Nitrogen-rich biomass can be suitable for utilization as a substrate in anaerobic co-digestion (AC-D) instead of animal manure. This biomass combined with other substrates could replace animal waste in certain cases in which animal waste cannot be used to obtain methane gas. Methane is the majority component of the biogas produced in AC-D used as an energy source. In this research, a comparative study has been developed between leguminous plant biomass and pig manure in AC-D in a semicontinuous regime at different Organic Load Rate (OLR) values (1.2–1.8 g VS LD−1 d−1). The most elevated methane yield (494 NL CH4 kg VS−1) belongs to assays developed with nitrogen-rich biomass at 1.4 g VS LD−1 d−1. Methane-yield results of nitrogen-rich biomass are higher than pig manure results for all OLR studied values. The digestate obtained in the AC-D is a fertilizer of interest due to its nitrogen content and ability to save energy by replacing mineral fertilizers.

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The circular economy is based on using waste generated from any process to obtain products with zero residues' criteria. This research was focused on pepper waste from the polyphenolic extraction method. Pepper waste was evaluated in batch and semi-continuous regime anaerobic digestion, adding, as catalysts, absorbent nanoparticles and/or using pretreatment strategies. The best methane yields were obtained from SB1 (assay without pretreatment in pepper waste): 464 ± 25 NL kg VS−1 for batch assays; and from period II (1.47 g VS L−1 d−1) of S2 (assay of pig manure and pepper waste with thermal pretreatment): 160 NL/kg VS−1 for semi-continuous experiments. However, a kinetic study showed a methane production rate higher for SB2 (assay with nanoparticles as catalyst) than SB1 in batch assays.