International Journal of Scientific & Engineering Research, Volume 2, Issue 12, December-2011 1
ISSN 2229-5518
Acidogenic and Methanogenic activities in
Anaerobic Ponds
Effebi K.R, Baya T, Jupsin H, Vasel J.L
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Anaerobic ponds are used for treatment of concentrated or- ganic wastewater from domestic and industry especially in hot climates. Its design is based on empiric rules and consid- eration is given to the organic volumetric load. Anaerobic ponds are rather efficient on the elimination of organic matter based on sedimentation and anaerobic degradation.The an- aerobic digestion is a complex process in which organic matter is converted into a mixture of methane and carbon dioxide. The overall conversion is carried out by a mixture of micro- organisms through several biochemical reactions in series and in parallel [1]. Anaerobic reactions taking place in the sedi- ment include solubilization of biodegradable particulate mat- ter followed by acidogenesis, acetogenesis and methanogene- sis. Generally the reactions occurring in the liquid layer are often neglected and are attributed to the convection move- ments and gas bubble (methane production) in the bottom related by the sediment layer.The anaerobic conversion of or- ganic matter leads to the intermediate formation of volatile fatty acids (VFA), mainly butyrate, propionate and acetate, subsequently butyrate and propionate degradation due to syn- trophic metabolism, results in the production of acetate. Ace- tate is further degraded by acetoclastic methanogens into CO2 and CH4, acidogenic activity is usually higher than methano- genic rate because it takes place first and its product (acetate) is used during methanogenesis.
The substrate used for acidogenic activity determination is
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Effebi K.R. University of Abobo-Adjamé Ivory Cost, UFR Science and
Management of the Environment , 02 BP 801 ABIDJAN 02
Tel. :+22509292549, +22522442124, E-mail : effeb2001@yahoo.fr
Baya T, Jupsin H, Vasel J.L .University of Liege, Department of Science and
Management of the Environment, Sanitation and Environment Unit, 185
Avenue de Longwy, 6700 Arlon, Belgium.
usually glucose, which is considered as the main intermediate in the pathway of anaerobic digestion of carbohydrate com- plex organic [2]. About methanogenic activity determination VFA were used, especially acetic acid.
However few studies deal with the kinetics parameters of aci- dogenic and methanogenic activity in anaerobic ponds. Accordingly, the work presented here assesses the biological activity both in liquid phase and in sediments accumulated at the bottom of an anaerobic pond. So we defined a methodol- ogy for kinetic measurement of acidogenic and methanogenic phases.
Acidogenic and methanogenic kinetics characterised by the
increase (production of HAc) and decrease (consumption of
HAc) of acetic acid respectively, were quantified on biomasses
samples in a full scale anaerobic pond located in Tunisia.
This study deals with the anaerobic waste stabilisation pond of the experimental plant of INRST (National Institute of Sci- entific and Technical Research) in Tunisia. We focalised on the measurement and on the comparison of biological activities in the liquid layer and in the sediments from anaerobic pond. This plant is in operation since 1992. Wastewater is settling in a primary settling tank and them distributed in the other ponds. The wastewater treatment system consists of 5 ponds connected in series. Out of these one is anaerobic pond, fol- lows by facultative pond and three maturation ponds. This station received surfacic load in BOD5 of 2930 kg/ha/d and a flow of 45 m3/d for the anaerobic pond. Our study is only on the anaerobic pond and its main characteristics are: surface area (7.22*4.10) m2; depth 3.25 m and 96 m3 as volume. The removal efficiencies of the anaerobic pond only is 32%, 12%,
14% and 28% respectively for SS, soluble COD, raw COD and
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International Journal of Scientific & Engineering Research, Volume 2, Issue 12, December-2011 2
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raw BOD, for a theoretical residence time of 27 days.
Two liters of water from the liquid layer and 25 ml of sedi- ment of anaerobic pond were sampled and centrifuged at 3000 rpm during 15 minutes separately. The collected biomass were rinsed out twice two times with physiological liquid and cen- trifuged again. Then biomass from liquid layer and sediment
The methodology and procedures described above were ap- plied to determine the kinetic parameters. In this section we give the results of acidogenic and methanogenic activities in liquid and sediment layer of anaerobic pond. Examples of measurements are provided on Fig. 1 and Fig. 2.
layer were kept separately in 500 ml glass bottles filled with physiological liquid. We injected nitrogen gas in each glass bottle to maintain anaerobic condition. 25 ml of each glass bot- tle were analysed for SS and VSS to evaluate the kinetic per gram of dry biomass.
Introduction into a new glass bottle (500 ml) of 150 ml of glucose (1.5g/l) and 150 ml of acetic acid (0.1g/l) solu- tions as substrate for acidogenic and methanogenic phases respectively;
(a)
10
9
8
7
6
5
4
3
2
1
0
y = 0.8417x + 2.8603
R² = 0.9002
Addition of 25 ml of the biomass suspension (from liquid layer or from sediment) for the measurement of acido- genic or methanogenic activity in liquid or sediment layer,
0 2 4 6 8
Time (hour)
y = 0.9428x + 6.726
and 125 ml of physiological liquid (NaCl at 9g/l);
Addition of 200 ml of deaerated distilled water;
After homogenisation by shaking the glass bottle, nitro-
gen gas was bubbled to maintain anaerobic condition;
Then the glass bottle was closed down with septum and
conserved at 37° C.
Production (acidogenic phase) or consumption (methanogenic phase) in liquid or sediment layer from anaerobic pond of
(b)
16
14
12
10
8
6
4
2
0
R² = 0.9847
acetic acid was monitoring just after the operating procedure.
Samples were collected every hour, centrifuged at 3000 rpm
during 15 minutes and 0.5 ml of the supernatant was used for measurement of acetic acid (HAc).
Parameters including SS, VSS, T°C, O2 were analysed accord- ing to Standard Methods [3].
The kinetics of acidogenic and methanogenic were assessed and acetic acid was measured by the colorimetric method de- scribed by CEBEDEAU [4]. The principle of this spectropho- tometric method is based on the variation of the solution colo- ration which is proportional to the AGV concentration. The AGV react with ethylene glycol and concentrated sulfuric acid to form esters in condition well define of temperature (100° C) and time (3mn); the esters formed give the hydroxymic acids and in presence of ferric chloride (FeCl3) colour the solution which is read at 500 nm of optical density. The measurement is done tree times for each sample and the average represents the exact value of HAc express in equivalent HAc.
0 2 4 6 8
Time (hour)
Fig. 1: Graphs of acetic acid production in liquid biomass (a) and sediment biomass (b) (Acidogenic Activity/ substrat: glucose (1.5 g/l))
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International Journal of Scientific & Engineering Research, Volume 2, Issue 12, December-2011 3
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(a)
6
y = -0.3947x + 5.4402
R² = 0.9159
5
4
3
2
1
0
0 2 4 6 8
Time (hour)
(b)
9
8
7
6
5
4
3
2
1
0
y = -0.8162x + 8.4288
R² = 0.946
0 2 4 6 8
Time (hour)
Fig. 2: Graphs of acetic acid consumption in liquid biomass (a) and sediment biomass (b) (Methanogenic Activity/ substrat: acetic acid: (0.1 g/l))
[5], who obtained kinetics values in the range 0.426-0.994 from acidogenic activity and 0.994-2.13 gCOD/gVSS/d from methanogenic activity when organic matter in wastewater is dominated by dissolved easily degradable matter or by acetic acid respectively. Or [2] who used gas chromatography for measurement obtained results similar to our study.
This difference could be related to the physiological status of biomass in the liquid phase where the conditions (ORP for example) are probably not optimal for anaerobic activity. In our case there was also a delay between sampling of biomass and kinetic measurements.
We provide here a methodology to measure acidogenic and methanogenic activities in liquid and sediment biomass of anaerobic pond. The obtained values confirm that part of the activity is located in the liquid phase. In a further step those kinetics will be used to modelise and quantify anaerobic de- gradation combined with settling suspended solids in anae- robic ponds.
[1] Henze, M.; Harremoës, P., "Anaerobic treatment of wastewater in fixed film reactors", Water Science and Technology, vol. 15, pp 1-101, 1983.
[2] Soto, M.; Méndez, R.; Lema, J.M., "Methanogenic and non-methanogenic activity tests. Theoretical basis and
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International Journal of Scientific & Engineering Research, Volume 2, Issue 12, December-2011 4
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experimental set up", Water Research, vol. 27, pp
1361-1376, 1993.
[3] "Standard methods for the examination of water and wastewater", American Public Health Association/ American Water/ Works Association/Water Environment Federation, Washington, DC, USA, 1998.
[4] CEBEDEAU "Mode opératoire du dosage des acides gras volatils et leurs sels", 2000.
[5] Henze, M.; Harremoës, P.; La Cour Jansen, J.; Arvin, E., "Wastewater treatment : Biological and chemical processes", Heidelberg, Allemagne; p 383, 1995.
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