Fractal Analysis of pH Time-Series of an Anaerobic Digester for Cheese Whey Treatment

Cheese whey is a byproduct of the cheese industry and contains high concentrations of organic matter. Anaerobic digestion (AD) technology is an attractive solution to whey disposal since it allows the reduction of organic matter and simultaneously generates energy via biogas. The biological degradation of cheese whey is characterized by an unstable operation. A critical operational issue in the AD treatment of cheese whey is the tendency of rapid acidification of the waste requiring robust monitoring and control systems for reliable and efficient operation. Recent studies show that techniques based on fractal analysis of time series can be used for the indirect monitoring of critical variables of AD process (i.e., COD, VFA and methane production) for agro-industrial wastewaters. In this work, the application of the fractal analysis of pH time series obtained from an up-flow digester for cheese whey treatment is presented. The results suggest that fractal analysis can be applied to the indirect monitoring of a representative and high strength dairy wastewater. Furthermore, although the complex phenomena underlying in pH in the AD of cheese whey, the fractal analysis can unveil correlations of fractal parameters with key process variables.