Aeration-Driven Dynamics and Compositional Transformation of Dissolved Organic Carbon in Surface Water Containing Microplastics and Microalgae.

Dissolved organic carbon (DOC) is a key indicator of water quality, shaped by biological activity and anthropogenic inputs, including microalgal metabolism and microplastic degradation. This study investigated DOC dynamics and compositional changes in Surabaya River surface water during a 30-day aeration experiment. In the surface water-algal (SWA) and surface water-microplastic (SWP) systems, DOC concentrations after aeration reached 18.78 and 22.75 ± 0.042 mg L-1, respectively. The combined system (SWAP) demonstrated the highest DOC accumulation, with an approximately 2.3-fold increase, suggesting synergistic interactions between microalgae and microplastics. Correspondingly, SUVA value in SWAP decreased markedly by about 15-fold, indicating a substantial shift from aromatic toward more hydrophilic DOC fractions. FTIR analysis confirmed the presence of O-H, C-H, CH2/CH₃, and amide functional groups, reflecting mixed contributions from microalgal biomass and microplastic-derived polymers. These findings highlight the critical role of organic matter sources in controlling DOC dynamics and carbon cycling in freshwater systems.