Enhancing xanthan biosynthesis in aerobic granular sludge for resource recovery: The role of organic loading rate, carbon-to-nitrogen ratio, and feeding strategy

Recovering high-value biopolymers from wastewater offers a sustainable strategy for both pollution control and resource generation. This study is the first to examine xanthan biosynthesis and recovery in aerobic granular sludge (AGS) wastewater treatment systems, providing an alternative to conventional carbohydrate-rich fermentation, which is energy-intensive, feedstock-dependent, and costly. Valorizing xanthan from wastewater supports circular economy principles and integrated water–resource management. The effects of organic loading rate (OLR), carbon-to-nitrogen ratio (C/N), and feeding strategy on xanthan yield were assessed in nine experimental runs treating synthetic wastewater. AGS performance remained stable under all conditions, with excellent settling (5-min sludge volume index < 40 mL/g) and high COD removal (95 ± 5%). Ammonia-nitrogen and phosphorus removals averaged 73 ± 23%, and 72 ± 18%, respectively. Maximum xanthan yields occurred at OLR = 2.1 kg COD/m³∙d and C/N = 10 (41 ± 7 mg/g biomass, run 3) and at OLR = 2.1 kg COD/m³∙d and C/N = 20 (35 ± 10 mg/g biomass, run 1). Pearson correlation analysis showed a strong positive relationship between OLR and xanthan yield (r = 0.831, p = 0.006), and a moderate, non-significant negative correlation with C/N (r = –0.512, p = 0.158). Feeding strategy showed minimal influence (r = 0.042, p = 0.915). Fourier transform infrared and proton nuclear magnetic resonance spectroscopies confirmed structural similarity between recovered and commercial xanthan gum. These results demonstrate that AGS can be engineered to recover xanthan while maintaining high treatment performance, advancing sustainable wastewater management, biopolymer production, and circular economy objectives. • Xanthan was recovered from the aerobic granular sludge wastewater treatment system • OLR of 2.1 kg COD/m³∙d favored xanthan yield resulting in 41±7 mg xanthan/g biomass • Strong positive correlation (r = 0.831) between OLR and xanthan yield (p = 0.006) • Optimal conditions for xanthan biosynthesis: 2.1 kg COD/m³∙d and C/N ratio of 10