Notice of Retraction: Upgrading of anaerobic digestion of thickened waste activated sludge by microwave-assisted alkali pretreatment

Pretreatment of thickened waste activated sludge (TWAS) can facilitate the hydrolysis step of mesophilic anaerobic digestion (MAD) and improves the digestibility. This study examined the effects of microwave/alkali pretreatment on TWAS disintegration and its subsequent batch and semi-continuous MAD. The maximum solubilization ratio of volatile suspended solids, 77%, achieved at 210°C with 0.15 g-NaOH/g-TSS and 10 min holding time. In the biochemical methane potential tests, the vials fed with pretreated TWAS produced 18-46% higher biogas compared to the control. The semi-continuous reacter fed with the pretreated TWAS without neutralization was stable, and the VS reductions and methane yield were 21% and 14% higher than those of the control, respectively.