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Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature J. Arreola-Vargas, N. E. Jaramillo-Gante, L. B. Celis, R. I. Corona-González, V. González-Álvarez and H. O. Méndez-Acosta
ABSTRACT In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH– W
W
W
W
temperature combinations: 7 and 32 C; 7 and 38 C; 8 and 32 C and 8 and 38 C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all W
the tested conditions, while the highest methane yield was obtained at pH 7 and 38 C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the fullscale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions. Key words
J. Arreola-Vargas N. E. Jaramillo-Gante R. I. Corona-González V. González-Álvarez H. O. Méndez-Acosta (corresponding author) Departamento de Ingeniería Química, CUCEI-Universidad de Guadalajara, Blvd. M. García Barragán 1451, C.P. 44430 Guadalajara, Jalisco, México E-mail: [email protected] L. B. Celis División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica A.C., Camino a la Presa San José No. 2055, Col. Lomas 4a Sección, C.P. 78216 San Luis Potosí, SLP, México
| anaerobic digestion, AnSBR, stillage, tequila vinasses, wastewater treatment
INTRODUCTION Worldwide, the fermentation process is the main pathway used for ethanol production. According to EspañaGamboa et al. (), this process generated approximately 95% of the 79 billion litres of ethanol produced worldwide in 2008. The increasing trend of ethanol production by fermentation has also brought an increase of highly polluted effluents that are very difficult and complex to dispose of. Such effluents, commonly known as vinasses or stillage, are generated during the distillation phase, where ethanol as either pure chemical or distilled alcoholic beverage is separated from the fermentation broth (Moraes et al. ). The environmental problems caused by the inadequate disposal of these effluents have led to a very active research area in recent years (López-López et al. ; España-Gamboa et al. ; Robles-González et al. ; Jáuregui-Jáuregui et al. ; Moraes et al. ). In Mexico, the production of tequila (an alcoholic beverage obtained from Agave tequilana) has substantially doi: 10.2166/wst.2015.520
increased in recent years, raising by consequence the generation of tequila vinasses (Méndez-Acosta et al. ). Currently, around 80% of the tequila vinasses generated are directly discharged to water streams and bodies (rivers, lakes, etc.), causing severe environmental damages (LópezLópez et al. ; Méndez-Acosta et al. ). The main concerns that have hindered the implementation of suitable wastewater treatments for tequila vinasses are (i) the high production rate (10–12 L per litre of tequila produced), (ii) the presence of recalcitrant compounds and (iii) its highly variable composition that changes not only from industry to industry but from batch to batch (Méndez-Acosta et al. ). For instance, chemical oxygen demand (COD) and total solids concentrations of the tequila vinasses may reach 60–100 g/L and 25–50 g/L, respectively (LópezLópez et al. ; Méndez-Acosta et al. ). Recently, the anaerobic digestion process has emerged as an attractive alternative for the treatment of tequila
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vinasses, since it has proved to be effective for not only COD removal but also biogas production, enabling energy recovery along with the improvement of the industry’s commercial and environmental sustainability (Méndez-Acosta et al. ). Even though different reactor configurations have been evaluated at full-scale for the anaerobic digestion of industrial and municipal wastewaters, the up-flow anaerobic sludge blanket (UASB) reactors are commonly selected above other technologies (López-López et al. ; España-Gamboa et al. ). Nonetheless, alternative reactor configurations may reduce operational costs and improve the methane production yield. In this regard, different continuous reactor configurations such as the continuous stirred tank reactor (CSTR) and fixed-bed reactor have been evaluated at laboratory and pilot scales for the treatment of tequila vinasses (Méndez-Acosta et al. ; Jáuregui-Jáuregui et al. ; Méndez-Acosta & GonzálezÁlvarez ). In general, high COD removals (85–95%) and methane production yields (0.28–0.33 L CH4/g COD removed) have been reported by using hydraulic retention times (HRTs) from 2 to 6 days. Nevertheless, the operation of continuous anaerobic digestion processes is particularly challenging, since their proper operation requires a deep knowledge of the process as well as the implementation of advanced monitoring schemes, which are not always available, particularly for small and medium size tequila factories. From the above, it is clear that evaluation of different reactor configurations that allow cost reduction as well as an easy process operation is still necessary. In this sense, the anaerobic sequencing batch reactor (AnSBR) represents an attractive alternative due to its lower cost and less land requirements compared to continuous systems (i.e. CSTR and UASB), the high process flexibility and easy operation, the better control of the microbial population due to the cyclic operation, and the decoupling of the solids retention time from the HRT, which enables operation at high organic loading rates (OLRs) (Mace & Mata-Alvarez ). It is important to highlight that even though dark fermentation of tequila vinasses has been previously reported in AnSBRs (Buitrón & Carvajal ; Buitrón et al. ), to the best of our knowledge, there is no report related to the treatment of this type of wastewater by means of anaerobic digestion under this reactor configuration. Therefore, the aim of this study was to evaluate the feasibility of using an AnSBR for the anaerobic digestion of tequila vinasses. The AnSBR was operated at different pH–temperature combinations by using four different batches of tequila
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vinasses obtained from different periods of tequila production in order to evaluate the robustness and performance of the process in terms of COD removal and biogas-methane production. It is worth mentioning that the experiments were evaluated at the mesophilic range (32 and 38 C) because, according to a recent review (Mao et al. ), the mesophilic systems exhibit higher stability than thermophilic ones. Regarding the pH, the values were selected (7 and 8) in accordance to the range reported as the favorable one for anaerobic digestion processes (Mao et al. ). W
MATERIALS AND METHODS Inoculum and substrate Anaerobic granular sludge from a full-scale UASB reactor that treats effluents from a local brewery in GuadalajaraJalisco, Mexico was used as inoculum. The anaerobic granular sludge was characterized in terms of total suspended solids and volatile suspended solids (VSS), obtaining values of 44 g/L and 30 g/L, respectively. On the other hand, the tequila vinasses were obtained from a tequila distillery located in Arandas-Jalisco, Mexico. As was previously mentioned, the vinasses composition is highly variable. Therefore, in order to evaluate the effect of such variations on the process performance, the AnSBRs were fed with different batches obtained from the same distillery at different time periods.
Operational conditions The performance and robustness of the AnSBR was evaluated in four independent experiments under different pH– temperature combinations: (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C and (D) 8 and 38 C. Due to the previously mentioned variability of the tequila vinasses composition, the four AnSBR experiments were randomly fed with four different batches of tequila vinasses obtained from different periods of tequila production. Table 1 shows the composition of these batches in terms of volatile fatty acids (VFAs) because these compounds are the main substrates for methanogens in the anaerobic digestion process. The values presented in Table 1 correspond to an adjusted vinasses concentration of 8 ± 0.5 g COD/L, which was the concentration used in the feeding medium of the AnSBRs. W
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Table 1
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VFA composition of the diluted vinasses for the four experiments
Experiment Compound
A
B
C
D
(mg COD/L) Formate
291.8
35.6
137.4
32.2
Acetate
1,553.9
4,336.8
2,687.8
504.5
Propionate
139.9
Nd
Nd
238.1
Butyrate
Nd
Nd
Nd
118.3
Isobutyrate
1,011.1
1,659.9
2,480.1
Nd
Isovalerate
Nd
Nd
Nd
3,439.1
Nd ¼ not detected; Experiment A (pH 7 and 32 C); Experiment B (pH 7 and 38 C); Experiment C (pH 8 and 32 C); Experiment D (pH 8 and 38 C). W
W
W
W
Reactor setup The AnSBR was made of polyvinyl chloride with a working volume of 5.1 L. The reactor was instrumented in order to enable the online measurement of variables such as temperature, pH, pressure and biogas flow rate (Figure 1). A National Instruments cRIO-9004 device equipped with analogical and digital cards was used in the acquisition, treatment and storage of the data. A graphical interface was designed by using the LabVIEW 8.2® software. At the beginning of each experiment, the AnSBR was inoculated with 6.5 g VSS/L of anaerobic granular sludge and then fed with tequila vinasses at 8 ± 0.5 g COD/L. Filling and discharging of the medium was carried out by means of peristaltic pumps. The following stages were followed during each cycle: filling (7 min), reaction (from 3 to 9 days, until stationary substrate consumption was attained), settling (30 min) and discharge (7 min). In order to induce homogeneous conditions during the reaction time, the reactor was mixed by means of a recirculation loop. The exchange ratio was 80% of the working volume, which means that practically all the liquid content was removed at the end of each cycle. The temperature and pH were controlled by using a water jacket and by adding 2 N NaOH solution through an on–off control scheme, respectively.
Figure 1
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AnSBR scheme. (1) Feeding/discharging pipe; (2) water jacket; (3) 2 N NaOH solution; (4) phase separator; (5) diffuser/decanter; (6) sampling port; (7) recirculation pump; (8) biogas counter; (9) temperature sensor; (10) pressure sensor; (11) pH/oxidation reduction potential sensor; (12) cRIO controller; (13) PC. Liquid streams: gray line; gas stream: black line; data transmission: dotted line.
and partial alkalinities (α ¼ IA/PA). On the other hand, COD was measured according to Arreola-Vargas et al. () and VFAs and biogas composition were determined as previously reported by means of high-performance liquid chromatography and gas chromatography with a thermal liquid detector, respectively (Méndez-Acosta et al. ).
RESULTS AND DISCUSSION
Analytical methods
Tequila vinasses degradation
In addition to the online readings, offline measurements were also taken. Partial (pH ¼ 5.75) and intermediate (pH ¼ 4.3) alkalinities that are related to bicarbonate and VFA buffer capacities respectively were measured according to Ripley et al. () in order to calculate the alkalinity factor, which is given by the ratio between the intermediate
The robustness of the AnSBR was evaluated at four different pH–temperature conditions (A: 7 and 32 C; B: 7 and 38 C; C: 8 and 32 C and D: 8 and 38 C) since it is well-known that these parameters have a great influence on the anaerobic digestion process (Montañés et al. ). The duration of each experiment was defined by the time required to obtain W
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reproducibility in both COD removal and methane production in at least two contiguous cycles. Regarding COD removal, Figure 2 shows that the degradation of tequila vinasses was quite similar in all the assays, suggesting a high robustness of the process. COD removals between 84.4 and 85.4% were obtained for the different tested conditions (Figure 2(b)). In addition, the cycles at each condition were very reproducible. For instance, Figure 2(a) shows the typical kinetic profile obtained during the performance of Experiment A, in which a quite similar trend for COD removal can be observed in the performed cycles. The dotted line shows the COD concentration at which the degradation rate of tequila vinasses was negligible and therefore a new cycle was performed. It is worth mentioning that the kinetic trend observed in Figure 2(a) is highly representative of the rest of the experiments (data not shown). Despite the high COD removal efficiencies attained under the different AnSBR experiments, around 15% of recalcitrant COD remained in the liquid phase after the anaerobic treatment (Figure 2). Therefore, further research
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on effluent post-treatment is needed in order to comply with the stringent wastewater regulations. In this sense, a possible effective sequential treatment could be an anaerobic–aerobic process, which has been successfully proven for other type of vinasses (Moletta ). Biogas production Biogas production and methane content were also recorded to compare the energy recovery potential among the different AnSBR experiments. The reported values in Figure 3 are presented at standard conditions (1 atm and 0 C). Overall, the experiments performed at pH 7 achieved higher biogas production than those performed at pH 8. Nonetheless, the content of methane in biogas was higher in the experiments performed at pH 8 (around 90%) than those at pH 7 (around 75%). Regarding methane production, Figure 3(b) shows that similar values were obtained in all the experiments: around 9.6 L per cycle for Experiments A, B and C, and 8.1 L per cycle for Experiment D. In the W
Figure 3 Figure 2
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(a) Typical kinetic profile of biogas production (Experiment A). (b) Global biogas
(a) Typical kinetic profile of vinasses degradation (Experiment A). (b) Global
and methane production obtained during the four experiments at different
COD removals obtained during the four experiments at different pH and
values of pH and temperature. (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C; (D) 8 and 38 C. Bars represent the average of the last two cycles at each
W
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W
temperature values. (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C; (D) 8 and 38 C. Bars represent the average of the last two cycles at each condition. All W
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W
condition. All the AnSBRs were operated for a period of 30 ± 6 days until no
the AnSBRs were operated for a period of 30 ± 6 days until no variation in COD
variation in COD removal and biogas production was observed in two contig-
removal and biogas production was observed in two contiguous cycles.
uous cycles.
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particular case of Experiment D, the slightly lower methane production registered even when the COD removal was similar to the other experiments (Figure 2(b)) is explained by some faults that developed in the biogas counter during the last cycle, which can be confirmed by the larger standard deviation (see Figure 3(b)). Nevertheless, in general the cycles were very reproducible in all the experiments (for instance see Figure 3(a)), confirming the robustness observed in the COD removal efficiencies (Figure 2). It is worth noting that the unusual high methane content in the experiments performed at pH 8 could be related to solubilization of CO2 in the liquid phase. According to Tippayawong & Thanompongchart (), at this alkaline pH, CO2 absorption may have taken place by transference of this compound from the gas phase to the gas/liquid interface, and then to the bulk of the liquid phase, where the following reactions take place. 1. CO2 þ 2OH ! CO2 3 þ H2 O 2. CO2 þ CO2 þ H O ! 2HCO 2 3 3
Figure 4
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Profiles of VFAs obtained during the AnSBR experiments at different pH– temperature values: (▪) 7 and 32 C; (●) 7 and 38 C; (▴) 8 and 32 C; (♦) 8 and W
W
W
W
38 C. Symbols represent the average of the last two cycles at each condition.
VFA analysis According to Table 1, the main components of tequila vinasses were VFAs, which are the most important intermediates in the anaerobic digestion process because they are the main substrate used by syntrophic bacteria and methanogenic archaea to produce methane. However, under certain conditions VFAs can also be accumulated in the digester, resulting in a digester failure called process acidification (Zhang et al. ). This feature led to a close monitoring of the VFA degradation or production during the anaerobic digestion experiments. Overall, the complete degradation of formate, acetate, isobutyrate and isovalerate was observed in all the experiments (Figure 4). It is worth noting that, even though the presence of isovalerate and isobutyrate at concentrations greater than 15 mg/L has been previously related to reactor instability (Hill & Bolte ), during the present work such an effect was not observed despite the extremely high initial concentration of such VFAs in the different batches of vinasses used to fed the AnSBRs (Table 1). A possible explanation for this behavior is that syntrophic communities in the reactor were able to consume these acids for further methanization. Conversely, Figure 4 also shows that microbial populations were also able to consume butyrate and propionate. However, it is clear that most of such acids were produced during the anaerobic digestion process, which was very likely due to degradation of other VFAs.
According to Ripley et al. (), the successful (stable) operation of anaerobic digesters depends on both proper control to avoid an excessive VFA accumulation and the adequate maintenance of the bicarbonate buffering. Therefore, the operational stability of the AnSBR experiments was also followed by means of the alkalinity factor (α). Results were also very reproducible during all the experiments (Figure 5). The initial values of α were between 0.6 and 1.0 but suddenly decreased during the first hours until
Figure 5
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Profiles of alkalinity factor obtained during the AnSBR experiments at different pH–temperature values: (▪) 7 and 32 C; (●) 7 and 38 C; (▴) 8 and 32 C; (♦) 8 W
W
W
W
and 38 C. Symbols represent the average of the last two cycles at each condition.
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reaching values from 0.25 to 0.3. The latter values are in accordance to those reported as the adequate ones (below 0.3) for achieving a stable operation of the anaerobic digestion process (Ripley et al. ).
The AnSBR experiments were conducted for a minimum of 24 and a maximum of 36 days, equivalent to 4 to 6 operation cycles (Table 2). The OLR was equivalent to 0.9 ± 0.2 g/L*d, which is much lower than those organic loading rates applied in continuous reactors such as the UASB, up to 40 g/L*d (España-Gamboa et al. ). Nonetheless, the present study did not aim to increase the OLR. On the other hand, it is worth noting that regardless of the differences in both the pH–temperature conditions evaluated as well as the tequila vinasses composition, the AnSBR performance was reasonably good with excellent robustness properties. Regarding COD removal efficiencies, values were slightly higher (85 vs. 80%) than those reported by Batstone et al. () in which an AnSBR was used for the treatment of winery vinasses. However, for the specific case of tequila vinasses, COD removal efficiencies higher than 90% have been reported in a CSTR (Méndez-Acosta et al. ). Nonetheless, the AnSBR still represents a viable alternative for the treatment of tequila vinasses because of its high robustness and easy operation as shown in the present study. Regarding methane yield, Table 2 shows that, overall, lower methane yields than the theoretical one (0.35 L CH4/g COD) were |
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attained; around 80% of the original COD was converted to methane. Nonetheless, the yields obtained in the present study are higher than those reported in previous studies for the treatment of vinasses in UASB reactors (0.22 L CH4/g COD, at standard conditions) (Akarsubasi et al. ). Finally, concerning the specific degradation and methane production rates, such parameters were also maintained at similar values, confirming the overall operation stability of the process. The latter results along with the reasonable good methane yields and COD removals confirm the potential of the AnSBR technology for its use in the treatment and energy recovery from tequila vinasses.
Overall performance
Table 2
Water Science & Technology
CONCLUSIONS In the present work, the use of an AnSBR for the treatment of tequila vinasses was evaluated at four different pH and temperature conditions. Furthermore, four different vinasses batches were used in order to simulate the high variability in vinasses composition at which full-scale reactors are operated. Overall, results demonstrated that AnSBR technology is effective for tequila vinasses treatment in terms of COD removal and methane yield. Interestingly, even though previous works have reported negative effects because of the presence of long chain VFAs, the AnSBR was able to operate under high concentrations of such acids. High robustness regarding COD removal and methane production was also observed at the different evaluated conditions, which means that any of
Overall performance of the AnSBR experiments at different pH and temperatures
Experiment Parameter
A
B
C
D
Number of operated cycles
5
4
5
6
Total operation days
36
30
24
36
Organic loading rate (g/L*d)
0.89
0.67
1.04
1.01
Initial COD (g/L)
8.1 ± 0.1
7.9 ± 0.4
8.3 ± 0.1
7.9 ± 0.2
Initial CODVFA (%)
37.1 ± 0.1
75.9 ± 0.3
63.9 ± 0.2
56.9 ± 0.3
COD removal (%)
85.4 ± 0.1
84.4 ± 0.4
84.8 ± 0.3
84.5 ± 0.5
Biogas production (L/cycle)
13.2 ± 0.3
12.7 ± 0.6
10.3 ± 0.2
8.7 ± 0.3
Methane content in biogas (%)
72.4 ± 3.8
74.5 ± 3.7
91.5 ± 3.8
92.4 ± 6.6
Methane yield (L CH4/g COD added)
0.29
0.29
0.28
0.25
Methane production rate (L CH4/h)
0.48
0.46
0.49
0.42
0.79
0.83
Specific degradation rate (g COD/g VSS*d) W
0.83 W
0.76 W
W
Experiment A (pH 7 and 32 C); Experiment B (pH 7 and 38 C); Experiment C (pH 8 and 32 C); Experiment D (pH 8 and 38 C). Values are the average of the last two cycles of each experiment. Initial CODVFA: % of initial COD attributed to VFAs.
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these conditions can be used for the treatment of tequila vinasses. Therefore, it is shown that the implementation of the AnSBR configuration is quite encouraging, particularly for small and medium size tequila industries that operate under seasonal conditions, due to its low cost, easy operation and high robustness to process load disturbances.
ACKNOWLEDGEMENT J. Arreola-Vargas acknowledges CONACyT for the support under the retention and repatriation program (232166).
REFERENCES Akarsubasi, A., Ince, O., Oz, N., Kirdar, B. & Ince, B. Evaluation of performance, acetoclastic methanogenic activity archaeal composition of full-scale UASB reactors treating alcohol distillery wastewaters. Process Biochemistry 41, 28–35. Arreola-Vargas, J., Ojeda-Castillo, V., Snell-Castro, R., CoronaGonzález, R. I., Alatriste-Mondragón, F. & Méndez-Acosta, H. O. Methane production from acid hydrolysates of Agave tequilana bagasse: evaluation of hydrolysis conditions and methane yield. Bioresource Technology 181, 191–199. Batstone, D., Torrijos, M., Ruiz, C. & Schmidt, J. Use of an anaerobic sequencing batch reactor for parameter estimation in modelling of anaerobic digestion. Water Science and Technology 50 (10), 295–303. Buitrón, G. & Carvajal, C. Biohydrogen production from Tequila vinasses in an anaerobic sequencing batch reactor: effect of initial substrate concentration, temperature and hydraulic retention time. Bioresource Technology 101, 9071–9077. Buitrón, G., Kumar, G., Martinez-Arce, A. & Moreno, G. Hydrogen and methane production via a two-stage processes (H2-SBRþ CH4-UASB) using tequila vinasses. International Journal of Hydrogen Energy 39, 19249–19255. España-Gamboa, E., Mijangos-Cortes, J., Barahona-Perez, L., Dominguez-Maldonado, J., Hernández-Zarate, G. & AlzateGaviria, L. Vinasses: characterization and treatments. Waste Management & Research 29, 1235–1250. Hill, D. T. & Bolte, J. P. Digester stress as related to isobutyric and iso-valeric acids. Biological Wastes 28, 33–37. Jáuregui-Jáuregui, J. A., Méndez-Acosta, H. O., González-Álvarez, V., Snell-Castro, R., Alcaraz-González, V. & Godon, J. J. Anaerobic treatment of tequila vinasses under seasonal
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operating conditions: start-up, normal operation and restart-up after a long stop and starvation period. Bioresource Technology 168, 33–40. López-López, A., Davila-Vazquez, G., León-Becerril, E., Villegas-García, E. & Gallardo-Valdez, J. Tequila vinasses: generation and full scale treatment processes. Reviews in Environmental Science and Bio/Technology 9, 109–116. Mace, S. & Mata-Alvarez, J. Utilization of SBR technology for wastewater treatment: an overview. Industrial and Engineering Chemistry Research 41, 5539–5553. Mao, C., Feng, Y., Wang, X. & Ren, G. Review on research achievements of biogas from anaerobic digestion. Renewable and Sustainable Energy Reviews 45, 540–555. Méndez-Acosta, H. O. & González-Álvarez, V. Methane production from tequila vinasses. In: Energy and Environment Nowadays (L. G. Torres & E. R. Bandala, eds). Nova Science Publishers, New York, USA, pp. 165–168. Méndez-Acosta, H. O., Snell-Castro, R., Alcaraz-González, V., González-Álvarez, V. & Pelayo-Ortiz, C. Anaerobic treatment of Tequila vinasses in a CSTR-type digester. Biodegradation 21, 357–363. Méndez-Acosta, H. O., Hernandez-Martinez, E., Jáuregui-Jáuregui, J. A., Alvarez-Ramirez, J. & Puebla, H. Monitoring anaerobic sequential batch reactors via fractal analysis of pH time series. Biotechnology and Bioengineering 110, 2131–2139. Moletta, R. Winery and distillery wastewater treatment by anaerobic digestion. Water Science and Technology 51 (1), 137–144. Montañés, R., Pérez, M. & Solera, R. Anaerobic mesophilic co-digestion of sewage sludge and sugar beet pulp lixiviation in batch reactors: effect of pH control. Chemical Engineering Journal 255, 492–499. Moraes, B. S., Junqueira, T. L., Pavanello, L. G., Cavalett, O., Mantelatto, P. E., Bonomi, A. & Zaiat, M. Anaerobic digestion of vinasse from sugarcane biorefineries in Brazil from energy, environmental, and economic perspectives: Profit or expense? Applied Energy 113, 825–835. Ripley, L., Boyle, W. & Converse, J. Improved alkalimetric monitoring for anaerobic digestion of high-strength wastes. Journal (Water Pollution Control Federation) 58, 406–411. Robles-González, V., Galíndez-Mayer, J., Rinderknecht-Seijas, N. & Poggi-Varaldo, H. M. Treatment of mezcal vinasses: a review. Journal of Biotechnology 157, 524–546. Tippayawong, N. & Thanompongchart, P. Biogas quality upgrade by simultaneous removal of CO2 and H2S in a packed column reactor. Energy 35, 4531–4535. Zhang, C., Su, H., Baeyens, J. & Tan, T. Reviewing the anaerobic digestion of food waste for biogas production. Renewable and Sustainable Energy Reviews 38, 383–392.
First received 14 June 2015; accepted in revised form 1 October 2015. Available online 12 October 2015
© IWA Publishing 2016 Water Science & Technology
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Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature J. Arreola-Vargas, N. E. Jaramillo-Gante, L. B. Celis, R. I. Corona-González, V. González-Álvarez and H. O. Méndez-Acosta
ABSTRACT In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH– W
W
W
W
temperature combinations: 7 and 32 C; 7 and 38 C; 8 and 32 C and 8 and 38 C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all W
the tested conditions, while the highest methane yield was obtained at pH 7 and 38 C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the fullscale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions. Key words
J. Arreola-Vargas N. E. Jaramillo-Gante R. I. Corona-González V. González-Álvarez H. O. Méndez-Acosta (corresponding author) Departamento de Ingeniería Química, CUCEI-Universidad de Guadalajara, Blvd. M. García Barragán 1451, C.P. 44430 Guadalajara, Jalisco, México E-mail: [email protected] L. B. Celis División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica A.C., Camino a la Presa San José No. 2055, Col. Lomas 4a Sección, C.P. 78216 San Luis Potosí, SLP, México
| anaerobic digestion, AnSBR, stillage, tequila vinasses, wastewater treatment
INTRODUCTION Worldwide, the fermentation process is the main pathway used for ethanol production. According to EspañaGamboa et al. (), this process generated approximately 95% of the 79 billion litres of ethanol produced worldwide in 2008. The increasing trend of ethanol production by fermentation has also brought an increase of highly polluted effluents that are very difficult and complex to dispose of. Such effluents, commonly known as vinasses or stillage, are generated during the distillation phase, where ethanol as either pure chemical or distilled alcoholic beverage is separated from the fermentation broth (Moraes et al. ). The environmental problems caused by the inadequate disposal of these effluents have led to a very active research area in recent years (López-López et al. ; España-Gamboa et al. ; Robles-González et al. ; Jáuregui-Jáuregui et al. ; Moraes et al. ). In Mexico, the production of tequila (an alcoholic beverage obtained from Agave tequilana) has substantially doi: 10.2166/wst.2015.520
increased in recent years, raising by consequence the generation of tequila vinasses (Méndez-Acosta et al. ). Currently, around 80% of the tequila vinasses generated are directly discharged to water streams and bodies (rivers, lakes, etc.), causing severe environmental damages (LópezLópez et al. ; Méndez-Acosta et al. ). The main concerns that have hindered the implementation of suitable wastewater treatments for tequila vinasses are (i) the high production rate (10–12 L per litre of tequila produced), (ii) the presence of recalcitrant compounds and (iii) its highly variable composition that changes not only from industry to industry but from batch to batch (Méndez-Acosta et al. ). For instance, chemical oxygen demand (COD) and total solids concentrations of the tequila vinasses may reach 60–100 g/L and 25–50 g/L, respectively (LópezLópez et al. ; Méndez-Acosta et al. ). Recently, the anaerobic digestion process has emerged as an attractive alternative for the treatment of tequila
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Effect of pH and temperature in the AD of tequila vinasses
vinasses, since it has proved to be effective for not only COD removal but also biogas production, enabling energy recovery along with the improvement of the industry’s commercial and environmental sustainability (Méndez-Acosta et al. ). Even though different reactor configurations have been evaluated at full-scale for the anaerobic digestion of industrial and municipal wastewaters, the up-flow anaerobic sludge blanket (UASB) reactors are commonly selected above other technologies (López-López et al. ; España-Gamboa et al. ). Nonetheless, alternative reactor configurations may reduce operational costs and improve the methane production yield. In this regard, different continuous reactor configurations such as the continuous stirred tank reactor (CSTR) and fixed-bed reactor have been evaluated at laboratory and pilot scales for the treatment of tequila vinasses (Méndez-Acosta et al. ; Jáuregui-Jáuregui et al. ; Méndez-Acosta & GonzálezÁlvarez ). In general, high COD removals (85–95%) and methane production yields (0.28–0.33 L CH4/g COD removed) have been reported by using hydraulic retention times (HRTs) from 2 to 6 days. Nevertheless, the operation of continuous anaerobic digestion processes is particularly challenging, since their proper operation requires a deep knowledge of the process as well as the implementation of advanced monitoring schemes, which are not always available, particularly for small and medium size tequila factories. From the above, it is clear that evaluation of different reactor configurations that allow cost reduction as well as an easy process operation is still necessary. In this sense, the anaerobic sequencing batch reactor (AnSBR) represents an attractive alternative due to its lower cost and less land requirements compared to continuous systems (i.e. CSTR and UASB), the high process flexibility and easy operation, the better control of the microbial population due to the cyclic operation, and the decoupling of the solids retention time from the HRT, which enables operation at high organic loading rates (OLRs) (Mace & Mata-Alvarez ). It is important to highlight that even though dark fermentation of tequila vinasses has been previously reported in AnSBRs (Buitrón & Carvajal ; Buitrón et al. ), to the best of our knowledge, there is no report related to the treatment of this type of wastewater by means of anaerobic digestion under this reactor configuration. Therefore, the aim of this study was to evaluate the feasibility of using an AnSBR for the anaerobic digestion of tequila vinasses. The AnSBR was operated at different pH–temperature combinations by using four different batches of tequila
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vinasses obtained from different periods of tequila production in order to evaluate the robustness and performance of the process in terms of COD removal and biogas-methane production. It is worth mentioning that the experiments were evaluated at the mesophilic range (32 and 38 C) because, according to a recent review (Mao et al. ), the mesophilic systems exhibit higher stability than thermophilic ones. Regarding the pH, the values were selected (7 and 8) in accordance to the range reported as the favorable one for anaerobic digestion processes (Mao et al. ). W
MATERIALS AND METHODS Inoculum and substrate Anaerobic granular sludge from a full-scale UASB reactor that treats effluents from a local brewery in GuadalajaraJalisco, Mexico was used as inoculum. The anaerobic granular sludge was characterized in terms of total suspended solids and volatile suspended solids (VSS), obtaining values of 44 g/L and 30 g/L, respectively. On the other hand, the tequila vinasses were obtained from a tequila distillery located in Arandas-Jalisco, Mexico. As was previously mentioned, the vinasses composition is highly variable. Therefore, in order to evaluate the effect of such variations on the process performance, the AnSBRs were fed with different batches obtained from the same distillery at different time periods.
Operational conditions The performance and robustness of the AnSBR was evaluated in four independent experiments under different pH– temperature combinations: (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C and (D) 8 and 38 C. Due to the previously mentioned variability of the tequila vinasses composition, the four AnSBR experiments were randomly fed with four different batches of tequila vinasses obtained from different periods of tequila production. Table 1 shows the composition of these batches in terms of volatile fatty acids (VFAs) because these compounds are the main substrates for methanogens in the anaerobic digestion process. The values presented in Table 1 correspond to an adjusted vinasses concentration of 8 ± 0.5 g COD/L, which was the concentration used in the feeding medium of the AnSBRs. W
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Table 1
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VFA composition of the diluted vinasses for the four experiments
Experiment Compound
A
B
C
D
(mg COD/L) Formate
291.8
35.6
137.4
32.2
Acetate
1,553.9
4,336.8
2,687.8
504.5
Propionate
139.9
Nd
Nd
238.1
Butyrate
Nd
Nd
Nd
118.3
Isobutyrate
1,011.1
1,659.9
2,480.1
Nd
Isovalerate
Nd
Nd
Nd
3,439.1
Nd ¼ not detected; Experiment A (pH 7 and 32 C); Experiment B (pH 7 and 38 C); Experiment C (pH 8 and 32 C); Experiment D (pH 8 and 38 C). W
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Reactor setup The AnSBR was made of polyvinyl chloride with a working volume of 5.1 L. The reactor was instrumented in order to enable the online measurement of variables such as temperature, pH, pressure and biogas flow rate (Figure 1). A National Instruments cRIO-9004 device equipped with analogical and digital cards was used in the acquisition, treatment and storage of the data. A graphical interface was designed by using the LabVIEW 8.2® software. At the beginning of each experiment, the AnSBR was inoculated with 6.5 g VSS/L of anaerobic granular sludge and then fed with tequila vinasses at 8 ± 0.5 g COD/L. Filling and discharging of the medium was carried out by means of peristaltic pumps. The following stages were followed during each cycle: filling (7 min), reaction (from 3 to 9 days, until stationary substrate consumption was attained), settling (30 min) and discharge (7 min). In order to induce homogeneous conditions during the reaction time, the reactor was mixed by means of a recirculation loop. The exchange ratio was 80% of the working volume, which means that practically all the liquid content was removed at the end of each cycle. The temperature and pH were controlled by using a water jacket and by adding 2 N NaOH solution through an on–off control scheme, respectively.
Figure 1
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AnSBR scheme. (1) Feeding/discharging pipe; (2) water jacket; (3) 2 N NaOH solution; (4) phase separator; (5) diffuser/decanter; (6) sampling port; (7) recirculation pump; (8) biogas counter; (9) temperature sensor; (10) pressure sensor; (11) pH/oxidation reduction potential sensor; (12) cRIO controller; (13) PC. Liquid streams: gray line; gas stream: black line; data transmission: dotted line.
and partial alkalinities (α ¼ IA/PA). On the other hand, COD was measured according to Arreola-Vargas et al. () and VFAs and biogas composition were determined as previously reported by means of high-performance liquid chromatography and gas chromatography with a thermal liquid detector, respectively (Méndez-Acosta et al. ).
RESULTS AND DISCUSSION
Analytical methods
Tequila vinasses degradation
In addition to the online readings, offline measurements were also taken. Partial (pH ¼ 5.75) and intermediate (pH ¼ 4.3) alkalinities that are related to bicarbonate and VFA buffer capacities respectively were measured according to Ripley et al. () in order to calculate the alkalinity factor, which is given by the ratio between the intermediate
The robustness of the AnSBR was evaluated at four different pH–temperature conditions (A: 7 and 32 C; B: 7 and 38 C; C: 8 and 32 C and D: 8 and 38 C) since it is well-known that these parameters have a great influence on the anaerobic digestion process (Montañés et al. ). The duration of each experiment was defined by the time required to obtain W
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reproducibility in both COD removal and methane production in at least two contiguous cycles. Regarding COD removal, Figure 2 shows that the degradation of tequila vinasses was quite similar in all the assays, suggesting a high robustness of the process. COD removals between 84.4 and 85.4% were obtained for the different tested conditions (Figure 2(b)). In addition, the cycles at each condition were very reproducible. For instance, Figure 2(a) shows the typical kinetic profile obtained during the performance of Experiment A, in which a quite similar trend for COD removal can be observed in the performed cycles. The dotted line shows the COD concentration at which the degradation rate of tequila vinasses was negligible and therefore a new cycle was performed. It is worth mentioning that the kinetic trend observed in Figure 2(a) is highly representative of the rest of the experiments (data not shown). Despite the high COD removal efficiencies attained under the different AnSBR experiments, around 15% of recalcitrant COD remained in the liquid phase after the anaerobic treatment (Figure 2). Therefore, further research
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on effluent post-treatment is needed in order to comply with the stringent wastewater regulations. In this sense, a possible effective sequential treatment could be an anaerobic–aerobic process, which has been successfully proven for other type of vinasses (Moletta ). Biogas production Biogas production and methane content were also recorded to compare the energy recovery potential among the different AnSBR experiments. The reported values in Figure 3 are presented at standard conditions (1 atm and 0 C). Overall, the experiments performed at pH 7 achieved higher biogas production than those performed at pH 8. Nonetheless, the content of methane in biogas was higher in the experiments performed at pH 8 (around 90%) than those at pH 7 (around 75%). Regarding methane production, Figure 3(b) shows that similar values were obtained in all the experiments: around 9.6 L per cycle for Experiments A, B and C, and 8.1 L per cycle for Experiment D. In the W
Figure 3 Figure 2
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(a) Typical kinetic profile of biogas production (Experiment A). (b) Global biogas
(a) Typical kinetic profile of vinasses degradation (Experiment A). (b) Global
and methane production obtained during the four experiments at different
COD removals obtained during the four experiments at different pH and
values of pH and temperature. (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C; (D) 8 and 38 C. Bars represent the average of the last two cycles at each
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temperature values. (A) 7 and 32 C; (B) 7 and 38 C; (C) 8 and 32 C; (D) 8 and 38 C. Bars represent the average of the last two cycles at each condition. All W
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condition. All the AnSBRs were operated for a period of 30 ± 6 days until no
the AnSBRs were operated for a period of 30 ± 6 days until no variation in COD
variation in COD removal and biogas production was observed in two contig-
removal and biogas production was observed in two contiguous cycles.
uous cycles.
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particular case of Experiment D, the slightly lower methane production registered even when the COD removal was similar to the other experiments (Figure 2(b)) is explained by some faults that developed in the biogas counter during the last cycle, which can be confirmed by the larger standard deviation (see Figure 3(b)). Nevertheless, in general the cycles were very reproducible in all the experiments (for instance see Figure 3(a)), confirming the robustness observed in the COD removal efficiencies (Figure 2). It is worth noting that the unusual high methane content in the experiments performed at pH 8 could be related to solubilization of CO2 in the liquid phase. According to Tippayawong & Thanompongchart (), at this alkaline pH, CO2 absorption may have taken place by transference of this compound from the gas phase to the gas/liquid interface, and then to the bulk of the liquid phase, where the following reactions take place. 1. CO2 þ 2OH ! CO2 3 þ H2 O 2. CO2 þ CO2 þ H O ! 2HCO 2 3 3
Figure 4
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Profiles of VFAs obtained during the AnSBR experiments at different pH– temperature values: (▪) 7 and 32 C; (●) 7 and 38 C; (▴) 8 and 32 C; (♦) 8 and W
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38 C. Symbols represent the average of the last two cycles at each condition.
VFA analysis According to Table 1, the main components of tequila vinasses were VFAs, which are the most important intermediates in the anaerobic digestion process because they are the main substrate used by syntrophic bacteria and methanogenic archaea to produce methane. However, under certain conditions VFAs can also be accumulated in the digester, resulting in a digester failure called process acidification (Zhang et al. ). This feature led to a close monitoring of the VFA degradation or production during the anaerobic digestion experiments. Overall, the complete degradation of formate, acetate, isobutyrate and isovalerate was observed in all the experiments (Figure 4). It is worth noting that, even though the presence of isovalerate and isobutyrate at concentrations greater than 15 mg/L has been previously related to reactor instability (Hill & Bolte ), during the present work such an effect was not observed despite the extremely high initial concentration of such VFAs in the different batches of vinasses used to fed the AnSBRs (Table 1). A possible explanation for this behavior is that syntrophic communities in the reactor were able to consume these acids for further methanization. Conversely, Figure 4 also shows that microbial populations were also able to consume butyrate and propionate. However, it is clear that most of such acids were produced during the anaerobic digestion process, which was very likely due to degradation of other VFAs.
According to Ripley et al. (), the successful (stable) operation of anaerobic digesters depends on both proper control to avoid an excessive VFA accumulation and the adequate maintenance of the bicarbonate buffering. Therefore, the operational stability of the AnSBR experiments was also followed by means of the alkalinity factor (α). Results were also very reproducible during all the experiments (Figure 5). The initial values of α were between 0.6 and 1.0 but suddenly decreased during the first hours until
Figure 5
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Profiles of alkalinity factor obtained during the AnSBR experiments at different pH–temperature values: (▪) 7 and 32 C; (●) 7 and 38 C; (▴) 8 and 32 C; (♦) 8 W
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and 38 C. Symbols represent the average of the last two cycles at each condition.
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reaching values from 0.25 to 0.3. The latter values are in accordance to those reported as the adequate ones (below 0.3) for achieving a stable operation of the anaerobic digestion process (Ripley et al. ).
The AnSBR experiments were conducted for a minimum of 24 and a maximum of 36 days, equivalent to 4 to 6 operation cycles (Table 2). The OLR was equivalent to 0.9 ± 0.2 g/L*d, which is much lower than those organic loading rates applied in continuous reactors such as the UASB, up to 40 g/L*d (España-Gamboa et al. ). Nonetheless, the present study did not aim to increase the OLR. On the other hand, it is worth noting that regardless of the differences in both the pH–temperature conditions evaluated as well as the tequila vinasses composition, the AnSBR performance was reasonably good with excellent robustness properties. Regarding COD removal efficiencies, values were slightly higher (85 vs. 80%) than those reported by Batstone et al. () in which an AnSBR was used for the treatment of winery vinasses. However, for the specific case of tequila vinasses, COD removal efficiencies higher than 90% have been reported in a CSTR (Méndez-Acosta et al. ). Nonetheless, the AnSBR still represents a viable alternative for the treatment of tequila vinasses because of its high robustness and easy operation as shown in the present study. Regarding methane yield, Table 2 shows that, overall, lower methane yields than the theoretical one (0.35 L CH4/g COD) were |
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attained; around 80% of the original COD was converted to methane. Nonetheless, the yields obtained in the present study are higher than those reported in previous studies for the treatment of vinasses in UASB reactors (0.22 L CH4/g COD, at standard conditions) (Akarsubasi et al. ). Finally, concerning the specific degradation and methane production rates, such parameters were also maintained at similar values, confirming the overall operation stability of the process. The latter results along with the reasonable good methane yields and COD removals confirm the potential of the AnSBR technology for its use in the treatment and energy recovery from tequila vinasses.
Overall performance
Table 2
Water Science & Technology
CONCLUSIONS In the present work, the use of an AnSBR for the treatment of tequila vinasses was evaluated at four different pH and temperature conditions. Furthermore, four different vinasses batches were used in order to simulate the high variability in vinasses composition at which full-scale reactors are operated. Overall, results demonstrated that AnSBR technology is effective for tequila vinasses treatment in terms of COD removal and methane yield. Interestingly, even though previous works have reported negative effects because of the presence of long chain VFAs, the AnSBR was able to operate under high concentrations of such acids. High robustness regarding COD removal and methane production was also observed at the different evaluated conditions, which means that any of
Overall performance of the AnSBR experiments at different pH and temperatures
Experiment Parameter
A
B
C
D
Number of operated cycles
5
4
5
6
Total operation days
36
30
24
36
Organic loading rate (g/L*d)
0.89
0.67
1.04
1.01
Initial COD (g/L)
8.1 ± 0.1
7.9 ± 0.4
8.3 ± 0.1
7.9 ± 0.2
Initial CODVFA (%)
37.1 ± 0.1
75.9 ± 0.3
63.9 ± 0.2
56.9 ± 0.3
COD removal (%)
85.4 ± 0.1
84.4 ± 0.4
84.8 ± 0.3
84.5 ± 0.5
Biogas production (L/cycle)
13.2 ± 0.3
12.7 ± 0.6
10.3 ± 0.2
8.7 ± 0.3
Methane content in biogas (%)
72.4 ± 3.8
74.5 ± 3.7
91.5 ± 3.8
92.4 ± 6.6
Methane yield (L CH4/g COD added)
0.29
0.29
0.28
0.25
Methane production rate (L CH4/h)
0.48
0.46
0.49
0.42
0.79
0.83
Specific degradation rate (g COD/g VSS*d) W
0.83 W
0.76 W
W
Experiment A (pH 7 and 32 C); Experiment B (pH 7 and 38 C); Experiment C (pH 8 and 32 C); Experiment D (pH 8 and 38 C). Values are the average of the last two cycles of each experiment. Initial CODVFA: % of initial COD attributed to VFAs.
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these conditions can be used for the treatment of tequila vinasses. Therefore, it is shown that the implementation of the AnSBR configuration is quite encouraging, particularly for small and medium size tequila industries that operate under seasonal conditions, due to its low cost, easy operation and high robustness to process load disturbances.
ACKNOWLEDGEMENT J. Arreola-Vargas acknowledges CONACyT for the support under the retention and repatriation program (232166).
REFERENCES Akarsubasi, A., Ince, O., Oz, N., Kirdar, B. & Ince, B. Evaluation of performance, acetoclastic methanogenic activity archaeal composition of full-scale UASB reactors treating alcohol distillery wastewaters. Process Biochemistry 41, 28–35. Arreola-Vargas, J., Ojeda-Castillo, V., Snell-Castro, R., CoronaGonzález, R. I., Alatriste-Mondragón, F. & Méndez-Acosta, H. O. Methane production from acid hydrolysates of Agave tequilana bagasse: evaluation of hydrolysis conditions and methane yield. Bioresource Technology 181, 191–199. Batstone, D., Torrijos, M., Ruiz, C. & Schmidt, J. Use of an anaerobic sequencing batch reactor for parameter estimation in modelling of anaerobic digestion. Water Science and Technology 50 (10), 295–303. Buitrón, G. & Carvajal, C. Biohydrogen production from Tequila vinasses in an anaerobic sequencing batch reactor: effect of initial substrate concentration, temperature and hydraulic retention time. Bioresource Technology 101, 9071–9077. Buitrón, G., Kumar, G., Martinez-Arce, A. & Moreno, G. Hydrogen and methane production via a two-stage processes (H2-SBRþ CH4-UASB) using tequila vinasses. International Journal of Hydrogen Energy 39, 19249–19255. España-Gamboa, E., Mijangos-Cortes, J., Barahona-Perez, L., Dominguez-Maldonado, J., Hernández-Zarate, G. & AlzateGaviria, L. Vinasses: characterization and treatments. Waste Management & Research 29, 1235–1250. Hill, D. T. & Bolte, J. P. Digester stress as related to isobutyric and iso-valeric acids. Biological Wastes 28, 33–37. Jáuregui-Jáuregui, J. A., Méndez-Acosta, H. O., González-Álvarez, V., Snell-Castro, R., Alcaraz-González, V. & Godon, J. J. Anaerobic treatment of tequila vinasses under seasonal
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operating conditions: start-up, normal operation and restart-up after a long stop and starvation period. Bioresource Technology 168, 33–40. López-López, A., Davila-Vazquez, G., León-Becerril, E., Villegas-García, E. & Gallardo-Valdez, J. Tequila vinasses: generation and full scale treatment processes. Reviews in Environmental Science and Bio/Technology 9, 109–116. Mace, S. & Mata-Alvarez, J. Utilization of SBR technology for wastewater treatment: an overview. Industrial and Engineering Chemistry Research 41, 5539–5553. Mao, C., Feng, Y., Wang, X. & Ren, G. Review on research achievements of biogas from anaerobic digestion. Renewable and Sustainable Energy Reviews 45, 540–555. Méndez-Acosta, H. O. & González-Álvarez, V. Methane production from tequila vinasses. In: Energy and Environment Nowadays (L. G. Torres & E. R. Bandala, eds). Nova Science Publishers, New York, USA, pp. 165–168. Méndez-Acosta, H. O., Snell-Castro, R., Alcaraz-González, V., González-Álvarez, V. & Pelayo-Ortiz, C. Anaerobic treatment of Tequila vinasses in a CSTR-type digester. Biodegradation 21, 357–363. Méndez-Acosta, H. O., Hernandez-Martinez, E., Jáuregui-Jáuregui, J. A., Alvarez-Ramirez, J. & Puebla, H. Monitoring anaerobic sequential batch reactors via fractal analysis of pH time series. Biotechnology and Bioengineering 110, 2131–2139. Moletta, R. Winery and distillery wastewater treatment by anaerobic digestion. Water Science and Technology 51 (1), 137–144. Montañés, R., Pérez, M. & Solera, R. Anaerobic mesophilic co-digestion of sewage sludge and sugar beet pulp lixiviation in batch reactors: effect of pH control. Chemical Engineering Journal 255, 492–499. Moraes, B. S., Junqueira, T. L., Pavanello, L. G., Cavalett, O., Mantelatto, P. E., Bonomi, A. & Zaiat, M. Anaerobic digestion of vinasse from sugarcane biorefineries in Brazil from energy, environmental, and economic perspectives: Profit or expense? Applied Energy 113, 825–835. Ripley, L., Boyle, W. & Converse, J. Improved alkalimetric monitoring for anaerobic digestion of high-strength wastes. Journal (Water Pollution Control Federation) 58, 406–411. Robles-González, V., Galíndez-Mayer, J., Rinderknecht-Seijas, N. & Poggi-Varaldo, H. M. Treatment of mezcal vinasses: a review. Journal of Biotechnology 157, 524–546. Tippayawong, N. & Thanompongchart, P. Biogas quality upgrade by simultaneous removal of CO2 and H2S in a packed column reactor. Energy 35, 4531–4535. Zhang, C., Su, H., Baeyens, J. & Tan, T. Reviewing the anaerobic digestion of food waste for biogas production. Renewable and Sustainable Energy Reviews 38, 383–392.
First received 14 June 2015; accepted in revised form 1 October 2015. Available online 12 October 2015
