Energetic, economic and environmental assessment for the anaerobic
digestion of pretreated and codigested press mud
Lisbet Mailin López González
, Ileana Pereda Reyes
, Julio Pedraza Garciga
, Ernesto L. Barrera
Osvaldo Romero Romero
Universidad de Sancti Spíritus ‘‘José Martí Pérez”(UNISS), Centro de Estudios de Energía y Procesos Industriales (CEEPI), Avenida de los Mártires 360, CP 60100 Sancti Spíritus, Cuba
Universidad Tecnológica de La Habana ‘‘José Antonio Echeverría”(Cujae), Centro de Estudios de Ingeniería de Procesos (CIPRO), Calle 114 No. 11901 e/ Rotonda y Ciclovía,
Marianao, CP 19390 La Habana, Cuba
Received 16 May 2019
Revised 27 October 2019
Accepted 28 October 2019
Press mud and vinasse
This study investigates the feasibility of anaerobic digestion (AD) of press mud previously pretreated,
using two methods: Liquid Hot Water (LHW) and Thermo-Alkaline (TA), from an economic, energetic
and environmental point of view. Two scenarios, a sugar mill with and without distillery were studied,
considering monodigestion and vinasse codigestion. The results have shown that the LHW and TA pre-
treatments are self-sufﬁcient in terms of thermal requirements since they can recover heat from the bio-
gas engine, but the maximum electric and thermal net energy (64 MWh d
and 95 MWh d
respectively) was obtained during co-digestion with vinasse. The results of the environmental Life
Cycle Analysis (LCA) show that the alternatives improve the environmental proﬁles, in both scenarios.
The endpoint impact category ‘‘Human health” had the highest contribution because of both: the burning
of fossil fuel at reﬁnery to supply the required electricity; and the production of Ca(OH)
was fed. The AD of pretreated press mud by LHW in CSTR reactors was the most viable for the scenario
of a sugar mill without distillery, while the alternative co-digestion with the vinasse of the press mud
without pretreatment was the most viable for the scenario of a sugar mill with distillery. This research
shows that both the environmental and energetic proﬁles and the proﬁtability of methane production
can improve when the pretreatment and co-digestion of these wastes from the sugar – alcohol produc-
tion process are considered.
Ó2019 Elsevier Ltd. All rights reserved.
Anaerobic digestion (AD) for biogas production is one of the
most efﬁcient technologies for providing clean and renewable
energy from organic waste (Moraes et al., 2017). The technology
can increase the renewable contribution to the energy matrix of
developing countries such as Cuba, with a great potential unex-
ploited yet. According the Ministry of Energy and Mines (MINEM),
the Cuban policy concerning renewable energy has set a goal for
supplying 24% of the energy demand from renewable energy
sources by 2020, but the focus is on solar, wind energy and bio-
mass as bagasse and marabou for its use in bioelectric (MINEM,
2019). The biogas contribution has been few, as it has been focused
mainly to treat cow and pig manure, but others biomass with a
great potential for energy generation by way of biogas would be
used, while also reducing greenhouse gas (GHG) emissions.
Among them are the vinasse and press mud, main organic
wastes from bioethanol and sugar production, respectively. Typi-
cally, press mud is used as fertilizer/soil improver, being directly
(or after composting) applied to the soil in association or not with
minerals. From an environmental point of view, the composting
process is considered one of the most suitable alternatives to man-
age and treat organic solid waste, but higher consumption values
of transport, energy, water, infrastructure, waste and emissions
of volatile organic compounds are involved when industrial com-
posting is applied (Oliveira 2017).
Vinasse is mainly used for irrigation and fertilization (ferti-
irrigation) of the sugar cane plantations, however its indiscrimi-
nate usage cause soil salinization and groundwater contamination,
as well as methane and nitrous oxide emissions during temporary
storage and transportation (Moraes et al., 2017). Environmental
impacts from vinasse and press mud disposition may be reduced
by AD treatment to produce biogas.
The AD from press mud and vinasse for biogas production has
been previously reported in full and laboratory scale studies
0956-053X/Ó2019 Elsevier Ltd. All rights reserved.
E-mail address: email@example.com (L.M. López González).
Waste Management 102 (2020) 249–259
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/wasman
(Barros et al., 2016; Janke et al., 2017). Main difﬁculties during the
AD were improved by pretreatment and codigestion (Janke et al.,
2016; López González et al., 2014; López González et al., 2017;
López González et al., 2013), but these reports were only focused
to determine the methane yield for different severity conditions
and mixtures ratio, without considering energetic and economic
aspects. However, it is important to probe if the net energy and
economical gain attained by a pretreatment, prior to anaerobic
digestion step, can cover investment and operational costs, as well
as energetic pretreatments requirements.
A number of studies can be found in the literature analysing the
effect of substrate pretreatments on proﬁtability indicators and net
energy production in biogas plants (Budde et al., 2016; Cano et al.,
2014; Janke et al., 2017; Monlau et al., 2013; Shaﬁei et al., 2013;
Zeynali et al., 2017). Solid cattle manure pretreated in thermobar-
ical pretreatment at 160 °C by 20 min delivered 202.7 kW h
, but need only 169.2 kW h
. The pretreatment
revealed short payback periods (3.25 years) (Budde et al., 2016).
Shaﬁei et al. (2013) obtained an increase by 13% in the total invest-
ment costs using steam explosion pretreatment, but reducing the
manufacturing cost by 36% the economy of the biogas plant was
Anaerobic digestion can achieve GHG emission reduction when
compared to conventional fossil reference systems, being able to
improve the environmental proﬁle of the national electric grid.
However, the environmental results obtained were strongly
dependent of the speciﬁc substrate selected, substrate transport
distances, digestate management and heat valorization (Bacenetti
et al., 2013; Lijó et al., 2017; Styles et al., 2016). Some of the criteria
needed to meet the requirements of sustainable biogas production
include secure energy supply, avoid competition with food produc-
tion, socio-economic development including creation of local
employment and reduced environmental impacts (Jacobs et al.,
2017). Therefore, the use of food and alcohol industry wastes as
substrate for biogas production is recommended, since no emis-
sions are usually assigned to the production of waste streams
and these are converted into value-added products. In this sense,
previous works were addressed to the environmental sustainabil-
ity of biogas production from sugar-alcohol production residues.
They demonstrated that the anaerobic digestion improved the
environmental proﬁle reducing up to 77% the total score with
respect to the lagooning of Cuban vinasse (Barrera et al., 2016),
while GHG emissions were reduced by at least 48%, in comparison
with storage/transport and ﬁeld application of Brazilian vinasse
(Moraes et al., 2017). It is difﬁcult to draw conclusions from earlier
studies on the comparison between different treatment technolo-
gies and codigestion when energetic, economic and environmental
criteria have not been included. Therefore, this paper assesses the
feasibility of press mud AD previously pretreated by LHW and TA,
and untreated press mud in co-digestion with vinasse, from an eco-
nomic, energetic and environmental point of view.
2. Materials and methods
2.1. Case study and alternatives description
As case study to assess the energetic, economic and environ-
mental feasibility for the AD of pretreated and codigested press
mud, Melanio Hernandez sugar-ethanol factory located in Tuinucu,
Sancti Spiritus, Cuba, was selected. Biogas plants were modelled
according to laboratory tests and others data published in the liter-
ature (Barrera et al., 2016; López González et al., 2014; López
González et al., 2017; López González et al., 2013; Parsaee et al.,
2019). As sugar mill can be integrated or not with ethanol distil-
leries in the cuban context, the following scenarios (A and B) were
Scenario A.Sugar mill without ethanol distillery. The nominal
capacity of the sugar mill was considered as 4600 t d
average operation time of 130 days a year, producing 161 t d
(3.5% of the milled sugar cane) of press mud (Data taken from Mel-
anio Hernandez sugar-ethanol factory located in Tuinicu, Sancti
Spiritus, Cuba). However, in order to reduce reactor volume while
increasing operation time for the biogas plant; it was considered
that the biogas plant operates 300 days a year, with a daily feeding
of 70 tons d
of press mud. The remaining period of the year
(65 days), the biogas plant is kept in standby for a proper mainte-
nance until the sugar harvest is started again. The feeding of press
mud with or without pretreatment (according to the optimal oper-
ating conditions (López González et al., 2014; López González et al.,
2013) into a continuously stirred tank reactor (CSTR) formed the
alternatives A1, A2 and A3. The alternatives for Scenario A were
grouped as follows:
A1: press mud without feeding a CSTR.
A2: pretreated press mud using LHW (150 °C, 20 min) feeding a
A3: pretreated press mud using TA (10 g Ca(OH)
1 h, 100 °C) feeding a CSTR.
Scenario B.Sugar mill with ethanol distillery. The ethanol dis-
tillery produces 600 hL d
of ethanol, and operates 300 days per
year, generating 964 m
of vinasse (16 L of vinasse per L of
ethanol). In addition, the 70 tons d
of press mud was considered
for AD according to Scenario A. The Upﬂow Anaerobic Sludge Blan-
ket (UASB) reactor was considered for the AD of vinasse; and the
CSTR for the AD of press mud with and without pretreatment, as
well as for the co-digestion of press mud and vinasse. The feeding
of press mud with or without pretreatment into a CSTR, while the
feeding of vinasse into UASB reactors formed the alternatives B1,
B2 and B3. In addition, alternative B4 considered the co-digestion
of press mud (without pretreatment) and vinasse in a CSTR accord-
ing to the optimal operating conditions reported (López González
et al., 2014; López González et al., 2017; López González et al.,
2013). The alternatives for Scenario B were grouped as follows:
B1: press mud without pretreatment feeding a CSTR and
vinasse feeding a UASB reactor.
B2: pretreated press mud using LHW (150 °C, 20 min) feeding a
CSTR and vinasse feeding a UASB reactor.
B3: pretreated press mud using TA (10 g Ca(OH)
, 100 g
1 h, 100 °C) feeding a CSTR and vinasse feeding a UASB reactor.
B4: co-digestion of press mud (without pretreatment) and
vinasse in a CSTR (25% press mud and 75% vinasse, based on
Chemical Oxygen Demand (COD)).
The environmental mitigation potential of the biogas produc-
tion was assessed with respect to reference scenarios (current con-
ditions): ¨Sugar mill without ethanol distillery¨(A0) (Fig. 1A); and
¨Sugar mill with ethanol distillery¨(B0) (Fig. 1B). They can be
described as follows:
A0: 70 t of press mud are treated daily in a typical windrow
composting facility (producing 2.2 t of organic carbon). The
compost produced is sold to farmers as bio-fertilizer.
B0: 70 tons of press mud are treated daily in a typical windrow
composting facility (producing 2.2 t of organic carbon). Simulta-
neously, 964 m
of vinasse are treated daily in lagoons (produc-
ing 6.0 t of organic carbon). After laggoning, this liquid waste
can be used for ferti-irrigation.
250 L.M. López González et al. / Waste Management 102 (2020) 249–259
Windrow composting is carried out in piles. The windrows are
turned weekly during 60 days using a compost turner. Fuel con-
sumption is that of collection and transportation of wastes,
turning-aeration and windrow management. GHG emission is from
the direct emission of the composting process during the decom-
position of organic matter. Other activities as shredding, screening
and compost spreading are out of the system boundary.
Schemes of the biogas plant for both scenarios are shown in the
The input data and assumptions used to determine the biogas
production for each alternative is shown in the Table 1. The inﬂu-
ent composition referred to functional unit is presented in the Sup-
2.2. General assumptions
The calculation of the reactor volume was based on the organic
load in the feeding substrate, using the design organic loading rates
(OLR) for the CSTR. Hydrolysis provided by pretreatment was able
to accelerate the conversion of digestible solids into degradable
substrate (Janke et al., 2017). Therefore, OLR fed to the reactor
was higher. The values used were:
– 1 kg Volatile Solids (VS) m
when feeding press mud with-
– 3 kg VS m
when feeding pretreated press mud and
untreated press mud in co-digestion with vinasse (López
González et al., 2017).
For UASB reactors OLR of 10 kg COD m
was used when
feeding vinasse to the UASB reactor (Parsaee et al., 2019).
The water for dilution was only consumed during the
sugar cane non-harvest season, whereas during the harvest
season, 2760 m
of wastewater from the sugar mill was
considered available for press mud and vinasse dilution. Press
mud dilution was needed to control the TS content inside the
CSTR to 8% (w/w), while the dilution of the vinasse was
required to reduce the COD concentration from 62 to 20 kg
The produced biogas will be burned in a combined heat and
power (CHP) system, generating electrical energy for the national
electric grid and thermal energy to produce steam at low pressure
from the exhaust gases. The heat recovered from the exhaust gases
will be used as energy source to supply the thermal demand for
press mud pretreatments.
Fig. 1. System boundaries for A1–A3 (A) and B1–B4 (B) alternatives and reference scenarios (TSC: Production by the traditional supply chain).
L.M. López González et al. / Waste Management 102 (2020) 249–259 251
The speciﬁc assumptions for the energetic, economic and envi-
ronmental assessment are described in details in the next sections.
2.3. Energetic assessment
The energy balance was carried out to assess the energy
demand for pretreatments versus energy recovered from the pro-
duced biogas. The main parameters for the energetic assessment
are shown in the Supplementary data.
The thermal energy consumed during pretreatment (TE
), the thermal energy recovered from the produced biogas
), the thermal energy required based on the efﬁciency
of the hydrolysis reactor (TE
, kWh d
), and the electrical energy
), were calculated according o Eqs. (4.1),
(4.2),(4.3) and (4.4), respectively.
Fig. 1 (continued)
252 L.M. López González et al. / Waste Management 102 (2020) 249–259
where m is the mass of the mixture (press mud and water) to be fed
is the heat capacity of the mixture (considered as
4.18 kJ kg
T is the temperature increments during pre-
treatment (K), t
is the pretreatment time per day (h), 3600 is the
conversion factor of kJ to kWh, y
is the biogas production (m
is the generation index from biogas (kWh m
thermal efﬁciency of the CHP system (%),
is the electrical efﬁ-
ciency of the CHP system (%), and
is the hydrolysis reactor efﬁ-
ciency (%). The values for
are selected according to the
capacity of internal combustion engine (Supplementary data).
An index of 3.1 kWh tTS
was used to calculate the electricity
) during pretreatments (Budde et al.,
2016), while 0.44 kWh m
biogas were used for the electricity
consumption in UASB reactors (Obaya et al., 2005). The electricity
consumption for CSTR was assumed as 10% of the produced energy
according to GIZ (2013).
Finally, the net electricity (EE
) was calculated from the differ-
ences between EE and EE
; whereas the net thermal energy
) was obtained from the differences between TE
2.4. Economic assessment
For the economic assessment, the Total Capital Investment, the
Total Product Cost and the Cash Flow were determined for each
alternative according to the methodology recommended by
Peters and Timmerhaus (1991). The cost indexes and prices for
the calculations are also shown in the Supplementary data.
The six-tenths-factor rule updating their values to the current
prices with the Chemical Engineering Plant Cost Index was used
to calculate the purchased equipment (E) for LHW pretreatment
and equipment for biogas plant with CSTR reactors (without CHP
system). The base costs are shown in the Supplementary data.
The E value for biogas plant with UASB reactors was estimated
by an index of 2.80 USD/m
vinasse fed per year (Salomon et al.,
2011). The E value for TA pretreatment was calculated by
Matches (2019), based on the volume of the lime preparation tank
and the hydrolysis reactor (according to the daily feeding and the
pretreatment time) (Supplementary data).
Biogas puriﬁcation unit was included in the base cost for the
equipment for biogas plants when CSTR is the type of reactor used.
The method of removing H
S is the in-situ desulphurization in the
biogas digester itself by dosing air to the gas phase.
For alternatives using UASB reactors the biogas puriﬁcation unit
was based on biological oxidation as described before, but in this
case it is performed ex-situ in bioﬁlters with immobilized
The Evalues for the CHP system were calculated from indexes
reported in the Catalog of CHP Technologies (EPA, 2015). This is
1040 and 975 USD kW
for 848 and 1059 kW installed,
A linear depreciation was considered over 10 years for installed
technical equipment. It was considered an interest rate of 10% over
the total investment cost, an inﬂation rate of 8%, and a tax rate of
30%. As revenues for the biogas plant, the sale of electricity, the
sales of organic fertilizers, as well as the service for ferti-
irrigation were considered.
The net present value (NPV), internal rate of return (IRR) and
payback period (PBP) were calculated for three conditions: ‘‘Pes-
simistic, Baseline and Optimist”. A price of 0.14 USD kWh
tricity generated using biogas (as renewable fuel) according the
Cuban Electrical Enterprise was considered for the ‘‘Pessimistic”
and ‘‘Baseline” conditions. The sale price of the organic fertilizers
was considered as 0 USD for the ‘‘Pessimistic” condition, while
for the ¨Baseline¨condition a price of 49.54 USD per ton and
67.11 USD per ton were considered for the fertilizers produced
from CSTR and UASB reactors, respectively. ¨Optimist¨condition
was proposed according to increase by 20% of the price for the
main products (electricity and fertilizer) (Supplementary data).
2.5. Environmental Life Cycle Assessment (LCA)
The environmental assessment was carried out by using the Life
Cycle Assessment (LCA) methodology according to the ISO
Input data and biogas production for the assessed scenarios.
A1 A2 A3 B1 B2 B3 B4
Press mud tons d
70 70 70 70 70 70 70
964 964 964 964
Press mud m
351 567 427
Press mud + Vinasse m
Press mud % 56 56 56 56 56 56
Vinasse % 60 60 60
Press mud + Vinasse % 60
Organic matter fed
ton VS day
16 16 16 15.63 15.63 15.63
ton COD day
59.78 59.78 59.78
Press mud + Vinasse ton VS day
Biogas production m
5484 8856 6668 29,396 32,768 30,580 31,341
VS: Volatile Solids, COD
: Chemical Oxygen Demand.
López González et al. (2017).
López González et al. (2014).
López González et al. (2013).
López González et al. (2017).
López González et al. (2017).
20 kg COD m
L.M. López González et al. / Waste Management 102 (2020) 249–259 253
14040/44 guidelines (ISO 14040, 2006, ISO 14044, 2006) and the
ILCD handbook (European-Commission, 2010).
2.5.1. Goal and scope deﬁnition
The goal and scope of the environmental LCA was to compare
the alternatives for the use of press mud (with and without pre-
treatment) and vinasse for anaerobic digestion (biogas plants) in
sugar mill with and without ethanol distilleries (Scenarios A and
B). The functional unit, system boundaries, scenarios description,
allocations principles and main assumptions are described in detail
18.104.22.168. Functional unit and system boundaries. Considering that the
main function of the studied system is the treatment of the avail-
able press mud and press mud/vinasse according the scenario A or
B, the functional unit for Scenario A was the daily treatment of 70
tons of press mud, and for Scenario B the daily treatment of 70 tons
of press mud and 964 m
In general, Fig. 1A&B showed the gaseous emissions from
lagooning and composting, as well as the combustion gasses emis-
sion from the energy generation, to the ecosphere. The oxygen in
air and the land used were the resources taken from the ecosphere;
whereas energy, vinasse, press mud, calcium hydroxide and tap
water were the resources taken from the technosphere. The prod-
ucts of both scenarios were electricity, heat and organic carbon.
Traditional supply chains (TSC) are the common suppliers of prod-
ucts (e.g. electricity production from fuel oil in centralized power
plants); they take resources from the technosphere to produce
the required products for the market.
To make a fair comparison between the alternatives an equal
basket of beneﬁts was constructed, which implies that TSC always
need to complete the market demand and fulﬁll an equal basket of
beneﬁts. For example, when press mud is pretreated by LHW (A2),
18.0 MWh of electricity net are obtained, as this is the maximum
value among the alternatives A0, A1, A2 and A3, the difference
between the electricity net in A2 and the electricity net in A0, A1
and A3 must be supplied from the TSC (i.e. electricity production
from fuel oil in centralized power plants). The same was implicit
for all the alternatives and products, considering that electricity
is supplied from the Cuban electricity mix (fuel oil that is used in
centralized and decentralized thermal power plants (81.66%), com-
bined cycles with gas turbine using liqueﬁed petroleum gas
(13.04%), cogeneration systems using bagasse (4.63%), and other
technologies using renewable resources (0.67%), the heat is sup-
plied as steam from fuel oil and the organic carbon is extracted
from the soil as ‘‘Carbon, in organic matter, in soil” (Barrera
et al., 2016).
22.214.171.124. Allocation principles and main assumptions. The main
assumptions for this study were as follows:
– All calculations are based on 1 day of operation.
– The press mud transport to AD/composting plant is carried out
by trucks. The distance from sugar mill to AD and composting
plant are 500 m and 4 km, respectively. The compost and biofer-
tilizer transportation as well as the spreading are out of the sys-
– An index for diesel consumption of 1.8 L / t press mud for com-
posting management was used (data provided by the Melanio
Hernandez sugar-ethanol factory).
– For press mud composting process, the emissions were consid-
ered as 0.004 kg of CH
and 0.003 kg N
O per kg of waste (IPCC,
– Digestate was separated in a liquid and solid phase by means of
a screw press. The energy consumption was estimated as
(Drosg et al., 2015).
- The gaseous emissions from the lagoons were calculated from
the multiplication of biogas productivity E
occupied area in lagoons (equation (4.5)), where Tis the average
environment temperature (°C) (Picot et al., 2003). A methane
content of 65% in the biogas was considered.
– The organic carbon content (Corg) in the sludge produced in the
UASB reactor was assumed to be 0.0313 kmol C / kg COD bio-
mass (Batstone et al., 2002), where the COD in the biomass
was 1.222 kg COD / kg biomass (Kalyuzhnyi and Fedorovich,
– Sludge production was determined from the mass balance
assuming that 10% of the removed COD is anaerobically con-
verted to biomass (Braun, 2007).
2.5.2. Life cycle inventory (LCI)
From the allocations principles and main assumptions previ-
ously described in Section 126.96.36.199, the LCI was carried out.
Others assumptions were:
– The electricity and heat produced from biogas, as well as
organic fertilizer (Corg) were variable among the alternatives,
while the amount of N, P and K, and the consumption of fuel
used for the transportation of substrates, wastewater and fertil-
izer were considered constant.
– Organic carbon was taken from the Ecoinvent Database 2.2 as
‘‘Carbon, in organic matter, in soil” and it was assumed to be
¨consumed¨in the all the alternatives, except the one with the
highest organic carbon production which does not consume/
extract organic carbon from the soil.
– A 4% of biogas losses were assumed during the production pro-
cess, power generation and storage of the digested efﬂuent
(Hrad et al., 2015).
The inputs and outputs of the studied alternatives in the LCI
were calculated by using material and energy balances, ensuring
data reliability and validity. Mass consistency was checked by
means of total and partial mass balances; whereas the energy
requirements were taken from their calculation in Section 2.3.
Infrastructure was excluded from this study. The Ecoinvent Data-
base 2.2 was used to model datasets in the background system.
2.5.3. Life cycle impact assessment (LCIA)
To account for emissions and resources the RECIPE methodol-
ogy with endpoint indicators and the hierarchic perspective was
used (Goedkoop et al., 2008). Consequently, the endpoint impact
categories ‘‘ecosystem quality”, ‘‘human health” and ‘‘natural
resources” were determined. The environmental impacts were
quantiﬁed in ‘‘Points” for the endpoint impact categories and for
the total score (sum of the endpoint scores). The open source soft-
ware for the sustainability assessment, OpenLCA version 1.3.1
(http://www.openlca.org/) was used to calculate the environmen-
3. Results and discussion
3.1. Energetic assessment
The energy balances for the electrical and thermal energy con-
sumption for both scenarios (A and B) are shown in Fig. 2A–D.
3.1.1. Energetic assessment for scenario A
The biogas production of 5484, 8856 and 6668 m
alternatives A1, A2 and A3 requires the implementation of an
254 L.M. López González et al. / Waste Management 102 (2020) 249–259
energy generation system with 848, 1059 and 848 kW installed
power capacity, respectively (Table 1).
The net, produced and consumed electrical (EE,EE
) and thermal (TE
) energy for alternatives
A1, A2 and A3 are shown in Fig. 2A&B, respectively. For these alter-
natives the EE
represented 11% of EE; and consequently, EE
values were higher for the alternatives producing the higher
amount of biogas (A2 > A3 > A1) (Fig. 2A). The TE
feeding the CSTR with pretreated press mud using TA (A3) and
LHW (A2) were 21 and 58% higher, respectively, than the one
obtained when feeding the CSTR with untreated press mud (A1).
Although both pretreatment consumed TE (9.4 and 12.1 MWh
for TA and LHW, respectively), they were self-sufﬁcient
0). Despite the TE
was slightly higher (29%) for A2 with
respect to A3 (because of the higher temperature used, 150 °C). A
thermal output of 384.0 kWh t
FM, higher than required for pre-
treatment of 172.2 kWh t
FM was obtained for LHW pretreat-
ment (A2). The results were similar to those obtained by Budde
et al. (2016), where a higher recovery of thermal energy from the
pretreated solid cattle manure at 140 °C by 20 min (183.8 kWh
FM) than required for pretreatment (145.8 kWh t
In general, the EE
for the studied alternatives were
from 11 to 18 MWh d
and from 11 to 17 MWh d
(Fig. 2A&B). Speciﬁcally, the alternative that considers press mud
without pretreatment (A1) rendered the highest net thermal
energy (17 MWh d
), whereas the one considering pretreatment
by LHW (A2) rendered the highest net electrical energy
(18 MWh d
3.1.2. Energetic assessment for scenario B
The biogas production of 29396, 32768, 30580 and 3134 m
for the alternatives B1, B2, B3 and B4 requires the implementation
of an energy generation system with 4.0, 4.2, 4.0 and 4.2 MW
installed power capacity, respectively (Table 1).
was approximately 17% of EE for B1, B2 and B3
(alternatives considering CSTR and UASB reactors for AD), being
10% of EE for B4 (alternatives considering only a CSTR) (Fig. 2C).
This is due to the high consumption of electricity during the oper-
ation of the UASB reactors (10 MWh d
). Consequently, the max-
(64 MWh d
) was obtained for alternative B4, where
press mud without pretreatment was co-digested with vinasse in a
Regarding thermal energy (Fig. 2D), the alternatives considering
pretreatment (B2 and B3) had a consumption of 13 and 12 MWh
, respectively, mainly due to the requirements of the biogas
plant; whereas the maximum TE
(95 MWh d
) was obtained
also for B4.
In general, the electric and thermal net energy for these alterna-
tives (B1, B2, B3 and B4) ranged from 55 to 64 MWh d
84 to 95 MWh d
, respectively (Fig. 2C&D); which would cover
100% of the daily demand of the ethanol distillery in Melanio
Hernández sugar-ethanol factory.
3.2. Economic assessment
3.2.1. Economic assessment of scenario A
The components of the Total Capital Investment (TCI) for alter-
natives A1, A2 and A3 are shown in Supplementary data. The high-
est TCI was obtained for A2 (5.07 MMUSD), due to the high
Purchased equipment cost (E) of the LHW pretreatment unit and
the fact that A2 had the highest CHP power capacity (1059 kW).
A cost index of 279 USD/m
of reactor was obtained for A1, being
lower than the one considered by Janke et al. (2017) for sugarcane
straw (413 USD/m
reactor). For the alternatives A2 and A3 the
cost index was higher (948 and 702 USD/m
reactor) because of
the higher Evalues when including the press mud pretreatment,
which was not included by Janke et al. (2017).
The alternatives considering the feeding of pretreated press
mud to the CSTR reactor (A2 and A3), showed the highest revenues
from the electricity sales (828 and 624 MUSD/year, respectively)
(Supplementary data). However, the revenues obtained from the
organic fertilizer in A1 were similar than the one obtained from
electricity, because of the lower biogas yield of the untreated press
mud. The sales of electricity and biofertilizer rendered between 48
and 61% of the revenues in all the alternatives.
The electricity and raw material cost represented approxi-
mately, 68 and 73% of the Direct Production Cost for the alterna-
Fig. 2. Daily energy balance for study alternatives A1–A3 (A, B) and B1–B4 (C, D).
L.M. López González et al. / Waste Management 102 (2020) 249–259 255
tives A1 and A2, respectively. However, calcium hydroxide (con-
sumption of 2 t d
) had the highest contribution (42%) to the
Direct Production Cost in A3, because of the calcium requirement
for TA pretreatment.
The investment feasibility was assessed for the three condi-
tions: ¨Pessimistic¨,¨Baseline¨and ¨Optimistic¨(Table 2).
For the ¨Pessimistic¨condition, the NPV was negative for all the
alternatives indicating that investment would not be recovered
during its lifespan if sales of fertilizer are not considered. However,
for the ¨Baseline¨and ¨Optimistic¨conditions these alternatives
were economically feasible showing positive NPV, IRR above 10%,
and PBP below 9 years. The alternative considering the LHW pre-
treatment was the most proﬁtable with an NPV of 2.81 MMUSD,
IRR of 21% and PBP of 5.5 years for the ¨Optimistic¨condition
According the sensibility analysis (Fig. 3), decreasing by 15% the
amount fed of press mud, the NPV was < 0, while NPV was > 0
when the biogas yield changed from 15% to 15%.
3.2.2. Economic assessment of scenario B
The highest TCI value was for B2 (14.4 MMUSD), due to the high
Evalues of the LHW pretreatment unit and the highest CHP power
capacity (1059 kW + 3177 kW) (Supplementary data).
The total revenues ranged from 4.56 to 4.90 MMUSD per year in
Scenario B (Supplementary data). The highest contribution was
obtained from the electricity sale (63–66%).
The costs of electricity consumption account for 35–52% of the
Direct Production Cost, which is the main contribution for all the
alternatives, except B4, where calcium hydroxide consumption
accounted for 34%.
The dynamic indicators of the investment showed economic
proﬁts for the ¨Baseline¨and ¨Optimistic¨conditions in all the alter-
natives (Table 2), while for the ¨Pessimistic¨condition only the B4
alternative had a NPV positive.
The highest proﬁtability was found for the alternative consider-
ing the co-digestion of press mud with vinasse (B4) with IRR from
15.7 to 36.0%, PBP from 3.4 to 7.2 years, and NPV from 2.84 to
15.22 MMUSD. The main economic advantages of this alternative
were: 1) the substitution of the water required for dilution by
using vinasse; 2) the lower electricity consumption than the alter-
natives considering the feeding of vinasse to an UASB reactor (B1,
B2, and B3). These aspects caused a signiﬁcant reduction (from 43
to 46%) of the Direct Production Cost in B4, in comparison with the
remainder alternatives, increasing the economic proﬁts.
In general, the economic assessment for Scenario B (sugar mill
with ethanol distillery) showed the highest beneﬁts for the alter-
native considering the co-digestion of press mud (without pre-
treatment) and vinasse in a CSTR, in the ¨Pessimistic¨,¨Baseline¨
and ¨Optimistic¨conditions (Table 2).
According the sensibility analysis (Fig. 4), ranging from 15% to
15% the amount fed of press mud and vinasse, as well as the biogas
yield obtained from AD process, the NPV was >0 for all the alterna-
tives evaluated. Higher biogas yield implies larger biogas CHP
installation and cost increased due to electricity consumption,
which led to a slight decrease of the NPV for B4.
An economic viability for electrical power of 848 and 1059 kW
for monodigestion, and 4236 kW for codigestion were found in this
work. These values are in the optimum size of biogas plants in
mono-digestion (>740 kW) and co-digestion (>1000 kW) recom-
mended by Velásquez Piñas et al. (2019).
Payback periods between 1.8 and 11.5 years are reported in the
literature for biogas plants (Balussou et al., 2012; Budde et al.,
2016; Cano et al., 2014; Carlini et al, 2017; Dahunsi et al., 2019;
Montoro et al., 2019; Ruiz et al., 2018; Salomon et al., 2011). How-
ever, interstudy comparisons are almost impossible due to the
variability of the scenarios.
German co-digestion biogas plants, which employed biowaste
and sewage sludge for electricity production reported than diges-
tate treatment and personnel costs were responsible by 43.3% for
the operational costs, while for plants feeding energy crops, sub-
strates costs were responsible by 40% for the operational costs
(Balussou et al., 2012).
Salomon et al. (2011) studied the economic feasibility of biogas
production from vinasse in UASB reactors, showing a payback of
3.6 years and 28.4 of IRR for the use of biogas in the electricity gen-
eration using reciprocating combustion engines. Main incomes
were due the electricity sale.
Orive et al. (2016) reported payback time periods of 6.7 and
9.2 years for full scale anaerobic co-digestion and anaerobic
mono-digestion plants, respectively. In both the major revenue
was due to the sales of compost, because of the amount produced
and the high sale price (70 euros/ton). If the compost sale price was
half, revenues generated by the sale of electricity (only for the
mono-digestion plant) was uppermost.
The proﬁtability of a biogas plant processing biowastes was pri-
marily related to the income obtained from the gate fees charged
for the management of the biowastes (80.7%) and electricity sales
(17.4%) (Ruiz et al., 2018). They estimated the revenues from elec-
tricity sale with an average price of 5.03 c
/kWh, 2.8 times lower
than that used in this work.
The results obtained suggested than it will be better to treat by
AD both residues than press mud only. Besides the vinasse – press
mud codigestion have a both less investment cost (USD 10.5 mil-
lions) and payback period (4 years).
Results of the ﬁnancial and economical assessment.
Conditions A1 A2 A3 B1 B2 B3 B4
NPV (MMUSD) 2.30 1.32 1.45 1.76 0.78 0.91 2.84
PBP(years) >10 >10 >10 5.00 4.80 4.70 7.20
IRR (%) 3.96 3.15 0.27 7.05 8.78 8.43 15.65
NPV (MMUSD) 0.44 1.42 1.29 7.10 8.08 8.60 10.89
PBP (years) 8.60 7.10 6.50 5.70 5.50 5.10 4.00
IRR (%) 12.18 15.89 17.14 20.41 21.23 22.97 29.40
NPV (MMUSD) 1.44 2.81 2.43 10.66 11.60 11.51 15.22
PBP (years) 6.70 5.50 5.20 4.70 4.60 4.40 3.40
IRR (%) 16.78 21.11 22.78 25.08 25.58 26.87 36.02
Pessimistic condition: Electricity Price 0.14 USD/kWh, Biofertilizer Price (CSTR reactor): 0 USD/t. Base condition: Electricity Price 0.14 USD/kWh, Biofertilizer Price (CSTR
reactor): 49.54 USD/t, Biofertilizer Price (UASB reactor): 67.11 USD/t. Optimistic condition: Electricity Price 0.168 USD/kWh, Biofertilizer Price (CSTR reactor): 59.44 USD/t,
Biofertilizer Price (UASB reactor): 80.53 USD/t.
256 L.M. López González et al. / Waste Management 102 (2020) 249–259
3.3. Environmental LCA
3.3.1. Environmental LCA for scenario A
The environmental LCA shows that the alternatives A1, A2 and
A3 improve (with respect to the reference scenario A0) the envi-
ronmental proﬁles (Fig. 5A), decreasing up to 93% the total score.
The best results were obtained when press mud was pretreated
by LHW to feed the CSTR reactor. This is explained by the highest
methane production in this alternative, the production of the high-
est amount of electricity and heat and consequently the lower
energy demanded from TSC to achieve the equal basket of beneﬁts.
The worst results were for the reference scenario A0 because it
would have to supply 14.7 MWh of electrical energy and 17.0
MWh of thermal energy from fuel oil in centralized power plants,
and 2.4 t of organic carbon extracted from the soil.
The endpoint impact category ‘‘Human health” presented the
highest contribution (40–66%) to the total score for all the alterna-
tives. This result was mainly attributed to the midpoint impact cat-
egory ‘‘Climate change” (16–51%) and ‘‘Human toxicity” (37–81%),
due to the burning of fossil fuel at reﬁnery to supply the required
electricity. The midpoint impact category ‘‘Formation of particulate
material” (9–24%) provided a lower contribution to the total
3.3.2. Environmental assessment of scenario B
The environmental LCA shows that the alternatives B1, B2, B3
and B4 improve the environmental proﬁles with respect to the ref-
erence scenario B0 (Fig. 5B), reducing the total score from 84 to
The best results were obtained for the alternative B4, as the
highest amount of electricity and heat and consequently the lower
energy demanded from TSC to achieve the equal basket of beneﬁts.
Similar to Scenario A, the endpoint impact category ‘‘Human
health” represented the highest contribution (44–54%) to the total
score in Scenario B, being attributed to the contribution of the mid-
point impact categories ‘‘Climate change” (43–59%) and ‘‘Human
health”, because of both: the burning of fossil fuel at reﬁnery to
supply the required electricity; and the production of Ca(OH)
when vinasse was fed.
The endpoint impact category ‘‘Ecosystem quality” and ‘‘Natural
resources” contributed from 28 to 42% and 14 to 21%, respectively,
to the total score, respectively.
According the worst score found for the reference scenarios A0
and B0, it is suggested that electricity from biogas was environ-
mentally more sustainable than electricity generated from a
fossil-intensive electricity mix. Similar ﬁndings have been reported
(Fusi et al., 2016; Lijó et al., 2017; Styles et al., 2016).
Fig. 3. Sensitivity analysis for t/d of press mud fed (PM) and biogas yield (YB) for the alternatives A1 (r), A2 (j) and A3 (d).
Fig. 4. Sensitivity analysis for t/d of press mud fed (PM), m
/d of vinasse fed (V) and biogas yield (YB) for the alternatives B1 (r), B2 (j), B3 (▲) and B4 (d).
L.M. López González et al. / Waste Management 102 (2020) 249–259 257
The results of the environmental Life Cycle Analysis (LCA) show
that the alternatives improve the environmental proﬁles, in both
scenarios. The endpoint impact category ‘‘Human health” had the
The LCA results agree with environmental beneﬁts reported for
the anaerobic digestion in the Cuban sugar factories (Barrera et al.,
2016; Contreras et al., 2009). However, direct comparison with the
results in the current study is not possible as different functional
units, types of systems, assumptions and life cycle impacts assess-
ment methodologies were used.
Four alternatives for using by-products and wastes from the
sugar mill and ethanol distilleries were compared, from a life cycle
perspective, in a study carried out by Contreras et al. (2009). The
highest beneﬁts were obtained for the alternatives considering bio-
gas production from press mud, sugar mill wastewater, and
vinasse. In another by Barrera et al. (2016) a comparative assess-
ment of anaerobic digestion power plants as alternative to lagoons
for vinasse treatment was reported. In this study the environmen-
tal proﬁle was improved with respect to the lagooning of Cuban
vinasse, reducing up to 77% the total score. The endpoint impact
category ‘‘ecosystem quality” contributed to more than 37% of
the total score, where the midpoint impact category ‘‘agricultural
land occupation” had the largest contribution (60%). This result
was mainly attributed to differences in the required surface area
for lagooning when 70% of the organic matter is removed at the
This research shows that both the environmental and energetic
proﬁles and the proﬁtability of methane production can improve
when the pretreatment and co-digestion of these wastes from
the sugar – alcohol production process are considered.
LHW and TA pretreatments are self-sufﬁcient in terms of ther-
mal requirements since they can recover heat from the biogas
engine. According to the results obtained from the energetic, eco-
nomic and environmental analysis of press mud pretreatment
alternatives for AD and co-digestion with vinasse, the digestion
of the press mud; pretreated by LHW in CSTR reactors (A2) was
the most viable for the scenario of a sugar mill without distillery,
while the alternative co-digestion with the vinasse of the press
mud without pretreatment (B4) was the most viable for the sce-
nario of a sugar mill with distillery.
Declaration of Competing Interest
The authors declare that they have no known competing ﬁnan-
cial interests or personal relationships that could have appeared
to inﬂuence the work reported in this paper.
This research was supported by the VLIR-UOS project entitled
‘‘Biogas production from waste from local food, wood and sugar-
cane industries for increasing self-sufﬁciency of energy in Sancti
Appendix A. Supplementary material
Supplementary data to this article can be found online at
Bacenetti, J., Negri, M., Fiala, M., Gonzalez-Garcia, S., 2013. Anaerobic digestion of
different feedstocks: impact on energetic and environmental balances of biogas
process. 464, 541–551.
Balussou, D., Kleyböcker, A., McKenna, R., Möst, D., Fichtner, W., 2012. An economic
analysis of three operational co-digestion biogas plants in Germany. 3, 23–41.
Barrera, E.L., Rosa, E., Spanjers, H., Romero, O., De Meester, S., Dewulf, J., 2016. A
comparative assessment of anaerobic digestion power plants as alternative to
lagoons for vinasse treatment: life cycle assessment and exergy analysis. J.
Clean Prod. 113, 459–471. https://doi.org/10.1016/j.jclepro.2015.11.095.
Barros, V., Duda, R., Oliveira, R., 2016. Biomethane production from vinasse in
upﬂow anaerobic sludge blanket reactors inoculated with granular sludge. Braz.
J. Microbiol. 47, 628–639. https://doi.org/10.1016/j.bjm.2016.04.021.
Batstone, D.J., Keller, J., Angelidaki, I., Kalyuzhnyi, S.V., Pavlostathis, S.G., Rozzi, A.,
Sanders, W.T.M., Siegrist, H., Vavilin, V.A., 2002. The IWA Anaerobic Digestion
Model No 1 (ADM1). Water Sci. Technol. 45, 65–73.
Braun, R., 2007. Anaerobic digestion: a multi-faceted process for energy,
environmental management and rural development. In: Ranalli P (Ed.),
Improvement of crop plants for industrial end uses. Springer, Dordrecht, pp.
Budde, J., Prochnow, A., Plöchl, M., Suárez Quiñones, T., Heiermann, M., 2016. Energy
balance, greenhouse gas emissions, and proﬁtability of thermobarical
pretreatment of cattle waste in anaerobic digestion. Waste Manage. 49, 390–
Cano, R., Nielfa, A., Fdz-Polanco, M., 2014. Thermal hydrolysis integration in the
anaerobic digestion process of different solid wastes: energy and economic
feasibility study. Bioresour. Technol. 168, 14–22. https://doi.org/10.1016/j.
Carlini, M., Mosconi, M.E., Castellucci, S., Villarini, M., Colantoni, A., 2017. An
economical evaluation of anaerobic digestion plants fed with organic agro-
industrial waste. 10. 10.3390/en10081165.
Contreras, A.M., Rosa, E., Perez, M., Langenhove, H.V., Dewulf, J., 2009. Comparative
life cycle assessment of four alternatives for using by-products of cane sugar
production. J. Clean Prod. 17, 772–779. https://doi.org/10.1016/j.
Dahunsi, S.O., Adesulu-Dahunsi, A.T., Osueke, C.O., Lawal, A.I., Olayanju, T.M.A.,
Ojediran, J.O., Izebere, J.O., 2019. Biogas generation from Sorghum bicolor stalk:
effect of pretreatment methods and economic feasibility. 5, 584–593.
Drosg, B., Fuchs, W., Seadi, T.A., Madsen, M., Linke, B., 2015. Nutrient recovery by
biogas digestate processing. <http://www.iea-biogas.net/ﬁles/daten-
pdf> (Accessed 29.08.19).
EPA, 2015. Environmental Protection Agency Combined Heat and Power
Partnership. Catalog of Technologies: Section 2. Technology Characterization
Fig. 5. Environmental impacts for the alternatives A0–A3 (A) and B0–B4 (B).
258 L.M. López González et al. / Waste Management 102 (2020) 249–259
– Reciprocating Internal Combustion Engines. <https://www.epa.gov/sites/
pdf> (Accessed 10. March. 2018).
European-Commission, 2010. Joint Research Centre. Institute for Environment and
Sustainability. International Reference Life Cycle Data System (ILCD) Handbook
– general guide for life cycle assessment – detailed guidance, ﬁrst ed.
Publications Ofﬁce of the European Union, Luxembourg.
Fusi, A., Bacenetti, J., Fiala, M., Azapagic, A., 2016. Life cycle environmental impacts
of electricity from biogas produced by anaerobic digestion 26 26 Front Bioeng.
Biotechnol. 4. https://doi.org/10.3389/fbioe.2016.00026.
Goedkoop, M., Heijungs, R., Huijbregts, M., Schryver, A.D., Struijs, J., Zelm, R.v., 2008.
ReCiPe. A life cycle impact assessment method which comprises harmonised
category indicators at the midpoint and the endpoint level, First edition. Report
Hrad, M., Piringer, M., Huber-Humer, M., 2015. Determining methane emissions
from biogas plants – operational and meteorological aspects. Bioresour Technol
191, 234–243. https://doi.org/10.1016/j.biortech.2015.05.016.
IPCC, 2006. Directrices del IPCC de 2006 para los Inventarios Nacionales de Gases de
Efecto Invernadero: Desechos- Tratamiento y eliminación de aguas residuales,
ISO 14040, 2006. Environmental management — Life cycle assessment — Principles
and framework, Switzerland, 2nd ed.
ISO 14044, 2006. Environmental management — Life cycleassessment —
Requirements and guidelines. In: INTERNATIONAL STANDARD (Ed.), 1st ed,
Jacobs, A., Auburger, S., Bahrs, E., Brauer-Siebrecht, W., Christen, O., Götze, P., Koch,
H.-J., Mußhoff, O., Rücknagel, J., Märländer, B., 2017. Replacing silage maize for
biogas production by sugar beet – a system analysis with ecological and
economical approaches. 157, 270–278. https://doi.org/10.1016/j.
Janke, L., Leite, A.F., Nikolausz, M., Radetski, C.M., Nelles, M., Stinner, W., 2016.
Comparison of start-up strategies and process performance during
semicontinuous anaerobic digestion of sugarcane ﬁlter cake co-digested with
bagasse. Waste Manage. 48, 199–208. https://doi.org/10.1016/j.
Janke, L., Weinrich, S., Leite, A.F., Terzariol, F.K., Nikolausz, M., Nelles, M., Stinner, W.,
2017. Improving anaerobic digestion of sugarcane straw for methane
production: Combined beneﬁts of mechanical and sodium hydroxide
pretreatment for process designing. 141, 378–389. https://doi.org/10.1016/j.
Kalyuzhnyi, S.V., Fedorovich, V.V., 1998. Mathematical modelling of competition
between sulphate reduction and methanogenesis in anaerobic reactors.
Bioresour. Technol. 65, 227–242. https://doi.org/10.1016/S0960-8524(98)
Lijó, L., González-García, S., Bacenetti, J., Moreira, M., 2017. The environmental
effect of substituting energy crops for food waste as feedstock for biogas
López González, L.M., Pereda Reyes, I., Dewulf, J., Budde, J., Heiermann, M.,
Vervaeren, H., 2014. Effect of liquid hot water pre-treatment on sugarcane
press mud methane yield. Bioresour. Technol. 169, 284–290. https://doi.org/
López González, L.M., Pereda Reyes, I., Romero Romero, O., 2017. Anaerobic co-
digestion of sugarcane press mud with vinasse on methane yield. 68, 139–145.
López González, L.M., Vervaeren, H., Pereda Reyes, I., Dumoulin, A., Romero Romero,
O., Dewulf, J., 2013. Thermo-chemical pre-treatment to solubilize and improve
anaerobic biodegradability of press mud. Bioresour Technol 131, 250-257.
Matches, 2019. Matches’ Process Equipment Cost Estimates. <http://
www.matche.com> (Accessed 1. February. 2019).
MINEM, 2019. Energías renovables. <https://www.minem.gob.cu/energias-
renovables> (Accessed 21.08.2019).
Monlau, F., Latrille, E., Da Costa, A.C., Steyer, J.P., Carrere, H., 2013. Enhancement of
methane production from sunﬂower oil cakes by dilute acid pretreatment. Appl
Energ 102, 1105–1113. https://doi.org/10.1016/j.apenergy.2012.06.042.
Montoro, S.B., Lucas, J., Santos, D.F.L., Costa, M.S.S.M., 2019. Anaerobic co-digestion
of sweet potato and dairy cattle manure: a technical and economic evaluation
for energy and biofertilizer production. 226, 1082–1091. https://doi.org/
Moraes, B.S., Petersen, S.O., Zaiat, M., Sommer, S.G., Triolo, J.M., 2017. Reduction in
greenhouse gas emissions from vinasse through anaerobic digestion. Appl
Energy 189, 21–30. https://doi.org/10.1016/j.apenergy.2016.12.009.
Obaya, M.C., Valdés, E., Lorenzo, Y., Gallardo, M., León, O.L., Diez, K., Morales, M.,
2005. Mecanismos de desarrollo limpio en una planta de tratamiento de vinazas
de azúcar con reactores UASB. Consideraciones técnicas y económicas sobre su
aplicación. Tecnología del agua 263, 52–59.
Orive, M., Cebrián, M., Zufía, J., 2016. Techno-economic anaerobic co-digestion
feasibility study for two-phase olive oil mill pomace and pig slurry. 97, 532–
Parsaee, M., Kiani, M.K.D., Karimi, K., 2019. A review of biogas production from
sugarcane vinasse. Biomass Bioener 122, 117–125. https://doi.org/10.1016/j.
Peters, M.S., Timmerhaus, K.D., 1991. Plant design and economics for Chemical
Engineers, Singapore, 4th.
Picot, B., Paing, J., Sambuco, J.P., Costa, R.H.R., Rambaud, A., 2003. Biogas production,
sludge accumulation and mass balance of carbon in anaerobic ponds. Water Sci.
Technol. 48, 243–250. https://doi.org/10.2166/wst.2003.0127.
Ruiz, D., San Miguel, G., Corona, B., Gaitero, A., Domínguez, A., 2018. Environmental
and economic analysis of power generation in a thermophilic biogas plant. 633,
Salomon, K.R., Lora, E.E.S., Rocha, M.H., Olmo, O.A.D., 2011. Cost calculations for
biogas from vinasse biodigestion and its energy utilization. Sugar Ind 136, 217–
Shaﬁei, M., Kabir, M.M., Zilouei, H., Horváth, I.S., Karimi, K., 2013. Techno-
economical study of biogas production improved by steam explosion
pretreatment. Bioresour. Technol. 148, 53–60. https://doi.org/10.1016/j.
Styles, D., Dominguez, E.M., Chadwick, D., 2016. Environmental balance of the UK
biogas sector: an evaluation by consequential life cycle assessment. 560-561,
Velásquez Piñas, J.A., Venturini, O.J., Silva Lora, E.E., del Olmo, O.A., Calle Roalcaba,
O.D., 2019. An economic holistic feasibility assessment of centralized and
decentralized biogas plants with mono-digestion and co-digestion systems.
139, 40–51. https://doi.org/10.1016/j.renene.2019.02.053.
Zeynali, R., Khojastehpour, M., Ebrahimi-Nik, M., 2017. Effect of ultrasonic pre-
treatment on biogas yield and speciﬁc energy in anaerobic digestion of fruit and
vegetable wholesale market wastes. Sustain. Environ. Res. 27, 259–264. https://
L.M. López González et al. / Waste Management 102 (2020) 249–259 259