Assessing toxicity of municipalsolid waste incineration residues with MARA and Microtox bioassays
| Autor: | Tsung-Lin Tsai, 蔡宗霖 |
|---|---|
| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 This study investigated the change of potential hazards associated with preand post-stabilization of municipal solid waste incinerator (MSWI) residues, including bottom ash and fly ash. Both chemical and ecotoxicological characterization of leachates from residue TCLP were conducted: chemically, concentrations of regulated heavy metal species were quantified; toxicologically, commercial microbially-based bioassays were used to evaluate the toxicity of leachates, including Microbial Assay for Risk Assessment (MARA)- a battery test in which ten bacterial and one yeast species are incorporated, and Microtoxan in vitro testing system that employs a bioluminescent bacterium (Vibrio fischeri, aka Allivibrio fischeri) to detect toxic substances in samples. To gauge which bioassay would be more suitable for solid waste toxicity assessment, reproducibility, repeatability and sensitivity of the results obtained from both assays were compared. In addition, the correlation between chemical and ecotoxicological characteristics of the MSWI leachates was discussed. Over the course of experiments, it was found that due to the inherent buffer capacity of the assay medium, MARA did not require pH adjustment on samples; in contrast, acidification of samples to circumneutral pH was a necessitate for Microtox in order to eliminate the interference resulting from elevated hydroxide levels of MSWI residues. In addition, observable toxicity was not equilibrated in Microtox within 30 min that is often suggested by the protocol, indicating that to avoid underestimation of sample toxicity, appropriate exposure periods should be aware of. Notably, discrepancy was observed between these two assays with respect to toxicity change before and after stabilization of MSWI ash. Given that the matrix effect in the assay medium seems to play a critical role in governing the exhibited toxicity, at this point superiority of MARA over Microtox or vice versa is not ascertained. Regardless, results of this study showed that after carbonization, half effect concentrations (EC50) of the ash samples were too low to be detected in Microtox; further, the microbial toxic concentration (MTC) measured in MARA ranged from 35.55 to 52.13%, which exceeded the 20% threshold that is generally set for the bacterial toxicity assay. Accordingly, none of the bottom and fly ashes after carbonate mineralization in this study can be classified as toxic samples and may not significantly exert adverse ecotoxicity. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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