ORIGINAL PAPER

Eco-friendly Technologies Based on Banana Peel Usefor the Decolourization of the Dyeing Process Wastewater

Carolyn Palma • Elsa Contreras • Johana Urra •

Marıa Jesus Martınez

Received: 12 March 2010 / Accepted: 26 October 2010

� Springer Science+Business Media B.V. 2010

Abstract This study analyzed some alternatives to the

valorization of agricultural residues considering its use in

the treatment of colored effluents. The acid–base behavior

of the banana peel surface was thus determined in order to

establish the feasibility of its use as a bioadsorbent for

dyes. The adsorption capacity of Acid Black 1 was eval-

uated, through the equilibrium isotherm and the kinetics of

this uptake process was also analyzed. Additionally,

banana peel was used as substrate-support to evaluate the

growth of Inonotus sp SP2, Stereum hirsutum RU 104 and

Pleurotus eryngii IJFM 169 and their ligninolytic enzymes

production. The decolourization ability of strain fungi was

moreover screened. The concentration of functional basic

groups in the banana peel surface was determined in

5.5 mmol g-1 as six and a half times higher than acid

groups, while the lowest value of the maximum adsorption

capacity of Acid Black 1 was 250 mg g-1. The adsorption

kinetics of this dye was suitably represented by a pseudo

second order model, obtaining correlation coefficients

greater than 0.98. Additionally, the banana peel was

demonstrated to be a source of carbon available for growth

of the fungi studied. Reducing sugars supplied for banana

peel were abruptly consumed up to the 5th day by S.

hirsutum and Inonotus sp, while a slower consumption was

observed in the case of P. eryngii. Manganese Peroxidase

was produced by the three fungal strains, Inonotus sp.

additionally produces Laccase and Aryl-alcohol oxidase.

Screening assays showed that all of the dyes were decol-

orized, resulting in efficiencies between 50 and 99% by the

three strains, with the exception of Basic Violet 4. Acid

Black 1 was decolorized efficiently by Inonotus sp and S.

hirsutum. In conclusion, banana peel is a promising

material for development of an integral bioremediation

strategy for wastewater containing hazardous compounds.

Keywords Agricultural waste � Valorization � White rot

fungi � Banana peel � Dye

Introduction

A significant amount of lignocellulosic biomass is gener-

ated every year during cultivation, harvesting, processing

and consumption of agricultural products, such as straw,

stover, stalks, seeds, bagasse, peels, among others [1].

There are opportunities for adding—value to these ligno-

cellulosic residues using them as raw material to produce

biosorbents and low-cost adsorbents [2], support-substrate

for the production of biomass, enzymes and metabolites [3,

4], or feedstock for producing biofuels and biochemicals

[5]. Additionally, using these residues to obtain value-

added products can contribute to their removal from the

environment, avoiding their handling as solid waste [6].

Fungi, the major recyclers of carbon, are decomposers-

organisms capable to hydrolyze complex organic compounds,

such as agricultural waste. At present many filamentous fungi

are utilized as producers of enzymes of industrial interest

using same lignocellulosic residues as a source of carbon and

energy. The use of the agricultural residues as a nutrient source

for microorganisms of biotechnological interest is an alter-

native which continues to be explored. White rot fungi (WRF)

have been extensively studied for their ability to produce

C. Palma (&) � E. Contreras � J. Urra

Chemical Engineering Department, Universidad de Santiago de

Chile, Alameda 3363, Estacion Central, Santiago, Chile

e-mail: carolyn.palma@usach.cl

M. J. Martınez

Centro de Investigaciones Biologicas, CSIC,

Ramiro de Maeztu 9, E-28040 Madrid, Spain

123

Waste Biomass Valor

DOI 10.1007/s12649-010-9052-4

extracellular ligninolytic enzymes usually during the sec-

ondary metabolism, which are involved in the degradation of

lignin and other recalcitrant aromatic compounds [7, 8]. The

white rot fungi are able to produce various kinds of lignino-

lytic enzymes such as laccase and peroxidase in liquid or

solid-state fermentation cultures [9, 10], but their secretion

depends on the type of fungi, the strain and the culture con-

ditions. In all cases, a good carbon/nitrogen ratio is necessary

to make fungi grow, and glucose is the more usual carbon

source when using a defined medium. The search for alter-

native sources of nutrients, such as agricultural residues, has a

double advantage: they add value to this waste while lowering

the costs of producing enzymes.

Another interesting feature of lignocellulosic residues is

the physical–chemical properties of the functional groups

available on their surface. These groups are responsible for

the adsorption capacity of some specific solutes through

ionic interactions. Naturasorbents have been obtained from

agricultural waste, such as corn cobs, coconut shell, sugar

cane bagasse and fruit peel like orange and banana [2].

Banana peel is a solid waste with high carbohydrate

content, around 60% of dry matter. It is thus possible that it

supports fungal growth [3]. The production of bananas and

plantains in the world exceeded 94 million tons by 2008,

with Africa, Latin America and the Caribbean being the

major exporters [11]. At the time of harvest, a banana plant

is estimated to have a weight of 100 kg, of which 15 kg

correspond to leaves, 50 kg to pseudo-stalks, 33 kg to fruits

and 2 kg to rachis [12]. At harvest, the percentage of

rejected products due to size, contamination, handling,

transport and storage is estimated at about 20% [13]. The

proportion of the banana which is wasted as peel is 18–20%.

The disposal, minimization and valorization of this organic

waste have become a major task. In Central America for

example, the wastes from both, banana farming and com-

mercial packaging, are normally disposed in large open-air

dumps located in the same plantations, where the decom-

position process is very slow due to high fibre contents.

Additionally, bacterial degradation is affected by the pres-

ence of chemicals in the disposal area. Poor disposal and

lack of an appropriate treatment for these bio-degradable

wastes also causes the proliferation of pathogenic organ-

isms. At the same time, the lixiviated liquid causes a neg-

atively impact over soil and groundwater [14].

The immediate use of this waste has been for animal

feed but there are periods of restricted use, such as when

natural forage is plentiful. Banana residues are highly

fermentable due to the high starch content while still green

(about 72% dry basis). Then during ripening, the presence

of simple sugars (saccharose, glucose and fructose) facili-

tates silage [15]. The fibers extracted from banana leaves

and stem have been used in the production of particle

boards for construction of social housing [16, 17]. From the

environmental standpoint, the banana peel has been used as

bioadsorbent of soluble contaminants, such as dyes [2],

metals [18, 19], and phenolic compounds [20]. In addition,

its use in the production of pectin [21, 22] and ethanol [23,

24], as well as for production of biomass and metabolites of

biotechnological interest [3, 4, 25], has also been reported.

The release of dyes into industrial wastewater causes

serious environmental problems, because their chemical

structure gives them a persistent and recalcitrant nature. The

discharge into natural waterways may have an inhibitory

effect on photosynthesis affecting aquatic ecosystem.

Besides, dye molecules are broken down during the anaer-

obic processes occurring in the sediment, generating toxic

amines that may also pose a serious environmental problem.

According to this background, it is interesting to explore

the feasibility of colored wastewater bioremediation by a

ligninolytic enzyme system of white rot fungi using banana

peel as substrate-support. This substrate contains biopoly-

mers, such as starch, cellulose and lignin, whose functional

groups may have a significant affinity for the adsorption of

dyes. Therefore, it is important to determine which exten-

sion belongs to the process involved: bioadsorption and

biodecolorization.

The aim of this study was to analyze some alternative

valorization of agricultural residues, considering its use in

the treatment of colored effluents. The physical–chemical

properties of the banana peel surface were determined in

order to establish the feasibility of its use as dyes bioad-

sorbent. Additionally, banana peel was evaluated as sub-

strate-support for the growing Inonotus sp SP2, Stereum

hirsutum RU 104 and Plerotus eryngii IJFM 169, and the

ligninolytic enzymes secreted by these fungi during the

biodecolorizing process were evaluated. Finally the ability

of decolorization/degradation of various types of dyes by

these fungal strains was investigated.

Materials and Methods

Agricultural Waste

Banana peel (Mussa ssp) was obtained from fruit

(CHIQUITA) purchased at a local market. The banana

fruits were selected according to their ripening classifica-

tion based on the Color Index corresponding to stage 6 or

entirely Yellow [26]. The banana peel (BP) was dried in an

oven for 1 week, reaching the equilibrium moisture content

of around 10.5% (wt). Then the solid waste was crushed

and screened, selecting the [-18 ? 60] mesh cut which

corresponds to particles larger than 0.25 mm and smaller

than 1 mm. The sample was then separated using different

opening of the superior sieve, obtaining three cuts which

are denominated 0.25, 0.5 and 1 mm.

Waste Biomass Valor

123

Dry matter, ash and nitrogen contents of BP were

determined by a Proximate Analysis and the elemental

composition (C, H and O) was obtained by Ultimate

Analysis. Furthermore, the correlation between the con-

tents of BP in the culture medium and the concentration of

the available reducing sugars were established.

Microorganisms

Inonotus sp SP2 and Stereum hirsutum RU 104, (isolated in

the Araucanıa region of southern Chile by the group of

researchers at the Laboratory of Environmental Biotech-

nology, University of La Frontera) and Pleurotus eryngii

IJFM 169 (provided by Dr. Maria Jesus Martinez from

CIB-CSIC, Madrid, Spain). The fungi were maintained on

malt extract agar plates at 4�C.

Dyes

The dyes used were as shown in Table 1. All of them were

of analytical grade and from Sigma–Aldrich Co.

Physical Characterization of Banana Peel

Density

Density is evaluated with the mercury intrusion technique

using the Porosimeter 2000 instrumental equipment

(CARLO ERBA INSTRUMENTS).

Particle size Distribution

Particle size Distribution is determined by laser diffraction

using the Mastersizer X equipment (MALVERN

INSTRUMENTS, MSX1). In this analysis a wet method

was used. The sample was dispersed in a support solution,

which is not soluble and does not alter its physical and

chemical properties.

Specific Surface

Specific Surface is determined by nitrogen gas adsorption

according to Brunauer, Emmett and Teller (BET) isotherm

method. In comparison, Methylene Blue (Basic Blue 9)

adsorption using the Langmuir isotherm was also obtained.

Samples with an initial concentration between 50 and

600 mg L-1 of dye and a dose of 2 g of BP per liter of

solution were used. These samples were continuously

stirred in a thermostated shaker at 20�C for 24 h. Finally

the residual dye concentration in the solution was deter-

mined by visible spectrophotometry at 665 nm (Helios

Gamma UV–vis spectrophotometer).

Physical–Chemical Characterization of Banana Peel

Surface

Surface Acidity and Basicity

Surface acidity and basicity were determined by potentio-

metric titration of the sodium hydroxide or chloride acid

excess, after contacting 0.5 g of BP with 50 mL of NaOH

0.01 M (acidity) or 50 mL of 0.1 M HCl (basicity) until the

equilibrium was reached. An aliquot of 20 mL filtrate obtained

from contact assay (24 h) was then analyzed by titration with

0.01 M HCl (acidity) or 0.1 M NaOH (basicity) [27].

Point Zero Charge (pHPZC)

Point zero charge (pHPZC) a set of BP suspensions were

prepared adding 10, 7.5, 5, 2.5 and 1.25 mL of 0.1 M HCl

to 1 g of BP. Similarly, BP suspensions were prepared with

the same volumes of 0.1 M NaOH. Then, in all cases 5 mL

of KCl 0.1 M were added and the volume was completed

with distilled water until 100 mL. A sample with KCl

0.1 M and distilled water was also included. The flasks

were agitated for 1 h and then, pH values (pH1) were

recorded. Subsequently 5 mL of KCl 1 M were added to

each sample, maintaining the agitation an extra 1 h. Then

the final pH of each sample (pH2) was measured. The pH

solution value, which makes the surface charge of BP is

equal to zero, was determined by the method informed by

Navas and Carrasquero [28].

Bioadsorption of Dyes In Banana Peel

Determination of Contacting Time

Determination of contacting time 50, 200 and 500 mg L-1

of AB1 dye solution was contacted with 2 g L-1 dose of

BP. The dynamic process was identified through the evo-

lution of residual concentration of dye in solution for dif-

ferent contact times. For this, the BP was separated by

filtration and the dye concentration of filtrate was deter-

mined by absorbance measurements in a UV–Vis spec-

trophotometer (Spectronic Helios Gamma model) at

maximum absorbance wavelength.

Adsorption Dyes Isotherms

2 g L-1 of BP was contacted with different concentration

of AB1 dye solution (50–500 mg L-1) in the thermostatted

and agitated system (20 ± 2�C, 150 rpm) during 2 days.

The samples were filtrated in a vacuum system and the dye

concentration in the solution was determined by the

absorbance measures at maximum wavelength in a Helios

Gamma model UV–Vis spectrophotometer.

Waste Biomass Valor

123

Growth, Decolorization Ability and Ligninolytic

Enzyme Production of Fungi

Previous studies indicate that strains of Inonotus sp SP2

and Stereum hirsutum RU 104 grow in media with

10 g L-1 glucose; in contrast Pleutorus eryngii requires

twice the concentration of glucose. Experiments were

designed based on this information. In the assays using BP,

the equivalent concentration of BP was added.

Carbon Assimilation

Carbon assimilation a pre-inoculate was prepared in a

Fernsbatch (2 L) which contained 10–12 plugs (5 mm in

diameter) as an inoculate with 100 mL of sterilized

glucose-peptone medium (5 g L-1 peptone, 2 g L-1

Malt Extract, 1 g L-1 KH2PO4, 0.5 g L-1 MgSO4

7H2O). The cultures were incubated at 28�C for

5–8 days. Then, the mycelium was homogenized and

Table 1 Characteristics of dyesDye Chromophore k (nm) Structure

Acid black 1 (AB1) Diazo 618.5

Acid red 27 (AR27) Azo 522.5

Basic blue 41 (BB41) Azo 617.0

Basic blue 24 (BB24) Thiazine 633.0

Basic orange 2 (BO2) Azo 454.0

Basic violet 4 (BV4) Triphenylmethane 595.0

Reactive black 5 (RB5) Diazo 597.5

Reactive blue 19 (RB19) Anthraquinone 592.5

Reactive orange 16 (RO16) Azo 493.0

Waste Biomass Valor

123

inoculated in a 10% (v/v) proportion in Erlenmeyer

flasks (250 mL) which contained 81 mL of BP-peptone

medium. In this medium the glucose was replaced by

36.16 and 60.56 g L-1 BP, for Inonotus sp SP2, Stereum

hirsutum RU 104 and Pleutorus eryngii, accordingly.

The cultures (in triplicate) were incubated at 28�C in a

shaker, at 150 rpm. Reducing sugars were determined by

the dinitrosalicylic acid method, using D-glucose as a

standard [29].

Decolorization Screening

This test was carried out in order to establish the degrading

capacity of the recently isolated strains Inonotus sp and

S. hirsutum. The assay was conducted in an Erlenmeyer

(100 mL) flask covered with cotton and gauze stoppers,

with 1.5 mL homogenized mycelium and 13.5 mL of

glucose-peptone medium supplemented with 50 and

100 mg L-1 of dyes. The medium was autoclaved. Biotic

and abiotic controls were carried out in parallel. The biotic

controls were realized with mycelium and culture medium,

and abiotic controls consisted of water and culture medium

supplemented with dye. All cultures (in triplicate) were

incubated for 15 days at 28�C in an air atmosphere with

100% relative humidity.

Enzyme Activities

Laccase activity was measured using 5 mM 2,6-dime-

thoxyphenol (DMP) in 100 mM sodium citrate buffer

(pH 5.0; e469 = 27,500 M-1 cm-1, referred to DMP

concentration) [30]. Mn– oxidizing peroxidase activity

(named as MnP) was estimated by the development of

Mn?3-tartrate complex (e238 = 6,500 M-1 cm-1) during

the oxidation of 0.1 mM MnSO4 in 100 mM sodium

tartrate buffer (pH 5) in the presence of 0.1 mM H2O2

[31]. Lignin peroxidase (LiP) activity was determined

with 2 mM veratryl alcohol in 0.1 M sodium tartrate at

pH 3 and 0.1 mM H2O2 [32]. Aryl-alcohol oxidase

(AAO) was determined by the development of veratral-

dehyde from 5 mM veratryl alcohol 0.1 M sodium

phosphate, pH 6 [33].

Results and Disscusion

Characterization of Banana Peel

The pore size distribution of BP shows that the 40% of void

volume has pore radius lower than 1 l, the remaining 60%

corresponds to macropores, which leads to denominate this

biomaterial as mesoporous. Consequently its density is

1.45 g L-1. The surface structure of these particles was

observed with scanning electron microscopy (SEM). The

electron micrographs revealed that the particles are of

irregular shape and its surface exhibits a micro-rough

texture, which can promote the adherence of the mycelium

in a similar way to that found in natural habitats (Fig. 1).

The particle size distribution of cut-off so-called 0.25 mm

shows that the mode and median of the frequency distri-

bution curve are 72.50 and 50.36 lm, respectively. These

results agree with the mean particle size corresponding to

57.49 lm.

The specific surface determined by the BET method has

a very low value of 5 m2 g-1, probably due to de opera-

tional complexity for degassing samples lignocellulosic

[34]. Other authors have reported values of specific surface

for BP between 13–23.5 m2 g-1 using the same method

[18, 35]. On the other hand, estimation of the same prop-

erty by the methylene blue adsorption method yielded

Fig. 1 SEM analysis of banana

peel. a inside surface b outside

surface

Waste Biomass Valor

123

510.2 m2 g-1, value which has the same order of magni-

tude that obtained for other bioadsorbent of low-cost such

as bamboo cane, olive stones, peanut shells, peat moss

(350–550 m2 g-1) [36, 37].

The carbon and nitrogen contents in BP were 41.1 and

1.27 (wt)%, respectively (Table 2). These results make BP

an alternative substrate well-suited for carrying out the

enzyme production processes [4]. BP also presents signif-

icant oxygen contents (33.4 (wt) %) from carbohydrates

and fiber, which are in the range of those report in the

literature are 59 and 32 (wt) %, respectively [3, 37]. This

high content of polymers, such as cellulose and hemi-cel-

lulose, suggest that BP could be a promising bioadsorbent

of synthetic organic contaminants, such as dyes [38].

The mechanism governing the adsorption of the syn-

thetic organic compounds into lignocellulosic waste is

difficult to predict, since their diverse origin prevents us

from knowing the chemical structure and the functional

groups existing in the particle surface. The physicochem-

ical characterization of the bioadsorbent surface, in par-

ticular the acid—base behavior of functional groups, might

play a crucial role in ionic interactions occurring during the

process, and thus it is fundamental to postulate the mech-

anisms involved, such as complexation reactions, ionic

exchange and electrostatic interactions, among others. For

example, the selective uptake of basic dyes on starch–based

polymer was achieved by ionic exchange mechanism

involving the acid carboxylic groups [39]. The deproto-

nation of these functional groups contributed to the

adsorption occurring by electrostatic interactions between

the COO- and cationic groups of basic dyes [40]. During

the adsorption of the dyes, there were interactions between

the ionic groups of the dye and the opposite polarity of the

adsorbent sites. The higher the available number of sites

capable of polarization and the stronger the interaction with

the dye molecules, the greater the adsorption capacity of

the biosorbent [41]. All bioadsorbents are characterized by

having two main regions with a buffering capacity in the

pH region between 3–5 and 8–10. According to the

literature, the first zone could correspond to carboxylic

groups and the second, to hydroxyl groups [42].

The knowledge of pHpzc allows us to hypothesize on the

ionization of functional groups and their interaction with

ionic species in solution. The zero-charge point of BP cor-

responds to solution pH value of 2.41 (Fig. 2). This result is

of the same order of magnitude as that reported value for

peat moss which is 3.1, so it indicates that the concentration

of basic sites is greater than that of acid sites and therefore

BP can be classified as a bioadsorbent with a basic character.

The concentrations of adsorption sites of acidic type and

basic type corroborate this result. Indeed, the concentration

of basic functional groups is six and a half times higher than

acids, i.e. 5.50 and 0.84 mmol g-1, respectively. Moreover,

the basicity is five times higher than the values informed for

peat moss and activated carbon (F-400), while the acidity is

in the same order of magnitude. If the pH of a solution is

higher than the value of pHpzc, the surface of the biosorbent

has a negative net charge since the acid groups are de-pro-

tonated and could preferably interact with cationic species.

In solutions with a lower pH than pHpzc, the net charge of

solid surface is positive since the basic groups have the

ability to share electrons, i.e., they are proton acceptors, and

could do with those negatively charged. According to these

results, BP could be a low-cost bioadsorbent to uptake acid

dyes from industrial wastewater.

Adsorption of Acid Black 1 dye

According to the contact times studied, it was established

that the equilibrium between AB1 and BP is reached at 30 h,

period in which removal was achieved up to 80% for oper-

ating conditions corresponding to particle size identified as

0.25 mm and 500 mg L-1 of dye. The system was operating

unbuffered, so that the process was conducted at the pH

given by the dye solution (6.5). At this pH value, the charge

of the BP surface is slightly negative (Fig. 2) and therefore

Table 2 Chemical composition of banana peel

Method

Carbon Ultimate analysis 41.1% (Dry wt.)

Hydrogen Ultimate analysis 5.32% (Dry wt.)

Oxygen Ultimate analysis 33.4% (Dry wt.)

Total solid AOAC 17 15.7% (wt)

Nitrogen AOAC 992.23 MOD combust 1.27% (wt)

Ash AOAC 18 17.3% (wt)

Chloride AOAC 16 1.47% (wt)

Sulfur AOAC 990.08C, EPA 2007 855 mg kg-1

Phosphorus AOAC 990.08C, EPA 2007 1,749 mg kg-1

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0 2 4 6 8 10 12

pH Suspension

pH2-

pH

1

0.25 mm 0.5 mm 1 mm

Fig. 2 Point zero charge of banana peel

Waste Biomass Valor

123

there will be medium-scale repulsive forces with AB1 dye.

The kinetic of the dye removal process under the studied

conditions was accurately interpreted by a pseudo second

order model [43] shown in the following Eq. 1.

dqt

dt¼ k2 qe � qð Þ2 ð1Þ

where the integrated form, considering the following

boundary conditions, is presented in Eq. 2: t = 0 =[qt = 0 and t = t =[ qt = qt

qt ¼t

1k2q2

eþ t

qe

: ð2Þ

k2 is the kinetic rate constant (g mg-1 min-1) qe is the

maximum capacity of adsorption (mg g-1) and, k2 qe2 = h

represents the initial rate of adsorption (mg g-1 min-1)

Table 3 provides information on model parameters

obtained for each particle size. The effect of particle size

was observed for initial dye concentrations above

200 mg L-1, for example, the maximum capacity of

adsorption decreased approximately 40% for the largest

particle size (1 mm). Moreover, for the particles of smaller

size (0.25 and 0.5 mm) the maximum capacity of adsorp-

tion increased when increasing the initial concentration of

dye, tripling its value. An effect of initial dye concentration

in the kinetic rate constant was observed for all particle

size studied. The highest value of kinetic rate constant was

obtained for the lower concentration. The result indicated

that this concentration is insufficient to saturate the outer

surface of the particle and therefore the adsorption process

is governed by the diffusion of the dye from the bulk

solution to the solid–liquid interface. If the system is

operating with the higher concentrations, the driving force

is greater and therefore the sites of the outer surface are

saturated. The mechanism which controls the process is

under these conditions, the intraparticle diffusion through

of the mesopores. The combined effect of both phenomena

causes the lower value of the kinetic rate constant to be

obtained at 250 mg L-1 of dye. No significant effect was

observed from these variables in the initial rate of dye

uptake process with the exception of smaller particle size.

Although there are many models proposed in the liter-

ature to describe the equilibrium biosorption, the most used

are the Langmuir and Freundlich isotherms, which are

shown in Eqs. 3 and 4.

qe ¼kLqmCe

1þ kLCeð3Þ

qm: maximum adsorption capacity (complete monolayer)

(mg g-1) which correspond to the ratio between

parameters kL and aL, kL: affinity between sorbate and

adsorbent (L g-1), aL: parameter associated with the

energy of adsorption (L mg-1)

qe ¼ kFC1n

e ð4Þ

kF: equilibrium constant (mg g-1 (L mg-1)1/n, n: parame-

ter associated with the affinity between sorbate and

adsorbent)

Figure 3 presents the equilibrium concentration of

adsorption of AB1 dye on BP and fitted curves for Lang-

muir and Freundlich models at different particle sizes. The

isotherms parameters are given in Table 4. The experi-

mental equilibrium data can be fit adequately by both

models (correlation coefficients [0.99). The values of

maximum adsorption capacity of AB1 onto banana peel,

which depends on the particle size, are in the range

250–620 mg g-1; whereas, in other bioadsorbents such as

magellanic moss peat [44] and cells fodder yeast (Kluy-

veromyces fragilis) magnetically modified [45], the maxi-

mum adsorption capacity of AB1 reported, is in the range

of 25.0 and 29.8 mg g-1, respectively. The maximum

adsorption capacity increases 20% when the particle

diameter decreases by half, while the effect is not signifi-

cant for kL constant.

Carbon Assimilation by WRF

Several lignocellulosic wastes, such as agricultural wastes

and by-products of this sector, have been used for enzyme

production. The main reason is the carbohydrate content as

well as the presence of sources of N and other inducers on

Table 3 Effect of the

operations conditions in the

kinetics parameters of AB1

adsorption onto BP

dp (mm) C (mg L-1) qe (mg g-1) k2 (g mg-1 min-1)*105 h (mg g-1 min-1)*103 r2

0.25 50 22.27 9.77 2.17 0.99

200 62.50 1.53 0.96 0.98

500 63.69 3.58 2.28 0.97

0.5 50 22.47 14.63 3.29 0.99

200 57.47 5.36 3.08 0.98

500 62.11 5.04 3.13 0.98

1 50 22.68 13.46 3.05 0.99

200 37.17 6.73 2.50 0.99

500 37.07 8.27 3.06 0.99

Waste Biomass Valor

123

the soluble fractions of these residues. As a result, these

biomaterials have become an excellent substitute for syn-

thetic sources of C and N. The origin and composition of

these residues is critical for the type and amount of

enzymes that could produce white fungus putrefaction. The

production of extracellular oxidative enzymes occurs dur-

ing secondary metabolism, usually in media in which one

of the sources (C, N or S) is the limiting factor of growth.

However, this phenomenon does not seem to be general for

all fungi [46].

Figure 4 shows that the fungal strains assayed consumed

the carbon source provided by BP. Reducing sugar was

abruptly consumed up to the 5th day for S. hirsutum and

Inonotus sp. cultures. Slower consumption was observed in

cultures of P. eryngii, keeping from day 5 a residual con-

centration of about 40%. While a banana ripens, increases

the contents of soluble sugar in the peel and consequently,

the starch contents will be lower. In order to induce the

growth of WRF using BP as a source of nutrients, high

maturity fruits were selected (Color Index = 6) [26].

Ligninolitic enzyme activities were analyzed in the

supernatants obtained after biomass separations with the

sole purpose of detecting enzyme expression. Table 5,

identifies the ligninolitic enzymes produced by each fungal

strain studied. MnP activity was detected in all fungal

strains. LiP was not detected in any culture. Laccase and

AAO were detected only in the Inonotus sp culture.

Numerous studies report the application of degradation

processes on a large variety of effluents and recalcitrant

compounds through the action of white-rot fungi by means

of a highly oxidative, nonspecific, extracellular ligninolytic

enzymatic system. In order to evaluate the degrading

capacity of the phenoloxidase enzyme produced by WRF,

dyes with an azoic structure were preferably selected

(Table 6).

Azo dyes are synthetic organic compounds most used in

textile processing dyeing, paper printing and manufacture

of foods and pharmaceutical drugs, among others. This

type of dyes, which is characterized by the presence of at

least one azo bond besides having aromatic rings, corre-

sponds to the most marketed dyestuff. They represent 70%

0

50

100

150

200

250

0 20 40 60 80 100 120

Ce (mg L-1)

q e (

mg

g -1

)1 mm 0.5 mm 0.25 mm Langmuir Freundlich

Fig. 3 Adsorption isotherms of AB1 in banana peel

Table 4 Parameters of the adsorption equilibrium isotherms models

of acid black 1

Langmuir model Freundlich model

dp

(mm)

qm

(mg g-1)

kL

(L g-1)

r2 kF (mg g-1)

(mg L-1)-nn r2

0.25 322. 14 8.57 0.99 16.78 0.61 0.99

0.5 256.44 7.42 0.99 17.24 0.54 0.99

1 623.56 9.04 0.94 13.18 0.78 0.99

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10

Time (d)

Con

cent

rati

on R

elat

ive

(C/C

o)

Pleurotus Stereum Inonotus

Fig. 4 Banana peel’s carbon assimilation by WRF

Table 5 Phenoloxidases enzymes production by WRF

Enzyme PleurotuseryngiiIJFM 169

Inonotussp. SP2

StereumhirsutumRU 104

MnP 4 4 4

Lacasse 4

AAO 4

Table 6 Dyes screening

Dye Pleurotus eryngiiIJFM 169

Inonotussp. SP2

Stereum hirsutumRU 104

Decolorization (%)

AB1 81.68 ± 2.11 96.88 ± 0.45 –

AR27 70.06 ± 29.48 96.52 ± 0.52 95.74 ± 0.63

BB24 ND 86.79 ± 2.41 63.3 ± 5.55

BB41 63.33 ± 4.71 97.3 ± 1.42 96.75 ± 3.58

BO2 70.05 ± 5.83 56.17 ± 5.73 47.46 ± 5.73

BV4 8.73 ± 1.80 ND ND

RB19 45.05 ± 1.95 97.69 ± 2.13 93.33 ± 9.33

RB5 96.96 ± 0.68 98.83 ± 0.56 98.13 ± 0.01

RO16 78.90 ± 1.59 99.32 ± 0.98 86.64 ± 5.38

Waste Biomass Valor

123

of the world-wide market of dyes and 5–10% of this

amount is discharged in industrial effluents, thus being a

major environmental concern [47].

Decolorization experiments were carried out by using S.

hirsutum, Inonotus sp and P. eryngii. The fungi were

incubated under static conditions transformed at 28�C with

100 mg L-1 of dye during 15 days. As shown in Table 6,

all those dyes whose azoic group is joined to benzene-

naphthalene rings or naphthalene-naphthalene rings, such

as AB1, AR27, RB5 and RO16, were highly decolorized

(mean value above 90%). On the contrary, dyes with a

triphenylmethane structure, such as BV4, were not degra-

ded by P. eryngii and Inonotus sp. Only S. hirsutum

decolorized BV4, but scarcely (8.7%). Biodegradation of

triphenylmethane dyes has been studied by bacteria, acti-

nomycetes, yeasts, and fungi. In the specific case of WRF,

degradation by laccases has only been reported [48]. Cur-

rently the degradation pattern of the dyes by the fungi is

being studied as well as the development of an effluents

treatment system based in their metabolism.

Based on the above presented results, a combined two

stage strategy of coloured wastewater treatment is pro-

posed. In the first stage, the dye is adsorbed by the banana

peel. In the second stage, a process of bioremediation of the

solid phase by means of a treatment with ligninolytic

enzymes is carried out. The enzyme production can be

performed using the same banana peel as carbon source.

Conclusion

In conclusion, it is possible to use banana peel as promising

material for the development of a global bioremediation

strategy for wastewater containing hazardous compounds,

such as dyes. Its high adsorption capacity of Acid Black 1

(250 mg g-1) as well as the high decolourizing efficiency

of the ligninolytic enzymes produced by Inonotus sp SP2

(97%) and Stereum hirsutum RU 104 (82%) allow to

postulate the use of BP to implement a hybrid strategy of

remediation based on the combination of physicochemical-

biological treatments.

Acknowledgments We wish to thank Maria Cristina Diez (Uni-

versity of La Frontera, Chile) for providing the Inonotus sp. SP2 and

Stereum hirsutum RU 104. This research has been partially funded by

Fondecyt Project 1090098 and a collaboration project between Spain

and Chile (CSIC-USACh 2008-CL0030).

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