Date of Award
May 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemical Engineering
First Advisor
Yun Ji
Abstract
The main contaminants in wastewater can be classified as suspended solid, dissolved inorganic and organic molecules. The dissolved inorganics in wastewater are salinity such as sodium chloride and sodium sulfate. Evaporation is one possible method to separate dissolved salt from high salinity wastewater, but the proper application of energy-saving evaporation depends on many conditions. Microplastic is a part of total suspended solids and can be effectively removed through settling process, and the removal efficiency can be predicted by settling model. Biological treatment eliminates organic matters and biosolids are the inevitable by-products. Air drying is a sustainable approach for reducing water content in the biosolid, but the influence of several factors on specific evaporation rates needs to be investigated in the experiment. The gasification process can recover the energy from biosolid and can be simulated by stoichiometric thermodynamic equilibrium model. This dissertation studied and evaluated four typical chemical processes applied in the wastewater treatment – high saline wastewater evaporation, microplastic settling, biosolid air drying and biosolid gasification – using different research methodologies, such as experiment, data mining, theorical modelling, and exergy analysis. The decision tree analysis was built according to some parameters of the experimental data, and it successfully classified our samples. Exergy analysis demonstrated mechanical vapor recompression could be designed with the exergy advantage over multi-effects evaporation when the wastewater boiling point elevation is less than 13.5°C. A settling model was constructed based on Reynolds number, drag coefficient and settling mechanism. The calculated removal efficiency of microplastics according to density, size distribution, different shape, and the surface loading rate was in a reasonable removal efficiency range. Biosolid air drying experiments under room temperature results revealed that the specific evaporation rate decreased as solid content increased and wind speed decreased, and the developed regression model can effectively predict the specific evaporation rate; under winter outdoor temperature, the results revealed the surrounding temperature has a great effect on the sublimation rate. A stoichiometric thermodynamic equilibrium model was constructed for biosolid gasification based on the biosolid properties, thermodynamic database, and equilibrium constants. The simulation results indicated exergy efficiency depended more on the operation conditions than the feedstock type; H2 concentration of the dry syngas in biosolid gasification exhibited a curve both against the given temperature under isothermal condition and against the moisture content under autothermal condition. The results of performance assessment of evaporation, microplastic settling, biosolid air drying and gasification can be used to guide the development and design of cutting-edge wastewater treatment processes.
Recommended Citation
Li, Fangtian, "Performance Assessment Of Wastewater Treatment Processes: Evaporation, Microplastic Settling, Biosolid Air Drying And Gasification" (2024). Theses and Dissertations. 6373.
https://commons.und.edu/theses/6373