Model-based evaluation of the impacts of aeration on tightly bound and loosely bound extracellular polymeric substance production under non-steady-state conditions

Abstract

Tightly bound extracellular polymeric substances (TB-EPS) and loosely bound extracellular polymeric substances (LB-EPS) affect the flocculability and settleability of sludge and the transfer of oxygen, which are highly related to aeration. In this study, we systemically evaluated the expanded unified model-TL2.1 for its long-term simulation of TB-EPS and LB-EPS. Two different aeration conditions and three different influent carbon sources were used to evaluate the model, and the simulation results fit well with the experimental data. TB-EPS and LB-EPS production increased with aeration intensity. The influence of aeration parameters on TB-EPS and LB-EPS production in a short-term batch system and long-term sequencing batch reactor (SBR) system was compared. The aeration parameters included the total transfer coefficient (k_La) and the concentration of dissolved oxygen at the interface (C_S). To ensure a high removal rate of substrates and ammonia nitrogen and achieve a stable active biomass concentration, the following aeration parameters can be adopted to reduce energy wastage during aeration: when C_S is 2 mg/L, k_La can be set above 30 h^-1 and below 50 h^-1; when k_La is 50 h^-1, C_S can be set above 1 mg/L and below 1.5 mg/L. This study systematically revealed the influence of aeration on TB-EPS and LB-EPS formation in an SBR system through a mathematical model, and it provides a theoretical basis for better understanding aeration.

Keywords: Aeration efficiency; Loosely bound extracellular polymeric substances; Mathematical modeling; Tightly bound extracellular polymeric substances; Total transfer coefficient.