Sustainable Solid Biofuel Production: Transforming Sewage Sludge and Pinus sp. Sawdust into Resources for the Circular Economy

The lack of adequate sanitation in Brazil overloads the health system and causes deaths. The utilization of sewage sludge hinders advancements in water treatment. This study aimed to assess the feasibility of producing briquettes by blending sewage sludge with Pinus sp. sawdust. The sewage sludge was sourced from a water treatment facility, while the Pinus sp. sawdust was obtained from a sawmill. Elemental analysis, proximate analysis, and calorific value were evaluated for both biomasses. Briquettes were manufactured using a hydraulic press, varying the proportion of sewage sludge from 0% to 95%, followed by thermogravimetric analysis. Pinus sp. sawdust exhibited higher carbon, oxygen, and hydrogen content, whereas sewage sludge contained more nitrogen and sulfur. The sawdust had greater fixed carbon content, volatile matter, and calorific value, while the sewage sludge had higher ash content. Samples with higher sewage sludge content showed better thermal resistance, with 100% sewage sludge retaining 63.3% mass after exposure to 950 °C. Briquettes with higher sewage sludge content had increased energy density. Considering the elevated nitrogen, sulfur, and ash content, sewage sludge should be limited to 5% in briquette production with Pinus sp. sawdust. This research underscores a significant avenue for sewage sludge utilization and sustainable bioenergy production.