Caracterização e potencial energético do bio-óleo pirolítico oriundo de lodo de estação de tratamento de esgoto da Paraíba

Abstract

Biofuels are one of the most promising alternatives to fossil fuels and play a significant role in the global energy scenario. The main characteristics of alternative fuels are that they are sustainable, cost-effective, efficient and less harmful to the environment than conventional fossil fuels. Among the waste that is difficult to dispose of is sewage sludge. Most of the contaminants found in the effluent from sewage treatment plants (STPs) are concentrated in the sludge, which must be disposed of safely and reasonably. Sludge contains harmful and toxic substances, so inadequate treatment poses a serious threat to the environment. In this sense, pyrolysis stands out as an efficient sanitization process, as well as being able to transform organic sewage sludge into valuable bioproducts that are simple to store, transport and use. Bio-oil is the most common by-product of high-temperature pyrolysis, which can be used as a fuel or converted into a chemical product. The study used the ProKnoW-C methodology and the VOSviewer tool to analyze the research topic, revealing an increase in publications over the years, with a final portfolio of 52 articles. The bibliometric analysis highlighted pyrolysis, sewage sludge and bio-oil as the main focuses, with China leading the publications and Brazil absent, indicating a gap in national research. The systemic analysis showed that bio-oil production faces challenges such as the management of toxic emissions and the complexity of the process, but brings benefits such as waste reduction and the production of usable fuel. The experimental stage involved the characterization of pyrolytic bio-oils from wastewater treatment plant sludge from the cities of Campina Grande and João Pessoa, called LCG and LJP, respectively. The bio-oil samples resulting from the Campina Grande and João Pessoa sludge, BOCG and BOJP, respectively, had an average calorific value of 39,675.33 J/g for BOCG and 40,841 J/g for BOJP, showing increases of 325% and 365%, respectively, in relation to the original sewage sludge samples. The samples had an alkaline pH, which can reduce corrosion in fuel systems, and densities of 838 kg/m³ (BOCG) and 842 kg/m³ (BOJP), comparable to light oils. The corrected API grade was 36.37° for BOCG and 35.57° for BOJP, classifying them as light fuels, valued on the market. FTIR analysis showed hydroxyl groups, aliphatic compounds and aromatic rings, making the biooil suitable for biofuels or renewable chemical products. Thermogravimetry showed similar thermal behavior between the samples, with a mass loss of 95%. The activation energy increased with conversion, indicating more complex reactions, crucial for optimizing processes such as bio-oil distillation. The results show sewage sludge pyrolytic bio-oil as a sustainable alternative to fossil fuels, with high energy potential and thermal stability. The BOJP sample reached 42,349 J/g, similar to non-renewable diesel, suggesting energy competitiveness with fossil fuels. Thus, this study contributes to the objectives of sustainable development and environmental, social and governance criteria, promoting sustainable practices and benefiting the environment and society, offering guidelines for public policies.