垃圾焚化底碴資源化之道路基層應用研究

Abstract

行政院環保署於91.10.11公告垃圾焚化底碴再利用規定，目前國內已有26座大型垃圾焚化廠，於民國91年產生垃圾焚化底碴達110萬公噸，由於國內底碴再利用情形多為掩埋場覆土等用途，其再利用途徑有限。底碴產量約佔垃圾處理量的20%，則隨著垃圾處理量的增加，開發可大量消耗底碴並與環境相容及提高附加價值的再利用途徑成為目前非常迫切需要解決的環保問題。 參考美國、日本、德國、荷蘭、丹麥、法國及英國等高科技國家，多將垃圾焚化底碴應用於道路基底層、土木工程、土壤改良劑、隔音牆填充材、道路基底層、建材、基礎填充料、停車場鋪面及掩埋覆土材。本研究則是選擇可大量消化垃圾焚化底碴的道路基層為評估研究的方向，以北市某垃圾焚化廠垃圾焚化底碴為對象，經過篩分、破碎、磁選及渦電流等前處理，再經由化學成份分析、毒性特溶出試驗（TCLP）、工程材料性質試驗及環境相容性評估，以推估其應用於道路基層之可行性。 垃圾焚化底碴經化學組成分析、毒性特性溶出程序（TCLP）實驗、級配篩分析、洛杉磯磨耗試驗、硫酸鈉之健性實驗及加州承載比試驗，研究結果顯示其重金屬溶出量低於環保限值、且具有良好的承載力及抗風化的特性。但研究亦發現其燒失量(L.O.I.)在6~11%以上，較一般傳統粒料高，且垃圾焚化底碴的級配分析結果並不符合一般道路基層混合料比例，同時垃圾焚化底碴表面水份蒸發乾燥的過程會有膠狀鹽類滲出物，以X-光螢光分析（XRF），發現此水溶性鹽類主要成分為Ca、Cl、Al、K、S、Na等，這些鹽類遇水即溶解，當水份失去時則易形成底碴表面的結晶，經觀察這些鹽類結晶在析出時，會使夯實的垃圾焚化底碴土柱膨脹崩裂。 綜合以上各項化學及工程物理特性分析結果，顯示垃圾焚化底碴其本身部分的工程物理特性適合應用為路基粒料，但因仍含6~11%有機成份、水溶性鹽類及底碴的級配分析並不符合道路基層混合料比例等，將會影響工程品質後續的穩定性，故建議再利用前應增加前處理步驟以降低有機成份及水溶性鹽類含量，同時在實際應用時必須重新調整底碴的粒徑組成比例。 本研究期能建立垃圾焚化底碴資源再利用的全盤評估程序，包括檢討目前再利用技術所遇到的瓶頸及後續對環境可能造成的二次污染的追蹤模擬程序，期能減少垃圾焚化底碴再利用後對環境造成的衝擊，以積極的態度持續推動垃圾焚化底碴資源再利用之工作。

1.1 million tons of Municipal Solid Wast (MSW) incineration bottom ash was produced by 22 incinerators across the island by 2002. At present, the major application of bottom ash is to be utilized as the layering at the sanitary landfill sites. Other possibilities of employing excessive incineration ash need to be established. This study investigated the incinerated bottom ash with an aim to assess the reuse feasibility in subbase course. Both heavy metal contents and chlorinated salts in the raw bottom ashes were tested with Toxic Characteristic Leaching Procedure (TCLP) technique. An analysis for the comprehensive engineering properties was also conducted. Experiment results have shown that the amount of heavy metal contents is lower than the EPA limits. In addition, the results have also indicated that the raw material of incineration bottom ash, being well screen-separated, is suitable for subbase course material and engineering fillers. The compressive strength and weather-resistance value have suggested the incineration bottom ash is qualified for the sub base course. During the process, some gel-like substance was observed. The substance was tested with X-ray Fluorescence Spectroscopy (XRF) and the result has shown that the composition of the gel-like substance contains chemical elements such as Ca, Cl, Al, K, S, and Na. When the substance dries, the salts tend to crystallize and this may damage the sub-base course due to the expansion of volume. Therefore it is suggested that a tested sample in a greater quantity should be conducted before further establishing a reclamation management program for the bottom ash use. To sum up the results of this study, incineration bottom ash, with proper treatment, may be used as sub-base course material. Otherwise, it may lead to permanent damage to the roads due to varied organic compounds, inorganic salts, and other contents. A scheme of potential assessment procedure is suggested in section 6.2 to assist further equivalent studies. The procedure may help researchers investigate the proper use of incineration bottom ash in order to achieve the ultimate goal of ‘WTE’ (waste to energy).