The effect of temperature on the biodegradation of a nonylphenol polyethoxylate in river water

In this paper a study is made of the biodegradability of a non-ionic surfactant, a nonylphenol polyethoxylate, in river water by means of monitoring the residual surfactant matter and the metabolites that may be generated. The influence of temperature on the extent of primary and ultimate biodegradation, and the kinetics of degradation are also determined. The method used was the river die-away test, and the biodegradation process was monitored by normal and reversed phase high-performance liquid chromatography (HPLC). These results are supported by other indirect measurements and indicators of the existence of microbial degradation process, as well as the parameters for the control of the process. The results obtained indicate that temperature has a strong influence on the period of acclimation of the microorganisms and on the rate of biodegradation. The percentages of primary biodegradation vary from 68% at 7 degrees C to 96% at 25 degrees C, and at all the temperatures studied, metabolites are generated during the biodegradation process which do not totally disappear at the end of the assay. The percentages of mineralization reached in the various assays, ranging from 30% at 7 degrees C to 70% at 25 degrees C, also show the great influence of temperature. Finally, a kinetic study of the biodegradation process has been carried out, with excellent fit of the experimental data to the kinetic model of Quiroga and Sales. (C) 1999 Elsevier Science Ltd. All rights reserved.