Transforming Livestock and Aquaculture Waste into Renewable Energy and Materials—A Review

In recent years, concerns about sustainability in livestock farming have been raised. The livestock sector is accused of substantial greenhouse gas emissions, environmental pollution (i.e., wastewater with high COD and rich in N and P that can pollute freshwater and cause eutrophication), and resource consumption. The use of fossil resources to produce synthetic fertilizers is the major source of pollution indirectly attributable to livestock farming. However, the polluting load of the livestock sector can be used to produce energy and materials, increasing its sustainability. The scope of this work was to critically review the methods of management and valorization of waste from the livestock sector (slurry, manure, abattoir wastewater, slaughterhouse waste, and aquaculture waste). The various technologies for energy valorization (i.e., bio-H2 and bio-CH4) will be represented. The perspectives and challenges for the exploitation of these wastes to produce high-added-value molecules, extraction of bioactive molecules, alternative proteins, biofertilizers, and biopolymers will also be discussed in view of enhancing sustainability. Examples of possible large animal waste-based integrated biorefineries have also been proposed.