Fundamental Behaviors of Assimilable Organic Carbon and Bacterial Regrowth Potential in Yodo River through Water Treatment Processes.

Biodegradable organic substances in Yodo River water, its coagulated water and the ozonated water were analyzed in terms of the concentration of assimilatable organic carbon (AOC), the apparent molecular weight and the E260 absorbability. The fundamental behaviors of AOC through coagulation and ozonation were investigated. Yodo River water contained a relatively high content of macro organic compounds (>5,000 Da) that did not exhibit E260 absorbing features. However, these compounds were not detected as AOC. Coagulation resulted in decreases in the concentration of AOC by up to 75%, due to reductions in the phosphorus concentration. During ozonation, the AOC concentration increased rapidly with the reduction of E260 and increased slowly following the change of some large molecular organic compounds to small ones. However, 30-50 % of AOC that could be increased through ozonation was reduced by pre-coagulation.In addition, water samples prepared under the condition of different limiting substrates were subjected to AOC measurements and batch incubation tests for bacteria living in Yodo River. Experimental results indicated that the AOC concentration converted to acetate equivalent could not represent the concentration of the available carbon for assimilation. However, its apparent value was probably reflective of the growth potential of bacteria even under the phosphorus limitation. Thus, it was suggested that the apparent AOC concentration is a useful indicator for evaluating the regrowth potential of native bacteria in Yodo River.