化、系統化的決策程序，以有效推動焚化底渣再生資源再利用，以減少土石資源之開發，降低環境負荷，促進資源永續利用，進而提高國家環境及經濟競爭力。
本研究針對焚化底渣再利用於控制性低強度回填料之可行性進行實驗與探討，以底渣取代骨材進行配比試驗，探討工程應用之可行性，及其施工階段及完工後對民眾健康之風險評估。另就焚化底渣再利用於瀝青混凝土之可行性進行實驗與探討，觀察瀝青混凝土之工程性質及環境性質，探討含底渣之瀝青混凝土應用之可行性及環境相容性。
本研究依據焚化底渣之理化特性、工程性質、工程材料之應用情形、再利用用途之健康風險評估、生態風險評析等面向之研究探討綜合結果，提出具科學量化指標的焚化底渣再利用風險評估系統，以供再利用決策評估程序之參考。
本研究現階段之結論如下：
一、焚化底渣理化性質：焚化底渣的主要成份（大於1％者）為氧化矽（SiO2）、氧化鋁（Al2O3）、氧化鐵（Fe2O3）及氧化鈣（CaO）等，為異質性大之非均質性物質，含水率較高，約18~25%，呈灰黑色且會散發出類似腐敗之異味，與一般無機物的成份相似，但含有Mg、Na、K等易溶於水的鹼金屬及鹼土金屬等鹽類，使底渣易隨著水分的乾濕變化而脹縮變動，造成焚化底渣再利用的產品品質不易穩定。粒徑分析結果屬級配優良之砂土-SW級（USCS）或A-1-b級（AASHTO），屬具有良好的滲透性、剪力強度、壓縮性及施工性之材料，適合作為結構基礎或路基材料。
二、含焚化底渣的CLSM工程性質：底渣顆粒類似天然砂土，其夯實性質似亦符合路基材料之要求。其流度、泌水率、強度及滲透性等之配比試驗結果均符合工程性質要求，以灰水比(C/W)為0.4，水固比(W/S)0.35∼0.40為最佳配比條件。惟因含氯之故，建議僅適用於非金屬管溝之回填並遠離地下水位。
三、含焚化底渣的瀝青混凝土工程性質：單位重與含油量之關係與傳統瀝青混凝土相似，均隨含油量增加而先升後降，且單位重曲線之最高點所對應之瀝青含量，有隨底渣含量增加而增加之趨勢。馬歇爾試體之穩定值、流度值、空隙率、粒料間孔隙與含油量關係曲線皆與一般瀝青混凝土相似，顯見底渣取代骨材與瀝青混凝土拌合是可行的再利用方式。整體而言，配比條件以添加20 % ~ 25 %底渣之瀝青混凝土，其工程性能之安全度為最佳。
四、含焚化底渣的CLSM對大眾健康的影響：分析計算CLSM施工期間及完工後對不同暴露族群的吸入、飲水及地下水等暴露途徑之致癌風險均低於10-6，吸入、飲水及地下水之非致癌危害商數均低於1，為可接受條件（acceptable）。以増加產品使用規模的10倍進行敏感度分析，結果發現，飲水的致癌風險値會隨使用量增加，呈現增加的趨勢，當超過評定基準，則須降低使用量，以符合風險評定標準，此可作為管制使用地區或面積之建議參考。
五、含焚化底渣的瀝青混凝土環境性質：一般瀝青混凝土、100%焚化底渣瀝青混凝土與焚化底渣之溶出液中七種重金屬濃度均低於TCLP標準限值。而比較焚化底渣與100%焚化底渣瀝青混凝土之重金屬溶出總量，發現焚化底渣經瀝青材料包裹後，重金屬溶出總量均小於未經處理的焚化底渣。以水蚤為指標的毒性試驗，顯示焚化底渣屬中毒性以上，100%焚化底渣的瀝青混凝土為中毒性以下，一般瀝青混凝土則為低毒性以下。整體而言，焚化底渣經與瀝青拌合後，毒性強度可降至低毒性以下，顯示添加適量焚化底渣的瀝青混凝土，可提高其環境相容性，有利於再生利用。
六、再利用之決策程序：依序將再生材料的工程性質及施工規範、健康風險的評估標準及生態風險（水中生物毒性試驗）的評量基準列為決策程序之依據，可充分符合優先考量工程應用安全之基本需求，其次衡量對暴露族群的健康風險，再以對生態環境的影響為最後把關。由此評估程序，如果次一程序的評估結果發現超過標準，則需回上一程序檢討、降低底渣的使用或添加比例，或另以添加穩定劑或其他處理製程將底渣予以改質，以減少污染物之釋出潛勢，確保產品使用之安全性。

關鍵字

健康風險評估 ； 生態風險評估 ； CLSM ； 瀝青混凝土 ； 水蚤毒性試驗 ； 環境相容性 ； 決策程序

並列摘要

The Taiwan Environmental Protection Administration has studied the treatment and reuse of MSWI ashes for many years and collected references on international experience accumulated by developed nations for establishing policies on treatment and reuse of MSWI ashes. The total number of incinerators is expected to increase to 27 with treatment capacity of 27,450 tons per day in service, operated daily to generate about 6,500 tons of incinerator bottom ash and 1,500 tons of incinerator fly ash, serving almost all cities in Taiwan by 2007. The citations were analyzed as the basis for current governmental decision making on policies and factors to be considered for establishing decisions on recycle and reuse of MSWI ashes. Feasible applications include utilization of ashes, which after sieving and separation of metal particles, produce secondary construction materials. When secondary construction materials comply with TCLP limitations, they can be utilized as cement additives, asphalt aggregate or road base. The decision making procedures of evaluation have been proposed in the performance criteria, health risk assessment, ecological risk assessment, to be included in the proposed process of ash utilization.

This study was associated with the assessment of CLSM with bottom ash. The assessment method that combines engineering criteria and risk assessment, then be used to select the available substitution ratio for practice. The results were showed best condition was C/W 0.4, W/S 0.35∼0.40. Therefore, the achievements of the study could serve as the basis for the decision making and risk management related to reuse of bottom ash. The health risk assessment of CLSM with bottom ash were evaluated, the cancer risk of exposure route under construction and road service was lower than 10-6, and hazard quotient for noncancer was lower than 1.

The physical and environmental properties of asphalt mixtures using various incinerator bottom ash as fine aggregate substitution were investigated. The Marshall mix design method was used to determine the asphalt content and evaluate the potential performance of IBA–asphalt mixtures. Leachates, from laboratory and outdoor leaching tests, were measured the concentration of heavy metals and daphnia toxicity. While with adequate Marshall stability, the IBA–asphalt mixtures were shown to have excessively high Marshall flow and excessively low VMA. The results of the wheel tracking tests indicated that the mixtures had low rutting resistance. The results of the water sensitivity test showed that the mixtures had a higher tensile strength ratio. Considering the environmental compatibility, the outdoor leachates showed that IBA had a high level of daphnia toxicity. From the ecological risk perspective, IBA could be identified as hazardous waste. However, after being mixed with asphalt, the concentration of heavy metals and the levels of daphnia toxicity were significantly reduced. The leachates of 10-day flat plate leaching tests indicated that the heavy metal were undetectable and the daphnia toxicity was ineffective. The IBA substitution rate would be suggested as less than 25% for surface course and less than 50% for base course

To address public concerns, TEPA has adopted stringent regulations to reduce risk in bottom ash utilization and minimize the emission of pollutants in the flue gas from MSWI. In addition to providing technical guidelines for bottom ash utilization, TEPA has initiated the demonstration projects for obtaining field data to affirm the utilization policy and to revise the technical criteria, if needed. In this way, risk in the whole utilization process will be minimized, and the benefit and cost-effectiveness of the selected strategies on utilization will be maximized. The author offers the decision making process for the utilization of bottom ash with the engineering specification, environmental risk and ecological risk.

並列關鍵字

health risk assessment ； ecological risk assessment ； CLSM ； asphalt concrete ； daphnia toxicity ； environmental compatiblity ； decision making process

參考文獻

吳淵洵（1994），應用自流性飛灰為土方回填材料之研究，國科會專題研究計畫成果報告，NSC 82-0113-E-216-023-T。

吳淵洵（1999），自流性填方材料之工程性質及其可行性研究，國科會專題研究計畫成果報告，NSC 88-2218-E-216-005。

楊萬發、黃錦明（2002），修訂一般廢棄物貯存清除處理方法及設施標準專案工作計畫，行政院環保署委託。

行政院環保署（2000b），資源回收再利用法治之評估及立法建議。

工業技術研究院化學工業研究所（1996），焚化灰渣資源化研究。