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Anaerobic Bioconversion of Sucrose to Biogas Promoted by the Mineral Kissiris
Process Biochemisny 29 ( 1994) 285-288
Anaerobic Bioconversion of Sucrose to Biogas Promoted by the Mineral Kissiris A. A. Koutinas, T. Tsoutsas & A. Kaliafas Department of Chemistry, University of Patras, Patras, Greece (Received 22 September 1992; revised version received 20 January 1993; accepted 3 1 March 1993)
The effect of the mineral kissiris on the fermentation of sucrose solutions in an UpFlow Plug Anaerobic Bioreactor (UPAB) was examined. Increased acid generation and a decrease in the time needed for the start-up of the process were obtained. Biogas was produced at volatile fatty acid (VFA) concentnztions of 104&l 772 g/&e and at a pH close to 6, Loadings in the range of 13-3-374 g COD/Iitre/day and 43-68% COD removal efficiencies after a day were also obtained. In the absence of kissiris no methane fermentation was produced.
INTRODUCTION
cane.4 A disadvantage of the treatment of vinasse in the UAF, DAF and UASB reactors is the delay in the start-up of the process and further research to accelerate this is needed. To improve the rate of methane fermentation and accelerate its start-up, the mineral kissiris was employed as a support material in an Up-Flow Plug Anaerobic Bioreactor (UPAB). Kissiris is also known in Greece as e‘ laphropetra’ or T ‘ hiraiki gi’. It is a volcanic rock comprised of volcanic glasses and with a petrification similar to that of granite. Kissiris is usually formed by the foam thickening of volcanic lava and characterized as a natural glass foam. The gas volume released during its formation is equal to the glass mass, and this is the reason for its porosity and specific surface area. In Greece it occurs in the Aegean islands, Sandorini, Milos and Nissiros in layers 30-50 m thick. Its composition is similar to igneous rock type of alkali granite5 and it contains more than 70% SiO,, 13% Al,O, and other inorganic oxides such as TiOz, Fe*O,, FeO, MnO, MgO, CaO, Na,O, KzO and P205_ Kissiris pro-
Although many workers have attempted to increase the rate of the anaerobic treatment of waste-waters by the use of high loading rates, the use of a solid support material to promote methane fermentation has received little attention. The treatment of vinasse in an Up-Flow Anaerobic Filter (UAF ) and a Down-Flow Anaerobic Filter (DAF )’ used loadings no higher than 10 g COD/W-e/day, A loading of 25 g COD/litre/day was obtained by Wheatley and CasselZ after biofiltration of vinasse. Similarly, a loading of 20 g COD/litre/day was reported in the treatment of vinasse in an UpFlow Anaerobic Sludge Bed (UASB) reactor systema Furthermore, the use of a screen in the centre of the UASB reactor to maintain the granulated sludge, increased the loading to 40 g COD/ litre/day in the treatment of vinasse from sugar Corresponding author: A. A. Koutinas. Fax: 0030 61 997 118.
285
Process Biochemistry 0032-9592/94/$7.00
Q 1994
Elswier ScienceLimited,England.
286
A. A. Koutinas, T Tsoutsas, A. Kaliafm
alcoholic fermentation using Succharocerevisiae6 and is suitable for myces immobilization of the yeasL7 The aims of the present work were: (a) to examine kissiris in the anaerobic fermentation of synthetic media containing sucrose in order to improve the process rate and (b) to accelerate the start-up of the fermentation. motes
MATERIALS
AND METHODS
The Greek mineral kissiris was used throughout this work. All samples were washed with fap water and dried overnight at room temperature. The reactor was fed with a synthetic medium containing sucrose and designed to obtain COD values of 40, 60, 80 and 110 g/litre. NH, and H,PO, 50% were added to achieve a COD : N: P ratio of 100 : 5 : 1. The media also contained 0.4% NaHCO, and 0.4% yeast extract. The pH was adjusted with sodium hydroxide solution to values presented in Table 1. The experimental apparatus which consisted of a continuous reactor is shown in Fig. 1. It was a glass tower reactor of 15 litre total working volume. Pieces of kissiris were used in order to fiIl the reactor. The continuous fermentation medium was pumped in an up-flow stream with a high accuracy peristaltic pump (Cole Parmer Instrument Co., Chicago, IL). For better mixing the effluent was recycled via the bottom of the reactor with a volumetric rate 10 times higher than the effluent passed through the reactor.
The inoculum was synthetic media containing 50 g/We sucrose which was mixed with an equal volume of liquid culture from granulated sludge which was taken from an operated UASB reactor. The pH of the mixture was adjusted to 8. After filling the reactor, circulation of the mixture was started and recycling continued for 2 h. The circulation was then stopped and the mixture allowed to ferment for a day without feeding. Vigorous fermentation was observed at this stage and the reactor was fed continuously with the synthetic media containing a constant sucrose concentration in a loading of 13.3 g COD/We/day. The concentration of sucrose was changed successively to obtain the COD values described above. For every concentration used a new start-up of the process was carried out. The steady state in the reactor was obtained a few days after the start-up
Kissirir _
Water
bath
Fig. 1. Pilot plant operation for continuous methane fermentation of synthetic media containing sucrose, using kissiris as support material.
Table 1. Results obtained in continuous methane fermentation of synthetic media containing sucrose using kissiris as support material Influent
Flow ivlte (litrelday)
pH
COD (gllitre)
Bioreactor Loading (g COD/litre/day)
PH
VFA (gllipe)
Biogas
Efluent Start
COD (g/We)
COD retmy
Production (litre/duy)
Composition @c&)
ZY) 0.5 z::
12.7 12.7 12.8
39.9 399 39.9
13.3 13.3
6.36 6.05 6.32
8.28 -
:
13.1 19.5 13.0
67 52
0.5 0.5 0.5 ;::
13.3 13.2 13.2 13-6 135
59% 59.8 59.8 79.2
19.9 19.9 199 2697 26.7
5.97 6.00 610 6.40
932 10.48 -
1
68 z::
-1
19.2 26.6 257 45.3 24.8
68
0.5 ;::
13.6 138
79.2 112.3
26.7 37.4
6.45 6.25 6.00
17.72 -
-1
41.3 61.3 48.7
t; 57
0.5
13.85
112.3
37.4
6.30
-
62.3
tz
1.5 2.5 7.2 8.6 10.2 10.6 12.2 95 13.1 24.0 245 18.6
(%“u9;,
52 51 51 60 52 51
48 49 49 f: 49
;; 51
1: 49
$2 52
f: 48
287
Anaerobic bioconwrsion of sucrose to biogas
of the anaerobic digestion and did not exceed a week. At the steady state, samples were collected from the effluent, the liquid in the reactor and the biogas. The reactor liquid was analysed for pH and VFA, the biogas for methane and carbon dioxide, and the effluent for COD. The experiments were carried out in the order presented in Table 1. To compare the fermentation rate with and without kissiris as support material, a reactor similar to that described above and having 1 litre total working volume was operated without kissiris. All operations of this reactor was performed in the same way as that in which kissiris was present. The COD and VFA were determined by standard methods.8 The composition of biogas was estimated by the Orsat method. For pH measurements, a CFG-D 6900 pH meter was used. RESULTS AND DISCUSSION The bioreactor containing kissiris was fed with relatively high loadings of 13.3, 19*9,26.7 or 37.4 g COD/litre/day and the results of this experiment are summarized in Table 1. Data from comparative experiments without kissiris are presented in Table 2. Kissiris promoted methane fermentation even at high concentrations of VFA. In the absence of kissiris the fermentation was stopped and then no methanogenic fermentation occurred. In the presence of kissiris the start-up time was only 1 day and at high loading in the range of 13-3-37.4 g COD/W-e/day the COD removal efficiency was 43-68%. The biogas contained 5 l-60% CH4 and the pH of the liquid of the reactor was 6-6.45. The anaerobic digestion took place at high VFA concentrations close to 18 g/litre. The pH of the influent was at 12-7-13.85 to maintain the pH in the reactor higher than 6.
As the concentration of sucrose in the influent increased the pH of sucrose solution and VFA in the bioreactor also increased. These results clearly indicate that in the presence of kissiris, methane fermentation takes place at high VFA concentrations and the biogas is formed at pH values and VFA concentrations which usually inhibit methanogenesis. It is known that microorganisms can be immobilized in kissit-is’ and it may be that the attached methane-forming bacteria survive at higher pH values because the acidity of the medium is neutralized by the basic character of the A&O, contained in this mineral. Immobilization also facilitates an increase in loading and flow rates without a reduction in the fermentation rate, which the removal of free cells in this case does not affect significantly. In contrast, no methane fermentation was performed in the absence of mineral kissiris. This was probably due to the low pH and the relatively high VFA concentrations produced as well as the removal of free cells. The reduction on time required for the start-up of the fermentation in the presence of kissiris may be due to: (i) the high biomass concentration achieved within a few hours, (ii) the immobilization of this biomass. The acceleration of the startup is of technological importance because it is a key problem in anaerobic digestion. The promotional effect of kissiris on the anaerobic digestion of sucrose solutions and especially its effect on the increase in fermentation rate, may be attributed to one or more of the following factors: (a) kissiris promotes the acid generation step. This is indicated by the increase in VFA concentrations and that the high alkalinity of the influent is required to maintain the pH of the reactor higher than 6. The acid generation and the pH of the influent are higher than those obtained by Koutinas et al9 using y-alumina pellets. (b) There is the possibility that cells immobilized on the surface of kissiris are more active than free ones. (c) Kissiris may
Table 2. Results obtained in continuous methane fermentation of synthetic media containing sucrose without kissiris Run
1 2
E#7uent
Influent Flow rate (l&e/day)
PH
O-50 05.5 O-43 o-43
9.8 9-8 10-3 lo.3
COD (gllitre)
COD loading (g/he/day)
PH
56.7 57.5 77.1 77.1
28.4 31.6 33-2 33-2
::; 5.8 5.7
(gEe) l-68 1 l-75 12-43 12-48
Time after continuous feeding (days)
Production of biogas @e/day)
; 2 2
x 0 0
288
A. A. Koutinas,
T. Tsoutsas, A. Kahafas
the catalytic action of some of the enzymes involved in the process although this has not been examined. To gain more information about (b) and (c) and to estimate the relative contribution of these factors to the promoting action of kissiris, obviously needs further experimentation. enhance
4.
5. 6.
REFERENCES Barnes, D., Bliss, P. J., Grauer, R. B. & Robins, K., Pretreatment of high strength wastewater by an anaerobic fluid&d bed process. Part II: Response to organic load transients. Environ. Technol. Lett., 6 (2) ( 1985) 73-8. Wheatley, A. D. & Cassel, L., Effluent treatment by anaerobic biofiltration. Water Pollut. Contr.. 84 (19851 ~ 10-22. Pfeifer, W., Temper, U., Steiner, A., Carorzi, A. & Van Mucke, J., Anaerobic wastewater treatment. Results of a
7.
8. 9.
literature review. Proceedings of Anaerobic Treatment. A Grown UP Technology. Water
Anaerobic Bioconversion of Sucrose to Biogas Promoted by the Mineral Kissiris A. A. Koutinas, T. Tsoutsas & A. Kaliafas Department of Chemistry, University of Patras, Patras, Greece (Received 22 September 1992; revised version received 20 January 1993; accepted 3 1 March 1993)
The effect of the mineral kissiris on the fermentation of sucrose solutions in an UpFlow Plug Anaerobic Bioreactor (UPAB) was examined. Increased acid generation and a decrease in the time needed for the start-up of the process were obtained. Biogas was produced at volatile fatty acid (VFA) concentnztions of 104&l 772 g/&e and at a pH close to 6, Loadings in the range of 13-3-374 g COD/Iitre/day and 43-68% COD removal efficiencies after a day were also obtained. In the absence of kissiris no methane fermentation was produced.
INTRODUCTION
cane.4 A disadvantage of the treatment of vinasse in the UAF, DAF and UASB reactors is the delay in the start-up of the process and further research to accelerate this is needed. To improve the rate of methane fermentation and accelerate its start-up, the mineral kissiris was employed as a support material in an Up-Flow Plug Anaerobic Bioreactor (UPAB). Kissiris is also known in Greece as e‘ laphropetra’ or T ‘ hiraiki gi’. It is a volcanic rock comprised of volcanic glasses and with a petrification similar to that of granite. Kissiris is usually formed by the foam thickening of volcanic lava and characterized as a natural glass foam. The gas volume released during its formation is equal to the glass mass, and this is the reason for its porosity and specific surface area. In Greece it occurs in the Aegean islands, Sandorini, Milos and Nissiros in layers 30-50 m thick. Its composition is similar to igneous rock type of alkali granite5 and it contains more than 70% SiO,, 13% Al,O, and other inorganic oxides such as TiOz, Fe*O,, FeO, MnO, MgO, CaO, Na,O, KzO and P205_ Kissiris pro-
Although many workers have attempted to increase the rate of the anaerobic treatment of waste-waters by the use of high loading rates, the use of a solid support material to promote methane fermentation has received little attention. The treatment of vinasse in an Up-Flow Anaerobic Filter (UAF ) and a Down-Flow Anaerobic Filter (DAF )’ used loadings no higher than 10 g COD/W-e/day, A loading of 25 g COD/litre/day was obtained by Wheatley and CasselZ after biofiltration of vinasse. Similarly, a loading of 20 g COD/litre/day was reported in the treatment of vinasse in an UpFlow Anaerobic Sludge Bed (UASB) reactor systema Furthermore, the use of a screen in the centre of the UASB reactor to maintain the granulated sludge, increased the loading to 40 g COD/ litre/day in the treatment of vinasse from sugar Corresponding author: A. A. Koutinas. Fax: 0030 61 997 118.
285
Process Biochemistry 0032-9592/94/$7.00
Q 1994
Elswier ScienceLimited,England.
286
A. A. Koutinas, T Tsoutsas, A. Kaliafm
alcoholic fermentation using Succharocerevisiae6 and is suitable for myces immobilization of the yeasL7 The aims of the present work were: (a) to examine kissiris in the anaerobic fermentation of synthetic media containing sucrose in order to improve the process rate and (b) to accelerate the start-up of the fermentation. motes
MATERIALS
AND METHODS
The Greek mineral kissiris was used throughout this work. All samples were washed with fap water and dried overnight at room temperature. The reactor was fed with a synthetic medium containing sucrose and designed to obtain COD values of 40, 60, 80 and 110 g/litre. NH, and H,PO, 50% were added to achieve a COD : N: P ratio of 100 : 5 : 1. The media also contained 0.4% NaHCO, and 0.4% yeast extract. The pH was adjusted with sodium hydroxide solution to values presented in Table 1. The experimental apparatus which consisted of a continuous reactor is shown in Fig. 1. It was a glass tower reactor of 15 litre total working volume. Pieces of kissiris were used in order to fiIl the reactor. The continuous fermentation medium was pumped in an up-flow stream with a high accuracy peristaltic pump (Cole Parmer Instrument Co., Chicago, IL). For better mixing the effluent was recycled via the bottom of the reactor with a volumetric rate 10 times higher than the effluent passed through the reactor.
The inoculum was synthetic media containing 50 g/We sucrose which was mixed with an equal volume of liquid culture from granulated sludge which was taken from an operated UASB reactor. The pH of the mixture was adjusted to 8. After filling the reactor, circulation of the mixture was started and recycling continued for 2 h. The circulation was then stopped and the mixture allowed to ferment for a day without feeding. Vigorous fermentation was observed at this stage and the reactor was fed continuously with the synthetic media containing a constant sucrose concentration in a loading of 13.3 g COD/We/day. The concentration of sucrose was changed successively to obtain the COD values described above. For every concentration used a new start-up of the process was carried out. The steady state in the reactor was obtained a few days after the start-up
Kissirir _
Water
bath
Fig. 1. Pilot plant operation for continuous methane fermentation of synthetic media containing sucrose, using kissiris as support material.
Table 1. Results obtained in continuous methane fermentation of synthetic media containing sucrose using kissiris as support material Influent
Flow ivlte (litrelday)
pH
COD (gllitre)
Bioreactor Loading (g COD/litre/day)
PH
VFA (gllipe)
Biogas
Efluent Start
COD (g/We)
COD retmy
Production (litre/duy)
Composition @c&)
ZY) 0.5 z::
12.7 12.7 12.8
39.9 399 39.9
13.3 13.3
6.36 6.05 6.32
8.28 -
:
13.1 19.5 13.0
67 52
0.5 0.5 0.5 ;::
13.3 13.2 13.2 13-6 135
59% 59.8 59.8 79.2
19.9 19.9 199 2697 26.7
5.97 6.00 610 6.40
932 10.48 -
1
68 z::
-1
19.2 26.6 257 45.3 24.8
68
0.5 ;::
13.6 138
79.2 112.3
26.7 37.4
6.45 6.25 6.00
17.72 -
-1
41.3 61.3 48.7
t; 57
0.5
13.85
112.3
37.4
6.30
-
62.3
tz
1.5 2.5 7.2 8.6 10.2 10.6 12.2 95 13.1 24.0 245 18.6
(%“u9;,
52 51 51 60 52 51
48 49 49 f: 49
;; 51
1: 49
$2 52
f: 48
287
Anaerobic bioconwrsion of sucrose to biogas
of the anaerobic digestion and did not exceed a week. At the steady state, samples were collected from the effluent, the liquid in the reactor and the biogas. The reactor liquid was analysed for pH and VFA, the biogas for methane and carbon dioxide, and the effluent for COD. The experiments were carried out in the order presented in Table 1. To compare the fermentation rate with and without kissiris as support material, a reactor similar to that described above and having 1 litre total working volume was operated without kissiris. All operations of this reactor was performed in the same way as that in which kissiris was present. The COD and VFA were determined by standard methods.8 The composition of biogas was estimated by the Orsat method. For pH measurements, a CFG-D 6900 pH meter was used. RESULTS AND DISCUSSION The bioreactor containing kissiris was fed with relatively high loadings of 13.3, 19*9,26.7 or 37.4 g COD/litre/day and the results of this experiment are summarized in Table 1. Data from comparative experiments without kissiris are presented in Table 2. Kissiris promoted methane fermentation even at high concentrations of VFA. In the absence of kissiris the fermentation was stopped and then no methanogenic fermentation occurred. In the presence of kissiris the start-up time was only 1 day and at high loading in the range of 13-3-37.4 g COD/W-e/day the COD removal efficiency was 43-68%. The biogas contained 5 l-60% CH4 and the pH of the liquid of the reactor was 6-6.45. The anaerobic digestion took place at high VFA concentrations close to 18 g/litre. The pH of the influent was at 12-7-13.85 to maintain the pH in the reactor higher than 6.
As the concentration of sucrose in the influent increased the pH of sucrose solution and VFA in the bioreactor also increased. These results clearly indicate that in the presence of kissiris, methane fermentation takes place at high VFA concentrations and the biogas is formed at pH values and VFA concentrations which usually inhibit methanogenesis. It is known that microorganisms can be immobilized in kissit-is’ and it may be that the attached methane-forming bacteria survive at higher pH values because the acidity of the medium is neutralized by the basic character of the A&O, contained in this mineral. Immobilization also facilitates an increase in loading and flow rates without a reduction in the fermentation rate, which the removal of free cells in this case does not affect significantly. In contrast, no methane fermentation was performed in the absence of mineral kissiris. This was probably due to the low pH and the relatively high VFA concentrations produced as well as the removal of free cells. The reduction on time required for the start-up of the fermentation in the presence of kissiris may be due to: (i) the high biomass concentration achieved within a few hours, (ii) the immobilization of this biomass. The acceleration of the startup is of technological importance because it is a key problem in anaerobic digestion. The promotional effect of kissiris on the anaerobic digestion of sucrose solutions and especially its effect on the increase in fermentation rate, may be attributed to one or more of the following factors: (a) kissiris promotes the acid generation step. This is indicated by the increase in VFA concentrations and that the high alkalinity of the influent is required to maintain the pH of the reactor higher than 6. The acid generation and the pH of the influent are higher than those obtained by Koutinas et al9 using y-alumina pellets. (b) There is the possibility that cells immobilized on the surface of kissiris are more active than free ones. (c) Kissiris may
Table 2. Results obtained in continuous methane fermentation of synthetic media containing sucrose without kissiris Run
1 2
E#7uent
Influent Flow rate (l&e/day)
PH
O-50 05.5 O-43 o-43
9.8 9-8 10-3 lo.3
COD (gllitre)
COD loading (g/he/day)
PH
56.7 57.5 77.1 77.1
28.4 31.6 33-2 33-2
::; 5.8 5.7
(gEe) l-68 1 l-75 12-43 12-48
Time after continuous feeding (days)
Production of biogas @e/day)
; 2 2
x 0 0
288
A. A. Koutinas,
T. Tsoutsas, A. Kahafas
the catalytic action of some of the enzymes involved in the process although this has not been examined. To gain more information about (b) and (c) and to estimate the relative contribution of these factors to the promoting action of kissiris, obviously needs further experimentation. enhance
4.
5. 6.
REFERENCES Barnes, D., Bliss, P. J., Grauer, R. B. & Robins, K., Pretreatment of high strength wastewater by an anaerobic fluid&d bed process. Part II: Response to organic load transients. Environ. Technol. Lett., 6 (2) ( 1985) 73-8. Wheatley, A. D. & Cassel, L., Effluent treatment by anaerobic biofiltration. Water Pollut. Contr.. 84 (19851 ~ 10-22. Pfeifer, W., Temper, U., Steiner, A., Carorzi, A. & Van Mucke, J., Anaerobic wastewater treatment. Results of a
7.
8. 9.
literature review. Proceedings of Anaerobic Treatment. A Grown UP Technology. Water