Development and application of an automatic feeding control to manage anaerobic co-digestion of winery wastes

This paper deals with the optimization of anaerobic digestion of winery wastes considering the behavior of biogas production rate between two consecutive reactor feeds. Processes operating at different hydraulic retention times (23 and 40 d) were monitored and the specific biogas productions were comparable (0.386 and 0.378 m3/kgCODfed for retention time of 23 and 40 d, respectively). The biogas production rate reduced after 11–14 h in both the processes, this time corresponds to the necessary period to consume readily biodegradable and easily hydrolysable COD. In order to maximize biogas production, a system able to increase feeding frequency was set-up. The system activated the feeding pump when a reduction of biogas production rate (below 0.4 m3biogas/(m3reactord)) was detected. Consequently, hydraulic retention time decreased to 21 d and organic loading rate reached 6.2 kg COD/(m3reactord). Moreover, these conditions favored the growth of microorganism involved into degradation of soluble COD fraction and faster kinetics were observed in this conditions. Finally, two kinetic models (first order and step-diffusional) were applied to manually and automatically fed processes, in order to understand how the retention time and automatic control affected the degradation rate of the different types of compounds and to confirm the results obtained from the preliminary kinetic study. Step-diffusional model better predicted the trend of degradation rates (R2 0.97–1.00) because it considered three groups of compounds and the same number of parameters.