This thesis aimed to evaluate methane production in batch reactors and a laboratory-scale hybrid UASB reactor during physically pretreated slaughterhouse wastewater treatment. Therefore, the experiment was carried out in three stages:In the first stage, the slaughterhouse wastewater (SWW) underwent a thermal pretreatment (120 °C, 1 atm, 60 min), in which two phases appeared, a liquid (pretreated water) and a semisolid (T). The semisolid went through a mechanical pretreatment (TM), which consisted of homogenization at 30,000 rpm for 1 minute, reducing the particle size from 118.17 to 68.79 μm and increasing the specific surface area from 0.412 to 0.966 m 2 /g. Both semisolids (T and TM) and SWW were the substrates in biochemical methane potential (BMP) tests, evaluating five different substrate/inoculum (S/I) ratios (1:1, 2:1, 3:1, 4:1, and 5:1). The results showed that both semisolids produced up to fourteen times more methane than SWW; also, the cumulative methane production curves had a stepped form, while with the SWW, they were sigmoidal. Moreover, the highest methane production occurred with the 4:1 S/I ratio; however, in the second experimental stage, the 3:1 S/I ratio was employed to avoid the risk of acidification.