Performances comparison between laboratory and full-scale anaerobic digesters treating a mixture of primary and waste activated sludge

Laboratory-scale semi-continuously digesters were used as test platforms to evaluate a full-scale application of anaerobic co-digestion of primary sludge (PS) and activated sludge (AS) in Tunisia. Effects of the PS:AS ratio and the organic loading rate (OLR) on digester performances were examined at a hydraulic retention time (HRT) of 20 d. Increasing PS proportion in the feedstock significantly improved the biogas production yield. The digester that was fed with a PS:AS ratio of 80:20 showed the highest total volatile solids (TVS) removal efficiency and specific biogas production (SBP) of 72.1% and 0.6 L g−1 TVS added, respectively. However, the digester that was fed with a PS:AS ratio of 20:80 as the full-scale fed stock showed 51% and 0.38 L g−1 TVS added of TVS removal and SBP, respectively. The full-scale digester showed a biogas production rate up to 11,000–12,000 m3 d−1 with a SBP of 0.31 L g−1 TVS added. The comparison between the two scale results demonstrates that lab-scale experiments with real substrates and close to reality digestion conditions can serve to predict the digestion capability of the full-scale digester.