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Sistema de Información Científica
Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
Rev. Int. Contam. Ambie. 27 (1) 61-74, 2011
UTILIZATION OF BY-PRODUCTS FROM THE TEQUILA INDUSTRY.
PART 10: CHARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave
tequilana
WEBBER BAGASSE USING FTIR SPECTROSCOPY, THERMOGRAVIMETRIC
ANALYSIS AND SCANNING ELECTRON MICROSCOPY
Gilberto Íñiguez
1*
, Alex Valadez
2
, Ricardo Manríquez
1
and María V. Moreno
2
1
Universidad de Guadalajara, Departamento de madera, celulosa y papel, km 15.5 carretera Guadalajara-Nogales,
Las Agujas, Mpio. de Zapopan, Jalisco, Apartado Postal 52-93, C.P. 45020, Guadalajara, Jalisco, México
2
Unidad de Materiales, Centro de Investigación Científca de Yucatán, A.C. Calle 43 130, C±uburná de ²i-
Calle 43 130, C±uburná de ²i-
dalgo, Mérida Yucatán Mexico, C.P. 97200
(Recibido abril 2010, aceptado enero 2011)
Key words: composting evolution, tequila residues, biodegradation
ABSTRACT
Composting evolution oF two diFFerent agave bagasse provided by two tequila Factories
was monitored at
0, 28, 56, 84, 112 and 126 days using ³ourier transForm inFrared spec-
troscopy (³TIR), t±ermogravimetric analysis (TGA) and scanning electron microscopy
(SEM) to assess t±eir degree oF decomposition. Stages oF decomposition were assessed
using t±eir IR spectral pattern since t±e c±aracteristic bands undergo c±anges during
t±e biological treatment oF t±e agave bagasse. Additionally, t±e samples were analyzed
using t±e temperature range From 40 to 600 ºC in nitrogen atmosp±ere in order to assess
t±e c±anges. Agave bagasses (wit±out composting) ±ad t±e ±ig±er mass loss percentage
in TGA and t±ese losses diminis±ed as t±e composting process progressed. T±e DTG
curves s±owed two peaks w±ic± can be attributed to t±e degradation oF t±e ±emicel-
luloses and cellulose. Scanning electronic microscope observations s±owed signifcant
c±anges in t±e structure oF t±e vascular bundle in agave bagasse samples aFter 126
days oF composting and massive Fungal invasion t±at led to t±e cracking oF t±e fber.
Weakening t±e structure oF t±e vascular bundles oF t±e agave bagasse by composting
can improve water retention capacity oF bagasse t±at is to be used as a substrate For
green±ouse vegetable production.
Palabras clave: evolución del compostaje, residuos del tequila, biodegradación
RESUMEN
En este trabajo se estudió la evolución durante el compostaje de diFerentes bagazos de
agave proveniente de dos Fabricas de tequila, al tomar muestras los días 0, 28, 56, 84,
112 y 126, para valorar su grado de descomposición mediante espectroscopía inFrarroja
de transFormadas de ³ourier, análisis termogravimétrico (TGV) y microscopía elec-
trónica de barrido. Los estados de descomposición Fueron valorados teniendo como
reFerencia el espectro patrón en inFrarrojo ya que las bandas características del bagazo
de agave presentaron cambios durante el tratamiento biológico. Adicionalmente las
muestras Fueron sometidas al análisis termogravimétrico de 40 a 600 ºC en atmósFera
G. Íñiguez
et al.
62
de nitrógeno para valorar los cambios de descomposición por temperatura. Las muestras
de bagazo de agave sin compostaje tuvieron en el análisis TGV el porcentaje más alto
de pérdida de masa, pérdidas que fueron disminuyendo conforme avanzó el proceso
de compostaje. Las curvas derivadas del análisis TGV mostraron dos picos que se
atribuyeron a la degradación de la emicelulosa y celulosa. Observaciones en el mi-
croscopio electrónico de barrido, mostraron cambios signiFcativos en la estructura del
az vascular en las muestras de bagazo de agave después de 126 días de compostaje y
la invasión masiva de ongos que llevó a desquebrajamiento de la Fbra. Debilitando la
estructura del az vascular del bagazo de agave mediante el compostaje puede mejorar
la capacidad de retención de agua del bagazo, para ser utilizado como sustrato en la
producción de ortalizas en invernadero.
INTRODUCTION
Agave bagasse is t e residual Fber remaining after
cooked agave eads are s redded, milled and t e sugar
water-extracted. T e bagasse is primarily t e rind and
Fbrovascular bundles dispersed t roug out t e interior
of t e agave ead. It represents about 40 % of t e to-
tal weig t of t e milled agave on a wet weig t basis.
Bagasse is available all year in only two main regions
of t e tequila producing areas in México: t e Tequila
region and t e Jalisco ±ig lands. In recent years, t e
tequila market as grown and gained international rec-
ognition. Market growt is expected to continue due to
t e recently recognized “tequila origin denomination”
by t e European Union, w ic means more tequila
will be produced wit a substantial improvement of
t e process and tequila quality. T is will mean even
more bagasse, increasing t e disposal problems for
t e tequila companies.
In recent years, t e largest tequila companies
ave adopted t e composting process as t e only
way to manage and dispose of agave bagasse. T e
composting process as been carried out empirically,
by trial and error. In order to optimize t e process and
improve utilization of t e composting product, it is
important to generate knowledge about t e p ysical
and c emical transformations undergone by t e ba-
gasse during composting, eit er as compost for soil
improvement or as a substrate for green ouses.
T e stabilization of organic waste matter is a
crucial requirement before being used as compost or
substrate for plant growt . T e quality of compost
mainly depends on t e level of organic matter stabil-
ity (Wu
et al
. 2000). Application of non-stabilized
organic material soils could affect bot crop growt
and t e environment because of t e presence of p y-
totoxic compounds (Butler
et al
. 2001). During com-
posting, t e most biodegradable organic compounds
are degraded and partly converted into umic-like
substances (±su and Lo 1999, Sánc ez Monedero
et al
. 1999, Wu and Ma 2002). Several indexes and
met ods ave been proposed for evaluating compost
stability (Bernal
et al
. 1998, Itävaara
et al
. 2002, Wu
et al
. 2000, Wu and Ma 2001). ±owever, to date,
t ere is no single met od t at can be successfully
used alone for c aracterizing composts from differ-
ent organic residues (Barberis and Nappi 1996, C en
et al
. 1996, Itävaara
et al
. 2002) due to t e widely
different c emical c aracteristics of organic wastes.
T e utilization of different parameters and indexes
t at focus on t e different properties provided by
composting materials can give a more complete
picture of t e degree of transformation ac ieved
by t e organic materials. T e composition of t e
organic matter in waste materials is very complex
due to t e wide range of c emical compounds and
t e variety of decomposed and synt esized products.
Organic matter and inorganic compounds can build
up organic-mineral complexes. T e separation of
organic substances is not possible wit out c emical
c anges. New analytical met ods and establis ed
met ods wit new applications provide insig t into
t e entire sample of material and its c emical prop-
erties, contributing to a better understanding of t e
decomposition and stabilization processes taking
place. Spectroscopic tec niques, including ²ourier
transform infrared (²TIR) spectroscopy and t er-
mogravimetric analysis (TGA), are among t e more
promising tools for c aracterizing t e c emical trans-
formation of organic matter. Infrared spectroscopy is
based on t e interaction of infrared lig t wit matter
and is sensitive to t e presence of c emical functional
groups (±esse
et al
. 1995, Smit 1999). ±umic sub-
stances originating from composts were c aracterized
by C en
et al
. (1996), ²ilip
et al
. (2000), and Zac
and Sc wanninger (1999). ²TIR spectra revealed t e
transformation of organic matter during a composting
process (C en and Inbar 1993). ²TIR spectroscopy
was applied for assessing compost maturity (Smidt
et
al
. 2002). T ermogravimetry is a tec nique in w ic
C
ARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave tequilana
WEBBER BAGASSE
63
t±e weig±t c±ange is measured during t±e incremental
±eating of t±e sample. T±e ²rst derivative of t±e TG
trace (DTG) permits a better resolution: it does not
contain any new information.
owever, it clearly
identi²es t±e temperatures at w±ic± mass loss is at a
maximum, as well as superimposed transformations
appear more clearly as DTG peaks. T±ermogravim-
etry and scanning calorimetry (DSC) were used to
assess compost stability and maturity
(Blanco and
Almendros 1994, 1997, Dell’Abate
et al
. 1998, 2000,
Dell’Abate and Tittarelli 2002).
T±e basic principle of t±e scanning electron mi-
croscope (SEM) is to scan t±e specimen wit± a ²nely
focused electron beam of keV energy. T±e electrons
interact wit± t±e atoms of t±e material and produce
signals containing information about t±e sample’s
surface topograp±y, composition and ot±er properties.
SEM ±as been used, for instance, for t±e analyses of
microbial matrix formation on bot± t±e surface and
t±e inside of a clay residue used during composting
(Jolanun and Towprayoon 2010) and for t±e analyses
of formation of struvite crystals in a simulated food
waste aerobic composting process (DU Xian-yuan
et al.
2010).
T±e aim of t±is work is to investigate t±e struc-
tural transformations and t±ermal c±aracterization of
compost samples from two different agave bagasse
residues at different stages of composting, combining
FTIR spectroscopy, TGA and
SEM, in order to ²nd
out t±e applicability of t±ese met±ods in operational
processes under realistic conditions.
METHODS
Materials and pretreatment
Agave bagasse, supplied by two tequila facto-
ries, La Codradía and La Regional, were used for
t±e c±aracterization of different composting stages
w±ere t±e principal difference between bagasses was
t±e fermentable sugars extraction system. Compost
samples of t±e La Regional tequila factory originated
from an agave bagasse obtained as follows: agave
±eads of tequilana Weber plants were cooked for nine
±ours in a steel autoclave, cooled and s±redded. T±e
s±redder ±ad a set of ±orizontally aligned wedge-
s±aped cutters arranged in t±e form of an arrow ±ead,
moving against anot±er ²xed set of identical cutters.
T±e s±redded material passed t±roug± a series of four
follow-up operations for was±ing and pressure ex-
traction of t±e fermentable sugars. Compost samples
of t±e La Cofradía tequila factory originated from
an agave bagasse obtained as follows: agave ±eads
of tequilana Weber plants were cooked for 36 ±ours
in brick ovens, cooled and cut in a s±redder simi-
lar to t±at described above. T±e s±redded material
passed t±roug± two ²ber-pit± separators consisting
of ±orizontal stainless steel cylinders wit± a central
s±aft equipped wit± several sets of blades arranged
perpendicular to eac± ot±er to facilitate pit± detac±-
ment and to ensure adequate movement of t±e s±red-
ded material t±roug± t±e cylinder. T±roug± valves at
t±e top of t±e cylinder, water is injected for was±ing
t±e material. At t±e bottom, sieves allow t±e juices
and t±e detac±ed pit± to be collected and fermented.
T±e follow-up treatment was similar to t±at at t±e La
Regional tequila factory.
Agavae bagasse, t±e organic ²brous byproduct
emanating from bot± processes, was subsequently
composted for 126 days and sampled at de²ned
time intervals, and analyzed by scanning electron
microscopy, FTIR and t±ermogravimetric analyses.
Composting conditions
T±e composting process of La Cofradía and
La Regional agave bagasse ±as been reported by
Íñiguez
et al
. (2009). T±ese two sources of bagasse
were composted for 126 days in four piles, two for
eac± bagasse source. Ammonium nitrate (N
4
NO
3
)
was used as nitrogen source to adjust t±e agave ba-
gasse C:N ratio to 25:1, to favor t±e ²brous residue
biodegradation (Willson 1989, Rynk 1992). Every
week, t±e piles were moved to facilitate aeration and
added wit± water as needed to keep water content of
about 40-65 %, recommended for proper compost-
ing (Rynk 1992). T±e maximum temperatures of t±e
piles reac±ed on day 23 were 59 ºC and 60 ºC for La
Cofradía and La regional bagasse respectively. After
126 days of composting, bot± bagasses ±ad an eart±y
smell wit± a dark brown color.
Sampling and sample preparation
During t±e composting process, compost samples
were taken on days 0, 28, 56, 84, 112 and 126. On
every sampling date, nine samples were taken, t±ree
near t±e bottom, t±ree at t±e middle and t±ree near
t±e top of eac± composting pile. T±ese samples were
mixed into a composite sample w±ic± was air-dried
for furt±er c±emical and p±ysical analyses.
Analytical methods (measurement parameters)
Thermogravimetry
T±ermogravimetric analysis (TGA) was carried
out in order to evaluate t±e t±ermal stability of t±e
samples using a t±ermal analyzer Perkin Elmer model
TGA 7. In order to obtain good reproducibility t±e
G. Íñiguez
et al.
64
material was ground wit a pestle and an average of
approximately 7 mg of eac sample was used. T e
samples were eated from 40 to 600 ºC wit a eating
rate of 10 ºC min
–1
under nitrogen atmosp ere wit
a nitrogen Fow rate of 20 mL min
–1
.T e weig t loss
and its derivative (DTG) as a function of temperature
were recorded.
FTIR spectroscopic investigations
±or spectroscopic investigations, t e material was
ground wit a pestle in order to obtain good reproduc-
ibility of t e recorded spectra. Two milligrams of t e
sample were mixed wit 200 mg KBr (±T-IR grade)
and pressed into a pellet. T e pellet was immediately
measured after preparation in t e spectrometer using
t e transmission mode. T e measurements were car-
ried out in t e mid-infrared range 4000 cm
-1
to 400
cm
-1
wit a Nicolet model Protege 460 Magna ±TIR
spectrometer equipped wit OMNIC software. T e
resolution was set to 4 cm
–1
; 100 scans were recorded,
averaged for eac spectrum, and corrected against
ambient air as background.
Scanning electron microscopy (SEM)
T e morp ology of t e composted bagasse
samples were observed using a scanning electron
microscope JEOL JSM 6360 operated at 20 keV. T e
samples were coated wit gold prior t e analysis.
2.4.4. Chemical determinations
T e p² and conductivity were measured on aque-
ous extracts of 1g of eac sample treated wit 50 mL
of distilled water CWMI (1976). As , moisture and
total Kjelda l nitrogen (TKN) were determined as
described in t e Standard Met ods for t e Examina-
tion of Water and Wastewater (AP²A 1985). Total
organic carbon (TOC) content was calculated by
t e following equation (Golueke 1977): % TOC =
(100 – % as residue)/1.8. As residue was measured
after ignition at 550 ºC for 2 ours in a mufFe furnace.
T e C:N ratio was computed on t e basis of t ese
analyses. Total Na, Cu, Be, Al, Ba, Cd, Ca, Cr, Pb,
Co, ±e, Mg, Mn, Mo, Ni, P, K, Ag, Zn, Sb, Tl and V
were measured by ICP-AES after digestion wit an
aqua regia procedure according to TMECC (2001).
RESULTS AND DISCUSSION
Characterization using FTIR spectroscopy
T e most important bands found in t e spectra of
t e original agave bagasses and t eir usual be avior
during degradation are compiled in
table I
. T e
arrows indicate t e development of bands during
t e composting process. In
fgures 1
and
2
a great
resemblance can be observed between t e four ±TIR
spectra for t e original agave bagasse collected from
TABLE I.
SUMMARY O± RELEVANT IN±RARED ABSORPTION BANDS, T²E ±UNCTIONAL GROUP ASSIGNMENT AND
T²EIR DEVELOPMENT WIT² TIME DURING T²E COMPOSTING PROCESS
(↑ = INCREASE, ↓ = DECREASE,
→ = STEADY)
Wavenumber
(cm
–1
)
Vibration
±unctional group
or component
References
Development
(days)
< 28
> 28
3400
O-² stretc
Bonded and non-bonded
ydroxyl groups and water
Socrates (2001)
2920-2850
C-² stretc
Met ylene
Smit (1999)
1740-1720
C=O stretc
Alde yde, ketone,
carboxylic acids
Ouatmane
et al
. (2000)
Tan (1993), Smit (1999),
(Bodîrlău and Teacá 2009)
1640
C=O stretc
Carboxylates, amides I
Naumann
et al
. (1996), Smit (1999)
C=C stretc
Alkenes, aromatic compounds
²esse
et al
. (1995), Smit (1999),
Nanny and Ratasuk (2002)
1510-1520
Aromatic skeletal
Lignin and lignocellulose
Ouatmane
et al
. (2000), ±aix (1991)
1384
N-O stretc
Nitrate
Smit (1999), Smidt
et al
. (2002),
Zacc eo
et al
. (2002)
1320
C-N stretc
Aromatic prim. and sec. amines
Smit (1999)
1200-900
C-O-C, C-O
Polysacc arides
Grube
et al
. (1999)
1080
C-O-C, C-² stretc
Polysacc arides and
emicelluloses
Grube
et al
. (1999),
(Bodîrlău and Teacá, 2009)
C
ARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave tequilana
WEBBER BAGASSE
65
t±e tequila factories La Regional (pile 1 and pile 2)
and La Cofradía (pile 1 and pile 2) and t±eir resulted
composts. C±anges in t±e IR spectra of eac± sample
represent different stages of composting process (0,
28, 56, 84, 112 and 126 days). A broad band centered
at 3400 cm
–1
is due to t±e stretc±ing vibrations of
bonded and non-bonded ±ydroxyl groups as well as
water in t±e samples. T±is band was more marked
before initiating t±e composting period. At 28 days
and after t±is time, t±e O
band tends to decrease
and broaden, indicating t±at an environmental c±ange
in t±e groups ±as been initiated according to t±e
composting mec±anism (Smidt and Meissl 2007).
At zero time (before composting)
fgures
1
and
2
are practically similar for t±e two samples of agave
bagasse (La Cofradía pile 1 and pile 2, La Regional
pile 1 and pile 2). T±e results are not surprising given
t±at t±e two bagasse samples ±ave t±eir origin from
t±e same variety of agave plant (
Agave tequilana
Weber blue). T±e fermentable sugars extraction
system is t±e principal difference between t±e two
lignocelullosic residues, as mentioned in materials
and met±ods.
owever, despite t±is difference, t±eir
c±emical composition is basically t±e same, differ-
ing only quantitatively; for example, t±eir cellulose,
±emicellulose and acid detergent lignin content (Íñi-
guez
et al
. 2011). T±e decrease of t±e C-
stretc±ing
bands corresponding to alip±atic met±ylene bands at
2920 and 2850 cm
–1
can be an indicator of t±e deg-
radation process. T±ese alip±atic met±ylene groups
are part of many organic molecules present in t±e
samples. T±eir degradability varies in a wide range.
Fig. 1.
Relevant indicator bands and IR-spectroscopy c±aracteristics of different composting stages of La Cofradía agave bagasse
t=126 days
t=112 days
t=84 days
t=56 days
t=28 days
t=0 days
t=126 days
t=112 days
t=84 days
t=56 days
t=28 days
t=0 days
1520
1520
1384
1384
1320
1320
3400
2920
2850
1740
1640
1200
1160
1620
1620
1080
3400
2920
2850
1740
1640
1200
1160
1080
LA COFRAIDA PILE 1
LA COFRAIDA PILE 2
WAVENUMBER CM
–1
WAVENUMBER CM
–1
4000
3500
3000
2500
2000
1500
500
1000
4000
3500
3000
2500
2000
1500
500
1000
ABSORBANCE
ABSORBANCE
Fig. 2.
Relevant indicator bands and IR-spectroscopy c±aracteristics of different composting stages of La Regional agave bagasse
t=126 days
t=112 days
t=84 days
t=56 days
t=28 days
t=0 days
t=126 days
t=112 days
t=84 days
t=56 days
t=28 days
t=0 days
1520
1384
1320
3400
2920
2850
1740
1640
1200
1160
1620
1080
1520
1384
1320
3400
2920
2850
1740
1640
1200
1160
1620
1080
LA REGIONAL PILE 1
LA REGIONAL PILE 2
WAVENUMBER CM
–1
4000
3500
3000
2500
2000
1500
500
1000
WAVENUMBER CM
–1
4000
3500
3000
2500
2000
1500
500
1000
ABSORBANCE
ABSORBANCE
G. Íñiguez
et al.
66
Mineralization, volatilization or transformation
of easily degradable molecules and metabolites
cause t e most signiFcant decrease of t ese bands
wit in t e Frst weeks. T e decrease of t e alip atic
met ylene bands were more marked in t e spectra
of t e sample La Regional pile 1 in comparison wit
La Regional pile 2 (see
Fig. 2
). Nevert eless, accord-
ing to t ese bands, t e composting process was more
omogeneous for t e La Cofradía agave bagasse
since t e alip atic met ylene bands for pile 1 and 2
samples were very similar (
Fig. 1
). T e weak band at
1740 cm
–1
is caused by emicellulose; t is indicates
t e C=O stretc in non-conjugated ketones, carbonyls
and in ester groups (Owen and T omas 1989, ±ergert
1971, Bodîrlău and Teacá 2009). It appears as a
s oulder in t e fres La Regional and La Cofradía
agave bagasse samples (pile 1 and 2).
±owever, it
disappeared completely after 84 days of composting
in t e La Regional bagasse indicating decomposition
of t ose early metabolic products. In contrast, in
La Cofradía samples t is band did not disappear
completely. T is p enomenon probably was due to
t e different composting conditions between bot
bagasses. Unfortunately, a microbiological analysis
of bot bagasses (La Cofradía and La Regional) was
not carried out. T e band at 1640 cm
–1
(
Figs. 1
and
2
) t at is also attributed to t e C=O stretc ing vibra-
tion, is due to carboxylates (Smit 1999), amides I
(Naumann
et al
. 1996, Smit 1999) and to t e C=C
stretc ing vibration of alkenes and aromatic rings
(Smit 1999, ±esse
et al
. 1995, Nanny and Ratasuk
2002) s owing a divergent be avior. It means t at
t is band represents bot synt esis and decomposi-
tion in t e same composting process. ²ormation of
carboxylates due to t e release of carboxylic acids
from decomposed lipids contributes to t e rise as
well. W en degradation of substances t at absorb
at t is wavenumber exceeds synt esis, t e band
eig t decreases. Aromatic skeletal vibration from
lignin and lignocellulose absorbs at 1510-1520 cm
–1
(²aix 1991). Biowaste materials are identiFed by
t is weak but c aracteristic band. Despite its small
size, it is ardly overlapped by ot er bands and,
t erefore, is an indicator for biogenic waste of t e
agave bagasse and its composts. On t e ot er and,
t e development of t e band at 1510-1520 cm
–1
after
28 (La Cofradía pile 1, La Regional pile 1), 56 (La
Cofradía pile 2) and 84 days (La Regional pile 2)
of composting was probably due to t e amide for-
mation (overlapped amide II band formed at 1546
cm
–1
(Grube
et al
. 1999, Smit 1999). T ese amide
compounds can be promoted by t e addition of am-
monium nitrate (as a nitrogen source) to t e agave
bagasse at t e beginning of t e composting in order
to adjust t e C:N rate to 30:1. T e added nitrate
is visible as a narrow and constant band eig t at
1384 cm
–1
(
Figs.
1
and
2
) in all samples after t e 28
day of composting (Smidt
et al
. 2002, Smit 1999,
Zacc eo
et al
. 2002). Moreover t is band seems to
remain unaffected or wit small c anges during t e
composting process. T is fact can explain t e weak
presence of amide II observed at 1546 cm
–1
. T e
C-N band of aromatic amines at 1320 cm
–1
(Smit
1999) observed in bot
fgures 1
and
2
were s own
clearly at 28, 56, 84, 112 and 126 days of compost-
ing as t e result of t e microbial activity. T e C-
O-C and C-O vibrations of polysacc arides content
in t e initial agave bagasse samples are found in
t e region between 1200 cm
–1
and 900 cm
–1
(Tan
1993, Grube
et al
. 1999). At t e 28t day of com-
posting, t is band (
Figs. 1
and
2
) tended to ³atten
and lengt en, indicating polysacc arides started
being assimilated by t e microorganisms present
in t e compost w ic increases t e temperature in
t e pile. ²urt ermore, t e weak band (s oulder)
at 1160 cm
–1
and 1080 cm
–1
(at t e beginning of
composting,
fgure 1
and
2
) can also be assigned to
polysacc arides as reported by Grube
et al
. (1999),
w o found absorption bands of glycogen at t ese
IR frequencies. T is Fnding was conFrmed by t e
addition of starc or polysacc arides containing
components (miscant us, straw) to t e waste mate-
rial (Smidt 2001). ²inally, t e band at 1080 cm
–1
can be attributed to aromatic C-± bending t e plane
(Bodîrlău and Teacá 2009).
Characterization using thermogravimetric analysis
Figures 3(a)
and
4(a)
s ow t e t ermograms for
parent and composted La Cofradía and La Regional
agave bagasse samples (piles 1 and 2) after 0, 28, 56,
84, 112 and 126 days of composting. T ese Fgures
s ow t e percentage of residual weig t (percentage
of total sample weig t) as a function of tempera-
ture. It can be seen t at bot piles (pile 1 and 2)
of bot kinds of parent agave bagasses undergo a
major mass percentage of weig t loss in t e range
of 50-600 ºC. It is also evident t at, as t e number
of composting days increase, t e total weig t loss
in t e range 50-600 ºC decreases steadily; i.e., t e
residual weig t at 600 ºC increases monotonically.
Several aut ors ave pointed out t at t is be avior
is consistent wit t e compost stabilization process
(Dell’Abate
et al
. 1998, Melis and Castaldi 2004,
Gómez
et al
. 2007, Droussi
et al
. 2009), Som
et al
.
2009, Tsui and Juang 2010. ²inally, t e classical
de ydration process (Wielage
et al
. 1999, Wang
et
C
ARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave tequilana
WEBBER BAGASSE
67
al
. 2007, Carballo
et al
. 2008, Korosec
et al
. 2009)
is observed in all curves in t±e range 50-150 ºC;
w±ic± represents around 3 to 5 % of t±e total weig±t
of t±e samples. T±e derivative t±ermogravimetry
(DTG) curves are s±own in
fgures 3(b)
and
4(b)
for
parent and composted La Cofradía and La Regional
agave bagasses (piles 1 and 2) at 0, 28, 56, 84, 112
and 126 days of composting. In t±e DTG pro²les,
two principal ranges can be distinguis±ed between
150 and 600 ºC, w±ic± indicate t±e ±ig±est losses
of organic matter. T±e ²rst range lies between 150
and 400 ºC and t±e second one appears between
400 and 600 ºC. T±e peaks in t±e ²rst range can be
attributed to t±e pyrolysis of carbo±ydrates suc± as
±emicelluloses and cellulose, w±ereas t±e peak in
t±e range between 400 and 600 ºC are due to lignin
pyrolysis (Grandmaison
et al.
1987, Aggarwal
et al.
1997, Sun
et al.
1998, Álvarez
et al.
2005, Mo±an
et al.
2006, Yang
et al.
2007, Kumar
et al.
2008,
Luangkiattik±un
et al.
2008, Cagnon
et al.
2009).
T±ese are t±e main components present in t±e agave
tequilana bagasses. It is evident from
fgures 3
and
4
t±at, as t±e composting time increases, t±e
t±ermal be±avior of t±e samples taken from t±e
several piles c±anges as a result of t±e composting
process.
Table II
summarizes t±e weig±t loss (% of
total sample) corresponding to t±e 150-400 ºC and
400-600 ºC ranges and content (%) of sample c±ar
residue at 600 ºC obtained from t±e t±ermograms
of
fgures 3(a)
and
4(a)
. It can be seen t±at, as t±e
composting time increases, t±e weig±t losses in
t±e carbo±ydrates t±ermal decomposition range
decrease steadily, w±ereas t±e losses in t±e lignin
range remain practically constant. On t±e ot±er
±and, t±e c±ar yield also increases wit± composting
time. According to t±e literature t±is trend suggests
a progressive transformation of t±e biomass in t±e
macromolecules known as ±umi²ed matter. T±us
Fig. 3.
TG (a) and DTG (b) curves for t±e nitrogen pyrolysis of La Cofradía agave bagasse (piles 1and 2) before and after 0,
28, 56, 84, 112 and 126 days of composting
200
400
600
30
60
90
Residual Weight (%)
–1
–2
–3
–4
–5
–6
–7
0
1
DTG (wt. % min
–1
)
–1
–2
–3
–4
–5
–6
DTG (wt. % min
–1
)
Temperature (°C)
200
400
600
Temperature (°C)
200
400
600
Temperature (°C)
0 days
28 days
56 days
84 days
112 days
126 days
0 days
28 days
56 days
84 days
112 days
126 days
0 days
28 days
56 days
84 days
112 days
126 days
LA COFRADIA PILE 1
LA COFRADIA PILE 1
LA COFRADIA PILE 2
200
400
600
30
60
90
Residual Weight (%)
Temperature (°C)
0 days
28 days
56 days
84 days
112 days
126 days
LA COFRADIA PILE 2
(a)
(b)
G. Íñiguez
et al.
68
we obtain t e increase in molecular weig t, stabil-
ity, and aromatization degree during t e compost-
ing process (S arma 1990, Dell’Abate
et al.
1998,
Dell’Abate
et al.
2000, Li
et al.
2001, Ranalli
et
al.
2001, Zacc eo
et al.
2002, Melis and Castaldi
2004, Dresboll and Magid 2006, Spaccini and Pic-
colo 2007, 2009, Carballo
et al.
2008, Droussi
et
al.
2009, Som
et al.
2009).
In order to evaluate t e composting process, we
can use t e ratio between t e weig t loss associated
wit t e frst and t e second degradation steps (R1).
T e R1 was previously identifed as a reliable param-
eter For evaluating t e level oF maturation oF organic
matter in composts (Dell’Abate
et al.
2000, Mondini
et al.
2003, Mar uenda-Egea
et al
. 2007). T is value
indicates t e relative amount oF t e most t ermally
stable Fraction oF t e organic matter wit respect to
t e stable one. T e R1 ratio increases during com-
posting (
Table II
) t us revealing t e ig sensitivity
oF t is parameter to t e c emical c anges induced
by t e bio-transFormation oF organic materials. T e
variation in t e R1 ratio and c ar residues (%) during
t e composting process are similar For pile 1 and pile
2 oF eac parent bagasse; owever, it can be seen t at
t e apparent stability oF t e compost obtained From
t e La Regional bagasse is slig tly ig er t an t e
La CoFradía one.
Characterization using scanning electron mi-
croscopy
Scanning electron microscopy (SEM) micro-
grap s oF uncomposted (day 0) and composted
(day 126) La CoFradía and La Regional agave
bagasse fbers are s own in
fgures 5
and
6
. Bot
fbers (
Figs. 5a
and
6a
) s ow t e c aracteristic
surFace topograp y reported in t e literature For
ard fbers like sisal (Barkakaty 1976) and
en-
equén (Valadez-González
et al
. 1999).
Figure 5a
200
400
600
20
40
60
80
100
Residual Weight (%)
DTG (wt. % min
–1
)
DTG (wt. % min
–1
)
Temperature (°C)
0 days
28 days
56 days
84 days
112 days
126 days
LA REGIONAL PILE1
200
400
600
30
60
90
Residual Weight (%)
Temperature (°C)
0 days
28 days
28 days
56 days
112 days
126 days
LA REGIONAL PILE 2
200
400
600
-7
-6
-5
-4
-3
-2
-1
0
1
Temperature (° C)
0 days
28 days
56 days
84 days
112 days
126 days
LA REGIONAL PILE 1
100
200
300
400
500
600
-5
-4
-3
-2
-1
0
Temperature ( ºC)
0 days
28 days
56 days
84 days
112 days
126 days
LA REGIONAL PILE 2
(a)
(b)
Fig. 4.
TG (a) and DTG (b) curves For t e nitrogen pyrolysis oF La Regional agave bagasse (piles 1 and 2) beFore and aFter 0, 28,
56, 84, 112 and 126 days oF composting
C
ARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave tequilana
WEBBER BAGASSE
69
s±ows intact vascular bundles at t±e beginning of
t±e composting process covered by parenc±yma
cells w±ic± are ±ig±lig±ted by a w±ite contour. In
fgure 5b
a still intact vascular bundle is s±own at
t±e end of 126 days of composting process, covered
by lig±tly degraded parenc±yma cells s±owing pit-
ted cell walls (w±ite contour), fungal ±yp±ae and
exposed ²bers.
Figure 5b
s±ows t±e presence of
fungal ±yp±ae and spores at t±e surface of partially
degraded parenc±yma cells wit± strongly pitted and
locally cracked cell walls.
Figure 6a
, as in
fgure
5a
, s±ows intact vascular bundles at t±e beginning
of t±e composting process covered by parenc±yma
cells of different s±ape (see w±ite contour).
Fig-
ure 6b
presents vascular bundles at t±e end of t±e
126 composting period s±owing degraded surface,
fungal ±yp±ae and exposed vascular and ²brous tis-
sue.
Figure 6c
s±ows a magni²ed area indicated in
fgure 6b
t±at s±ows an exposed vessel wit± spiral
t±ickening, fractures and breakdown areas of cell
walls, and fungal ±yp±ae.
Table III
presents some c±emical c±aracteristics
of t±e composts obtained of t±e agave bagasse from
t±e tequila factories La Cofradía and La Regional.
Bot± composts presented low p
values (5.5 and
5.8) in comparison to ot±er composts. For instance
Íñiguez
et al
. (2005) reported p
values of 9.2, 9.1,
9.1 and 9.1 for composts prepared wit± uncooked
agave bagasse, uncooked agave bagasse compos-
ted wit± tequila vinasses, uncooked agave bagasse
enric±ed wit± urea, and uncooked agave bagasse
enric±ed wit± urea composted wit± tequila vinasses.
For t±e C:N ratio it can be concluded bot± studied
composts were mature composts.
arada
et al
.
(1981) concluded t±at a mature compost product
s±ould ±ave a C:N ratio of less t±an 20:1. [Before
composting (0 day) t±e C:N ratio was 25:1 for bot±
agave bagasse] (Íñiguez
et al
. 2011]. Practically in
all t±e c±emical elements analyzed, except for Na
and Be, t±e elements concentration was ±ig±er for
compost produced wit± La Regional agave bagasse
t±at compost produced wit± La Cofradía agave
bagasse. T±is is due to t±e different met±ods of ob-
taining t±e agave bagasse described in t±e met±ods
section w±ere t±ere is a very marked difference in
t±e extraction system of fermentable sugars. T±is
marked difference refers to a ²brous material and
pit± content of 65.6 % and 34.4 % respectively for
t±e La Cofradía agave bagasse, w±ereas for t±e La
Regional agave bagasse, t±e ²brous material and
pit± content were 43.7 % and 56.3 % respectively
after passing t±e agave bagasse samples t±roug± a
sieve wit± an opening of 1cm (wet basis analysis)
(Íñiguez
et al
. 2010). On t±e ot±er ±and, Íñiguez
et
al.
(2010) reported different contents of ±emice-
lulose, cellulose, and acid detergent lignin (ADL)
content for bot± bagasses before composting. For
La Cofradía agave bagasse, t±e ±emicelulose, cel-
lulose and ADL content were 7.9, 14.2 and 32.3 %
respectively, w±ereas La Regional agave bagasse,
t±e ±emicelulose, cellulose and ADL content was
14.8, 14.1 and 28.8 % respectively.
Of all potential quality standards in compost, t±at
of ±eavy metals ±as been t±e focus of most attention.
In t±e case of ±eavy metals (Cu, Cd, Cr, Pb, Ni, Zn)
in t±e compost of La Cofradía and La Regional, no
problems are expected in t±e application of t±ese
composts in agricultural soils according to ±eavy
metals limits (mg/kg) for some European countries
and t±e USA. For instance, t±e ±eavy metals limits
TABLE II.
MASS LOSSES (% OF TOTAL SAMPLE) CO-
RRESPONDING TO T
E MAIN EXOT
ERMIC
REACTIONS AND CONTENT (%) OF SAMPLE
RESIDUE AT 600 ºC FOR T
E LA COFRADÍA
AND LA REGIONAL PILE 1 AND 2. R1 REFERS
TO T
E 2
nd
STEP MASS LOSS TO T
E 1
st
STEP
MASS LOSS RATIO
Composting
Mass loss
(%)
Mass loss
(%)
Residue
Time (days)
1
st
step
2
nd
step
(%)
R1
0
a
52.00
18.20
23.20
0.350
28
51.38
17.42
24.90
0.339
56
46.80
18.50
29.00
0.395
84
42.60
18.00
34.10
0.423
112
41.35
17.90
35.60
0.433
126
37.40
18.15
39.85
0.485
0
b
52.90
18.20
23.20
0.344
28
47.80
18.00
28.20
0.377
56
45.60
18.90
28.70
0.414
84
45.00
19.00
31.70
0.422
112
41.00
18.80
35.70
0.459
126
37.30
17.30
41.40
0.464
0
c
54.00
20.00
20.00
0.370
28
49.20
19.00
25.50
0.386
56
45.70
21.30
27.00
0.466
84
38.70
18.30
36.00
0.473
112
34.13
16.62
41.00
0.487
126
32.70
18.20
43.00
0.557
0
d
54.00
20.00
20.00
0.370
28
50.00
19.50
24.50
0.390
56
47.50
20.00
26.50
0.421
84
43.10
18.90
31.70
0.439
112
36.70
18.40
37.90
0.501
126
35.00
18.50
40.50
0.529
a
La Cofradía pile 1
b
La Cofradía pile 2
c
La Regional pile 1
d
La Regional pile 2
G. Íñiguez
et al.
70
Fig. 6.
SEM micrograp s of La Regional agave bagasse Fbers composted at 0 (a) and 126 days (b,c) (Pile 1)
a
b
c
a
c
b
Fig. 5.
SEM micrograp s of La Cofradía agave bagasse Fbers composted at 0 (a) and 126 days (b,c)
(Pile 1). T e asterisk (*) s ows locally cracked cell walls
C
ARACTERIZATION OF DIFFERENT DECOMPOSITION STAGES OF
Agave tequilana
WEBBER BAGASSE
71
TABLE III.
C
EMICAL C
ARACTERISTICS OF TWO COMPOSTS OBTAINED OF
LA COFRADÍA AND LA REGIONAL AGAVE BAGASSE
C±aracteristic
a
Compost
La Cofradía
La Regional
p
5.5
²
0.12
5.8
²
0.22
Total Kjelda±l nitrogen (%)
3.0
²
0.50
3.1
²
0.60
Total organic carbon (%)
49.0
²
1.15
42.5
²
1.50
C/N ratio
16.2
14.8
As± (%)
b
11.8
²
1.00
18.6
²
0.9
P
b
676.84
²
81.40
1 619.34
²
49.77
K
b
3 576.63
²
394.74
6 067.96
²
251.72
Ca
b
6 931.00
² 6 556.67
17 196.60
² 17420.23
Mg
b
1 711.17
²
109.35
17323.62
² 17366.45
Na
b
565.53
²
21.09
494.34
²
29.75
Cu
b
3.36
²
3.75
10.62
²
0.43
Be
b
2.05
²
2.30
1.00
²
0.04
Al
b
447.30
²
123.57
1 041.67
²
62.36
Ba
b
62.35
²
50.30
40.58
²
19.56
Cd
b
0.13
²
0.15
0.31
²
0.07
Cr
b
0.89
²
0.92
2.12
²
0.62
Pb
b
0.53
²
0.59
2.43
²
1.33
Co
b
0.45
²
0.01
1.12
²
0.29
Fe
b
361.93
²
26.58
091.83
²
48.63
Mn
b
37.55
²
1.42
73.38
²
1.26
Mo
b
1.36
²
0.14
3.79
²
0.38
Ni
b
0.73
²
0.80
1.99
²
0.17
Ag
b
<0.04
<0.29
Zn
b
81.00
²
4.51
116.14
²
24.31
Sb
b
1.27
²
0.48
4.20
²
0.75
Tl
b
50.35
²
4.41
77.43
²
1.60
V
b
3.79
²
0.33
9.22
²
0.19
a
Mean and standard deviation of two compost piles
b
mg kg
–1
, dry basis
in t±e
USA for Cd, Cr, Cu,
g, Ni, Pb and Zn are
0.7-10, 70-200, 70-600, 0.7-10, 20-200, and 70-1.000
and 210-4.000, respectively (Brinton 2000).
CONCLUSIONS
T±e results s±owed t±at IR spectroscopy as well as
TG/DTG analysis gave complementary information
on t±e c±emical c±ange composition of t±e initial and
partial composted agave bagasse materials. Furt±er-
more, bot± tec±niques ±ave proven to be appropriate
tools for assessing t±e degree of stabilization obtained
by organic matter under aerobic treatment. Alt±oug±
minimal c±anges were observed by t±e FTIR analysis
concerning t±e c±emical composition of La Regional
and La Cofradia bagasses samples during t±e com-
posting process, environmental c±anges are clearly
detected in early stages, suc± as 28 days. Moreover, in
all samples t±e presence of some metabolic products
suc± as alde±ydes, ketones and amides during inter-
media stages was observed. In addition, some of t±ose
compounds were lost in t±e last stages as a result of
progressive biodegradation of t±e organic matter. On
ot±er ±and, it was found t±at agave bagasse (wit±out
composting) ±ad t±e ±ig±er mass percentage loss in
TGA and t±ese losses diminis±ed as t±e composting
process progressed. DTG and FTIR results agreed in
t±at agave bagasse samples are principally composed
of ±emicelluloses, cellulose and lignin. In particular,
evaluation of TG/DTG curves allowed for clearly
distinguis±ing t±e stages of agave bagasse stabiliza-
tion. In fact, t±e R1 parameter based on compost
TG and DTG curves increased wit± t±e progress
of t±e composting. Finally, by analyzing scanning
electronic microscopy samples of agave bagasse
during composting, it was found t±at bagasse was
susceptible to being attacked by fungi w±ic± leads
to t±e breakdown of t±e vascular bundle and may
represent an improvement in t±e water retention ca-
G. Íñiguez
et al.
72
pacity of bagasse and can be used as a substrate for
t e production of green ouse vegetables.
ACKNOWLEDGMENT
T e aut ors want to acknowledge t e contribu-
tion of Roger M. Rowell Professor Emeritus of t e
University of Wisconsin-Madison for t e assistance
in t e preparation and invaluable comments on t e
manuscript. Also t anks to Q.I Tanit Toledano-
T ompson for t e SEM p otomicrograp s and to
±ilda Palacios Juárez and ±. G. Ric ter for t e elp
wit t e interpretation of t e SEM images.
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