Thermal characterization of granular sludges from biologic treatments and its application to the generation of biogas S. Almeida 1 • E. F. Horta 2,3 • M. C. A. A. Castro 2,4 • M. S. Crespi 1 • S. I. Maintinguer 3,4 Received: 12 September 2018 / Accepted: 28 July 2019 Ó Akade ´miai Kiado ´, Budapest, Hungary 2019 Abstract The application of granular sludge from biological treatment plants can become an economically and environmentally viable process as a renewable source of energy. It is available in most countries, and its application can diversify the local energy potential. However, in order to achieve such benefits and make possible the development of more efficient conversion processes, prior knowledge of the composition of these materials is essential. In this sense, samples of granular sludge were obtained from upflow anaerobic sludge blanket reactors for the treatment of: (1) poultry slaughterhouse waste (Tiete ˆ—SP); (2) poultry slaughterhouse waste (Pereiras—SP); (3) wastewater treatment plant (Sa ˜o Carlos—SP) and (4) a mix of sludges 1, 2 and 3. Biogas generation tests in anaerobic batch reactors fed with sodium acetate and glucose separately as carbon sources were performed with samples 1, 2, 3 and 4, at initial pH 7.0 and 30 °C. Characteristic decomposition profiles were observed in the granular sludge tested. The two poultry slaughterhouse waste (samples 1 and 2) presented higher proportions of organic substrate molecules for the methanogenesis than the sanitary sewage sludge (sample 3), thus facilitating the production of the highest biogas, as verified in the tests carried out. The thermal characterization of the samples was relevant to the methane generation tests demonstrating the potential for the generation of this fuel. Keywords Biogas Á Methane Á Organic matter Á Thermal stability Á Granular sludge Introduction The world energy matrix is made up of about 80% of non- renewable sources, such as oil and coal, and this scenario has contributed to environmental degradation and global climate [1]. The use of biogas from anaerobic biological processes can be a sustainable alternative in the use of renewable energies. Methane is the main gas that causes the greenhouse effect, and it is generated in biological waste treatment plants by anaerobic processes [2–4]. However, the biogas can be recovered energetically to the vehicular and resi- dential uses and commercial installations [5]. A potential biofuel with an energy capacity of 50.0 kJ g -1 is consid- ered, whose energy capacity is higher than that of the fuels used in the supply of automotive vehicles such as gasoline and ethanol, which release 48 kJ g -1 and 27 kJ g -1 , respectively [4, 6, 7]. In addition, the calorific value of methane is 5000 to 7000 kcal m -3 and 1 m 3 of this biogas is equivalent to: 0.61 L of gasoline; 0.58 L of kerosene; 0.45 L of cooking gas or 1.5 kg of firewood [8]. In addi- tion, a biogas with 70% of methane can contain 23,380 kJ/ m 3 ; these values are about 70% of the capacity of natural gas (composed of methane, butane and propane), which has 37,300 kJ m -3 [9]. The major motivation for methane production is the possibility of employing a wide variety of organic wastes as substrate source. Besides it is abundant, granular sludge from UASB (upflow anaerobic sludge blanket) reactor, & S. Almeida avopsalmeida42@gmail.com 1 Department of Analytical Chemistry, Institute of Chemistry, Sa ˜o Paulo State University, Av. Prof. Francisco Degni, 55, Jardim Quitandinha, Araraquara, SP 14800.900, Brazil 2 Geosciences and Exact Sciences, Sa ˜o Paulo State University, Araraquara, Brazil 3 Research Institute for Bioenergy, Sa ˜o Paulo State University, Araraquara, Brazil 4 Uniara - University of Araraquara, Araraquara, SP, Brazil 123 Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-019-08654-2