Valorisation of textile waste by fungal solid state fermentation: An example of circular waste-based biorefinery

TLDR: In this article, the feasibility of using textile waste as feedstock for cellulase production through solid state fermentation was investigated, and the results indicated that using autoclaved textile blending cotton/polyester of 80/20 led to the highest cellulase activity.

Abstract: This study investigated the feasibility of using textile waste as feedstock for cellulase production through solid state fermentation. Aspergillus niger CKB was selected with the highest cellulase activity (0.43 ± 0.01 FPU g −1 ) after 7 days of cultivation on pure cotton. Material modification techniques including autoclaving, alkali pretreatment and milling were applied on six types of textiles with various cotton/polyester blending ratios. The results indicated that using autoclaved textile blending cotton/polyester of 80/20 led to the highest cellulase activity (1.18 ± 0.05 FPU g −1 ) with CMCase, β-glucosidase and avicelase activities of 12.19 ± 0.56 U g −1 , 1731 ± 4.98 U g −1 and 2.58 ± 0.07 U g −1 , respectively. The fungal cellulase was then extracted and applied to textile waste hydrolysis, in which a sugar recovery yield of 70.2% was obtained. The present study demonstrates a novel circular textile waste-based biorefinery strategy with recovery of glucose and polyester as value-added products.

Figures

Figure 1. Microscopic pictures of fungal growth on pure cotton fabrics after 7 days of SSF. 212 213 At the end of SSF (i.e. day 7), cellulase produced from different strains was extracted and the 214 total cellulase activity (FPase) was analyzed as results presented in Figure 2. It was found that 215 A. niger CKB and A. niger N402 produced the highest level of FPase activity. In comparison, 216 Trichoderma species exhibited poor adaption to textile substrate as indicated by the low 217

Table 4. Enzyme dosages of hydrolysis using fungal celluase or commercial cellulase. 371

Figure 6. Textile hydrolysis by commercial cellulase and fungal cellulase from textile waste. 375 376 Currently, the process optimisation and upscaling of SSF on textile waste and fungal 377 enzymatic hydrolysis of textile waste are under investigation in our group. Fungal cellulase is 378 going to be produced from larger quantities of textile waste using 1 L bioreactor, which 379 would promote the applicability of the proposed method in industry. 380 381

Figure 3. The effect of different modification techniques on various types of textile substrate 255 used in SSF. 256 257 Freezing alkali/urea pretreatment has been reported as an effective pretreatment to decrease 258 cellulose crystallinity (Mohsenzadeh et al., 2012). As shown in Figure 3, this method indeed 259 contributed to increase cellulase activity. However, the alkali pretreated textile required 260 cleaning by abundant DI water flushing, and its high alkalinity (i.e. pH 9-10) would inhibit 261 the fungal growth and cellulase production as compared to those using autoclaved substrate. 262 Similarly, Rahnama et al. (2013) reported that alkali pretreated rice straw generated much 263 lower cellulase activity in comparison with crude substrate. As to the milling modification, 264 the addition of mineral solution agglomerated the fine powder formed textile to semi-wet 265 blocks, which however reduced the contacting area of the substrate and nutrients accessible to 266 fungal enzymes. The situation of SSF on pure cotton and pure PET were different that milling 267

Table 1. Fungal cellulase production by solid state fermentation. 69

Table 3. Individual cellulase activities produced via SSF. 335

Full text

1
1
Valorisation of textile waste by fungal solid state fermentation: an example
2
of circular waste-based biorefinery
3
Yunzi Hu
1
, Chenyu Du
2
, Shao-Yuan Leu
3
, Houde Jing
3
, Xiaotong Li
1
,
4
Carol Sze Ki Lin
1,
*
5
1
School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong
6
2
School of Applied Sciences, University of Huddersfield, Huddersfield, HD1 3DH, United Kingdom
7
3 Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University
8
* Corresponding author. Tel: +852-3442 7497, E-mail: carollin@cityu.edu.hk
9
10
Abstract
11
This study investigated the feasibility of using textile waste as feedstock for cellulase
12
production through solid state fermentation. Aspergillus niger CKB was selected with the
13
highest cellulase activity (0.43±0.01 FPU g
-1
) after 7 days of cultivation on pure cotton.
14
Material modification techniques including autoclaving, alkali pretreatment and milling were
15
applied on six types of textiles with various cotton/polyester blending ratios. The results
16
indicated that using autoclaved textile blending cotton/polyester of 80/20 led to the highest
17
cellulase activity (1.18±0.05 FPU g
-1
) with CMCase, β-glucosidase and avicelase activities of
18
12.19±0.56 U g
-1
, 1,731±4.98 U g
-1
and 2.58±0.07 U g
-1
, respectively. The fungal cellulase
19
was then extracted and applied to textile waste hydrolysis, in which a sugar recovery yield of
20
70.2% was obtained. The present study demonstrates a novel circular textile waste-based
21
biorefinery strategy with recovery of glucose and polyester as value-added products.
22
Keywords: Aspergillus niger; cellulose hydrolysis; circular textile; fungal cellulase; solid
23
state fermentation; textile waste recycling
24
1. Introduction
25

2
Disposal and management of textile waste have risen increasing global concerns. Textile
26
waste includes the waste generated from streams of fibre, textile and clothing manufacturing
27
process, commercial service and consumption (Pensupa et al., 2017). The worldwide textile
28
consumption increased from 47 million tonnes to 90 million tonnes in the recent decade (Shui
29
and Plastina, 2013), and it is forecasted to keep rising along with the population growth and
30
general increase of household purchasing power (Statista, 2016). The annual generations of
31
textile waste in China, the United Kingdom and the United States are estimated to be 26.0,
32
1.7 and 15.1 million tonnes, respectively (SMaRT, 2016; WRAP, 2016; Yang and Yuan,
33
2016). On global average, 32 kg of textile wastes are discarded per capita each year, of which
34
around 85% end up in landfill (EPA, 2015). Since the post-consumer textile waste is not
35
easily decomposed, accumulation of such waste would lead to infectious diseases, attract
36
pests and spread odors in the environment (Gordon and Hsieh, 2006). According to the
37
evaluation by Waste & Resource Action Programme (UK), 95% of landfilled textile waste is
38
recyclable, whereas only 14 - 15% recycling rate has been achieved at this stage (WRAP,
39
2012).
40
41
Biorefinery is the process to convert biomass to fuels, valuable chemicals and materials
42
(Clark et al., 2006). As an alternative to fossil fuels, renewable biomass source would be a
43
major contributor in the future supply. Cellulose contributes to approximately 35 - 40% of
44
textile waste, which could become a potential feedstock for production of biological products
45
(e.g. ethanol and biogas) (Jeihanipour et al., 2010; Shen et al., 2013). Bioconversion of textile
46
waste has been investigated recently through pretreatment and hydrolyzing cellulose to
47
fermentable glucose. The general idea in various pretreatment technologies is to expose
48
cellulosic fibre to cellulase by increasing surface area and removing inhibitors such as sizing
49
agent coated on textile surface. Gholamzad et al. (2014) reported the conversion of polyester-
50

3
cotton textile to ethanol via alkaline pretreatment followed by simultaneous saccharification
51
and fermentation. Jeihanipour et al. (2013) examined a high-rate biogas production scheme
52
from post-consumer jeans (100% cotton) through N-methylmorpholine-N-oxide (NMMO)
53
pretreatment and anaerobic digestion, yielding 400 mL methanol g
-1
volatile solids day
-1
.
54
55
Degradation of highly crystalline structure of cellulose requires synergy of endoglucanases
56
(EC 3.2.1.4), exoglucanases (EC 3.2.1.91) and β-glucosidases (EC 3.2.1.21) in a complete
57
cellulase system. It was estimated that the cost of cellulase accounts for 10 - 40% of the total
58
production cost in current biorefinery process (Deswal et al., 2011; Johnson, 2016).
59
Therefore, exploring low-cost cellulase producing techniques and substrates is currently
60
under intensive study. Microbial cellulase production using cellulosic residues via submerged
61
fermentation or solid state fermentation have been investigated, and the later has greater
62
advantages as relatively low energy consumption and simple downstream processing (Hölker
63
et al., 2004; Soccol et al. 2017). Fungal cellulase secreted by microorganisms such as
64
Aspergillus niger or Trichoderma reesei on horticulture waste, agriculture and kitchen waste
65
have been studied, as summarised in Table 1. Whereas cotton-based textile waste has not
66
been utilized as substrate and carbon source in SSF or in cellulase production.
67
68
Table 1. Fungal cellulase production by solid state fermentation.
69
Strain
Substrate
Moisture
(%)
Time
(day)
FPase activity
(FPU g
-1
)
Reference
Aspergillus terreus
Rice straw
86
7
11.0
Narra et al.
(2012)
Aspergillus
fumigatus SK1
Oil palm trunk
80
7
3.4
Ang et al.
(2013)
Trichoderma reesei
RUT-C30
Horticultural
waste
80
7-8
15.0
Xin and
Geng (2010)

4
Trichoderma reesei
RUT-C30
Wheat bran
37
7
3.8
Singhania
et al. (2007)
Aspergillus niger
P47C3
Soybean bran
60
5
5.6
Delabona
et al. (2013)
Aspergillus niger
NS-2
Wheat bran
60
4
17.0
Bansal
et al. (2012)
Aspergillus niger
Wheat bran
50
3
2.9
Chandra
et al. (2007)
Aspergillus niger
USM AI 1
Sugarcane
bagasse
70
2
2.3
Lee et al.
(2010)
Aspergillus sp.
SEMCC-3.248
Rice grass
70
5
1.1
Liang et al.
(2012)
70
71
The present study aims to develop an integrated biorefinery strategy in textile waste
72
valorisation. Cotton-based textile waste was utilized as substrate for fungal cellulase
73
production by solid state fermentation. The cellulase obtained was subsequently applied in
74
textile waste hydrolysis to recover sugar and polyester (PET) for material recycling and
75
reuse. The proposed strategy enable the capture of the embodied value of the PET fibre,
76
which contributes to the transition of a circular textiles industry.
77
78
2. Materials and methods
79
2.1 Textile waste
80
Different types of textile waste blending of cotton and polyester provided by H&M (Hennes
81
& Mauritz, Far East) were used as raw feedstock in this study. Pure cotton, pure PET and
82
jeans (99% cotton and 1% elastane) were also employed. Each type was classified by
83
component and dyestuff as listed in Table 2. Dyestuff is a category of substances for staining
84
or coloring on fabrics.
85
86

5
Table 2. Textile waste used in this study.
87
Component (w/w %)
Dyestuff
Pure cotton
Reactive dyestuff
Cotton/PET (80/20)
Reactive dyestuff
Cotton/PET (60/40)
Reactive dyestuff
Cotton/PET (40/60)
Reactive dyestuff
Pure PET
Disperse dyestuff
Jeans (cotton 99% and elastane 1%)
Indigo dyestuff
88
89
2.2 Microorganisms
90
Different cellulase producing fungal strains were used in solid state fermentation.
91
Trichoderma reesei ATCC 24449 was collected from American Type Culture Collection.
92
Aspergillus niger N402 was obtained from Prof. David Archer in the University of
93
Nottingham in the United Kingdom. Aspergillus niger CKB and Rhizomucor variabilis were
94
obtained from Dr. Diannan Lu at Tsinghua University in China. Aspergillus oryzae was
95
isolated from a soy sauce starter by the Amoy Food Ltd., Hong Kong (Leung et al., 2012).
96
Trichoderma longibrachiatum was collected from Prof. Colin Webb from The University of
97
Manchester in the United Kingdom. All strains were cultivated on potato dextrose agar
98
(PDA) medium in petri dishes at 28 °C for 7 days. The spores were collected in 30% glycerol
99
solution and stored in -80 °C freezer until use.
100
101
2.3 Textile waste modification
102
The textile waste used in this study were grinded into small pieces (around 0.8×0.8 cm
2
), and
103
pretreated by three different modification methods, i.e. autoclaved modification, freezing
104

Frequently asked questions

Q1. What are the contributions in this paper?

11 This study investigated the feasibility of using textile waste as feedstock for cellulase 12 production through solid state fermentation. The present study demonstrates a novel circular textile waste-based 21 biorefinery strategy with recovery of glucose and polyester as value-added products. 

Q2. how many mL of cmcase was used as test substrate?

CMCase and avicelase activities were 157 measured by mixing 0.5 mL enzyme solution with 0.5 mL substrate at 50 °C water bath for 158 30 min. 

Q3. How much did the fungal cellulase produce in textile waste hydrolysis?

Fungal cellulase produced from SSF 364 contributed to a yield of 70.2% in textile waste hydrolysis, which is comparable to the yield 365 of 77.2% from commercial enzyme product. 

Q4. What is the effect of -glucosidase on cellulas?

322 The subsequently secondary hydrolysis which is catalyzed by increasing β-glucosidase 323 started to dominate in the later phase. 

Q5. What is the way to achieve the optimal synergistic effect?

In order to achieve the optimal 290 synergistic effect, the investigation on the time courses of total cellulase activity and 291 individual cellulase activities are of prime importance. 

Q6. What is the effect of the -glucosidase activity on the cell?

Meanwhile notably, after the initial increase in the first 5 days, a slight reduction in 305 CMCase activity was observed on day 7 along with a retardation of β-glucosidase activity. 

Q7. What is the proposed strategy for the capture of the embodied value of the PET fibre?

The proposed strategy enable the capture of the embodied value of the PET fibre, 76 which contributes to the transition of a circular textiles industry. 

Q8. How many spores were collected in a petri dish?

For each 115 SSF, 2 g (dry weight) of crude or modified textile waste sample was inoculated with 0.3 mL 116spore suspension (2×10 8 spores mL -1 ) in a petri dish. 

Q9. What is the highest activity of the proposed circular textile waste biorefinery strategy?

β-glucosidase obtained by the proposed circular textile waste-based 333 biorefinery strategy is the highest activity reported worldwide, to date. 

Q10. What was the enzymatic hydrolysis of textile waste?

Enzymatic hydrolysis of textile waste 176The textile waste cotton/PET 80/20 (0.8×0.8 cm 2 , modified by freezing alkali/urea soaking) 177 was subjected to enzymatic hydrolysis. 

Q11. What was the composition of the mineral solution used in this study?

The mineral solution consisted of 117following compositions (g L -1): urea, 0.3; KH2PO4, 2; (NH4)2SO4, 1.4; MgSO4, 0.3; CaCl2, 118 0.4; FeSO4, 0.005; MnSO4, 0.0016; ZnSO4; 0.0014; CoCl2, 0.002 (Mandels and Weber, 119 1969). 

Q12. What is the reason for the decrease in activity of -glucosidase?

Other explanations 311 for the activity decline occurred on FPase, CMCase and avicelase are attributed to depletion 312 of nutrients after a period of 9 days or denaturation of the enzymes (Xin and Geng, 2010). 

Q13. How long does it take to reach the peak?

315 316 As review by Yoon et al (2014), in most SSF, β-glucosidase usually takes longer incubation 317 time to reach the peak, as compared to CMCase or avicelase. 

Q14. What is the time to harvest -glucosidase?

For instance, the CMCase from 318 SSF on wheat bran was harvested on day 11, while β-glucosidase had the best activity on day 319 15 (Elisashvili et al., 2008). 

Q15. What was the enzymatic effect of the enzyme product in textile hydrolysis?

This enzyme product was applied in 388 textile hydrolysis to recover glucose from cellulose with comparable enzymatic effect to 389 commercial cellulase. 

Q16. What was the activity of endoglucanase and exoglucanas?

Endoglucanase activity and exoglucanase activity 153Endoglucanase and exoglucanase were evaluated by carboxymethyl cellulase (CMCase) and 154 avicelase using the procedure developed by International Union of Pure and Applied 155 Chemistry (IUPAC) (Ghose, 1987). 

Q17. how long did the commercial cellulase 362 take to hydrolyze?

Although from 0 - 48 h, commercial cellulase 362 presented a relatively better efficiency, the final hydrolysis yields from commercial cellulase 363 and fungal cellulase were close after 96 h of hydrolysis. 

Q18. What was the highest FPase activity from cotton/PET?

279 280Results from this study showed that the highest FPase activity 1.09±0.05 FPU g -1 was 281obtained from the textile cotton/PET 80/20, while the lowest (< 0.20 FPU g -1 ) was produced 282 on pure PET substrate. 

Q19. How much avicelase was used in the textile waste hydrolysis?

The highest total cellulase activity of 3861.18±0.05 FPU g -1 was harvested on day 9 with CMCase of 12.19±0.56 U g -1 , β-glucosidase 387of 1,731±4.98 U g -1 and avicelase of 2.58±0.07 U g -1 . 

Q20. What is the effect of autoclaving on the morphology of the textile?

242 243 Autoclaving is a widely used pretreatment or modified technique applied to substrate for 244 fermentation, although its effect on material morphology is rarely discussed.