Characterization of released metabolic organics during AOC analyses by P17 and NOX strains using 3-D fluorescent signals.

Assimilable organic carbon (AOC) serves as an indicator of the biostability of drinking water distribution systems; however, the properties of the released organic metabolites by Pseudomonas fluorescens (P17) and Spirillum (NOX) used in AOC bioassays are seldom discussed. In this study, fluorescence excitation emission matrix (FEEM) was selected to characterize organic metabolites after substrate biotransformation and their divergences at different growth stages of both strains in AOC bioassay. Excellent correlation between ATP and colony-forming units (CFUs) was observed for both strains. The concentration of ATP per colony was six times higher in the P17 strain than in the NOX strain. A retarding phenomenon was observed for the NOX strain in the presence of high acetate-C content (100-150 µg acetate-C/L). The fluorescence wavelength peaks were wider for the protein-like substance released by the P17 strain than for those released by the NOX strain. However, fluorescent fulvic-like substances only existed in the NOX strain. Relative humus accumulation (RHA), the ratio of protein-like fluorescence intensity to humus-like fluorescence intensity, decreased in the P17 strain but substantially increased in the NOX strain in the logarithmic growth phase. RHA showed a descending trend for the P17 strain as compared to that of the NOX strain during the progress from logarithmic to stationary growth phase at three different acetate-C concentrations; however, the opposite was observed at 100 µg acetate-C/L, indicating that high acetate-C content may affect the properties of released organic matter from both strains.