Biological Fluidized Bed Reactor Research Articles

Statistical Characterization of Full-Scale Thermophilic Biological Systems to Inform Process Optimization

This paper focuses on using a novel approach to assess the statistical variability of management data from an aerobic thermophilic biological plant (AWTP) utilizing a fluidized bed biological reactor. A proper statistical characterization of full-scale thermophilic biological systems, in fact, may inform process optimization in the light of a future automation of treatment plants. We present a case study that spans the period from 2018 to 2023 and encompasses various high-strength aqueous waste (AW) in continuous mode. Key aspects of the proposed analytical approach include: (i) utilizing advanced descriptive statistics, such as violin graphs, to depict the variability of monitored parameters over five years; (ii) conducting correlation analyses (Spearman and Pearson correlation matrices) specifically focusing on nitrogenous forms within the AW; (iii) applying multivariate statistical analysis to assess the correlation between pollutants released and the plant’s energy and oxygen consumption; and (iv) reconstructing parameter trends by considering periodic and random components, thus enhancing the understanding of the system’s behavior over time. The findings presented in this paper offer valuable insights into the performance and optimization of AWTPs, potentially leading to a proper planning of the loads and consequent feeding of the plants. If properly enacted, our approach may provide a significant contribution to the field of aqueous waste management.

Estimation of thermal energy released by thermophilic biota during sludge minimization in a fluidized bed reactor: Influence of anoxic conditions

Thermophilic biological fluidized bed reactors operating in aerobic/anoxic alternate conditions proved to be a feasible solution for sewage sludge minimization. However, to date, no data about energy released by thermophilic biota (ThBio) are available in literature. This work aims to estimate specific thermal energy released by ThBio highlighting the influence of daily anoxic conditions. A pilot-scale reactor (1 m3) was fed continuously with mesophilic sewage sludge and monitored for more than four months and a thermophysical model was applied to estimate thermal energy released by ThBio (kT,biota and kT,COD). Results suggested that the increase of daily anoxic time stimulated COD removal (92.7 ± 1.3 % vs. 81.3 ± 4.9 %, with 6 h and 0 h of daily anoxic time, respectively). The thermal energy released by ThBio was strictly dependent on anoxic conditions. In fact, increasing anoxic conditions from 0 h d−1 to 6 h d−1, kT,biota and kT,COD reduced from 1.8 ± 1.3 Mcal kg−1VS kg−1COD and 26.6 ± 13.7 Mcal kg−1COD to 0.5 ± 0.1 Mcal kg−1VS kg−1COD and 15.6 ± 4.2 Mcal kg−1COD, respectively. Although, biological mechanism responsible of this behaviour is not completely clear, this work can serve as reference for future studies about the optimization of conditions to maximize thermal energy release from ThBio during organic substance degradation alternate aerobic/anoxic, in view of subsequent energy recovery.

Thermophilic biological fluidized bed reactor in sludge line reduces greenhouse gas emissions in wastewater treatment system

Greenhouse gas (GHG) emissions represent one of the main drawbacks of wastewater (WW) treatment. However, results of a detailed estimation of the emissions can be a valid tool to define optimal solutions for minimizing impact of WW treatment system on the environment. Thermophilic biological fluidized bed reactor (TBFBR) has been recently proposed as an alternative solution for biological sludge minimization in wastewater treatment plant (WWTPs). In this work, 5 diverse scenarios of sludge line composition were studied and combined with 5 diverse sludge disposal options. GHG emissions in 25 combinations were fully investigated to define optimal sludge treatment and disposal option. Results suggested that TBFBR help to reduce net emitted GHGs with respect to scenario with conventional stabilization treatment in sludge line (anaerobic digestion) (−32.3 ± 3.55 %) thanks to (i) the reuse in water line of the aqueous residue of TBFBR as alternative carbon source, (ii) the significant minimization of sludge production, and (iii) the contained impact of gross GHG emissions due to the energy consumption of this process. The strong minimization of sludge also led to a decisive reduction in GHG emissions in the subsequent phases of transport, additional treatments, and final disposal making the choice of the disposal option indifferent on the overall GHG emission estimation. Moreover, the coupling of processes for the simultaneous and preventive maximization of energy recovery (TCH, and AnaD) before sludge minimization in TBFBR determined a limited reduction of GHG emission compared to scenario with TBFBR alone (−3.71 ± 1.47 %).

Strong minimization of biological sludge production and enhancement of phosphorus bioavailability with a thermophilic biological fluidized bed reactor

Identify sustainable biological sewage sludge (BSS) management represents a current challenge. In this work, pre-thickened BSS taken from a large-scale urban wastewater treatment plant (WWTP) was fed continuously for about 9 months to a semi-industrial scale thermophilic biological fluidized bed reactor (TBFBR) operating in alternate conditions. The BSS treated in TBFBR was strongly reduced (89–92%) and the production was evaluated in 0.0007–0.0023 kg kgCODremoved−1 d−1 and 0.0004–0.0014 kg kgCODremoved−1 d−1 of TS and VS, respectively. The 92% of the P-PO43- and P-org precipitated in inorganic form and accumulated in thermophilic biological sludge (TBS). In basic soils with chelating activity, phosphorus contained in TBS presented a higher bioavailability (84.0 ± 25.3%) with respect to untreated sludge. The analysis of four diverse scenarios highlighted that TBFBR located after pre-thickening could save 73–96% of operating costs with respect to current situation.

A comprehensive review on application of bioreactor for industrial wastewater treatment.

In the recent past, wastewater treatment processes performed a pivotal role in accordance with maintaining the sustainable environment and health of mankind at a proper hygiene level. It has been proved indispensable by government regulations throughout the world on account of the importance of preserving freshwater bodies. Human activities, predominantly from industrial sectors, generate an immeasurable amount of industrial wastewater loaded with toxic chemicals, which not only cause dreadful environmental problems, but also leave harmful impacts on public health. Hence, industrial wastewater effluent must be treated before being released into the environment to restrain the problems related to industrial wastewater discharged to the environment. Nowadays, biological wastewater treatment methods have been considered an excellent approach for industrial wastewater treatment process because of their cost-effectiveness in the treatment, high efficiency and their potential to counteract the drawbacks of conventional wastewater treatment methods. Recently, the treatment of industrial effluent through bioreactor has been proved as one of the best methods from the presently available methods. Reactors are the principal part of any biotechnology-based method for microbial or enzymatic biodegradation, biotransformation and bioremediation. This review aims to explore and compile the assessment of the most appropriate reactors such as packed bed reactor, membrane bioreactor, rotating biological contactor, up-flow anaerobic sludge blanket reactor, photobioreactor, biological fluidized bed reactor and continuous stirred tank bioreactor that are extensively used for distinct industrial wastewater treatment.

High-rate microbial selenate reduction in an up-flow anaerobic fluidized bed reactor (FBR)

Wastewater contaminated with high concentrations of selenium oxyanions requires treatment prior to discharge. Biological fluidized bed reactors (FBRs) can be an option for removing selenium oxyanions from wastewater by converting them into elemental selenium, which can be separated from the treated effluent. In this study, a lab-scale FBR was constructed with granular activated carbon as biofilm carrier and inoculated with a consortium of selenate reducing bacteria enriched from environmental samples. The FBR was loaded with an influent containing ethanol (10 mM) and selenate (10 mM) as the microbial electron donor and acceptor, respectively. The performance of the FBR in reducing selenate was evaluated under various hydraulic retention times (HRTs) (120 h, 72 h, 48 h, 24 h, 12 h, 6 h, 3 h, 1 h and 20 min). After process acclimatization, selenate was completely removed with no notable selenite produced when the HRT was stepwise decreased from 120 h to 6 h. However, decreasing the HRT to 3 h resulted in selenite accumulation (0.17 ± 0.023 mM) in the effluent although selenate removal efficiency remained at 99.8 ± 0.20%. At 1 h HRT, the FBR removed 90.8 ± 1.4% of the selenate at a rate of 9.6 ± 0.15 mM h−1, which is the highest selenate reduction rate reported in the literature so far. However, 1 h HRT resulted in notable selenite accumulation (up to 2.4 ± 0.27 mM). Further decreasing the HRT to 20 min resulted in a notable decline in selenate reduction. Selenate reduction recovered from the “shock loading” after the HRT was increased back to 3 h. However, selenite still accumulated until the FBR was operated in batch mode for 6 days. This study affirmed that FBR is a promising treatment option for selenate-rich wastewater, and the process can be efficiently operated at low HRTs.

Achieving nitritation in an aerobic fluidized reactor for coking wastewater treatment: Operation stability, mechanisms and model analysis

The presence of toxic compounds in coking wastewater is challenging for water treatment, but it also offers opportunities for the selection of specific bacterial populations based on different sensitivities. The potential selective inhibitory effect of toxic compounds in coking wastewater was employed here to inhibit nitrite oxidizing bacteria (NOB), allowing stable nitritation in a long-term experiment using a biological fluidized bed reactor. The main challenge was to identify the appropriate toxic compound loading range that would effectively inhibit NOB but allow ammonium oxidizing bacteria (AOB) to work, by variation of organic loading rate (OLR) and dissolved oxygen (DO). An OLR of 0.80–1.35 kg·m−3d−1 permitted nitritation with a nitrite accumulation rate (NAR) above 80.5%. DO regulation was used to control the extent of nitritation which resulted in different NH4+-N/NO2−-N ratios. The bacterial populations present under the various operation conditions were characterized by high-throughput sequencing, demonstrating presence of Nitrosomonas species as the main AOB, while Nitrospira species (typical NOB) were successfully suppressed. Batch activity experiments with the sludge demonstrated stronger inhibition from SCN− on NOB (IC50 = 40.01 mg·L−1) than on AOB (IC50 = 308.12 mg·L−1). A mathematical model was developed based on the differential inhibition by SCN− and phenol on NOB and AOB, which predicted the optimal conditions for stable nitritation, in line with the experimental data. These findings may help to promote the design and optimization of operation condition for nitritation of coking wastewater, and has potential for nitrogen removal via nitrite (e.g. Anammox) in the treatment of industrial wastewater containing toxic compounds.

Biological synthesis of iron nanoparticles using hydrolysates from a waste-based biorefinery.

The purpose of this work was to produce iron nanoparticles (Fe-NP) by microbial pathway from anaerobic bacteria grown in anaerobic fluidized bed reactors (AnFBRs) that constitute a new stage of a waste-based biorefinery. Bioparticles from biological fluidized bed reactors from a biorefinery of organic fraction of municipal solid wastes (that produces hydrolysates rich in reducing sugars) were nanodecorated (embedded nanobioparticle or nanodecorated bioparticle, ENBP) by biological reduction of iron salts. Factors "origin of bioparticles" (either from hydrogenogenic or methanogenic fluidized bed reactor) and "type of iron precursor salt" (iron chloride or iron citrate) were explored. SEM and high-resolution transmission electron microscopy (HRTEM) showed amorphous distribution of nanoparticles (NP) on the bioparticles surface, although small structures that are nanoparticle-like could be seen in the SEM micrographs. Some agglomeration of NPs was confirmed by DLS. Average NP size was lower in general for NP in ENBP-M than ENBP-H according to HRTEM. The factors did not have a significant influence on the specific surface area of NPs, which was high and in the range 490 to 650m2g-1. Analysis by EDS displayed consistent iron concentration 60-65% iron in nanoparticles present in ENBP-M (bioparticles previously grown in methanogenic bioreactor), whereas the iron concentration in NPs present in ENBP-H (bioparticles previously grown in hydrogenogenic bioreactor) was more variable in a range from 8.5 to 62%, depending on the iron salt. X-ray diffraction patterns showed the typical peaks for magnetite at 35° (3 1 1), 43° (4 0 0), and 62° (4 0 0); moreover, siderite diffraction pattern was found at 26° (0 1 2), 38° (1 1 0), and 42° (1 1 3). Results of infrared analysis of ENBP in our work were congruent with presence of magnetite and occasionally siderite determined by XRD analysis as well as presence of both Fe+2 and F+3 (and selected satellite signal peaks) observed by XPS. Our results on the ENBPs hold promise for water treatment, since iron NPs are commonly used in wastewater technologies that treat a wide variety of pollutants. Finally, the biological production of ENBP coupled to a biorefinery could become an environmentally friendly platform for nanomaterial biosynthesis as well as an additional source of revenues for a waste-based biorefinery.

Treatment of the real boiler cleaning wastewater in an anaerobic fluidized bed microbial fuel cell: Organic matter degradation, bioelectrochemistry, and kinetics

A single chambered air cathode anaerobic fluidized bed microbial fuel cell (AFB‐MFC) was simultaneously used to dispose of the real boiler cleaning wastewater (BCW) containing a high concentration of citric acid and to generate renewable energy. At the temperature of 40 °C and flow rate of 5.22 mL/s, the removal efficiency and power density were improved in AFB‐MFC with the abiotic cathode of the Pt/C modified carbon cloth. With the real boiler cleaning wastewater fed as substrate, the maximal removal efficiency of chemical oxygen demand (COD) in AFB‐MFC was up to 90 %, which was higher than the corresponding value of 84 % obtained in the anaerobic biological fluidized bed reactor (ABFBR). The maximum voltage and the maximum power density were 424.6 mV and 18.68 mW/m2, respectively, when the external resistance was 5000 Ω. Furthermore, the Haldane inhibition model was well fitted with experiment data (R2 = 0.97–0.98) in AFB‐MFC/ABFBR. The inhibition of citric acid degradation in ABFBR was stronger than that of AFB‐MFC. The bioelectrochemical system of AFB‐MFC not only improved the charge transfer and but also accelerated the reaction rate of citric acid. The reduction of the ferric ion and oxidation of ferrous ion in AFB‐MFC played important roles in the degradation reaction of critic acid.

Treatment of Dairy Effluents in Biological Fluidized-Bed Reactors using Oyster Shells as Ecological Garnishing

We investigated the effectiveness of a new ecological garnishing of natural origins in MBBR reactors: The shells of oysters, used for the biological treatment of dairy effluents, in the presence of fungi <em>Aspergillus niger</em> and <em>Penicillium chrysogenum</em>. The abatement performance of organic matter was compared with the same bioreactor design in the presence of a common reference support (Kaldnes K3), conventionally used on an industrial scale. Pollution parameter monitoring results (Chemical Oxygen Demand COD, total nitrogen soluble NKT, phosphorus P, suspended matter SM and biochemical oxygen demand BOD5) obtained using oyster shells as garnishing media, are favorable after only 24 h of biological treatment. Organic matter removal efficiencies are comparable sometimes even better than K3 media. All the results show that oyster shells can provide an ecological support for biofilm colonization in MBBR reactors and allow for a satisfactory pollution abatement rate.

Microbial community dynamics in aerated biological fluidized bed (ABFB) with continuously increased p-nitrophenol loads

Biodegradability of PNP has been reported widely in recent years, but the community composition of PNP-degrading microorganisms was still unclear today. In this paper, the biodegradation process with continuously PNP loading from 0 to 6.50 kg m−3 d−1 in 58 days in an aerobic biological fluidized bed (ABFB) reactor has been investigated. The results show that COD and PNP removal stabilized at 95% and 99% during the operation period with a maximum PNP concentration of 1250 mg/L. The high concentration of PNP in substrate led to a significant increase in extracellular polymeric substances (EPS) component of biomass and obvious morphological changes of microbial colonies during the degradation process. In addition, high-throughput sequencing was employed to reveal the highly diverse bacterial and fungal populations in the reactor. At the same time, genera Sphingobium, Penicillum and Debaryomyces belonging to phyla Proteobacteria and Ascomycota were identified to be the dominant species in high concentration PNP degradation process. This work investigated the tolerable degree of aerobic microbes to PNP toxicity as well as the characteristics of microbial communities at different PNP concentration levels. It might add some new insights into bacterial and fungal communities in high p-nitrophenol concentration degradation processes.

Arsenic removal from acidic solutions with biogenic ferric precipitates

Treatment of acidic solution containing 5g/L of Fe(II) and 10mg/L of As(III) was studied in a system consisting of a biological fluidized-bed reactor (FBR) for iron oxidation, and a gravity settler for iron precipitation and separation of the ferric precipitates. At pH 3.0 and FBR retention time of 5.7h, 96–98% of the added Fe(II) precipitated (99.1% of which was jarosite). The highest iron oxidation and precipitation rates were 1070 and 28mg/L/h, respectively, and were achieved at pH 3.0. Subsequently, the effect of pH on arsenic removal through sorption and/or co-precipitation was examined by gradually decreasing solution pH from 3.0 to 1.6 (feed pH). At pH 3.0, 2.4 and 1.6, the highest arsenic removal efficiencies obtained were 99.5%, 80.1% and 7.1%, respectively. As the system had ferric precipitates in excess, decreased arsenic removal was likely due to reduced co-precipitation at pH<2.4. As(III) was partially oxidized to As(V) in the system. In shake flask experiments, As(V) sorbed onto jarosite better than As(III). Moreover, the sorption capacity of biogenic jarosite was significantly higher than that of synthetic jarosite. The developed bioprocess simultaneously and efficiently removes iron and arsenic from acidic solutions, indicating potential for mining wastewater treatment.

Contrasting microbial community composition and function perspective in sections of a full-scale coking wastewater treatment system.

To characterize the microbial community of the coking wastewater (CWW) treatment system and to study the effects of CWW characteristics and operational parameters on microbial communities, active sludge samples were collected from a full-scale CWW treatment plant using three-phase fluidized bed biological reactors. High-throughput MiSeq sequencing was used to examine the 16S rRNA genes of microbiology, revealing a distinct microbial composition among the active sludge samples of three sequential bioreactors. Pseudomonas, Comamonas, and Thiobacillus-related sequences dominated in the anaerobic bioreactor A, aerobic bioreactor O1, and aerobic bioreactor O2 active sludge with relative abundance of 72.59, 56.75, and 27.82 %, respectively. The physico-chemical characteristics of CWW were analyzed by standard methods and operational parameters were recorded to examine their effects on the microbial communities. The redundancy analysis (RDA) results showed that the bacterial communities of bioreactors A, O1, and O2 correlated strongly with cyanides, phenols, and ammonia, respectively. These results expand the knowledge about the biodiversity and population dynamics of microorganisms and discerned the relationships between bacterial communities and environmental variables in the biological treatment processes in the full-scale CWW treatment system.

Mixing regime as a key factor to determine DON formation in drinking water biological treatment

Dissolved organic nitrogen (DON) can act as precursor of nitrogenous disinfection by-products formed during chlorination disinfection. The performances of biological fluidized bed (continuous stirred tank reactor, CSTR) and bio-ceramic filters (plug flow reactor, PFR) were compared in this study to investigate the influence of mixing regime on DON formation in drinking water treatment. In the shared influent, DON ranged from 0.71mgL−1 to 1.20mgL−1. The two biological fluidized bed reactors, named BFB1 (mechanical stirring) and BFB2 (air agitation), contained 0.12 and 0.19mgL−1 DON in their effluents, respectively. Meanwhile, the bio-ceramic reactors, labeled as BCF1 (no aeration) and BCF2 (with aeration), had 1.02 and 0.81mgL−1 DON in their effluents, respectively. Comparative results showed that the CSTR mixing regime significantly reduced DON formation. This particular reduction was further investigated in this study. The viable/total microbial biomass was determined with propidium monoazide quantitative polymerase chain reaction (PMA-qPCR) and qPCR, respectively. The results of the investigation demonstrated that the microbes in BFB2 had higher viability than those in BCF2. The viable bacteria decreased more sharply than the total bacteria along the media depth in BCF2, and DON in BCF2 accumulated in the deeper media. These phenomena suggested that mixing regime determined DON formation by influencing the distribution of viable, total biomass, and ratio of viable biomass to total biomass.

Biodegradation Performance of an Inner-Loop Three-Phase Fluidized-Bed Bioreactor to Treat Petrochemical Wastewater

In order to remove the petroleum hydrocarbons in petrochemical wastewater, an airlift inner-loop three-phase fluidized-bed (AITF) bioreactor was designed independently, combining the chemical embedding technique to treat petrochemical wastewater continuously. This biological fluidized bed reactor had an excellent antishock ability on the hydraulic loading capacity and the chemical oxygen demand (COD) loading capacity. Moreover, because the microbial biodegradation of petrochemical wastewater was difficult, the reactor also maintained good potential biodegradation capability, and the average COD removal rate was about 87% and average total petroleum hydrocarbons removal rate was about 95% in the steady continuous stage. The volumetric loading capacity of the AITF bioreactor is two to five times of that of traditional activated sludge methods.

Fluidized-bed denitrification for mine waters. Part II: effects of Ni and Co

The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7-8 and 22 °C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7-8 °C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.

The Hydraulic Characteristics of Inner Loop Biological Fluidized Bed Set Ring-Type Baffle

The flow field of the traditional inner loop biological fluidized bed reactor (ILBFBR) and a new biological fluidized bed reactor set ring-type baffle was calculated by computational fluid dynamics. The results show that the gas holdup of drop zone in ILBFBR set the ring-type baffle can increase significantly, the flow rate of drop zone in ILBFBR with the ring-type baffle is faster than that in traditional ILBFBR, and turbulence intensity distributed more evenly all in rising zone and drop zone in ILBFBR set the ring-type baffle than that in traditional ILBFBR, but static pressure difference of ILBFBR set ring-type baffle is higher than that of the traditional ILBFBR.

Research on Enzymatic Reaction Kinetics for Sugar Factory Wastewater Treatment

Enzymatic reaction kinetics for sugar factory wastewater biological treatment was investigated. A laboratory scale completely mixed reactor was used for the study. By using the Runge-Kutta method and modified simple, estimation of kinetic parameters was conducted. The kinetic parameters rmax (the maximum reaction velocity) and Km (Michaelis constant) were found to be 0.7952×10 mg/min.L and 0.2519×103mg/L for COD, and 0.1359×10 mg/min.L and 0.2062×103 mg/L for NH3-N, respectively. These parameters could be utilized for the design of the three phase biological fluidized bed reactor for sugar factory wastewater treatment.

Operating Conditions and Kinetics of Wastewater Treatment in a Three-Phase Biological Fluidized Bed Reactor

Systematic experiments were carried out with synthetic wastewater in order to investigate the operating conditions and kinetics of wastewater treatment in a three-phase biological fluidized bed reactor. It is found that with the COD loading rate changed stepwise from 3.5 to 11.2 kg COD/m3•d, the reactor can rapidly restore from each impact of COD load and maintain the removal rate for COD at 85% or above, presenting a high flexibility for the variation of organic loading rate (OLR) in the influent. While the operating OLR keeps constant, the increase of influent COD and NH3-N concentrations will be followed by the correspondingly increased removal rates, so that the COD and NH3-N concentrations in the effluent keep nearly constant. The batched experiments under different air supply conditions show that there exists an optimal air flow rate at which the most effective treatment can be achieved. Finally, a kinetics model of the continuous treatment process was derived based on mass balance and Monod equations, and the kinetic constants were determined by the experimental data at steady operating OLR.

Biological Treatment of Wastewater from Sugar Production Process by using Three-Phase Fluidized Bed Reactor

The biodegradation of wastewater from the sugar industry is investigated in a three-phase biological fluidized bed reactor. In the inoculation experiment, the immobilized biofilm was found to keep dominant over the suspended biomass, and a stable biofilm of 175 microns thick was formed after 12 days. The continuous experiments for biodegradation of wastewater showed that, under the operation with hydraulic retention time of 3 h, the average COD and NH3-N removals reached to 85% and 80%, respectively, and the resultant effluent COD and NH3-N achieved the Chinese Discharge Standard of Water Pollutants for Sugar Industry (GB 21909-2008). The experiment for impact load showed that as the influent COD load changed stepwise from 2.3 to 5.1 kgCOD/m3·d, the reactor achieved the treatment effect without being affected in the performance. Finally, tracer experiments were performed to measure the internal circulation and residence time distribution (RTD) of wastewater in the reactor. It was found that the internal circulation of wastewater evidently exists in the reactor. Meanwhile, the RTD characteristics were described with the tanks-in-series model, and under the operating conditions, the calculated model parameter n was ranged from 1.19 to 1.27, which indicated that the flow pattern in the reactor is close to that in a CSTR. The internal circulation causes the organic matters in the influent to be effectively diluted within the reactor, and also promotes the organic matters to be fully degraded, so that the reactor can present high adaptability to the variation of organic load and high removal efficiency to COD and NH3-N. As a result, the biological fluidized bed reactor is suggested to be a prospective unit for the treatment of wastewater from sugar production process.