Impact of operating cycle type on alginate-like exopolysaccharide and tryptophan production in aerobic granular sludge systems

Abstract

As wastewater treatment advances, there is a growing need to remove pollutants and recover valuable resources. This study focuses on the optimization of the aerobic granular sludge process, exploring the impact of varying the anaerobic period on the production of bioresources, i.e., on the synthesis of extracellular polymeric substances (EPS), alginate-like exopolysaccharides (ALE — like exopolysaccharides), and tryptophan (TRP). To this end, two sequential batch reactors (SBRs) were used, R1 and R2, fed with acetic and propionic acid, respectively, and subjected to different durations of the anaerobic phase (100, 70, 35, and 0 min) in the total cycle time of 6 h. The results were similar regarding COD, N, and P removal. However, R2 showed greater nitrate accumulation. Statistical analyses highlighted significant variations in SPE concentrations in the different phases (p<0.05) in both systems. ALE production in R1 was highest in the initial phase, decreasing with the reduction of the anaerobic period. However, this trend was not observed in the R2 system (p≈0.13). Tryptophan production remained stable across all phases for both systems. The results reveal that the duration of the anaerobic period significantly influences bioresource production, emphasizing the importance of defining optimal operational conditions for efficient resource recovery in wastewater treatment.