Effect of disintegration methods on the characteristics of biological sludges and the biogas production in anaerobic digestion

Pretreatment has become popular to enhance digestibility and minimization of the sludge by increasing its solubility. This study investigated the effects of ultrasonic, microwave and alkaline pretreatments on the efficiencies of aerobic and anaerobic sludge digestion processes. The digestion efficiency was measured in terms of sludge minimization, pathogen reduction and biogas production. In the first part of the study, application conditions of pretreatment techniques were determined. In the second part, unpretreated (control) and pretreated sludge samples were digested aerobically at room temperature and anaerobically at 37oC for 30 d. Sludge pretreatments improved the efficiencies of both aerobic and anaerobic digestion processes by increasing the solubility of sludge solids. In aerobic digestion, VS removal efficiencies improved by 23-68%, 24-33%, 28-78% for sludge pretreatment ratios (SPR) of 10%, 20%, and 25%, respectively. In anaerobic digestion, pretreatments led to 18-53% increase in VS removal efficiency and 41-77% increase in methane production efficiency. The highest biogas yield of 0.52 Lbiogas/gVSadded and methane yield of 0.37 LCH4/gVSadded were obtained from microwave pretreated sludge samples. Sludge dewaterability was deteriorated with the application of pretreatments to 10% of the samples (SPR:10%), dewaterability of alkaline and microwave pretreated sludge samples improved when SPR increased to 20% and 25%.