Influence of conventional and advanced anaerobic digestion on the composition and phytotoxicity of biosolids: towards beneficial use
The aim of this project was to evaluate the influence of conventional anaerobic digestion (CAD) and advanced anaerobic digestion (AAD) of sewage sludge in the composition (i.e. physicochemical and microbiological characteristics, and the concentration of micropollutants) and in the direct and indire...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2019 |
| País: | Chile |
| OAI Identifier: | oai:repositorio.anid.cl:10533/241765 |
| Acceso en línea: | https://hdl.handle.net/10533/241765 |
| Access Level: | acceso abierto |
| Palabra clave: | Ingeniería y Tecnología Ingeniería Ambiental Ingeniería Ambiental y Geológica |
| Sumario: | The aim of this project was to evaluate the influence of conventional anaerobic digestion (CAD) and advanced anaerobic digestion (AAD) of sewage sludge in the composition (i.e. physicochemical and microbiological characteristics, and the concentration of micropollutants) and in the direct and indirect phytotoxicity of the biosolids (BS) generated. The hypothesis was that the ADF produced more favorable changes in the composition and phytotoxicity of the BS than those generated by CAD, considering as a final purpose the beneficial application of the BS. For 200 days, two laboratory-scale anaerobic reactors under mesophilic conditions were operated at sludge retention time of 30 days. One was fed directly with sewage sludge (CAD) and the other one was fed with the same sewage sludge but pre-treated (AAD). A sequential pre-treatment of ultrasound followed by a thermal low temperature (55°C) stage was used. During the operation time the performance of both reactors was evaluated by determining the total solid (TS) reduction, organic matter estimated as chemical oxygen demand (COD) and the methane yield. The BS generated by both reactors were used for different purposes. A fraction was used to perform physicochemical characterizations such as determination of TS, volatile solids (VS), pH, conductivity, humidity, metal content, nutrient content (nitrogen, phosphorus and potassium), organic matter, among others. Another fraction was used to determined pathogens as total and fecal coliforms. Another fraction of the BS was used for direct and indirect phytotoxicity assay. A final fraction was used in the determination of microcontaminants (tonalide, galaxolide, triclosan, butylated hydroxytoluene, phenanthrene, pyrene, 4-nonylphenol, tert-octylphenol, bisphenol A and 17β-ethinyl estradiol). The anaerobic digestion performance improved with the incorporation of the sequential pre- treatment of ultrasound followed by a low-temperature thermal stage. With COD and VS removals 12.89% and 4.25% higher than the CAD system. And the methane yield in AAD was 30.24% higher than the CAD system. Regarding the physicochemical characteristics of the BS, the concentration of total nitrogen, total phosphorus, ammonium, copper, zinc, and mercury; were between 1.05-1.58 20times higher in the BS from AAD compared to those from CAD. Behavior related mainly to the solubilization of organic matter due to pre-treatment. Considering the 10 microcontaminants determined, both systems resulted in the accumulation of 8 of the microcontaminants. Triclosan being the only compound removed during CAD and AAD, and 17β-ethinyl estradiol the compound that was not detected in either SS or BS. However, AAD resulted in a decrease of 7 of the 9 compounds detected with respect to CAD. The direct and indirect phytotoxicity of the BS and the parental SS, which was evaluated by two dicotyledonous plants and one monocotyledonous; Lactuca sativa, Raphanus sativus, and Triticum aestivum, respectively. The results showed the high phytotoxicity of sewage sludge, related to putrescible organic matter, that is, the lack of stabilization. Indirect phytotoxicity of BS from CAD caused positive effects in R. sativus and T. aestivum, but for L. sativa high toxicity was observed. In the case of the BS from AAD, these showed a beneficial effect or the absence of phytotoxic substances for the three plants tested. In the case of direct phytotoxicity, the BS from CAD was slightly more beneficial than those from AAD, with increases between 4-20% in the germination index of CAD compared to AAD and with an average EC 50 of 164 g/kg and 159 g/kg, for the BS from CAD and AAD, respectively. Therefore, the hypothesis is rejected. Although the application of sequential pre-treatment of ultrasound followed by a low temperature treatment (55°C) improved the conversion of organic matter, the methane production increased, the elimination of pathogens and microcontaminants increased. The results of the direct and indirect phytotoxicity of the biosolids from conventional and advanced anaerobic digestion, showed no significant differences. |
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