The Gym Effect: Unveiling the Role of Microbial Adaptation in Organic Carbon Redistribution and Metabolic Optimization in Anaerobic Side-Stream Reactors

Although anaerobic side-stream reactor (ASSR) technology has been proven effective in achieving sludge reduction, current research primarily focuses on specific cellular processes, such as cell lysis-cryptic growth, uncoupled metabolism, and endogenous metabolism. This narrow perspective overlooks the holistic impact of ASSR on mainstream systems. Therefore, this study developed a novel exogenous organic carbon balance model, providing a quantitative framework for analyzing carbon redistribution within the system. The results showed that alternating aerobic and deep anaerobic conditions induced significant microbial community reorganization, selectively enriching functional microorganisms such as polyphosphate-accumulating organisms and denitrifiers. This adaptation altered organic carbon flow, reducing assimilatory metabolism (from 3606.4 mg COD/d in the control group to 2872.5 and 2184.3 mg COD/d in the ASSR group), while enhancing aerobic dissimilatory metabolism (from 1866.1 mg COD/d in the control group to 2175.8 and 2616.4 mg COD/d in the ASSR group), thereby promoting pollutant mineralization and sludge reduction. The innovative concept of the "Gym Effect" was introduced to explain how environmental stress drives microbial adaptation, optimizes metabolic pathways, and enhances pollutant (nitrogen and phosphorus) removal processes (from 34.8 mg COD/g VSS·h in the control group to 49.8 and 66.7 mg COD/g VSS·h in the ASSR group). These findings redefine our understanding of the mechanisms underlying sludge reduction, establishing the relationship between sludge reduction and organic carbon flow redistribution, and providing a robust theoretical foundation for enhancing sludge reduction strategies.