*Article* **Increasing the Content of Olive Mill Wastewater in Biogas Reactors for a Sustainable Recovery: Methane Productivity and Life Cycle Analyses of the Process**

**Souraya Benalia, Giacomo Falcone, Teodora Stillitano \*, Anna Irene De Luca, Alfio Strano, Giovanni Gulisano, Giuseppe Zimbalatti and Bruno Bernardi**

> Dipartimento di Agraria, Università degli Studi Mediterranea di Reggio Calabria, Località Feo di Vito, 89122 Reggio Calabria, Italy; soraya.benalia@unirc.it (S.B.); giacomo.falcone@unirc.it (G.F.); anna.deluca@unirc.it (A.I.D.L.); astrano@unirc.it (A.S.); ggulisano@unirc.it (G.G.); gzimbalatti@unirc.it (G.Z.); bruno.bernardi@unirc.it (B.B.)

**\*** Correspondence: teodora.stillitano@unirc.it

**Abstract:** Anaerobic codigestion of olive mill wastewater for renewable energy production constitutes a promising process to overcome management and environmental issues due to their conventional disposal. The present study aims at assessing biogas and biomethane production from olive mill wastewater by performing biochemical methane potential tests. Hence, mixtures containing 0% (blank), 20% and 30% olive mill wastewater, in volume, were experimented on under mesophilic conditions. In addition, life cycle assessment and life cycle costing were performed for sustainability analysis. Particularly, life cycle assessment allowed assessing the potential environmental impact resulting from the tested process, while life cycle costing in conjunction with specific economic indicators allowed performing the economic feasibility analysis. The research highlighted reliable outcomes: higher amounts of biogas (80.22 <sup>±</sup> 24.49 NL.kgSV<sup>−</sup>1) and methane (47.68 <sup>±</sup> 17.55 NL.kgSV<sup>−</sup>1) were obtained when implementing a higher amount of olive mill wastewater (30%) (*v*/*v*) in the batch reactors. According to life cycle assessment, the biogas ecoprofile was better when using 20% (*v*/*v*) olive mill wastewater. Similarly, the economic results demonstrated the profitability of the process, with better performances when using 20% (*v*/*v*) olive mill wastewater. These findings confirm the advantages from using farm and food industry by-products for the production of renewable energy as well as organic fertilizers, which could be used in situ to enhance farm sustainability.

**Keywords:** anaerobic codigestion; biomethane; life cycle assessment (LCA); life cycle costing (LCC); olive mill by-products
