Doctor of Philosophy
Chemical and Biochemical Engineering
The combination of biological nutrient removal (BNR) with fluidization technology has demonstrated advantages over suspended growth systems. Previous studies about fluidized bed bioreactor (FBBR) mainly focused on the BNR performance, rarely paid attention to the operation and energy consumption, while high energy consumption is the main hurdle for the industrial application of FBBR systems.
In this work, the BNR performance of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic wastewater was studied. TCOD removal efficiencies of ˃84% were achieved, concomitantly with complete nitrification. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less. Bacterial community structures of attached and detached biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of AOB and NOB in aerobic attached biomass were 0.451% and 0.110%, respectively. The IFBBR system was further studied of BNR performance with synthetic high particulate COD wastewater. 87% COD, 73% TN, and 48% TP removal was achieved at OLR of 2.8 kg COD/(m3 d) and nitrogen loading rate (NLR) of 0.26 kg N/(m3 d). Organic shock test was conducted to examine the system sustainability with short term response to the variance of influent COD. A calibrated IFBBR model built in Biowin was efficient to simulate COD and nitrogen concentrations.
Although the energy consumption of IFBBR system was reduced, the maximum OLR of 2.8 kg/(m3 d) achieved in the IFBBR system was approximately half of the maximum OLR of 5.3 kg/(m3 d) in the CFBBR system due to high shear force in the aerobic zone and small specific surface area for biomass attachment. The selection of carriers is a crucial issue for FBBRs. Minimum fluidization velocity (Ulmf) affects system design and operation. Four carrier particles (L-HDPE, S-HDPE, pottery, and zeolite) were chosen to study the Ulmf under gas velocities of 0-12.4 mm/s. Partial nitrification (PN) was an alternative way to eliminate ammonia. An FBBR with S-HDPE as carriers was operated to study PN performance at NLRs of 1.2-4.8 kg N/(m3 d). Stable PN was successfully achieved with low effluent NO3-N concentration of <15 mg/L. At NLR of 3.6 kg N/(m3 d), the system effluent NO2-N/NH4-N ratio was 1.27.
Summary for Lay Audience
Based on the idea of growing bacteria on small particle surface, the circulating fluidized bed bioreactor (CFBBR) was developed to combine the advantages of biological nutrient removal (BNR) process and fluidized bed technology. Previous studies showed that CFBBR system could achieve efficient nutrient removal at short hydraulic retention time of 2-3h with low biomass yield. However, high energy consumption was the main hurdle for the industrial application of CFBBR system. Two approaches were proposed to address this problem - changing carrier particles and employing new BNR processes.
A novel inverse fluidized bed bioreactor (IFBBR) with polypropylene beads (true density of 904 kg/m3) as carrier media for biomass attachment was built to study the BNR performance of treating synthetic wastewater. TCOD removal efficiencies of ˃84% were achieved, concomitantly with complete nitrification. The energy consumption of this IFBBR system was 59% less than that of CFBBR system. Bacterial community structures of anoxic, aerobic and effluent biomass were tested by 16S rRNA sequencing. The dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. Biomass were classified into different functional groups based on the functions of genera and a new method to calculate sludge retention time was proposed. An organic shock test was conducted to examine the system short-term resilience to influent variations. A calibrated IFBBR model was built in Biowin and this model was efficient of simulating COD and nitrogen removal performance.
Minimum fluidization velocity (Ulmf) affects system design, operation, and energy consumption. Ulmf of four carrier particles (L-HDPE, S-HDPE, pottery, and zeolite) were studied under different gas velocities of 0-12.4 mm/s for carrier selection. S-HDPE has the lowest Ulmf at all gas velocities. The experimental results were examined by semiempirical equations. Partial nitrification (PN) was an emerging BNR process to eliminate ammonia. An FBBR system with S-HDPE as carriers was operated to study PN performance. Stable PN was successfully achieved with effluent nitrate of <15 mg/L. At a nitrogen loading rate of 3.6 kg N/(m3 d), the system effluent with NO2-N/NH4-N of 1.27 could be directly used as the influent to anaerobic ammonia oxidation process, hence significantly reducing aeration energy demand.
Wang, Haolong, "Energy Reduction in Fluidized Bed Bioreactors for Municipal and Ammonia-rich Wastewater Treatment" (2019). Electronic Thesis and Dissertation Repository. 6348.