Preliminary Considerations on the Co-Production of Biomethane and Ammonia from Algae and Bacteria

Ammonia is a critical compound for numerous industrial processes; however, the conventional methods for its production present substantial environmental challenges. Co-producing biofuels and ammonia from biomass through anaerobic digestion offers a promising alternative to address these concerns. This study presents a theoretical assessment of the co-production of biomethane and ammonia from microalgae and cyanobacteria, utilising water from abandoned mine and quarry pit-lakes—specifically focusing on the Alessandria district as a case study. The analysis is based on the average values reported in the literature for the anaerobic digestion of selected biomass types. The results highlight Arthrospira platensis, Chlamydomonas reinhardtii, Chlorella spp., and Chlorella pyrenoidosa as the most promising species due to their superior yields of both ammonia and biomethane. This work aims to promote new opportunities for repurposing disused mining pit-lakes, contributing to the development of sustainable pathways for the integrated production of biofuels and ammonia. In this context, exploring integrated biorefinery systems within a bio-based economy represents an auspicious direction for future research, potentially enhancing the process efficiency and reducing costs.