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

Abstract

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 alginatedegrading 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 UV 254nm 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.

Identification of Extracellular Key Enzyme and Intracellular Metabolic Pathway in Alginate-Degrading Consortia via an Integrated Metaproteomic/Metagenomic Analysis

“…Similarly, the m / z value of alginate hydrolysate by using MALDI-TOF-MS was 447.8 (Figure C). These data were similar to that of our recent work (454 Da) . Since the monomer MW is 192 Da, disaccharides shall be the final hydrolysate of alginate, which is analogous to the conversion of cellulose to cellobiose by cellulase .…”

“…degradation pathways can also be identified to produce pyruvate in Figure S11 and lumped in Figure . Since galacturonate and glucuronate are identified in St-EPS, ADC may also utilize these components to produce methane from WAS, which supports the better performance of dosing ADC to promote methane production in our recent work …”

“…By the end of 2019, it is estimated that the production of sludge (80% water content) in China is up to 39 million tons . There is a strong drive to minimize this amount, and anaerobic digestion of WAS is greatly desired. ,, Felz et al recently reported that the contents of neutral sugars and uronic acids in EPS were comparable (10.7 and 13.2%) . Several researchers reported that uronic acids containing polymers in EPS are resistant to anaerobic degradation. , In this work, we demonstrate that Bacteroides -dominated ADC with the trait to excrete alginate lyases (EC 4.2.2.3) can enhance EPS conversion in WAS.…”

“…16 The enriched ADC demonstrates the expected performance of enhancing the methane production from WAS, which could increase the biological methane potential from 131 to 172 mL/gVSS. 17 This value is comparable to that of thermal or mechanical pretreatment technologies for enhancing methane production from WAS. However, the core enzymes and metabolic pathway for alginate conversion in ADC are not well documented, which is mainly due to two reasons: (1) a low percentage of 12 putative bacteria (<0.1%, such as A. lectus and Bacteroides sp.…”

“…Previously, we enriched a freshwater alginate-degrading consortium (ADC) from anaerobic sludge using alginate as the substrate for the first time . The enriched ADC demonstrates the expected performance of enhancing the methane production from WAS, which could increase the biological methane potential from 131 to 172 mL/gVSS . This value is comparable to that of thermal or mechanical pretreatment technologies for enhancing methane production from WAS.…”