Insights into the Anaerobic Hydrolysis Process for Extracting Embedded EPS and Metals from Activated Sludge

Area of Science:

• Environmental Microbiology
• Biotechnology
• Waste Management

Background:

• Global increase in sewage sludge generation necessitates advanced treatment and valorization strategies.
• The biorefinery concept offers a sustainable approach to convert waste streams into valuable products using microbial processes.
• Controlling microbial pathways in anaerobic environments remains a significant challenge for effective waste-to-value conversion.

Purpose of the Study:

• To investigate the impact of high organic loading rate and short hydraulic retention time (HRT) on extracellular polymeric substance (EPS) and metal solubilisation in waste activated sludge.
• To understand the microbial community dynamics under these specific anaerobic fermentation conditions.
• To assess the potential for enhanced metal removal from sewage sludge.

Main Methods:

• Two anaerobic fermentation tests were conducted using real waste activated sludge.
• High organic loading rate (10 g COD L⁻¹d⁻¹) and short HRT were applied.
• Analysis of EPS quantity, chemical oxygen demand (COD) to EPS ratio, and solubilised metals (As, Be, Cu, Ni, V, Zn).
• Microbial community analysis using 16S rRNA sequencing to identify dominant phyla.

Main Results:

• EPS recovery increased over time, with a consistent COD to EPS ratio (1.31-1.45).
• Slightly acidic conditions and sludge floc disintegration facilitated EPS matrix disruption and release.
• Significant solubilisation of organically bound toxic metals (As, Be, Cu, Ni, V, Zn) was observed.
• Dominant microbial phyla identified were Bacteroidetes, Firmicutes, and Chloroflexi, indicating enhanced hydrolytic and acidogenic activity.

Conclusions:

• Short HRT and high organic loading promote EPS solubilisation and disruption in anaerobic sludge fermentation.
• This process enhances the removal of toxic metals from sewage sludge, contributing to biorefinery goals.
• The observed microbial community structure supports the increased hydrolytic and acidogenic activity under short HRT conditions.