| 摘要: | 我國污水處理廠產出之脫水污泥，大部分逕自委外清運處理，不僅費用高昂，對於污泥的確實流向也無法有效掌握。污泥於廠內雖經濃縮及脫水等程序處理，但產出之脫水污泥含水率仍高達75％～85％，徒增清運處理費用，也容易污染環境。
本研究以國內北部某二級污水處理廠為實例，將脫水污泥進行乾燥處理，為避免因高溫而破壞污泥含有之可再利用成分，乾燥溫度設定最高為105℃，將乾燥污泥含水率降至30％左右。紀錄乾燥過程中操作參數，評估乾燥處理所需消耗的能源及成本，以評估乾燥減量效益。
此外，將乾燥後污泥委託合格實驗室檢驗其成份及重金屬含量，依其檢驗結果，建議合宜之再利用方式，並參考日本橫濱市污泥聯合處理方式，評估區域化聯合處理模式於我國之適用性。
綜合目前國內對於污泥再利用之相關法令及限制，發現污泥重金屬含量，例如鎘、汞、鉻、鎳及鋅等，超出我國肥料管理法中「雜項堆肥」或是「雜項有機栽培介質」有害成分之限值，故污泥「肥料化」再利用目前暫不適用於我國。
本案例廠乾燥減量率為53％，每公噸污泥乾燥成本介於2,005元至3,600元，較原本逕自委外清運處理費用每公噸4,500元，具有相當的減量經濟效益，且大幅減少污泥重量，方便廠內清運整理，提升後續再利用的多元化。
污泥「燃料化」屬於生質能應用，國內因未設置污泥專用焚化爐，故將乾燥污泥與生活垃圾共同混燒作為焚法處理方式。本研究以台北市及新北市為例，探討利用各區域範圍內之垃圾焚化處理廠，焚化處理各區域污水處理廠產出之污泥，將污泥乾燥後「燃料化」再利用，藉由焚化廠汽電共生系統回收電能，焚化後之灰渣可作為建材原料之「材料化」再利用，提高污泥再利用率，達到完全零廢棄的可行性。本研究期盼結合國內污泥減量、處理及再利用技術，開創污泥多元化再利用市場，善用既有處理設施，填補政府額定保證交付焚化量，提升垃圾焚化廠之焚化率，以及減少掩埋場之負荷，充分發揮「污染減量」、「節能減碳」及「資源回收」等三重效益，符合國際能源回收趨勢，確實解決污泥最終處理處置問題。
In Taiwan, the dewatered sludge of sewage treatment plant is mostly contracted out for transportation. Not only its cost is expensive, but also its exact destination is hard to efficiently control. Although sewage sludge is processed by thickening and dewatering in the treatment plant, the water content of the dewatered sludge is still high, ranging from 75% to 85%. Therefore, it will directly cause the increase of the transportation cost of the sludge, and is liable to pollute the environment.
This study is based on a real case to dry the dewatered sludge of a secondary treatment plant in the northern Taiwan. To prevent from the high-temperature deterioration of the reusable material, the highest drying temperature was set at 105℃ and the water content of the dry sludge was reduced to about 30%. The relevant operational parameters were recorded on energy consumption and cost, followed by the benefit assessment of sludge-drying deduction.
In addition, the examinations of constituents and heavy metals of the dried sludge were outsourced to the qualified laboratories. According to the examination results, the adaptable reuse method was recommended. Furthermore, to evaluate the adaptability of the localization model of the combined treatment of the sludge in Taiwan, the approach of Yokohama City in Japan was referred.
Based on the prevailing regulations and limitations on the sludge reuse in Taiwan, it is found that the heavy metal contents, such as Cd, Hg, Cr, Ni, and Zn, are higher than those of the hazardous constituents limited in the ancillary compost fertilizer or the ancillary organic plantation media of the Fertilizer Management Law.
In the case study of drying deduction of 53%, the sludge drying cost per metric ton ranges from NTD2,005 to NTD3,600. Compared with the directly outsourcing hauling and transportation cost of NTD4,500 per metric ton, it has potential economic benefit from drying deduction, in addition to reducing the sludge weight on a large scale, facilitating to clearance in plant, and promoting subsequent multipurpose reuse.
Recovery energy from sludge is the application of biomass energy. Because there is no sludge-exclusive incinerator in Taiwan, the incineration of the dry sludge is usually mixed with the municipal waste. This study was based on the practical cases in Taipei City and New Taipei City to use the existing municipal waste incinerators in the regions to burn the sewage sludge in the regions concerned. Through the reuse of the recovery energy from sludge in the sewage treatment plant, and the power generation of the co-generation and the reuse of the materialized ash of the incinerators, the re-usage rate of the sludge will be increased and the complete zero waste will be reached.
It is expected to associate with the sludge deduction, treatment, and reuse technologies in Taiwan to initiate the market of the multipurpose reuse, to well use the existing treatment facilities to fill up the rated garbage delivery amount guaranteed by the government, to increase the incineration rate of the garbage incinerator, to reduce the loading of the landfill, to achieve a triple benefit of pollution reduction, energy saving and carbon reduction, and resource recycle, and to comply with the international trend toward the energy recycle for exact solving the problem with the final treatment and disposal of sludge. |
