Trace Organic Contaminants and Microbial Diversity in Integrated Fixed-film Activated Sludge Wastewater Treatment Systems
- Restrictions on Access:
- Open Access.
- Trace organic contaminants (TrOCs) often pass through conventional activated sludge wastewater treatment plants (CAS-WWTPs) and are discharged into surface waters, where they can threaten aquatic ecosystems and human health by mimicking natural hormones (e.g. estrogen) and disrupting the endocrine systems of exposed individuals. These pollutants often occur in complex mixtures and are transformed within WWTPs to various degrees producing largely unknown metabolites. The use of in vitro bioassays to characterize the reduction of endocrine disrupting activity is an important compliment to targeted chemical analysis in order to determine the overall effectiveness of wastewater treatment technologies. While CAS-WWTPs are inconsistent in their removal of TrOCs and associated endocrine disrupting activity, a process modification known as integrated fixed-film activated sludge (IFAS) has been indicated to better remove TrOCs in bench- and pilot-scale studies. State-of-the-art IFAS-WWTPs incorporate mobile plastic carrier media into the activated sludge basins of existing CAS-WWTPs in order to promote the growth of biofilm within the system. IFAS technology is gaining popularity as a means of upgrading existing wastewater treatment infrastructure to improve overall plant capacity and nitrification, without the expansion of the WWTP footprint. Despite its increasing popularity and prior evidence of enhanced TrOC removal, there is currently very limited published data regarding the removal of TrOCs in full-scale IFAS-WWTPs, and no data regarding the removal of estrogenic activity in full-scale IFAS-WWTPs. Differences in the suspended biomass and biofilm microbial communities of IFAS-WWTPs are also poorly characterized, especially for fungi, which are versatile eukaryotic members of activated sludge WWTP microbial communities with the potential to degrade complex organic contaminants. In addition to fungi native to the WWTP environment, exogenous fungi, such as the white-rot fungi (WRF), possess a widely proven ability to degrade TrOCs and present an interesting opportunity for bioaugmentation of activated sludge WWTPs if their ability to grow in wastewater, remain metabolically active, and compete with heterotrophic bacteria can be demonstrated.In this work, a preliminary assessment of the ability of the WRF Trametes versicolor to grow in WWTP effluent, produce enzymes, and remove of a mixture of TrOCs and associated estrogenic activity was carried out. In addition, six full-scale IFAS-WWTPs were surveyed to characterize the removal of TrOCs and estrogenic activity as well as the microbial communities (fungi, bacteria, and archaea) present in suspended biomass and biofilm. Together, these efforts provide a basis for future research on the augmentation and enrichment of fungi and other TrOC-degrading microorganisms via biofilm formation in existing CAS wastewater treatment infrastructure. The survey of TrOC removal in full-scale IFAS-WWTPs supported the conclusions of previous bench- and pilot-scale studies for a number of compounds (atenolol, diclofenac, gemfibrozil, DEET, 4-nonylphenol, 4-tert-octylphenol, azithromycin, bisphenol A, metoprolol, and naproxen). For these compounds, the median removal efficiency observed for IFAS-WWTPs exceeded median/average values reported in the literature for CAS-WWTPs by greater than ten percentage points. In addition to compounds identified in previous bench- and pilot-scale studies, two chlorinated flame retardants TCIPP and TDCIPP, which are commonly reported to show no removal in CAS-WWTPs, were removed to a significant degree (median removal > 45%) in IFAS-WWTPs. Effluent estrogenic activity in IFAS-WWTPs ranged from ND to 10.9 ng l-1 and 1.9 to 19.4 ng l-1 for ER and ER, respectively, which was similar to values reported in the literature for full-scale CAS-WWTPs in Europe (< 0.5 ng l-1 to 17.9 ng l-1). A slight correlation between hydrophobicity and TrOC removal was observed, but correlations between WWTP operating conditions and overall performance could not be established with certainty. Core fungal and bacterial taxa (present in > 75% of samples from standard sampling locations) were identified for both suspended biomass and biofilm, many of which were shared between the two growth types; however, differences in relative abundance and the presence of non-core taxa led to significant overall differences between suspended biomass and biofilm community structure for both fungal and bacterial populations. Despite the hypothesized enrichment of slow-growing fungi in IFAS biofilms, core biofilm fungi were found to be a subset of core fungi identified in suspended biomass, and the overall alpha diversity of biofilms was roughly half that of suspended biomass, indicating that biofilm is in fact a selective environment where only a subset of the fungi dominant in suspended biomass are able to survive. The use of a state-of-the-art algorithm for denoising and quality filtering sequencing data revealed fungal diversity in suspended biomass which was lower than had been previously reported for CAS-WWTPs. Although core fungal genera were mainly yeasts, members of most of those genera have been previously found to be able to degrade recalcitrant organic compounds. Differences in the relative abundance of key functional bacteria in biofilms retained in different redox zones and in basins with different nutrient loadings were also revealed. Both nitrifying and denitrifying genera were found to be dominant in aerobic biofilms, while archaeal methanogens and sulfate reducing bacteria were among the dominant genera in anoxic, but not aerobic biofilms. Across all six IFAS-WWTPs, nitrifying bacteria were found to be highly enriched in the biofilm, as compared to suspended biomass. A previously untested strain of T. versicolor (NRRL 66313) grew comparably well and produced modest amounts of extracellular enzymes in both nutrient media and carbon-amended secondary WWTP effluent. T. versicolor grown in wastewater was able to decrease the concentration of four of the nine TrOCs (mainly estrogens and bisphenol A) spiked to 350 g l-1 within 3.5 hours, with a corresponding reduction in estrogenic activity of > 98% after 12 h. Estrone was found to be the primary metabolite of 17-estradiol degradation, and was subsequently removed from solution. Relatively low extracellular enzyme activities (e.g. < 1U l-1) in cultures degrading TrOCs suggests the potential involvement of intracellular enzymes (e.g. cytochrome P450).Overall, this study further demonstrates the potential for IFAS technology to play a role in mitigating the release of TrOCs to the environment, both as it is currently deployed and potentially further through process modifications to enhance the TrOC degrading potential of biofilms.
- Dissertation Note:
- Ph.D. Pennsylvania State University 2018.
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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