實驗室堆肥反應槽及戶外堆肥反應槽之食品廢棄物與綠色廢棄物混合堆肥

Abstract

綠色廢棄物及食品廢棄物為都市固體廢棄物中最大宗的有機物來源，此類廢棄物經過適當的處理之後，可以作為土壤改良劑或有機肥料。最常見的處理方式為土地掩埋或是焚化法。近年來，由於台灣土地取得困難，使得土地掩埋法的處理量逐漸下降；而食品廢棄物及綠色廢棄物中的高含水率若進入焚化爐，不僅降低焚化的效率，也會對焚化爐造成損害，甚至產生戴奧辛等二次污染。因此，低成本、低技術門檻及最終產物可再利用的堆肥法在近幾年逐漸成為熱門的技術。本研究主要目的為利用實驗室規模的堆肥反應槽來進行食品廢棄物及綠色廢棄物的混合堆肥，利用實驗設計的方式找出最佳操作條件，並設計一無電力及自動控制系統之戶外堆肥反應槽，測試此最佳操作條件是否適用於戶外堆肥反應槽。

實驗結果顯示，採用槽式堆肥之食品廢棄物及綠色廢棄物之混合堆肥能在12天內被分解，高於過去文獻之堆肥反應速率且達到相當高的去除效率 (>30%)。碳氮比及含水率為堆肥實驗之重要參數，藉由中央合成設計法調整碳氮比及含水率並利用反應曲面法可得到最佳操作條件。中央合成設計法及反應曲面法所得之結果顯示，食品廢棄物及綠色廢棄物之混合堆肥之最佳含水率為60%；碳氮比在本研究中並非顯著之因子，但碳氮比表示綠色廢棄物及食品廢棄物之比例，進而影響堆肥物種之孔隙率及氧氣傳輸效率，因此，含水率及碳氮比之交互作用之影響為顯著的。此外，總揮發性固體物之去除率符合二階模型，其R2 高於95％。

本實驗所使用之戶外堆肥反應槽可在無電力系統之環境下運作，其設計結構並無自動攪拌以及曝氣系統；實驗結果顯示，同樣之操作條件下，戶外堆肥反應槽可達到較高之溫度及較高之總揮發性固體物去除率。旋轉戶外堆肥反應槽本體以達到攪拌效果，並可提供較高之攪拌效率，因此也達到較佳之實驗結果。此結果顯示，在設計反應槽以及實驗時，攪拌方式比攪拌頻率以及攪拌時間更重要。除此之外，以蘿蔔種子進行之種子發芽率測試以及重金屬測試結果顯示，戶外堆肥反應槽之堆肥產品能直接利用做為土壤改良劑。

Both food and green wastes are the most organic sources in municipal solid wastes, which can be reused as soil amendments or organic fertilizer for land application after proper treatment. Land filling/dumping and incineration are the most common ways to treat these organic wastes. Several dumpsites have been closed down in recent years due to the confined land availability in various countries including Taiwan. Furthermore, the high moisture content of organic waste reduces the incineration efficiency, and damages the incinerator as well as the process performance, thus resulting in the secondary pollution. Therefore, composting has become more popular due to its low energy cost, low technology demand, as well as the reusability of the end product. The main objectives of this study are to convert green waste and food waste into stable reusable products using lab-scale composting at optimal operating conditions and to design a field-scale reactor to mimic these conditions.

The results showed that food waste and green waste can be decomposed in 12 days with in-vessel composting, a shorter composting time than in previously published literature, and produced better total volatile solids (TVS) reduction ratio (>30%). A central composite design and response surface method were applied to obtain optimal operating conditions at different design moisture contents and carbon to nitrogen ratios. The central composite design and response surface method results indicated that the optimal moisture content for co-composting of food waste and green waste was 60%. Whereas the change in moisture content was a highly significant factor, the central composite design and response surface method results indicated that the carbon to nitrogen ratio was not. The TVS reduction ratio was modeled by a second-order equation with a correlation R2 value higher than 95%.

A field-scale composting reactor was designed without an agitator or aeration pump to save on electrical power use. The performance of the field-scale reactor yielded better results than the lab-scale reactor, producing a higher temperature and TVS reduction ratio. The better performance of the field-scale reactor is due to the increase in agitation efficiency. The results indicated that the agitation type is more important than agitation time when designing a composting reactor. The samples collected from the field scale reactor have nearly reached the value of standard germination index of radish seed, which shows that compost produced in this study can be applied as soil amendment.