Accelerated aerobic granulation using alternating feed loadings: alginate-like exopolysaccharides

Area of Science:

• Environmental microbiology
• Biotechnology
• Wastewater treatment

Background:

• Aerobic granules are crucial for efficient wastewater treatment.
• Alginate-like exopolysaccharides (ALE) are known to contribute to aerobic granule strength.
• The specific mechanisms driving ALE production and its role in granulation require further elucidation.

Purpose of the Study:

• To investigate the role of organic loading rates (OLRs) in aerobic granule formation.
• To determine the relationship between OLR, microbial activity, and ALE production.
• To understand the precursor materials involved in accelerated aerobic granulation.

Main Methods:

• Cultivation of aerobic granules using propionate wastewater at varying OLRs (4.4–17.4 kg/m³-d).
• Analysis of microbial community shifts and extracellular polymeric substance (EPS) production under different OLR conditions.
• Monitoring of cyclic diguanylate (c-di-GMP) and ALE production in response to sudden OLR changes.

Main Results:

• Sudden increases in OLR triggered microbial secretion of cyclic diguanylate (c-di-GMP).
• Elevated c-di-GMP led to excess ALE production, forming sticky precursors for aerobic granules.
• Accelerated granulation was directly linked to the formation of excess ALE, not poly guluronic acid enrichment.

Conclusions:

• ALE production, stimulated by c-di-GMP under high OLRs, is essential for rapid aerobic granulation.
• Microbial response to fluctuating OLRs is a key factor in initiating the granulation process.
• This study highlights ALE as a critical component in the biogenesis of functional aerobic granules for wastewater treatment.