Frequency response analysis of naphthalene biotransformation activity in a biological treatment system

A systems analysis technique known as the frequency response method was used to characterize the system structure and robustness of naphthalene biotransformation in an activated sludge-type biological treatment system. The continuous system was perturbed with a complex wastewater feed stream containing a sinusoidally-varying naphthalene concentration while all other feed constituents, total feed flow rate, and other reactor operating parameters were held nearly constant. Time series offgas analysis for naphthalene provided a sensitive output parameter that was readily measured and related to the naphthalene reactor liquid concentration.

The feed input perturbation period was varied in successive intervals from 64 to 1 hr, and intervening intervals of constant naphthalene feed concentration allowed the system to relax after each perturbation interval. Using an unsteady-state naphthalene material balance and assuming a first-order naphthalene biotransformation rate process, a first-order biotransformation rate parameter was calculated and was used as a baseline to interpret the unusually complex naphthalene biotransformation activity.

Frequency response analysis on mixed microbial systems was found to be a feasible and useful tool with which to probe the dynamic behavior of biotransformation activity in an operating biological treatment system. This new information gives rise to new hypotheses regarding the nature of biotransformation of naphthalene in complex systems for testing in future experimental work.