Sewage sludge treatment is gaining more importance worldwide because humanity is currently facing the highest levels of urbanism in its history. Processing by anaerobic fermentation is considered the most effective method of its treatment. The ratios of C to other nutrients (especially N and P) are established as a key part process management. The deployment of hydrothermal pretreatment (also known as steam-explosion) is increasingly becoming popular because it accelerates the subsequent fermentation process and thereby enables savings in reactors' volume. However, experiments in the pilot plant that was equipped with the above-mentioned units indicate that the established C analytical methods cannot fully respect the changes in nutrients bioavailability that are being caused by the pretreatment. A new, simple, and cheap method that better respects the bioavailability of the C pool is presented. Process optimization using the new methods has outperformed the traditional techniques from both the technological and economical points of view.