Factors affecting the degradation of Biphenol A by activated sludge

Abstract

Bisphenol A (BPA) has been described as a estrogenic compound.However, it is used in the production of polycarbonate, epoxy resins and otherplastics. Mixed microbial cultures, such as activated sludge, have been proposed as a feasible methodology to achieve the decontamination ofwastewater containing BPA In this book, the biodegradation of bisphenol A (BPA) using activatedsludge not previously exposed to BPA (native activated sludge) was described.In addition, the acclimation process to BPA and the strategies of acclimation ofthe biomass to the xenobiotic compound were analyzed. The kinetics andstoichiometry of the biodegradation of BPA and its metabolic products were determined. Finally, the biodegradation of BPA in the presence of a biogenicsubstrate in semi-continuous activated sludge reactors was studied.Results demonstrate that BPA concentrations lower than 40 mg L-1 had a negligible effect on the growth of native activated sludge.Activated sludge (AS) samples from reactors operated at sludge ages (SA) of 30 and 45 days were acclimated to BPA using two strategies: constant orincreasing the initial BPA concentration. Although acclimation to BPA was achieved using both strategies, no net biomass growth was detected. SpecificBPA degradation rate of acclimated AS ranged from 65 to 90 mgBPA gTSS-1 d-1.BPA degradation was not affected by the biogenic substrates (cheese whey or acetate); acclimation to BPA did not cause a negative effect on thebiodegradation of these substrates. During the degradation of cheese whey, specific mean oxygen uptake rate (qO2mean) and specific mean substrateconsumption rate (qSmean) of non-acclimated AS were similar to those corresponding to acclimated ones. When acetate was tested, qO2mean and qSmeanvalues corresponding to acclimated AS were about twofold the values of the non-acclimated ones. This enhancement of the biodegradation processoccurred because acetate is an intermediate of the metabolism of BPA.The kinetics of the biodegradation of BPA and its metabolic products, 4- hidroxyacetophenone (4HAP), 4-hidroxybenzaldehyde (4HB) and 4-hidroxybenzoic acid (4HBA), was influenced by the sludge age, the acclimation process, and the concentration of the analyzed compound. The stoichiometry ofthe reactions was not affected by the studied conditions. The average oxidationcoefficients YO/S were 10.0 ± 0.5, 5.2 ± 0.2, 3.7 ± 0.2, and 3.0 ± 0.1 molO2 molS- 1 for BPA, 4HAP, 4HB, and 4HBA, respectively. Based on the obtained YO/Svalues, a biodegradation pathway was suggested.Additionally the simultaneous degradation of BPA and cheese whey (CW) in semi-continuous activated sludge reactors was studied. The acclimationprocess and the microbial growth on BPA, CW and BPA+CW were analyzed; the effect of increasing CW concentration on the BPA degradation by acclimatedactivated sludge was also studied. In the semi-continuous reactors, the presence of CW increased the acclimation time to 40 mg L-1 of BPA. Once thecapability of degrading BPA was acquired, the removal of BPA was not affected by the presence of CW. Increasing the CW concentration did not affect theremoval of BPA by the acclimated activated sludge. Additionally, the CW consumption was not modified by the presence of BPA. Kinetic andstoichiometric coefficients can be useful in developing mathematical models to describe the simultaneous aerobic biodegradation of a biogenic substrate, suchas CW, and BPA by activated sludge.