The pig manure produced by intensive pig farming is known to have significant impacts on the environment. The nitrogen and phosphorus compounds in the manure contaminate the soil and bodies of water. However, these nutrients can also become a good source to cultivate microalgae. The aim of the present work was to evaluate the environmental impact of microalgae-based pig production systems using high-rate algal ponds (HRAPs) through mass balances, energy balances and life cycle assessment (LCA). 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 from the anaerobic digestion could be applied as organic fertilizers to farmland replacing mineral fertilizers. The environmental performances of four scenarios including (i) conventional application; (ii) anaerobic digestion (AD) only; (iii) AD and HRAPs; and (iv) co-AD and HRAPs were compared. As shown in the results of the analysis, the pig feed production contributed to the most environmental impact in all scenarios. For the overall system in four scenarios, the impact generated by the suggested system (scenario 3) can reduce the CO2e by up to 54% compared to the conventional system (scenario 1). Additionally, the sensitivity analysis of each scenario indicated that substituting pig feed to microalgae became the main factor in improving GHG performance.