| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 107 === The pig manure generated from intensive pig farming is known to have significant impacts on the environment. The nitrogen and phosphorus compounds in the piggery wastewater contaminate the soil and bodies of water. However, these nutrients can also become a good source to cultivate microalgae. The present work aimed to evaluate the environmental impact of microalgae-based pig production system using high-rate algal pond (HRAP) through mass balances, energy balances and life cycle assessment. The system involved simultaneous treatment of piggery wastewater using microalgae, co-anaerobic digestion of pig manure and microalgal biomass, biogas cogeneration, and substitution of pig feed. The organic residues after the anaerobic digestion could be applied as fertilizers to farmland and replace mineral fertilizers. The environmental performances of four scenarios including (1) conventional application; (2) anaerobic digestion (AD) only; (3) AD and HRAP; and (4) co-AD and HRAP were compared. As shown in the results, pig feed production contributed to the most environmental impact in all scenarios. For the overall system, the ReCiPe midpoint indicators of proposed systems (scenario 3 and 4) decreased in most of the categories and ReCiPe endpoint indicators were also saved by 40%, and 29% respectively compared to scenario 1. Although scenario 2 generated the most net energy, the nutrient footprint revealed that proposed systems significantly improved the nutrient recovery.
Additionally, the sensitivity analysis was implemented in three aspects: feedstuff, anaerobic digestion, and HRAP for proposed systems. The results indicated that the feed conversion rate was the main factor in improving environmental performance. In summary, combining microalgae-based wastewater treatment into pig farming system has advantages of net energy production, better nutrient recovery and better performance concerning environmental impacts.
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