Sludge liquefaction and stratification enable ultra-high digestion rate and resource recovery for waste activated sludge treatment

Most of the energy, nitrogen/N and phosphorus/P entering wastewater treatment plants (WWTPs) accumulates in waste activated sludge (WAS). While these resources are theoretically recoverable through anaerobic digestion (AD), conventional sludge AD faces long-standing challenges of low organic loading rate and limited N/P recovery. Here, building on an innovative sludge liquefaction and stratification technique, we present a novel process entitled SPREAD that boasts 10 times higher organic loading rates and recovers 5 folds of N/P resources, relative to conventional sludge AD. We develop an anaerobic digestion database (ADDB) for multi-omics analyses of digestion microbiomes, and pinpoint the mechanism underlying the exceptionally high organic loading rate and remarkable N/P recovery in SPREAD. Importantly, we identify a negative correlation between the Gibbs free energy (ΔG) and the relative abundance of methanogens, enabling identification of bottleneck steps for stimulation and augmentation of methanogenic digestion. Our study provides a game-changing technology for the treatment and resource recovery from WAS and opens a new avenue for sustainable management and carbon/energy-neutrality of WWTPs.