臺北市都市生質廢棄物之都市代謝研究

Abstract

人類活動往往伴隨著廢棄物數量的增長，都會區尤其如此；然而，這些廢棄物中往往包含些都市生質廢棄物，例如廚餘，因此都市生質廢棄物再利用為能資源或視為廢棄物將會對都會區造成不同的影響。基於上述所說，本研究分為三部分：首先，本研究運用網絡型都市代謝概念加以分析臺北市都市生質廢棄物能(包含廚餘、污泥與垃圾)能資源轉化處理與再利用，並建立都市代謝效率與衝擊指標，用以評價都市生質廢棄物能資源轉化處理與再利用對於2004年與2013年臺北市都市代謝之影響；接續，本研究選擇廚餘作為對象，並且設定四種廚餘轉化再利用情境進行生命週期評估；最後，本研究提出新都市代謝衝擊指標用以改善原指標之缺點。 結果顯示臺北市近十年代謝效率指標上升(都市資源之使用效率提升)，但同時代謝衝擊指標亦上升，導因於都市人口與都市生質廢棄物數量的上升。接續，本研究選擇廚餘進行生命週期評估，並且依照臺北市現行廚餘能資源轉化再利用現況設計四種情境，分別為廚餘轉製生質酒精(情境1)、廚餘堆肥處理(情境2)、廚餘先行高溫蒸煮前處理後堆肥(情境3)、廚餘與污泥行厭氧共消化(情境4)，其結果顯示四種情境之總環境衝擊大小依序為情境1(4.11 mPt)、情境2(-2.83 mPt)、情境4(-29.96 mPt)、情境3(-64.59 mPt)，從評估結果可以看出廚餘轉化再利用情境最佳方案為情境3，主要係因其廚餘高溫蒸煮後堆肥產物之有機肥料替代效益量大所致；最後，本研究提出一都市代謝衝擊指標Mwj(LCA)，乃由於原先都市代謝衝擊指標無法反映出都市所承受之真實衝擊，畢竟其環境衝擊是以質量做計算；反之，新都市代謝衝擊指標Mwj(LCA)能將都市生質廢棄物數量(fRj)與都市生質廢棄物能資源轉化技術造成之排放量(yj)轉化為總環境衝擊(single score)，可完整呈現一都市之代謝衝擊指標。 本研究以網絡型都市代謝探討城市物資與能源之流動，並結合生命週期評估方法量化廚餘處理之環境衝擊，且建立一新都市代謝衝擊指標，成功連結廚餘廢棄物能資源化與都市代謝之關聯性；綜合以上結果顯示，此整合研究方式可顯現都市廢棄物處理及再利用方式對於都市代謝之影響，進而能輔助政策之制定。

Anthropogenic activities have increased waste volumes dramatically, particularly in urban environments. This waste often includes biodegradable matter, such as food scraps. Treating this matter as a resource or as waste will result in different consequences in an urban system. With that in mind, this research can divided into three parts: 1) use the concept of network Urban Metabolism (UM) in order to analyze the influence of recycling and reuse of urban bio-waste, including food waste (FW), municipal sewage sludge (MSS) and municipal solid waste (MSW) to Taipei City in 2004 and 2013 and establish UM efficiency and impact indicators to assess it, 2) choose FW as target and set four FW treatment scenarios for life cycle assessment (LCA), 3) propose new UM impact indicator in order to improve on the existing system. The network UM results showed that the total metabolic efficiency in Taipei rose over the last decade, which means the resource use efficiency in Taipei City has increased. However, the total metabolic impacts also increased, as a result of growth in population and bio-waste. This study chose FW for LCA and set four treatment scenarios based on current treatment in Taipei: 1) transforming FW into bio-ethanol, 2) direct composting treatment, 3) composting after pre-treatment of high temperature cooking, 4) anaerobic co-digestion with SWS. The LCA results showed that the order of environmental impact was scenario 1 (4.11 mPt), scenario 2 (-2.83 mPt), scenario 4 (-29.96 mPt), and scenario 3 (-64.59 mPt). Scenario 3 was the best plan because of the benefit of organic fertilizer. Additionally, this study proposes the new UM indicator MWj(LCA), for the original one cannot reflect the actual impact sustained by a city since all environmental impacts were calculated in mass units. MWj(LCA) , on the other hand, can transform both the amount of bio-waste and the impact from different FW treatment into a single, final environmental impact score. In conclusion, this study used the concept of network UM to inspect the material and energy flow in a city and incorporated the LCA method into UM to quantify the environmental impact of four FW treatment scenarios. Most importantly, this study proposed a new UM indicator MWj(LCA) so that the relation between UM and bio-waste(FW) conversion can be connected. And the result showed that under such integrated method can actually reflect the influence of urban bio-waste to the city, which can be a significant tool for policy decision.