Doctor of Philosophy
Chemical and Biochemical Engineering
With the ever-increasing emission standards and space constraints, the traditional bioreactors with a suspended growth process face more difficult in meeting the requirements, so that more and more new bioreactors with the attached growth process have been developed for wastewater treatment, especially fluidized bed bioreactors. Among them, a recently developed inverse fluidized bed bioreactor (IFBBR) combined with biological nutrient removal (BNR) has demonstrated good performance for high carbon/nitrogen (C/N) ratio municipal wastewater treatment and lower energy consumption than other fluidized bed bioreactors such as circulating fluidized bed bioreactor (CFBBR). However, the performance of IFBBR for low C/N ratio wastewater treatment has not been studied, and neither has been the hydrodynamics of IFBBR with bioparticles.
A 3.2L lab-scale gas-liquid-solid inverse fluidized bed bioreactor (GLS-IFBBR) was used to test the performance for synthetic wastewater treatment with different media, which were polypropylene (PE), carbon-coated PE (PEC), zeolite-coated PE (PEZ), lava rock-coated PE (PEL), multi-plastic-coated PE (PEM). The optimal media was found based on the performance: over 90% COD and NH4-N removal were achieved at organic loading rate (OLR) of 1.64 kg COD/(m3·d) and nitrogen loading rate (NLR) of 0.17 kg N/(m3·d) in the GLS-IFBBR system with PEZ as the carrier particles.
Then, a 32.4L lab-scale integrated anoxic and aerobic zone IFBBR was used to investigate the performance for treating lower C/N (C/N=5, 3, and 2) wastewaters with PEZ as media in comparison with carbon-coated polypropylene (PPC) as media for C/N=5 wastewater treatment. At OLR of 0.93-1.65 kg COD/(m3·d) and NLR of 0.32-0.49 kg N/(m3·d), the IFBBR system with PEZ particles achieved 85%-93% total COD removal, 90%-94% NH4-N removal, 40%-75% total nitrogen removal and the low observed biomass yields of 0.098-0.152 g VSS/g SCOD. The NH4-N removal efficiency and the amount of aerobic attached biomass in IFBBR with the PEZ particles were higher than that in IFBBR with the PPC particles. The energy consumption of the IFBBR system with PEZ was lower than that with PPC based on ThCOD and ThCODR. A simple IFBBR model was built in BioWin® (5.3) and calibrated with the experimental data.
Finally, the hydrodynamic characteristics of the liquid-solid inverse fluidized bed (LSIFB) with PE, PEC, PEZ, and bioparticles having different biofilm thicknesses were studied in preparation for industrial design and use. The same was also studied in the gas-liquid-solid inverse fluidized bed (GLSIFB) with PE, PEZ, and PPC particles, and PPC particles with biofilm. In LSIFB, the solids loading did not affect the minimum liquid fluidization velocity (Ulmf). The Ulmf of bioparticles decreased with the increase of biofilm thickness and a dimensionless equation was proposed to predict Ulmf for the bioparticles. The bed expansion ratio (BER) of bioparticles increased with the increase of the biofilm thickness. In GLSIFB, the initial fluidization gas velocity (Ug,if) and the complete fluidization gas velocity (Ug,cf) increased with the particle diameter and decreased with the particle density. As the biofilm attached on the particles, both Ug,if and Ug,cf decreased. When Ug was higher than Ug,if, the BER of the particles and bioparticles increased with the increase of superficial gas velocity.
Summary for Lay Audience
Wastewater contains various nutrients such as organic carbon, ammonium, which can cause eutrophication and many potential hazards to human and animal health. Therefore, it is necessary to remove carbon and nitrogen from the wastewater before reusing or discharging directly into the environment. There are many technologies for wastewater treatment. However, with the increase of emission standards and physical space constraints, the traditional bioreactors with the suspended growth process are difficult to meet the requirements due to some disadvantages: (1) large space requirement; (2) high excess sludge; (3) low loading rate. Currently, a new inverse fluidized bed bioreactor (IFBBR), which used the particles attached microorganisms as media for municipal wastewater treatment due to smaller “footprint”, lower sludge production, higher removal efficiency compared with traditional suspended growth technologies and its energy consumption is lower than other fluidized bed bioreactors such as circulating fluidized bed bioreactor (CFBBR). However, the performance of IFBBR for low carbon/nitrogen (C/N) ratio wastewater treatment and hydrodynamics of bioparticles such as minimum liquid fluidization velocity that related to the design and operation of IFBBR were not studied.
First, the performance of gas-liquid-solid inverse fluidized bed bioreactor (GLS-IFBBR) with different particles as media for synthetic wastewater treatment was tested to find optimal particles. Then the performance of the IFBBR system with the optimal particles as media for treating the different low C/N ratio wastewaters was investigated and compared with the PPC particles as media for C/N=5 wastewater treatment. Meanwhile, energy consumption was calculated for each stage. A simple IFBBR model was built in BioWin® (5.3) and calibrated with the experimental data in order to further use it to predict the performance in the scale up IFBBR system. Finally, the hydrodynamic characteristics of the particles and bioparticles at different solids loadings and biofilm thicknesses in LSIFB and GLSIFB to provide the data support for the design, scale-up, and operation of IFBBR.
Wang, Lin, "Extended Study of the Inverse Fluidized Bed Bioreactor for Low C/N Ratio Wastewater Treatment and Hydrodynamics" (2020). Electronic Thesis and Dissertation Repository. 7145.
Available for download on Monday, September 01, 2025