Effect of UV-C irradiation on dissolved organic matter and its bioavailability

Laboratory batch experiments of bacterial cultures and ultraviolet-C (UV-C)irradiation were conducted using surface water samples collected from Huangpu River and its upper tributaries. Dissolved organic carbon (DOC) concentrations, UV-Visible absorption spectra and fluorescence spectra were measured to investigate the bioavailability and photodegradation of dissolved organic matter (DOM). The results showed that the removals of DOC, fluorescent dissolved organic matter (FDOM) and chromophoric dissolved organic matter (CDOM) varied with different treatments. Approximately 5%-27% of DOC and 5% of CDOM were consumed during the microbial growth progress. However, the FDOM intensity increased slightly. After 24-hour UV-C irradiation, further loss of DOC (7%-36%) was much lower than those of CDOM (79%-96%) and FDOM (more than 95%). The removal rates of CDOM and FDOM during the UV-C irradiation were much higher than those during the microbial degradation. Besides, some SLDOM (semiactive DOM), which were difficult to be utilized by microorganisms, can be used once again. It indicated that UV-C irradiation can change the bioavailability of DOM. In this study, 4%-28% of DOC and 5%-14% of CDOM were further biodegraded after UV-C irradiation.