Investigation on Temperature Phased Anaerobic Digestion (TPAD) of Dairy Industrial Fat-Rich Sludge

In the present investigation, a Temperature-Phased Anaerobic Digestion (TPAD) system was evaluated for treating dairy industry fat-rich waste sludge. Results showed that both biogas yield and methane content were higher than those obtained from a conventional anaerobic digester. The configuration of two reactors in series, with the thermophilic unit as the initial stage, succeeded by the mesophilic unit, was optimized for both thermophilic and mesophilic conditions. The second mesophilic stage finalizes the digestion process, transforming partially digested organics into methane and carbon dioxide, so totally recovering the energy by-product from dairy waste sludge. The pH value in the TPAD varied from 6.91 to 7.51. The maximum volatile solids (VS) removal efficiency of 39.6% achieved in the TPAD system as the thermophilic operation time was maintained initially for 10 days during the start-up of the batch TPAD experiment. The methane production increased from 220 to 435 ml of CH₄ g^-1 of VS, and the methane content varied from 51.9% to 62.4%. This value exceeded the yields attained by the conventional anaerobic digester at solids retention time (SRT) of 35 days obtained as 357 ml of CH₄ g^-1 of VS with 58.1% methane content. Using the TPAD technique, anaerobic digestion of dairy industrial waste sludge effectively recovered the energy as methane. As a result, in comparison to traditional anaerobic systems, the TPAD system allowed higher methane outputs and superior operational performance.