Open Access

Pretreatment of garden biomass using Fenton’s reagent: influence of Fe2+ and H2O2 concentrations on lignocellulose degradation

  • Vivek P Bhange1,
  • SPM Prince William2Email author,
  • Abhinav Sharma2,
  • Jagdish Gabhane2,
  • Atul N Vaidya2 and
  • Satish R Wate2
Journal of Environmental Health Science and Engineering201513:12

DOI: 10.1186/s40201-015-0167-1

Received: 13 June 2014

Accepted: 14 February 2015

Published: 25 February 2015

Abstract

Garden biomass (GB) is defined as low density and heterogeneous waste fraction of garden rubbish like grass clippings, pruning, flowers, branches, weeds; roots. GB is generally different from other types of biomass. GB is mostly generated through maintenance of green areas. GB can be processed for bio energy production as it contains considerably good amount of cellulose and hemicellulose. However, pretreatment is necessary to delignify and facilitate disruption of cellulosic moiety. The aim of the present investigation was to pretreat GB using Fenton’s reagent and to study the influence of Fe2+ and H2O2 concentrations on degradation of lignin and cellulose. The data were statistically analyzed using ANOVA and numerical point prediction tool of MINITAB RELEASE 14 to optimize different process variables such as temperature, concentration of Fe2+ and H2O2. The results of the present investigation showed that Fenton’s reagent was effective on GB, however, concentration of Fe2+ and H2O2 play crucial role in determining the efficiency of pretreatment. An increase in H2O2 concentration in Fenton’s reagent significantly increased the rate of cellulose and lignin degradation in contrast to increasing concentration of Fe2+ ion which led to a decrease in lignocellulosic degradation.

Keywords

Fenton’s reagent Pretreatment Lignin Cellulose Garden biomass

Introduction

Biomass, in general, fourth largest energy source in the world, provides about 13% of world energy consumption [1]. Globally, biomass has an annual primary production of 220 billion oven dry ton [2]. Many cities, large or small, have developed gardens and recreational parks. The number of parks and other recreational centers, home gardens etc. contribute to the sizable quantum of garden biomass (GB) generation. Maintenance of green areas produces significant amount of waste in the form of GB [3]. GB is generally different from other types of biomass, and it is defined as low density and heterogeneous waste fraction of garden rubbish like grass clippings, pruning, flowers, branches, weeds, roots. The disposal of garden biomass is mainly through open burning, dumping and composting in India. Although these methods of disposal are universally applicable they neither recover energy nor eco-friendly except for composting.

GB contains recalcitrant or complex compounds such as cellulose and lignin, and relatively small amounts of saccharides, amino acids, proteins, aliphatic compounds and carbohydrates [3,4]. As GB is rich in cellulose, it can be used as a raw material for bio energy production after suitable pretreatment. Pretreatment is necessary to delignify and facilitate the disruption of lignocellulosic moiety. Pretreatment alters the structure of cellulose and making it more accessible to the enzyme that convert carbohydrate polymer into fermentable sugar [5,6].

There are different methods of pretreatment available for various substrates. However, it is necessary to evaluate every pretreatment process as the efficiency of pretreatment differs from substrate to substrate. Generally, pretreatment methods are either physical or chemical. Some methods incorporate both effects [7]. However, it is necessary to evaluate pretreatment processes for different substrates. Fenton’s reagent defined as a mixture of hydrogen peroxide and ferrous ion is one of the most effective methods for the oxidation of organic compounds.

Fenton process is a reaction between hydrogen peroxide (H2O2) and ferrous ion (Fe2+), producing the hydroxyl radical (•OH). •OH radical is a strong oxidant capable of oxidization and degradation of various organic compounds into carbon dioxide and water. Thus, the degradation process could be increased with increasing •OH concentration and vice versa [8-12].
$$ {\mathrm{Fe}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to\ {\mathrm{Fe}}^{3+}+{\mathrm{O}\mathrm{H}}^{-}{+}^{\bullet}\mathrm{O}\mathrm{H} $$
The ferric ions produced during the reaction further react with hydrogen peroxide regenerating ferrous ions, thus continuing the process [13].
$$ {\mathrm{Fe}}^{3+} + {\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{Fe}}^{2+} + \mathrm{H}\mathrm{O}\mathrm{O}\bullet + {\mathrm{H}}^{+} $$

However, the efficiency of Fenton’s reaction depends mainly on H2O2 concentration, Fe2+/H2O2 ratio, pH and reaction time [14].

In the present study we aimed at evaluating the effectiveness of Fenton’s reaction for pretreatment with a major emphasis on the influence of Fe2+ and H2O2 concentrations on degradation of lignin and cellulose.

Materials and methods

Preparation of the feedstock

Garden biomass (GB) consisting of grass cuttings, fallen leaves, flowers, roots, twigs etc. were collected from the garden area of National Environmental Engineering Research Institute (NEERI). After initial screening, GB was air-dried for24 hours followed by 3 days of sun drying. The dried material was pulverized using a pulveriser to the size of 1 to 5 mm for further experiments and stored in an air tight container.

Pretreatment by Fenton’s reagent

Fenton’s reagent was prepared by mixing FeSO4.7H2O and H2O2 in distilled water in different proportions. The FeSO4.7H2O concentration varied from 250 ppm to 1000 ppm and H2O2 concentration varied from 1000 ppm to 10000 ppm. Every time Fenton’s reagent was prepared fresh and used in the experiment. All the experiments were carried out with 5 g of GB and 100 mL of Fenton’s reagent of different composition. All the reactions were initially carried out at 30°C and repeated at 50 and 80°C. The reaction was carried out in a shaker and reaction time was varied from 60 min to 180 min. The reaction mixture was filtered and then the treated GB was thoroughly washed and dried at 60°C for 2 days. The concentration of lignin and cellulose was estimated as described in section 2.3.

Analytical methods

The dried sample of GB was ground to powder for chemical analysis. The organic carbon content of GB was estimated by combustion method according to Nelson & Sommers, 1982 [15]. Known quantity (mg) of substrate (GB) and its hydrolysed residue after pretreatment was taken and analyzed for cellulose by HNO3- ethanol method. Lignin content of samples was estimated by 72% (w/w) H2SO4 method and hemicellulose by Liu method [16]. The total nitrogen (TN) content of the sample was estimated using LECO Protein-Nitrogen Analyzer (Model FP528).

Evaluation of cellulose and lignin degradation

Degradation of cellulose and lignin was evaluated on the basis of solid recovery [17,18] and actual degradation was calculated on the basis of residual concentration after pretreatment.

Cellulose recovery

Actual degradation (g) and actual degradation (%) of cellulose and solid recovery was calculated according to following formula:
$$ \begin{array}{c}\mathrm{Solid}\ \mathrm{r}\mathrm{ecovery}\ \left(\%\right)=\frac{\mathrm{Dry}\ \mathrm{weight}\ \mathrm{o}\mathrm{f}\ \mathrm{sample}\ \mathrm{after}\ \mathrm{pretreatment}}{\mathrm{Initial}\ \mathrm{weight}\ \mathrm{o}\mathrm{f}\ \mathrm{sample}\ \left(\mathrm{g}\right)} \times 100\\ {}\mathrm{Recovered}\ \mathrm{cellulose}\ \left(\mathrm{g}\right)=\frac{\mathrm{Conc}.\ \left(\%\right)\ \mathrm{o}\mathrm{f}\ \mathrm{cellulose}\ \mathrm{after}\ \mathrm{pretreatment} \times \mathrm{Solid}\ \mathrm{r}\mathrm{ecovery}}{\mathrm{Material}\ \mathrm{taken}\ \mathrm{f}\mathrm{o}\mathrm{r}\ \mathrm{pretreatment}}\end{array} $$
Actual degradation (g) and Actual degradation percentage (%) of cellulose was calculated by following formula:
$$ \begin{array}{c}\mathrm{Actual}\ \mathrm{degradation}\ \left(\mathrm{g}\right)\ \mathrm{of}\ \mathrm{cellulose} = \mathrm{Initial}\ \mathrm{conc}.\ \mathrm{of}\ \mathrm{cellulose}\ \hbox{--}\ \mathrm{Recovered}\ \mathrm{cellulose}\\ {}\mathrm{Actual}\ \mathrm{degradation}\ \left(\%\right)\ \mathrm{of}\ \mathrm{cellulose} = \frac{100 \times \mathrm{Actual}\ \mathrm{degradation}\ \left(\mathrm{g}\right)\ \mathrm{of}\ \mathrm{cellulose}}{\mathrm{Initial}\ \mathrm{conc}.\ \mathrm{of}\ \mathrm{cellulose}}\end{array} $$

Lignin recovery

Actual degradation (g), actual degradation (%) of lignin and solid recovery was calculated according to following formula:
$$ \begin{array}{c}\mathrm{Solid}\ \mathrm{r}\mathrm{ecovery}\ \left(\%\right)=\frac{\mathrm{Dry}\ \mathrm{weight}\ \mathrm{o}\mathrm{f}\ \mathrm{sample}\ \mathrm{after}\ \mathrm{pretreatment}}{\mathrm{Initial}\ \mathrm{weight}\ \mathrm{o}\mathrm{f}\ \mathrm{sample}\ \left(\mathrm{g}\right)} \times 100\\ {}\mathrm{Recovered}\ \mathrm{lignin}\ \left(\mathrm{g}\right)=\frac{\mathrm{Conc}.\ \left(\%\right)\ \mathrm{o}\mathrm{f}\ \mathrm{lignin}\ \mathrm{after}\ \mathrm{pretreatment} \times \mathrm{Solid}\ \mathrm{r}\mathrm{ecovery}}{\mathrm{Material}\ \mathrm{taken}\ \mathrm{f}\mathrm{o}\mathrm{r}\ \mathrm{pretreatment}}\end{array} $$
Actual degradation (g) and Actual degradation percentage (%) of lignin was calculated by following formula:
$$ \begin{array}{c}\mathrm{Actual}\ \mathrm{degradation}\ \left(\mathrm{g}\right)\ \mathrm{of}\ \mathrm{lignin} = \mathrm{Initial}\ \mathrm{conc}.\ \mathrm{of}\ \mathrm{cellulose}\ \hbox{--}\ \mathrm{Recovered}\ \mathrm{cellulose}\\ {}\mathrm{Actual}\ \mathrm{degradation}\ \left(\%\right)\ \mathrm{of}\ \mathrm{lignin}=\frac{100 \times \mathrm{Actual}\ \mathrm{degradation}\ \left(\mathrm{g}\right)\ \mathrm{of}\ \mathrm{lignin}}{\mathrm{Initial}\ \mathrm{conc}.\ \mathrm{of}\ \mathrm{lignin}}\end{array} $$

Statistical guided experimental design and procedure

The Fenton’s pretreatment was statistically evaluated by applying statistical methodology viz. analysis of variance (ANOVA) followed by response surface methodology for process optimization [19,20]. The experimental runs were designed to cover variables that assess impact of pretreatment on cellulose and lignin degradation. The effects of Fe2+ concentration (X1), Hydrogen peroxide concentration (X2) and Temperature (X3) on lignin and cellulose degradation were described statistically. The regression analysis was performed to estimate the response function as a second-order polynomial:
$$ Y = {\beta}_0+{\displaystyle \sum_{i=1}^K}{\beta}_i{X}_i^2+{\displaystyle \sum_{i=1}^K}{\beta}_{ij}{X}_i^2+{\displaystyle \sum_{i=1}^{k-1}}\times {\displaystyle \sum_{j=2}^k}{\beta}_{ij}{X}_i{X}_j $$
(1)

Where Y is the predicted response, β i , β j , β ij are coefficients estimated from regression, they represent the linear, quadratic and cross-products of X 1 ,X 2 ,X 3 on response.

A statistical program package MINITAB RELEASE 14, was used for regression analysis of the data obtained and to estimate the coefficient of regression equation. The equations were validated by analysis of variance (ANOVA) analysis. The significance of each term in the equation is to estimate the goodness of fit in each case. Response surfaces were drawn to determine the individual and interactive effects of test variable on degradation of respective components.

Results & discussion

Initial characterization of GB

GB was analyzed to find out concentration of various constituents such as lignin, cellulose, hemicellulose, organic matter, organic carbon etc. (Table 1).
Table 1

Initial characterization of garden biomass

Parameter

Concentration (%)

Total organic matter

94.10

Organic carbon

49.12

Cellulose

38.54

Hemicellulose

26.24

Lignin

25.68

Nitrogen

1.65

A perusal of results showed that GB contained 94.10% of total organic matter, 49.12% of organic carbon, 38.54% of cellulose, 25.68% of lignin and 26.24% of hemicellulose. The total nitrogen content of GB was found to be 1.65%.

Model fitting

The Levels of process variables, design of experiment along with experimental and predicted responses is given in Table 2, 3 and 4, respectively.
Table 2

Levels of process variables in un-coded form for Fenton pre-treatment

Process variables

Levels of process variables

Fe2+ concentration ppm (X1)

250

500

1000

Hydrogen Peroxide concentration (ppm) (X2)

1000

5000

10000

Reaction temperature (°C) (X3)

30

50

80

Table 3

Design matrix along with predicted and experimental values for cellulose degradation (%) by Fenton’s pretreatment

Runs

Fe 2+ (ppm)

H 2 O 2 (ppm)

Reaction temperature (°C)

Cellulose degradation (%)

Observed value

Predicted value

 

250

1000

30

26.433

24.591

 

250

1000

50

27.337

28.535

 

250

1000

80

20.000

19.662

 

250

5000

30

30.767

30.552

 

250

5000

50

31.340

34.495

 

250

5000

80

27.000

25.622

 

250

10000

30

43.067

41.901

 

250

10000

50

47.230

45.844

 

250

10000

80

35.000

36.971

 

500

1000

30

13.367

16.098

 

500

1000

50

*

*

 

500

1000

80

10.000

11.168

 

500

5000

30

24.267

22.058

 

500

5000

50

*

*

 

500

5000

80

20.000

17.129

 

500

10000

30

31.267

33.408

 

500

10000

50

40.790

37.351

 

500

10000

80

26.000

28.478

 

1000

1000

30

16.933

15.496

 

1000

1000

50

17.487

19.440

 

1000

1000

80

14.000

10.567

 

1000

5000

30

19.467

21.457

 

1000

5000

50

*

*

 

1000

5000

80

15.000

16.527

 

1000

10000

30

32.800

32.806

 

1000

10000

50

38.230

36.749

 

1000

10000

80

27.000

27.876

*Outliers removed.

Table 4

Design matrix along with predicted and experimental values for lignin degradation (%) by Fenton’s pretreatment

Runs

Fe 2+ (ppm)

H 2 O 2 (ppm)

Reaction temperature (°C)

Lignin degradation (%)

Observed value

Predicted value

1

250

1000

30

43.000

41.940

2

250

1000

50

52.000

52.634

3

250

1000

80

39.800

36.885

4

250

5000

30

46.500

45.032

5

250

5000

50

55.113

55.725

6

250

5000

80

39.340

39.976

7

250

10000

30

47.630

48.821

8

250

10000

50

57.390

59.515

9

250

10000

80

43.520

43.766

10

500

1000

30

33.580

36.155

11

500

1000

50

45.210

46.848

12

500

1000

80

28.660

31.099

13

500

5000

30

41.563

39.246

14

500

5000

50

48.560

49.940

15

500

5000

80

36.220

34.190

16

500

10000

30

42.900

43.036

17

500

10000

50

55.230

53.729

18

500

10000

80

40.300

37.980

19

1000

1000

30

35.940

32.680

20

1000

1000

50

44.317

43.374

21

1000

1000

80

26.733

27.625

22

1000

5000

30

33.580

35.772

23

1000

5000

50

47.437

46.466

24

1000

5000

80

28.750

30.716

25

1000

10000

30

37.550

39.562

26

1000

10000

50

53.230

50.255

27

1000

10000

80

33.420

34.506

Full quadratic multiple regression analysis of experimental data yielded the following regression equations for the degradation of cellulose and lignin achieved through Fenton’s pretreatment:

Cellulose degradation

$$ {\mathrm{Y}}_1=16.7866-0.0667432*{X}_1+0.000970293*{X}_2+0.985852*{X}_3+0.0000436*{X}_1*{X}_1+0.0000000866*{X}_2*{X}_2-0.00985*{X}_3*{X}_3 $$
(2)

Lignin degradation

$$ {\mathrm{Y}}_2=1.81315-0.0393363*{X}_1+0.000782833*{X}_2+2.23014*{X}_3+0.0000216*{X}_1*{X}_1 - 0.00000000166\ *{X}_2*{X}_2-0.02119*{X}_3*{X}_3 $$
(3)

Where Y 1 is the % cellulose degradation achieved by Fenton’s pretreatment, Y 2 is % lignin degradation by Fenton’s pretreatment, X 1 is Fe2+ concentration, X 2 and X 3 are hydrogen peroxide concentration (ppm) and reaction temperature, respectively.

Tables 3 and 4 show degradation of cellulose and lignin at different concentrations of Fe2+ and H2O2 in Fenton reagent. A perusal of results indicated that Fenton’s reagent is effective on GB. The degradation of cellulose and lignin responded positively to the concentration of H2O2 and reaction temperature. Whereas increasing concentration of Fe2+decreased the rates of lignin and cellulose degradation. The best effective concentration (BEC) of Fe2+ and H2O2 was found to be 250 ppm and 10000 ppm, respectively at a temperature of 50°C. Though the degradation of lignin and cellulose was significant at this BEC, compared to the other conventional methods such as alkali or H2O2 oxidation tried on other lignocellulosic biomass, Fenton’s pretreatment pronounced only a low level of delignification [21,22]. However, there is no such report to our search which exclusively deals with the effects of Fenton’s reagent on lignin and cellulose degradation in GB. The cellulose reduction rates as observed (47.23%) in the present investigation are slightly higher than that of Liu and Cheng [23] who reported maximum of 20.28% removal of cellulose and 20.09% of lignin using acid pretreatment on herbal residue. However, Ayeni et al. [24] reported 17% lignin removal by alkaline peroxide assisted wet air oxidation with no loss of cellulose. The effect of H2O2 alone on wood waste was also studied by Ayeni et al. [24] who reported 11% lignin removal without loss of cellulose.

The regression coefficients values for Fenton pretreatment with respect to cellulose and lignin removal is close to one (R2 > 95%), indicating the aptness of second order polynomial in predicating the response in terms of the chosen independent values, moreover the predicted values were found to be in close agreement with the experimental results (Table 2). The adjusted R2 value (94.31% and 93.76% respectively) obtained by correcting the R2 value for sample size and number of terms for cellulose removal is indicative of high significance of the model. The ANOVA model for the degradation of lignin and cellulose is shown in Table 5.
Table 5

Analysis of variance (ANOVA) of model parameters

Terms

Coefficient

F

P

Cellulose degradation (%)

   

Constant

16.7866

  

Fe (X1)

−0.0667432

61.47

0.000

H2O2 (X2)

0.000970293

222.65

0.000

Reaction temperature (X3)

0.985852

19.48

0.000

Fe * Fe (X1* X1)

4.36930E-05

24.77

0.000

H2O2* H2O2 (X2 * X2)

8.66348E-08

2.55

0.129

Reaction temperature * Reaction temperature (X3 * X3)

−0.00985858

25.89

0.000

R-Sq = 95.79% R-Sq(pred) = 91.36% R-Sq(adj) = 94.31%

Lignin degradation (%)

   

Constant

1.81315

  

Fe (X1)

−0.0393363

86.45

0.000

H2O2 (X2)

0.000782833

47.74

0.000

Reaction temperature (X3)

2.23014

25.77

0.000

Fe * Fe (X1* X1)

2.15921E-05

0.006

0.006

H2O2* H2O2 (X2 *X2)

−1.66049E-09

0.970

0.970

Reaction temperature * Reaction temperature (X3 * X3)

−0.0211932

0.000

0.000

R-Sq = 95.20% R-Sq(pred) = 91.26% R-Sq(adj) = 93.76%

The ANOVA demonstrates that the model is more significant. This is evident from the calculated F-values 64 and 66 for effect of Fenton’s pretreatment on cellulose and lignin removal respectively (P = <0.05). The ANOVA results also Indicate that the coefficients for linear effects are significant (P = <0.01) for cellulose degradation and for lignin removal. The positive linear effect for H2O2 concentration and temperature indicate an increase in cellulose and lignin removal with increase in peroxide concentration and temperature in contrast to the observed negative linear effect for Fe2+ concentration. The concentration of Fe2+ ions present in the pretreatment solution should be in catalytic amounts as over dosage leads to adsorption on the substrate which may lead to subdued processing activity after treatment.

Many studies reported in literature have revealed that the use of a much higher concentration of Fe2+ could lead to the self-scavenging of •OH radical by Fe2+ and induce the decrease in degradation rates [25-27]. According to Neyens & Baeyens, 2003, when the amount of Fe2+employed exceeds that of H2O2, the treatment tends to have the effect of chemical coagulation. When the two amounts are reversed, the treatment tends to have the effect of chemical oxidation [28].

The effects of Fe2+ ion and H2O2 concentration on lignin and cellulose degradation when temperature was set at their centre point are shown in Figures 1 and 2. An increase in H2O2 concentration during pretreatment lead to considerable increase in lignin and cellulose degradation in contrast to increasing Fe2+ ion concentrations which lead to a decrease in cellulose removed from biomass. For example the cellulose and lignin removal increased from 13% to 31% & from 33% to 42% respectively at 500 ppm Fe2+ ion concentration when the H2O2 concentration was increased from 1000 to 10000 ppm.
Figure 1

Cellulose degradation (% w/w) as a function of Fe 2+ concentration (ppm) and H 2 0 2 concentration (ppm).

Figure 2

Lignin degradation (% w/w) as a function of Fe2 + concentration (ppm) and H 2 0 2 concentration (ppm).

The interactive effect of reaction time was however insignificant in Fenton pretreatment for lignin and cellulose removal and hence omitted from the regression analysis.

Overall, there is a predominance of the linear effects over the quadratic and interactive effects for both lignin and cellulose removal from the biomass. Higher peroxide concentrations lower Fe2+ concentrations higher reaction temperatures favour cellulose and lignin removal from the biomass.

Conclusion

Effect of Fenton’s pretreatment on lignin and cellulose degradation of GB was studied. The results showed that Fenton’s reagent was effective on GB, however, concentration of Fe2+ and H2O2 play crucial role in determining the effectiveness of lignin and cellulose degradation. An increase in H2O2 concentration in Fenton’s reagent significantly increased the rates of cellulose and lignin degradation in contrast to increasing Fe2+ ion concentrations which led to a decrease in lignin and cellulose degradation. Further studies are necessary to compare and contrast Fenton’s pretreatment with other pretreatments and to understand the compatibility of Fenton’s pre-treated biomass for bioenergy production.

Declarations

Acknowledgement

The encouragement and support provided by the Principal and Management of Priyadarshini Institute of Engineering and Technology, Nagpur to Mr. Vivek P. Bhange is greatly acknowledged.

Authors’ Affiliations

(1)
Department of Biotechnology, Priyadarshini Institute of Engineering and Technology
(2)
Solid and Hazardous Waste Management Division, National Environmental Engineering Research Institute

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Copyright

© Bhange et al.; licensee BioMed Central. 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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