Maximising bio-oil yield from industrial dairy sludge: a paradigm on pyrolysis temperature and heating rate in the context of the EU FLEXBY project

The dairy industry produces significant quantities of sludge, which is characterised by its high organic content. If these by-products are not recovered, they are classified as wastes and therefore have to be managed as such, which entails a number of environmental and economic disadvantages. The physical and chemical characteristics of biological sludge generated in wastewater treatment processes depend on the type of wastewater treated and the treatment processes employed.

As the world increasingly transitions away from fossil fuels, recycling different industrial residues into biofuels is emerging as an environmentally and economically sustainable strategy. Pyrolysis, defined as the process of thermal decomposition of a substance in the absence of oxygen, has been extensively studied for the purpose of converting residue into biofuels, with conventional pyrolysis being the most widely used method. Several experimental variables, such as pyrolysis temperature or heating rate, play a crucial role in determining the yield and quality of the final biofuel products (Kaur et al. 2015). Lower temperatures tend to favor the production of biochar, while higher temperatures enhance the yield of liquid bio-oil and gas (Vilas-Boas et al. 2021). Slow pyrolysis is the most effective technology for high-yield biochar production, while fast pyrolysis provides higher bio-oil yields, and intermediate pyrolysis produces a balanced distribution of biochar, bio-oil and gas (S. Safarian, 2023). The conversion of dairy sludge into biofuels through pyrolysis processes offers a comprehensive value proposition for the management of such waste, while reducing dependence on fossil fuels and promoting sustainable energy practices.

The aim of this study is to assess the feasibility of using sludge from the dairy industry to produce biofuels or biomaterials through