Wastewater Treatment for Removal of Recalcitrant Compounds: A Hybrid Process for Decolorization and Biodegradation of Dyes

SEPARATION SCIENCE AND ENGINEERING Chinese Journal of Chemical Engineering, 19(4) 621ü625 (2011)

Wastewater Treatment for Removal of Recalcitrant Compounds: A Hybrid Process for Decolorization and Biodegradation of Dyes* Carolyn Palma1,**, Andrea Carvajal2, Carlos Vásquez3 and Elsa Contreras3 1 2 3

Chemical Engineering and Environmental Department, Santa Maria University, Vicuña Mackenna 3939, Santiago, Chile Chemical Engineering and Environmental Technology Department, University of Valladolid, 47011 Valladolid, Spain Chemical Engineering Department, University of Santiago de Chile, Av. Libertador Bernardo O’Higgins 3363, Santiago, Chile

Abstract While conventional wastewater treatments for urban effluents are fairly routine and have proved highly effective, industrial wastewater requires more complex and specific treatments. This paper provides a technological strategy for removal of recalcitrant contaminants based on a hybrid treatment system. The model effluent containing a binary mixture of synthetic dyes is treated by a combination of a preliminary physicochemical stage followed by a biological stage based on ligninolytic enzymes produced by Phanerochaete chrysosporium. This proposal includes biosorption onto peat as pretreatment, which decreases the volume and concentration to be treated in the biological reactor, thereby obtaining a completely decolorized effluent. The treated wastewater can therefore be reused in the dyeing baths with the consequent saving of water resources. Keywords wastewater, hybrid and advanced treatment, bioprocess

1

INTRODUCTION

The continuous discharge of contaminated water into a body of water and soil prevents their capability for self-purification. Thus, the organic and inorganic compounds in wastewater must be eliminated by specific treatments. The process type and sequence depends on the origin of wastewater and the destination and/or the use it will have. The wastewater characterization is also essential for an adequate design of efficient treatment technologies. The treatment of industrial wastewaters is more complex than sewage wastewater, and therefore often requires tertiary/advanced treatment. The development of technologies leading to higher efficiency in the removal, elimination and/or mineralization of compounds that are recalcitrant to conventional treatments seem to have been the major motivation for the development and implementation of the Advanced Oxidation Processes (AOP). This kind of compound is highly stable and toxic, generally resistant against degradation from the bacterial, aerobic and/or anaerobic association because it is not recognized as substrate by the existing degrading enzymes [1]. The manufacture of dyestuffs for the dyeing processes in various industrial sectors such as textile and leather generates large amounts of wastewater with intense coloration. Most of the dyes are synthetic compounds that have a high chemical resistance due to the aromatic structure stabilized by the resonance that they possess. Also the chemicals used for their synthesis are hazardous for human life and some azo dyes have been linked to human cancer and aberra-

tions in mammalians cells [2]. The wastewater generated from textile processes, particularly from dyeing baths, are mixtures of different solutes, mainly dyes. According to the type of fiber, different dyes are used: acid dyes are used for dying silk, cotton, nylon and acrylic fibers; reactive dyes are applied in cotton and cellulose fibers, and basic dyes are utilized with acrylic fibers. The textile dyes are complex aromatic compounds, and therefore advanced processes should be used such as chemical or enzymatic oxidation. However, the large volume of wastewater generated by the textile wet processes suggests using some pretreatment to reduce the feed flow to an ulterior oxidation stage. Therefore, the effectiveness of different treatments for each type of dyes should be evaluated in order to establish an integral strategy for the management of these discharges. These limitations have recently been overcome by the application of hybrid technologies, i.e., different combinations of physical, chemical and biological processes. A wide range of hybrid treatment techniques are reported in the literature [3]. A large number of studies have reported the implementation of AOP and their combinations for wastewater treatment purposes. However, their operational costs are relatively high as compared with biological treatments. Biological systems, in addition to the various combinations among themselves, have also been explored together with virtually all sorts of physicochemical treatments [4]. In the case of wastewater, textiles use a physicochemical process, e.g. biosorption, as pre-treatment to allow for the reduction of the concentration and volume to be treated by a subsequent biodegradation process [57]. The residual liquid and solids from

Received 2010-06-28, accepted 2011-04-08. * Supported by the Proyecto Fondecyt (1040089, 1090098). Work originally presented on the 2nd Int. Symp. Sustainable Chemical Product and Process Engineering, held at Hangzhou, China from May 9 to 12, 2010. ** To whom correspondence should be addressed. E-mail: [email protected]

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pre-treatment can be later bio-remediated by using the extracellular oxidizing enzyme system with white rot fungi [810]. The purpose of this study was to evaluate the performance of a hybrid system that is feasible to apply for the treatment to wastewater from dyeing process, which is based on sequential stages of biosorption onto sphagnum moss peat and biodegradation using Phanerochaete chrysosporium immobilized in foam. 2 2.1

MATERIALS AND METHODS Materials

2.1.1 Biomass or adsorption support The agricultural waste (banana peel, orange peel and barley bagasse) used as support for adsorption tests were dried, crushed and sieved. A medium particle diameter of 1.5 mm was selected for the adsorption assays. The moss peat (Sphagnum magellanicum) which is marketed by ANASAC S.A. of Chile was dried at ambient temperature until it reached 15% moisture, and then it was sieved to select the particle size ranging from 0.25 to 1.00 mm. 2.1.2 Microorganisms The white-rot fungi used were Phanerochaete chrysosporium BKM-F-1767 (ATCC24725) and Inonotus sp. SP2 (isolated in the Araucanía region of southern Chile by research group of Environmental Biotechnology Laboratory, University of La Frontera). 2.1.3 Dyes All dyes used are of analytical grade and were obtained from Sigma Aldrich. 2.2 Decolorization screening of individual treatment 2.2.1 Uptaking of dyes by biomass Dyes solution (50 mg·L1) were contacted with 4 1 g·L of biosorbent in Erlenmeyer flasks (100 ml), which were maintained in a thermostated agitated system [(20±2) ºC, 150 r·min1] for 2 d. 2.2.2 Fungal decolorization Biotic static assays were conducted in an Erlenmeyer flasks (100 ml) covered with cotton and gauze stoppers, with 1.5 ml homogenized mycelium (P. chrysosporium or Inonotus sp. SP2) and 13.5 ml of glucose-peptone autoclaved medium supplemented with 50 mg·L1 of dyes. Abiotic controls without mycelium were carried out in parallel. All cultures (in triplicate) were incubated for 15 d at 28 ºC in an air atmosphere with 100% relative humidity. In both assays, the samples were centrifuged and the residual dye concentration in the solution was determined by the absorbance measures at maximum wavelength in a Helios Gamma model UV-Vis spectrophotometer (Spectronic, UK).

2.3

Hybrid treatment of binary mixture of dyes

2.3.1 Wastewater The study was conducted using “model” effluent designed on the basis of a binary aqueous solution of dyes. Three different mixtures of dyes were selected: (a) acid dyes: Acid Black 1 (AB1) and Acid Orange 6 (AO6); (b) reactive dyes: Reactive Blue 19 (RB19) and Reactive Orange 16 (RO16) and (c) basic dyes: Basic Violet 4 (BV4) and Basic Blue 24 (BB24) whose concentration is shown in Table 1. The concentrations of basic dyes in the mixture were defined considering their maximum adsorption capacities onto peat, which are 667 and 714 mg·g1 for BB24 and BV4, respectively [5]. The concentration of others dyes, reactive and acid, were established so as to avoid the inhibitory effects in the manganese peroxidase production (11, 12). Table 1

Composition of model effluents Dye concentrations/mg·L1

Acid dyes

Reactive dyes

Basic dyes

AB1

AO6

RB19

RO16

BV4

BB24

150

50

150

50

300

100

2.3.2 Hybrid treatment system The system was implemented using as first stage a column of biosorption, segregating the outflow stream that was obtained from the beginning of the operation until the rupture point (when the outlet concentration reaches a value 80% of input concentration) so it can be reused. The volume collected during the period that began at the rupture point until the condition of exhaustion (outlet concentration equal to 1 mg·L1) was accumulated. This volume was later treated in the continuous reactor with P. chrysosporium as immobilized biomass, which corresponds to the second stage of the hybrid treatment (Fig. 1). 2.3.3 Biosorption stage The biosorption system is a modular column of 17 mm of diameter and 55 cm of height. It was loaded with 7.4 g of magellanic peat whose height is 40 cm. In the bottom and in the top a packed bed of sand was added (3 cm of height) to avoid loss of adsorbent material. The flux across the column was induced by gravity. Table 2 shows the operational conditions for each mixture of dyes. Table 2

Operation conditions of biosorption column pH

Feed flow/ml·min1

acid dyes

Buffered 2.7

17

reactive dyes

Buffered 2.7

17

basic dyes

4.0 (unbuffered)

27.3

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Figure 1 Diagram of hybrid process system T-1ümodel wastewater tank; T-2üeffluent of biosorption stage tank; T-3üconcentrated medium tank; T-4ütreated waste water tank; P-1üperistaltic pump pumping wastewater to biosorption column; P-2, P-3üperistaltic pump pumping dyes and culture medium to bioreactor

2.3.4 Bioreaction stage The second stage of the treatment was realized in a continuous bioreactor with P. chrysosporium as immobilized biomass in foam. The reactors are 4.5 cm and 20 cm of diameter and height, respectively, and the effective volume is 203 ml. The inoculation method and operation of the reactors were previously described [11]. The effluent from the biosorption stage was accumulated. After that it was mixed with concentrated culture medium described in [13] with a volume ratio of 25Ή75. The bioreactors were operated with a flow rate of 203 ml·d1, whose hydraulic retention time was 24 h. 2.4 Analytical assays 2.4.1 Decolorization efficiency assay The concentration of dyes into the wastewater was quantified by absorbance scans in the visible spectrum region, between 380 and 750 nm. The measure was performed with a UV-visible spectrophotometer (Spectronic, Helios Gamma model). The area under the curve was obtained through the use of the program Curve Expert v1.3®. The removal of the dyes was evaluated by area reduction. 2.4.2 Enzymatic activities assay MnP (manganese peroxidase) activity was estimated by the method of oxidation of 2,6-dimetoxifenol [14]. One activity unit represents 1 Pmol of oxidised dimethoxyphenol product per minute. LiP (lignin peroxidase) activity was determined by the veratryl alcohol method [15].

3

RESULTS AND DISCUSSION

The individual physical-chemical and biological treatments to remove dyes from a solution were evaluated. In the first case was assessed the uptake potential of different kind of biomass for the removal of dyes, and in the second case we investigated the oxidative potential of ligninolytic enzymes, extracellular biocatalysts produced by white rot fungi (WRF). Table 3 reports the removal efficiencies of different dyes obtained by us using screening assays performed in submerged batch culture of P. chrysosporium and Inonotus sp. SP2, as well as by biosorption onto magellanic peat and agricultural wastes (banana peel, orange peel and bagasse barley). These results show that Mn-dependent ligninolytic enzymes produced by these fungi have degrading capability against some type of dye, preferably acid and reactive dyes. Acid Black 1, Acid Red 27, Reactive Black 5 and Reactive Orange 16 were highly labile to the action of the manganese peroxidase achieving decolorization efficiencies over 90%. In contrast, basic dyes are poorly degraded (Basic Orange 2) or not degraded at all (Basic Violet 4). However, a physicochemical treatment such as the biosorption on peat and/or agricultural waste had the best performance for the basic dyes removal, obtaining an uptake of above 98% for dyes such as Basic Blue 3, Basic Orange 2 and Basic Blue 24 (Table 3). According to these results, to use a hybrid technology should be more effective than individual

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Table 3

Removal efficiency of dyes by individual systems of treatment

Biological treatment Dye

Phanerochaete Inonotus sp. chrysosporium SP2

Physical-chemical treatment Banana peel

Magellanic Peat Un-buffered

Orange peel

Buffered at pH 2.5

Bagasse barley

Un-buffered

Buffered at pH 2.5

Un-buffered

Acid Black 1

99.1 ± 0.6

97.7 ± 0.4

29.1

20.4

93.9

29.4

64.7

42.9

Acid Orange 6

6.9 ± 1.2

90.5 ± 4.3

50.7

77.2

55.2

ü

ü

ü

Basic Blue 3

ü

ü

98.5

ü

ü

ü

ü

ü

Acid Red 27

96.9 ± 3.6

99.0 ± 1.0

2.3

20.9

81.3

ü

ü

ü

Basic Orange 2

39.5 ± 3.6

26.4 ± 2.0

99.9

ü

ü

51.4

ü

ü

Basic Blue 24

74.6 ± 4.6

22.5 ± 0.92

99.3

ü

ü

98.0

ü

ü

Basic Blue 41

84.3 ± 0.2

99.5 ± 0.6

ü

ü

ü

81.5

ü

65.5

Basic Green 4

ü

ü

99.9

ü

ü

ü

ü

ü

Basic Violet 4

ND

30.7 ± 1.4

ü

ü

ü

ü

ü

ü

Reactive Black 5

97.5 ± 0.6

98.1 ± 0.5

9.4

ü

ü

8.80

23.7

65.5

Reactive Blue 19

30.7 ± 7.9

100.0 ± 0.0

75.7

ü

ü

ü

ü

ü

Reactive Orange 16

91.6 ± 4.8

89.0 ± 8.3

42.6

ü

ü

ü

ü

ü

treatments. Based on this hypothesis, the present strategy was proposed that considers a first stage of adsorption in peat moss. Whereas the peat has an ability of cationic exchange, this physicochemical operation would be a pre-treatment that will be transferred from the mixture preferably to the basic dyes. The adsorption stage onto peat of acid and reactive dyes was realized with a buffered model effluent, taking into account the previous results obtained by the authors with respect to the acid-base behavior of this biosorbent. Thus, pH values lower than pHpzc, which corresponds to 3.1, favor the adsorption of anionic dyes such as acid and reactive dyes [16]. On the contrary, a pH higher than 3.1 has a high affinity for basic dyes. Since peat moss has a buffering capacity at pH 4.5 the mixture of basic dyes was not buffered [17]. The adsorption capacities achieved in the biosorption column for mixtures of acid dyes, basic dyes and reactive dyes were 17.7 mg·g1, 10.1 mg·g1 and 283.1 mg·g1, respectively. Since basic dyes were preferably removed at the physicochemical stage, the further bioremediation of exhausted bioadsorbent is required, which may be realized by solid state fermentation [18]. On the other hand, the effluent obtained from the biosorption column when operating with acid and reactive dyes must be detoxified in the biological stage. Degradation and/or mineralization of the carbon and nitrogen fraction of these coloured compounds that are present in liquid phase obtained from the adsorption process, was subsequently realized through oxidative biological treatment using a bioreactor with P. chrysosporium immobilized [9]. The operation of bioreactor was initiated with a supply of culture medium without dyes [11] and the

consumption of nutritional (carbon and nitrogen) sources and the enzymatic activity were monitored. The MnP activity was detected after the 10th day. LiP activity was not detected. Then a conditioning period of the fungus was performed in each bioreactor for which the feed stream was supplemented with peat leachate in the first instance, and subsequently with a dye solution AB1. Finally, we proceeded to add the effluent accumulated in the stage of biosorption in the respective bioreactor. The bioreactor that was operated with a mixture of acid dyes, reached levels of MnP close to 300 U·L1. However, the reactor supplemented with the mixture of reactive dyes showed a sudden drop of the MnP activity. Finally, in the reactor that was operated with basic dyes, the MnP activity remained constant. Nevertheless, the MnP activity was not lower than 50 U·L1, sufficient to promote decolorization because at least 10 U·L1 is required to obtain acceptable efficiencies [19]. Decolorization throughout the process was over 85%, and the spectrophotometric scanning of the effluent of each bioreactor did not show the characteristic peaks of the dyes that were fed. Finally, Fig. 2 shows the effectiveness of each treatment stage for the three mixtures of dyes studied. The volume completely decolorized by biosorption with respect to the total volume fed to the column [Fig. 2 (a)], corresponding to 11%, 15% and 68% for mixtures of acid dyes, basic dyes and reactive dyes, respectively, which could be reused in the dyeing baths. The contribution of each stage to decolorization is different depending on the type of dyes; the input from the biosorption stage to the mixture of acid dyes was 65.5%, and the fungal treatment was 29.7%,

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3 4

(a) Volume treated 5

6

7

(b) Dyes removal Figure 2 Hybrid treatment effectiveness

8 9

46.2% and 46.9% for the reactive dyes, respectively. In the case of basic dyes, 97.5% was achieved by physicochemical treatment, while 2.2% by the biodegradation process [Fig. 2 (b)]. 5

CONCLUSIONS

In summary, the proposed hybrid treatment enables an efficient treatment of textile wastewater because the stage of biosorption can decrease the volume and concentration to be treated in the biological stage, making it possible to obtain a completely decolorized effluent. Accordingly, the treated wastewater can be reused in the dyeing baths with a consequent saving of the freshwater source. In conclusion, the proposed treatment promotes a substantial improvement in water management at the textile sector.

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ACKNOWLEDGMENTS

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The authors are most grateful to financial support from the Proyecto Fondecyt 1040089 and 1090098. The first author is also most grateful to the organizers of SCPPE2010 for the opportunity to present this work and for their partial financial support to attend this conference.

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