(示意圖/圖片來源:Stockvault)

處在消費發達的現代社會,肉類生產已隱隱發展成一個龐大的產業,但畜牧場的動物廢棄物卻是常被遺忘,除留下難聞的氣味,其去化產生的的問題,如水源與土地退化、溫室氣體排放、營養鹽污染、以及人類與環境健康問題,對人類生存環境產生極大的困擾。透過發展生質能系統,可將這些廢棄物作為原料再利用,達成減少污染同時轉成再生能源的雙贏局面。

糞肥處理後產生的固體、液體及氣體,均具利用價值

沼氣屬於永續且碳中和的能源,將糞肥收集即可作為原料,處理後的糞肥不但能夠轉為能源,也同時具有其他用途。糞肥處理後轉換成固體、液體及氣體,每個部分都可以有效利用。固體因保有養分,可作為農田肥料;液體經處理後可用於灌溉或清潔用水;氣體則可轉換成能源。處理過的固體殘留物作為肥料使用時,釋放到大氣中的氮氣較其他肥料更少,因此可減少溫室氣體排放量。採用此種具永續性的清除處理方式,可大幅降低對於動物廢棄物的處理成本,並有助於減少畜牧業所產生之氣味。

(資料來源:Masse et al., 2011)

 豬糞最具發電效益,5,000頭以上規模養豬場,具有經濟及技術可行性

所有禽畜糞肥皆可產生沼氣,但豬隻糞肥無論在產量或生產週期上,都證實是最有效率的原料。豬隻廢棄物若未處理會造成環境及衛生問題,臺灣的養豬場豬糞產量龐大,養豬場沼氣發電量一直到最近才有所成長。以經濟規模分析,小規模的養豬場可能不會考慮設立電廠,但對於臺灣其他100多家擁有5,000頭以上豬隻規模的養豬場,使用沼氣技術具有經濟規模可行性。

雖然沼氣的期初投資成本較高,但長期成本具有經濟誘因,發展沼氣有助於減輕政府未來處理廢棄物的財務負擔。彰化東螺的沼氣發電廠是第一座由地方政府出資設立,目的在降低畜產業廢棄物處理成本。第一座沼氣發電廠成功後,臺灣其他的地方政府及企業也開始發展此類廢棄物能源轉換技術。

(沼氣發酵槽示意圖/圖片來源:Max Pixel)

更有效率的沼氣發電場方式,是結合動物廢棄物與農業或工業食品廢棄物,有助於減少垃圾掩埋場之排放量,並且減少廢棄物掩埋場空間。另一種增加效率的方式則是將糞肥與動物屍體混燒,排除重大疾病所造成的大量禽畜死亡,混燒可清除屍體且不必擔地面及水體污染、傳播疾病或造成優養化問題。另外,如同其他以農業廢棄物為料源的生質能,安全性是主要的考量之一,證明有害細菌能夠完全控制及消除後,動物廢棄物才有可能成為常見的能源原料。

動物廢棄物能源轉換的機會來自產業生態體系的良性運作,故需政府從中扮演積極的協調角色

建立動物廢棄物能源轉換的良好營運系統,涉及多重面向,如開發高效率技術的龐大成本、投資報酬回收期太長、需要高額投資及跨界合作克服困難,若沒有政府的支持,大多數農民不可能投入生產,因此政府必須從中扮演積極角色。能源業者與其他產業間的合作也同樣重要,以確保生質能具有成本效益,並在未來創造更好的經濟機會,建立最佳廢棄物能源化系統。

(責任翻譯:劉恩廷)

(責任編輯:羅時芳)

 


Manure to Energy: Exploring Energy Production via Animal Waste

There is a third form of agricultural waste which can be utilized for energy production which is often forgotten: animal waste. With meat production being the large industry it is today, there is a huge amount of unharnessed potential in this waste; but instead of utilizing the energy, is often left to build to toxic levels. Animal waste is a major pollutant, and will lead to severe environmental problems if not managed properly. In fact, manure often leads to water and land degradation, greenhouse gas emissions, nutrient loss, and human and environmental health (Masse et al., 2011). By creating a bioenergy system that can use this waste product, the amount of pollution will decrease while energy is produced in a more sustainable manner: a win-win situation.

(Source: Masse et al., 2011)

Biogas is a sustainable and carbon neutral source of energy, making the harvest of manure for energy production a viable option (Masse et al., 2011). Treated manure is not just used for energy production, but rather is a multifunctional product. When treated, it breaks into solids, liquids, and gases, and each part can be used in a beneficial way. Solids can be used as fertilizer for agricultural fields, keeping nutrients within the system, liquids can be treated to use in irrigation or cleaning,and the gases are left for energy production (Far Eastern Agriculture, 2013). The solid leftovers, when used as fertilizer, emits less nitrogen gases into the atmosphere than other fertilizers, and therefore reduces the amount of greenhouse gases produced (Masse et al., 2011). The sustainable removal and treatment of this waste also drastically reduces disposal costs, and helps to manage the odors associated with animal farming (Ahn et al., 2009).

While the waste of all animals can be used in biogas production, swine waste was proven to be the most efficient, both in terms of amount produced and period of viable production (Ahn et al., 2009). Taiwan raises pigs in substation numbers, but until recently, the waste produced was released untreated into the environment where it created environmental and health problems (Far Eastern Agriculture, 2013). Since the country produces vast quantities of pig manure, it makes sense that they look into the possibilities of biogas for energy production.

One of the largest incentives to biogas is the long-term cost. While initial costs are expensive, they would help to mitigate the governments future financial responsibilities associated with cleaning up waste after is has become a problem (Far Eastern Agriculture, 2013). Changhua Country’s Dongluo treatment plant was the first to be funded by a local government in order to reduce the overarching costs of waste treatment (Far Eastern Agriculture, 2013). Following the success of this first plant, other governments and companies in Taiwan have looked towards developing their own waste to energy technologies (Yang and Lee, 2015). While many of the small scale farms may not be considered, it is believed to be economically feasible for any facility raising at least 5,000 pigs, which Taiwan has over 100 of, to use this energy conversion technology (Yang and Lee, 2015).

There are also ways to create a more effective biogas plant, including combining manure with agriculture waste or industrial food waste (Masse et al., 2011). This would help to reduce the amount of waste in landfills releasing emissions and unnecessarily taking up space (Masse et al., 2011). Another option for co-firing is using animal carcasses with manure, which, barring major diseases with heavy fatalities, is a viable option of removing bodies without worrying about contamination to the ground, water, or spreading sickness and creating nutrient problems (Masse et al., 2011).

As with other forms of bioenergy from agricultural waste, one of the major concerns is safety for bystanders. Until it has been proven that any harmful bacterias are controlled and eliminated prior to processing, it is unlikely to become a common energy source (Masse et al., 2011). Some of the other barriers include cost of operation and cooperation required in order to create the best system for all (Masse et al., 2011). Without government cooperation, the cost of developing efficient technology is too high with too long of a payoff period for it to be feasible for most farmers (Masse et al., 2011). Therefore the government needs to be willing to play an active role in bioenergy production. However, it is equally important that energy companies and other industries cooperate to create the best system (Masse et al., 2011). This is in order to ensure that bioenergy is more cost effective and will produce better economic opportunities in the future.

 

Reference

  1. Ahn, H.K., M.C. Smith, S.L. Kondrad, J.W. White. (2010). Evaluation of Biogas Production Potential by Dry Anaerobic Digestion of Switchgrass–Animal Manure Mixtures. Applied Biochemistry and Biotechnology. 160(4), 965–975.
  2. Far Eastern Agriculture. (2013). Taiwan builds plant to turn pig waste into biogas. http://fareasternagriculture.com/live-stock/pig/taiwan-builds-plant-to-turn-pig-waste-into-biogas
  3. Masse, D.I., G. Talbot, Y. Gilbert. (2011). On farm biogas production: A method to reduce GHG emissions and develop more sustainable livestock operations. Animal Feed Science and Technology. 166–167, 436-445.
  4. Yang, S. and Lee, M. (2015).Turning pig manure into electricity. Focus Taiwan News Channel. http://focustaiwan.tw/search/201512050023.aspx?q=
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