The citrus industry produces a considerable amount of solid and liquid waste, which are mostly wasted. Anaerobic digestion of sewage sludge is an attractive option as it can produce fuels in the form of methane gas. However, the presence of complex organic compounds and pathogenic microorganisms significantly hinders the effectiveness of this process. The objective of this work is the selection of a source of inoculum free of pathogenic microorganisms by means of a thermal pretreatment and in this way is conducive to the treatment of residual sludge from the Citrus industry. The inoculum was taken from a geomembrane reactor which uses cattle manure as a substrate. 6 biodegradability kinetics were performed, varying the substrate-inoculum ratio, three of them with inoculum without pretreatment and another three with treatment, all under mesophilic conditions. SV parameters, pH, and biogas production were determined.