Modelling the rheological properties of sludge during anaerobic digestion in a batch reactor by using electrical measurements

• Sludge anaerobic digestion was performed in a batch reactor.
• Electrical and rheological properties were measured.
• Digested sludge electrical signature is modelled based on inputs properties.
• Using electrical model parameters, sludge apparent viscosity is predicted.
• Hypotheses are made to relate the model parameters and anaerobic digestion phases.

Anaerobic digestion is a significant process leading to biogas production and waste management. Despite this double interest, professionals still face a lack of efficient tools to monitor and manage the whole procedure. This is especially true for rheological properties of the material inside the reactor, which are of major importance for anaerobic digestion management. However, rheological properties can hardly be determined in-situ and it would be very helpful to determine indicators of their evolution. To solve this problem, this paper investigates the evolution of sewage sludge rheological and electrical properties during the anaerobic digestion in a batch reactor. We especially focus on apparent viscosity and complex impedance, measured by electrical impedance spectroscopy. Both of them can be modelled by a linear combination of raw sludge and inoculum properties, weighted by time-dependent coefficients. Thus, by determining digested sludge electrical signature, it is possible to obtain those coefficients and model sludge apparent viscosity. This work offers many theoretical and practical prospects.