Influence of upflow velocity on performance and biofilm characteristics of Anaerobic Fluidized Bed Reactor (AFBR) in treating high-strength wastewater
© Jaafari et al.; licensee BioMed Central Ltd. 2014
Received: 25 May 2014
Accepted: 29 October 2014
Published: 25 November 2014
One of the key parameters in Fluidized Bed reactors is the control of biofilm thickness and configuration. The effect of upflow velocity on performance and biofilm characteristics of an Anaerobic Fluidized Bed Reactor was studied in treating Currant wastewater at various loading rates. The reactor used this study was made of a plexiglass column being 60 mm diameter, 140 cm height, and a volume of 3.95 L. The results demonstrated that the AFBR system is capable of handling an exceptionally high organic loading rate. At organic loading rates of 9.4 to 24.2 (kg COD m−3) at steady state, reactor performances with upflow velocities of 0.5, 0.75 and 1 (m min−1) were 89.3- 63.4, 96.9 – 79.6 and 95 – 73.4 percent, respectively. The average biomass concentration per unit volume of the AFBR (as gVSSatt L−1 expended bed) decreased with the increase of upflow velocity in the range of 0.5–1 m min–1 at all applied organic loading rates. The total biomass in the reactor increased with increases in the organic loading rate. The peak biomass concentration per unit volume (as gVSSatt L−1 expended bed) was observed at the bottom part of the reactor, then it droped off slowly towards the top. The biofilm thickness increased from the bottom to the top of the reactor representing a stratification of the media in the AFBR. The bed porosity increased from the bottom to the top of the reactor.
KeywordsBiofilm characteristics Biomass concentration Anaerobic Fluidized Bed Reactor Currant wastewater Upflow velocity
In recent years many alternatives have been performed to treatment of high-strength wastewaters -. Anaerobic Fluidized Bed Reactors (AFBR) were originally a chemical engineering tool used to perform phase transformations, reactions, and diffusions of various chemicals existing in solid, liquid, and vapor phases. With the concept of maximum diffusion and maximum chemical reaction within a minimum volume in mind, AFBRs have been used in biological wastewater treatment and are utilized in several process configurations -. The results from recent studies have consistently illustrated the technical advantage of the fluidized bed over most other suspended and attached growth biological systems. Typically, in a similar capacity, efficiency of the AFBR can be more than 10 times of the activated sludge system while the total space occupied by AFBR is about 10 percent of the required space for stirred tank in activated sludge process . This is due to the AFBR ability in maintaining high concentration of biomass compared with conventional activated sludge system (40,000 mg L−1 vs. 3000 mg L−1) . Fluidization can overcome operating problems such as bed clogging and high pressure drop, which happen if the media with high surface area used in packed-bed reactor. Another advantage of using media is possibility of elimination of secondary clarifiers . Anaerobic Fluidized bed reactors (AFBR) are high-load wastewater treatment systems, which have been studied by numerous authors to treat different industrial wastewaters. For example, this system has been used for treatment of textile wastewater , ice-cream wastewater , and brewery wastewater , winery wastewater from Grape-Red and tropical fruit , currant  and sanitary landfill leachate . The microbial population is the critical parameter in the performance of biological process that the influenced by operational parameters, physicochemical properties of the carrier material (density, roughness, porosity) on the fixed bed process are critical considerations ,. One of the key operational parameters in attached biofilm reactors is the control of biofilm thickness and configuration, and research on biofilm formation and detachment has developed considerably in the past years, although there is no design rule for the rate of detachment. The prediction of biofilm structure (density, porosity, roughness, shape) and thickness is most important in designing and operation of biofilm processes, because hydrodynamics, mass transfer and conversion in biofilm processes depend on these variables. In attached growth process, biofilm accumulation is a dynamic process that is the net result of growth and the detachment processes. This is affected by several external factors, including composition and concentration of the feed, concentration of particles, particle–particle collisions, and particle–wall collisions, and velocity of the liquid phase (shear stress). This is the most important factor influencing formation, structure and stability of biofilms. In a biofilm system, higher hydrodynamic shear force take a stronger biofilm, and the biofilm tends to become a heterogeneous, porous and weaker structure when the shear force is too weak -.
The main objective of this study was to investigate the influence of different upflow velocity on performance and biofilm characteristics of Anaerobic Fluidized Bed Reactor in treating a real Currant wastewater in various HRT and loading rates.
Materials and methods
Anaerobic Fluidized bed reactor
Organic loading and characteristics of fed during the start-up
COD loading (kg COD/m3)
Currant wastewater a
0.5 - 4
4 - 7
7 - 11
11 - 13
13 - 15
13 - 15
Characteristics of currant wastewater used in the present study
Samples were analyzed for COD according to standard method . Temperature was measured by a thermometer and pH was measured by a pH-meter (E520 Metrohm Herisau). The biofilm thickness was measured using the method of Schreyer and Coughlin , according to the following method. A slurry sample of known volume was smoothly washed to remove the suspended solids and then filtered. The wet bio-particles were carefully removed from the filter into a ceramic dish and weighed to determine its wet mass. After oven-drying for 24 h at 105°C, then cooled in a desiccator and weighed. The dried sample was ignited in a 550°C furnace for 30 min, cooled in a desiccator and then weighed. The difference between two dried weights would yield the weight of immobilized biomass as attached volatile solids (AVS). Also for ensure the results obtained from the Schreyer and Coughlin procedure, the biofilm thickness was measured using a high-resolution microscope equipped with a micrometer  method. In comparison of two measurements, the relative error was always less than 10%. The bio-particle density was measured from its settling velocity and diameter of bio-particle .
Results and discussion
Operational parameters obtained at the end of start-up period for AFBR
OLR, kg COD/m3
Upflow velocity (m/min)CBU
Volume of expanded bed (cm3)
M support (g)
g VSatt/g support
g VSatt/l expanded bed
Effect of organic loading rate and upflow velocity on COD removal
Summary of the average results of the three sets of experiments at steady state
Expanded bed (mm)
9.4 ± 0.2
9.4 ± 0.2
9.4 ± 0.2
10.8 ± 0.2
10.8 ± 0.2
10.8 ± 0.2
13.7 ± 0.3
13.7 ± 0.3
13.7 ± 0.3
18 ± 0.3
18 ± 0.3
18 ± 0.3
24.2 ± 0.5
24.2 ± 0.5
24.2 ± 0.5
Higher biodegrading rates were generally achieved at relatively lower superficial velocities. However there was a minimum practical velocity (0.5 m min−1) below which would agglomeration of media occur in the reactor and the anaerobic process might disrupt. Also the subsequent decrease of the fluidization percentage in 0.5 m min−1 upflow velocity, which is below the minimum fluidization velocity, might have mass transfer limitations caused by accumulation of fatty acids in the reactor . The substrate utilization rate in the biological process, correlated to diffusion resistance, is strongly dependent on reactor design and mixing intensity . In the third set in Vs of 1 m min−1, the reactor performance was lower in compare with the second set with the Vs of 0.75 m min−1, because the biofilm was detached and washed out of the system as a result of the increased shearing force and bed porosity. In the treatment of high-strength distillery wastewater by anaerobic fluidized bed reactor with natural zeolite, COD removals of 80% were achieved at OLR of 20 g COD L.d-1 and HRT of 11 h . In another study with anaerobic fluidized bed reactor for treating ice-cream wastewater, at an organic COD loading rate of 15.6 g L-1. d and HRT of 8 h, COD removal efficiencies of 94.4% was achieved . In the treatment of thin stillage wastewater using an anaerobic fluidized bed with OLR of 29 g COD L.d-1 and HRT of 3.5 h, COD removal efficiencies of 88% was achieved . In the stage 1 and 2, with increasing the upflow velocity, COD removal rate due to appropriate mass balance was improved. But, in the stages 3 to 5, in three set with 0.75 m min−1 upflow velocity, Vs was increased due to the decrease in the biomass concentration, which resulted increase in shearing force and increase in bed porosity, while the organic loading rate in the reactor was increasing.
Effect of the upflow velocity and organic loading rate on the biomass concentration
Biomass concentration, biofilm thickness and particle density profiles along the AFBR
Figure 8 shows the typical pattern of particle density along the AFBR. The biofilm created on the lower levels will be, probably, more dense than that formed in the upper levels as a result of the higher pressure exerted in this zone of the reactor, and this will create denser bio-particles. In the upper part of the bed, a biofilm with a lower density and, proportionally, greater thickness will develop because of the lower pressure presented in this zone. As reported by Zhang and Bishop, the biofilm densities differ with depth within the biofilm layers for the reason that the tops of biofilm are more porous as reported by Zhang and Bishop . The densities in the top layers are usually 5–10 times higher than those in the top layers, and the porosities in the top layers are in the range of 84–93%, while it is in the range of 58–67% in the bottom layers . The lower part of the reactor had denser bio-particles and consequently had lower bed porosity.
Anaerobic fluidized bed reactor with particles made of PVC as the supporting material is highly effective for COD removal for high strength wastewater from currant wastewater. The results demonstrated that the AFBR system is capable of handling an exceptionally high organic loading rate with very high removal efficiency, up to 96.6%. The average biomass concentration per unit volume of the AFBR (as gVSSatt L−1 expended bed) decreased with increase in the upflow velocity at all the applied organic loading rates up to some loading rate as a result of the increase in the bed porosity. The total biomass in the reactor increased with increases in the organic loading rate. The peak biomass concentration (as gVSSatt L−1 expended bed) was observed at the bottom part of the reactor, then it droped off slowly towards the top. The biofilm thickness increased from the bottom to the top of the reactor representing a stratification of the media in the AFBR. The bed porosity increased from the bottom to the top of the reactor.
The overall implementation of this study including experimental design, data analysis and manuscript preparation were done by JJ, AHM, RN, ARM and HK. MH critically reviewed and revised the article. All authors read and approved the final manuscript.
The authors are most grateful to the laboratory staff of the Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Iran, for their collaboration in this research.
- Mahvi A: Application of ultrasonic technology for water and wastewater treatment. Iranian J Public Health 2009, 38: 1–17.Google Scholar
- Karimi B, Ehrampoush MH, Jabary H: Indicator pathogens, organic matter and LAS detergent removal from wastewater by constructed subsurface wetlands. J Environ Health Sci Eng 2014, 12: 52. 10.1186/2052-336X-12-52View ArticleGoogle Scholar
- Mahvi A: Sequencing batch reactor: a promising technology in wastewater treatment. Iranian J Environ Health Sci Eng 2008, 5: 79–90.Google Scholar
- Naghizadeh A, Mahvi A, Vaezi F, Naddafi K: Evaluation of hollow fiber membrane bioreactor efficiency for municipal wastewater treatment. Iranian J Environ Health Sci Eng 2008, 5: 257–268.Google Scholar
- Rajasimman M, Karthikeyan C: Aerobic digestion of starch wastewater in a fluidized bed bioreactor with low density biomass support. J Hazard Mater 2007, 143: 82–86. 10.1016/j.jhazmat.2006.08.071View ArticleGoogle Scholar
- Lohi A, Alvarez Cuenca M, Anania G, Upreti S, Wan L: Biodegradation of diesel fuel-contaminated wastewater using a three-phase fluidized bed reactor. J Hazard Mater 2008, 154: 105–111. 10.1016/j.jhazmat.2007.10.001View ArticleGoogle Scholar
- Chen C-L, Wu J-H, Tseng I-C, Liang T-M, Liu W-T: Characterization of active microbes in a full-scale anaerobic fluidized bed reactor treating phenolic wastewater. Microbes Environments/JSME 2008, 24: 144–153. 10.1264/jsme2.ME09109View ArticleGoogle Scholar
- Rabah FKJ: Denitrification of high-strength nitrate wastewater using fluidized-bed biofilm reactors. Elsevier, City; 2003.Google Scholar
- Shieh WK, Sutton P, Kos P: Predicting reactor biomass concentration in a fluidized-bed system. J Water Pollut Control Fed 1981, 1574–1584.
- Fernandez N, Montalvo S, Borja R, Guerrero L, Sأ،nchez E, Cortأ©s I, Colmenarejo MF, Travieso L, Raposo F: Performance evaluation of an anaerobic fluidized bed reactor with natural zeolite as support material when treating high-strength distillery wastewater. In Book Performance evaluation of an anaerobic fluidized bed reactor with natural zeolite as support material when treating high-strength distillery wastewater. Elsevier, City; 2008:2458–2466.Google Scholar
- Haroun M, Idris A: Treatment of textile wastewater with an anaerobic fluidized bed reactor. In Book Treatment of textile wastewater with an anaerobic fluidized bed reactor. Elsevier, City; 2009:357–366.Google Scholar
- Borja R, Banks CJ: Response of an anaerobic fluidized bed reactor treating ice-cream wastewater to organic, hydraulic, temperature and pH shocks. In Book Response of an anaerobic fluidized bed reactor treating ice-cream wastewater to organic, hydraulic, temperature and pH shocks. Elsevier, City; 1995:251–259. 251–259Google Scholar
- Alvarado-Lassman A, Rustrian E, Garcia-Alvarado MA, Rodriguez-Jimenez GC, Houbron E: Brewery wastewater treatment using anaerobic inverse fluidized bed reactors. In Book Brewery wastewater treatment using anaerobic inverse fluidized bed reactors. Elsevier, City; 2008:3009–3015.Google Scholar
- Montalvo S, Guerrero L, Borja R, Cortأ©s I, Sأ،nchez E, Colmenarejo MF: Effect of the influent COD concentration on the anaerobic digestion of winery wastewaters from grape-red and tropical fruit (guava) wine production in fluidized bed reactors with Chilean natural zeolite for biomass immobilization. Chem Biochem Eng Q 2010, 24: 219–226.Google Scholar
- Jafari J, Mesdaghinia A, Nabizadeh R, Farrokhi M, Mahvi AH: Investigation of Anaerobic Fluidized Bed Reactor/Aerobic Mov-ing Bed Bio Reactor (AFBR/MMBR) System for Treatment of Currant Wastewater. Iran J Public Health 2013, 42: 860–867.Google Scholar
- Turan M, Gulsen H, Celik MS: Treatment of landfill leachate by a combined anaerobic fluidized bed and zeolite column system. J Environ Eng 2005, 131: 815–819. 10.1061/(ASCE)0733-9372(2005)131:5(815)View ArticleGoogle Scholar
- Hobson PN, Wheatley A: Anaerobic digestion: modern theory and practice. Elsevier applied science, London; 1993.Google Scholar
- Speece RE: Anaerobic biotechnology for industrial wastewater treatment. In Book Anaerobic biotechnology for industrial wastewater treatment. ACS Publications, City; 1983:416A-427A.Google Scholar
- Kwok WK, Picioreanu C, Ong SL, Van Loosdrecht MCM, Ng WJ, Heijnen JJ: Influence of biomass production and detachment forces on biofilm structures in a biofilm airlift suspension reactor. In Book Influence of biomass production and detachment forces on biofilm structures in a biofilm airlift suspension reactor. John Wiley & Sons, City; 1998:400–407.Google Scholar
- Chang HT, Rittmann BE, Amar D, Heim R, Ehlinger O, Lesty Y: Biofilm detachment mechanisms in a liquid fluidized bed. In Book Biofilm detachment mechanisms in a liquid fluidized bed. Wiley Online Library, City; 1991:499–506. 499–506Google Scholar
- Van Loosdrecht MCM, Eikelboom D, Gjaltema A, Mulder A, Tijhuis L, Heijnen JJ: Biofilm structures. In Book Biofilm structures. Elsevier, City; 1995:35–43.Google Scholar
- Alves CF, Melo LF, Vieira MJ: Influence of medium composition on the characteristics of a denitrifying biofilm formed by < i > Alcaligenes denitrificans</i > in a fluidised bed reactor. In Book Influence of medium composition on the characteristics of a denitrifying biofilm formed by < i > Alcaligenes denitrificans</i > in a fluidised bed reactor. Elsevier, City; 2002:837–845.Google Scholar
- Koloini T, Farkas E: Fixed bed pressure drop and liquid fluidization in tapered or conical vessels. Can J Chem Eng 2009, 51: 499–502. 10.1002/cjce.5450510416View ArticleGoogle Scholar
- Hsu H: Characteristics of tapered fluidized reactors: two phase systems. In Book Characteristics of tapered fluidized reactors: two phase systems. Dept. of Chemical, Metallurgical and Polymer Engineering; Oak Ridge National Lab., TN (USA), City: Tennessee Univ., Knoxville (USA); 1978.Google Scholar
- Shi YF, Yu Y, Fan L: Incipient fluidization condition for a tapered fluidized bed. Industrial Eng Chem Fundamental 1984, 23: 484–489. 10.1021/i100016a018View ArticleGoogle Scholar
- Peng Y, Fan LT: Hydrodynamic characteristics of fluidization in liquid–solid tapered beds. In Book Hydrodynamic characteristics of fluidization in liquid–solid tapered beds. Elsevier, City; 1997:2277–2290.Google Scholar
- Sen S, Demirer G: Anaerobic treatment of real textile wastewater with a fluidized bed reactor. Water Res 2003, 37: 1868–1878. 10.1016/S0043-1354(02)00577-8View ArticleGoogle Scholar
- Haroun M, Idris A: Treatment of textile wastewater with an anaerobic fluidized bed reactor. Desalination 2009, 237: 357–366. 10.1016/j.desal.2008.01.027View ArticleGoogle Scholar
- Standard Methods for the Examination of Water and Wastewater In Book Standard Methods for the Examination of Water and Wastewater. Mc Graw Hill, City; 2005.
- Schreyer HB, Coughlin RW: Effects of stratification in a fluidized bed bioreactor during treatment of metalworking wastewater. In Book Effects of stratification in a fluidized bed bioreactor during treatment of metalworking wastewater. Wiley Online Library, City; 1999:129–140.Google Scholar
- Hidalgo M: Start-up, microbial adhesion in anaerobic fluidized bed bioreactors (Estudio de la puesta en marcha y adhesi!on de microorganismos en biorreactores anaerobios de lecho fluidizado). University of Valladolid, Spain; 1999.Google Scholar
- Farhan MH, Chin Hong PH, Keenan JD, Shieh WK: Performance of Anaerobic Reactors during Pseudo Steady State Operation. J Chem Tech Biotechnol 1997, 69: 45–57. 10.1002/(SICI)1097-4660(199705)69:1<45::AID-JCTB638>3.0.CO;2-2View ArticleGoogle Scholar
- Koloini T, Farkas EJ: Fixed bed pressure drop and liquid fluidization in tapered or conical vessels. In Book Fixed bed pressure drop and liquid fluidization in tapered or conical vessels. Wiley Online Library, City; 1973:499–502.Google Scholar
- García-Bernet D, Buffiere P, Elmaleh S, Moletta R: Application of the down-flow fluidized bed to the anaerobic treatment of wine distillery wastewater. Water Sci Technol 1998, 38: 393–399. 10.1016/S0273-1223(98)00716-1View ArticleGoogle Scholar
- Perez M, Romero L, Sales D: Comparative performance of high rate anaerobic thermophilic technologies treating industrial wastewater. Water Res 1998, 32: 559–564. 10.1016/S0043-1354(97)00315-1View ArticleGoogle Scholar
- Rozzi A: Operational and control parameters in anaerobic processes. In Book Operational and control parameters in anaerobic processes. City; 1986.
- Kato MT, Field JA, Kleerebezem R, Lettinga G: reatment of low strength soluble wastewaters in UASB reactors. In Book Treatment of low strength soluble wastewaters in UASB reactors. 77th edition. Elsevier, City; 1994:679.Google Scholar
- Andalib M, Hafez H, Elbeshbishy E, Nakhla G, Zhu J: Treatment of thin stillage in a high-rate anaerobic fluidized bed bioreactor (AFBR). Bioresour Technol 2012, 121: 411–418. 10.1016/j.biortech.2012.07.008View ArticleGoogle Scholar
- Rabah FKJ, Dahab MF: Biofilm and biomass characteristics in high-performance fluidized-bed biofilm reactors. In Book Biofilm and biomass characteristics in high-performance fluidized-bed biofilm reactors. 38th edition. Elsevier, City; 2004:4262–4270.Google Scholar
- Zhang TC, Bishop PL: Density, porosity, and pore structure of biofilms. Water Research 1994, 28: 2267–2277. 10.1016/0043-1354(94)90042-6View ArticleGoogle Scholar
- Zhang TC, Bishop PL: Structure, activity and composition of biofilms. In Book Structure, activity and composition of biofilms. 29th edition. City; 1994:335–344.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.