processes

Article
Effect of Vinasse Recycling on Effluent Reduction from
Distilleries: Case of Metehara Distillery, Ethiopia
Ayele Alemu 1, * , Minale Getachew 2 , Gulam Mohammed Sayeed Ahmed 2,3 , Vineet Tirth 4,5
and Ali Algahtani 4,5

1 Sugar Technology and Engineering Research Program, Research and Development Center, Sugar Corporation,
Wonji 15, Ethiopia
2 Mechanical Engineering Department, Adama Science and Technology University, Adama 1888, Ethiopia;
minalegz@gmail.com (M.G.); gmsayeed.ahmed@astu.edu.et or drgmsa786@gmail.com (G.M.S.A.)
3 Center of Excellence (COE) for Advanced Manufacturing Engineering, Adama Science and Technology
University, Adama 1888, Ethiopia
4 Mechanical Engineering Department, College of Engineering, King Khalid University,
Abha 61421, Saudi Arabia; vtirth@kku.edu.sa (V.T.); alialgahtani@kku.edu.sa (A.A.)
5 Research Center for Advanced Materials Science (RCAMS), King Khalid University, Guraiger, P.O. Box 9004,
Abha 61413, Saudi Arabia
* Correspondence: aylkas15@gmail.com

Abstract: This study was conducted at the ethanol plant of Metehara sugar factory, at a laboratory
scale, to assess the effect of recycling vinasse into the fermentation process on effluent reduction.
Vinasse is an effluent produced from distilleries. The experimental design included vinasse concen-
trations at 4 dilution rates (0 (control), 20, 35, 50, and 65% of process water) with 2 replicates and
6 responses, as follows: ethanol yield, fermentation efficiency, residual sugar concentration, cell count,



cell viability, and calcium oxide content. In this study, the actual operational parameters of the ethanol

 plant were maintained during the experiment. The result of the experiment indicates that, with
Citation: Alemu, A.; Getachew, M.; up to 20% vinasse recycling, there was no influential impact on the ethanol yield, the fermentation
Ahmed, G.M.S.; Tirth, V.; efficiency, the residual sugar concentration, or the calcium oxide content, attributable to the recycling,
Algahtani, A. Effect of Vinasse as compared to the control. Above 20% vinasse recycling, ethanol yield and fermentation efficiency
Recycling on Effluent Reduction from decreased sharply from those of the control. In addition, with 20% vinasse recycling put into practice,
Distilleries: Case of Metehara the amount of vinasse generated will be reduced by about 19.5% and about 114.2 tons of water will
Distillery, Ethiopia. Processes 2022, 10, be saved per day. Moreover, the excess amount of vinasse produced by the distillery, which is beyond
7. https://doi.org/10.3390/
the handling capacity of bio-compost plant of the distillery, will reduce from 105 to 36.8 tons per day.
pr10010007
Therefore, it is possible to recycle vinasse into the fermenter up to 20% on dilution water of Metehara
Academic Editor: Davide Dionisi distillery, without causing any impacts on the distillery’s performance.
Received: 3 November 2021
Accepted: 29 November 2021
Keywords: distillery effluent; vinasse; recycling; molasses fermentation; ethanol production
Published: 22 December 2021

Publisher’s Note: MDPI stays neutral

with regard to jurisdictional claims in 1. Introduction
published maps and institutional affil-
Ethanol is widely used as fuel for IC (internal combustion) engines, blended with
iations.
gasoline. Nowadays, it has become an alternative energy source to alleviate the fuel
shortage. It is an eco-friendly fuel, with relatively lower greenhouse gas emissions than
petroleum-based fuels [1]. A feedstock commonly used for bio-ethanol production is
Copyright: © 2021 by the authors.
molasses, which is one of the by-products of the sugar industry. It contains mainly non-
Licensee MDPI, Basel, Switzerland.
crystallizable residue that is disposed of as by-product during recovery of crystal sugar.
This article is an open access article
Some of the advantages of using molasses as a raw material for ethanol production are the
distributed under the terms and following: it is available in abundant quantities, it is a relatively inexpensive feedstock,
conditions of the Creative Commons and it does not require hydrolysis of starch [2].
Attribution (CC BY) license (https:// Fermentation is the common method used to produce ethanol from molasses. Ethanol
creativecommons.org/licenses/by/ can be produced with various grades from molasses. Ethanol production from sugarcane
4.0/). molasses is carried out by three important processes, i.e., molasses treatment, fermentation,

Processes 2022, 10, 7. https://doi.org/10.3390/pr10010007 https://www.mdpi.com/journal/processes

Processes 2022, 10, 7 2 of 9

and distillation. However, the heart of the ethanol production system is the fermenta-
tion process, since the other processes are used for raw material preparation and for the
separation of the manufactured products [3].
The mineral composition of sugarcane substrate varies; it is dependent on sugarcane
variety, sugarcane maturity, climate, soil conditions, the processing of sugarcane into juice,
and the proportion of the molasses used to formulate the media [4].
Vinasse is an effluent produced from distilleries and it is one of the most difficult
wastes to dispose of. This is due to the fact that the volume of vinasse that is generated
is high; typically, one liter of alcohol produced from molasses-based ethanol distilleries
generates 8–15 L of vinasse. It has high temperature, a low pH, a high ash content, a
dark brown color, and a high percentage of dissolved organic and inorganic matters [5–8].
Vinasse also has substantial value as a source of potash; therefore, it can be returned to
the fields where the cane was cultivated, using the existing sugarcane irrigation system.
Irrigation is the simplest and cheapest method. However, care must be taken not to
overload the soil, otherwise, excessively high buildups of both organic and inorganic
component levels may occur, resulting in salt accumulation and a fall-off in the cane
yield [3,5,6,9].
Evaporating the vinasse to obtain concentrated effluent is another method of handling
the effluent. The concentrated effluents reduce the quantity of the vinasse and hence
transfer costs to outlying fields. However, the high capital cost of stainless-steel evaporators,
the need to clean with aggressive chemicals, and the additional steam required, generally
makes this an unfavorable option. It is also possible to evaporate the vinasse in large,
shallow ponds, using solar energy. Application of a spray drying system, preceded by
evaporation, is also used to produce a concentrated feed for animals [3,5,9]. Residual
stream, obtained after evaporating the vinasse, can also be used as a fuel for stillage-fired
boilers, which can be used to produce energy in excess of distilleries’ requirements [6].
Anaerobic fermentation of vinasse produces methane as a by-product, which is a
feasible method of handling the effluent. The gas produced can be used as a fuel to
supplement the fuel required for ethanol plants. However, the required anaerobic reactors
are large and cumbersome. The effluent from the anaerobic digester still requires further
treatment, since it has a high chemical oxygen demand (COD) content: about 113,000 mg/L
with molasses as a feedstock, for disposal, or for reuse [3,5,6,9].
To reduce the effluent generated during ethanol production from distilleries, it is also
possible to produce yeast from vinasse. However, the high cost of production makes this
alternative an unfavorable option [5,9].
Adding the vinasse to filter cakes—which are one of the by-products of the cane sugar
industry—on large concrete slabs, is used to produce compost. Very good quality compost,
high in potash, is produced within about 30 days [3]. This option has been used by the
Metehara distillery; however, the quantity of vinasse produced is beyond the handling
capacity of the bio-compost plant. This study was initiated with the aim to devise a method
of handling the excess vinasse that is produced by the distillery.
Metehara Sugar Factory (MSF) is located 200 km from the capital Addis Ababa,
Ethiopia, in the southeast direction. The factory was constructed by a Dutch company called
HVA (Handelsvereniging Amsterdam), in a joint venture with the Ethiopian Government,
and started production in 1962. The ethanol plant of the MSF start production in 2011
with annual production capacity of 12.5 million liter. The plant produces 28 m3 /h of
fermented wash, using 4 continuously stirred tank reactors, arranged in series. The amount
of concentrated vinasse, process condensate, and spent lees generated by the plant are
about 350, 236, and 87.4 tons/day, respectively. The bio-compost plant of the factory has a
capacity to handle 245 tons of concentrated vinasse per day, and the remaining concentrated
vinasse is accumulated in the pond for later use.
Recirculation of the vinasse back to the fermenters, alike to dilution water, has been
proposed as an option for reducing the volume of vinasse generated. However, studies
Processes 2022, 10, 7 3 of 9

revealed that the presence of inhibitors, such as acetic acid, limits the practical applications
of vinasse recirculation [10].
Several consultants recommended that the factory should use the distillery effluent in
the place of dilution water in the fermentation section. According to them, it is possible
to use all effluent generated from the rectifier column—which is called spent lees—and
process the condensate from the vinasse-concentrating evaporator as a source of dilution
water in the fermenter. They also stated that it is possible to recirculate about 50% of the
spent wash that is generated, back into the fermentation plant. In addition, to reduce
effluent generation from distilleries, back sloping can be carried out in the fermentation
station, with the view of improving pH to controlling bacteria growth, the nutrients
needed by the yeast for rapid growth, the buffering action of the fermented wash, and the
utilization of process water and steam ([11] p. 19). For a typical sugar cane molasses feed,
the inhibitory effects would not be observed if vinasse recycling was limited to a maximum
of one-third of the feed rate [12]. Studies conducted at Egyptian distilleries revealed that
vinasse generated from the fermentation of sugarcane molasses can be recycled safely up
to 50% for ethanol production in distilleries, without causing any significant differences in
either ethanol yield or fermentation efficiency [13]. Fresh water consumption of a distillery
is reduced with vinasse recycling. It can be reduced further, if the liquid fraction of the
vinasse is recycled after it is separated from the vinasse [14].
The vinasse generated during the production of ethanol can be a serious source of
water pollution. However, it is also possible to recover useful by-products from the vinasse,
such as animal feed, fertilizer, and methane gas. Therefore, production of by-products from
vinasse can be a valuable resource [3,5,9]. The selection of an optimum vinasse management
system is a trade-off between economic, energy, and environmental considerations [9].
By comparison, 10–20% of mash volume is typically recycled in commercial final
molasses fermentation; however, 30% recycled volume is reported to adversely affect
productivity [12]. However, studies focusing on effect of vinasse recycling on effluent
reduction in the case of the Metehara distillery have not yet studied in literature for
practical applicability.
The MSF produces about 350 tons/day of concentrated vinasse, while its bio-compost
plant has the capacity to handle 245 tons/day. Handling and proper treatment of the excess
vinasse is a problem; hence, the factory accumulates the remaining in the pond for later
use. In addition, during storage, the vinasse undergoes different chemical and biological
reactions and produces a pungent smell. Handling excess vinasse is a big problem for the
factory, because if the excess vinasse overflows the pond, it will become a big threat to the
environment. Therefore, this study aiming to assess the effect of recycling vinasse as a
fermenter on effluent reduction, through an experimental study for the case of the MSF.

2. Materials and Methods

The experiment was conducted at the MSF ethanol plant, using a laboratory-scale
experimental setup. The experiments were carried out in 2 replicates and the treatment
involved the recycling of vinasse at 4 percentage dilution rates (0 (control), 20, 35, 50 and
65% of dilution water), assessing 6 responses: the ethanol yield, the fermentation efficiency,
the residual sugar concentration, the cell count, the cell viability, and the calcium oxide
content. A total of 10 runs were conducted with 2 replications. In this study, the operational
parameters of the ethanol plant are used in the experiment.
Sugarcane molasses produced by the MSF were taken and analyzed in the laboratory.
The molasses were used without any pretreatment in this research.
A study conducted to assess the capability of the yeast strains to produce ethanol
showed that all the strains produced an almost similar percentage of ethanol (9.2% v/v)
during both laboratory- and pilot-scale demonstrations [15]. Therefore, the strain used by
the ethanol plant was used during this laboratory-scale experiment. The distillery uses a
strain of baker’s yeast (Saccharomyces cerevisiae) [16]. Molasses, diluted with water, was
used as a medium, to culture the yeast strain. The water that was used for dilution was
Processes 2022, 10, 7 4 of 9

blended with vinasse at different concentrations (0, 20, 35, 50, and 65% of the total volume)
to study the effect of vinasse recycling on effluent reduction.
During media preparation, 100 gm molasses was taken into a 1000 mL beaker and
565 mL water was added to obtain 14 Brix, then 1 gm urea and 0.5 gm DAP were added.
The media was sterilized for 1 min at boiling point, and after cooling to 30 ◦ C, the pH
was adjusted to 4.3 using 98% concentrated sulfuric acid. A measure of 500 mL media
was taken into a 1000 mL Erlenmeyer flask, then 125 mL of culture was added, and it was
incubated for 24 h. The fermentation was carried out at 33 ◦ C, 4.3 pH, and 7.94 reduced
sugar concentration. The same procedure was used during the vinasse test, except that
the percentage of water for the dilution of the molasses changed to 20, 35, 50, and 65% of
vinasse, instead of water.
In this study, vinasse was collected from the ethanol plant of the MSF. Then it was
used at 20, 35, 50, and 65% to prepare the fermentation medium. After fermentation, the
obtained fermented wash was boiled in a 1000 mL beaker for each concentration, and
stirred at 700 rpm until the alcohol percentage dropped below 0.2%.
The vinasse obtained from fermentation process was used for recycling tests, equiva-
lent to 20, 35, 50, and 65% of the water of the dilution for the following fermentation.
A rapid method was used to the determine sugar concentration of the feed (sugarcane
molasses). A measure of 5 mL of fermented sample was taken and dissolved in 100 mL
of distilled water, mixed with 5 mL of concentrated HCl acid (98%), and was heated at
70 ◦ C for a period of 10 min. The obtained samples were neutralized by adding NaOH,
prepared up to 1000 mL, and transferred into a burette solution. A measure of 5 mL of
Fehling A and 5 mL of Fehling B were taken and mixed with 10–15 mL of distilled water in
a conical flask, then methylene blue indicator was added. The conical flask solution was
titrated with burette solution in boiling conditions until the blue color disappeared. The
total fermentable sugar in gm/l—which is sugar concentration—was calculated using the
following formula:

Total fermentable sugar = (Dilution factor × Fahling factor/Titrate volume) × 100, (1)

where the Fehling factor is the quantity of invert sugar in grams required to completely
reduce the Fehling solution (usually 5 mL of both Fehling A and B solutions).
An Ebulliometer (Electronic Ebulliometer BLUTEH 2000, Star Zagora, Bulgaria) was
used to measure ethanol yield of the fermented samples (yield) in % v/v. The theoretical
yield is calculated as follows [16]:

Theoretical ethanol yield = Total fermentable sugar × 0.64. (2)

Fermentation efficiency in % (FE) was determined as the percentage of actual ethanol

yield for each of the vinasse concentrations, in relation to the theoretical ethanol yield [17].

Fermentation efficiency = Ethanol yield/Theoretical ethanol yield × 100. (3)

Reducing sugar (RS) consists primarily, but not exclusively, of glucose and fructose,
and was obtained through the hydrolysis of sucrose. Reducing sugar, measured in %, was
measured according to the Lane and Eynon method using Fehling solution, as per SASTA,
2005. The percentage reducing sugars in the sample was calculated as indicated below:

Reducing sugar = MRS/(10 × MJ), (4)

where MRS is the mass of reducing sugar (mg) in 100 cm3 and MJ is mass of juice (g) in
100 cm3 .
Cell count (CC) was determined using a microscope, with the help of a Haemocytome-
ter. Methylene blue indicator was used to check cell viability. The dead cells were stained
with the blue indicator, while viable cells remained uncolored.
Processes 2022, 10, 7 5 of 9

Cell viability in % (CV) is determined using the following relation:

Cell viability = Viable cell/Total number of cell × 100. (5)

In heat transfer equipment of the Metehara distillery, it has been observed that scale
formation rate is rapid and due to which the distilleries and evaporator units serve for
shorter period and must be cleaned frequently. So, due to frequent cleaning of the equip-
ment, production halted. Recycling of vinasse may aggravate the situation by recirculating
scale-causing compounds back to the fermenter. Therefore, measuring the CaO content
of the vinasse produced at each vinasse concentration level can be used to examine the
effect of vinasse recycling on the formation of scales on heat transfer surfaces. Studies have
reported that mineral salts are not assimilated by yeast [12].
CaO content in the vinasse was determined by using complexometric titration against
EDTA solution [18].
All experiments were carried out in two replicates, and all reported data were given
in mean values. Significances and standard deviation were calculated using the analysis of
variance (ANOVA) using Version 7.0.0 software (p-value < 0.05). The response variables of
the experiment were evaluated with reference to the control (with no recycled vinasse).

3. Results
The effect of vinasse recycling on ethanol fermentation was tested in molasses medium
at different vinasse concentrations and results are presented below. The results of the labora-
tory experiment, analyzing different vinasse concentrations, are tabulated in Tables 1 and 2.
Table 1. Effect of vinasse concentration on yield, FE, and RS.

Vinasse (%) Yield (%) FE (%) RS (%)

0 9.58 88.92 1.90
20 9.55 88.78 1.78
35 8.80 82.31 1.81
50 7.64 71.80 1.92
65 7.08 66.06 2.23

Table 2. Effect of vinasse concentration on CC, CV. and CaO content.

Vinasse (%) CC CV (%) CaO (ppm)

0 2.95 × 108 86.37 2135.30
20 2.78 × 108 83.51 2181.20
35 2.72 × 108 85.42 2324.70
50 2.5 × 108 76.84 2548.56
65 2.1 × 108 70.88 2801.12

3.1. Effect of Vinasse Concentration on Yield, Fermentation Efficiency, and Residual Sugar
The fermentation process was conducted with 0, 20, 35, 50, and 65% vinasse concentra-
tions to study the effect of vinasse recycling on ethanol production; the results are shown
in Table 1. Ethanol yield was 9.58% without vinasse, which was used as the control. The
result indicated that the ethanol yield decreased from 9.55 to 7.08% as vinasse concentration
increased from 20 to 65% (Figure 1a).
The effects of FE during vinasse recycling at different percentages in water are also
presented in Table 1. It was found that the fermentation efficiency ranged between 66.06
and 88.92%. The results indicate that fermentation efficiency decreased sharply as vinasse
concentration increased.
Residual sugar concentration (RS) was measured and is also tabulated in Table 1. The
results indicate that the RS value slightly increased as concentration of vinasse increased
from 20 to 50%. However, the RS value increased sharply once vinasse concentration was
above 50%. The value of RS was found to be between 1.8 and 2.2%.
Processes 2021, 9, x FOR PEER REVIEW 6 of 10
Processes 2022, 10, 7 6 of 9

(a) Effect
Figure 1. (a) Effect of
of vinasse concentration on yield. (b)
(b) Effect
Effect of vinasse concentration on FE.

3.2. Effect of Vinasse Concentration on Cell Count, Cell Viability, and Calcium Oxide Content
The effects of FE during vinasse recycling at different percentages in water are also
Vinasse
presented was recycled
in Table 1. It wasatfound different
that concentrations
the fermentation forefficiency
molassesranged dilution to prepare
between 66.06 a
fermentation medium, and the results concerning cell count
and 88.92%. The results indicate that fermentation efficiency decreased sharply as vinasse and cell viability are tabulated
in Table 2. During
concentration the experiment, it was found that cell count ranged between 2.78 × 108
increased.
and 2.1 × 108 and
Residual sugar cell viability ranged
concentration (RS)between
was measured 84.38 and and73.33%, within 20 in
is also tabulated to Table
65% vinasse
1. The
recycling, respectively. The result indicates that cell count decreased
results indicate that the RS value slightly increased as concentration of vinasse increased continuously as the
from 20 to 50%. However, the RS value increased sharply once vinasse concentrationup
percentage of vinasse recycling increased. Whereas cell viability decreased slightly, wasto
35% concentration; however, after 35% concentration,
above 50%. The value of RS was found to be between 1.8 and 2.2%. it decreased shapely.
The fermentation process of molasses, supplemented with various vinasse recycling
rates concentrations,
3.2. Effect revealed that
of Vinasse Concentration on calcium
Cell Count, oxide
Cellconcentration increased
Viability, and Calcium as the
Oxide concen-
Content
tration of vinasse recycling increased. The CaO content was 2135.3 ppm, without vinasse
Vinasse
recycling using was recycled
fresh water at fordifferent
dilution, concentrations
and this value was for molasses
taken as adilution
referencetofor prepare
compar- a
fermentation medium, and the results concerning cell count
ison. It was noted that an increase in the vinasse recycling resulted in an increase in CaO and cell viability are tabu-
lated
content in Table 2. During
concentration the 2181.2
from experiment,
to 2801.12it was found that cell count ranged between 2.78
ppm.
× 108 and 2.1 × 108 and cell viability ranged between 84.38 and 73.33%, within 20 to 65%
vinasse recycling, respectively. The result indicates that cell count decreased continuously
4. Discussion
as theEthanol
percentageyieldofdecreased
vinasse recycling increased.
slightly from 9.58 toWhereas
9.55% as cell viability
vinasse decreasedincreased
concentration slightly,
up to 35% concentration; however, after 35% concentration,
from 0 to 20%. Above 35% of vinasse, ethanol yield decreased sharply as the concentration it decreased shapely.
The fermentation
of vinasse increased. The process
effects of molasses,
of vinassesupplemented
on ethanol yield with various vinasse
depended recycling
on its concentra-
rates concentrations, revealed that calcium oxide concentration
tion [10,13]. Castro and Gil [19] stated that the presence of inhibitors, such as solids increased as the concen-
and
tration of vinasse recycling increased. The CaO content
acetic acid, limit the recirculation percentage and the number of recycles possible. was 2135.3 ppm, without vinasse
Thus,
recycling
the reasonusing behind fresh
the water
decreaseforin dilution,
ethanoland this valuemay
productivity wasbetaken as a reference
an increase in solubleforsolids
com-
parison. It was noted that an increase in the vinasse recycling
and inhibiters in the medium. In this study, it was found that the highest yield (9.55) was resulted in an increase in
CaO content
obtained concentration
at 20% vinasse, and from 2181.2
there was to no2801.12 ppm.
significant difference with the control.
The fermentation efficiency decreased as vinasse concentration increased. It was found
4. Discussion
that the highest fermentation efficiency (88.78) was obtained at 20% vinasse, and there was
no significant
Ethanol yield difference from slightly
decreased the control.fromThe 9.58result obtained
to 9.55% by Fadelconcentration
as vinasse et al. (2014) [13] in-
showed from
creased that up 0 to 30% v/v
to20%. vinasse,
Above 35% ofreplacing
vinasse,water,ethanol hasyield
no effect on fermentation
decreased sharply asefficiency.
the con-
Rein [3] mentioned
centration of vinasse that molassesThe
increased. has effects
to be diluted to keep
of vinasse on dissolved
ethanol yield solids concentrations
depended on its
at levels low enough
concentration [10,13].that fermentation
Castro and Gil [19] is not affected
stated that bythea presence
high osmotic pressure. such as
of inhibitors,
solidsTheandamount residual
acetic acid, limitsugar after fermentation
the recirculation percentage is important.
and the number The residual sugar
of recycles in-
pos-
creased with an increase in vinasse concentration; however,
sible. Thus, the reason behind the decrease in ethanol productivity may be an increase in RS increased sharply above a
vinasse concentration of 50%. The RS value was between
soluble solids and inhibiters in the medium. In this study, it was found that the highest1.8 and 2.2%, which is in good
agreement
yield (9.55) with the findings
was obtained at 20%of similar
vinasse, studies,
and therewhich was show values between
no significant 1.9 and
difference with2.5%,
the
with respect to concentrations of 20–60% vinasse [13].
control.
In this
The study, the result
fermentation indicates
efficiency that cellasviability
decreased vinasseincreases
concentration slightly from 20 to
increased. It 35%;
was
however, after 35%, it decreases sharply. Less than one-third
found that the highest fermentation efficiency (88.78) was obtained at 20% vinasse, and of the bleed could be recycled
beforewas Ca2no + inhibition would reduce cell production by 20% [12]. A study showed that
there significant difference from the control. The result obtained by Fadel et al.
osmotic
(2014) stress
[13] showedhas impact
that upon to yeast
30% v/vpopulation
vinasse, dynamics.
replacing water,It is caused
has noby greatonamounts
effect fermenta- of
salts present in sugarcane molasses [4]. Reduction in cell viability
tion efficiency. Rein [3] mentioned that molasses has to be diluted to keep dissolved solids may be attributed to salt
 agreement with the findings of similar studies, which show values between 1.9 and 2.5%,
with respect to concentrations of 20–60% vinasse [13].
In this study, the result indicates that cell viability increases slightly from 20 to 35%;
however, after 35%, it decreases sharply. Less than one-third of the bleed could be recy-
Processes 2022, 10, 7 cled before Ca2+ inhibition would reduce cell production by 20% [12]. A study showed 7 of 9
that osmotic stress has impact on yeast population dynamics. It is caused by great
amounts of salts present in sugarcane molasses [4]. Reduction in cell viability may be at-
tributed to salt concentration increasing as vinasse concentration increases in the medi-
concentration
ums, which, inincreasing as vinasse
turn, results concentration
in increased increases in the mediums, which, in turn,
osmotic pressure.
results in increased osmotic pressure.
The percentage of CaO contents increased sharply after 20% of vinasse, as shown in
TableThe percentage
2. This of that
indicates CaOthe
contents increased
CaO content sharply
in the after 20%media
fermentation of vinasse, as shown
increased duringin
Table 2. This indicates that the CaO content in the fermentation media increased during
recycling of vinasse at different rates, with respect to the vinasse concentration percent-
recycling of vinasse at different rates, with respect to the vinasse concentration percentage.
age. The osmotic stress, caused by salts, is a matter of concern; additionally, high levels of
The osmotic stress, caused by salts, is a matter of concern; additionally, high levels of
calcium, potassium, and magnesium found in the substrate may substantially exceed the
calcium, potassium, and magnesium found in the substrate may substantially exceed the
requirements for yeast nutrition [4].
requirements for yeast nutrition [4].
A study conducted at an ethanol plant indicated that the CaO content of the scale
A study conducted at an ethanol plant indicated that the CaO content of the scale
samples taken from the distillation column of the factory was 63.87% [20] (pp. 36–38). Vi-
samples taken from the distillation column of the factory was 63.87% [20] (pp. 36–38).
nasse recycling must be limited to a maximum of one-third of the feed rate for a typical
Vinasse recycling must be limited to a maximum of one-third of the feed rate for a typical
sugarcane molasses feed [12]. The percentage of increase in CaO content as shown in Fig-
sugarcane molasses feed [12]. The percentage of increase in CaO content as shown in
ure 2, up to 20% vinasse recycling, was below 5%, which is 2.15%.
Figure 2, up to 20% vinasse recycling, was below 5%, which is 2.15%.

Figure 2.
Figure Percentage of
2. Percentage of CaO
CaO content
content as
as aa function
function of
of vinasse
vinasse concentration.
concentration.
In this study, it was found that the maximum yield achieved in the case of vinasse
In this
recycling wasstudy,
9.55%,it was
which found
was that the maximum
obtained yieldalso
at 20%. It was achieved
found in the
that thecase of vinasse
maximum FE
recycling was 9.55%, which was obtained at 20%. It was also found
(88.78%) was obtained at the same vinasse concentration. Hence, both yield and FE havethat the maximum FE
(88.78%) was obtained
no significant difference atfrom
the same vinasseifconcentration.
the control, the concentrationHence, both yield
of vinasse wasandkeptFEwithin
have
no
thesignificant
20% rangedifference fromBesides,
(Figure 1a,b). the control, if the
the CaO concentration
content was the of vinasse
lowest wasvinasse.
at 20% kept within
the 20% range
Based on (Figure 1a,b).ofBesides,
the findings the 20%
this study, CaOvinasse
contentconcentration
was the lowest at be
can 20% vinasse.to the
recycled
Based on the findings of this study, 20% vinasse concentration can
fermenter instead of process water; water savings were calculated based on 20% recycled be recycled to the
fermenter instead of process water; water savings were calculated based
vinasse. It was found that there was a proportional reduction in water consumption, with on 20% recycled
vinasse.
about a It was found
19.5% that therereduction
(68.2 ton/day) was a proportional
in vinassereduction
volume. inWithout
water consumption, with
vinasse recycling,
about a 19.5%
the excess (68.2generated
vinasse ton/day) reduction in vinasse
is 105 ton/day; volume.
however, withWithout vinasse
20% vinasse recycling,
recycling, the
it will
excess vinasse
be reduced to generated
38.6 ton/day,is 105as ton/day;
shown in however,
Table 3. with
The 20% vinasse
treatment recycling,
cost it reduce,
will also will be
reduced to 38.6
accordingly, ton/day,
during as shown
compost in TableThe
preparation. 3. The treatment
total reductioncost will also
amount reduce,isaccord-
of vinasse within
ingly, during
the range compost
specified preparation.
by similar studiesThe total reduction amount of vinasse is within the
[10].
rangeTherefore,
specified bythesimilar
total amount
studiesof[10].
vinasse reduction will be 114.2 ton/day, only by using
20% of vinasse for molasses dilution. Based on the process layout of the factory, vinasse can
be recycled from the primary column re-boiler to the fermenter: the process flow diagram
is shown in Figure 3. In order to increase the amount of vinasse recycled to above 20%
and reduce excess vinasse, further study should be carried out by treating the molasses.
Moreover, after this successful laboratory-scale experiment, it is vital to harness the benefits
of the findings of the research by implementing the vinasse recycling at the ethanol plant
of the MSF.
 Operating Parameter Capacity (ton/day)
Molasses 206
Process water 571
Vinasse supplied to the evaporator 586
Processes 2022, 10, 7 Concentrated vinasse % of supplied vinasse 59.73 8 of 9
Bio-compost capacity 245
Without recycling With recycling
Recycled amount (20% of process water) - 114.2
Table 3. Water balance with 20% vinasse recycling.
Net amount to be evaporated 586 471.8
Operating Parameter Amount of concentrated vinasse Capacity (ton/Day) 350 281.8
Molasses Reduction of concentrated vinasse 206 - 68.2 (19.5%)
Process water 571
Vinasse supplied to the evaporator 586 will be 114.2 ton/day, only by using
Therefore, the total amount of vinasse reduction
Concentrated vinasse % of supplied
20% of vinasse for molasses dilution. Based on 59.73the process layout of the factory, vinasse
vinasse
can be recycled from the primary column re-boiler to the fermenter: the process flow dia-
Bio-compost capacity 245
gram is shown in Figure 3. Inrecycling
Without order to increase the amount of With
vinasse recycled to above
recycling
20%
Recycled amount (20% of process and reduce excess vinasse,
water) - further study should be carried out by treating the molas-
114.2
ses. Moreover, after this successful
Net amount to be evaporated 586 laboratory-scale experiment, it 471.8
is vital to harness the
Amount of concentrated vinasse
benefits of the findings of the350
research by implementing the vinasse281.8
recycling at the etha-
Reduction of concentrated vinasse
nol plant of the MSF. - 68.2 (19.5%)

Figure 3. Mass balance

Figure of thebalance
3. Mass evaporation
of theplant with vinasse
evaporation plant recycling.
with vinasse recycling.

5. Conclusions
5. Conclusions
The fermentation of molasses by recycling vinasse at different concentrations indicated
The fermentation of molasses by recycling vinasse at different concentrations indi-
that 20% vinasse dilution rate results in 9.55% ethanol yields and 88.78% fermentation
cated that 20% vinasse dilution rate results in 9.55% ethanol yields and 88.78% fermenta-
efficiency at the operating conditions of the Metehara distillery. The effect of 20% recycled
tion efficiency at the operating conditions of the Metehara distillery. The effect of 20%
vinasse on sugarcane molasses fermentation indicated that yield and fermentation efficiency
recycled vinasse on sugarcane molasses fermentation indicated that yield and fermenta-
had no significant difference from the control. With the 20% recycled vinasse, 114.2 tons of
tion efficiency had no significant difference from the control. With the 20% recycled vi-
fresh water was saved per day, and the amount of vinasse volume generated decreased by
nasse, 114.2 tons of fresh water was saved per day, and the amount of vinasse volume
19.5% (68.2 ton/day). The excess amount of vinasse, beyond the handling capacity of the
generated decreased by 19.5% (68.2 ton/day). The excess amount of vinasse, beyond the
bio-compost plant of the distillery, also decreased from 105 to 36.8 tons/day. The study
handling capacity of the bio-compost plant of the distillery, also decreased from 105 to
showed that up to 20% vinasse can be used instead of fresh water for ethanol production,
36.8 tons/day.
without Thesignificant
causing study showed that
effects onup to 20%
either vinasse
ethanol canor
yield befermentation
used instead efficiency.
of fresh water
It is
for ethanol production, without causing significant effects on either ethanol
also indicated that the CaO content of the vinasse increased sharply above 20% yield or fer-
recycling.
mentation efficiency. It is also indicated that the CaO content of the vinasse increased
sharply above 20% recycling.
Author Contributions: A.A. (Ayele Alemu), conceptualization; A.A. (Ayele Alemu) and M.G.,
methodology; A.A. (Ayele Alemu) and G.M.S.A., software; A.A. (Ayele Alemu) and M.G., vali-
Author
dation; Contributions: A.A. (Ayele
A.A. (Ayele Alemu), formal Alemu),
analysis; conceptualization;
A.A. (Ayele Alemu)A.A.
and(Ayele
M.G., Alemu) and M.G.,
investigation; A.A.
methodology;
(Ayele Alemu),A.A. (Ayele Alemu)
resources; and G.M.S.A.,
A.A. (Ayele Alemu), software; A.A. (Ayele
writing—original Alemu)
draft and M.G.,
preparation; valida-
M.G. and
tion; A.A. (Ayele
G.M.S.A., Alemu), formal
writing—review analysis;G.M.S.A.,
and editing; A.A. (Ayele Alemu) andA.A.
visualization; M.G., investigation;
(Ayele A.A. (Ayele
Alemu), supervision;
A.A. (Ali Algahtani), project administration; V.T. and A.A. (Ali Algahtani), funding acquisition. All
authors have read and agreed to the published version of the manuscript.
Funding: The authors gratefully acknowledge the Deanship of Scientific Research, King Khalid
University (KKU), Abha-Asir, Saudi Arabia, for funding this research work under the grant number
RGP.2/58/42.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Processes 2022, 10, 7 9 of 9

Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Acknowledgments: The authors extend their appreciation to the Research and Development Center
of Sugar Corporation, Ethiopia, for technical expertise and financial assistance in carrying out
experiments. The authors gratefully acknowledge the Deanship of Scientific Research, King Khalid
University (KKU), Abha-Asir, Saudi Arabia, for funding this research work under the grant number
RGP.2/58/42.
Conflicts of Interest: The authors declare no conflict of interest.

References
1. Amin, R.M.; Hossain, S.M.; Sarker, M. Simulation of Ethanol Production by Fermentation of Molasses. J. Eng. (JOE) 2013, 1, 69.
2. Patrascu, E.; Rapeanu, G.; Bonciu, C.; Hopulele, T. Bio-Ethanol Production from Molasses by Different Strains of Saccharomyces
Cerevisiae. In Fascicle VI—Food Technology, Proceedings of the International Symposium Euro-Aliment 2009, 9–10 October 2009; Galati
University Press: Galati, Romania, 2009; p. 49.
3. Rein, P. Cane Sugar Engineering; Verlas Dr. Albert Bartens KG: Berlin, Germany, 2007; pp. 726–731.
4. Basso, L.C.; Basso, T.O.; Rocha, S.N. Ethanol Production in Brazil: The Industrial Process and Its Impact on Yeast Fermentation. In
Biofuel Production-Recent Developments and Prospects; Dos Santos Bernardes, M.A., Ed.; IntechOpen: London, UK, 2011; pp. 88–92.
5. Christofoletti, C.A.; Escher, J.P.; Correia, J.E.; Marinho, J.F.U.; Fontanetti, C.S. Sugarcane Vinasse: Environmental Implications of
Its Use. Waste Manag. 2013, 33, 2754–2758. [CrossRef] [PubMed]
6. Olguin, E.J.; Doelle, H.W.; Mercado, G. Resource Recovery through Recycling of Sugar Processing By-products and Residuals.
Resour. Conserv. Recycl. 1995, 15, 90–92. [CrossRef]
7. Ansari, F.; Awasthi, A.K.; Srivastava, B.P. Physico-chemical Characterization of Distillery Effluent and Its Dilution Effect at
Different Levels. Arch. Appl. Sci. Res. 2012, 4, 1705–1706.
8. Mikucka, W.; Zielińska, M. Distillery Stillage: Characteristics, Treatment, and Valorization. Appl. Biochem. Biotechnol. 2020, 192,
772–773. [CrossRef] [PubMed]
9. Willington, I.P.; Marten, G.G. Options for Handling Stillage Waste from Sugar-Based Fuel Ethanol Production. Resour. Conserv.
1982, 8, 111–129. [CrossRef]
10. Castro, G.A.; Caicedo, L.A. Reduction of Stillage’s Volume in the Production of Ethanol by Recirculation Applying Liquid-Liquid
Extraction. Available online: http://www.nt.ntnu.no/users/skoge/prost/proceedings/ecce6_sep07/upload/3292.pdf (accessed
on 15 February 2020).
11. Mirkena, B. Optimization of Molasses Fermentation to Ethanol to Reduce Effluent Generation: The Case of Metahara Sugar
Factory. Master’s Thesis, Addis Ababa University, Addis Ababa, Ethiopia, 2014.
12. Maiorella, B.L.; Blanch, H.W.; Wilke, C.R. Feed and Component Inhibition in Ethanol Fermentation. Biotechnol. Bioeng. 1984, 26,
1155–1166. [CrossRef] [PubMed]
13. Fadel, M.; Zohri, A.A.; Makawy, M.; Hsona, M.S.; Abdel-Aziz, A.M. Recycling of Vinasse in Ethanol Fermentation and Application
in Egyptian Distillery Factories. Afr. J. Biotechnol. 2014, 13, 4390–4397. [CrossRef]
14. Gumienna, M.; Lasik, M.; Szambelan, K.; Czarnecki, Z. Reduction of Water Consumption in Bioethanol Production from Triticale
by Recycling the Stillage Liquid Phase. Acta Sci. Pol. Technol. Aliment 2011, 10, 473.
15. Fakruddin, M.; Quayum, M.; Ahmed, M.M.; Choudhury, N. Analysis of Key Factors Affecting Ethanol Production by Seccha-
romyces Cerevisiae. Biotechnology 2012, 11, 251.
16. Gasmalla, M.A.A.; Yang, R.; Nikoo, M.; Man, S. Production of Ethanol from Sudanese Sugar Cane Molasses and Evaluation of Its
Quality. J. Food Process. Technol. 2012, 3, 1–3.
17. Hamed, I.H.; Hussein, N.N.; Hekmat, R.M.; Salem, S.A.; Nour, S.E. Statistical Optimization of Batch Ethanol Fermentation of
Sugarcane Molasses by Candida Tropicalis Strain HSC-24. Int. J. ChemTech Res. 2015, 8, 2.
18. Kassa, H. Handbook of Laboratory Methods and Chemical Control for Ethiopian Sugar Factories; Ethiopian Sugar Development Agency
Research Directorate: Wonji, Ethiopia, 2009; pp. 63–65.
19. Castro, G.A.; Gil, I.D. Development of an Ethanol Production Process with Stillage Recycling at Pilot Plant-Scale. Available online:
http://www.nt.ntnu.no/users/skoge/prost/proceedings/ecce6_sep07/upload/3561.pdf (accessed on 15 February 2020).
20. Firdissa, T. Design and Optimization of Molasses Treatment to Reduce Scale Formation in Ethanol Production (The Case of
Metahara Sugar Factory Ethanol Plant). Master’s Thesis, Addis Ababa University, Addis Ababa, Ethiopia, 2012.