Chemistry">
Sseor, Gestor - A de La Revista, 519-1365-1-SM
Sseor, Gestor - A de La Revista, 519-1365-1-SM
Sseor, Gestor - A de La Revista, 519-1365-1-SM
CHEMICAL ENGINEERING
Abstract
Vinasse is the most important waste from the bioethanol plants due to its high polluting potential, for this it has received
special attention because of interest to develop new treatment alternatives. It was evaluated the removal capacity of
solids content and other parameters of vinasse by using electro-dissolution of iron and chemical flocculation through
separate stages. The appropriate operating conditions for electro-dissolution were established by means of linear
polarization sweeps and electrochemical impedance spectroscopy analyses. During the flocculation were conducted
jar tests by using Ca(OH)2 as coadjuvant agent and as pH modifier. In this way, was possible to diminish 84% total
solids, 54% chemical oxygen demand, 88% dissolved organic carbon and 76% color. The electrical consumption
during electro-dissolution was 0.25 kWh/m3.
Resumen
La vinaza es el residuo más importante de las plantas de bioetanol debido a su alto potencial contaminante, por esto
ha recibido gran atención debido al interés de desarrollar nuevas alternativas de tratamiento. Se evaluó la capacidad
de reducción del contenido de sólidos y otros parámetros de la vinaza empleando electrodisolución de hierro y
floculación química a través de etapas separadas. Las condiciones de operación adecuadas para llevar a cabo la
electrodisolución de hierro se establecieron a través de barridos de polarización lineal y análisis de espectroscopia
de impedancia electroquímica. Durante la floculación se llevaron a cabo pruebas de jarras empleando Ca(OH)2
como modificador de pH y como agente coadyuvante. De esta manera fue posible disminuir 84% los sólidos totales,
54% la demanda química de oxígeno, 88% el carbono orgánico disuelto, y 76% el color. El consumo eléctrico
durante la electrodisolución fue 0.25 kWh/m3.
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ozone in diluted raw vinasse (2,500 ppm COD) potentiostat PC4-750. The effects of pH and
and was achieved complete discoloration and the current density during the electrodissolution
83% reduction in COD (Asaithambi, et al. 2012). were evaluated by supplying the same specific
The ozone dosage was 15 L min-1 for two hours of electrical charges (15,000 C L-1). The solution
treatment and required power consumption in the resistance behavior, the charge transfer resistance
electrocoagulation was 5.1 kWh m-3. and double-layer capacitance during the iron
electrodissolution process were established by
Electrocoagulation is a process based on the using Electrochemical Impedance Spectroscopy
electrolytic dissolution of a metal as iron or
(EIS). Three EIS spectra were taken at 30 minutes
aluminum and in situ production of insoluble
intervals, keeping the current density (J) at 0.3
amorphous species. However, this method has
mA cm-2.
severe limitations when the suspension to be
treated has high buffer-capacity, like the raw
Final tests. The experiments were conducted by
vinasse, due to it is increased the electrical
varying the theoretical dosage of iron (through of
energy consumption. The purpose of this study
the specific electric charge magnitude supplied)
was to evaluate the removal of total solids
content in untreated vinasse by combining iron- and by setting the initial pH at 4.5 and current
electrodissolution and chemical-flocculation. density at 0.3 mA/cm2. The parameter Rc was
defined to relate the theoretical amount of iron
2. Matherials and methods supplied during the electrodissolution and the
solids content of the vinasse, then was calculated
2.1 Iron-electrodissolution by Eq. (1).
The lab-scale cell consisted of a plexiglas i×t
Rc = (1)
recipient with volume of 1,000 mL and flat St
electrodes (monopolar configuration) with six
316 stainless steel cathodes and five anodes of where i represents the current supplied in
carbon-steel (ASTM-A-36). The electrodes had amperes, t is time in seconds, and St represents
dimensions of 9×6 cm with 3 mm gap among the total solids concentration (%) in the treated
them and total anodic area was 900 cm2. The raw
vinasse. Also, it was studied the influence of
vinasse was recycled through a centrifugal pump
three Rc values: 1,000; 1,500 and 2,000 during
which supplied an upward flow of 1.9 L min-1.
the electrodissolution stage and its effect on the
Direct current was supplied by an Extech® source
of 5A, which was used in galvanostatic mode. flocculation stage. Under these considerations
Before testing the electrodes were subjected to and for comparison effects, the iron content in
dry abrasion with abrasive paper No. 500 and the solution was measured by atomic absorption
then with abrasive paper No. 1,200 to get a shiny and the physiochemical characteristics of samples
appearance. Afterward, the electrodes were rinsed were determined according the standard methods
with distilled water and immersed in acetone for (AHPA, 1998). For all tests were established the
about ten minutes to remove any traces of oil or power consumption, W in kWh m-3, through the
grease. Finally they were rinsed with distilled Eq. 2.
water before use them in electrodissolution.
v×i×t
W= (2)
Preliminary tests. The current density magnitude 3,600 × vol
in the lab-scale cell was established by recording
the linear polarization resistance in a three where v represents the voltage supplied in volts
electrodes cell assembly by using a Gamry and vol is the volume of sample in liters.
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Important information was obtained from the Electrochemical impedance spectroscopy (EIS).
study of the iron-electrodissolution process and The linear polarization does not demonstrate the
the electrode passivation in the electrolytic reactor electrode behavior with time whilst EIS provides
through of techniques as linear anodic polarization information related with reaction mechanism.
and electrochemical impedance spectroscopy. Nyquist diagrams revealed three arcs with
increasing diameters when iron-electrodissolution
Linear anodic polarization. The electrodissolution took place (Figure 2); therefore, the transient
of Fe2+ showed faradic behavior (Figure 1) up behavior of the anode can be described by a
to 13.5 mA cm-2 (540 mV vs Ag/AgCl) where Randles circuit. This would indicate that only
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Figure 4 shows the behavior of the lab-cell voltage chemical bridge due to the increased concentration
and the pH after 4 hours of operation for two of ions as HPO4-2, Ca2+, Fe2+ y Mg2+ contents in the
values of J. When it was applied the lower J value, vinasse (Voegelin, et al. 2010).
the cell voltage and the pH were kept constant;
conversely, these two variables were increased
when it was operated at 0.8 mA cm-2. The increase
in the voltage was particularly high (80 mV to
1,200 mV) in the last two hours of operation. This
can be attributed to the presence of insoluble iron
oxy-hydroxides attached to the electrode surface
causing its partial passivation. The presence of
these insoluble species at a pH above 5.5 can cause
inefficient metal electrodissolution (Linares-
Hernández, et al. 2009; Cañizares, et al. 2009).
Figure 4. Cell voltage and pH behavior vs. J. [(•) 0.3 3.3 Chemical flocculation
mA/cm2; (∆) 0.8 mA cm-2]
Figure 6 shows the behavior of the residual
turbidity and lime consumption in the range of
Effect of Rc. Figure 5 shows the behavior of the
pH tested for flocculation. As the pH increased
reducing turbidity (% RT) and reducing total solids
in flocculation, the residual turbidity in the
(% RS) when was varied Rc during subsequent
supernatant was reduced achieving a maximum
flocculation tests. The lowest turbidity removal
reduction at pH of 11.5.
was achieved when Rc=1,000 which would
indicate that the applied electric charge was not
sufficient to obtain the necessary concentration of It has been shown (Semerjian & Ayoub, 2003)
iron cations. that the process of clarification of wastewaters
with high content of Mg2+, Ca2+, CO32-, and
For Rc greater or equal to 1,500 and to the extent HPO43, like vinasse, is strongly favored at pH
that the content of solids in the vinasse increased, greater to 11 due to precipitation of insoluble
the turbidity removal and solids removal were salts. The following equations show the possible
improved. The possible cause is related to the reactions of different ions in the solution during
destabilization of colloids by incorporating a the flocculation process.
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4. Conclusions
By coupling iron electrodissolution and chemical
flocculation processes, a reduction of 84% of
total solids content, 54% of chemical oxygen
demand, 88% of dissolved carbon content and
76% of color were achieved in raw vinasse with
low power consumption (0.25 kWh/m3). The Figure 8. Micrograph of sludge obtained (SEM)
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best results were achieved when the process of distillery using inorganic coagulants. Colloids
electrodissolution was performed with 0.3 mA/cm2 and Surfaces A: Physicochem. Eng. Aspects. 296,
and an Rc of 1,500. This current density is within 238-247.
the working range found by linear polarization
tests and EIS. Flocculation tests showed that the Dávila, J., Machuca, F., & Marriaga, N. (2011).
most appropriate condition was obtained at pH Treatment of vinasses by electrocoagulation–
= 11.5 using Ca(OH)2 as a coagulation adjuvant electroflotation using the Taguchi method.
and as a pH modifier. It was verified that it was Electrochimica Acta. 56, 7433-7436.
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