豬糞廢水對環境的影響是豬養殖業所面臨的主要挑戰之一。直接將糞肥或液體厭氧消化物施用於土地上可能會因其含有的氮和磷養分而污染土壤和附近的水系。通過將基於微藻的過程納入系統中，先前被浪費的養分可以被利用。此外，產生出來的微藻生物可以作為豬飼料添加劑。這種方法通過回收材料並減少過程系統之外的外部資源需求，體現了一種循環經濟。

最近文獻中進行的生命週期評估已經證明了整合微藻的養豬系統之環境效益。本論文比較了四種情景的經濟表現，包括：（1）僅豬養殖（PF）；（2）PF和厭氧消化（AD）；（3）PF、AD和帶有飼料回收的微藻系統（MS）；以及（4）PF、AD和無飼料回收的MS。情景1至4的內部收益率分別為18.8%、13.3%、15.0%和12.3%。情景3實踐了循環經濟，並能夠提供環境和經濟效益，確保可持續性。值得注意的是，與情景4相比，情景3的內部收益率更高，而生命週期評估中的終點指標則更低。

The environmental impact of pig manure is one of the major challenges faced by the pig farming industry. Direct land application of manure or liquid digestate could contaminate the soil and nearby water systems due to their nitrogen and phosphorus nutrient contents. By incorporating a microalgae-based process into the system, the previously wasted nutrients can be utilized. Additionally, the resulting microalgae biomass product can serve as pig feed additive. This approach embodies a circular economy by recovering materials and reducing the need for external resources beyond the process system.

Environmental benefits of the integrated process have been demonstrated by Life Cycle Assessment conducted in recent literature. In this project, the economic performances of four scenarios including (1) Pig Farming (PF) only; (2) PF and Anaerobic Digestion (AD); (3) PF, AD and Microalgae System (MS) with feed recycle; and (4) PF, AD and MS without feed recycle were compared. Scenario 1 to 4 have IRRs of 18.8%, 13.3%, 15.0% and 12.3% respectively. Scenario 3, which embraces circular economy practices, is capable of providing both environmental and economic benefits, ensuring sustainability. It is also worth noting that Scenario 3 has a higher IRR with a lower endpoint indicator compared to Scenario 4.

[1] J. Kirchherr, D. Reike, and M. Hekkert, "Conceptualizing the circular economy: An analysis of 114 definitions," Resources, conservation and recycling, vol. 127, pp. 221-232, 2017.
[2] W. R. Stahel, "The circular economy," Nature, vol. 531, no. 7595, pp. 435-438, 2016.
[3] FAO, "World Food and Agriculture – Statistical Yearbook 2021," 2021.
[4] T. L. T. Nguyen, J. E. Hermansen, and L. Mogensen, "Fossil energy and GHG saving potentials of pig farming in the EU," Energy Policy, vol. 38, no. 5, pp. 2561-2571, 2010.
[5] X. Liu and X. Xiao, "The optimization of cyclic links of live pig-industry chain based on circular economics," Sustainability, vol. 8, no. 1, p. 26, 2015.
[6] A. Xia and J. D. Murphy, "Microalgal cultivation in treating liquid digestate from biogas systems," Trends in Biotechnology, vol. 34, no. 4, pp. 264-275, 2016.
[7] B. da Silva Vaz, J. B. Moreira, M. G. de Morais, and J. A. V. Costa, "Microalgae as a new source of bioactive compounds in food supplements," Current Opinion in Food Science, vol. 7, pp. 73-77, 2016.
[8] C. C. Chong et al., "Anaerobic digestate as a low-cost nutrient source for sustainable microalgae cultivation: A way forward through waste valorization approach," Science of The Total Environment, vol. 803, p. 150070, 2022.
[9] D. Nagarajan, S. Varjani, D.-J. Lee, and J.-S. Chang, "Sustainable aquaculture and animal feed from microalgae–nutritive value and techno-functional components," Renewable and Sustainable Energy Reviews, vol. 150, p. 111549, 2021.
[10] G. A. McAuliffe, D. V. Chapman, and C. L. Sage, "A thematic review of life cycle assessment (LCA) applied to pig production," Environmental Impact Assessment Review, vol. 56, pp. 12-22, 2016.
[11] W. Wu, L.-C. Cheng, and J.-S. Chang, "Environmental life cycle comparisons of pig farming integrated with anaerobic digestion and algae-based wastewater treatment," Journal of environmental management, vol. 264, p. 110512, 2020.
[12] NAIF, "2020 Taiwan Pig Production Statistics," 2020.
[13] J. F. Patience, M. C. Rossoni-Serão, and N. A. Gutiérrez, "A review of feed efficiency in swine: biology and application," Journal of animal science and biotechnology, vol. 6, no. 1, pp. 1-9, 2015.
[14] B. Xu et al., "Effects of fermented feed supplementation on pig growth performance: A meta-analysis," Animal Feed Science and Technology, vol. 259, p. 114315, 2020.
[15] C.-Y. Chen et al., "Microalgae-based carbohydrates for biofuel production," Biochemical Engineering Journal, vol. 78, pp. 1-10, 2013.
[16] K. K. Sharma, H. Schuhmann, and P. M. Schenk, "High lipid induction in microalgae for biodiesel production," Energies, vol. 5, no. 5, pp. 1532-1553, 2012.
[17] C. E. de Farias Silva and E. Sforza, "Carbohydrate productivity in continuous reactor under nitrogen limitation: effect of light and residence time on nutrient uptake in Chlorella vulgaris," Process Biochemistry, vol. 51, no. 12, pp. 2112-2118, 2016.
[18] R. Davis, J. Markham, C. Kinchin, N. Grundl, E. C. Tan, and D. Humbird, "Process design and economics for the production of algal biomass: algal biomass production in open pond systems and processing through dewatering for downstream conversion," National Renewable Energy Lab.(NREL), Golden, CO (United States), 2016.
[19] M. Ras, J.-P. Steyer, and O. Bernard, "Temperature effect on microalgae: a crucial factor for outdoor production," Reviews in Environmental Science and Bio/Technology, vol. 12, no. 2, pp. 153-164, 2013.
[20] AHDB, "2019 pig cost of production in selected countries," 2019.
[21] M. ten Hoeve, N. J. Hutchings, G. M. Peters, M. Svanström, L. S. Jensen, and S. Bruun, "Life cycle assessment of pig slurry treatment technologies for nutrient redistribution in Denmark," Journal of Environmental Management, vol. 132, pp. 60-70, 2014.
[22] B. Riaño and M. García-González, "On-farm treatment of swine manure based on solid–liquid separation and biological nitrification–denitrification of the liquid fraction," Journal of Environmental Management, vol. 132, pp. 87-93, 2014.
[23] R. Dalgaard, N. Halberg, and J. E. Hermansen, "Danish pork production: an environmental assessment," 2007.
[24] H. Wenzel and B. Petersen, "Life cycle assessment of slurry management technologies. Environmental Project No. 1298. Danish Ministry of the Environment," Environmental Protection Agency, Copenhagen, Denmark, 2009.
[25] (2021). Combined Heat and Power – Technologies, A detailed guide for CHP developers - Part 2.
[26] G. A. Lyons et al., "Review of two mechanical separation technologies for the sustainable management of agricultural phosphorus in nutrient-vulnerable zones," Agronomy, vol. 11, no. 5, p. 836, 2021.
[27] H. Hosseinizand, C. J. Lim, E. Webb, and S. Sokhansanj, "Economic analysis of drying microalgae Chlorella in a conveyor belt dryer with recycled heat from a power plant," Applied Thermal Engineering, vol. 124, pp. 525-532, 2017.
[28] H. Hosseinizand, S. Sokhansanj, and C. J. Lim, "Studying the drying mechanism of microalgae Chlorella vulgaris and the optimum drying temperature to preserve quality characteristics," Drying Technology, vol. 36, no. 9, pp. 1049-1060, 2018.
[29] G. Muhammad, M. A. Alam, W. Xiong, Y. Lv, and J.-L. Xu, "Microalgae biomass production: An overview of dynamic operational methods," Microalgae biotechnology for food, health and high value products, pp. 415-432, 2020.
[30] C.-L. Chen, J.-S. Chang, and D.-J. Lee, "Dewatering and drying methods for microalgae," Drying technology, vol. 33, no. 4, pp. 443-454, 2015.
[31] J. N. Rogers et al., "A critical analysis of paddlewheel-driven raceway ponds for algal biofuel production at commercial scales," Algal research, vol. 4, pp. 76-88, 2014.
[32] K. L. Kadam, "Environmental implications of power generation via coal-microalgae cofiring," Energy, vol. 27, no. 10, pp. 905-922, 2002.
[33] K. H. Min, D. H. Kim, M.-R. Ki, and S. P. Pack, "Recent progress in flocculation, dewatering, and drying technologies for microalgae utilization: Scalable and low-cost harvesting process development," Bioresource Technology, vol. 344, p. 126404, 2022.
[34] R. Hoste, "International comparison of pig production costs 2018," 2020.
[35] J. Zhang, H. Cho, and A. Knizley, "Evaluation of financial incentives for combined heat and power (CHP) systems in US regions," Renewable and Sustainable Energy Reviews, vol. 59, pp. 738-762, 2016.
[36] D. Vineyard, A. Hicks, K. Karthikeyan, and P. Barak, "Economic analysis of electrodialysis, denitrification, and anammox for nitrogen removal in municipal wastewater treatment," Journal of cleaner production, vol. 262, p. 121145, 2020.
[37] A. Aui, W. Li, and M. M. Wright, "Techno-economic and life cycle analysis of a farm-scale anaerobic digestion plant in Iowa," Waste Management, vol. 89, pp. 154-164, 2019.
[38] RainBird. "High Density Polyethylene Pipe Reference Table." (accessed.
[39] NREL. "Algae Production via Open Pond Cultivation: NREL Algae Farm Model (Excel TEA Tool)." https://www.nrel.gov/extranet/biorefinery/aspen-models/ (accessed.
[40] COA, "民國108年 臺灣主要畜禽產品生產費用與收益分析," 2019.
[41] Taipower, "台灣電力公司電價表," 2022.
[42] "農業統計年報," 2019.
[43] F. Molist. "7 Strategies to reduce feed costs." https://www.pigprogress.net/health-nutrition/7-strategies-to-reduce-feed-costs/ (accessed.
[44] D. Humbird et al., "Process design and economics for biochemical conversion of lignocellulosic biomass to ethanol: dilute-acid pretreatment and enzymatic hydrolysis of corn stover," National Renewable Energy Lab.(NREL), Golden, CO (United States), 2011.
[45] U. S. B. o. L. Statistics. "Labor Indicies Series ID CEU3232500008." https://data.bls.gov/cgi-bin/srgate (accessed.
[46] (2022). 附表二　111 年度再生能源（太陽光電除外）發電設備電能躉購.
[47] L. Jurgutis, A. Šlepetienė, J. Šlepetys, and J. Cesevičienė, "Towards a full circular economy in biogas plants: Sustainable management of digestate for growing biomass feedstocks and use as biofertilizer," Energies, vol. 14, no. 14, p. 4272, 2021.
[48] C. M. Beal, I. Archibald, M. E. Huntley, C. H. Greene, and Z. I. Johnson, "Integrating algae with bioenergy carbon capture and storage (ABECCS) increases sustainability," Earth's Future, vol. 6, no. 3, pp. 524-542, 2018.
[49] Carboncredits.com. "Live Carbon Prices Today." https://carboncredits.com/carbon-prices-today/ (accessed.
[50] UNDP. "What are carbon markets and why are they important?" https://climatepromise.undp.org/news-and-stories/what-are-carbon-markets-and-why-are-they-important (accessed.
[51] J. Fernando. "Discounted Cash Flow (DCF) Explained With Formula and Examples." https://www.investopedia.com/terms/d/dcf.asp (accessed.
[52] A. C. Dimian, C. S. Bildea, and A. A. Kiss, "Economic evaluation of projects," in Computer aided chemical engineering, vol. 35: Elsevier, 2014, pp. 717-755.
[53] COA, "養豬頭數調查報告 中華民國108 年11 月底," 2019.
[54] (2014). Develop Anaerobic Digestion/Combined Heat & Power.
[55] R. L. Pastor, M. Pinna-Hernández, and F. A. Fernández, "Technical and economic viability of using solar thermal energy for microalgae drying," Energy Reports, vol. 10, pp. 989-1003, 2023.
[56] J. Fernando. "Net Present Value (NPV): What It Means and Steps to Calculate It." Investopia. https://www.investopedia.com/terms/n/npv.asp (accessed.
[57] D. S. t. a. P. Sustainabilit, SimaPro database manual. 2022.