Enhanced Methane Recovery from Waste-Activated Sludge by Alginate-Degrading Consortia: The Overlooked Role of Alginate in Extracellular Polymeric Substances

The hydrolysis of extracellular polymeric substances (EPS) in waste-activated sludge (WAS) is considered as the rate-limiting step in anaerobic digestion. Uronic acids such as alginate are one of main polysaccharide components in EPS; however, their roles on WAS conversion are overlooked until now. Previously, we described alginate-degrading consortia (ADC) that have high activity for alginate conversion. In this work, ADC was studied for polysaccharide hydrolysis and methane production from WAS for the first time, which increased the methane production by 115%–185%. Dosing ADC also increased the values of biological methane potential from 131 to 172 mL/gVSS. An alginate-like exopolysaccharide was extracted from WAS, and the content was 65 mg/g-VSS. Then, the molecular weight profiles at UV254nm showed that disaccharides were the final hydrolysates of alginate by ADC enzyme. Extracted EPS could be utilized by ADC for methane production with acetate as the main intermediate. The mechanism was proposed that ADC played a key role in WAS conversion. These results indicated that alginate in EPS shall not be overlooked, which offers a new microbial method to enhance methane recovery from WAS. The microbial changes in ADC for the stability of WAS digestion should be investigated in the future.