前處理程序對垃圾焚化飛灰固化掩埋降低長期環境危害之研究

A study on the pretreatment processes for solidification followed by landfilling of MSWI fly ash to reduce long-term environmental hazard

黃柔恩(Jou-En Huang)

指導教授 ： 高思懷

淡江大學/工學院/水資源及環境工程學系碩士班/碩士(2019年)

https://doi.org/10.6846/TKU.2019.01006

摘要

論文提要內容：
　　垃圾經焚化處理後所產生的飛灰，其重金屬通常遠超出有害事業廢棄物認定標準，目前全球多採用穩定化或水泥固化處理後掩埋。由於飛灰中含有大量氯鹽等可溶性鹽類，於固化掩埋期間，易受雨水浸蝕溶出，將導致固化體形成空洞，使穩定固化效果降低，進而造成風化龜裂及重金屬有再溶出之危機。
　　機械化學濕式研磨處理對於水洗後之焚化飛灰具有優異的重金屬長期穩定效果，同時有助於氯鹽的溶出，因此本研究期望探討以水洗配合機械化學穩定處理，取代水泥固化過程添加重金屬螯合劑之效果。除了評估固化體抗壓強度的影響之外，利用毒性特性溶出程序(TCLP)以及向上流動滲濾試驗法，評估固化物抵抗酸雨之能力以及在掩埋場環境之長期安全性。
　　研究結果發現，焚化飛灰經水洗處理，其重量約減少40%，水洗灰穩定固化體之強度因水洗過程造成鈣之流失，其抗壓強度不如原灰固化者；然而固化體重金屬溶出則較低。水洗研磨固化體與原灰穩定固化者相較，以每公斤原始焚化飛灰為計算基準，其氯鹽含量由1,046降至374 mg/kg；抗壓強度相似。TCLP鉛由5.32 mg/kg降至低於偵測極限；總鉻由低於偵測極限提升至9.24 mg/kg。
　　向上流動試驗7天鉛溶出總量由35.22下降至12.00 (2小時研磨)與0.39 mg/kg (4小時研磨)；總鉻之溶出量於原灰穩定固化試體是略為下降而後上升，至第7天甚至比第1天還高；而研磨穩定固化試體則是略為下降後趨於平緩，其長期溶出趨勢顯著較低。經向上流動滲濾試驗7日後，原灰試體重量損失高達30 %，水洗灰穩定固化試體約20 %，研磨灰試體則降為10 %。此結果證實水洗及研磨前處理因有效去除氯鹽，降低了受到風化而使重金屬溶出量逐漸增加之風險，其中以水洗研磨前處理對於降低環境長期危害風險最為顯著。

關鍵字

垃圾焚化飛灰 ； 穩定化 ； 固化 ； 機械化學研磨穩定

並列摘要

Abstract:
Heavy metal leaching characteristic of municipal solid waste incinerator (MSWI) fly ash, is usually far exceeded the hazardous waste regulation, at present, chemical stabilization followed by cement solidification pretreatment is popular adopted before landfilling in the world. Since chloride is abundant in MSWI fly ash, it is easily dissolved by the rainfall in the environment, speeding the weathering and decreasing the effect of stabilization/solidification treatment, and increasing the potential of heavy metal leaching hazard.
Mechano-chemical wet milling has good long-term stabilization effect for the washed MSWI fly ash, which can also enhance the dissolution of chloride. In this study, it was explored to compare with the effect of traditional chemical stabilization without pre-washing. Beside the compressive strength test and TCLP for the solidified matrix, up-flow percolation test was studied to evaluate the long-term leaching potential of heavy metals in the environment.
The results showed, washing pretreatment could decrease the ash weight around 40%, while the compressive strength were decreased due to the release of calcium, nevertheless, heavy metals TCLP were decreased compare to the stabilization/ solidification of raw fly ash. Calculating by the bases of the weight of raw MSWI fly ash, the substitution of traditional chelating stabilization by washing/milling stabilization, chloride content of cement solidified matrix was decreased from 1,046 to 374 mg/kg, the compressive strength was similar, while the lead of TCLP was decreased from 5.32 mg/kg to below detectable level.
The results of 7-day up-flow percolation test showed, the cumulative Pb leaching of solidified matrix was decreased from the raw ash sample 35.22 to 12.00 (2 hr milling) and 0.39 mg/kg (4 hr milling) respectively. The T-Cr dissolution trend of raw fly ash sample was slightly decreased then increased, on the 7th day was even higher than the first day; the milled fly ash sample was a slight decline and then flat, and the long-term dissolution risk was lower. The total weight loss of raw fly ash sample was 30%, while the washed fly ash and milled fly ash samples decreased to 20 and 10% respectively. Both pretreatment can remove the chloride in the ash effectively, which could prevent the weathering and has a significant contribution to reducing the risk of long-term environmental hazard.

並列關鍵字

MSWI fly ash ； stabilization ； solidification ； mechano-chemical stabilization

參考文獻

參考文獻

Cheriaf, M., Cavalcante Rocha J., and Pera J. (1999) “Pozzolantic properties of pulverized coal combustion bottom ash”, Cement and Concrete Research, 29, 1387-1391.

Kiattekomol, K., Chai J., Smith S., and Cutubtim, S. (2001) “A study of gound coarse fly ashes with different fineness from various sources as pozzolanic materials”, Cement and Concrete Research, 23, 335-343.

Luca, B., C. Maddalena, C. Davide, Q. C. Alessandro, Carsana and C. Mario, “MSWI Ashes as Mineral Additions in Concrete,” Cement and Concrete Research, Vol.34(10), pp.1899-1906, 2004.

Malhotra and Metha, P.K. (2005) “High-Performance,High-Volum Fly Ash Concrete”, 2nd Ed.