Sludge liquefaction and stratification

The energy, nitrogen/N and phosphorus/P resources in wastewater treatment plants (WWTPs) as resource factories are concentrated in waste activated sludge (WAS), which can be recovered through sludge anaerobic digestion (AD). Nonetheless, low organic loading rate and N/P recovery (<10%) represent the long-standing challenges for traditional sludge AD. Here, based on a new finding of sludge liquefaction and stratification, a novel process entitled SPREAD was developed to enhance the organic loading rate for 10 times and recover 46.3% N and 58.3% P resources from WAS in forms of crude protein and struvite. A new anaerobic digestion database (ADDB) was devised to support meta-omics analyses of methanogenic digestion microbiomes, pinpointing the mechanism underlying the ultrahigh organic loading rate and exhaustive N/P recovery in SPREAD. Interestingly, we observed a negative correlation between the Gibbs free energy (?G) and the relative abundance of methanogens, enabling assessment of bottleneck steps for biostimulation and bioaugmentation of methanogenic digestion microbiomes. This study open a new avenue for sustainable management of WWTPs, and advance our understanding of methanogenic digestion microbiomes.