CONFERENCE PROCEEDINGS VOLUME I

Transcription

1 FILTECH 005 CONFERENCE PROCEEDINGS VOLUME I Conference Date: October -3, 005 Venue: Organizer: Rhein-Main-Hallen Rheintr Wiebaden Germany Filtech Exhibition Germany PO Box Meerbuch Germany phone: +49 (0) fax: +49 (0) Info@FiltechEuropa.com web: CONTENT VOLUME I L-Seion Scientific Committee I- Seion Survey I- 3 Plenary Lecture I- Paper L-Seion I-4 Keyword Lit (Page Indicator) I- 659 CONTENT VOLUME II G-Seion M-Seion Scientific Committee II- Seion Survey II- 3 Paper G-Seion II- Paper M-Seion II- 49 Keyword Lit (Page Indicator) II- 687 FILTECH 005 Page I-

2 SIMULATION OF LIQUID PHASE ACCUMULATION AT CENTRIFUGAL DEWATERING OF ACTIVATED SLUDGE M. Mota *, J. Teixeira, G.N. Abaev, I. Yelhyna, and A. Yelhin Centro de Eng. Biológica, Univerity of Minho, Campu de Gualtar, Braga, Portugal Polotk State Univerity, BY-440, Novopolotk, Belaru ABSTRACT Centrifugation of activated ludge i a frequently ued dewatering proce but there i a need for a fitting function for moderate and high ludge concentration. In particular, liquid phae accumulation kinetic during centrifugation may be ued a a ource of information about edimentation propertie and governing mechanim of the cake formation. Thi will allow the obtention of the optimal parameter for the dewatering control and proce optimiation. For thi purpoe, activated ludge at different concentration wa invetigated on a laboratory centrifuge with centrifugation factor 667. The following ludge were ued in the experiment: ) activated ludge from thickener (with and without floculant treatment); ) ludge after indutrial centrifuge decanter Flottweg Z6-4 collected from dumping pound; ludge () after anaerobic treatment; ludge () with a dipered olid additive. Baed on the obtained data, the following aumption wa made: ettling of the olid phae and cake compaction depend on the hindered ettling velocity and ediment compreion. Due to the applied centrifuge force, a primary cake keleton from particular aggregate and floc i formed. During thi tage, free water i diplaced from the pace between aggregate/floc with a further tranition to the compaction of the ediment with the water being diplaced from the pore of the floc by a filtration mechanim until an equilibrium condition i reached. The liquid volume V v. time t at hindered ettling and ediment dewatering can n be repreented in the form V t, where n.0. Therefore, in log-log coordinate, the kinetic of liquid accumulation have a linear dependence lg( V ) n lg( t) in both ettling and compaction tage. Thi aumption wa confirmed for different type of activated ludge. Uing aymptotical analyi in the function form F ( t, V ), a dimenionle fitting function wa obtained that decribe the centrifugation of activated ludge. For highly concentrated ludge, it wa found that the dewatering occur a cake compreion. Analyi of deformation model lead to the concluion that for the compreible cake it i neceary to introduce a parameter characteriing the cake platicity dependence on the centrifugation time. Developed model wa ued for fitting numerou experimental data. The main advantage of propoed model i the poibility to fit the liquid phae accumulation kinetic during centrifugation in a wide range of the activated ludge concentration, from upenion up to tructured and pate-like cake conitency. The extenion of thi model to other lurrie require further invetigation. KEYWORDS Activated Sludge, Centrifugation, Dewatering, Filtration, Simulation FILTECH 005 Page I- 4

3 Introduction Analyi of upenion edimentation and centrifugation i preented in numerou work -4. The exitence of different phyico-chemical factor involved in the centrifugal decanting proce i not favourable for the obtention of a general olution of the problem. Frequently model are baed on data for defined initial and boundary and a large volume of experimental meaurement i required. Neverthele, with changing lurry (for intance, activated ludge) propertie, model prediction can ignificantly deviate from experimental. That i the reaon for the application of emi-empirical model for edimentation and centrifugation 5. In the work 6 the ediment growth velocity i given a dh dt k ( h h ) () / where h i the ediment thickne, t the edimentation time, h i the equilibrium thickne of the ediment at t, and k i the coefficient. In Eq. () h h may be conidered a a meaure of the dipered ytem deviation from the equilibrium. If we conider the edimentation in the form of a normalied variable v V / V, where V and V e are the decanted liquid volume at time t and at equilibrium, repectively, then k t ln( ) and v v exp( k t ) () Another model, propoed for an activated ludge, take the form of double exponentional decay 7 dv dt Aexp( k t) B exp( k ) (3) / t where A, B, k and k are coefficient. Centrifugation of activated ludge i a frequently ued dewatering proce but, due to the wide range of ludge propertie, relation adequately decribing the dewatering kinetic data are till miing. There i a need for a fitting function for moderate and high ludge concentration, in particular, for the liquid phae accumulation kinetic during centrifugation. Activated ludge at different concentration wa invetigated on a laboratory centrifuge with centrifugation factor K c = 667: ) activated ludge from thickener (with and without floculant treatment); ) ludge after indutrial centrifuge decanter Flottweg Z6-4 collected from dumping pound; ludge () after anaerobic treatment; ludge () with a dipered olid additive. Analyi of the centrifugation kinetic and model determination Baed on the obtained data, preented below in Fig 6-9, the following aumption wa made: ettling of the olid phae and cake compaction depend on the hindered ettling velocity and ediment compreion. Due to the applied centrifuge force, a primary cake keleton from particular aggregate and floc i FILTECH 005 Page I- 4

4 formed. During thi tage, free water i diplaced from the pace between aggregate/floc with a further tranition to the compaction of the ediment with the water being diplaced from the pore of the floc by a filtration mechanim till an equilibrium condition i reached at t. The liquid volume at hindered edimentation and ediment dewatering can be n repreented in the form V t, where n.0. Therefore, in log-log coordinate, the kinetic of liquid accumulation mut have a linear dependence lg( V ) n lg( t), if the proce i controlled by a ingle mechanim, or compoed by a erie of different linear function if during dewatering one mechanim change to another. Thi aumption wa confirmed for different type of activated ludge. In Fig., a an example, the dependence of the liquid volume on time for different type of activated ludge i hown, where TDS mean the total diolved olid V, ml 0 3 V, ml t, min 0, 0 00 (a) (b) Figure. Experimental data on the centrifugation of activated ludge. (a): activated ludge with.6 % TDS, activated ludge treated by flocculant Sedipure (.9 mg Sedipure/g TDS), 3 activated ludge centrifuged on an indutrial decanter centrifuge after anaerobic treatment with 6.64 % of TDS. (b): activated ludge centrifuged on an indutrial decanter centrifuge with 0.6 % TDS, the ame with.67 % TDS, 3 the ame with.7 % TDS + cement in amount of 50 % of TDS. A may be een, Fig., the oberved dependence are well fitted by a linear relation. A model that may cover the entire range of concentration of the activated ludge will be developed. In thi model, the liquid phae volume V obtained during centrifugation i aumed a the main variable. Uing aymptotical analyi in the function form F ( t, V ) atifying the condition lim F F0( V ) and lim F F ( V ), the obtained dimenionle fitting function i t 0 t t, min p p V / V v ( t / t*) /[ a ( t / t*) ] (4) Where, in our cae, F 0 ( V ) = 0 and F ( V ) V ; v [0, ]; a, t * and p are the model p parameter. At ( t / t*), v.0. Due to the pecific propertie of the activated ludge, parameter a, t * and p are variable. For intance, the activated ludge ettling propertie are affected by the coagulation/flocculation pre-treatment coagulation/flocculation, the ratio of FILTECH 005 Page I- 43

5 organic/non-organic component in olid, etc. and, therefore, the ettling kinetic will be different. However, if the centrifugal dewatering play a key role, the ettling kinetic in the coordinate v t will reult in erie of imilar curve, Fig.. Figure. Dependence of v on t for the activated ludge preented in Fig. a. Auming Eq. (4) a the bai of the model, the value of the model parameter a, t * and p are obtained. Centrifuge ettling. Uually in the edimentation model, the main variable i the ediment (cake) thickne, Eq. (). By analogy, in centrifuge dewatering, the volume of the obtained fugate can be repreented a: v k ( v) t (5) where k i a parameter dependent on the centrifugal force and ludge propertie, ha the dimenion of [ / t ] and can be conidered a the proce velocity contant. A follow from Eq. (5), the experimental data mut fit the relation v /( v) t, at leat in the initial dewatering tage. Fig. 3 preent the experimental data for the activated ludge centrifugate together with the expecting linear trend. (a) (b) Figure 3. Experimental data and linear relation v /( v) v. t obtained from the data preented in Fig.. Legend ee in Fig.. FILTECH 005 Page I- 44

6 Rearranging Eq. (5) the equation for hindered ettling i obatined: v k t /( k t) (6) Comparing Eq (4) and (6), the following value of the model parameter are obtained: a =.0; p =.0 and t * / k. At the initial ettling tage, when k t, v k t. Moreover, if t t * then v = 0.5, hence, parameter t * correpond time when v = 0.5 or V V /. Centrifugal queezing. From the tructured cake, queezing under centrifuge force can remove an additional volume of liquid. In thi phae, the cake poroity become a function of the time. The dewatering for highly concentrated ludge occur a cake i compreed and it platicity change. Analyi of deformation model lead to the concluion that for the compreible cake, the time coefficient t * become dependent on the dewatering time t. It i poible to aume * m m * t p t t* t / k, where 0 m and when m = 0 then t p t *. For the cae of p =, Eq. (4) become: m m v k t /( k t ) (7) Parameter m characterie the cake platicity dependence on the centrifugation time and need further invetigation and analyi. The value of m can be calculated from the dewatering kinetic data at any i -th ( t, v ) point by: i i lg[ vi /( vi ) / k ] m (8) lg( t ) Effect of parameter t * ( / k ) and m are hown in Fig. 4. A can be een, with an increae in the hydraulic reitance (increaing of / k ) the time needed to reach a defined centrifugate volume increae and the initial dewatering velocity decreae. i (a) (b) Figure 4. Dependence v on t * at (a) m = 0, hindered ettling regime, and (b) m 0, / = 0.5 min, queezing regime. k FILTECH 005 Page I- 45

7 m In the initial dewatering tage, the inequality kt.0 i valid and Eq. (7) become b m v k t (9) b Equation (9) ha imilaritie with the empirical filtration equation V kt, where parameter b characterie the filtration complexity (for intance, cake pore blocking) and i in the range The limiting value b =.0 correpond filtration of pure liquid through tationary cake (wahing regime). The parameter b ha the imilar meaning and, therefore, when m = 0 then b =.0 and the dewatering proce in thi condition characterie by the liquid removal from interparticle (inter-floc) pace by pore. At b <.0 the dewatering proce tranform to the queezing of tructured cake aggregate with changing the cake poroity with time and releae inta-floc liquid. The knowledge of the dewatering velocity dv / dt i important for the proce control and optimiation. Dewatering velocity w i obtained from Eq. (7) at m > 0: m m w dv / dt k ( m) /[ t ( k t ) ] (0) When m = 0, Eq. (0) decribe the dewatering velocity at hindered ettling regime w k /( kt). In the limited cae of m.0, w 0. In Fig. 5 the dependence of dv / dt on the dewatering time i preented (a) at k =.0 (min - ), for different value of m and (b) at different regime, repectively. Effect of k variation i hown in Fig. 5b at m = 0 and 0.. (a) Figure 5. (a) Dependence of dv / dt on t, Eq. (0), (a): for (b) k = min - for different value of m and (b) effect of k on dv / dt ; curve 5, m = 0 (ettling regime) and curve 5, m = 0. (queezing). Value of k are the following: and 5.0; and.0; 3 and 3.0; 4 and 4 0.5; 5 and From Fig 5, it follow that the dewatering kinetic i characteried by two period of moderate and fat reduction of the dewatering velocity w dependence on k and FILTECH 005 Page I- 46

8 m. Conidered model confirm conventional obervation that the dewatering efficiency increae with m 0 and with the reduction of the ediment (cake) hydraulic reitance / k. Fig. 6 repreent the dependence of the decanted fluid volume on time, for activated ludge at different concentration. The dependence of t * / k on the flocculant doage i given in Fig. 7 together with correponding fitting function. A may be een, parameter t * i well correlated with the flocculant concentration making poible to define the optimal doage for maximum dewatering of the ludge. V, ml t*, min t, min flocculant, mg/g TDS Fig. 6 Fig. 7 Figure 6. Dependence of the decanted fluid volume on t for activated ludge with different TDS: -.8% TDS; - 0.6% TDS; % TDS (obtained by mixing equal volume of dumped ludge with 3.96 % TDS and ludge with.56 % TDS treated by flocculant Sedipure at a 0.9 g/kg concentration). Solid line correpond to Eq. (7) at m = 0 (line and ) and m = 0.5 (line 3). Figure 7. Dependence of t * (Eq. 6) on the flocculant concentration in the activated ludge with % TDS. Line and are, repectively, cubic and quare fitting function. It wa determined that up to TDS 7 8% the value of the parameter m for activated ludge dewatering in centrifuge can be aumed equal zero. Dependence of t * on TDS i hown in Fig. 8. An increae in the parameter / k i oberved until 7 8 %TDS activated ludge, remaining contant for larger TDS value. The data i fiited by the function / k.5/{ / exp[( 0 3.4) / 0.79]} with a regreion coefficient of Starting from 7 8% TDS, a tranition from ettling regime to the filtration regime with m > 0 i oberved correponding to qualitative change in the cake tructural propertie. The validity of the model decribed by Eq. 7 validity at high TDS concentration i hown in Fig. 9 for anaerobic treated mixture of activated ludge and potato peel. Volumetric proportion between ludge and peel i :. Sample to 4 are treated by flocculant Sedipure. Centrifugated lurrie are repreented by a non-homogeneou tructured ytem that ignificant hamper the dewatering proce. Value of m were: 0.5, - 0.8, 3 0.4, and FILTECH 005 Page I- 47

9 Fig. 8 Fig. 9 Figure 8. Dependence of / k on TDS: AS activated ludge; AS+Floc AS treated by flocculant; CAS AS after indutrial centrifuge decanter; AnAS anaerobic AS; AS+M mixture of AS with clay (:3); AS-CAS mixture AS and CAS (:volume). Figure 9. Centrifugation kinetic of an anaerobic treated mixture of activated ludge and potato peel (: volume). organic fraction 0.47 in 5,78% TDS; the ame a () treated by 8.7 g flocculant/kg TDS; 3 organic fraction 0.6 in 8.58% TDS with 5.4 g flocculant/kg TDS; 4 organic fraction 0.5 in 3.99% TDS with 4.8 g flocculant/kg TDS. The main advantage of the propoed model i the poibility to fit the liquid phae accumulation kinetic during centrifugation in a wide range of the activated ludge concentration, from upenion up to tructured and pate-like cake conitency. Reference. Wahlberg, E.J., Keinath, T.M Development of ettling flux curve uing SVI. J. Water Pollut. Contr. Fed., 60 (), Tiller, F.M., Hyung, N.B Unifying the theory of thickening, filtration, and centrifugation. Wat. Sci. Tech., 8 (), Garrido, P., Bürger, R., Concha, F Settling velocitie of particulate ytem:. Comparion of the phenomenological edimentation conolidation model with publihed experimental reult. Int. J. Miner. Proce., 60, Bürger, R., Concha, F., Tiller, F.M Application of the phenomenological theory to everal publihed experimental cae of edimentation procee. Chem. Eng. J. 80, Tarrer, A.R A model for continuou thickening. AIChE Symp. Ser., 74 (73), Romankov, P.G., Kurochkina, M.I. 98. Hydro-mechanical Procee of the Chemical Technology. Khimia: Leningrade. 7. Lin, D.P., Leen, C., Cooper, P Kinetic and tatitical approach to activated ludge edimentation. J. Water Pollut. Contr. Fed., 5 (7), FILTECH 005 Page I- 48