Properties of alginate-like exopolymers recovered from flocculent and granular microbial sludges of different biological treatment systems treating real municipal wastewater

Treatment of excess microbial sludge and its safe disposal is a major challenge in wastewater treatment plants (WWTPs) due to pathogens, economic and regulatory issues. There is a considerable interest in developing newer technologies for the excess sludge treatment and recovering value-added products. This study investigated re-covery of biopolymers from the microbial sludge generated in three different biological treatment systems such as conventional activated sludge process (ASP), activated sludge sequencing batch reactor (AS-SBR) and aerobic granular sludge SBR (AGS-SBR). Alginate-like exopolymer (ALE) was the dominant biopolymer in AS and AGS irrespective of the employed treatment system. ALE content was determined to be 32%, 39% and 44% in the microbial sludge of ASP, AS-SBR and AGS-SBR, respectively. ALE extraction markedly decreased the biosolids content by up to 54%. ALE recovered from AS harvested from ASP had poor gelation properties and did not form beads with calcium. Whereas, the ALE recovered from AS and AGS from the SBRs exhibited gelation properties and formed nice beads with calcium ions. The biopolymer recovered from the microbial sludge developed in the SBRs contained high guluronic (G) acid in the form of poly-guluronic acid (GG) blocks, responsible for excellent gelation property. Extraction of biopolymers mitigates sludge management challenges, pathogens-spread and improves resource recovery in WWTPs.

Automated summary

Treatment and safe disposal of excess microbial sludge in wastewater treatment plants is challenging due to pathogens, economic and regulatory issues. This study explored the recovery of biopolymers from different biological treatment systems and found that alginate-like exopolymer (ALE) was the dominant biopolymer in all systems. ALE extraction significantly reduced biosolids content and mitigated sludge management challenges, pathogen spread, and improved resource recovery in wastewater treatment plants.