Municipal solid waste management through vermicomposting employing exotic and species of earthworms

Municipal solid waste management through vermicomposting employing exotic and local species of earthworms

Kaviraj a, Satyawati Sharma b,*

a School of Energy and Environmental Studies, DAVV, Indore (M.P.) 452017, India

b Centre for Rural Development and Technology, Indian Institute of Technology, New Delhi 110016, India

Received 10 March 2003; received in revised form 22 March 2003; accepted 26 March 2003

Abstract

A comparative study was conducted between exotic and local (epigeic-Eisenia fetida and anaecic-Lempito mauritii, respectively) species of earthworms for the evaluation of their efficacy in vermicomposting of municipal solid waste (MSW). Vermicomposting of MSW for 42 days resulted in significant difference between the two species in their performance measured as loss in total organic carbon, carbon-nitrogen ratio (C:N) and increase in total Kjeldahl nitrogen, electrical conductivity and total potassium and weight loss of MSW. The change in pH and increase in number of earthworms and cocoons and weight of earthworms were non-signi-ficant.

Keywords: MSW; Eisenia fetida; Lempito mauritii; Vermicomposting

1. Introduction

A rapidly increasing population and high rate of in-dustrialization has increased the problem of solid waste management. The problem has further increased in cities because of shortage of dumping sites and strict envi-ronmental legislation, so scientists are seeking for management alternatives, which should be ecofriendly, cheap and fast. Municipal solid waste (MSW) is highly organic in nature, so vermicomposting has become an appropriate alternative for the safe, hygienic and cost effective disposal of it. Earthworms feed on the organics and convert material into casting (ejected matter) rich in plant nutrients. The chemical analyses of casts show two times available magnesium, 15 times available nitrogen and seven times available potassium compared to the surrounding soil (Bridgens, 1981). A number of refer-ences are available on the potential of earthworms in vermicomposting of solid waste particularly household waste (Appelholf et al., 1998). Advanced systems for vermicomposting are based on top feeding and bottom discharge of a raised reactor thus providing stability and control over the key areas of temperature, moisture and aerobicity (Price, 1988). An improved mechanical sepa-rator, having a novel combing action, for removing live earthworms from vermicomposts has also been intro-duced by Price and Phillips (1990).

The action of earthworms in the process of vermi-composting of waste is physical and biochemical. The physical process includes substrate aeration, mixing as well as actual grinding while the biochemical process is influenced by microbial decomposition of substrate in the intestine of earthworms (Hand et al., 1998). Various studies have shown that vermicomposting of organic waste accelerates organic matter stabilization (Neuha-user et al., 1998; Frederickson et al., 1997) and gives chelating and phytohormonal elements (Tomati et al., 1995) which have a high content of microbial matter and stabilised humic substances.

In India the exotic epigeic species, like Eudrilus euginae (Ashok, 1994), Parionyx excavatus (Kale et al., 1982) and Eisenia fetida (Hartenstein et al., 1979) are being used for vermicomposting. The hazards of using alien species are well known. History is littered with examples of confrontations between indigenous and foreign organisms (Mackenzie, 1991). The introduction of foreign species has been justified by a few scientists (Lavelle et al., 1989; Murphy, 1993), though it is

170Kaviraj, S. Sharma / Bioresource Technology 90 (2003) 169-173

extremely unnecessary and undesirable to tamper with local biodiversity (Ismail, 1995). Keeping this in view E. fetida and Lempito mauritii (exotic and local species respectively) were chosen for the comparative study of their potential in vermicomposting of MSW.2.5. Species observation

The increase in growth rate, number of earthworms and cocoons and weight of earthworms were observed weekly. The mean of three replicates was used to express the results.

2. Methods

2.1. Collection and culturing of earthworms

The earthworms E. fetida were obtained from an earthworm bank (pit) in Micromodel, IIT Delhi where it has been cultured for the last 4 years (initially the species was collected from G.H.V.K. University, Banglore). The species L. mauritii was collected from the soil of Mi-cromodel, IIT Delhi and was identified by Prof. Julka, National Zoological Survey of India, Solan, India.2.6. Statistical analysis

All the reported data are the means of three repli-cates. Two way analysis of variance (ANOVA) was done to determine any significant difference among the pa-rameters analysed in vermicompost. "Student's t-distri-bution’’ was done to determine any significant difference between the numbers and weights of earthworms (E. fetida and L. mauritii) used.

3. Results and discussion

2.2. Collection of MSW

The organic waste used as substrate (MSW), was collected from the waste collection site, IIT Delhi where organic waste was being separated out manually. The waste was predecomposed for eight days prior to study.

2.3. Experimental setup

The experiments were conducted in earthenpots, each of capacity 2 kg waste, with a small hole at the bottom.

A total of 54 earthen pots were used and kept in three sets of 18 pots for E. fetida, L. mauritii and control (without any earthworms). One kilogram of waste was taken in each pot along with 200 g of cowdung and soil (100 g cowdung and 100 g soil) to provide an initial favorable environmental condition for the worms. Twenty healthy earthworms of the same size (E. fetida and L. mauritii) were introduced in each of two sets of earthen pots. Moisture content was maintained between 40% and 60% during the study. The duration of experi-ments was six weeks.

2.4. Chemical analysis

The chemical analysis of raw organic waste used and vermicompost samples, collected weekly, was done for total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total potassium (TK), electrical conductivity (EC) and pH. The TKN and TOC were estimated by micro-Kjeldahl (Singh and Pradhan, 1981) and Walkey and Black's Rapid Titration methods (1934), respec-tively. TK was estimated by Flame Emission Technique while EC and pH were determined using conductivity meter and pH meter.

Table 1 summarizes data pertaining to TOC, TKN, and C:N ratio. The initial TOC, TKN and C:N ratio of MSW were 17.6%, 0.31% and 56.7%. Data revealed a significant difference in percentage decrease of the TOC in all three treatments (L. mauritii, E. fetida and con-trol). The maximum carbon reduction, after 42 days, was obtained with E. fetida (44.3%) followed by L. mauritii (44.1) and control (17.3). Our data are sup-ported by Elvira et al. (1998) who observed 2O^12%> loss of carbon as CO2 during vermicomposting of paper mill and dairy sludges.

Total nitrogen content increased as a result of carbon loss with significant differences between the treatments (Table 1(Panel A)). The loss of dry mass (organic car-bon) in terms of CO2 as well as water loss by evapora-tion during mineralization of organic matter (Viel et al., 1987) might have determined the relative increase in nitrogen. However in general the final content of nitrogen in vermicomposting is dependent on initial nitrogen present in the waste and the extant of decom-position (Crawford, 1983; Gaur and Singh, 1995). De-crease in pH may be an important factor in nitrogen retention as this element is lost as volatile ammonia at high pH values (Hartenstein and Hartenstein, 1981).

Table 2 summarizes the data related to K and EC. A 10% increase was observed in TK by E. fetida and 5% increase by L. mauritii (control did not show any TK increase). The TK difference between treatments was significant while it was found to be non-significant rel-ative to the duration (Table 2(Panel A)). The E. fetida was superior to L. mauritii in this regard. The microflora also influences the level of available potassium. Acid production by the micro-organisms is the major mech-anism for solubilizing of insoluble potassium. The im-portant acids in phosphorus solubilisation are carbonic, nitric, and sulfuric. The enhanced number of microflora

Kaviraj, S. Sharma / Bioresource Technology 90 (2003) 169-173171

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All the treatments showed a similar pattern of change in EC, which increased from the initial value of 1.60-1.86 ms/cm in the case of E. fetida, 1.73 in L. mauritii and 1.64 ms/cm in control after the whole period of decomposition. A gradual increase in EC was observed with increase in decomposition time.These results are corroborated by Wong et al. (1997).The increase in EC might have been due to the loss of weight of organic matter and release of different mineral salts in available forms (such as phosphate, ammonium,potassium).

The results related to the weight loss and pH are depicted in Table 3. There was a decrease in total bulk weight of the substrates with the passage of time. On analysing the result by ANOVA, the decrease in weight of substrate varied significantly between the treatments and days. The pH decline in all the cases was believed to occur because of the high mineralization of the nitrogen and phosphorus into nitrates/nitrites and orthophos-phate.

Interesting results were obtained pertaining to the growth of earthworms. Although the doubling rate in terms of number was greater in the case of E. fetida (51)than in L. mauritii (46), the latter gained more weight (0.39 g/earthworm) than did E. fetida (0.20 g/earth-worm) in 42 days (Table 4). Ismail (1995), who got double numbers of L. mauritii in 38.0 days, supports our data. When the results were analyzed by t-test the dif-ferences between these two species were found to be non-significant. The increase in population might also be attributed to the C:N ratio decreasing with time (Nedgwa and Thompson, 2000).

4. Conclusion

On the basis of chemical analysis, the observations indicated the E. fetida to be superior in performance over L. mauritii, in terms of loss of TOC, reduction in carbon to nitrogen ratio, increase in EC and TK.Though the epigeic species of earthworms (i.e. E. fetida)are capable of working hard to convert all the organic waste into manure, they are of no significant value in modifying the structure of soil. The anaecic (like L.mauritii) however, are capable of both organic waste consumption as well as of modifying the soil structure.Moreover L. mauritii can also be used for other pur-poses i.e. medicinal (Reynolds and Reynolds, 1972; Hori et al., 1974), as a rich source of protein (Hennuy and Gaspar, 1986) or pig feed (Hardwood and Sabine, 1978;Makarda et al., 1979) and in nematode control (Dash et al., 1980; Yeates, 1981) besides vermicomposting.

172Kaviraj, S. Sharma / Bioresource Technology 90 (2003) 169-173

Table 2

Chemical analysis of compost produced with different treatments for EC and TK (Panel A), ANOVA of days and species for TK and EC (Panel B)

Days Panel A

7

14

21

28

35

42

Panel B Days Treatments Residual Exotic

EC

1.60 ±0.05

1.60 ±0.06

1.61 ±0.08

1.61 ±0.03

1.72 ±0.09

1.79 ±0.07

1.86 ±0.02

SS

TK

0.0004

0.0003

0.0003

TK

0.20 ±0.02

0.20 ±0.03

0.20 ±0.01

0.20 ±0.09

0.21 ±0.05

0.22 ±0.03

0.22 ±0.02

EC

0.0157

0.0625

0.0227

Local

EC

1.60 ±0.06

1.60 ±0.08

1.61 ±0.07

1.61 ±0.02

1.67 ±0.03

1.72±0.01

1.73 ±0.01

DF

TK

6

2

12

TK

0.20 ±0.09

0.20 ±0.02

0.20 ±0.03

0.21 ±0.01

0.21 ±0.05

0.21 ±0.06

0.21 ±0.02

EC

6

2

12

Control

EC

1.60 ±0.03

1.60 ±0.02

1.60±0.01

1.62 ±0.08

1.62 ±0.02

1.64 ±0.03

1.64 ±0.05

MSS

TK

0.01576

0.00015

0.00030.02

TK

0.20 ±0.01

0.20 ±0.05

0.20 ±0.03

0.20 ±0.04

0.20 ±0.03

0.20 ±0.02

0.20 ±0.01

EC

0.0026

0.0312

0.0018

F-value

TK EC

3.0 8.72

7.5 17.33

-

All values are the mean of three replicates; all values of K are given in the percentage and EC in ms/cm.

Table 3

Chemical analysis of compost produced with different treatments for weight loss and pH (Panel A), ANOVA of days and treatments for weight loss and pH (Panel B)

Days Panel A

7

14

21

28

35

42

Panel B Days Treatments Residual Exotic

Wt. losspHWt.loss

0±0.00

3.3 ±0.01

6.6 ±0.02

9.4 ±0.03

13.5±0.02

20.0±0.12

39.3±0.12

SS

Wt. losspHWt.loss

1422.3

257.8

341.8

pH

8.9 ±0.09

8.4±0.12

7.4±0.12

6.9±0.11

7.1 ±0.09

6.9 ±0.01

6.9 ±0.02

pH

5.10

5.85

40.39

Local

Wt. loss

0±0.00

3.3 ±0.09

5.5 ±0.08

5.5 ±0.06

16.8 ±0.02

16.8±0.16

30.71 ±0.10

DF

Wt. loss

6

2

12

pH

8.9 ±0.09

8.4±0.12

7.0±0.13

7.0 ±0.09

7.2 ±0.08

7.2 ±0.09

7.1 ±0.02

pH

6

2

12

Control

Wt. loss

0±0.00

2.3 ±0.08

3.6±0.06

3.6 ±0.02

8.0 ±0.06

8.0 ±0.02

9.4 ±0.03

MSS

Wt. loss

237

128.9

28.4

pH

8.9 ±0.02

8.4 ±0.03

7.2±0.01

7.2±0.01

6.7 ±0.02

6.7 ±0.06

6.7 ±0.03

pH

8.50

2.92

3.36

F-value

Wt. loss

8.34

4.53

-

pH

0.25

0.86

-

All values are the mean of three replicates; the value of weight loss is given in percentage. Table 4

Change in growth rate, number of earthworms and cocoons and weight of earthworms

Days 0

7

14 21 28 35 42Exotic

NW

20.0

20.0

20.0

21.0

22.0

37.0

51.0

GR

0.0

0.0

20.0

4.5

8.5

85.5

156.5

NC

0.00

0.10

0.26

0.80

1.60

9.60

14.0

Wt.

4.0

4.1

4.2

4.4

5.2

11.6

12.0

Local

NW

20.0

20.0

21.0

22.0

22.0

29.0

46.0

GR

0.0

0.0

3.0

6.5

7.5

46.5

130.0

NC

0.00

0.05

0.13

0.75

1.60

6.60

8.60

Wt.

6.0

6.2

6.2

6.6

7.6

13.6

18.6

N W—m e a n number of earthworms; G R—g r o w t h rate of earthworms (number) in percentage; N C—m e a n number of cocoons; Wt.—mean weight of earthworms (gm); t-calculated: earthworms' number = 0.20, earthworms' weight = 0.96.

Kaviraj, S. Sharma / Bioresource Technology 90 (2003) 169-173173

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