Impacts of Contact-to-Stabilization Time Ratio and Organic Loading on Feast-Famine Regime and Microbial Kinetics in High-rate Contact Stabilization Process

Abstract

High-rate contact stabilization (HRCS) process has emerged as a promising wastewater treatment process for carbon recovery from wastewater. However, the relationship between process performance and the actual induction of the feast-famine (FF) regime under varying contact-to-stabilization time ratios (tc/ts) remains poorly understood. This study investigated the effect of tc/ts ratios (0.2, 0.33, 0.5) on the metabolic characteristics of the HRCS process under varying organic loading rates. The results demonstrated that a low tc/ts ratio (0.2), characterized by a prolonged stabilization phase, exhibited superior organic removal efficiency. In contrast, the tc/ts condition failed to maintain performance during high loading, attributed to insufficient stabilization time, which induced substrate stress rather than metabolic activation. Crucially, these distinct performance outcomes are closely linked to the actual induction of the FF regime, which was successfully established in the low tc/ts. Furthermore, distinct metabolic profiles of polyhydroxybutyrate (PHB) and extracellular polymeric substances were confirmed depending on the tc/ts ratio and OLR, with the most active PHB metabolism observed in the tc/ts = 0.2 condition. Growth kinetic batch tests using flow cytometry revealed that specific growth rates (µ) increased as the tc/ts ratio decreased. Furthermore, biomass subjected to starvation exhibited accelerated µ compared to non-starved biomass. Taxonomic analysis revealed distinct community shift driven by operational conditions: Burkholderiales were enriched in the low tc/ts (0.2) condition, whereas the relative abundance of Rhodocyclaceae, including genus Zoogloea, increased as the tc/ts ratio increased. Consequently, these results suggest that the tc/ts ratio is a critical design parameter that determines the intensity of the FF regime, ensuring both process efficiency and operational stability.