Extended Study of the Inverse Fluidized Bed Bioreactor for Low C/N Ratio Wastewater Treatment and Hydrodynamics

Lin Wang, The University of Western Ontario

Abstract

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 ThCOD_R. 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 (U_lmf). The U_lmf of bioparticles decreased with the increase of biofilm thickness and a dimensionless equation was proposed to predict U_lmf 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 (U_g,if) and the complete fluidization gas velocity (U_g,cf) increased with the particle diameter and decreased with the particle density. As the biofilm attached on the particles, both U_g,if and U_g,cf decreased. When U_g was higher than U_g,if, the BER of the particles and bioparticles increased with the increase of superficial gas velocity.