Energy Reduction in Fluidized Bed Bioreactors for Municipal and Ammonia-rich Wastewater Treatment
Abstract
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.