Effects of feeding time and organic loading in an anaerobic sequencing batch biofilm reactor (ASBBR)
Journal of Environmental Management 85(2007)927–935
Effects of feeding time and organic loading in an anaerobic sequencing
batch bio?lm reactor (ASBBR)treating diluted whey
Leonardo H.S.Damasceno a ,Jose
A.D.Rodrigues b,?,Suzana M.Ratusznei b ,Marcelo Zaiat a ,Euge nio Foresti a
a Departamento de Hidra ′ulica e Saneamento,Escola de Engenharia de Sa ?o Carlos,Universidade de Sa ?o Paulo (USP),Sa ?o Carlos-SP,Brazil
b
Departamento de Engenharia Qu?
′mica e de Alimentos,Escola de Engenharia Maua ′,Instituto Maua ′de Tecnologia,Caetano do Sul-SP,Brazil Received 28June 2005;received in revised form 23October 2006;accepted 1November 2006
Available online 20December 2006
Abstract
An investigation was carried out on the performance of an anaerobic sequencing batch bio?lm reactor (ASBBR)treating diluted cheese whey when submitted to different feed strategies and volumetric organic loads (VOL).Polyurethane foam cubes were used as support for biomass immobilization and stirring was provided by helix impellers.The reactor with a working volume of 3L treated 2L of wastewater in 8-h cycles at 500rpm and 30 C.The organic loads applied were 2,4,8and 12gCOD L à1d à1,obtained by increasing the feed concentration.Alkalinity was supplemented at a ratio of 50%NaHCO 3/COD.For each organic load applied three feed strategies were tested:(a)batch operation with 8-h cycle;(b)2-h fed-batch operation followed by 6-h batch;and (c)4-h fed-batch followed by 4-h batch.The 2-h fed-batch operation followed by 6-h batch presented the best results for the organic loads of 2and 4gCOD L à1d à1,whereas the 4-h fed-batch operation followed by 4-h batch presented results slightly inferior for the same organic loads and the best results at organic loads of 8and 12gCOD L à1d à1.The concentration of total volatile acids varied with ?ll time.For the higher ?ll times maximum concentrations were obtained at the end of the cycle.Moreover,no signi?cant difference was detected in the maximum concentration of total volatile acids for any of the investigated conditions.However,the maximum values of propionic acid tended to decrease with increasing ?ll time considering the same organic load.Microbiological analyses revealed the presence of Methanosaeta -like structures and methanogenic hydrogenotrophic-like ?uorescent bacilli.No Methanosarcina -like structures were observed in the samples.r 2006Elsevier Ltd.All rights reserved.
Keywords:ASBBR;Feeding time;Organic loading;Whey
1.Introduction
Cheese whey possesses a high organic load with concentrations of approximately 60–80gCOD L à1.This characteristic,combined with others such as low alkalinity and high biodegradability,make anaerobic treatment in high rate reactors dif?cult (Malaspina et al.,1996;Yan et al.,1988).Alkalinity present in the system is quickly consumed due to rapid conversion of lactose into short-chain volatile acids,making it necessary to constantly monitor alkalinity as well as pH (Backus et al.,1988).Supplemental addition of alkalinity as bicarbonate,carbo-nate or hydroxide may also be necessary (Lo and Liao,1986;Wildenauer and Winter,1985).
Factors that may signi?cantly affect ASBR performance according to Zaiat et al.(2001)include feed strategy,agitation,reactor con?guration and initial ratio between substrate and biomass concentrations (F/M).In batch or fed-batch operated reactors the in?uence of feed strategy is related to the F/M ratio.According to Angenent and Dague (1995),increase in feed time would cause a reduction in total volatile acids (TVA)and consequently increase reactor performance,since by supplying substrate within a longer time,availability to microorganisms will be less,occasioning less accumulation of these acids.Bagley and Brodkorb (1999)corroborated the assumptions of Angenent and Dague (1995)in easily
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0301-4797/$-see front matter r 2006Elsevier Ltd.All rights reserved.doi:10.1016/j.jenvman.2006.11.001
?Corresponding author.Tel.:+551142393148;fax:+551142393131.
E-mail address:rodrigues@maua.br (J.A.D.Rodrigues).
degraded wastewaters,suggesting,however,investigations in complex substrates.
Kennedy et al.(1991)investigated the effect of feed time on the performance of an ASBR treating synthetic sucrose substrate with organic rates ranging from2.5–18:5gCOD Là1dà1and concentration of7gCOD Là1,varying?ll-and-react periods(?ll-to-react ratios of0.2,0.5and2).The process was not affected by volumetric organic loads (VOL)below9gCOD Là1dà1and for higher loads removal ef?ciency was reduced more than25%for low ratios between feed time and cycle timeet F=t CT. Suthaker et al.(1991)submitted an ASBR treating glucose based wastewater with a concentration of35 gCOD Là1to different operation conditions(temperature from25to34 C and t F=t C ratio from0to0.75),with a VOL of1:6gCOD Là1dà1.The maximum conversion achieved was73%for?ltered samples for a16-day cycle time and4-day feed time.They concluded that feed time has a stronger in?uence than t F=t C ratio,being of fundamental importance in de?ning feed strategy. Shizas and Bagley(2002)also investigated an ASBR treating glucose based wastewater.The system operating with a VOL of2:1gCOD Là1dà1suffered overload at 3:2gCOD Là1dà1.Reactor performance increased at high t F=t C and low initial substrate concentrations,indicating that operation can be optimized by altering these operation parameters.
Rodrigues et al.(2003),operating an ASBR with granulated biomass treating low-strength wastewater e0:5gCOD Là1T,concluded that long feed times(t F=t C greater than0.5)affects system performance related to organic matter removal ef?ciency,settleability character-istics and extra-cellular polymer synthesis.Ratusznei et al. (2003a),operating the ASBR with biomass immobilized on polyurethane foam and treating the same wastewater, observed a drop in ef?ciency at long feed times.This behavior was attributed to the time the immobilized mass was exposed to air,since during feeding the bed was gradually immersed,occasioning periods at which the biomass had no contact with the wastewater;at short feed times the bed was rapidly immersed in the substrate,which did not occur at longer feed times.
The main objective of this investigation was to assess the behavior of an ASBBR containing microorganisms im-mobilized on polyurethane foam treating diluted cheese whey when submitted to different VOL(2,4,8and 12gCOD Là1dà1Tand feed strategies(?ll times of10min, 2h and4h by a cycle time of8h).
2.Materials and methods
The reactor used was made of acrylic with internal diameter and height of200mm.A100-mm high basket was used in the reactor to contain the biomass,as shown in the scheme in Fig.1.This basket occupied half of the reactor volume to allow permanent immersion of the bed during fed-batch operation.The system operated in a chamber which maintained the temperature at30?1 C.Stirring at 500rpm was provided by two helix propellers.The helix propellers with diameter of60mm consisted of three blades;one positioned at20mm from the reactor bottom and the other above the bed at120mm from the reactor bottom.
The inert support used consisted of5-mm polyurethane foam cubes and was inoculated,according to methodology proposed by Zaiat et al.(1994),i.e.,(i)the biomass was squeezed through a1mm mesh sieve as a way to crush the granules present and facilitate attachment of the biomass in the foam;(ii)the5-mm foam cubes were added to the crushed inoculum and mixed in a way to saturate the foam completely with the sludge;and(iii)after2h the foam cubes containing the immobilized biomass were added to the reactor,taking care to avoid compression of the cubes. The sludge used was from a UASB reactor treating
Nomenclature
Symbols
BA bicarbonate alkalinity,mgCaCO3Là1
C I in?uent substrate concentration,mgCO
D Là1 C FS?ltered substrate concentration in the ef?uent,
mgCOD Là1
C TS non-?ltered substrate concentration in the ef-
?uent,mgCOD Là1
t F=t C ratios between feed time and cycle time, dimensionless
TVA total volatile acids concentration determined by titrimetric method,mgHAc Là1
TVA C total volatile acids concentration determined by chromatography method,mg Là1
V Cycle feed volume per cycle,L
VOL volumetric organic load,gCOD Là1dà1V Working working volume,L
Greek characters
e FS substrate removal ef?ciency considering?ltered
samples,%
e TS substrate removal ef?ciency considering non-
?ltered samples,%
Abbreviations
ASBR anaerobic sequencing batch reactor
ASBBR anaerobic sequencing batch bio?lm reactor COD chemical oxygen demand
F/M ratio between substrate and biomass concentra-tions
TSS total suspended solids
VSS volatile suspended solids
TS total solids
TVS total volatile solids
UASB up?ow anaerobic sludge blanket
L.H.S.Damasceno et al./Journal of Environmental Management85(2007)927–935 928
wastewater from a poultry slaughterhouse that had total volatile solids(TVS)and total solids(TS)of51and 62g Là1,respectively.
The wastewater used consisted of reconstituted dehy-drated cheese whey for which the ratio between dry whey and amount of COD was experimentally determined as1:1. Alkalinity supplementation was performed by adding sodium bicarbonate,utilizing g-NaHCO3/g-COD ratios proposed by Ratusznei et al.(2003b),i.e.,to guarantee that bicarbonate alkalinity(BA)was not a limiting factor.This way,at the start of each phase a g-NaHCO3/g-COD ratio of100%was used and after experimental veri?cation of stability this ratio was reduced to50%.The following organic matter concentrations were used:1gCOD Là1 (assay1),2gCOD Là1(assay2),4gCOD Là1(assay3)and 6gCOD Là1(assay4).
Bioreactor operation consisted of initially feeding3L wastewater to be treated in8-h cycles.In each cycle2L wastewater were discharged;the remaining1L residual volume in the reactor was used to dilute the following2L wastewater fed in the next cycle.
Feeding and discharge were performed by means of diaphragm pumps;discharge was done in10min.The study of feed in?uence was performed in the same bioreactor in three different periods,which de?ned the feeding strategies investigated.Each assay using a different feed strategy was performed with the same biomass without an acclimation period.
(i)8-h batch operation:Feeding of2L wastewater to be treated in10min and a g-NaHCO3/g-COD ratio of100% for initial alkalinity supplementation(phase I)and subse-quently of50%(phase II);
(ii)2-h fed-batch operation followed by6-h batch:Feeding of2L wastewater to be treated in2h and a g-NaHCO3/ g-COD ratio of50%for initial alkalinity supplementation (phase III);
(iii)4-h fed-batch followed by4-h batch:Feeding of2L wastewater to be treated in4h and a g-NaHCO3/ g-COD ratio of50%for initial alkalinity supplementation (phase IV).
This way,the VOL were approximately2gCOD Là1dà1 (assay1),4gCOD Là1dà1(assay2),8gCOD Là1dà1 (assay3)and12gCOD Là1dà1(assay4),determined by VOL?
V Cycle?N Cycles=Day?C I
V Useful
.(1) Monitoring was performed according to Standard Meth-ods for the Examination of Water and Wastewater(1995). The following parameters were analyzed:organic matter concentration(COD)for?lteredeC FSTand non-?ltered sampleseC TST,pH,BA,TVA,TS,TVS,total suspended solids(TSS)and volatile suspended solids(VSS). Moreover,intermediate volatile acids and biogas com-position were analyzed by gas phase chromatography. Composition of the biogas generated by anaerobic degradation was analyzed by gas chromatography using a Hewlett Packard s6890gas chromatograph equipped with a thermal conductivity detector.Sample volume was1mL, drag gas was hydrogen at a?ow rate of50:0mL hà1,and column,injector and detector temperatures were35,60and 160 C,respectively.Volatile fatty acid(VFA)samples were analyzed by gas chromatography,using a gas chromatograph HP6890with?ame ionization detector at 300 C and an HP-INNOWAX columne30m?0:25mm?0:25mmT.The injector temperature was kept at250 C;the oven was held at100 C for3min,after which it was heated at a rate of5 C minà1to180 C,and held at that temperature for5min.
After attainment of operation stability in each assay and in each implemented feed strategy,pro?les along cycles were taken of COD concentrations for?ltered samples,C S, pH,BA,TVA,intermediate volatile acids and biogas
Fig.1.Scheme of the anaerobic sequencing batch bio?lm reactor(ASBBR)containing immobilized biomass[(1)bioreactor,(2)stainless steel basket containing particles with immobilized cells,(3)impeller,(4)feed pump,(5)discharge pump,(6)substrate,(7)treated ef?uent,(8)timers].
L.H.S.Damasceno et al./Journal of Environmental Management85(2007)927–935929
composition.Microbiological identi?cation was performed by means of common optical and phase contrast micro-scopy employing an Olympus BH2microscope.3.Results and discussion
Average values of the monitored parameters are listed in Tables 1–4.Figs.2and 5show the variation in organic matter concentration in the ?ltered and non-?ltered samples,conversion ef?ciency,BA and TVA concentration in ef?uent samples for VOLs of 2–12gCOD L à1d à1.
For a VOL of 2gCOD L à1d à1(assay 1—see Table 1and Fig.2)high ef?ciency was obtained in all phases,presenting low values of TVA concentration and increase in BA values of the ef?uent in relation to the in?uent.The operation with 2-h fed-batch followed by 6-h batch (phase III)presented improved operation stability when compared to the batch operation.
At the condition with VOL of 4gCOD L à1d à1(assay 2—see Table 2and Fig.3)organic matter conversions in all phases were high,with improved performance for the 2-h fed-batch followed by 6-h batch (phase III).The system was stable presenting BA generation,reduced values of TVA and pH close to 7.Extra-cellular polymer formation,which affected the system performance,was also observed.This material was removed in the 42nd cycle (see Fig.3).During the assay with VOL of 8gCOD L à1d à1(assay 3—see Table 3and Fig.4)the system was less stable than in other conditions,but considering the ‘‘organic matter ef?ciency removal’’pro?les,the system may be considered slightly stable in all phases,despite a decrease in system ef?ciency and increase in TVA,both presenting a tendency to improve with longer ?ll times (phase IV).The high TVA concentrations did not occasion reactor instability,as no accumulation of these acids occurred.This fact was a consequence of the cycle time used,which did not allow
Table 2
Average values of the monitored variables in the assay with VOL of 4gCOD L à1d à1(assay 2)for batch mode (phase II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV)Variable
In?uent Ef?uent batch Ef?uent 2-h fed-batch Ef?uent 4-h fed-batch C TS (mgCOD L à1T2005?64e14T265?67e8T104?36e3T266?68e5TC FS emgCOD L à1T–115?45e8T59?18e3T147?36e5Te TS (%)–87?3e8T95?2e3T87?3e5Te FS (%)
–
94?2e8T97?1e3T93?2e5TTVA emgHAc L à1T83?13e10T56?26e9T46?20e4T90?13e6TBA emgCaCO 3L à1T553?13e10T653?23e5T672?12e4T626?12e6TpH
8:4?0:2e10T7:6?0:1e5T6:8?0:1e4T6:8?0:1e6TTS emg L à1T2345?369e8T1249?163e4T1117?61e3T1116?8e2TTVS emg L à1T1726?363e8T476?158e4T502?48e3T433?64e2TTSS emg L à1T78?31e8T71?35e4T98?11e3T101?7e2TVSS emg L à1T72?30e8T65?29e4T93?10e3T83?10e2TCH 4(%)
–
67:8e1T
71:8e1T
71e1T
Note :Values between brackets refer to the number of samples averaged.
Table 1
Average values of the monitored variables in the assay with VOL of 2gCOD L à1d à1(assay 1)for batch mode (phase II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV)Variable
In?uent Ef?uent batch Ef?uent 2-h fed-batch Ef?uent 4-h fed-batch C TS (mgCOD L à1T976?32e17T177?65e10T150?28e5T192?5e6TC FS (mgCOD L à1T–78?29e10T41?8e5T85?15e6Te TS (%)–82?7e10T85?3e5T80?1e6Te FS (%)
–
92?3e10T96?1e5T91?1e6TTVA emgHAc L à1T44?6e9T27?8e8T30?6e5T59?21e6TBA emgCaCO 3L à1T280?21e9T334?14e6T341?42e5T295?14e6TpH
8:3?0:2e9T7:2?0:4e6T6:8?0:2e5T6:8?0:2e6TTS emg L à1T1272?76e9T761?54e3T693?31e3T622?103e3TTVS emg L à1T974?69e9T430?70e3T372?55e3T313?69e3TTSS emg L à1T45?11e9T77?29e3T95?36e3T83?8e3TVSS emg L à1T40?9e9T65?36e3T91?34e3T75?17e3TCH 4(%)
–
71:2e1T
72:9e1T
71:2e1T
Note :Values between brackets refer to the number of samples averaged.
L.H.S.Damasceno et al./Journal of Environmental Management 85(2007)927–935
930
Table 3
Average values of the monitored variables in the assay with VOL of 8gCOD L à1d à1(assay 3)for batch mode (phase II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV)Variable
In?uent Ef?uent batch Ef?uent 2-h fed-batch Ef?uent 4-h fed-batch C TS (mgCOD L à1T4020?108e26T879?136e12T963?144e6T904?278e9TC FS emgCOD L à1T–650?135e12T615?142e6T566?285e9Te TS (%)–78?3e12T76?4e6T78?7e9Te FS (%)
–
84?3e12T85?4e6T86?7e9TTVA emgHAc L à1T134?10e12T321?80e14T301?67e7T285?97e9TBA emgCaCO 3L à1T1103?40e12T1103?121e10T1084?56e7T1096?92e9TpH
8:4?0:3e12T6:8?0:1e10T6:9?0:2e7T6:9?0:1e9TTS emg L à1T4858?216e11T2681?563e5T2402?226e2T2282?334e4TTVS emg L à1T3430?182e11T1018?112e5T928?209e2T978?85e4TTSS emg L à1T175?11e11T187?49e5T226?71e2T252?8e4TVSS emg L à1T153?15e11T166?36e5T195?75e2T226?7e4TCH 4(%)
–
63:7e1T
65:5e1T
67:8e1T
Note :Values between brackets refer to the number of samples averaged.
Table 4
Average values of the monitored variables in the assay with VOL of 12gCOD L à1d à1(assay 4)for batch mode (phase II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV)Variable
In?uent Ef?uent batch Ef?uent 2-h fed-batch Ef?uent 4-h fed-batch C TS (mgCOD L à1T5969?165e19T1782?399e8T2055?113e5T1687?237e5TC FS (mgCOD L à1T–1215?444e8T1626?141e5T1118?181e5Te TS (%)–70?7e8T66?2e5T72?4e5Te FS (%)
–
78?8e8T
73?2e5T81?3e5TTVA (mgHAc L à1T204?28e9T527?181e7T750?82e6T602?93e6TBA emgCaCO 3L à1T1689?77e9T1582?173e7T1429?72e6T1571?49e6TpH
8:4?0:3e9T7:1?0:1e7T7:1?0:2e6T7:1?0:1e6TTS emg L à1T7132?154e8T3537?352e4T3800?57e2T3502?238e2TTVS emg L à1T4960?164e8T1431?381e4T1602?34e2T1318?141e2TTSS emg L à1T302?71e8T295?55e4T318?37e2T442?21e2TVSS emg L à1T266?73e8T248?50e4T276?8e2T403?19e2TCH 4(%)
–
66:4e1T
63:6e1T
63:9e1T
Note :Values between brackets refer to the number of samples
averaged.
01002003004005000
102030405060708090
102030405060708090
Operation cycles
Operation cycles
C s (m g C O
D .l -1)
20406080100ε (%)
I II III IV
I II III
IV
0140280420560700B A (m g C a C O 3.l -1)
20406080100T V A (m g H A c .l -1)
Fig.2.Substrate concentrations in the ef?uent ( —C FS , —C TS Tand conversion ef?ciency (e FS —&,e TS —’),of bicarbonate alkalinity em Tand of total volatile acids en Tin the reactor operated at VOL of 2gCOD L à1d à1(assay 1)for batch mode (phases I and II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV).
L.H.S.Damasceno et al./Journal of Environmental Management 85(2007)927–935
931
adequate consumption of the acids formed.Moreover,the system managed to generate a certain amount of BA beyond that consumed,presenting values similar to those of the in?uent.An increase in in?uent organic matter concentration at a VOL of 12gCOD L à1d à1(assay 4—see Table 4and Fig.5)resulted in a reduction in conversion ef?ciency.The TVA concentration in the ef?uent was high;however,no
1002003004005000
10
203040506070
80
Operation cycles
1020304050607080
Operation cycles
C s (m g C O
D .l -1)
20406080100ε (%)
I
III
IV
025050075010001250B A (m g C a C O 3.l -1)
255075100125150T V A (m g H A c .l -1)II
I
III
IV
II
Fig.3.Substrate concentrations in the ef?uent ( —C FS , —C TS Tand conversion ef?ciency (e FS —&,e TS —’),of bicarbonate alkalinity em Tand of total volatile acids en Tin the reactor operated at VOL of 4gCOD L à1d à1(assay 2)for batch mode (phases I and II),2-h fed-batch (phase III)and 4-h fed-batch (phase
IV).
0500
1000
1500
2000
20
406080100120140Operation cycles
20
40
6080100120140
Operation cycles
C s (m g C O
D .l -1)
20
40
60
80100ε (%)
I
III
01000
2000
3000
B A (m g
C a C O 3.l -1)
125
250
375
500
T V A (m g H A c .l -1)
II
IV
I
III
II
IV
Fig.4.Substrate concentrations in the ef?uent ( —C FS , —C TS Tand conversion ef?ciency (e FS —&,e TS —’)of bicarbonate alkalinity em Tand of total volatile acids en Tin the reactor operated at VOL of 8gCOD L à1d à1(assay 3)for batch mode (phases I and II),2-h fed-batch (phase III)and 4-h fed-batch (phase
IV).
01000
20003000400050000102030405060708090
Operation cycles
102030405060708090
Operation cycles
C s (m g C O
D .l -1)
20406080100ε (%
)
1000
2000
3000
4000B A (m g C a C O 3.l -1)
200400
600
8001000T V A (m g H A c .l -1)
I
III
II
IV
I
III
II
IV
Fig.5.Substrate concentrations in the ef?uent ( —C FS , —C TS Tand conversion ef?ciency (e FS —&,e TS —’),of bicarbonate alkalinity em Tand of total volatile acids en Tin the reactor operated at VOL of 12gCOD L à1d à1(assay 4)for batch mode (phases I and II),2-h fed-batch (phase III)and 4-h fed-batch (phase IV).
L.H.S.Damasceno et al./Journal of Environmental Management 85(2007)927–935932
tendency to accumulate was observed,i.e.,values were erratic,being again a result of insuf?cient time for consumption of the generated acids.
Analyzing the behavior of the process variables mon-itored in assays 1and 2(at VOLs of 2and 4gCOD L à1d à1Tindicated that an increase in feed time did not signi?cantly alter reactor performance.For the process variables monitored in assays 3and 4(at VOLs of 8and 12gCOD L à1d à1Tsystem stability tends to increase with increasing feed time,as can be seen by the increase in both BA generation and organic matter in ?ltered and non-?ltered samples.
High concentrations of acetic and propionic acid were found at VOLs of 2and 4gCOD L à1d à1(assays 1and 2).At conditions of 8and 12gCOD L à1d à1(assays 3and 4)additionally butyric and valeric acid were detected.Assuming TVA as the sum of all acids encountered along the cycle (see Figs.6and 7),no signi?cant variation was seen in terms of their maximum values with increasing ?ll times.The difference occurred in the time at which the maximum value was attained.This time was longer as ?ll time increased.Moreover,acid accumulation increased with increasing organic load.
The effect of ?ll time (i.e.,fed-batch operation time)on the behavior of the volatile acids pro?le,considering the maximum value of volatile acids and the time when this maximum occurred,shows that the maximum value remained approximately the same (independently of ?ll time)and the time at which this occurred was shifted (approximately proportional to the increase in ?ll time).This fact may be explained by a possible need for a minimum concentration of volatile acids for the consump-tion rate of these acids (for instance by methanogenesis)to attain values suf?cient to promote their reduction.This behavior contradicts the expectation that a reduction in volatile acids formation rate brought about by longer ?ll time (i.e.,by the reduced availability of organic matter)would promote a reduction in the maximum value attained as the methanogenesis step facilitates consumption of these acids.
However,the propionic acid presented a behavior related to the feed strategy used (see Figs.8and 9).Analysis of the pro?le along the cycle shows that the longer the ?ll time,the lower the maximum concentration of this acid.Hence,the longer ?ll time does not seem to favor formation of propionic acid or favor its conversion to acetic acid.
All assays showed a big difference between organic matter concentration (COD)in the ?ltered and non-?ltered samples,affected by the formation of polymer-like material which was removed during discharge.This also explains the higher concentration of VSS and TSS determined in the
050100150
120
240360480
Time (minutes)
T V A C (m g .l -1)
120
240360
480
Time (minutes)
a
Fig.6.Pro?les of total volatile acids concentration by chromatography at VOL of 2gCOD L à1d à1(a—assay 1)and of 4gCOD L à1d à1(b—assay 2)for batch mode e —phase II),2-h fed-batch (’—phase III)and 4-h fed-batch ( —phase IV).
025050075010000
120
240360480
Time (minutes)
T V A C (m g .l -1
)
120
240360
480
Time (minutes)
a
Fig.7.Pro?les of total volatile acids concentration by chromatography at VOL of 8gCOD L à1d à1(a—assay 3)and of 12gCOD L à1d à1(b—assay 4)for batch mode ( —phase II),2-h fed-batch (’—phase III)and 4-h fed-batch ( —phase IV).
L.H.S.Damasceno et al./Journal of Environmental Management 85(2007)927–935
933
ef?uent in all operation conditions.Another important fact is the signi?cant reduction observed in polymer formation with increasing ?ll time.
Microbiological analyses showed that the foam suc-ceeded to immobilize the anaerobic microorganisms,evidenced by the large presence of Methanosaeta -like structures and methanogenic hydrogenotrophic-like ?uor-escent bacilli.No Methanosarcina -like structures were observed in the samples.Considering the average values obtained in all assays,after immobilization the bioparticles presented 1:4?0:1g TVS =g foam and 1:5?0:1g TS =g foam ,with TVS in the reactor of approximately 69g.4.Conclusions
At all investigated VOLs and feed times the ASBR containing immobilized biomass presented high organic matter conversions,indicating that this technology may be applied to the treatment of cheese whey at different operation conditions.It is worth to mention that the treatment of diluted whey may be the same as the treatment of raw whey considering as a design parameter the VOL and maintaining cycle length,volume treated per cycle and total volume of the medium in the bioreactor.However,since we deal with a biological process in which intermediate metabolites may play an important role,an investigation should be undertaken with an appropriate experimental protocol to verify this behavior.
Considering the organic matter removal ef?ciency beha-vior,for VOLs of 2and 4gCOD L à1d à1the 2-h feed time yielded improved conversion ef?ciency as well as better operation stability.For VOLs of 8and 12gCOD L à1d à1this behavior was observed at 4-h feed time.Furthermore,despite higher TVA concentrations found at the highest VOLs,there was no tendency toward acid accumulation,indicating that this behavior was due to cycle time which was not suf?cient for complete volatile acids consumption.
The pro?les showed that in terms of TVA concentration,there was no signi?cant difference between the maximum values at all conditions investigated.Yet,with increasing ?ll time these maximum values tended to occur at times near the end of the cycle.Moreover,a reduction was observed in the maximum values of propionic acid during a cycle for longer ?ll times,considering each applied organic load separately.The 4-h fed-batch operation followed by 4-h batch yielded lower maximum propionic acid concen-trations,indicating that this technology may also be used for substrates that produce elevated concentrations of this acid and impede anaerobic treatment.
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Fig.8.Pro?les of propionic acid concentration at VOL of 2gCOD L à1d à1(a—assay 1)and of 4gCOD L à1d à1(b—assay 2)for batch mode ( —phase II),2-h fed-batch (’—phase III)and 4-h fed-batch ( —phase IV).
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Fig.9.Pro?les of propionic acid concentration at VOL of 8gCOD L à1d à1(a—assay 3)and of 12gCOD L à1d à1(b—assay 4)for batch mode ( —phase II),2-h fed-batch (’—phase III)and 4-h fed-batch ( —phase IV).
L.H.S.Damasceno et al./Journal of Environmental Management 85(2007)927–935
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Acknowledgments
This study was supported by the Fundac-a o de Amparo a Pesquisa do Estado de Sa o Paulo–FAPESP(Sa o Paulo, Brazil),process number02/06.154-5.The authors grate-fully acknowledge Dr.Baltus C.Bonse for the revision of this paper.
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