Influence of alkalinity and VFAs on the performance of an UASB reactor with recirculation for the treatment of Tequila vinasses

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Influence of alkalinity and VFAs on the
performance of an UASB reactor with recirculation
for the treatment of Tequila vinasses
Alberto López-López, Elizabeth León-Becerril, María Elena Rosales-Contreras
& Edgardo Villegas-García
To cite this article: Alberto López-López, Elizabeth León-Becerril, María Elena Rosales-
Contreras & Edgardo Villegas-García (2015) Influence of alkalinity and VFAs on the
performance of an UASB reactor with recirculation for the treatment of Tequila vinasses,
Environmental Technology, 36:19, 2468-2476, DOI: 10.1080/09593330.2015.1034790
To link to this article: http://dx.doi.org/10.1080/09593330.2015.1034790
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Published online: 27 Apr 2015.
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Environmental Technology, 2015
Vol. 36, No. 19, 2468–2476, http://dx.doi.org/10.1080/09593330.2015.1034790
Influence of alkalinity and VFAs on the performance of an UASB reactor with recirculation for
the treatment of Tequila vinasses
Alberto López-López∗
, Elizabeth León-Becerril, María Elena Rosales-Contreras and Edgardo Villegas-García
Department of Environmental Technology, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A.C., Av.
Normalistas 800, Colinas de la Normal, 44270 Guadalajara, Jalisco, Mexico
(Received 31 October 2014; accepted 19 March 2015)
The main problem linked to the stability of upflow anaerobic sludge blanket (UASB) reactors during the treatment of
Tequila vinasse is the high acidity and the null alkalinity present in this effluent. This research evaluates the effect of
alkalinity and volatile fatty acids (VFAs) concentration on the performance of an UASB reactor with recirculation of the
effluent for removing organic matter and biogas production from Tequila vinasses. Recirculation of the effluent reduces the
impact of VFAs and organic matter concentration present in the influent, inducing the stability of the reactor. The UASB
reactor was operated during 235 days at organic loading rates from 2.5 to 20.0 kg m−3 d−1, attaining a removal efficiency
of COD greater than 75% with a methane yield of 335 ml CH4 g−1 COD at SPT, maintaining a ratio of VFAs/Alk ≤ 0.5.
Therefore, an optimal ratio of VFAs/Alk was established for the system operating in stable conditions for the treatment of
Tequila vinasses. Under these conditions, the alkalinity was recuperated by the system itself, without the addition of external
alkalinity.
Keywords: Tequila vinasse; anaerobic process; volatile fatty acids; alkalinity; methane; recirculation
Introduction
Tequila vinasses are the liquid residues generated after
the distillation of the must of fermented agave (Agave
tequilana Weber var. azul) in Tequila production. Tequila
vinasse is a dark brown liquid; it presents a pH of 3.5
and a high chemical oxygen demand (COD), which ranges
from 60 to 100 g l−1
; generating potential risks to the
environment if it is discharged without treatment to water
bodies.[1–4] Among the different treatments of vinasses,
the anaerobic process stands out as the most viable; it
has been used for the treatment of Tequila vinasse [2,5–7]
and for other distilled spirits.[3,8–10] Anaerobic processes
are considered energetically, environmentally and econom-
ically viable for the treatment of vinasses; biogas rich in
methane generated during the anaerobic process could be
used for electric energy generation. Also the treatment of
vinasse by anaerobic processes avoids the environmental
pollution of soil and water, decreasing the global warming
potential impacts and pollutant loads, while an economic
analysis promotes the anaerobic process because it gener-
ates energy instead of consuming it, which is beneficial to
the economy.[11]
In Mexico, anaerobic processes for treating Tequila
vinasses have been started in the 1990s, using several
configurations of anaerobic reactors, such as packed bed,
*Corresponding author. Emails: alopez103@yahoo.com; allopez@ciatej.mx
upflow anaerobic sludge blanket (UASB) and filter bed
reactors reaching moderate COD removal efficiencies,
from 50% to 70%.[12] The first results showed a low COD
removal efficiency, which is related principally with lack
of anaerobic biomass with a proper methanogen activ-
ity and with a slight adaptation of biomass to the low
alkalinity of the substrate. Nowadays, other reactor config-
urations have been used such as the anaerobic sequencing
batch reactor [13] and the continuous stirred tank reac-
tor (CSTR) [14,15]; however, the UASB reactor offers
advantages such as removal efficiencies of COD greater
than 80%, organic load rates (OLR) ranging from 5 to
20 kgCOD m−3
d−1
and methane yields from 250 to 400
mlCH4 g−1
COD.[4,5,16–18]
Start-up strategies for anaerobic reactors used gradual
increments in OLR until reaching the effluent concentra-
tion in COD and a constant average removal efficiency of
COD. During the treatment of vinasses, anaerobic reactors
present instabilities in their performance, due to the lack of
alkalinity, low pH and accumulation of volatile fatty acids
(VFAs); in consequence, the addition of external alkalinity
is primordial and different control parameters have been
defined for this purpose.[7,14,15,17]
Álvarez et al. [16] reported COD removal efficiencies
about 80% in an UASB reactor operated for 150 days,
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Environmental Technology 2469
OLR was increased gradually from 5 to 20 kgCOD m−3
d−1
and defined a control parameter, the alkalinity ratio (α)
between bicarbonate and total alkalinity, the desired value
being below 0.4. For OLRs greater than 15 kgCOD m−3
d−1
, α overshoots 0.4 control value, provoked by the high
concentration of VFAs.
Another operation parameter evaluated in the treatment
of vinasses to reduce the acidification of the reactor is the
effluent recirculation. Ilangovan et al. [5] used two UASB
reactors, one with effluent recirculation and the other with-
out recirculation; both reactors operated with an OLR of
7 kgCOD m−3
d−1
reaching COD removal efficiencies of
80%. The reactor with recirculation reached an OLR of
25 kgCOD m−3
d−1
and kept the COD removal of 80%;
however, the reactor without recirculation was affected
drastically when OLR increased to 20 kgCOD m−3
d−1
.
With recirculation, the concentration of VFAs at the inlet
diminished, reducing the effect of acidification in the reac-
tor. Indeed, external alkalinity was not supplied to the
reactor, however, an effect in the sludge was observed
–granular sludge became a mixed sludge (granular and
flocculent).[19]
Automatic control of reactors is another important
aspect developed to assess the effect of acidity and alka-
linity in the anaerobic treatment of vinasses.[7,14,20]
Mendez-Acosta et al. [14] operated a CSTR with auto-
mated operation parameters to treat Tequila vinasses,
removing organic matter with an efficiency of 90%, with a
biogas yield about 537l kg−1
COD removed, with a 60% of
methane. Anaerobic sludge was capable to tolerate changes
in OLR from 1 to 6 kgCOD m−3
d−1
, even with an imbal-
ance in COD/N/P proportion; the automatic control of
alkalinity ratio parameter α was maintained below 0.3 with
continuous addition of NaOH, maintaining a stable perfor-
mance of the reactor. Alcaraz-González et al. [7] proposed
a robust multivariable control model to guarantee the stable
operation of the anaerobic process. Authors demonstrated
that the regulation of VFAs and the strong ionic concen-
tration permit that the functional stability percentages in
terms of intermediate and total alkalinity could be satisfied
for any perturbation of the system.
Therefore, the high acidity of vinasses is associated
with the VFAs concentration, especially propionic and
butyric acids that can affect the performance of the aceto-
genic and methanogenic microorganisms in the anaerobic
digestion process.[5,7,12,14,21] Hence, the treatment of
Tequila vinasse by anaerobic digestion requires an ade-
quate control of operation parameters to avoid the VFAs
accumulation and to profit the internal alkalinity gener-
ated by the anaerobic process itself to ensure the stability
of the reactor. The objective of this research is orientated
to evaluate the effect of the alkalinity and VFAs on the
performance of an UASB reactor with a strategy of recir-
culation of the effluent for reducing the impact of acidity
for removing organic matter and biogas production from
the anaerobic digestion of Tequila vinasses.
Material and methods
Tequila Vinasse
Vinasse was collected after the distillation stage from a
Tequila factory; it was maintained at 4°C until it was used
for the experiments. Tequila vinasse was pre-treated to
eliminate settleable solids by centrifugation at 3000 rpm
for 30 min in a DAMON/IEC DIVISION CU-5000 cen-
trifuge. Before feeding vinasse to the UASB reactor, pH
was adjusted at 7, with solutions of NaOH and NaHCO3 at
1.0 N; the necessary doses were determined for a volume
sample of 100 ml of centrifuged vinasse.
UASB reactor
The UASB reactor consisted of a Pyrex glass column with
8 cm of diameter and 50 cm of height, with a total volume
of 2.25 l; the reactor was fed at the bottom and the efflu-
ent was recuperated at the top of the column. Temperature
was maintained at 35°C by a thermocirculator LabTech
D2010. The biogas (methane and carbon dioxide) gener-
ated during anaerobic process passed through a solution of
3 M NaOH in order to capture and convert the CO2 present
in the biogas to Na2CO3, then methane gas could be mea-
sured by displacement of water in a column; methyl orange
was used as an indicator of the saturation of NaOH solu-
tion (Figure 1). Methane yield was determined by the linear
regression analysis from the experimental data, CH4 gen-
erated (ml d−1
) and COD removed (mg d−1
), adjusted by
the method of least squares.
Figure 1. Schema of the experimental system.

2470 A. López-López et al.
Start-up of the UASB reactor
Inoculation
For the inoculation of the UASB reactor, granular sludge
(granules about 2.5 mm) from an anaerobic treatment plant
of vinasses was used. A sludge volume of 20% v/v with
respect to the UASB reactor volume was used, with a
volatile suspended solids (VSS) concentration of 18,750
mg l−1
, acclimatizes at pH = 7.0 and temperature of 35°C.
The specific methanogenic activity was ranging from 0.15
to 0.89 gCOD-CH4 (gVSS)−1
d−1
using acetate as sub-
strate.
Operating conditions of the UASB reactor
Hydraulic retention time was established from prelimi-
nary tests and based on results from the literature in 48
h,[4,5,18] with smaller hydraulic retention time values,
efficiencies of the UASB reactor decreased drastically
(results not shown). Temperature was fixed at 35°C.
The UASB reactor was started-up at OLR = 2.5 kg m3
d−1
equivalent to a 10% of the total COD concentration
of Tequila vinasse; demineralized water was used for the
dilutions of vinasse. OLR was increasing gradually until
20 kg m3
d−1
equivalent to 100% of the COD concentra-
tion of vinasse, changes in OLR were made when the
reactor was assumed stable, considering that the degrada-
tion rate of COD and methane yield were constant. Three
times a week, physicochemical parameters, such as COD,
VSS, VFAs, alkalinity and methane yield were determined,
in order to know if the reactor was operating within the
optimal conditions of an anaerobic treatment process.
A very important factor to be monitored was pH, avoid-
ing the drastic drop below 6; for reducing the addition
of external alkalinity by NaOH or NaHCO3 solutions, a
strategy of recirculation of the effluent was established
from day 10 to 50. It consisted of an initial recirculation
ratio of 1:1, defined as Qr/Qo = recirculation volumetric
flow/outlet volumetric flow; consequently, this ratio was
increased every 72 h, in one unity.
Analytical methods
Standard Methods were used to determine physicochemi-
cal parameters of vinasse.[22] Samples were taken at the
outlet of the reactor after the recirculation flow (at the
top) for be analysed, determining physicochemical param-
eters and VFAs. Concentrations of the main VFAs, such
as acetic, propionic and butyric acids were identified by
a gas chromatographer equipped with a flame ionization
detector (Agilent Technologies G1530A) with a capillary
column DB-FAP (0.25 mm × 30 m), using helium as the
carrier gas. Samples were prepared and conserved accord-
ing to the methodology proposed by Park et al. [23]. A
sample volume of 0.5 μl was injected at a gas flow rate
of 1 ml min−1
and a split ratio of 20:1. Initial temperature
was 80°C maintained for a minute, then it was increased
at a rate of 20°C per minute, until 120°C; then temper-
ature was increased for 6°C per minute, until it reached
205°C. VFAs were identified in a retention time range of
5–11 min. Injector temperature was 210°C and detector
temperature was 240°C.
Results and discussion
Physicochemical characteristics of vinasse
Table 1 presents the physicochemical characteristics of
raw vinasse; pH value is about 3.5; organic matter mea-
sured as COD and biochemical oxygen demand (BOD)
is about 49,000 and 27,500 mg l−1
, respectively; nearly
56% of the organic matter is biodegradable and 88%
is soluble. Setteable solids (SetS) are in the order of
Table 1. Physicochemical characteristics of Tequila vinasse.
Parameter Unit Vinasse
Centrifuged
Vinasse
pH (UP) 3.50 ± 0.06 3.65
Grease and
oils
mg l−1 106.00 ± 18.19 97.44
COD total mg l−1 48,991 ± 5,548 35,648.00
COD soluble mg l−1 43,658 ± 1,855 34,531.00
BOD total mg l−1 27,472 ± 2,029 21,040.00
BOD soluble mg l−1 24,251 ± 276 20,212.00
TS mg l−1 30,506 ± 3,956 24,275.00
TSS mg l−1 4,383 ± 4,081 136.00
Fixed
suspended
solids
mg l−1 178 ± 208 11.00
VSS mg l−1 4,205 ± 3,875 112.00
TDS mg l−1 26,152 ± 1,658 25,784.00
SetS ml l−1 175.00 ± 108.97 1.00
Total
alkalinity
mgCaCO3 l−1 1.50 ± 0.71 < 1.00
Total acidity mgCaCO3 l−1 3,097 ± 398 2,815.00
Fixed acidity mgCaCO3 l−1 2,299 ± 176 2,174.09
Volatile
acidity
mgCaCO3 l−1 797.71 ± 574.46 640.91
Calcium mg l−1 323.03 ± 64.11 97.38
Magnesium mg l−1 185.87 ± 37.83 213.80
Potassium mg l−1 312.67 ± 50.06 335.47
Total
phosphates
mg l−1 14.87 ± 0.70 ND
Total nitrogen mg l−1 78.03 ± 12.20 76.80
Organic
nitrogen
mg l−1 5.23 ± 0.64 65.20
Ammonia
nitrogen
mg l−1 72.80 ± 11.57 11.60
Reducing
sugars
% w/w 1.34 ± 1.02 ND
Direct sugars % w/w 0.45 ± 0.21 ND
Total sulphates mg l−1 1,100 ± 380 ND
Copper mg l−1 1.18 ± 0.28 ND
Iron mg l−1 20.17 ± 15.55 ND
Zinc mg l−1 0.90 ± 0.64 ND
Note: ND, not determined.

175 ml l−1
; concentration of total solids (TS) is 30,506
mgl−1
; about 86% of them are total dissolved solids (TDS)
and the remainder is total suspended solids (TSS); these
values are congruent with the soluble organic matter per-
centage. Acidity is about 3096 mg l−1
and alkalinity is
practically nil; therefore, pH has an acid value. Concen-
trations of calcium, magnesium and potassium are in the
order of hundreds of mg l−1
. Nitrogen and phosphates are
near 78 and 15 mg l−1
, respectively, and vinasse presents
smaller concentrations of copper, iron, zinc and sulphates
(SO−
4 ). Similar results for Tequila vinasses were found by
España-Gamboa et al. [3].
Pre-treatment of vinasse
Physicochemical characteristics of centrifuged vinasses
Centrifuged vinasse was also characterized and results are
given in Table 1; SetS were almost completely reduced,
likewise TSS were reduced to 90%; although TDS were
only reduced about 10%. As a consequence of SetS and
Figure 2. Neutralization of vinasse (a) with NaOH; (b) with NaHCO3.

TSS reduction, approximately a 25% reduction in COD
and BOD is observed, both total and soluble. Total acidity
decreased by 10% to 20%, such as magnesium, potassium,
copper, iron and zinc concentrations are less than 10%.
It is important to note that about 87% of organic mat-
ter in vinasse is soluble. A centrifugation pre-treatment to
eliminate total suspended solids of Tequila vinasses is con-
sidered a viable alternative, because at the same hydraulic
conditions the OLR is reduced, provoking the stability and
greater efficiency of the UASB reactor.[21]
Neutralization stage
Figure 2(a) and 2(b) shows that vinasse needs more vol-
ume of NaOH than NaHCO3 to increase pH; when NaOH
was used, an inflexion point was observed at pH = 5.5, in
this point it is possible to increase or decrease pH exponen-
tially. However, when NaHCO3 was used, pH behaviour
was practically linear. In order to avoid abrupt changes in
pH, first it is convenient to add NaOH until a value of
pH = 5.5 and then neutralize with NaHCO3, ensuring a
more stable system. Before feeding vinasse to the UASB
reactor, pH of vinasse was adjusted following these results.
Influence of the recirculation ratio
Drastic drop in pH was observed during the operation of
the UASB reactor; the first 50 days addition of NaHCO3,
according to Figure 2(b), was imperative for the mainte-
nance of pH around 7 and for keeping the stability of the
system. At the same time, for day 10–50, a strategy of
recirculation of the effluent was established. The optimal
ratio obtained was 10:1; at this value, upflow velocity in
the reactor was increased, and in consequence the mixing
between the vinasse and the biomass also increased. If the
recirculation rate increased, sludge washout was observed,
Figure 3. Profiles in the UASB reactor: (a) pH and alkalinity; (b) COD at the outlet and COD removal efficiency; (c) methane production
rate. (a) pH, alkalinity. (b) COD at the outlet; COD removal efficiency.

provoking perturbations in the performance of the reactor.
With the recirculation ratio 10:1, it was possible to recover
alkalinity generated from the anaerobic process, that is, the
carbon dioxide (CO2) reacts with water to form carbonic
acid (H2CO3); H2CO3 is a diprotic acid and dissociates
in two steps – first to bicarbonate (HCO−
3 ) and then to
carbonate (CO−2
3 ),[21] therefore, the addition of NaHCO3
solution was not necessary anymore.
When the recirculation ratio increased from 1:1 to 10:1,
an effect in the sludge morphology was observed; granular
sludge became granular and flocculent mixed sludge and
the average grain size of sludge was reduced from 2.5 to
1.5 mm approximately.
Influence of alkalinity
Figure 3(a) shows the influence of pH and alkalinity on
the performance of the UASB reactor in function of time
and OLR, pH is directly related with alkalinity, and in con-
sequence with removal efficiencies of COD. During the
first 50 days of the UASB reactor operation, the addition
of external alkalinity was necessary to assure the stability
of the reactor; from day 50, due to the recirculation, there
was no need for NaHCO3 addition, the reactor recovered
the alkalinity and was stable. A decrease in pH below 6.5
in several points during the reactor performance period can
be observed; it was provoked basically when the OLR was
increased, in consequence removal efficiencies of COD
dropped (Figure 3(b)). This decreasing COD removal effi-
ciency is due to the alkalinity in the reactor, which was
not sufficient to neutralize the acidity present in the inlet
of the reactor. In these cases, only the addition of NaHCO3
allowed to reach the stability of the UASB reactor opera-
tion. Smaller increments in OLR and a recirculation ratio
of effluent 10:1 assured the stabilization of the UASB reac-
tor for the treatment of Tequila vinasse. It is important to
remark that if alkalinity and pH decreased, then removal
efficiency of COD dropped below 50% (Figure 3(b)).
COD performance
Figure 3(b) shows the behaviour of COD concentration
at the outlet of the reactor and the COD removal effi-
ciency in function of time and OLR, during the period
of operation. In general, when the OLR increased, COD
removal efficiency also increased; in the same way, when
the OLR augmented, perturbations were provoked in the
performance of the UASB reactor, affecting the stability,
and in consequence the efficiency of the reactor dimin-
ished. The most important instabilities were observed at
days 48, 155 and 175. This phenomenon is associated with
the alkalinity decompensation due to an increment in the
acidity for the feeding of UASB reactor. After day 50, with
the optimal recirculation ratio, the average efficiencies of
removal of organic matter were 75%, obtained when the
pH and alkalinity of UASB reactor effluent were about 7
and 6900 mgl−1
, respectively.
Despite the high COD removal efficiencies achieved
from 75% to 80%, a significant fraction of organic matter is
still present in the effluent. Therefore, a post-treatment of
aerobic type needs to be considered to remove the resid-
ual COD, which could be an extended aeration process
with operating parameters that allow to remove not only
the organic matter but also the nutrients, in order to meet
the standards for discharge and/or agricultural reuse.[2]
Table 2 presents the overall COD balances for differ-
ent OLRs, since biomass-COD was not determined, the
proportion of influent COD converted to biomass was
assumed to be 10% [21,24]; therefore, it was possible to
calculate the overall COD recovery. The greater recover-
ies of COD were obtained for periods with high removal
efficiencies of organic matter as COD and methane yield
(OLR = 10, 12.5 kg m3
d−1
). The minimal recovery of
COD was at OLR = 7.5 kg m3
d−1
), corresponding to
lesser removal efficiencies of COD due to the accumulation
of VFAs in the reactor.
Methane yield
Biogas was produced as a consequence of the anaero-
bic digestion of vinasse; biogas composition is mainly
methane with 60–65% and carbon dioxide with 35–
40%.[20] Methane generation increased with OLR (Figure
3(c)), so it was directly proportional to the amount of
organic matter removed in the UASB reactor; therefore,
if organic matter removal efficiency diminishes, methane
production also decreases; contrarily, if the efficiency
increases then methane production also increases.
Methane generation was not significant when the
UASB reactor was unstable during the first 50 days of
Table 2. Overall COD balances at different OLRs.
OLR (kgm−3 d−1) Influent (A) (g) Effluent (B) (g) Biomass (C) (g) Gas (D) (g) B + C + D Recovery (%)
5.0 9.46 6.46 0.3 0.99 7.76 82.02
7.5 14.22 4.77 0.945 4.73 10.45 73.48
10.0 19.1 4.65 1.445 10.02 16.11 84.40
12.5 24.31 5.96 1.835 16.30 24.10 99.14
15.0 28.10 10.34 1.776 10.97 23.09 82.17
17.5 3.95 12.95 2.1 13.20 28.25 83.22
20.0 38.06 14.66 2.34 13.46 30.46 80.03

operation; after this period, when the OLR changed from
7.5 to 15 kg m−3
d−1
, methane generation increased con-
siderably and removal efficiencies from 70% to 80% were
achieved. These indicators of stability of the UASB reac-
tor are basically associated with the amount of alkalinity
present in the system.
Methane yield was determined graphically (Figure 4)
from values of removal of organic matter and methane
production. Methane production rate obtained was 452
mlCH4 g−1
COD at normal conditions (T = 308 K,
Guadalajara (Mexico) atmospheric pressure = 0.84 atm),
[25] equivalent to 335 ml CH4 g−1
COD at STP, which is
very similar to the theoretic value of 350 mlCH4 g−1
COD
at STP.[21]
VFAs production
Concentration profiles of VFAs expressed as mg l−1
as
acid acetic are presented in Figure 5(a). In the first 50
days of the UASB reactor operation, it can be observed
an important accumulation of VFAs, this fate provoked
the drop of alkalinity; after this period when the optimal
Figure 4. Graphical determination of methane production rate.
Figure 5. (a) VFAs profiles in the UASB reactor; (b) VFAs/Alk ratio behaviour in function of time.

recirculation ratio was applied, the VFAs concentration
diminished and the reactor recovered its stability. Also,
an important accumulation of VFAs was observed in days
100, 155, 175 and 215, directly related to a change in the
OLR; at the same time, a decrease in alkalinity and pH
is observed, thus removal efficiency of COD was reduced,
with an exception at day 215 where removal efficiency of
COD kept constant.
Butyric acid concentration was in the range from 0 to
886 mg l−1
in the first 50 days of operation and subse-
quently concentration was practically zero. Propionic acid
concentration was in the range from 0 to 1250 mg l−1
dur-
ing the first 100 days, on day 130 it dropped drastically and
progressively increased to reach values about 1950; 2400
and 2800 mg l−1
on days 155, 175 and 215, respectively.
Only acetic acid was accumulated, reaching values close to
5000 mg l−1
on day 50, then, average values remained on
650 mg l−1
. The accumulation of VFAs in different peri-
ods could be associated with an overload supply of VFAs
in the feed, or with a possible inhibition of methanogenic
bacteria by environmental factors. A high accumulation of
VFAs in the reactor could provoke the acidification of the
media and produce a failure in the digestion process.
Stability of the UASB reactor can also be analysed
considering the VFAs/Alk ratio behaviour in function of
time (Figure 5(b)).[23] When the VFAs/Alk ratio was in
the range of 0.1–0.5, the performance of the reactor was
stable without the risk of acidification, this period coin-
cides with the consideration of the effluent recirculation.
Nevertheless, for VFAs/Alk ≥ 0.8, the reactor was unsta-
ble; therefore, it is associated with a recirculation ratio
smaller than 10:1 of the effluent and the changes of OLR,
in both cases, the addition of NaHCO3 was necessary.
These results are similar to values reported for anaerobic
processes with VFAs/Alk = 0.1–0.4.[21]
Conclusions
In order to reach the best performance and stability of the
UASB reactor during the treatment of Tequila vinasses, a
strategy based on the recirculation ratio 10:1 of the effluent
was established, therefore the alkalinity was recuperated
from the self-anaerobic process, keeping VFAs/Alk ratio
about 0.5. Accumulation of VFAs in the UASB reactor was
determinant in the drop of pH and in consequence in main-
taining COD removal efficiency greater than 75%, reaching
a methane yield of 335 ml CH4g−1
COD at SPT and pre-
senting an opportunity to generate energy and later an
exploitation of source of energy in the anaerobic treatment
of Tequila vinasses.
Disclosure statement
No potential conflict of interest was reported by the authors.
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Influence of alkalinity and VFAs on the performance of an UASB reactor with recirculation for the treatment of Tequila vinasses

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Influence of alkalinity and VFAs on the performance of an UASB reactor with recirculation for the treatment of Tequila vinasses