A coupling model for EGSB bioreactors: Hydrodynamics and anaerobic digestion processes

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<ul><li><p>Chemical Engineering and Processing 50 (2011) 316324</p><p>Contents lists available at ScienceDirect</p><p>Chemical Engineering and Processing:Process Intensication</p><p>journa l homepage: www.e lsev ier .co</p><p>A coup dydigesti</p><p>Mauren Fa INGAR - (CONb Depto de Cienc CAIMI-UTN FRd Facultad de In</p><p>a r t i c l</p><p>Article history:Received 31 JaReceived in reAccepted 23 JaAvailable onlin</p><p>Keywords:Dynamic modThree-phase sEGSB reactorsWastewater tr</p><p>ouplgranic (gaed on. A nophences wood aropoctor.</p><p> 2011 Elsevier B.V. All rights reserved.</p><p>1. Introduction</p><p>The exphigh rate teby De Manin the lastbe considerblanket (UAanaerobic das proteins,amino acidtion to acetnally utiliz[46].</p><p>Both EGto form denthe EGSB reby a high resludge expcontact witSince highedemand CO</p><p> Correspon3657 (3000) S</p><p>E-mail add</p><p>duction is also higher, improving even more the mixing inside thereactor.</p><p>0255-2701/$ doi:10.1016/j.anded granular sludge bed (EGSB) reactor is a superchnology for wastewater treatment. It was introducedet al. [1] and has attained an increasing popularity</p><p>decade [2,3]. The conception of the EGSB reactor caned as an improvement of the upow anaerobic sludgeSB) reactor developed by Lettinga et al. [3]. In theigestion processes, complex organic substrates suchlipids, and carbohydrates are hydrolyzed into soluble</p><p>s, fatty acids, and sugars, followed by the fermenta-ate, formate, hydrogen, and carbon dioxide which areed by methanogenic microorganism to form methane</p><p>SB and UASB are based on the ability of microorganismse aggregates by autoimmobilization. However, insideactor, the higher upow velocities, which are causedcycle rate and a high height/diameter ratio, cause the</p><p>ansion through the whole reactor thus improving itsh the efuent and reduce the unit dead volume [7,8].r organic loading rates (up to 40kg of chemical oxygenDm3 d1) can be accommodated in EGSB, the gas pro-</p><p>ding author at: INGAR - Instituto de Desarrollo y Diseno- Avellanedaanta Fe, Argentina. Tel.: +54 342 4534451; fax: +54 342 4553439.ress: mfuentes@santafe-conicet.gov.ar (M. Fuentes).</p><p>The exact mixing pattern cannot be generalized, and it must beevaluated in each reactor by assessing the reactor hydrodynam-ics [9]. However, a fully expanded EGSB reactor can be consideredas a completely mixed tank [10,11], and liquid lm mass transferresistance seems to be negligible [12]. The knowledge of the bedexpansion plays an important role in the design and operation ofan EGSB reactor, because it is the key point to reach a compromisebetween bed expansion and sludge washout, and the stability andperformance of the EGSB system would be sensitive to the degreeof expansion [13].</p><p>Some ideas from solid dynamics in a three-phase uidizedbed reactor can be used to describe the multiple solidliquidgasinteractions that take place in EGSB reactors. In previous works,a heterogeneous model for three-phase anaerobic uidized bed(AFB) reactors was developed and validated [1416]. The aimof this work is to apply this methodology for modeling EGSBreactors. Thus, a heterogeneous model for EGSB bioreactors is pre-sented here. This modeling approach combines the dynamics ofthe three phases present in the reactor including biochemical,physico-chemical and hydrodynamic processes. Several details ofreactor design, sludge and wastewater characteristics, and opera-tional conditions are required formodel adjustment and validation.Almost all works published describe better the biochemical perfor-mance of EGSB reactors than their hydrodynamics. Due to the lackof information on some parameters that can be measured and are</p><p>see front matter 2011 Elsevier B.V. All rights reserved.cep.2011.01.005ling model for EGSB bioreactors: Hydroon processes</p><p>uentesa,b,, Nicols J. Scennaa,c, Po A. Aguirrea,d</p><p>ICET-UTN), Avellaneda 3657 (3000) Santa Fe, Argentinacias Bsicas - UTN FRSF, Lavaise 610 (3000) Santa Fe, ArgentinaR, Zeballos 1341 (2000) Rosario, Argentinag. Qca, UNL, Santiago del Estero 2829 (3000) Santa Fe, Argentina</p><p>e i n f o</p><p>nuary 2010vised form 10 January 2011nuary 2011e 1 February 2011</p><p>eling and simulationystems</p><p>eatment</p><p>a b s t r a c t</p><p>The aim of this paper is to present a cobic digestion processes in expandedThe bioreactor is modeled as a dynamimental data of three case studies basused to adjust and validate the modelfor calculating the biomass transportthis parameter. Bioreactor performanCOD, VFA and VSS concentration. A gvalues. It seems to indicate that the phydrodynamic successes in the bioream/locate /cep</p><p>namics and anaerobic</p><p>ing model for calculating both the hydrodynamic and anaer-ular sludge bed (EGSB) bioreactors for treating wastewaters.ssolidliquid) three-phase system. An existing set of exper-the start-up and operational performance of EGSB reactors isvel parameter, the specic rate of granule rupture, is denedomena. Values around 11020 dmd2 g1 are calculated forere analyzed through the main variable proles such as pH,greement was obtained among experimental and predicted</p><p>sed EGSB model is able to reproduce the main biological and</p></li><li><p>M. Fuentes et al. / Chemical Engineering and Processing 50 (2011) 316324 317</p><p>not reported, the authors should solve the initialization problemvia simulation, i.e. a sensitivity analysis of model results related tothese parameters is required.</p><p>The paper is organized as follows: in Section 2, main mathe-matical equhypothesesdiscussed.solution usment and vcase studieof EGSB readrawn in Se</p><p>2. Mathem</p><p>As mengassolidl(granules) cphase is comproducts, esingle suspThe gas phastages.</p><p>The globmodel prevare: (1) theand (3) thebetween bophase and hcuss theseequations h</p><p>2.1. Anaero</p><p>The ana(growth-upphysico-chegasliquidbioreactor.model para</p><p>[9,1416].H</p><p>are summaA novel a</p><p>aggregationmodeling threlated tobe considerbioreactor.than in granuid veloci</p><p>Tiwari etemperaturconcentraticoncluded talkalinity is(2) the natugranular difof the graniron may encellular polcementatioand mass tr</p><p>In this work, the parameter specic rate of granule rupture krhas been dened for calculating the biomass transport phenom-ena. This parameter explains how the process of granulation isaffected by all these environmental andoperational conditions, and</p><p>of thenzye invode</p><p>regaergy</p><p>n, </p><p>of eable A</p><p>krX</p><p>eteritivitted i</p><p>opar</p><p>eralh con. Thus, tch, het b</p><p>ss traed. Tbiopmake diah thusedn [1</p><p>2</p><p>d</p><p>mbesed be of o</p><p>VSVbp</p><p>utincalcu</p><p>dbp3</p><p>XST is(i</p><p>ydrod</p><p>ractesed bations of the global model are presented, and somerelated to thebioparticlemodel andhydrodynamics areComputational aspects of model implementation anding gPROMS are described in Section 3. Model adjust-alidation using an existing set of experimental data ofs based on the start-up and operational performancectors is presented in Section 4. Finally, conclusions arection 5.</p><p>atical model</p><p>tioned, the EGSB is modeled as a three-phaseiquid system. The solid phase consists of bioparticlesomposed by active and non-active biomass. The liquidposed by the chemical species in solution (substrates,</p><p>nzymes, ions, and water) and (active and non-active)ended cells, which are assumed to behave as solutes.se is formed by the gaseous products from degradation</p><p>al EGSB model results analogous to the AFB reactoriously published [1416]. The main subsystem modelsanaerobic digestion model; (2) the bioparticle model;hydrodynamics model. Since the main differences</p><p>th technologies are based on characteristics of the solidydrodynamics, the paper is essentially oriented to dis-</p><p>aspects. Some hypotheses and the main mathematicalave been rewritten for better comprehension.</p><p>bic digestion model</p><p>erobic digestion model involves the biochemicaltake, death, hydrolysis and disaggregating) andmical (system charge balance for calculating pH,mass transfer) processes which take place in theAll terms related with mass transfer processes,</p><p>meters and constants have been previously described</p><p>owever, themain rate expressions</p><p>j</p><p>Rjik +</p><p>j</p><p>T jik</p><p>rized in Table A.1 of Appendix A.spect in the EGSB model is related to modeling the dis-of single suspended cells from biomass granules. Fore disintegration of aggregates, some physical aspects</p><p>the structure and compactness of granules need toed. Hydrodynamics affects biomass processes inside aThese effects are more pronounced in uidized bedsular sludge bed reactors, attending to the operational</p><p>ty ranges [7,17].t al. [18] studied the inuence of some factors such ase, alkalinity, natureandstrengthof substrate, andcationon on granule formation in sludge bed reactors. Theyhat: (1) a careful temperature control and an adequaterequired for generation and maintenance of granules;re and strength of substrate in conjunction with intra-fusion to a large extent determines the microstructureules; and (3) the divalent cations such as calcium andhance granulation by ionic bridging and linking exo-</p><p>ymers. However, their presence in excess may lead ton due to precipitation leading to increased ash contentansfer limitation.</p><p>differsto thetors arother m(disaggthe en</p><p>functio</p><p>tration(see Ta</p><p>rri = SParamA senspresen</p><p>2.2. Bi</p><p>Genthe asfractioand thapproastant wNo maassumout the</p><p>Forgranuling witrate isfunctio</p><p>ddbpdt</p><p>=</p><p>The nuexpresvolum</p><p>Nbp =</p><p>Substitcan be</p><p>ddbpdt</p><p>=</p><p>where</p><p>phase</p><p>2.3. H</p><p>Chaexprese specic rate of biomass hydrolysis, which is relatedme attack on non-active biomass. Since several fac-olved in the stability and formation of granule, and noling approach has been published, the rate of granuleting) rupture is modeled as a rst-order function ondissipation parameter (which is an upow velocity</p><p>=Uo( p/ z), p/z = g</p><p>k</p><p>kk), and mass concen-</p><p>ch microbial species present in the biomass aggregates.1):</p><p>Si (1)</p><p>kr has been assumed the same for all biological species.y analysis of model results related to this parameter isn Section 4.</p><p>ticle model</p><p>ly, the granule composition has been described fromntent, moisture and (active and non-active) biomassese parameters can vary during the granule formation,he dry density of granules varies. As a rst modelingomogeneous biomass distribution on granules, con-iomass density and spherical geometry are assumed.nsfer limitations in the granule and the liquid bulk are</p><p>he substrate concentration has the same value through-article.ing the model workable, a simplifying assumption onmeter dbp is considered. A simple relationship deal-e net biomass growth-decay-hydrolysis-disaggregatingto calculate the average granule diameter as a time</p><p>9]:</p><p>2bp</p><p>dVbpdt</p><p>= 2d2bp</p><p>V</p><p>i,j</p><p>RjiS +</p><p>i,j</p><p>T jiS</p><p>Nbps(1 ACbp/100)(1 MCbp/100)(2)</p><p>r of bioparticles Nbp in the control volume (V) can bey dividing the total sludge volume (VS) by the averagene aggregate (Vbp):</p><p>= VSXST</p><p>S(1 ACbp/100)(1 MCbp/100)6</p><p>d3bp(3)</p><p>g Eq. (3) into Eq. (2), time variation of granule diameterlated as:</p><p>i,j</p><p>RjiS +</p><p>i,j</p><p>T jiS</p><p>SXST</p><p>(4)</p><p>the total concentration of biological species in the solid</p><p>(XSi a + XSina)</p><p>).</p><p>ynamics model</p><p>ristics of phase mixture and ow patterns arey the hydrodynamic model. Since the EGSB is assumed</p></li><li><p>318 M. Fuentes et al. / Chemical Engineering and Processing 50 (2011) 316324</p><p>Table 1Details of experimental studies used in the adjustment and validation of the model.</p><p>Parameter (dimension)/case studya R1 R2 R3</p><p>Reactor designWorking r 157Inner diam 2Height of t 50</p><p>Sludge charaBiomass c 4.6Initial load ndAsh conte ndMoisture c ndGranule m nd (Granule de nd (</p><p>Steps (distur ITime horiz 113</p><p>WastewaterInuent TC 126Inuent SC 56Inuent V 42Inuent pH 6.9Substrate XL</p><p>OperationalTemperatu 29.7HRT (d) 0.17OLR (gCOD 0.64Biomass c 6.4</p><p>HydrodynamStatic bed nd (Bed poros nd (Inuent o 945Liquid up 300Recycle o 0</p><p>a R1-Verone itten bb See section</p><p>to behave aof the highconsidered.</p><p>In EGSBsettling chasuggest thadancewithow rangewith the Allintermediatof the granabove work</p><p>Liu et alheight assucategory ofknown Richexpansion,velocity (Utstatement oselected hetions for calsupercial v</p><p>From thand makingcalculated a</p><p>H = H0(1 +</p><p>Since param(see Table BHo and o a</p><p>Biochemexpanded gtion, the coalgebraic eq</p><p>ase c</p><p>put</p><p>mats moeactor volume (dm3) 1.3eter (dm) 0.53he water level (dm) 6.2cteristicsoncent. (Gvss dm3) 43.4(dm3) 0.23</p><p>nt (%) 19ontent (%) 94.8ean diameter (102 dm) 2.30.2nsity (gdm3) 1026bances) I II IIIon/step (d) 28 30 20characteristicsOD (mgdm3) 44451 44451 44451OD (mgdm3) nd, 262 as SHAc nd nd</p><p>SS (mgdm3) 7536 7536 75368.90.4 8.90.4 8.90.4</p><p>composition (%COD)b XCHXPXLiSHAc: 3944116characteristicsre (C) 302.0 302.0 302.0</p><p>0.33 0.25 0.17dm3 d1) 1.33 1.78 2.66</p><p>oncent. (gVSSdm3) 10.00 10.06 10.43ic characteristicsheight (dm) nd (2.48)ity (dm3 dm3) nd (0.4)w rate (dm3 d1) 3.89 5.21 7.78ow velocity (dmd1) 2568 1968 2353w rate (dm3 d1) 563 429 511</p><p>z et al. [28], R2-Kato et al. [29], R3-Brito and Melo [12]. The assumed values are wrnomenclature for notation.</p><p>s a continuous stirred tank reactor due to the effectsrecirculation rate, a completely mixed ow pattern is</p><p>reactors, the bed expansion is closely related to theracteristics of the sludge. Almost all works publishedt the mean settling velocity of the granules is in accor-Stokes lawbecause the settlingprocess is in the laminar</p><p>for phB.</p><p>3. Com</p><p>Theproces[2022], whilst others suggest that it is in accordanceen formula because the settling process falls within thee ow range [23]. However, the settling characteristicsules have scarcely been discussed theoretically by theers.. [11] proposed the Eq. (5) for calculating the EGS bedming that the settling process of the granules is in theintermediate ow regime. The authors used the wellardson and Zaki [24] correlations to calculate the bedthe expansion coefcient (n) and the terminal settling). This approach is in accordancewith themathematicalf the generalized bubble and wake model (GBWM [25])re to describe the three-phase system. GBWM equa-culating uidization characteristics (phase holdup andelocity) are summarized in Table B.1 of Appendix B.</p><p>e denition of bed expansion, using the ow equation,mathematical transformations, the bed height can bes [11]:</p><p>e(ln U0/Ut)/n 01 e(ln U0/Ut)/n</p><p>)(5)</p><p>eters Ut and n are functions of biomass concentration.1), the bed height is also a biomass function. Propertiesre calculated at the static bed condition.ical processes are assumed to occur only in theranular sludge zone. As the bed height is a time func-ntrol volume assumed to compute the differential anduation (DAE) system varies. Mass balance equations</p><p>prise Ltd.).[26,27]. Lowinitial valustudies, 68%(XGL, XAA) aspecies areies describePentium IV</p><p>4. Results</p><p>4.1. Case st</p><p>An exist[28], Kato eup and opeadjust andstudies havof reactor dational con</p><p>4.2. Model</p><p>There arfor model aare not repoters related.5 0.480.4183.53</p><p>1170.09ndnd</p><p>2.3) 1.61026) nd (1026)</p><p>II III I92 124 nd</p><p>53 1800.150 15648 128022 7931 5519 128027 5429 6330 00.1 6.70.2 6.90.2 7</p><p>XCHXPSHAc: 2991151 SHAc: 100</p><p>1.7 30.32.0 321.9 240.17 0.17 0.070.92 0.80 18.299.2 8.0 19</p><p>12.06) 0.660.4) 0.4</p><p>945 945 6.85600 900 4800945 1890 652</p><p>etween parentheses.</p><p>omponents are described in Table B.1 of Appendix</p><p>ational aspects</p><p>hematicalmodelwas implementedandsolvedusing thedeling software tool gPROMS (Process Systems Enter-</p><p>A high-index DAE system (index&gt;1) was veriedsteady...</p></li></ul>