Recovery of extracellular biopolymers from conventional activated sludge: Potential, characteristics and limitation

•Biopolymers/ALE extraction from CAS ranged from 90 to 190 mg/g VSS.•Good performances of ALE from CAS mean a potential application as commercial alginates.•Compositional content and property of ALE from CAS were dependent.•Influent substrate and nutrient content affected the ALE formation.•Microbia...

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Published in:Water research (Oxford) 2021-10, Vol.205, p.117706-117706, Article 117706
Main Authors: Li, Ji, Hao, Xiaodi, Gan, Wei, van Loosdrecht, Mark C.M., Wu, Yuanyuan
Format: Article
Language:English
Subjects:
Alginate like extracellular polymers (ALE)
Conventional activated sludge (CAS)
Extracellular biopolymers
Extraction
Gel-forming capacity
Microbial community
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Summary:•Biopolymers/ALE extraction from CAS ranged from 90 to 190 mg/g VSS.•Good performances of ALE from CAS mean a potential application as commercial alginates.•Compositional content and property of ALE from CAS were dependent.•Influent substrate and nutrient content affected the ALE formation.•Microbial community was a decisive factor affecting the ALE formation. Extracellular polymeric substances (EPS) are biopolymers that can be recovered from excess sludge, which could contribute to a more sustainable wastewater treatment plant (WWTP) operation. An example is alginate like extracellular polymers (ALE) contained in the biopolymers could be a potential resource with a highly-added value. EPS extraction for ALE from aerobic granules sludge (AGS) has already been well studied and applied in the Netherlands. On the other hand, there is little attention to the recovery of biopolymers from conventional activated sludge (CAS). In this study, flocculent sludge from eight CAS-WWTPs in China was collected and their EPS/biopolymers were extracted to investigate their recovery potential, chemical & physical properties and limiting factors. The results revealed that the biopolymers extracted and purified from CAS ranged from 90 to 190 mg/g VSS. The compositional characteristics of the biopolymers were observed by FT-IR, 3D-EEM and UV-Visible spectra, demonstrating some differences in the composition and property of the biopolymers from the different WWTPs. The biopolymers had a similarity of about 60% to a commercial alginate with respect to chemical functional groups and the alginate equivalent was >400 mg/g biopolymers. Moreover, the biopolymers consisted of poly (guluronic acid) blocks (20%-30%) and poly (guluronic acid-mannuronic acid) blocks (8%-28%), and the ionic hydrogel formation tests indicated that condensed beads were immediately formed once the drops of the biopolymers came in contact with CaCl2 solution. These results demonstrated that the biopolymers extracted had a relatively high gel-forming capacity and might also have a potential application as commercial biopolymers. Furthermore, the factors influencing the biopolymers’ formation such as influent substrate, nutrient content and microbial community and the related mechanisms were investigated. Among them, increasing soluble organics (SCOD) content and low nutrient content (C/N/P) in the influent could promote the biopolymers’ formation. Also, different bacteria in BNR processes might have positive or
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2021.117706