Studies On The Adsorption And Biodegradation Characteristics Of Bisphenol A Onto Main Components In Surfacial Sediments

Bisphenol A [BPA, 2, 2-(4, 4-dihydroxydiphenyl) propane] is one of important organic chemicals as intermediate in the manufacture of polycarbonate plastic, epoxy resin, flame retardants, and other specialty products. BPA of low levels are directly released to surface waters and the atmosphere via permitted discharges in the manufacturing and processing facilities, and it may also be inadvertently released as fugitive dust emission from closed systems during processing, handling, and transportation. BPA has an acute toxicity toward aquatic organisms in the range of 1-10μg/L for freshwater and marine species, and it has also been reported to be mimic biological effect of the female hormone, estrogens. It is, therefore, identified as the endocrine disrupting chemicals (EDCs) by the USA Environmental Protection Agency (EPA), and is becoming a social issue of increasing interest in the public.BPA is subject to biodegradation, adsorption to suspended solids, sediments and soils, and possibly photo-degradation besides mixing with water. It is likely that adsorption process will be one of the most important pathways for the transportation and transformation of BPA, which may influence the rate of other processes such as biodegradation and photolysis. Solid phases such as surficial sediments (SSs) and natural surfacial coating samples (NSCSs) constitute the multi-phases system deciding the activities of BPA in the aquatic environment. However, distinct spatial position and forming conditions make the solid phases have great differences in contents of main components (Fe oxides, Mn oxides and organic matters). Moreover, microbial composition, crystalline structure, and surface property of corresponding components in these solid phases are different completely, even distinct evidently. The chemically reactive components in different solid phases have diverse binding abilities for BPA and accordingly affect BPA transportation, bioavailability and toxicity significantly. Up to now, the adsorption of BPA onto different adsorbents, such as aquatic colloids, soils, sediments, activated carbons, minerals and sewage sludge, and the biodegradation behavior were investigated. However, the complexities of the chemical components in NSCSs and SSs that would influence the adsorption and biodegradation behavior of BPA have not been understood completely. Thus, in this paper, Songhua River was chosen as natural water for collecting NSCSs and SSs and the adsorption characteristics of BPA onto NSCSs and SSs and their main components such as Fe oxides, Mn oxides and organic matters were assessed and compared, including adsorption capacity of the solid phases for BPA, distribution of BPA to main components in NSCSs and SSs and adsorption ability of corresponding components in them. Moreover, the degradation characteristics of BPA in the NSCSs and SSs by Pseudomonas sp. were investigated. Finally, the influences of surfactants on the adsorption and biodegradation of BPA in NSCSs and SSs were studied. It would be hoped to predict the transportation, transformation, and fate of BPA in the environment and to assess their potential impacts on soils/sediments, surface water, and ground water resources.Gas chromatography (GC) and high-performance liquid chromatography were employed to determine bisphenol A in water samples. The results showed that the detection limit of BPA analyzed by– the gas chromatographic method is 0.1μg/L, which is two orders of magnitude higher than that of the high-performance liquid chromatographic method. However, the samples should be extracted and concentrated for analyzing by gas chromatographic method, and the water samples can be directly injected into HPLC after filtration without preconcentration. And HPLC analyzing method is enough to determine the samples by the high-performance liquid chromatographic method in laboratory.Selective extraction techniques followed by batch adsorption experiments and statistical analyses were employed to investigate the adsorption behavior of BPA onto the NSCSs and SSs, and to estimate the relative contribution of components (i.e. Fe oxides, Mn oxides, organic materials and residues) to the total BPA adsorption. The results indicated that there was a similar trend for the concentrations of main components in the unextracted NSCSs and SSs following the order of organic materials > Fe oxides > Mn oxides. The chemical reagents of NH2OH·HCl, (NH4)2C2O4 and H2O2 can selectively remove manganese oxides, ferromanganese oxides, and organic matters, respectively. The amounts of the adsorbed BPA were increased linearly with the increasing time for quite a long time. The fast adsorption step completed within about 12h, and followed by a desorption stage. The time reaching the equilibrium for BPA adsorption onto NSCSs and SSs were about 24h. The amounts of adsorbed BPA onto NSCSs and SSs at 12h reached 98.6% and 97.1% of every maximal adsorbend amount, respectively. The amount of the adsorbed BPA onto SSs in the first 8h was more than that of NSCSs, and that of BPA adsorbed onto NSCSs increased dramatically in the following time. The adsorption reaction processes of BPA adsorption onto NSCSs and SSs tallied with the pseudo first order kinetic characteristics. Nonlinear Langmuir model can describe the adsorption behavior of BPA onto the NSCSs and SSs before and after extraction treatments with significance level of r>0.98. Compared with SSs, NSCSs had a better capacity for adsorbing BPA indicating that NSCSs on BPA transformation are more important than SSs. Adsorption contributions of the main components in NSCSs and SSs such as Mn oxides, Fe oxides and oranic matters were different from each other apparently. The removal of Mn oxides from the NSCSs and SSs led to a significant increase in BPA adsorption, which implied that Mn oxides inhibited BPA adsorption onto solid matrix, and Fe oxides played a positive role in BPA adsorption onto the NSCSs and SSs. However, the removal of organic materials (OMs) led to a dramatic decrease in BPA adsorption, suggesting considerable amounts of BPA adsorbed onto OMs in NSCSs and SSs.Pseudomonas sp. can degrade BPA in water samples. BPA in the systems of mineral salts cultures and SSs (NSCSs) were degraded by Pseudomonas sp. It was observed that when the initial concentrations of BPA were 10 mg/L, 50 mg/L, and 100 mg/L, the growth of the bacteria in the mineral salts cultures reached the maximum levels at approximately 36h, 24h, and 12h, respectively. Thereafter, the bacterium amount decreased markedly. The lag phase of bacteria growth was unconspicuous or relatively short and BPA was degraded rapidly in 3d after inoculation in each initial concentration. The logarithmic phase of 100 mg/L was longer than those of other concentrations, and the shortest for logarithmic phase of 10 mg/L. The degradation reaction tallied with the pseudo first order kinetic characteristics. When the initial concentration was 10 mg/L, the degradation rate was maximal (72.86%). The effects of the conditions of BPA-degrading rate were studied via shaking flasks, and it was determined that the optimum conditions for BPA degradation were the concentration of SSs or NSCSs 40 mL/g, and inoculum amount 8%. Moreover, selective extraction techniques have effects on the BPA degradation in the systems of SSs and NSCSs, ie. the removal of Fe/Mn oxides increased the contents of organic matters, and thereby the available carbon increased accordingly which result in promoting the degradation of BPA. However, H2O2 reagent extraction decreased the degradation rate, especially in SSs system.Surfactants have a significant influence on the adsorption of organic contaminants. Batch equilibrium experiments were conducted to investigate the influences of cationic surfactant cetyltrimethylammonium bromide (CTMAB), anionic surfactant sodium dodecylbenzenesulfonate (SDBS) and non-ionic surfactant Triton X-100 (TX-100) on bisphenol A (BPA) adsorption onto SSs and NSCSs. The results suggested that the application of CTMAB results in a dramatic increase in the adsorption of BPA, the increase being directly proportional to the concentration of CTMAB added, while increasing amount of SDBS led to a less pronounced increase in BPA adsorption. However, BPA exhibited a slightly enhanced adsorption onto SSs in the presence of TX-100 at high concentrations (>1.0 CMC), and a decrease adsorption in the presence of TX-100 at low concentrations (<1.0 CMC). Moreover, the addition orders of CTMAB have little influence on BPA adsorption onto SSs. And the influence of the physiochemical characteristics of the main components of NSCSs and SSs is far less than that of CTMAB. The surfactants can be adsorbed onto the the surface of NSCSs and SSs by ion exchangement, sedimentation and have effects on the BPA adsorption. Finally, the surfactants of different types on the biodegradation of BPA by Pseudomonas sp. in the systems of NSCSs and SSs were investigated. The results indicated that non-ionic surfactant Triton X-100 (TX-100) promoted the degradation of BPA, and the degradation rate was enhanced by 5%, while cationic surfactant cetyltrimethylammonium bromide (CTMAB) and anionic surfactant sodium dodecylbenzenesulfonate (SDBS) all inhibited the degradation of BPA in NSCSs and SSs systems. The degradation of BPA in NSCSs and SSs systems was inhibited in the presence of TX-100 at low concentrations (<1.0 CMC), however, it exhibited a slightly enhanced degradation in the presence of TX-100 at high concentrations (>1.0 CMC), and the degradation rate of BPA increased gradually with the increasing concentrations of BPA. The removal of the main components of NSCSs and SSs by the selective extraction techniques has an effect on the BPA degradation in the system of SSs and NSCSs, which led to a reduction of the degradation rate of BPA.