however, varies based on the feedstock utilized to produce
the ethanol, as well as the particular production process
how methane production varied as a function of one
2013), COD/sulfate ratio for sugarcane vinasse (Kiyuna et
method to estimate methane generation from vinasse by
assuming 90% BOD removal.
No previous study, however, has developed a more
general model to predict methane generation from
anaerobic digestion of vinasse of any composition at a
range of temperatures. It was hypothesized that the initial
vinasse COD concentration would affect the methane
production rate, since non-zero-order reaction rates are
functions of reactant concentrations. Glucose, which is
converted by microorganisms to methane, provides the
COD. Other initial constituents could potentially affect
microbial health and growth and thus impact reaction
rates. It was also hypothesized that digestion temperature
would impact reaction rates, since microbial-facilitated
reactions typically increase with temperature, up to an
optimal range.
easy to obtain. A more complex model may provide more
accurate estimates, but at the cost of additional data
inputs. First-order models are used with great success to
describe many processes of interest in environmental
engineering; they often represent a reasonable balance
though they do not account for all of the multiple steps
that occur in anaerobic degradation processes, first-order
models are widely used. For example, the US
Environmental Protection Agency’s widely used Landfill
Gas Emissions Model (LandGEM) is a first-order model.
Accordingly, an objective of this research was to develop
a first-order model to predict methane generation from
anaerobic treatment of vinasse.
MATERIAL AND METHODS
Vinasse compositions tested
In this research, synthetic compositions were used to
enable us to vary the range of constituent values tested,
and the ratios of constituent values, to aid in building a
model applicable to
a
wider range of vinasse
compositions. An experimental design (strength
2
limiting the constituents to levels not toxic to
methanogens. Preliminary tests were conducted using the
experimental design; however, only 4 of 18 batches
produced significant methane. The other vinasse
compositions likely contained constituent quantities and
ratios unsuitable for microbial growth. The four vinasse
compositions used for full testing and model building are
shown in Table 1. For comparison, vinasse constituent
values reported in the literature are shown in the second
row from the bottom.
The overall goal of this research was to test these
hypotheses, and to build a model VUMP (Vinasse
Utilization for Methane Production) to predict methane
generation for anaerobic treatment of vinasse from ethanol
production, based on readily available inputs of initial
vinasse composition and treatment temperature. Specific
research objectives were:
1. To develop and operate laboratory scale anaerobic
reactors to study the effect of vinasse composition and
temperature on methane generation over time.
2. Using the laboratory data, to develop multiple-
linear regression equations for predicting first-order rate
constants for methane generation in terms of initial
vinasse composition and temperature.
Temperatures tested
To study the effect of temperature, tests were
conducted at 3 temperatures (30, 35 and 40°C), spanning
the range of mesophilic methanogens. Each of the 4
compositions was operated at 3 mesophilic temperatures
(30, 35, and 40°C), for a total of 12 runs.
Anaerobic systems can be designed for temperatures
appropriate for mesophilic bacteria (30-40°C) or
thermophilic bacteria (50-60°C). Higher temperatures
increase microbial activity, with activity roughly doubling
for every 10°C increase within the optimal range (Khanal,
2008). Thermophilic systems thus produce methane 25-
demonstrates improved pathogen destruction. However,
start-up for thermophilic systems is slower, and systems
are more susceptible to changes in loading variations,
research, mesophilic temperatures were chosen, since
these systems operate with more stability.
Batch reactor set-up
Experiments were conducted in 3-L glass reactor
flasks. Each reactor was connected to an air-tight gas-
collection bag (22-L Cali-5-Bond™ Bag, Calibrated
Instruments, Inc.), as shown in Figure 1. Before filling, all
reactors were sealed with silicon sealant and leak-
checked. Reactors were filled with vinasse of different
compositions, according to Table 1. The synthetic vinasse
mixtures were prepared using appropriate concentrations
of glucose, ammonia, phosphoric acid, potassium
hydroxide, and calcium sulfate as sources of chemical
oxygen demand (COD), nitrogen (N), phosphorous (P),
To facilitate their use, the models should be based
on a limited number of input parameters that are fairly
To cite this paper: Kuusisto LM, Sattler ML, Chen VCP (2019). Predicting Bioenergy Potential from Vinasse Digestion: The VUMP Model (Vinasse Utilization for Methane
Production). J. Civil Eng. Urban., 9 (4): 36-42. www.ojceu.ir
37