Analysis of the influence of HiCS operating conditions on bioflocculation based on grey system theory

With the advancement of the “dual carbon” policy, the high-load contact stabilization (HiCS) process technology has attracted much attention because of its efficient carbon source capture and carbon redirection capabilities. However, the factors affecting extracellular polymers’ concentration and composition changes are complex, and their mechanism of action and correlation are unclear. This article uses grey relational analysis (GRA) from grey system theory (GST) to analyze the impact of HiCS process operating conditions on biological flocculation. Total EPS concentration, PN/PS ratio, and LB/TB ratio were used as reference sequences, while SRT, ts, tc/ts, DO, and SLR were used as comparison sequences. The results show that the effect of each factor on total EPS concentration was ts > SLR > tc/ts > SRT > DO; the effect on PN/PS ratio was ts > SRT > SLR > tc/ts > DO; and the effect on LB/TB ratio was SLR > ts > SRT > DO. In this paper, the influence of various factors on bio-flocculation-related indicators is expounded, which provides a reference for further optimizing the operating conditions of the flocculant process.