Acclimation of activated sludge to nonylphenol ethoxylates and mathematical modeling of the depolymerization process

Abstract

In this study, the aerobic depolymerization of nonylphenol ethoxylates (NPEOs) in activated sludge reactors was studied. Activated sludge (AS) from two different reactors treating different model wastewater (cheese whey or phenol) was used as the inocula for NPEOs biodegradation assays. Three commercial mixtures of NPEOs (NPEOav5, NPEOav9,NPEOav12) were tested as the sole carbon source. Soluble and total (soluble plus sorbed onto the biomass) NPEOs concentrations were measured by HPLC. The oxygen uptake rate (OUR) of the microorganisms during the aerobic degradation of NPEOs was measured using a respirometric technique. Results showed that only phenol-acclimated sludge was capable of degrading NPEOs. HPLC analysis suggested that biodegradation occurred via the non-oxidative depolymerization of NPEOs. Then, released ethoxylate units were the actual substrate for biomass growth and oxygen consumption. A lumped kinetic model was developed assuming that long-chain oligomers can be represented by a single oligomer Nz,being z the average polymerization degree of this lumped species, which is depolymerized by the biomass. The model was fitted to the experimental data and a satisfactory agreement was achieved. The developed model could be useful for predicting the depolymerizationprocess of NPEOs and the growth of biomass in aerobic activated sludge reactors.