The Physico-chemical Properties of Incinerator Bottom Ash and the Revegetation at Landfill Site

Abstract

本研究主要探討台中市焚化爐底灰物化特性及其溶出物質對覆土利用如掩埋場覆土生物分解穩定，植生覆土復育之潛在影響。實驗包括灰燼特性分析、灰燼溶出試驗、重金屬對厭氧污泥之結合與抑制作用、底灰對滲出液中總有機物之吸附與反應行為、底灰作為覆土與垃圾共同掩埋之覆土利用評估及底灰作為探討覆土植生復育之潛在影響、及鎘與滲出液對掩埋場植栽之影響研究。研究結果顯示：(1)底灰乾重部份總碳(TC)與總氮(TN)之平均含量分別為7379與174μgg-1且隨著不同顆粒粒徑減小而增加。Cu、Cd、Pb、Zn、Ni、及Cr之重金屬平均含量分別為7786、29、994、4006、224、及226μgg-1。(2)使用搖動或滾動兩種批次實驗方法將10克底灰置於500ml之蒸餾水中所獲得之溶出結果其滲出濃度值介於0-11μgg-1間。(3)灰燼在較低pH與較高溫度之環境參數條件時有較高之溶出濃度尤其是Zn、Pb、及Cu。(4)Zn、Cu、及Ni厭氧污泥50%程度抑制作用之濃度分別為650mg Znl-1與47.5mg Zng-1 乾污泥、360 mg Cul-1與40 mg Cug-1乾污泥、及380 mg Nil-1與39 mg Nig-1乾污泥。(5)底灰顯示有吸附有機物之潛力且受底灰濃度、pH、溫度、及顆粒大小等因素影響。吸附容量隨底灰濃度、pH、溫度、及粒徑之減少而增加。(6)底灰與垃圾共同厭氧消化顯示其添加有正面之效益。此項研究結果係於實驗室級厭氧消化槽進行而得，其反應槽溫度為35℃，固體停留時間為20天。所使用反應槽共有四個，其中兩個為對照組，另兩個為底灰添加組其添加比例分別為25/100與50/100。底灰添加處理組與對照組相較，其pH、鹼度、氣體產量較高而揮發酸之破壞較大且其滲出液中有機物較低。50/100底灰與垃圾添加比例反應槽較25/100底灰與垃圾添加比例反應槽有更顯著之促進生物分解有利結果，此結果可提供台灣以及其它世界各國以底灰當作掩埋覆土之操作基線實務依據。(7)底灰之鹼性金屬含量有緩衝厭氧消化程序所產生之揮發酸與調和土壤酸性之作用，其微量元素則可提供生物反應與植物生長之營養鹽而有促進其生長與除污之潛勢。(8)植栽復育研究中植栽之滲出水與鎘污染耐受實驗解釋掩埋場現場之種植比室內盆栽之種植其光合作用效率(Fv/Fm)較差，顯示其所受之環境壓力較大。

The thesis investigates the effects of environmental stress on the vegetation at landfill and the physico-chemical properties of bottom ash generated from Taichung City incinerator. Experiments undertaken include ash characterisation, ash leaching tests, binding and inhibition of heavy metals by means of anaerobic sludge, adsorption and interaction of organic pollutant in the leachate by bottom ash, biological assessment of co-disposal of refuse and bottom ash in an anaerobic bioreactor, and the effects of leachate and Cd on the vegetation at landfill site. The results of ash characterisation showed that total carbon (TC) and total nitrogen (TN) in different sieved particle sizes decreased as the particle size increased and the average total content was 7379 and 174μgg-1 respectively. The average total content of the six heavy metals Cu, Cd, Pb, Zn, Ni and Cr was 7786, 29, 994, 4006, 224 and 226 mgg-1 respectively but did not show the linear relationship between ash particle size and the content except Cr and Cd. The leaching results of 10 g bottom ash mixed with 500 ml deionized water using tumbling and reciprocating shaking showed that the leaching concentration was in the range of 0~11 mgg-1. Leaching from the ash was greater at the extreme pH and temperature having the greatest effect on leachate concentrations of Zn, Pb, and Cu. An inhibitory effect of heavy metals was shown at a 50% levels for Zn, Cu and Ni of 650mg Znl-1 and 47.5mg Zng-1 dry solid sludge, 360 mg Cul-1 and 40 mg Cug-1 dry solid sludge and 380 mg Nil-1 and 39 mg Nig-1 dry solid sludge respectively. Bottom ash showed potential adsorption capacity for organic matter which was influenced by ash concentration, pH, temperature and particle size. The adsorption capacity increased as the ash concentration, pH, temperature, and particle size decreased. The anaerobic co-digestion of bottom ash and simulated refuse showed the beneficial effect of bottom ash addition. These studies were conducted in laboratory scale anaerobic digesters with a retention time of 20 days and a temperature of 35℃. Four reactors were used, two of these (controls) had no ash addition whilst the other two had ash added with the batch fed refuse simulant in a ratio of 25/100 and 50/100 respectively. The beneficial effect of bottom ash addition was observed through the increase in pH, alkalinity, gas production, and the volatile solids destruction and the decrease of total organic carbon concentration of leachate compared with the control reactors. The more significant beneficial results were observed when a bottom ash/refuse ratio of 50/100 was used than that of 25/100. The physico-chemical properties of bottom ash showed that it had the potential to provide the buffer alkalinity to the biological treatment system and the soil vegetation. The trace elements in the bottom ash had the potential to provide the needs of biological treatment and vegetation. The values of Fv/Fm showed that the vegetation tolerance of leachate and Cd at landfill site was lower than that at indoor experiments which received lesser environmental stress than the field test.