Environmental life cycle comparisons of pig farming integrated with anaerobic digestion and algae-based wastewater treatment

This article shows environmental life cycle comparisons of four scenarios of manure management systems (MMS) for the intensive pig farming systems in terms of materials, transport, energy, and emissions. The MMS scenarios are categorized by different combinations of outside storage, anaerobic mono-/co-digester, and algae-based wastewater treatment (AWWT), where the conventional MMS scenario merely uses the outside storage (Scenario 1) or adopts an integrated anaerobic mono-digester and the outside storage (Scenario 2). The nonconventional MMS scenario uses an integrated anaerobic mono-digester and AWWT process (Scenario 3), notably the harvested algae biomass is used to fully substitute a few ingredients of swine diets. Using life cycle assessment (LCA) methodology, it is validated that Scenario 3 reduces the total environmental impact by 35.5%–40% as compared to Scenarios 1 and 2 and increases the nutrient recovery of nitrogen ratio from 58% (Scenario 1) to 81%. Scenario 4 uses an integrated anaerobic co-digester and AWWT process, where the harvested algae biomass is partially recycled to substitute the partial ingredients of swine diets and the remaining part is fed into the anaerobic co-digester for improving the biogas yield, to increase the algae biomass yield by 49% and also enhance the cogeneration of heat and power by 26.6% and 7%, respectively, as compared to Scenario 3.