Biomechanization potential of organic fraction of ... · Generally, organic fraction of municipal solid waste OFMSW is a very attractive waste for the biogas plants because it has

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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 2, No 4, 2012

© Copyright 2010 All rights reserved Integrated Publishing Association

Research article ISSN 0976 – 4402

Received on March 2012 Published on May 2012 2387

Biomechanization potential of organic fraction of municipal solid waste

(OFMSW) from co-digestion of PIG and COW DUNG Membere Edward. A, Ugbebor John, Akan Udoh. E

Department of Civil and Environmental Engineering, University of Port Harcourt, Port

Harcourt, Rivers State, Nigeria

[email protected]

doi: 10.6088/ijes.00202030120

ABSTRACT

The production of biogas, an alternative source of renewable energy from biomechanization

of (OFMSW) were studied in different reactors (A-D) using a 5- liter digester at room

temperature for a period of 30 days. The OFMSW were co-digested with pig and cow dung

as inoculum. OFMSW addition was varied through proximate analysis determination for

design dry weight of 6g, 16g, 18g and 26g for a fixed amount of pig and cow dung until

maximum biogas production was achieved. The determined empirical formular of the

OFMSW through ultimate analysis were A(C575H4300O300N12.5,S),B(C590H940O430N6S),

C(C670H1050O460N20S), D(C500H770O320N10S). Biogas production was measured indirectly by

water displacement method. The experimental result for digester D with 26g of OFMSW

gave a higher value of 2.31L. The predictive result of OFMSW showed a parabolic

relationship with a maximum volume of 2.52L and a mass of 68g beyond digester D. The

actual digester potential was determined using modified first order equation to adequately

described the cumulative biogas production from these digesters. It was observed that the rate

of substrate biodegradability and removal of the biodegradable fractions of the substrate

could be obtained by plotting 1/t ln (dyt/dt) against the inverse of time of digestion. This

modified first order model showed that digester containing 30g pig dung, 30g cow dung and

26g municipal solid waste had the highest short term anaerobic biodegradability index

(STABI) of 6.973 and removal rate constant of -0.013 at room temperature.

Keywords: Biogas, Organic Fraction of Municipal Solid Waste (OFMSW), Biodegradability

index, Digesters, Anaerobic.

1. Introduction

The need for alternative sources of energy from renewable feedstock including biomass is on

the increase. Biological methane production from renewable substrates (biomass) is one

method that has proven promising. Biomass is a flexible feedstock that can be converted to

solid, liquid and gaseous fuels by chemical and biological processes (Ramachandra,et.al.,

2000). Biological conversion of biomass to methane (CH4) by anaerobic digestion processes

from both hand and mechanically sorted municipal solid waste, various types of fruit and

vegetable solid waste, leaves, grasses, woods, weeds and marine/freshwater biomass has been

reported (Gunaseelan, 1997). Anaerobic digestion is a process carried out by microorganism

in an oxygen free-environment; with generation of biogas mainly methane and hydrogen as it

most significant products. (Burak, et.al., 2010).

Stiffens et. al., (2000) stated that biogas comprises about methane (55-75%), carbon dioxide

(25-45%) and hydrogen (0-1%), with calorific value of 20MJ/m3 (Myles, 1985).

Biomechanization potential of organic fraction of municipal solid waste (OFMSW) from co-digestion of PIG

and COW DUNG

Membere Edward. A, Ugbebor John, Akan Udoh. E

International Journal of Environmental Sciences Volume 2 No.4, 2012 2388

The utilization of energy in the form of biogas is one of the environmentally sound

alternative renewable energy sources. The organic waste produced by municipalities, industry

and agriculture have a potential energy value that could ensure the economic viability of the

process if fully utilized (Radha et al., 2006). OFMSW is very valuable substrate for

biogasification with biogas potential per ton of waste up to 10 times that of manure

(Braber, 1995). Further benefits include the reduction in waste volume and the production of

a bio-fertilizer retaining all the nutrients of the original material (Radha et al, 2006).

Generally, organic fraction of municipal solid waste OFMSW is a very attractive waste for

the biogas plants because it has high yield potential (Radha et al., 2006). With an ever

increasing amount of municipal solid waste (MSW), pretreatment of solid waste through

anaerobic digestion has become more and more important. Radha et al, (2006) stated that

anaerobic digestion as a pretreatment tool for organic fraction of municipal solid waste can be

considered a preferable technology, an alternative to aerobic composting, and it also has

many advantages over non-biological process.

Biogas as been previously described as a gas that could be produced naturally from decay

under water or the guts of animal, or artificially in an air tight digester (Igoni et al, 2008).

As a result, biogas has been described as “a methane-rich gas that is produced from the

anaerobic digestion of organic materials in a digester” (Itodo and Phillips, 2007).

GEMET (2000) says biogas is “gas rich in methane, which is produced by the fermentation of

animal dung, human sewage or crop residues in an air tight container”. A vast amount of

literature already exist on the applications and benefits of anaerobic digestion processes

(Burak et.al., 2010) with special emphasis focused initially on anaerobic digestion of

municipal solid waste for bioenergy production almost a decade ago (Braber, 1995).

2. Materials and method

2.1 Substrate collection

Substrates utilized in this research work were organic fraction of municipal solid waste

(OFMSW) collected from the University of Port Harcourt, Nigeria and cow and pig dung as

inoculums collected from poultry and slaughter houses. These substrates were sun dried for a

period of 20 days prior to being used for biogas production. These dried substrates are then

crushed mechanically using a motar pestle. The dry weights of these biomass were weighted

with a weighing balance (Mettler PN 163) into the digesters.

2.2 Experimental design

A set of four batch reactors were used as digesters. Each digester contained fixed amount of

pig and cow dung, but an increasing amount of municipal solid waste. These digesters were

labeled A,B,C and D respectively. Compositions of each digester are as follows:

1. Digester – A: Comprised 30g pig dung, 30g cow dung and 6g OFMSW in 1500ml of

water.

2. Digester –B: Comprised 30g pig dung, 30g cow dung and 16g OFMSW in 1500ml of

water.

3. Digester-C: Comprised 30g pig dung, 30g cow dung and 18g OFMSW in 1500ml of

water.


and COW DUNG



4. Digester –D: Comprised 30g pig dung, 30g cow dung and 26g OFMSW in 1500ml of

water.

The digesters were set up as described by Itodo et al. (1992), Momoh and Nwaogazie (2008),

and biogas measurement was carried out by using the water displacement method in which

the amount of saline water (20% Nacl) (w/v, pH 4) displaced was proportional to the volume

of biogas produced. Ambient temperature measurement was determined with an analog

thermometer.

The process layout is shown below:

Figure 1: Layout of biogas production

2.3 Analysis of OFMSW properties

( i) Moisture Content Determination : This is the amount of water present in solid waste

which can be expressed as percent wet or dry weight (Yusuf, 2011).

%MC (wetwt) = 100Xa

ba

%MC (drywt) = 1.100EqXb

ba

Where,

a = initial weight of sample as measured

b = weight of sample after drying

a - b = weight of moisture content

(ii) Total solid (TS)

% TS (wet wt) = 100% - % MC (wet wt)

% TS (dry wt) = 100% - %MC (dry wt) Eq 2

(iii) Total Solid for Digesters In 1500ml of Water

TSW = Mpd + Mcd + MOFMSW Eq 3

Where,

TsW = Total solid in 1500ml of water


and COW DUNG



Mpd = mass of pig dung

Mcd = mass of cow dung

MOFMSW = mass of OFMSW

(iii) Heating Value: Energy Content of SW.

This is that heat of combustion release when the waste is burn, there are two types of heat of

combustion.

1. The higher heating value

2. The lower heating value

The higher heating value can be determined by using the Dulong’s formular (Tchobanoglouse

et al. 1977)

Hh = 32857C +141989 4...........92638

EqSO

H

Where,

Hh = Higher heating value (Kj/kg)

C, H, O, S = fraction of carbon, hydrogen, oxygen and sulphur respectively.

Alternatively, an approximate value of the energy content can be determined using khan’s

equation (Tchobanoglouse et al. 1977).

Eh = 0.051 [F+3.6(CP)] + 0.35(PLR) Eq. 5

Where,

Eh = Energy content in mj/kg

F = % of food waste

C.P = % of cardboard and paper

PLR = % of plastic, leather and rubber

The lower heating value of solid waste can be given as (Yusuf, 2011).

Eh - QL = EL Eq. 6

Where,

Eh = Higher heating value (kj/kg)

QL = Latent heat of vaporization of water (kj/kg)

EL = Lower heating value (kj/kg)

QL = 2440 (w+9H)

W = kg of moisture in 1kg waste

H = kg of hydrogen in 1kg of dry moisture.

2.4 Kinetics of biogas production analysis

Substrate biodegradability were assessed in this study using mathematical model developed

by Yusuf et al, (2011) based on the first order kinetics.


and COW DUNG



For a batch reactor system the model is given as;

KInkInym

tdt

dytIn

t

11 Eq 7

Equation 7 is analogous to the straight line equation y = mx + c , in which (Inym + Ink)

represents the slope while, (-k) represents the intercept of the plot of

daydt

VskgMCdyt

t

/1

against the inverse of the retention time. The term (Inym + Ink) is a measure of the

availability of readily and moderately degradable fractions of the substrate.

3. Result and discussion

The proximate analysis, ultimate analysis and heating values of organic fraction of municipal

solid waste (OFMSW) of sample A1, B1, C1, and D1, before mixing with inoculums for

digestion in digester A,B,C and D are presented in Table 1 through Table 12.

The dry weights obtained are then used for biomechanization i.e. anaerobic digestion.

Table 1: Proximate analysis for sample A1

Components Wet wt

(g)

% moisture

content

Moisture (g) Dry wt (g)

Newspaper 0.01 6 0.0006 0.0094

Other paper 0.02 6 0.0012 0.0188

Plastics 1.52 2 0.0304 1.4896

Cardboard 2.01 5 0.1005 1.9095

Yard waste 0.98 60 0.588 0.392

Food waste 4.28 60 2.568 1.712

Total 8.82 5.53

Table 2: Ultimate analysis of for sample A1 before digestion

Components Mass of respective element

C H O N S Ash

Newspaper 0.004 0.000 0.004 0.000 0.000 0.000

Other paper 0.008 0.001 0.008 0.000 0.000 0.001

Plastics 0.894 1.490 0.343 - - 0.149

Cardboard 0.840 0.115 0.840 0.006 0.004 0.105

Yard waste 0.188 0.024 0.149 0.012 0.001 0.018

Food waste 0.856 0.103 0.651 0.051 0.004 0.045

∑mass

% mass

∑mole

∑residual

2.79

40.34

0.23

575

1.733

25.05

1.72

4300

1.995

28.84

0.12

300

0.069

1.00

0.005

12.5

0.012

0.17

0.004

1

0.318

4.60

-

Column (3) = constant value Empirical formula = C575H4300O300N12.5S

(Sincero et al. 1999). C/N = 46:1


and COW DUNG



Column (4) =

100

23 ColumnXColumn

Column (5) = column (2) - column (4)

)(% wtwetMc 37.30 %

)(% wtdryMc 59.49 %

)(% wtwetTs 62.7 %

)(% wtdryTs 40.51 %

Table 3: Heating value of OFMSW for sample A1

Components mass (g) Typical heating

value

Heating

value (kj)

Newspaper 0.00001 17,000 0.17

Other paper 0.00002 17,000 0.34

Plastics 0.00152 33,000 50.16

Cardboard 0.00201 17,000 34.17

Yard waste 0.00098 5,000 6.86

Food waste 0.00428 7,000 21.4

0.00882 ∑HV 113.1

Heating value Hv as discarded = weightwetkgkj /13.1282300882.0

1.113

Heating value as express in Dry basis = )(/35.16

917.6

1.113weightDrykgkj

Using Dulong formular;

Hh = 32851C + 141989

8

OH + 9263S

= 32851 (0.40) + 141989

8

288.0251.0 + 9263 (0.0017) = 43683. 782 KJ/kg

The same formulas were applied to compute the values for proximate, ultimate analysis and

heating value for (B1, C1 and D1).

Table 4: Proximate analysis for sample B1

Components Wet

wt (g)

% moisture content Moisture (g) Dry wt

(g)

Newspaper 5.02 6 0.3012 4.7188

Other paper 6.42 6 0.3852 6.0348

Plastics 0.09 2 0.0018 0.0882

Cardboard 3.59 5 0.1795 3.4105

Yard waste 0.18 60 0.108 0.072

Food waste 3.70 60 2.22 1.48

Total 19.00 15.8043


and COW DUNG



Table 5: Ultimate analysis for sample B1 before digestion


C H O N S Ash

Newspaper 2.076 0.283 2.076 0.014 0.009 0.260

Other paper 2.655 0.362 2.655 0.018 0.012 0.332

Plastics 0.053 0.006 0.020 - - 0.008

Cardboard 1.501 0.205 1.501 0.010 0.007 0.188

Yard waste 0.035 0.004 0.027 0.002 0.000 0.003

Food waste 0.74 0.089 0.562 0.0044 0.006 0.038

∑mass

% mass

∑mole

∑residual

7.06

44.68

0.59

590

0.949

6.01

0.94

940

6.841

43.29

0.43

430

0.088

0.56

0.006

6

0.034

0.22

0.001

1

0.829

5.25

-

)(% wtwetMc 16.82% Empirical formula = C590H940O430N6S

)(% wtdryMc 20.22% C/N = 98.3:1

)(% wtwetTS 83.18%

)(% wtdryTS 79.78%

Table 6: Heating value of OFMSW for sample B1


value

Heating value (kj)

Newspaper 0.00502 17000 85.34

Other paper 0.00642 17000 109.14

Plastics 0.00009 33000 2.97

Cardboard 0.00359 17000 61.03

Yard waste 0.00018 7000 1.26

Food waste 0.0037 5000 18.5

0.019 ∑HV 278.24

Heating value Hv as discarded = )(/2.664,14019.0

24.278weightwetkgkj

Heating value as express in Dry basis = )(/61.17801.15

24.278weightDrykgkj

Using Dulong formular , Hh = 15637.514KJ/kg

Table 7: Ultimate analysis for sample C I

Components Wet wt (g) % moisture

content

Moisture (g) Dry wt (g)

Newspaper 3.62 6 0.2172 3.4028

Other paper 2.61 6 0.1566 2.4534

Plastics 0.05 2 0.001 0.049

Cardboard 5.82 5 0.291 5.529

Yard waste 5.00 60 3 2

Food waste 10.42 60 6.252 4.168

Total 27.52 17.6022


and COW DUNG



Table 8: Ultimate analysis for sample C I


C H O N S Ash

Newspaper 1.497 0.204 1.497 0.010 0.007 0.187

Other paper 1.079 0.147 1.079 0.007 0.005 0.135

Plastics 0.029 0.003 0.011 - - 0.005

Cardboard 2.433 0.332 2.433 0.017 0.011 0.304

Yard waste 0.96 0.12 0.76 0.06 0.006 0.094

Food waste 2.084 0.250 1.584 0.125 0.017 0.108

∑mass

% mass

∑mole

∑residual

8.082

45.92

0.67

670

1.056

6

1.05

1050

7.364

41.84

0.46

460

0.219

1.24

0.02

20

0.046

0.26

0.001

1

0.833

4.73

-

-

)(% wtwetMc 36.04% Empirical formula = C670H1050O460N20S

)(% wtdryMc 56.34% C/N = 33.5:1

)(% wtwetTS 63.96%

)(% wtdryTS 43.66 %

Table 9: Heating value of OFMSW for sample C1

Components mass (g) Typical heating value Heating value (kj)

Newspaper 0.00362 17,000 61.54

Other paper 0.00261 17,000 44.37

Plastics 0.00005 33,000 1.65

Cardboard 0.00582 17,000 98.94

Yard waste 0.005 7,000 35

Food waste 0.01042 5,000 52.1

0.02752 ∑HV 293.6

Heating value Hv as discarded = )(/60.1066802752.0

6.293weightwetkgkj

Heating value as express in Dry basis= weightDrykgkj /68.166.17

6.293

Using Dulong formular, Hh = 16235.959KJ/kg

Table 10: Proximate analysis for sample D1

Components Wet wt (g) % moisture content Moisture (g) Dry wt (g)

Newspaper 2.62 6 0.1572 2.4628

Other paper 7.05 6 0.423 6.627

Plastics 1.95 2 0.039 1.911

Cardboard 5.82 5 0.291 5.529

Yard waste 10.16 60 6.096 4.064

Food waste 12.42 60 7.452 4.968

Total 40.02 25.5618


and COW DUNG



Table 11: Ultimate analysis for sample D1 before digestion


C H O N S Ash

Newspaper 1.084 0.148 1.084 0.007 0.005 0.135

Other paper 2.916 0.398 2.916 0.020 0.013 0.364

Plastics 1.147 0.134 0.440 - - 0.191

Cardboard 2.433 0.332 2.433 0.107 0.011 0.304

Yard waste 1.951 0.244 1.544 0.122 0.012 0.191

Food waste 2.484 0.298 1.888 0.149 0.020 0.129

∑mass

% mass

∑mole

∑residual

12.015

47.0

1.00

500

1.554

6.08

1.54

770

10.305

40.31

0.64

320

0.315

1.23

0.02

10

0.061

2.39

0.002

1

1.314

5.14

-

-

)(% wtwetMc

36.13% Empirical formula = C500H770O320N10S

)(% wtdryMc 56.56% C/N = 50:1

)(% wtwetTS 63.87%

)(% wtdryTS 43.44%

Table 12: Heating value of OFMSW for sample D1


value

Heating value (kj)

Newspaper 0.00262 17,000 44.54

Other paper 0.00705 17,000 119.85

Plastics 0.00195 33,000 64.35

Cardboard 0.00582 17,000 98.94

Yard waste 0.01016 7,000 71.12

Food waste 0.01242 5,000 62.1

0.04002 ∑HV 460.9

Heating value Hv as discarded = )(/74.1151604002.0

460weightwetkgkj

Heating value as express in Dry basis= weightDrykgkj /03.18564.25

9.460

Using Dulong formular Hh = 17169.989KJ/kg

However, the Total Solid composition in each digester are presented in Table 13.

Table 13: Total Solid Composition

Digester

(1)

Pig dung

(g)

(2)

Cow

dung (g)

(3)

OFM

SW

(g)

(4)

Total solid

in1500ml

of water

(5)

% composition

of solid in

1500ml

ofwater

*(6)

%

OFMSW

Composition

**(7)

A 30 30 6 66 4.21 9.09

B 30 30 16 76 4.82 21.05

C 30 30 18 78 4.94 23.08

D 30 30 26 86 5.4 30.23


and COW DUNG



* Column(6) = %100

1500)5(

)5(X

waterofgColumn

Column

**Column (7) = %100

)5(

)4(X

Column

Column

Eq 8

The relationship between % total solid concentration in 1500 mL of water column (6) and

amount of OFMSW(g) column (4) for the four digesters A – D showed a linear curve fit

represented by equation 9 depicted in figure 2 with a goodness of fit equal to 0.904.

Y = 0.077 x + 3.513 Eq 9

Where, x represent OFMSW concentration and y represent percent (%) of total solids in

500ml of water.

Figure 2: Plot of volume of biogas and percentage total solid Vs OFMSW (g).

This equation can be used as a regression model to deduce percent (%) total solid

concentration equivalent to producing maximum biogas volume.

However, the biomechanization (Anaerobic digestion process) predictive relationship

between the cumulative biogas that can be produced and the amount of organic fraction of

municipal solid waste (OFMSW) (g) fed into the digester is shown to follow a parabolic

relationship as depicted by figure 2 defined by equation 10 with a goodness of fit of 0.762.

Y = 0.000 x2 + 0.051 x +1.192 Eq 10

Where, y represent total biogas production and x represent amount of OFMSW (g). A

maximum biogas production of 2.52L was observed at OFMSW amount of 68g which is

beyond D.

Nevertheless, in order to reduce the uncertainty in digester selection for the potential of

biogas production for the given digesters A – D, the modified first order equation on biogas

kinetics on experimental time, temperature and volume are presented in figure 3- 6.


and COW DUNG



Figure 3: Plot of 1/t In (dyt (ml/kg Vs)/dt) against 1/t for digester A

Figure 4: Plot of 1/t In (dyt (ml/kg Vs)/dt) against 1/t for digester B

Figure 5: Plot of 1/t In (dyt (ml/kg Vs)/dt) against 1/t for digester C


and COW DUNG



Figure 6: plot of 1/t In (dyt (ml/kg Vs)/dt) against 1/t for digester D

From figure 3, the room temperature short term biodegradability of the substrate in digester A

for the period under study was observed to be 5.699 while the intercept, depicting the

removal rate of biodegradable fraction was estimated to be -0.026. The model was able to fit

the data set with a goodness of fit (R2) of 0.998. Similarly, digester B,C and D had room

temperature short term biodegradability of 0.471, 1.260 and 6.973 with a removal rate

constants of -0.018, -0.051 and -0.013 and a goodness of fit of -1.78, -0.81 and 0.997 as

shown in figure 4,5 and 6 respectively.

4. Conclusion

Biogas production of organic fraction of municipal solid waste (OFMSW) using pig dung and

cow dung as inoculums was established here to be feasible at room temperature. Application

of the modified first order equation in studying the biogas production was able to predict the

pattern of biogas production with time and reduce uncertainty in digester selection. It was

observed that the maximum biogas production could be obtained from substrate in digester D

followed by digester A, C and B respectively.

The more negative the value of (k), the faster the rates of removal of the biodegradable

fraction while the more positive the value of (k), the slower the rate of removal of

biodegradable fractions. Yusuf et al, (2011).

5. References

1. Braber, K., (1995), Anaerobic digestion of municipal solid waste: A modern waste

disposal option on the verge of break through, Biomass and bioenergy, 9, pp 365-367.

2. General Environmental Multilingual Thesaurus (GEMET) 2000 (online).

Available :http://glossary.eea.eu,int./eeaglossary/b/biogas

3. Gunaseelan, V.N., (1997), Anaerobic digestion of biomass for methane production: A

review, Biomass and bioenergy, 13(1), pp 83-114.


and COW DUNG



4. Igoni, A.H. M.F.N. Abowei, J.M. Ayotamunmo, and C.L. Eze., (2008), Effect of total

solids concentration of municipal solid waste in anaerobic batch digestion on the

biogas produced. Journal of food agriculture and environment, (5(2), pp 333-337.

5. Itodo, I.N. and Phillips T.K., (2007), Nomograph for determining temperature in

anaerobic digester from ambient temperatures in the tropical Agricultural engineering.

6. Momoh, O.L.Y. & Nwaogezie, I.L., (2008), Effect of waste paper on biogas

production from co-digestion of cow dung and water hyacinth in batch reactors.

Journal: Applied science and environmental management, 124, pp 95-98.

7. Myles, R.M., (1985), Practical guide to janata Biogas plant technology. New Dehi,

India, AFPRO Action Food Production.

8. Radha, A., Visvanathan C., Armaki, T. and Annach Hatre P., (2006), Sequential batch

and continuous anaerobic digestion of municipal solid waste in pilot scale digesters.

9. Ramachandra, T.V., Joshi, N.V., and Subramanian, D.K., (2000), Present and

prospective role of bioenergy in regional energy system. Renewable and sustainable

energy review, 4, p 375.

10. Sinero, A.P. and Sinero, G.A., (1999), Environmental engineering - A design

approach. New Delhi, Prentice-Hall of India private Limited. 795.

11. Stiffen, R. Szolar O., Braun, R., (2000), Feed stock for anaerobic digestion. Making

energy and solving modern waste problem. Available at: www.adnett.org (accessed

16 September, 2011).

12. Yusuf, M.O.L. Debora, A. and Ogheneruona, D.E., (2011), Ambient temperature

kinetic assessment of biogas production from co-digestion of horse and cow dung,

Research in Agricultural Engineering, 57, pp 97-104.

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Biomechanization potential of organic fraction of ... · Generally, organic fraction of municipal solid waste OFMSW is a very attractive waste for the biogas plants because it has