Identification and degradation of structural extracellular polymeric substances in waste activated sludge via a polygalacturonate-degrading consortium

By maintaining the cell integrity of waste activated sludge (WAS), structural extracellular polymeric substances (St-EPS) resist WAS anaerobic fermentation. This study investigates the occurrence of polygalacturonate in WAS St-EPS by combining chemical and metagenomic analyses that identify ∼22% of the bacteria, including Ferruginibacter and Zoogloea, that are associated with polygalacturonate production using the key enzyme EC 5.1.3.6. A highly active polygalacturonate-degrading consortium (GDC) was enriched and the potential of this GDC for degrading St-EPS and promoting methane production from WAS was investigated. The percentage of St-EPS degradation increased from 47.6% to 85.2% after inoculation with the GDC. Methane production was also increased by up to 2.3 times over a control group, with WAS destruction increasing from 11.5% to 28.4%. Zeta potential and rheological behavior confirmed the positive effect which GDC has on WAS fermentation. The major genus in the GDC was identified as Clostridium (17.1%). Extracellular pectate lyases (EC 4.2.2.2 and 4.2.2.9), excluding polygalacturonase (EC 3.2.1.15), were observed in the metagenome of the GDC and most likely play a core role in St-EPS hydrolysis. Dosing with GDC provides a good biological method for St-EPS degradation and thereby enhances the conversion of WAS to methane.