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Study of Biodegradability of Organic Fraction of Municipal Solids Waste
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Energy Procedia 19 (2012) 239 – 248
Study of Biodegradability of Organic Fraction of Municipal Solids Waste K. Derbal1a*, M. Bencheikh-lehocine1, A. H. Meniai1 1
Laboratoire de l’ingénierie des procédés de l’environnement (LIPE), département de chimie industrielle, faculté des sciences de l’ingénieur, université Mentouri de Constantine, Algeria
Abstract The present study aimed at assessing the anaerobic digestion process efficiency on the organic fraction of municipal solids waste. Batch mesophilic and thermophilic biochemical methane potential (BMP) tests were carried out and the methane potential as well as the biodegradability of all substrates was determined. The experimental studies indicated that the biological biogas production of organic fraction of municipal solids waste in mesophilic (T=35°C) and thermophilic (T=55°C) temperature were 0.450 m3 / kg and 0.481 m3 / kg respectively. Moreover, the average biogas composition in percentage for the mesophilic and thermophilic case were (CH4: 61.1 %, CO2: 38.9 %) and (CH4: 62.3 %, CO2: 37.7 %) respectively. The experimental study showed that the produced volume of biological biogas and it composition of methane in thermophilic case were higher than the produced volume and methane percentage obtained in mesophilic case (T = 35 °C). A possible reason for this could be the temperature.
© Elsevier Ltd.Ltd. Selection and/or peer review under responsibility of The MEDGREEN Society. © 2012 2010Published Publishedbyby Elsevier Selection and/or peer-review under responsibility of [name organizer] Anaerobic digestion, OFMSW, biodegradability, temperature, BMP test.
1. Introduction Anaerobic digestion is one of the most environmentally friendly and suitable treatment methods for of solid organic waste, in the last years this technology is widely applied for bio-energy production. Because of the increasing request for renewable energy. A consequence of the increasing implementation of this technology is the necessity to determine the ultimate biogas potential for several solid substrates [1]. Many researches in this field were presented, and a wide range of waste can be used as substrate for anaerobic digestion [2; 3] such as: Angelidaki [4] and Hansen [5], proposed a protocols for the * Corresponding author. Tel.: +213 31 81 88 80; fax: +213 31 81 88 80. E-mail address: [email protected].
1876-6102 © 2012 Published by Elsevier Ltd. Selection and/or peer review under responsibility of The MEDGREEN Society. doi:10.1016/j.egypro.2012.05.203
240
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
determination of the bio-methane potential of organic solid wastes, Moller [6] used biodegradability test to determine Methane productivity of manure, straw and solid fractions of manure. Others researchers were used the biodegradability test to determine the bio-methane produced from codigestion of coffee waste and sewage sludge [7]. Others researchers were interested to study the effects of different parameters on the biodegradability test such as: Effects of pH and substrate: inoculum ratio on batch methane [8], Influence of inoculum to substrate ratio on the biochemical methane potential of maize in batch tests [9]. In this paper the biodegradability test established by Owen [10] was used to determine the biodegradability of the organic fraction of municipal solid waste in mesophilic and thermophilic temperature. This protocol was applied because it is a simple and inexpensive procedure to monitor relative anaerobic biodegradability of substrates. Nomenclature
OLR
organic loading rate
COD
chemical oxygen demand
TS
total solid
TVS
total volatile solid
BMP
biological methane production
2. Characteristics of organic fraction of municipal solid waste (OFMSW) The organic fraction of municipal solid waste (OFMSW) was used in this study like substrate. It was collected and mechanically pre-treated and shredded in little granule. The waste sludge used as inoculum was obtained from the secondary decanter to the wastewater treatment plant. The characterization of total solids (TS), and volatile solids (TVS) were carried out using Standard Methods (APHA, 1998) for the inoculum and substrate (see table 1). Values of different parameters: TS, TVS and % TVS, characterizing the substrate (organic fraction of municipal solid waste (OFMSW)) and the inoculums are shown in table 1. The values of total solid (TS) and total volatile solids (TVS) are comparable with those are obtained in wastewater treatment plant [11], with a ratio of TVS/TS of 53.33 and 60.78 % for the inoculums and (OFMSW) respectively. The percentage of OFMSW in waste encourages their treatment by biological way (anaerobic digestion) and it energetic valorization (production of biogas). Table 1. Characteristic of organic fraction of municipal solids waste and sludge waste TS
TVS
% TVS
g/l
g/l
%
Inoculum (Sludge)
28,74
15,33
53,33
Substrate (OFMSW)
91,73
55,76
60,78
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
3. Biochemical methane potential (BMP) measurement The BMP was determined in duplicate anaerobic batch reactors of 1000 ml in volume. Ten (10) reactors were used for each case: mesophile (35°C) and thermophile (55°C). It was hermetically sealed with butyl rubber and stoppers and aluminium crimps. The effective volume for each bottle was 750 ml and head space for gas phase was 250 ml. Firstly the inoculum (sludge waste) was concentred using a filtration method. The obtained concentrate sludge was devised in two part of inoculum; the first one was stocked in autoclave in temperature of 35°C for one week. The second one was stoked for the same period but in temperature of 55°C. As mentioned previously, for the mesophilic case, we was used ten (10) duplicate reactors, each reactor was fed with 750 ml of inoculum (concentred and autoclaved sludge in temperature of 35°C). Than we added different quantity in mass of substrate (OFMSW) for each reactor (see table 2). Finally all the (10) reactors were incubated in autoclave with controlled temperature for one month. The temperature was fixed in the rage of 35°C. The same procedure was used for the preparation of the BMP test for the thermophilic case (55°C). The inoculum used in this case was obtained from the concentred sludge autoclaved in thermophilic temperature (55°C). For the quantity in mass of substrate (OFMSW) added for each reactor, see table 3. Each reactor was sacked daily for one minute before gas measurement. The amount of biogas production was measured dally by connecting the needle in the reactor hermetically sealed, water displacement aspirator bottles filled with acidified solution (pH = 2), this solution was used to minimize the solubility of carbon dioxide in water. The obtained volume biogas was measured in ml and atmospheric temperature and pressure. Table 2. Composition of substrate in each reactor, mesophilic case (T=35°C)
Reactor
Volume of inoculum (sludge)
Mass of (OFMSW)
ml
g
Reactor 1
Inoculum
750,0
00,00
Reactor 2
Inoculum
750,0
00,00
Reactor 3
OLR-1
750,0
13,11
Reactor 4
OLR-1
750,0
13,11
Reactor 5
OLR-2
750,0
26,22
Reactor 6
OLR-2
750,0
26,22
Reactor 7
OLR-3
750,0
39,34
Reactor 8
OLR-3
750,0
39,34
Reactor 9
OLR-4
750,0
52,45
Reactor 10
OLR-4
750,0
52,45
241
242
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Table 3. Composition of substrate in each reactor, thermophilic case (T=55°C)
Reactor
Volume of inoculum (sludge)
Mass of (OFMSW)
ml
g
Reactor 11
Inoculum
750,0
00,00
Reactor 12
Inoculum
750,0
00,00
Reactor 13
OLR-11
750,0
04,00
Reactor 14
OLR-11
750,0
04,00
Reactor 15
OLR-22
750,0
08,00
Reactor 16
OLR-22
750,0
08,00
Reactor 17
OLR-33
750,0
11,90
Reactor 18
OLR-33
750,0
11,90
Reactor 19
OLR-44
750,0
15,90
Reactor 20
OLR-44
750,0
15,90
4. Results and discussions 4.1. Characteristics of gas phase after incubation in mesophilic temperature (T =35°C) a) Cumulated biogas volume obtained from substrate (sludge + OFMSW) Figure 1, represents total cumulated volume of biogas produced from the incubation for one month of substrate composed of inoculums (sludge waste) and organic fraction of municipal solid waste (OFMSW), in mesophilic (T = 35°C) phase, and that for different value loading charge of (OFMSW: OLR-1, OLR-2, OLR-3 and OLR-4). According to figure 1, the produced biogas is relatively significant. It is proportional to the applied loading charge. The cumulated volume of produced biogas lies between 1200 and 1800 ml for OLR-1 and OLR-4 respectively. b) Cumulated biogas volume obtained from (OFMSW) The cumulated biogas produced from organic fraction of municipal solid waste (OFMSW), in the gas phase (in mesophilic temperature (T = 35°C)) was presented in figure 2. Noted that the biogas presented was the calculated biogas production of OFMSW, after subtraction of the biogas produced from inoculums (sludge waste). These values of biogas range between 300 ml for OLR-1 (4 g of OFMSW) and 900 ml for OLR-4 (15.9 g of OFMSW). From figure 2, it is obvious that a significant portion of the biogas produced totally evolved within the first 16 days (400 hours). while the experiment lasted one month months. Thus the volume of produced biogas increases with the increase in the applied loading charge of the OFMSW in the reactor.
Cumulated biogas volume (ml)
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248 OLR-1
2000
OLR-2
OLR-3
OLR-4
1800 1600 1400 1200 1000 800 600 400 200 0 0
70
192
263
406
531
601
Time (h)
Cumulated biogas volume (ml)
Fig. 1. Cumulated biogas volume (Sludge + OFMSW), (T=55°C) OLR-1
1000
OLR-2
OLR-3
OLR-4
900 800 700 600 500 400 300 200 100 0 0
70
192
263
406
531
601
Time (h)
Fig. 2. Cumulated biogas volume (OFMSW), (T=35°C)
c)
Cumulated methane and carbon dioxide obtained from (OFMSW)
Figure 3, represents the cumulated volume of the methane produced during the incubation period in mesophilic phase, which lies between 177 ml for OLR-1 and 534 ml for OLR-4. Thus the volume of produced methane is also relatively significant. In the same way figure 4, represents the variation of production of the carbon dioxide in reactor.
243
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Cumulated methane volume (ml)
244 OLR-1
600
OLR-2
OLR-3
OLR-4
500 400 300 200 100 0 0
70
192
263
406
531
601
Time (h)
Fig. 3. Cumulated CH4 volume (OFMSW), (T=35°C) OLR-1
Cumulated CO2 volume (ml)
400
OLR-2
OLR-3
OLR-4
350 300 250 200 150 100 50 0 0
70
192
263
406
531
601
Time (h)
Fig. 4. Cumulated CO2 volume (OFMSW) à (T=35°C)
Figure 5, represents the average composition of biogas expressed as a percentage of methane and carbon dioxide, during the incubation period. This figure shows clearly that the average percentage of methane in produced biogas is 61.1 %, this value reflect the good operation of anaerobic digestion process. Generally a percentage of methane ranging between 50 and 80 % remains acceptable in anaerobic digestion process.
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Biogas composition (%)
80 60 40 20 0
% CH4
% CO2
Fig. 5. Biogas composition (OFMSW), (T=35°C))
4.2. Characteristics of gas phase after incubation in thermophilic temperature (T =55°C) a) Cumulated biogas volume obtained from substrate (sludge + OFMSW) In the same way the volume and the composition of biogas are significant for the control and the monitoring of anaerobic digestion process. Indeed a consequent production of biogas reflects the good operation of digester. Figure 6, represents the cumulated volume of biogas produced in thermophilic phase from the substrate composed from sludge waste and organic fraction of municipal solid waste (OFMSW). Figure 6, shows clearly that the cumulated volume of produced biogas increases by increasing the loading charge of substrate (OFMSW). Thus the biogas produced by (OLR-11) is low compared with that produced by OLR-44. This increase can be explained by a good balance produced between concentration the microorganisms concentration and the applied loading charge of substrate in reactor. The cumulated volume of biogas lies between 1000 ml for OLR-11 and 1679 ml for OLR-44. b) Cumulated biogas volume obtained from substrate ( OFMSW) Figure 7, represents the variation of cumulated volume of produced biogas in thermophilic phase (T = 55°C), in this case only the OFMSW was considered. Thus the volume of produced biogas is proportional to the applied loading charge in digester. All obtained curve for different charge are characterized by exponential phase (maximum production of biogas) followed by low production of biogas. The cumulated volume of biogas lies between 242 ml for OLR-11 and 848 ml for OLR-44. c)
Cumulated bio-methane and carbon dioxide obtained from substrate ( OFMSW)
The composition of produced biogas anaerobic digestion process is a very significant parameter for the control and the monitoring of this process. Indeed a consequent production of biogas reflects the good operation of the digester. Figure 8, represents the cumulated volume of produced methane during the incubation period in thermophilic phase, the peoduced volume of methane is lies between 151 ml for (OLR-11) and 528 ml for OLR-44. Thus it is proportional to the applied loadin charge in digester. In the same way for the produced volume of carbon dioxide, see figure 9. This increase can be explained by the increase in concentration of the micro-organisms in the liquid phase, without neglecting the effect of the temperature on the increase of the degradation kinetics of substrate.
245
246
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Cumulated biogas volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
1800 1600 1400 1200 1000 800 600 400 200 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 6. Cumulated biogas volume (Sludge + OFMSW), (T=55°C)
Cumulated biogas volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
900 800 700 600 500 400 300 200 100 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 7. Cumulated biogas volume (OFMSW), (T=55°C)
Cumulated methane volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
600 500 400 300 200 100 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 8. Cumulated CH4 volume (OFMSW) à (T=55°C)
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Cumulated CO2 volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
350 300 250 200 150 100 50 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 9 Cumulated CO2 volume (OFMSW), (T=55°C)
Figure 10, represents the average composition of biogas expressed as a percentage of methane and carbon dioxide, during incubation period in thermophilic case. According to this figure, the percentage of methane is 62.3 %, it is relatively high compared with that obtained in mesophilic case, which is 61.1 %. As mentioned previously, practically, the good operation of anaerobic digestion process is characterized by a percentage of methane higher than 50 %. Thus the percentage obtained in this case reflects the good operation of the process.
Biogas composition (%)
80 60 40 20 0
% CH4
% CO2
Fig. 10. Biogas composition, (T=55°C)
5. Results and discussions In this study aimed at assessing the anaerobic digestion process efficiency on the organic fraction of municipal solids waste. Batch mesophilic and thermophilic biochemical methane potential (BMP) tests were carried out and the methane potential as well as the biodegradability of all substrates was determined. The experimental studies indicated that the biological biogas production of organic fraction of
247
248
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
municipal solids waste in mesophilic (T=35°C) and thermophilic (T=55°C) temperature were 0.450 m3 / kg and 0.481 m3 / kg respectively. Moreover, the average biogas composition in percentage for the mesophilic and thermophilic case were (CH4: 61.1 %, CO2: 38.9 %) and (CH4: 62.3 %, CO2: 37.7 %) respectively. The experimental study showed that the produced volume of biological biogas and it composition of methane in thermophilic case were higher than the produced volume and methane percentage obtained in mesophilic case (T = 35 °C). A possible reason for this could be the temperature.
References [1] Angelidaki I, Alves M, Bolzonella D, Borzacconi L, Campos J.L, Guwy A.J, Kalyuzhnyi S, Jenicek P and Van Lier J.B. Defining the biomethane potential (BMP) of solid organic wastes and energy crops: a proposed protocol for batch assays. Water science and technology 2009; 59(5):927-934. [2] Nallathambi Gunaseelan V. Anaerobic digestion of biomass for methane production: a review. Biomass Bioenergy 1997;13:83–114. [3] Erguder TH, Guven E, Demirer GN. Anaerobic treatment of olive mill wastes in batch reactors. Process Biochem 2000;36:243–248. [4] Angelidaki I, Sanders W. Assessment of the anaerobic biodegradability of macropollutants. Rev Environ Sci Biotechnol 2004;3:117–29. [5] Hansen TL, Schmidt JE, Angelidaki I, Marca E, Jansen JlC, Mosbaek H, et al. Method for determination of methane potentials of solid organic waste. Waste Manage 2004;24:393–400. [6] Moller HB, Sommer SG, Ahring BK. Methane productivity of manure, straw and solid fractions of manure. Biomass Bioenergy 2004;26:485–95. [7] Neves L, Oliveira R, Alves MM. Anaerobic co-digestion of coffee waste and sewage sludge. Waste Manage 2006;26:176–81. [8] Chen T-H, Hashimoto AG. Effects of pH and substrate: inoculum ratio on batch methane fermentation. Bioresour Technol 1996;56:179–86. [9] Raposo F, Banks CJ, Siegert I, Heaven S, Borja R. Influence of inoculum to substrate ratio on the biochemical methane potential of maize in batch tests. Process Biochem 2006;41:1444–50. [10] Owen W.F, Stuckey D.C, Healy J.B, Young L.Y, McCarty P.L. Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Res. 1979; 13: 485–492. [11] Metcalf & Eddy .Wastewater Engineering, treatment and reuse. USA 2003; (4th edition); McGraw-Hill book co.
Energy Procedia 19 (2012) 239 – 248
Study of Biodegradability of Organic Fraction of Municipal Solids Waste K. Derbal1a*, M. Bencheikh-lehocine1, A. H. Meniai1 1
Laboratoire de l’ingénierie des procédés de l’environnement (LIPE), département de chimie industrielle, faculté des sciences de l’ingénieur, université Mentouri de Constantine, Algeria
Abstract The present study aimed at assessing the anaerobic digestion process efficiency on the organic fraction of municipal solids waste. Batch mesophilic and thermophilic biochemical methane potential (BMP) tests were carried out and the methane potential as well as the biodegradability of all substrates was determined. The experimental studies indicated that the biological biogas production of organic fraction of municipal solids waste in mesophilic (T=35°C) and thermophilic (T=55°C) temperature were 0.450 m3 / kg and 0.481 m3 / kg respectively. Moreover, the average biogas composition in percentage for the mesophilic and thermophilic case were (CH4: 61.1 %, CO2: 38.9 %) and (CH4: 62.3 %, CO2: 37.7 %) respectively. The experimental study showed that the produced volume of biological biogas and it composition of methane in thermophilic case were higher than the produced volume and methane percentage obtained in mesophilic case (T = 35 °C). A possible reason for this could be the temperature.
© Elsevier Ltd.Ltd. Selection and/or peer review under responsibility of The MEDGREEN Society. © 2012 2010Published Publishedbyby Elsevier Selection and/or peer-review under responsibility of [name organizer] Anaerobic digestion, OFMSW, biodegradability, temperature, BMP test.
1. Introduction Anaerobic digestion is one of the most environmentally friendly and suitable treatment methods for of solid organic waste, in the last years this technology is widely applied for bio-energy production. Because of the increasing request for renewable energy. A consequence of the increasing implementation of this technology is the necessity to determine the ultimate biogas potential for several solid substrates [1]. Many researches in this field were presented, and a wide range of waste can be used as substrate for anaerobic digestion [2; 3] such as: Angelidaki [4] and Hansen [5], proposed a protocols for the * Corresponding author. Tel.: +213 31 81 88 80; fax: +213 31 81 88 80. E-mail address: [email protected].
1876-6102 © 2012 Published by Elsevier Ltd. Selection and/or peer review under responsibility of The MEDGREEN Society. doi:10.1016/j.egypro.2012.05.203
240
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
determination of the bio-methane potential of organic solid wastes, Moller [6] used biodegradability test to determine Methane productivity of manure, straw and solid fractions of manure. Others researchers were used the biodegradability test to determine the bio-methane produced from codigestion of coffee waste and sewage sludge [7]. Others researchers were interested to study the effects of different parameters on the biodegradability test such as: Effects of pH and substrate: inoculum ratio on batch methane [8], Influence of inoculum to substrate ratio on the biochemical methane potential of maize in batch tests [9]. In this paper the biodegradability test established by Owen [10] was used to determine the biodegradability of the organic fraction of municipal solid waste in mesophilic and thermophilic temperature. This protocol was applied because it is a simple and inexpensive procedure to monitor relative anaerobic biodegradability of substrates. Nomenclature
OLR
organic loading rate
COD
chemical oxygen demand
TS
total solid
TVS
total volatile solid
BMP
biological methane production
2. Characteristics of organic fraction of municipal solid waste (OFMSW) The organic fraction of municipal solid waste (OFMSW) was used in this study like substrate. It was collected and mechanically pre-treated and shredded in little granule. The waste sludge used as inoculum was obtained from the secondary decanter to the wastewater treatment plant. The characterization of total solids (TS), and volatile solids (TVS) were carried out using Standard Methods (APHA, 1998) for the inoculum and substrate (see table 1). Values of different parameters: TS, TVS and % TVS, characterizing the substrate (organic fraction of municipal solid waste (OFMSW)) and the inoculums are shown in table 1. The values of total solid (TS) and total volatile solids (TVS) are comparable with those are obtained in wastewater treatment plant [11], with a ratio of TVS/TS of 53.33 and 60.78 % for the inoculums and (OFMSW) respectively. The percentage of OFMSW in waste encourages their treatment by biological way (anaerobic digestion) and it energetic valorization (production of biogas). Table 1. Characteristic of organic fraction of municipal solids waste and sludge waste TS
TVS
% TVS
g/l
g/l
%
Inoculum (Sludge)
28,74
15,33
53,33
Substrate (OFMSW)
91,73
55,76
60,78
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
3. Biochemical methane potential (BMP) measurement The BMP was determined in duplicate anaerobic batch reactors of 1000 ml in volume. Ten (10) reactors were used for each case: mesophile (35°C) and thermophile (55°C). It was hermetically sealed with butyl rubber and stoppers and aluminium crimps. The effective volume for each bottle was 750 ml and head space for gas phase was 250 ml. Firstly the inoculum (sludge waste) was concentred using a filtration method. The obtained concentrate sludge was devised in two part of inoculum; the first one was stocked in autoclave in temperature of 35°C for one week. The second one was stoked for the same period but in temperature of 55°C. As mentioned previously, for the mesophilic case, we was used ten (10) duplicate reactors, each reactor was fed with 750 ml of inoculum (concentred and autoclaved sludge in temperature of 35°C). Than we added different quantity in mass of substrate (OFMSW) for each reactor (see table 2). Finally all the (10) reactors were incubated in autoclave with controlled temperature for one month. The temperature was fixed in the rage of 35°C. The same procedure was used for the preparation of the BMP test for the thermophilic case (55°C). The inoculum used in this case was obtained from the concentred sludge autoclaved in thermophilic temperature (55°C). For the quantity in mass of substrate (OFMSW) added for each reactor, see table 3. Each reactor was sacked daily for one minute before gas measurement. The amount of biogas production was measured dally by connecting the needle in the reactor hermetically sealed, water displacement aspirator bottles filled with acidified solution (pH = 2), this solution was used to minimize the solubility of carbon dioxide in water. The obtained volume biogas was measured in ml and atmospheric temperature and pressure. Table 2. Composition of substrate in each reactor, mesophilic case (T=35°C)
Reactor
Volume of inoculum (sludge)
Mass of (OFMSW)
ml
g
Reactor 1
Inoculum
750,0
00,00
Reactor 2
Inoculum
750,0
00,00
Reactor 3
OLR-1
750,0
13,11
Reactor 4
OLR-1
750,0
13,11
Reactor 5
OLR-2
750,0
26,22
Reactor 6
OLR-2
750,0
26,22
Reactor 7
OLR-3
750,0
39,34
Reactor 8
OLR-3
750,0
39,34
Reactor 9
OLR-4
750,0
52,45
Reactor 10
OLR-4
750,0
52,45
241
242
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Table 3. Composition of substrate in each reactor, thermophilic case (T=55°C)
Reactor
Volume of inoculum (sludge)
Mass of (OFMSW)
ml
g
Reactor 11
Inoculum
750,0
00,00
Reactor 12
Inoculum
750,0
00,00
Reactor 13
OLR-11
750,0
04,00
Reactor 14
OLR-11
750,0
04,00
Reactor 15
OLR-22
750,0
08,00
Reactor 16
OLR-22
750,0
08,00
Reactor 17
OLR-33
750,0
11,90
Reactor 18
OLR-33
750,0
11,90
Reactor 19
OLR-44
750,0
15,90
Reactor 20
OLR-44
750,0
15,90
4. Results and discussions 4.1. Characteristics of gas phase after incubation in mesophilic temperature (T =35°C) a) Cumulated biogas volume obtained from substrate (sludge + OFMSW) Figure 1, represents total cumulated volume of biogas produced from the incubation for one month of substrate composed of inoculums (sludge waste) and organic fraction of municipal solid waste (OFMSW), in mesophilic (T = 35°C) phase, and that for different value loading charge of (OFMSW: OLR-1, OLR-2, OLR-3 and OLR-4). According to figure 1, the produced biogas is relatively significant. It is proportional to the applied loading charge. The cumulated volume of produced biogas lies between 1200 and 1800 ml for OLR-1 and OLR-4 respectively. b) Cumulated biogas volume obtained from (OFMSW) The cumulated biogas produced from organic fraction of municipal solid waste (OFMSW), in the gas phase (in mesophilic temperature (T = 35°C)) was presented in figure 2. Noted that the biogas presented was the calculated biogas production of OFMSW, after subtraction of the biogas produced from inoculums (sludge waste). These values of biogas range between 300 ml for OLR-1 (4 g of OFMSW) and 900 ml for OLR-4 (15.9 g of OFMSW). From figure 2, it is obvious that a significant portion of the biogas produced totally evolved within the first 16 days (400 hours). while the experiment lasted one month months. Thus the volume of produced biogas increases with the increase in the applied loading charge of the OFMSW in the reactor.
Cumulated biogas volume (ml)
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248 OLR-1
2000
OLR-2
OLR-3
OLR-4
1800 1600 1400 1200 1000 800 600 400 200 0 0
70
192
263
406
531
601
Time (h)
Cumulated biogas volume (ml)
Fig. 1. Cumulated biogas volume (Sludge + OFMSW), (T=55°C) OLR-1
1000
OLR-2
OLR-3
OLR-4
900 800 700 600 500 400 300 200 100 0 0
70
192
263
406
531
601
Time (h)
Fig. 2. Cumulated biogas volume (OFMSW), (T=35°C)
c)
Cumulated methane and carbon dioxide obtained from (OFMSW)
Figure 3, represents the cumulated volume of the methane produced during the incubation period in mesophilic phase, which lies between 177 ml for OLR-1 and 534 ml for OLR-4. Thus the volume of produced methane is also relatively significant. In the same way figure 4, represents the variation of production of the carbon dioxide in reactor.
243
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Cumulated methane volume (ml)
244 OLR-1
600
OLR-2
OLR-3
OLR-4
500 400 300 200 100 0 0
70
192
263
406
531
601
Time (h)
Fig. 3. Cumulated CH4 volume (OFMSW), (T=35°C) OLR-1
Cumulated CO2 volume (ml)
400
OLR-2
OLR-3
OLR-4
350 300 250 200 150 100 50 0 0
70
192
263
406
531
601
Time (h)
Fig. 4. Cumulated CO2 volume (OFMSW) à (T=35°C)
Figure 5, represents the average composition of biogas expressed as a percentage of methane and carbon dioxide, during the incubation period. This figure shows clearly that the average percentage of methane in produced biogas is 61.1 %, this value reflect the good operation of anaerobic digestion process. Generally a percentage of methane ranging between 50 and 80 % remains acceptable in anaerobic digestion process.
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Biogas composition (%)
80 60 40 20 0
% CH4
% CO2
Fig. 5. Biogas composition (OFMSW), (T=35°C))
4.2. Characteristics of gas phase after incubation in thermophilic temperature (T =55°C) a) Cumulated biogas volume obtained from substrate (sludge + OFMSW) In the same way the volume and the composition of biogas are significant for the control and the monitoring of anaerobic digestion process. Indeed a consequent production of biogas reflects the good operation of digester. Figure 6, represents the cumulated volume of biogas produced in thermophilic phase from the substrate composed from sludge waste and organic fraction of municipal solid waste (OFMSW). Figure 6, shows clearly that the cumulated volume of produced biogas increases by increasing the loading charge of substrate (OFMSW). Thus the biogas produced by (OLR-11) is low compared with that produced by OLR-44. This increase can be explained by a good balance produced between concentration the microorganisms concentration and the applied loading charge of substrate in reactor. The cumulated volume of biogas lies between 1000 ml for OLR-11 and 1679 ml for OLR-44. b) Cumulated biogas volume obtained from substrate ( OFMSW) Figure 7, represents the variation of cumulated volume of produced biogas in thermophilic phase (T = 55°C), in this case only the OFMSW was considered. Thus the volume of produced biogas is proportional to the applied loading charge in digester. All obtained curve for different charge are characterized by exponential phase (maximum production of biogas) followed by low production of biogas. The cumulated volume of biogas lies between 242 ml for OLR-11 and 848 ml for OLR-44. c)
Cumulated bio-methane and carbon dioxide obtained from substrate ( OFMSW)
The composition of produced biogas anaerobic digestion process is a very significant parameter for the control and the monitoring of this process. Indeed a consequent production of biogas reflects the good operation of the digester. Figure 8, represents the cumulated volume of produced methane during the incubation period in thermophilic phase, the peoduced volume of methane is lies between 151 ml for (OLR-11) and 528 ml for OLR-44. Thus it is proportional to the applied loadin charge in digester. In the same way for the produced volume of carbon dioxide, see figure 9. This increase can be explained by the increase in concentration of the micro-organisms in the liquid phase, without neglecting the effect of the temperature on the increase of the degradation kinetics of substrate.
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Cumulated biogas volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
1800 1600 1400 1200 1000 800 600 400 200 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 6. Cumulated biogas volume (Sludge + OFMSW), (T=55°C)
Cumulated biogas volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
900 800 700 600 500 400 300 200 100 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 7. Cumulated biogas volume (OFMSW), (T=55°C)
Cumulated methane volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
600 500 400 300 200 100 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 8. Cumulated CH4 volume (OFMSW) à (T=55°C)
K. Derbal et al. / Energy Procedia 19 (2012) 239 – 248
Cumulated CO2 volume (ml)
OLR-1
OLR-2
OLR-3
OLR-4
350 300 250 200 150 100 50 0
0
68
165 213 332 380 428 524 595 697 745
Time (h)
Fig. 9 Cumulated CO2 volume (OFMSW), (T=55°C)
Figure 10, represents the average composition of biogas expressed as a percentage of methane and carbon dioxide, during incubation period in thermophilic case. According to this figure, the percentage of methane is 62.3 %, it is relatively high compared with that obtained in mesophilic case, which is 61.1 %. As mentioned previously, practically, the good operation of anaerobic digestion process is characterized by a percentage of methane higher than 50 %. Thus the percentage obtained in this case reflects the good operation of the process.
Biogas composition (%)
80 60 40 20 0
% CH4
% CO2
Fig. 10. Biogas composition, (T=55°C)
5. Results and discussions In this study aimed at assessing the anaerobic digestion process efficiency on the organic fraction of municipal solids waste. Batch mesophilic and thermophilic biochemical methane potential (BMP) tests were carried out and the methane potential as well as the biodegradability of all substrates was determined. The experimental studies indicated that the biological biogas production of organic fraction of
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municipal solids waste in mesophilic (T=35°C) and thermophilic (T=55°C) temperature were 0.450 m3 / kg and 0.481 m3 / kg respectively. Moreover, the average biogas composition in percentage for the mesophilic and thermophilic case were (CH4: 61.1 %, CO2: 38.9 %) and (CH4: 62.3 %, CO2: 37.7 %) respectively. The experimental study showed that the produced volume of biological biogas and it composition of methane in thermophilic case were higher than the produced volume and methane percentage obtained in mesophilic case (T = 35 °C). A possible reason for this could be the temperature.
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