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Enhancement of hydrogen and methane production from co-digestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e7
Available online at www.sciencedirect.com
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Enhancement of hydrogen and methane production from co-digestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation Suwimon Kanchanasuta a,b,*, Omjit Sillaparassamee a a
Department of Environmental Health Sciences, Faculty of Public Health, Mahidol University, Bangkok 10400, Thailand b Center of Excellence on Environmental Health and Toxicology, Bangkok, Thailand
article info
abstract
Article history:
Two-stage thermophilic hydrogen fermentation and mesophilic methanogenic process for
Received 19 September 2016
methane production with hydrogenic effluent from co-digestion of decanter cake (DC) and
Received in revised form
crude glycerol (GLC) was investigated. For the single stage, hydrogen reactor with 2% wv1
3 January 2017
total solid (TS) of DC and crude glycerol was operated at 4 days hydraulic retention time
Accepted 7 January 2017
(HRT) with varying glycerol loading of 0.75e1.5% GLC while methane reactor with 2% wv1
Available online xxx
total solid (TS) of DC was operated at 13 days HRT. The maximum hydrogen production rate and hydrogen yield in the single stage obtained from the 1.5% GLC co-digestion con-
Keywords:
dition were 461 mL H2 L1 d1 and 23 L H2 kg1 TSadded, respectively. Crude glycerol was
Two-stage fermentation
found to be an alternative pH-adjust substance in hydrogen reactor. At the condition of
Crude glycerol
0.75% GLC co-digestion, the pH was maintained in the range higher than 5.3 throughout the
Decanter cake
fermentation process. Semi-continuous methane production with 0.75% GLC hydrogenic
Energy recovery
effluent achieved the maximum methane production rate and methane yield about 736 mL
Co-digestion
CH4 L1 d1 and 44 L CH4 kg1 TSadded compared with the single stage with 2% TSDC and the second stage with 1% GLC hydrogenic effluent. Total energy recovery from two-stage fermentation about 0.056 kWh kg1 TSadded was achieved from the condition of 0.75% GLC hydrogenic effluent condition. It was improved by 6.2 and 1.6 times compared to the single stage in both hydrogen and methane reactor, respectively. This work demonstrated the practical enhancement of energy recovery and the efficiency of waste utilization by two-stage fermentation for hydrogen and methane production from decanter cake and crude glycerol. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Department of Environmental Health Sciences, Faculty of Public Health, Mahidol University, Bangkok 10400, Thailand. Fax: þ66 2354 8525. E-mail addresses: [email protected], [email protected] (S. Kanchanasuta). http://dx.doi.org/10.1016/j.ijhydene.2017.01.032 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Introduction Decanter cake is one type of waste produced from palm oil industry in the step of oil purification. Previous studies reported that typical palm oil mills generate 3.5% of oil palm decanter cake (OPDC) for each tonne of fresh fruit brunches (FFB) [1,2] and 42 kg per tonne fresh fruit brunches [3]. High biodegradable organic contents and nutrient rich compositions make palm oil decanter cake as an attractive feedstock for biogas production. Crude glycerol is a by-product from biodiesel industry. Because biodiesel production is rapidly expanding in Thailand in order to meet the increasing energy demand of transportation, the crude glycerol generated from the trans-esterification of vegetables oils, has also been generated in a large quantity. Although the various applications such as pure glycerol in food, pharmaceutical, cosmetics, and many other industries have been reported, they are too costly to refine the crude glycerol to a high purity, particularly for medium and small biodiesel producers. Moreover, some period of over biodiesel in the market results in the low cost of crude glycerol, so burning is the disposal method of this case. Many previous researches have been conducted and utilized of crude glycerol to produce the valuable products such as biohydrogen [4e7], 1,3 propanediol [8], bioethanol [9]. Hydrogen (H2) is regarded as one of the alternative source for clean and renewable energy and considered as an alternative non-polluting fuel for the future. Biohydrogen production is always accompanied by volatile fatty acids (VFAs) production such as acetate, butyrate, propionate and ethanol that are more appropriate substrates for methane production further in the second-stage [10]. Therefore, methane production is well considered as a suitable post-treatment unit of hydrogen production. In recent times, a two-stage process combining hydrogenesis and methanogenesis has been a focused technology. The significance of two-stage process includes, process stability, higher biogas yield, and high total energy recovery [11]. Sunyoto et al. [12] had studied two-phase anaerobic digestion of food waste and found that the maximum production rates of hydrogen by 32.5% and methane 41.6%, could improve hydrogen and methane yield about 31.0% and 10%, respectively. Likewise, Krishnan et al. [11] showed a feasibility of two-stage fermentation from palm oil mill effluent with total COD removal efficiency of 94% while hydrogen and methane yield were observed 215 L H2 kg COD1 and 320 L CH4 kg COD1, respectively. Co-digestion plays the important factor in biogas production process. During the fermentation, two or more organic substances should be degraded properly to enhance biogas production as compared to sole substrate. Previous studies revealed that co-digestion can improve biogas production from 25% to 400% over the mono-digestion of the same feedstocks [13,14]. Because the metabolic properties, nutritional requirements, growth rates and optimum operational factors are significantly different, so it is difficult to improve the overall of anaerobic co-digestion system in one-stage digester [15,16]. The two-stage system of biogas fermentation appears to be a more productive process compared to one-stage system. Therefore, it has been applied to solve the obstacles in the various problems found in
the one-stage system of biogas production [17,18]. Our previous study displayed the feasibility of decanter cake to be used as the indigenous source of inocula seed and the feedstock in anaerobic digestion process [19]. Besides, for co-digestion batch test, results indicated that the addition of decanter cake as co-feedstock and microbial source, containing hydrolytic and acidogenic bacteria, yielded a better performance in the biogas production and simulate glycerol utilization at the same time. Nowadays, there are few literatures reporting about twostage fermentation from co-digestion of agro-industrial waste such as decanter cake and crude glycerol. Therefore, this work aim to enhance the efficiency of hydrogen and methane production by two-stage fermentation of thermophilic hydrogen production and semi-continuous mesophilic methane production from co-digestion of decanter cake and crude glycerol.
Materials and methods Crude glycerol Brownish crude glycerol with 63.9% glycerol purity was obtained from Trang Palm Oil Co., Ltd. Trang, Thailand. The characteristic of the crude glycerol is as shown in Table 1.
Microbial inoculum Anaerobic sludge seed was obtained from a full-scale upflow anaerobic sludge blanket reactor treating beverage processing wastewater (Sermsuk Industry Co. Ltd., Pathumtani, Thailand). The anaerobic sludge seed have the characteristics shown in Table 1. Prior to use, the granule was sieved to the size <0.5 mm to remove coarse matters and then washed twice with tap water. The anaerobic granule sludge was recultivated in 0.5% (w/v) glucose solution until reach to steady state regarding the CH4 content and volume of CH4 production. Subsequently, it was washed twice with the distilled water before used as a seed microbial inoculum for the biogas fermentation.
Decanter cake Decanter cake, a feedstock for the biogas production and a source of indigenous microbes, was collected from palm oil milling plant, Suksomboon palm oil industry in Chonburi, Thailand. The sample was stored at 4 C before use. The characteristic of the palm oil decanter cake is as shown in Table 1.
Continuous stirred tank reactors Single stage of hydrogen production The reactor with working volume of 4 L was operated at 4 days HRT. It was started with co-digestion of 2% wv1 total solid (TS) of decanter cake (DC) and 1 g of glycerol (GLC) without the external anaerobic sludge. Subsequently, 1 L of new mixture substrate was daily fed into the reactor while digestate was removed to keep the operating volume at 4 L. The
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Table 1 e Characteristics of crude glycerol, sludge seed and palm oil decanter cake. Parameter
Crude glycerol
Sludge seed
Decanter cake
Total solids (TS) Total volatile solids Total COD Soluble COD Total carbon Total nitrogen Cellulose Hemicellulose Lignin pH Conductivity FOG Methanol Monoglyceride Diglyceride Triglyceride TOC
NA NA 443,262 mg kg1 115,248 mg kg1 NA NA NA NA NA 8.76 529 ms cm1 5222 mg L1 0.36 % vv1 0.03 % ww1 0.02 % ww1 0.07 % ww1 414,666 mg L1
22,233 mg L1 19,700 mg L1 40,153 mg L1 2881 mg L1 NA NA NA NA NA NA NA NA NA NA NA NA NA
197,670 mg kg1 169,740 mg kg1 NA NA 47.35 % ww1 4.34 % ww1 50.07 % ww1 30.74 % ww1 10.40 % ww1 NA NA NA NA NA NA NA NA
NA ¼ Not Analyzed.
concentration of glycerol was slightly increased by 0.25, 0.5 and 0.75% wv1 GLC, respectively while decanter cake was fixed at 2% TS throughout the fermentation process. Increase glycerol loading of 0.75% for 5 days, 1% for 7 days, 1.25% for 4 days and 1.5% for 12 days were added into the reactor afterward. Pattern of glycerol loading depends on the performance of hydrogen production in the reactor. The substrate was adjusted to pH 7 with 3 N NaOH or 3 N HCl. The reactor was operated under thermophilic condition (55 C).
Semi-continuous methane production The reactor was started with 2% TS of the decanter cake and 1 L of the anaerobic sludge. The reactor was maintained by feeding 300 mL of new substrate daily (2% TS of decanter) and removing digestate to keep the operating volume at 4 L. The second stage of methane production was started after 44 days cultivation by feeding hydrogenic effluent from hydrogen reactor of the single stage. Hydrogenic effluent of 0.75% GLC (300 mL) were fed into the reactor in the second stage for 14 days and 1% GLC for 7 days. All feeding substrates were adjusted to pH 7 with 3 N NaOH or 3 N HCl and 5000 mg CO3 2 =L with NaHCO3 and Na2CO3. The reactor was operated under mesophilic condition (37 C).
Analytical methods Total solids (TS), and chemical oxygen demand (COD) were measured according to Standard Methods 2540 G and 5220 B, respectively [20]. Glycerol was spectrophotometrically determined by chromotropic acid method (modified from Handel [21]). The amount of generated biogas was recorded using liquid displacement gasometers. Biogas content (H2, CH4, and CO2) was measured periodically everyday using a gas chromatograph (Shimadzu GC-8A, Kyoto, Japan) equipped with a thermal conductivity detector (TCD) with a Unibeads C 60/80 column (GL Sciences, Inc., Tokyo, Japan). Helium was used as a carrier gas. The temperatures of the injection port and the detector were 150 C and 80 C, respectively. Volatile fatty
acids (VFAs) were analyzed by gas chromatography (Shimadzu GC-7A system equipped with a flame ionization detector and a Stabilwax DA capillary column; Restek Corporation, PA, USA). The temperatures of the injection port and detector were maintained at 240 C [22].
Results and discussion Biohydrogen production from co-digestion of palm oil decanter cake with crude glycerol in the single stage Co-digestion of 2% TS palm oil decanter cake with the different concentrations of crude glycerol for hydrogen production by using the indigenous microorganism under the control thermophilic condition of 55 C and 100 rpm in the continuous stirred tank reactor (CSTR) was investigated. Organic loading of glycerol also strongly affected the overall fermentation process. Hydrogen production with the 1.5% GLC achieved the maximum hydrogen production and hydrogen content detected in the reactor of 1843 mL and 49%, respectively (Fig. 1). The methane content was not observed across the fermentation, indicating that there was no methanogenic activity in the reactor. Stability of pH (higher than 5.3) under the condition of 0.75% GLC co-digestion could be observed. Butyrate and acetate were the main metabolites accumulated since the first day fermentation for all cases and they trended to increase with the increase concentration of crude glycerol co-digestion (Fig. 2). The pH could be maintained in the range 5.0e5.4 throughout the fermentation process while the total concentration of undissociated acids accumulated in the reactor was higher than 50 mM for the 1, 1.25 and 1.5% GLC codigestion conditions (data not shown). In general, drop of pH during fermentation process resulted in imbalance of NADH2/ NADþ ratio and lower hydrogen production yield [23]. Not only butyrate and acetate were dominantly generated in the reactor, ethanol was also accumulated in the high level compared with the other metabolites (propionic acid and
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Fig. 1 e Hydrogen production and hydrogen content (%H2) from the single stage.
Fig. 2 e Metabolites and total volatile fatty acid from the single stage of hydrogen production. valeric acid). High accumulation of undissociated acid above 19 mM was found to be an inhibition factor for acidogenesis which was a threshold concentration for significant decreasing hydrogen yield and beginning solventogenesis [24]. Ethanol is one of more reduced substance produced in the solventogenesis reaction and this is an indicator for solventogenesis reaction in the reactor. This reaction can generate during the unbalance condition of proton and the detoxicity condition within the bacterial cell. In the acidity condition, undissociated acid form can be infiltrated through the cells and proton will be released inside the cells, thus, resulting in toxicity condition. Therefore, solventogenesis will be generated for maintaining the neutral condition for normal metabolism process. Reduction of hydraulic retention time may be an alternative solution to dilute the acidic condition in the reactor. The optimal HRT for hydrogen production from organic fraction of municipal solid wastes reported in the previous research is about 1e2 day [25]. Due to the characteristic of crude glycerol (high COD and pH of 8.76), it is not only used as co-digestion for hydrogen fermentation, it may
also be used as an alternative pH-adjust substance for maintaining the pH condition in the reactor resulting in continuous hydrogen production. In the batch experiment of our previous study [19], hydrogen fermentation process from the sole decanter cake was stopped after 24 h fermentation for most cases because of the acidic condition in the reactor (pH lower than 5). However, to improve the efficiency of hydrogen production in the first stage, not only the optimal condition, the addition of hydrogen producing bacteria and the stability of them across the fermentation have been further investigated.
Semi-continuous biomethane production For comparison with the single stage mesophilic digester, methane production with 2% TS of decanter cake by anaerobic sludge was initially operated for 43 days cultivation to acclimate the condition. Subsequently, hydrogenic effluent from the 0.75% GLC and 1% GLC co-digestion was fed into the reactor to start the second stage. The characteristics of hydrogenic effluent are presented in Table 2. Methane gas
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Table 2 e Characteristic of the hydrogenic effluent from hydrogen production process. Parameter pH Total volatile fatty acid (mg L1) Acetic acid (mg L1) Propionic acid (mg L1) Butyric acid (mg L1) Valeric acid (mg L1) Ethanol (mg L1)
0.75 % GLC
1% GLC
5.3 1313 164 24 1125 e 197
5.1 3274 224 16 3011 23 1561
production obtained from the CSTR reactor was showed in Fig. 3. The average methane production from single stage with 2% TS decanter cake and two-stage with 0.75 and 1% GLC of hydrogenic effluent were 2094, 2794 and 1992 mL respectively. The maximum methane production and methane content of 2943 mL and 71% were observed from two-stage with 0.75% GLC of hydrogenic effluent. Results revealed that the second stage of methane production from 0.75% GLC hydrogenic effluent achieved better performance in both methane production and methane content than those from single stage and two-stage with 1% GLC hydrogenic effluent. On the other
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hand, the maximum efficiency of waste reduction based on TS (59%), total COD (89%) and soluble COD (90%) removal were obtained from single stage methane production with the average of 54%, 83% and 78% respectively (Fig. 4). It may be due to a number of hydrolytic bacteria from the indigenous microbe in the first stage of hydrogen production. Besides, solid fraction after digesting by hydrolytic bacteria will remain only complex fraction which had to further digest in the next step. Therefore, adding the external anaerobic seed in the first stage is necessary for improving the overall process. Comparatively, the efficiency of waste reduction in both single stage and two-stage fermentation was lower than previously published reports of 92.5% TS and 94% total COD removal [11] and 93.4% total COD removal [26] from palm oil mill effluent. The difference in the removal efficiency could be due to more complex and solid structure of decanter cake. The maximum methane production rate of 736 mL CH4 L1 d1 and methane yield of 44 mL CH4 kg1 TSremoval d1 were achieved by twostage with 0.75% GLC hydrogenic effluent (Fig. 5). Furthermore, the average of biogas yield, biogas production rate and energy recovery compared between the single stage of hydrogen and methane production with the different condition and two-stage of hydrogen combined with methane
Fig. 3 e Methane production and methane content (% CH4) in the semi-continuous methane production.
Fig. 4 e TS, TCOD and SCOD removal efficiency in the semi-continuous methane production. Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Fig. 5 e Methane production rate and methane yield in the semi-continuous methane production.
Table 3 e The summary of biogas production rate, biogas yield and energy recovery compared between single stage and two-stage fermentation process. Process Single stage process H2 fermentation co-digestion of 2% TS - 0.75% wv1 GLC - 1% wv1 GLC - 1.25% wv1 GLC - 1.5% wv1 GLC CH4 fermentation - 2% DC - H2 eff (0.75 % wv1 GLC) - H2 eff (1% wv1 GLC) Two-stage process - H2 (0.75% GLC) þ CH4 (H2 eff) - H2 (1% GLC) þ CH4 (H2 eff)
Biogas production rate (mL L1 d1) DC
Yield (L kg1 TSadded)
with the varying organic loadings of crude glycerol 76 ± 10.8 3.8 ± 0.9 154 ± 11.2 6.0 ± 0.7 131 ± 10.2 6.6 ± 0.5 429 ± 16.2 19.1 ± 2.5
Energy recovery (kWh kg1 TS) 102
0.9 1.5 1.6 4.6
520 ± 21.3 669 ± 39.1 498 ± 42.8
26.0 ± 2.6 33.4 ± 4.3 24.9 ± 2.5
3.6 4.7 3.5
e e
e e
5.6 5.0
production were summarized in Table 3. The total energy recovery from two-stage fermentation with 0.75% GLC was improved by 6.2 and 1.6 times compared to the single stage hydrogen and methane fermentation, respectively.
Acknowledgments The authors would like to express their gratitude to Agricultural Research Development Agency (Public Organization) for the financial support (Grant no. PRP5805020300).
Conclusions The investigation of two-stage process for the hydrogen and methane production using co-digestion of decanter cake and crude glycerol was feasible and practical to enhance the efficiency of waste utilization and energy recovery. Energy recovery from two-stage fermentation with 0.75% GLC about 0.056 kWh kg1 TSadded was improved by 6.2 and 1.6 times compared to the single stage hydrogen and methane fermentation, respectively. The maximum yield and maximum rate of biogas production were obtained from the second stage of semi-continuous methane production with 0.75% GLC hydrogenic effluent. Finally, crude glycerol is not only used as co-digestion but it could be used as pH-adjust substance for hydrogen fermentation to maintain pH (higher than 5) throughout the fermentation process.
references
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Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Enhancement of hydrogen and methane production from co-digestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation Suwimon Kanchanasuta a,b,*, Omjit Sillaparassamee a a
Department of Environmental Health Sciences, Faculty of Public Health, Mahidol University, Bangkok 10400, Thailand b Center of Excellence on Environmental Health and Toxicology, Bangkok, Thailand
article info
abstract
Article history:
Two-stage thermophilic hydrogen fermentation and mesophilic methanogenic process for
Received 19 September 2016
methane production with hydrogenic effluent from co-digestion of decanter cake (DC) and
Received in revised form
crude glycerol (GLC) was investigated. For the single stage, hydrogen reactor with 2% wv1
3 January 2017
total solid (TS) of DC and crude glycerol was operated at 4 days hydraulic retention time
Accepted 7 January 2017
(HRT) with varying glycerol loading of 0.75e1.5% GLC while methane reactor with 2% wv1
Available online xxx
total solid (TS) of DC was operated at 13 days HRT. The maximum hydrogen production rate and hydrogen yield in the single stage obtained from the 1.5% GLC co-digestion con-
Keywords:
dition were 461 mL H2 L1 d1 and 23 L H2 kg1 TSadded, respectively. Crude glycerol was
Two-stage fermentation
found to be an alternative pH-adjust substance in hydrogen reactor. At the condition of
Crude glycerol
0.75% GLC co-digestion, the pH was maintained in the range higher than 5.3 throughout the
Decanter cake
fermentation process. Semi-continuous methane production with 0.75% GLC hydrogenic
Energy recovery
effluent achieved the maximum methane production rate and methane yield about 736 mL
Co-digestion
CH4 L1 d1 and 44 L CH4 kg1 TSadded compared with the single stage with 2% TSDC and the second stage with 1% GLC hydrogenic effluent. Total energy recovery from two-stage fermentation about 0.056 kWh kg1 TSadded was achieved from the condition of 0.75% GLC hydrogenic effluent condition. It was improved by 6.2 and 1.6 times compared to the single stage in both hydrogen and methane reactor, respectively. This work demonstrated the practical enhancement of energy recovery and the efficiency of waste utilization by two-stage fermentation for hydrogen and methane production from decanter cake and crude glycerol. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Department of Environmental Health Sciences, Faculty of Public Health, Mahidol University, Bangkok 10400, Thailand. Fax: þ66 2354 8525. E-mail addresses: [email protected], [email protected] (S. Kanchanasuta). http://dx.doi.org/10.1016/j.ijhydene.2017.01.032 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Introduction Decanter cake is one type of waste produced from palm oil industry in the step of oil purification. Previous studies reported that typical palm oil mills generate 3.5% of oil palm decanter cake (OPDC) for each tonne of fresh fruit brunches (FFB) [1,2] and 42 kg per tonne fresh fruit brunches [3]. High biodegradable organic contents and nutrient rich compositions make palm oil decanter cake as an attractive feedstock for biogas production. Crude glycerol is a by-product from biodiesel industry. Because biodiesel production is rapidly expanding in Thailand in order to meet the increasing energy demand of transportation, the crude glycerol generated from the trans-esterification of vegetables oils, has also been generated in a large quantity. Although the various applications such as pure glycerol in food, pharmaceutical, cosmetics, and many other industries have been reported, they are too costly to refine the crude glycerol to a high purity, particularly for medium and small biodiesel producers. Moreover, some period of over biodiesel in the market results in the low cost of crude glycerol, so burning is the disposal method of this case. Many previous researches have been conducted and utilized of crude glycerol to produce the valuable products such as biohydrogen [4e7], 1,3 propanediol [8], bioethanol [9]. Hydrogen (H2) is regarded as one of the alternative source for clean and renewable energy and considered as an alternative non-polluting fuel for the future. Biohydrogen production is always accompanied by volatile fatty acids (VFAs) production such as acetate, butyrate, propionate and ethanol that are more appropriate substrates for methane production further in the second-stage [10]. Therefore, methane production is well considered as a suitable post-treatment unit of hydrogen production. In recent times, a two-stage process combining hydrogenesis and methanogenesis has been a focused technology. The significance of two-stage process includes, process stability, higher biogas yield, and high total energy recovery [11]. Sunyoto et al. [12] had studied two-phase anaerobic digestion of food waste and found that the maximum production rates of hydrogen by 32.5% and methane 41.6%, could improve hydrogen and methane yield about 31.0% and 10%, respectively. Likewise, Krishnan et al. [11] showed a feasibility of two-stage fermentation from palm oil mill effluent with total COD removal efficiency of 94% while hydrogen and methane yield were observed 215 L H2 kg COD1 and 320 L CH4 kg COD1, respectively. Co-digestion plays the important factor in biogas production process. During the fermentation, two or more organic substances should be degraded properly to enhance biogas production as compared to sole substrate. Previous studies revealed that co-digestion can improve biogas production from 25% to 400% over the mono-digestion of the same feedstocks [13,14]. Because the metabolic properties, nutritional requirements, growth rates and optimum operational factors are significantly different, so it is difficult to improve the overall of anaerobic co-digestion system in one-stage digester [15,16]. The two-stage system of biogas fermentation appears to be a more productive process compared to one-stage system. Therefore, it has been applied to solve the obstacles in the various problems found in
the one-stage system of biogas production [17,18]. Our previous study displayed the feasibility of decanter cake to be used as the indigenous source of inocula seed and the feedstock in anaerobic digestion process [19]. Besides, for co-digestion batch test, results indicated that the addition of decanter cake as co-feedstock and microbial source, containing hydrolytic and acidogenic bacteria, yielded a better performance in the biogas production and simulate glycerol utilization at the same time. Nowadays, there are few literatures reporting about twostage fermentation from co-digestion of agro-industrial waste such as decanter cake and crude glycerol. Therefore, this work aim to enhance the efficiency of hydrogen and methane production by two-stage fermentation of thermophilic hydrogen production and semi-continuous mesophilic methane production from co-digestion of decanter cake and crude glycerol.
Materials and methods Crude glycerol Brownish crude glycerol with 63.9% glycerol purity was obtained from Trang Palm Oil Co., Ltd. Trang, Thailand. The characteristic of the crude glycerol is as shown in Table 1.
Microbial inoculum Anaerobic sludge seed was obtained from a full-scale upflow anaerobic sludge blanket reactor treating beverage processing wastewater (Sermsuk Industry Co. Ltd., Pathumtani, Thailand). The anaerobic sludge seed have the characteristics shown in Table 1. Prior to use, the granule was sieved to the size <0.5 mm to remove coarse matters and then washed twice with tap water. The anaerobic granule sludge was recultivated in 0.5% (w/v) glucose solution until reach to steady state regarding the CH4 content and volume of CH4 production. Subsequently, it was washed twice with the distilled water before used as a seed microbial inoculum for the biogas fermentation.
Decanter cake Decanter cake, a feedstock for the biogas production and a source of indigenous microbes, was collected from palm oil milling plant, Suksomboon palm oil industry in Chonburi, Thailand. The sample was stored at 4 C before use. The characteristic of the palm oil decanter cake is as shown in Table 1.
Continuous stirred tank reactors Single stage of hydrogen production The reactor with working volume of 4 L was operated at 4 days HRT. It was started with co-digestion of 2% wv1 total solid (TS) of decanter cake (DC) and 1 g of glycerol (GLC) without the external anaerobic sludge. Subsequently, 1 L of new mixture substrate was daily fed into the reactor while digestate was removed to keep the operating volume at 4 L. The
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Table 1 e Characteristics of crude glycerol, sludge seed and palm oil decanter cake. Parameter
Crude glycerol
Sludge seed
Decanter cake
Total solids (TS) Total volatile solids Total COD Soluble COD Total carbon Total nitrogen Cellulose Hemicellulose Lignin pH Conductivity FOG Methanol Monoglyceride Diglyceride Triglyceride TOC
NA NA 443,262 mg kg1 115,248 mg kg1 NA NA NA NA NA 8.76 529 ms cm1 5222 mg L1 0.36 % vv1 0.03 % ww1 0.02 % ww1 0.07 % ww1 414,666 mg L1
22,233 mg L1 19,700 mg L1 40,153 mg L1 2881 mg L1 NA NA NA NA NA NA NA NA NA NA NA NA NA
197,670 mg kg1 169,740 mg kg1 NA NA 47.35 % ww1 4.34 % ww1 50.07 % ww1 30.74 % ww1 10.40 % ww1 NA NA NA NA NA NA NA NA
NA ¼ Not Analyzed.
concentration of glycerol was slightly increased by 0.25, 0.5 and 0.75% wv1 GLC, respectively while decanter cake was fixed at 2% TS throughout the fermentation process. Increase glycerol loading of 0.75% for 5 days, 1% for 7 days, 1.25% for 4 days and 1.5% for 12 days were added into the reactor afterward. Pattern of glycerol loading depends on the performance of hydrogen production in the reactor. The substrate was adjusted to pH 7 with 3 N NaOH or 3 N HCl. The reactor was operated under thermophilic condition (55 C).
Semi-continuous methane production The reactor was started with 2% TS of the decanter cake and 1 L of the anaerobic sludge. The reactor was maintained by feeding 300 mL of new substrate daily (2% TS of decanter) and removing digestate to keep the operating volume at 4 L. The second stage of methane production was started after 44 days cultivation by feeding hydrogenic effluent from hydrogen reactor of the single stage. Hydrogenic effluent of 0.75% GLC (300 mL) were fed into the reactor in the second stage for 14 days and 1% GLC for 7 days. All feeding substrates were adjusted to pH 7 with 3 N NaOH or 3 N HCl and 5000 mg CO3 2 =L with NaHCO3 and Na2CO3. The reactor was operated under mesophilic condition (37 C).
Analytical methods Total solids (TS), and chemical oxygen demand (COD) were measured according to Standard Methods 2540 G and 5220 B, respectively [20]. Glycerol was spectrophotometrically determined by chromotropic acid method (modified from Handel [21]). The amount of generated biogas was recorded using liquid displacement gasometers. Biogas content (H2, CH4, and CO2) was measured periodically everyday using a gas chromatograph (Shimadzu GC-8A, Kyoto, Japan) equipped with a thermal conductivity detector (TCD) with a Unibeads C 60/80 column (GL Sciences, Inc., Tokyo, Japan). Helium was used as a carrier gas. The temperatures of the injection port and the detector were 150 C and 80 C, respectively. Volatile fatty
acids (VFAs) were analyzed by gas chromatography (Shimadzu GC-7A system equipped with a flame ionization detector and a Stabilwax DA capillary column; Restek Corporation, PA, USA). The temperatures of the injection port and detector were maintained at 240 C [22].
Results and discussion Biohydrogen production from co-digestion of palm oil decanter cake with crude glycerol in the single stage Co-digestion of 2% TS palm oil decanter cake with the different concentrations of crude glycerol for hydrogen production by using the indigenous microorganism under the control thermophilic condition of 55 C and 100 rpm in the continuous stirred tank reactor (CSTR) was investigated. Organic loading of glycerol also strongly affected the overall fermentation process. Hydrogen production with the 1.5% GLC achieved the maximum hydrogen production and hydrogen content detected in the reactor of 1843 mL and 49%, respectively (Fig. 1). The methane content was not observed across the fermentation, indicating that there was no methanogenic activity in the reactor. Stability of pH (higher than 5.3) under the condition of 0.75% GLC co-digestion could be observed. Butyrate and acetate were the main metabolites accumulated since the first day fermentation for all cases and they trended to increase with the increase concentration of crude glycerol co-digestion (Fig. 2). The pH could be maintained in the range 5.0e5.4 throughout the fermentation process while the total concentration of undissociated acids accumulated in the reactor was higher than 50 mM for the 1, 1.25 and 1.5% GLC codigestion conditions (data not shown). In general, drop of pH during fermentation process resulted in imbalance of NADH2/ NADþ ratio and lower hydrogen production yield [23]. Not only butyrate and acetate were dominantly generated in the reactor, ethanol was also accumulated in the high level compared with the other metabolites (propionic acid and
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Fig. 1 e Hydrogen production and hydrogen content (%H2) from the single stage.
Fig. 2 e Metabolites and total volatile fatty acid from the single stage of hydrogen production. valeric acid). High accumulation of undissociated acid above 19 mM was found to be an inhibition factor for acidogenesis which was a threshold concentration for significant decreasing hydrogen yield and beginning solventogenesis [24]. Ethanol is one of more reduced substance produced in the solventogenesis reaction and this is an indicator for solventogenesis reaction in the reactor. This reaction can generate during the unbalance condition of proton and the detoxicity condition within the bacterial cell. In the acidity condition, undissociated acid form can be infiltrated through the cells and proton will be released inside the cells, thus, resulting in toxicity condition. Therefore, solventogenesis will be generated for maintaining the neutral condition for normal metabolism process. Reduction of hydraulic retention time may be an alternative solution to dilute the acidic condition in the reactor. The optimal HRT for hydrogen production from organic fraction of municipal solid wastes reported in the previous research is about 1e2 day [25]. Due to the characteristic of crude glycerol (high COD and pH of 8.76), it is not only used as co-digestion for hydrogen fermentation, it may
also be used as an alternative pH-adjust substance for maintaining the pH condition in the reactor resulting in continuous hydrogen production. In the batch experiment of our previous study [19], hydrogen fermentation process from the sole decanter cake was stopped after 24 h fermentation for most cases because of the acidic condition in the reactor (pH lower than 5). However, to improve the efficiency of hydrogen production in the first stage, not only the optimal condition, the addition of hydrogen producing bacteria and the stability of them across the fermentation have been further investigated.
Semi-continuous biomethane production For comparison with the single stage mesophilic digester, methane production with 2% TS of decanter cake by anaerobic sludge was initially operated for 43 days cultivation to acclimate the condition. Subsequently, hydrogenic effluent from the 0.75% GLC and 1% GLC co-digestion was fed into the reactor to start the second stage. The characteristics of hydrogenic effluent are presented in Table 2. Methane gas
Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Table 2 e Characteristic of the hydrogenic effluent from hydrogen production process. Parameter pH Total volatile fatty acid (mg L1) Acetic acid (mg L1) Propionic acid (mg L1) Butyric acid (mg L1) Valeric acid (mg L1) Ethanol (mg L1)
0.75 % GLC
1% GLC
5.3 1313 164 24 1125 e 197
5.1 3274 224 16 3011 23 1561
production obtained from the CSTR reactor was showed in Fig. 3. The average methane production from single stage with 2% TS decanter cake and two-stage with 0.75 and 1% GLC of hydrogenic effluent were 2094, 2794 and 1992 mL respectively. The maximum methane production and methane content of 2943 mL and 71% were observed from two-stage with 0.75% GLC of hydrogenic effluent. Results revealed that the second stage of methane production from 0.75% GLC hydrogenic effluent achieved better performance in both methane production and methane content than those from single stage and two-stage with 1% GLC hydrogenic effluent. On the other
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hand, the maximum efficiency of waste reduction based on TS (59%), total COD (89%) and soluble COD (90%) removal were obtained from single stage methane production with the average of 54%, 83% and 78% respectively (Fig. 4). It may be due to a number of hydrolytic bacteria from the indigenous microbe in the first stage of hydrogen production. Besides, solid fraction after digesting by hydrolytic bacteria will remain only complex fraction which had to further digest in the next step. Therefore, adding the external anaerobic seed in the first stage is necessary for improving the overall process. Comparatively, the efficiency of waste reduction in both single stage and two-stage fermentation was lower than previously published reports of 92.5% TS and 94% total COD removal [11] and 93.4% total COD removal [26] from palm oil mill effluent. The difference in the removal efficiency could be due to more complex and solid structure of decanter cake. The maximum methane production rate of 736 mL CH4 L1 d1 and methane yield of 44 mL CH4 kg1 TSremoval d1 were achieved by twostage with 0.75% GLC hydrogenic effluent (Fig. 5). Furthermore, the average of biogas yield, biogas production rate and energy recovery compared between the single stage of hydrogen and methane production with the different condition and two-stage of hydrogen combined with methane
Fig. 3 e Methane production and methane content (% CH4) in the semi-continuous methane production.
Fig. 4 e TS, TCOD and SCOD removal efficiency in the semi-continuous methane production. Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032
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Fig. 5 e Methane production rate and methane yield in the semi-continuous methane production.
Table 3 e The summary of biogas production rate, biogas yield and energy recovery compared between single stage and two-stage fermentation process. Process Single stage process H2 fermentation co-digestion of 2% TS - 0.75% wv1 GLC - 1% wv1 GLC - 1.25% wv1 GLC - 1.5% wv1 GLC CH4 fermentation - 2% DC - H2 eff (0.75 % wv1 GLC) - H2 eff (1% wv1 GLC) Two-stage process - H2 (0.75% GLC) þ CH4 (H2 eff) - H2 (1% GLC) þ CH4 (H2 eff)
Biogas production rate (mL L1 d1) DC
Yield (L kg1 TSadded)
with the varying organic loadings of crude glycerol 76 ± 10.8 3.8 ± 0.9 154 ± 11.2 6.0 ± 0.7 131 ± 10.2 6.6 ± 0.5 429 ± 16.2 19.1 ± 2.5
Energy recovery (kWh kg1 TS) 102
0.9 1.5 1.6 4.6
520 ± 21.3 669 ± 39.1 498 ± 42.8
26.0 ± 2.6 33.4 ± 4.3 24.9 ± 2.5
3.6 4.7 3.5
e e
e e
5.6 5.0
production were summarized in Table 3. The total energy recovery from two-stage fermentation with 0.75% GLC was improved by 6.2 and 1.6 times compared to the single stage hydrogen and methane fermentation, respectively.
Acknowledgments The authors would like to express their gratitude to Agricultural Research Development Agency (Public Organization) for the financial support (Grant no. PRP5805020300).
Conclusions The investigation of two-stage process for the hydrogen and methane production using co-digestion of decanter cake and crude glycerol was feasible and practical to enhance the efficiency of waste utilization and energy recovery. Energy recovery from two-stage fermentation with 0.75% GLC about 0.056 kWh kg1 TSadded was improved by 6.2 and 1.6 times compared to the single stage hydrogen and methane fermentation, respectively. The maximum yield and maximum rate of biogas production were obtained from the second stage of semi-continuous methane production with 0.75% GLC hydrogenic effluent. Finally, crude glycerol is not only used as co-digestion but it could be used as pH-adjust substance for hydrogen fermentation to maintain pH (higher than 5) throughout the fermentation process.
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Please cite this article in press as: Kanchanasuta S, Sillaparassamee O, Enhancement of hydrogen and methane production from codigestion of palm oil decanter cake and crude glycerol using two stage thermophilic and mesophilic fermentation, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.032