2 LITREATURE REVIEW
2.1 Biogas
High oil prices, increasing population, industrialization, and the decline in energy security have all led
to an increase in global interest in biofuels. However,
despite this growth, the global market for biofuels is
still in its infancy. The future global potential for biofuel production is also difficult to estimate, due to
a number of factors including the limits of natural
resources and the need for food security above biofuel use. However, studies on biomass availability have
concluded that by 2050, the possible contribution of
biomass to global energy supply could vary from 100
EJ/year to 400 EJ/year, which represents 21%–85%
of the world‘s current total energy consumption, estimated at 470 EJ.Although biofuels are only a fraction
of total biomass, biofuels still have the potential to
play a significant role in meeting future global energy
demand, if developed through appropriate channels
(Bailis et al 2015).
Many developing countries are faced with the
dilemma of finding alternative energy sources with
reduced environmental impact. Wind energy, hydro,
solar, and biofuels energy sources are potential solutions. According to Earley et al. (2015), global ethanol
and biodiesel production increased from about 4.8 billion gallons in 2000 to about 21 billion gallons in 2008.
The goal of replacing fossil fuels with biofuels has
resulted in a high production of ethanol (Gil 2011).
Ethanol is a prominent biofuel because of its advantages; however, there is a challenge in disposing of
vinasse, which is the effluent from the distillation
columns of ethanol industries (Wilkie et al. 2000). It is
said that for each litre of ethanol produced, between 0.8
and 3.0 litres of vinasse are obtained (Asocaña 2011).
Vinasse has a dark colour and a low pH (Iqbal S. 2016).
The concentration of total solid and COD value are
very high. The pH condition of vinasse is 3.25–4.97,
while the total solid (TS) value in vinasse is 63,000–
79,000 mg/L (Iqbal S. 2016). Budiyonoet al.(2014)
reported that vinasse contains COD content of 299,250
mg/L. Wilkie et al.(2000) further stated that vinasse
is an organic liquid residue comprising about 93%
water, 5% organic matter mainly unfermented sugars
and other carbohydrates, and about 2%inorganic dissolved solids. Vinasse contains many kinds of organic
compounds, such as acetic acids, lactic acids, glycerol,
phenols, polyphenols, and melanoidins (Budiyono et
al. 2014).
Vinasse is wastewater that is a by-product of distillation from the production of ethanol by fermentation.
Besides containing high COD, vinasse has a strongly
acidic character (pH 3.67–4.98) (Lutoslawski et al.
2011; Siles et al. 2011). Vinasse characteristics pose
serious challenges to the environment in terms of disposal. The strongly acidic pH of vinasse causes the
remobilization of heavy metals in soil (Kafle et al.
2012). The dark colour in vinasse is not good for the
environment, being unsightly. Besides that, it also can
hamper penetration of sunlight into the rivers, so water
plants cannot photosynthesise (Iqbal S. 2016). Soluble
salts in vinasse can cause soil salinity and sodicity. It
can cause poor soil structure and reduce fertility. Vlyssideset al. (1997) stated that high concentration of P
and N nutrients cause eutrophication in water bodies.
The temperature of fresh vinasse from a distillation
unit is 65–105
◦ C. If vinasse is disposed of in water
bodies, without cooling, the temperature of water bodies can increase. It can also disturb fish activity (Siles
et al. 2011).
Attempts have been made to establish ways to dispose of vinasse with a minimum negative effect on
the environment. In Brazil, vinasse is applied directly
to the soil because of its organic matter and nutrient
content; potassium, nitrogen and phosphorus make it a
good organic fertilizer for sugarcane farms (Ferraz et
al. 2015).From an economic perspective, the soil application of vinasse represents the simplest and cheapest
solution. However, continuous application of vinasse
to the soil results in soil and groundwater contamination, leaching and salinization, and seed germination
inhibition (Ferraz et al. 2015).Dávila et al. (2009)
evaluated the electro-flotation/oxidation process for
vinasse, obtaining reductions in COD of 58%. Similarly, Yavuz (2007) achieved a 90% reduction in total
organic carbon in vinasse through electro-coagulation
with the use of a supporting electrolyte and the gradual addition of hydrogen peroxide. Goncalves (2006)
performed research for the treatment of the vinasse
by utilizing coagulation and flocculation. The study
evaluated several variables influencing COD removal
which was used to develop a model. The model demonstrated that the COD removal varied as a function of
the pH and mixing. The best results were achieved
when calcium oxide and ferrous sulfate were used, with
pH values of 12.4 the removal efficiencies were 52%
and 44%, respectively. The study established that the
resulting sludge could be used as a fertilizer because
it was rich in nutrient content. The major challenge in
utilizing sludge as organic fertilizer from vinasse is
the high pH of 12.4 which causes soil pollution. Tang
et al (2007) and Íñiguez-Covarrubias and Peraza-Luna
(2007) found that biological treatment such as active
sludge is expensive and it produces poison. According to Satyawali et al. (2007), anaerobic treatment
is the most attractive primary treatment of vinasse
due to the BOD and COD removal being over 80%,
and the energy recovery in the form of biogas. Ribas
(2006) stated that the anaerobic reactors are a promising alternative because they accomplish a high rate of
organic load removal and produce biogas. Iqbal (2016)
in his review concluded that it is more effective to
degrade organic materials through anaerobic digestion
than aerobic treatment. However, the value of COD
removal is not maximal. That is caused bythe presence
of phenolic compounds in vinasse. He further stated
that anaerobic digestion is a viable option for sugarcane vinasse processing and enables energy recovery
as biogas production. To further support and minimize these challenges, the current study will digest
vinasse.Wilkie et al (2000) also stated that anaerobic
297
2.1 Biogas
High oil prices, increasing population, industrialization, and the decline in energy security have all led
to an increase in global interest in biofuels. However,
despite this growth, the global market for biofuels is
still in its infancy. The future global potential for biofuel production is also difficult to estimate, due to
a number of factors including the limits of natural
resources and the need for food security above biofuel use. However, studies on biomass availability have
concluded that by 2050, the possible contribution of
biomass to global energy supply could vary from 100
EJ/year to 400 EJ/year, which represents 21%–85%
of the world‘s current total energy consumption, estimated at 470 EJ.Although biofuels are only a fraction
of total biomass, biofuels still have the potential to
play a significant role in meeting future global energy
demand, if developed through appropriate channels
(Bailis et al 2015).
Many developing countries are faced with the
dilemma of finding alternative energy sources with
reduced environmental impact. Wind energy, hydro,
solar, and biofuels energy sources are potential solutions. According to Earley et al. (2015), global ethanol
and biodiesel production increased from about 4.8 billion gallons in 2000 to about 21 billion gallons in 2008.
The goal of replacing fossil fuels with biofuels has
resulted in a high production of ethanol (Gil 2011).
Ethanol is a prominent biofuel because of its advantages; however, there is a challenge in disposing of
vinasse, which is the effluent from the distillation
columns of ethanol industries (Wilkie et al. 2000). It is
said that for each litre of ethanol produced, between 0.8
and 3.0 litres of vinasse are obtained (Asocaña 2011).
Vinasse has a dark colour and a low pH (Iqbal S. 2016).
The concentration of total solid and COD value are
very high. The pH condition of vinasse is 3.25–4.97,
while the total solid (TS) value in vinasse is 63,000–
79,000 mg/L (Iqbal S. 2016). Budiyonoet al.(2014)
reported that vinasse contains COD content of 299,250
mg/L. Wilkie et al.(2000) further stated that vinasse
is an organic liquid residue comprising about 93%
water, 5% organic matter mainly unfermented sugars
and other carbohydrates, and about 2%inorganic dissolved solids. Vinasse contains many kinds of organic
compounds, such as acetic acids, lactic acids, glycerol,
phenols, polyphenols, and melanoidins (Budiyono et
al. 2014).
Vinasse is wastewater that is a by-product of distillation from the production of ethanol by fermentation.
Besides containing high COD, vinasse has a strongly
acidic character (pH 3.67–4.98) (Lutoslawski et al.
2011; Siles et al. 2011). Vinasse characteristics pose
serious challenges to the environment in terms of disposal. The strongly acidic pH of vinasse causes the
remobilization of heavy metals in soil (Kafle et al.
2012). The dark colour in vinasse is not good for the
environment, being unsightly. Besides that, it also can
hamper penetration of sunlight into the rivers, so water
plants cannot photosynthesise (Iqbal S. 2016). Soluble
salts in vinasse can cause soil salinity and sodicity. It
can cause poor soil structure and reduce fertility. Vlyssideset al. (1997) stated that high concentration of P
and N nutrients cause eutrophication in water bodies.
The temperature of fresh vinasse from a distillation
unit is 65–105
◦ C. If vinasse is disposed of in water
bodies, without cooling, the temperature of water bodies can increase. It can also disturb fish activity (Siles
et al. 2011).
Attempts have been made to establish ways to dispose of vinasse with a minimum negative effect on
the environment. In Brazil, vinasse is applied directly
to the soil because of its organic matter and nutrient
content; potassium, nitrogen and phosphorus make it a
good organic fertilizer for sugarcane farms (Ferraz et
al. 2015).From an economic perspective, the soil application of vinasse represents the simplest and cheapest
solution. However, continuous application of vinasse
to the soil results in soil and groundwater contamination, leaching and salinization, and seed germination
inhibition (Ferraz et al. 2015).Dávila et al. (2009)
evaluated the electro-flotation/oxidation process for
vinasse, obtaining reductions in COD of 58%. Similarly, Yavuz (2007) achieved a 90% reduction in total
organic carbon in vinasse through electro-coagulation
with the use of a supporting electrolyte and the gradual addition of hydrogen peroxide. Goncalves (2006)
performed research for the treatment of the vinasse
by utilizing coagulation and flocculation. The study
evaluated several variables influencing COD removal
which was used to develop a model. The model demonstrated that the COD removal varied as a function of
the pH and mixing. The best results were achieved
when calcium oxide and ferrous sulfate were used, with
pH values of 12.4 the removal efficiencies were 52%
and 44%, respectively. The study established that the
resulting sludge could be used as a fertilizer because
it was rich in nutrient content. The major challenge in
utilizing sludge as organic fertilizer from vinasse is
the high pH of 12.4 which causes soil pollution. Tang
et al (2007) and Íñiguez-Covarrubias and Peraza-Luna
(2007) found that biological treatment such as active
sludge is expensive and it produces poison. According to Satyawali et al. (2007), anaerobic treatment
is the most attractive primary treatment of vinasse
due to the BOD and COD removal being over 80%,
and the energy recovery in the form of biogas. Ribas
(2006) stated that the anaerobic reactors are a promising alternative because they accomplish a high rate of
organic load removal and produce biogas. Iqbal (2016)
in his review concluded that it is more effective to
degrade organic materials through anaerobic digestion
than aerobic treatment. However, the value of COD
removal is not maximal. That is caused bythe presence
of phenolic compounds in vinasse. He further stated
that anaerobic digestion is a viable option for sugarcane vinasse processing and enables energy recovery
as biogas production. To further support and minimize these challenges, the current study will digest
vinasse.Wilkie et al (2000) also stated that anaerobic
297