Development of an ATP luminescence-based method for assimilable organic carbon determination in reclaimed water

Assimilable organic carbon (AOC) is an important indicator of the biological stability of reclaimed water. In this study, a new rapid and more stable method for AOC measurement in reclaimed water was proposed. Indigenous microbial culture from secondary effluent was used as the inoculum, and bacterial growth was determined by the quantity of adenosine triphosphate (ATP) in the form of luminescence instead of plate count. ATP luminescence had a high correlation with biogrowth both in pure acetate solutions and reclaimed waters. ATP luminescence analysis could be determined in 5 min. Three days of 10000 cells/mL inoculum incubated at 25 °C were enough for the bacteria to reach the stationary phase. The good correlations between ATP luminescence and the added acetate-C concentration illustrated the applicability of monitoring AOC level by luminescence method. And in reclaimed water samples, indigenous microbial culture produces the highest AOC results compared with the pure strains. This indicated that the integrity of indigenous microbial culture ensured the full utilization of matrix carbons, which demonstrated the advantage of indigenous microbial culture compared with the selected pure bacteria in the traditional AOC test. The average ATP content per cell of 3.95 × 10^-10 nmol/cell was derived, and this value was stable in both the acetate solutions and reclaimed waters. Furthermore, the average yield coefficient of 1.5 × 10⁵ RLU/μg acetate-C (4.1 × 10^-3 nmol ATP/μg acetate-C) was obtained from different indigenous cultures. Additionally, the indigenous microbial cultures from different secondary effluents would produce the similar AOC results for the same water sample, indicating the consistency of this assay. The ATP luminescence-AOC assay provides a faster, more stable and accurate approach for monitoring the biological stability of reclaimed waters.