Bioconversion of filter mud using vermicomposting employing two exotic and one local earthworm species

Bioresource Technology 100 (2009) 5846–5852

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Bioconversion of filter mud using vermicomposting employing two exotic and one local earthworm species Meena Khwairakpam a,*, Renu Bhargava b a b

Department of Civil Engineering, Malviya National Institute of Technology (MNIT), Jaipur 302017, India Department of Civil Engineering, Indian Institute of Technology Roorkee (IITR), Roorkee 247667, India

a r t i c l e

i n f o

Article history: Received 19 March 2009 Received in revised form 9 June 2009 Accepted 12 June 2009 Available online 15 July 2009 Keywords: Filter mud Vermicomposting Eisenia fetida Eudrilus eugeniae Perionyx excavatus

a b s t r a c t Three different earthworm species Eisenia fetida, Eudrilus eugeniae and Perionyx excavatus in individual (Monocultures) and combinations (Polycultures) were utilized to compare the suitability of worm species for vermicomposting of filter mud as well as the quality of the end product. The filter mud blended with saw dust can be directly converted into good quality fertilizer (vermicompost). Eight different reactors including three monocultures and four polycultures of E. fetida, E. eugeniae and P. excavatus and one control were used for the experiment. Vermicomposting resulted in significant reduction in C/N ratio, pH, total organic matter (TOC) but increase in electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP) and macronutrients (K, Ca and Na). Oxygen uptake rate (OUR) dropped up to 1.64–1.95 mg/g (volatile solids) VS/day for monoculture reactors and 1.45–1.78 mg/g VS/day for polycultures reactors, respectively, after 45 days of vermicomposting. Cocoon production and the earthworm biomass increased as vermicomposting progressed. On an overall the mono as well as polyculture reactors produced high quality stable compost free from pathogens and no specific differentiation could be inferred between the reactors. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction The present society, with its high population densities, heavy industrialization and intensive methods of agriculture produces ever increasing quantities of solid wastes. One of the industries that generate large quantities of recyclable organic materials is the sugarcane industry. Sugar is mainly manufactured from sugarcane and beetroot. In India, sugarcane is the key raw material for the production of sugar. India is the second largest sugar producer in the world (after Brazil), accounting for around 10–12% of world’s sugar production (ICRA, 2006). According to the Indian Directorate of Economics and Statistics, India produces on average 270 million tones of sugar cane per year and it is one of the most polluting industries. Sugarcane industry generates huge quantity of residue after the sugarcane juice has been clarified commonly known as filter mud. For about 134 million tones of sugarcane crushed, 4.0 million tones of filter mud are generated (Yadav, 1995). There is a major disposal problem for the filter mud although it is fairly rich in organic nutrients; it finds little use as agricultural fertilizer. The primary reason for this is the insoluble and imbalanced nature of the nutrient content in it. It generates intense heat (65 °C), foul odor and takes long time for natural decomposition (Sen and Chandra, 2006).

* Corresponding author. Tel.: +91 141 2713121; fax: +91 141 2529062. E-mail address: [email protected] (M. Khwairakpam). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.06.038

Disposal of this waste is becoming one of the major areas of concern for a developing country like India. Currently, a very meager quantity of the filter mud is usually used as fertilizer source and soil conditioner, or it is returned to cane fields. However, this approach is not desirable practice in view of the odor from biological degradation (Tsai et al., 2003). Available literature has proved that application of un-decomposed wastes or non-stabilized compost to land may lead to immobilization of plant nutrients and cause phytotoxicity (Butler et al., 2001). Several technologies are harnessed to deal with the organics that have the potential to pollute the environment. Existing technologies concentrate to oxidize the organics in the waste producing a new stream that has its own disposal problems. The need of the hour is to develop close loop technologies which harness the renewable energy and/or nutrient of these waste organics to fuel/ or amend the soil. Vermitechnology can be one of the appropriate techniques for the safe treatment and reuse of non-toxic filter mud by natural biodegradation. Filter mud is an ideal substrate for worms for bioconversion into fertilizer because of its fine particle size and presence of microbes. Vermitechnology application also helps in cost effective and efficient recycling of animal wastes, agricultural residues and industrial wastes. Several epigeics (Eisenia fetida, Eisenia andrei, Eudrilus eugeniae, Perionyx excavatus and Perionyx sansibaricus) have been identified as potential candidates to decompose organic waste materials (Suthar, 2007a). Some attempts have been made to biodegrade a variety of materials using vermitechnology

M. Khwairakpam, R. Bhargava / Bioresource Technology 100 (2009) 5846–5852

(Sangwan et al., 2007) however, little stress has been given to the proper treatment of filter mud emerging out of sugar industries. Therefore, the present paper is aimed at safe treatment and recycling of filter mud and production of good quality compost using vermitechnology. Three different earthworm species E. fetida, E. eugeniae, P. excavatus and their combinations were tried to compare the suitability of worm species for composting of filter mud from sugar industry as well as the quality of the end product.

2. Methods

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A quantity of 1.2 kg of initial substrate (FM) was added to each of the reactors. The quantity of FM was decided based on the findings that the earthworms can consume the material half their body weight per day under favorable conditions (Haimi and Huhta, 1986). C/N ratio plays an important role in determining the quality of compost hence, saw dust was added as a bulking agent to increase the C/N ratio to 25 as earthworm can grow better when C/ N ratio of material is about 25 (Ndegwa and Thompson, 2000a). The moisture level was maintained about 50–60% through out the study period by periodic sprinkling of adequate quantity of tap (potable) water. To prevent moisture loss, the reactors were covered with gunny bags.

2.1. Earthworm cultures 2.4. Compost analysis Three composting species of earthworms two exotic (E. fetida and E. eugeniae) and one indigenous (P. excavatus) were chosen for the experiment. E. fetida, being most commercially used worm for vermicomposting, was used for filter mud. Dominguez et al. (2001) reported that E. eugeniae is a fast-growing and productive earthworm in animal waste that is ideally suited as a source of animal feed protein as well as for rapid organic waste conversion. P. excavatus is reported to give excellent changes in organic waste resources and could be used efficiently to combat the problem of waste resources management at low-input basis (Suthar, 2007b). In the present study, exotic earthworms E. fetida and E. eugeniae were cultured in the laboratory and were randomly picked for experimentation. The indigenous species, P. excavatus was collected from the drainage area in Indian Institute of Technology Roorkee campus by hand sorting method. The species were identified at National Zoological Survey of India, Solan, India, before culturing in the field laboratory. 2.2. Filter mud (FM) Filter mud was procured from a sugar mill situated in the nearby area. Fresh filter mud was kept in shade for 2–3 weeks before using for the vermicomposting process. The partially degraded filter mud was then blended with saw dust as a bulking agent to increase the C/N ratio. The obtained mixture (FM) is used as the raw material for the vermicomposting process. The main characteristics of FM are: pH, 7.1 ± 0.2; EC, 0.1 ± 0.01 (S/m); ash content, 30.97 ± 1.3 (%); TOC, 40.03 ± 1.2 (%); TN, 1.6 ± 0.11 (%); TP, 12.61 ± 1.8 (g/kg); C/N, 24.89 ± 1.4; Na, 0.26 ± 0.05 (%); K, 0.44 ± 0.05 (%); Ca, 2.46 ± 0.75 (%). 2.3. Experimental set up The experiments were conducted in triplicate, in perforated cylindrical plastic containers of capacity 6 L. The containers were kept in temperature controlled experimentation room. The temperature in the experimentation room was maintained at 25 ± 1 °C which is the optimum temperature range for all the three species (Reinecke et al., 1992). Ten centimeter bedding was kept in all the containers using old vermicompost. Approximately 50 g (100–120 in numbers) of earthworms, having both clitellated and juvenile, were inoculated in the bedding for acclimatization of the earthworms to the new environment for 15–20 days then FM was added the next day. Eight different reactors including three monocultures and four polycultures of E. fetida, E. eugeniae and P. excavatus and one control were used for the experiment which are: (i) E. fetida (R1), (ii) E. eugeniae (R2), (iii) P. excavatus (R3), (iv) E. fetida + E. eugeniae (R4), (v) E. fetida + E. eugeniae + P. excavatus (R5), (vi) E. eugeniae + P. excavatus (R6), (vii) E. fetida + P. excavatus (R7), (viii) control (R8). The polycultures were prepared using the earthworm species in equal proportions and one control (without any worms) was kept for degradation.

About 110 g of homogenized wet samples (free from earthworms, hatchlings and cocoons) were taken out at zero day and 15th, 30th and 45th day of composting period. The zero day refers to the sample taken out before earthworm inoculation. Triplicate samples were collected and stored at 4 °C for stability parameters, i.e., oxygen uptake rate (OUR) and CO2 evolution as described in Kalamdhad et al. (2008). Bacterial population (1:10 w/v waste:water extract) including total coliforms (TC), fecal streptococci (FS) and fecal coliforms (FC) was measured by multiple fermentation method using Lactose broth (APHA, 1995). Subsamples were air dried, ground to pass to 0.2-mm sieve and stored for further analysis. Each sub-sample was analyzed for the following parameters: pH and electrical conductivity (EC) (1:10 w/v waste:water extract), ash content (550 °C for 2 h) (loss on ignition), total nitrogen (TN) using Kjeldahl method, ammonical nitrogen (NH4–N) and nitrate nitrogen (NO3–N) using KCL extraction (Tiquia and Tam, 2000), total organic carbon (TOC) determined by Shimadzu (TOC-VCSN) solid sample module (SSM5000A), total phosphorus (TP) by acid digestion using stannous chloride method (APHA, 1995), potassium (K), calcium (Ca) and sodium (Na) by acid digestion using flame photometer, trace elements including Cr, Ni, Fe, Cd, Pb, Zn and Cu (acid digest) were analyzed using atomic absorption spectroscopy (APHA, 1995). In addition earthworm growth related parameters like earthworm biomass; and total mortality were measured at the end of the vermicomposting process. 2.5. Statistical analysis All results reported are the means of three replicate. The results were statistically analyzed at 0.05 levels using one way analysis of variance (ANOVA) and Tukey’s HSD test was used as a posthoc analysis to compare the means (SPSS Package, Version 16).

3. Results and discussion 3.1. pH The end products from all the reactors showed a similar pattern of change in pH that falls in the range of 5 and 6.5, which is within the optimal range for plant growth (Goh and Haynes, 1977) which shows a shift from the initial neutral condition (7.1 ± 0.2) towards an acidic condition (Table 1). The decrease in pH may be due to mineralization of nitrogen and phosphorus into nitrites/nitrates and orthophosphates and bioconversion of the organic material into intermediate species of organic acids (Ndegwa and Thompson, 2000a). Ndegwa and Thompson (2000b) reported that the pH shift is dynamic and substrate dependent. The pH value for all the reactors varied significantly (P < 0.05) on 30th and 45th sampling days as per the ANOVA analysis of variance.

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Table 1 Variation in pH, EC and ash content during vermicomposting of filter mud. Reactors

R1 R2 R3 R4 R5 R6 R7 R8

pH

EC (S/m)

Ash content (%)

15 days

30 days

45 days

15 days

30 days

45 days

15 days

30 days

45 days

6.56 ± 0.15a 6.62 ± 0.1a 6.52 ± 0.14a 6.64 ± 0.18a 6.57 ± 0.13a 6.57 ± 0.15a 6.72 ± 0.16a 6.6 ± 0.15a

6.16 ± 0.1ac 6.46 ± 0.11ab 6.2 ± 0.12ac 6.06 ± 0.09c 6.2 ± 0.1ac 6.41 ± 0.1ab 6.7 ± 0.19b 6.26 ± 0.1ac

5.97 ± 0.09a 6.3 ± 0.11c 5.96 ± 0.1a 5.75 ± 0.1ab 5.94 ± 0.1a 5.56 ± 0.1bd 5.78 ± 0.1ab 5.46 ± 0.09d

0.15 ± 0.06a 0.14 ± 0.06a 0.14 ± 0.01a 0.14 ± 0.01a 0.16 ± 0.01a 0.23 ± 0.07a 0.22 ± 0.08a 0.14 ± 0.01a

0.28 ± 0.09a 0.26 ± 0.06a 0.27 ± 0.07a 0.28 ± 0.05a 0.26 ± 0.04a 0.36 ± 0.1a 0.25 ± 0.05a 0.19 ± 0.04a

0.19 ± 0.02ab 0.19 ± 0.01ab 0.22 ± 0.08ab 0.19 ± 0.02ab 0.21 ± 0.08ab 0.31 ± 0.08b 0.21 ± 0.08ab 0.14 ± 0.01a

31.3 ± 1.4a 31.9 ± 1.5ab 31.3 ± 1.4a 30.9 ± 1.3a 34.7 ± 1.6abc 35.7 ± 1.3bc 35.9 ± 1.3c 30.9 ± 1.3a

35.4 ± 1.4ac 34.8 ± 1.4ac 32.9 ± 1.4ac 37.3 ± 1.5a 35.5 ± 1.9ac 43.4 ± 1.8b 51.4 ± 2d 31.5 ± 1.3c

39.8 ± 2ad 37.3 ± 1.8ad 38.3 ± 2.1ad 43.4 ± 2.5ab 48.5 ± 2.4bc 53.1 ± 2.8c 53.6 ± 2.6c 33.9 ± 1.4d

Values followed by the same letter within each column are not significantly different.

3.2. Electrical conductivity (EC) A gradual increase in EC was observed in all the reactors with increase in decomposition time. An increment of 1.9–2.2, 1.2–3.7 and 1.42-folds were observed in the reactors with monocultures, polycultures and the control, respectively (Table 1). 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, and potassium) as reported by other researchers (Garg et al., 2006). There was no significant variation (P < 0.05) in EC for all the reactors in all the sampling days as per the ANOVA analysis of variance.

14.66%, 10.15%, 11.87%, 21.96%, 34.05%, 47.38%, 48.97% and 4.57% lower in the reactors R1, R2, R3, R4, R5, R6, R7 and R8, respectively, than initial substrate as shown in Table 2. The maximum reduction was observed in the reactor with the polyculture R7 (48.97%) and the minimum in R8 (4.5%). The observed results are supported by those of other researchers (Kaviraj and Sharma, 2003) who have reported 20–45% reduction of TOC as CO2 during vermicomposting of municipal or industrial wastes. TOC loss was reported more in worm inoculated reactors than the control. A highly significant variation (P < 0.05) was observed for all the reactors on all the sampling days as per the ANOVA analysis of variance. 3.5. Total phosphorous (TP)

3.3. Ash content Polycultures showed increase in ash content as compared to monocultures and control. The increment in the ash content for the monocultures and the control were 1.28, 1.20, 1.23, 1.09-fold while that of the polycultures were 1.40, 1.56, 1.71, 1.73-fold, respectively (Table 1). The maximum increase in ash content was observed in the polyculture R5 (1.73-fold). The maximum rate of increase in ash content was observed between 30th and 45th days of vermicomposting, which can be attributed to log phase of microbial activity, and increased palatability of substrate to earthworms due to its softening after initial decomposition (Metcalf and Eddy, 2003). The increase in the ash content shows that earthworms are consuming the wastes in a faster rate and the microbial assimilation is also performing the decomposition process in a good pace. The variation in ash content for all the reactors was highly significant (P < 0.05) for all the reactors on 15th, 30th and 45th days. 3.4. Total organic carbon (TOC) A large fraction of TOC was lost as CO2 as well as due to the consumption of the available carbon as a source of energy by the earthworms and the microorganisms. The TOC content was

The TP was higher in vermicompost obtained in all the reactors than the initial substrates as shown in Table 3. The TP content was 1.96, 1.93, 1.81, 1.91, 1.78, 2.03, 1.77 and 1.22 times higher in reactors with the monocultures (R1, R2 and R3), polycultures (R4, R5, R6 and R7) and the control (R8), respectively (Table 4). The maximum increment was observed in R6 with the final observed TP (25.7 g/ kg) followed by R1 (24.75), R2 (24.4) and R4 (24.17 g/kg). Increase in TP during vermicomposting is probably through mineralization and mobilization of phosphorus by bacterial and phosphatase activity of earthworms (Edwards and Lofty, 1972). The difference in TP content in the end products obtained from different reactors was significant (P < 0.05) for all the reactors in all the sampling days. 3.6. Total nitrogen (TN), ammonical nitrogen (NH4–N), nitrate nitrogen (NO3–N) The TN consists of the inorganic forms of nitrogen NH4–N and NO3–N. TN content was higher in the final products by 1.4–1.7, 1.7–2.1 and 1.1 times than the initial substrate in the monocultures (R1, R2 and R3), polycultures (R4, R5, R6 and R7) and the control (R8), respectively (Table 2). The maximum increase was observed

Table 2 Variation in TOC, TN and NH4–N during vermicomposting of filter mud. Reactors

R1 R2 R3 R4 R5 R6 R7 R8

TOC (%)

TN (%)

NH4–N (%)

15 days

30 days

45 days

15 days

30 days

45 days

15 days

30 days

45 days

39.8 ± 1a 39.4 ± 1.1a 39.7 ± 1.2a 40 ± 1.3ª 37.8 ± 0.9ª 37.2 ± 1a 37.1 ± 0.9a 40.1 ± 1.2a

37.4 ± 0.8ae 37.7 ± 0.7aed 38.8 ± 0.9ad 36.3 ± 0.8e 37.3 ± 0.7ae 32.7 ± 0.6b 28.1 ± 0.5c 39.6 ± 0.8d

34.9 ± 0.6a 36.3 ± 0.8a 35.7 ± 0.8a 32.8 ± 0.7b 29.8 ± 0.6c 27.1 ± 0.5e 26.8 ± 0.4be 38.2 ± 0.7d

1.78 ± 0.13ab 2.21 ± 0.2a 1.79 ± 0.15ab 2.06 ± 0.2ab 2.10 ± 0.2ab 1.87 ± 0.14ab 1.97 ± 0.16ab 1.70 ± 0.13b

2.06 ± 0.19ac 2.67 ± 0.22ab 2.16 ± 0.21ac 2.43 ± 0.23ab 2.89 ± 0.27b 2.23 ± 0.21ac 2.38 ± 0.24abc 1.77 ± 0.16c

2.28 ± 0.2ac 2.8 ± 0.26ab 2.44 ± 0.21ac 2.88 ± 0.29ab 3.36 ± 0.31b 2.76 ± 0.26ab 2.88 ± 0.27ab 1.80 ± 0.14c

0.30 ± 0.03a 0.42 ± 0.04b 0.36 ± 0.03ab 0.43 ± 0.04b 0.46 ± 0.04b 0.46 ± 0.05b 0.45 ± 0.05b 0.38 ± 0.03ab

0.28 ± 0.02acd 0.38 ± 0.03b 0.32 ± 0.03abcd 0.34 ± 0.03abc 0.30 ± 0.03cd 0.32 ± 0.03abcd 0.32 ± 0.03abcd 0.26 ± 0.02d

0.23 ± 0.02ac 0.34 ± 0.03c 0.26 ± 0.02a 0.20 ± 0.02a 0.20 ± 0.01a 0.22 ± 0.02a 0.19 ± 0.01a 0.38 ± 0.03b

Values followed by the same letter within each column are not significantly different.

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M. Khwairakpam, R. Bhargava / Bioresource Technology 100 (2009) 5846–5852 Table 3 Variation in NO3–N, K and TP during vermicomposting of filter mud. Reactors

R1 R2 R3 R4 R5 R6 R7 R8

NO3–N (%)

K (%)

TP (g/kg)

15 days

30 days

45 days

15 days

30 days

45 days

15 days

30 days

45 days

ND ND ND ND ND ND ND ND

0.03 ± 0.01a 0.15 ± 0.08a 0.08 ± 0.02a ND 0.12 ± 0.01a 0.2 ± 0.01a ND ND

0.12 ± 0.07ab 0.23 ± 0.15ab 0.17 ± 0.08ab 0.09 ± 0.01a 0.27 ± 0.16ab 0.47 ± 0.2b 0.09 ± 0.02b 0.05 ± 0.01b

0.49 ± 0.06a 0.7 ± 0.05b 0.46 ± 0.05a 0.45 ± 0.05a 0.48 ± 0.05a 0.66 ± 0.05b 0.48 ± 0.05a 0.47 ± 0.05a

0.68 ± 0.06acd 0.78 ± 0.06a 0.54 ± 0.06cbe 0.47 ± 0.06be 0.53 ± 0.04cde 0.77 ± 0.05a 0.66 ± 0.05ace 0.52 ± 0.05e

0.96 ± 0.07a 0.84 ± 0.06abd 0.75 ± 0.05bd 0.54 ± 0.03ce 0.93 ± 0.07ad 0.99 ± 0.06a 0.78 ± 0.07d 0.58 ± 0.05e

15.024 ± 2.1ab 14.256 ± 2ab 17.004 ± 2.5a 18.38 ± 2.6a 13.57 ± 2.1ab 12.864 ± 2ab 15.836 ± 1.9a 9.45 ± 1.5b

22.716 ± 2.49ae 21.56 ± 2.33ac 21.2 ± 2.15ac 19.26 ± 2.1ac 19.916 ± 2.1ac 23.65 ± 2.51c 16.984 ± 1.71ab 11.356 ± 1.51b

24.748 ± 2.78a 24.404 ± 2.88a 22.884 ± 2.19a 24.172 ± 2.91a 22.524 ± 2.3ab 25.7 ± 2.68a 22.352 ± 2.73ab 15.41 ± 1.81b

Values followed by the same letter within each column are not significantly different, ND: not detected.

Table 4 Variation in Na, Ca and Fe during vermicomposting of filter mud. Reactors

R1 R2 R3 R4 R5 R6 R7 R8

Na (%)

Ca (%)

Fe (%)

15 days

30 days

45 days

15 days

30 days

45 days

15 days

30 days

45 days

0.18 ± 0.04a 0.2 ± 0.03a 0.24 ± 0.03a 0.24 ± 0.04a 0.21 ± 0.04a 0.22 ± 0.04a 0.23 ± 0.04a 0.24 ± 0.04a

0.15 ± 0.03ab 0.17 ± 0.02ab 0.212 ± 0.03ab 0.196 ± 0.04ab 0.134 ± 0.04a 0.245 ± 0.03b 0.12 ± 0.03a 0.214 ± 0.04ab

0.12 ± 0.02a 0.1 ± 0.02a 0.08 ± 0.02a 0.14 ± 0.01a 0.113 ± 0.03a 0.07 ± 0.03a 0.09 ± 0.02a 0.197 ± 0.03a

2.68 ± 0.8a 2.54 ± 0.8a 2.48 ± 0.8a 2.58 ± 0.75a 2.54 ± 0.85a 2.567 ± 0.8a 2.489 ± 0.75a 2.47 ± 0.75a

2.74 ± 0.85a 2.66 ± 0.9a 2.52 ± 0.9a 2.768 ± 0.85a 2.784 ± 0.9a 2.78 ± 0.95a 2.67 ± 0.95a 2.62 ± 0.85a

2.83 ± 0.85a 2.787 ± 0.95a 2.78 ± 0.8a 2.88 ± 0.8a 2.872 ± 1a 3.07 ± 0.85a 2.92 ± 1a 2.76 ± 0.85a

0.17 ± 0.01a 0.48 ± 0.03bc 0.33 ± 0.01ab 0.38 ± 0.02b 0.60 ± 0.05c 0.60 ± 0.05dc 0.34 ± 0.02ab 0.49 ± 0.04bdc

0.37 ± 0.04ac 0.37 ± 0.04ac 0.38 ± 0.05ac 0.34 ± 0.02a 0.34 ± 0.03a 0.68 ± 0.07bc 0.62 ± 0.03c 0.32 ± 0.05a

0.43 ± 0.04ace 0.29 ± 0.02ae 0.34 ± 0.05ae 0.65 ± 0.03bcd 0.30 ± 0.04ae 0.56 ± 0.04cde 0.66 ± 0.06d 0.39 ± 0.04e

Values followed by the same letter within each column are not significantly different.

in the reactor R5 of the polycultures followed by a similar increment in the rest of the reactors; however, the control had the minimum increase. The reduction in dry mass (organic carbon in terms of CO2) due to substrate utilization by microbes and worms and their metabolic activities as well as water loss by evaporation during mineralization of organic matter (Viel et al., 1987) might have led to 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 extent of decomposition (Crawford, 1983). Earthworm activity enriches the nitrogen profile of vermicompost through microbial mediated nitrogen transformation, through addition of mucus and nitrogenous wastes secreted by earthworms (Suthar, 2007b). The exchangeable NH4–N in the vermicompost was always greater than the NO3–N during the experimentation period. A decrease in NH4–N occurred which corresponded with an increase in NO3–N at the end of the vermicomposting process (Table 2). However, the rapid decrease in NH4–N during composting did not coincide with a rapid increase in NO3–N. The difference between various forms of nitrogen would be due to immobilization/denitrification or both (Syers et al., 1979). High significance was observed in TN content variation as per the ANOVA analysis of variance (P < 0.05) for all the reactors on all the sampling days. However, significant variation (P < 0.05) was observed only on 30th and 45th days for NO3–N for all the reactors.

while it varied from 9 to 11 for polycultures (Fig. 1). However, the control showed a higher C/N value of 21.7. The C/N ratio is used as an index for maturity of organic wastes as well as a very important parameter because plants cannot assimilate nitrogen unless the ratio is in the order of 20 or less (Edwards and Bohlen, 1996). A decline in C/N ratio to less than 20 indicates an advanced degree of organic matter stabilization and reflects a satisfactory degree of maturity of organic wastes (Senesi, 1989). The decrease in C/N ratio over time might also be attributed to increase in the earthworm population (Ndegwa and Thompson, 2000a), which led to higher rate of substrate utilization and rapid decrease in organic carbon. The release of part of the carbon as carbon dioxide (CO2) in the process of respiration, production of mucus and nitrogen excrements, increases levels of nitrogen and lowers the C/N ratios (Senapati et al., 1980). The difference in C/N content in the end products obtained from different reactors was significant (P < 0.05) for all the reactors on all the sampling days.

3.7. C/N ratio The end product, i.e., vermicompost obtained in end of the experimental study had lower C/N ratio, as compared to the initial value. The C/N ratio reflects the spectra of changing carbon and nitrogen concentration of the substrate material during composting/vermicomposting process. The initial C/N ratio was maintained at 25 by adding saw dust as the bulking material. The final C/N ratios for the monocultures were observed in the range of 12–16

Fig. 1. Variation in C/N ratio during the vermicomposting of filter mud.

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3.8. Macronutrients (K, Na and Ca)

a significant variation in all the reactors (P < 0.05) for all sampling days.

The variations in the nutrient contents for all the reactors are statistically significant (P < 0.05) for all the reactors on all the sampling days. K content was 2.2, 1.9, 1.7, 1.2, 2.1, 2.3 and 1.8-fold higher in the reactors with monocultures (R1, R2 and R3) and polycultures (R4, R5, R6 and R7), respectively, as shown in Table 3. The enhanced number of microflora present in the gut of earthworms in the case of vermicomposting might have played an important role in this process and increased K2O over the control (Kaviraj and Sharma, 2003). According to Barois and Lavelle (1986) earthworm primes its symbiotic gut microflora with secreted mucus and water to increase their degradation of ingested organic matter and the release of assailable metabolites. Therefore, directly or indirectly earthworm enriches the substrate material with exchangeable-potassium. Na reduced by 53%, 61.53% and 69% for monocultures, 46%, 56.53%, 73% and 65% for polycultures and 58% for the control, respectively. There was significant variation (P < 0.05) on 15th and 30th sampling day for all the reactors for Na while no significant variation was observed on 45th day. There is only slight increase in the Ca content for all the reactors as shown in Table 4. The increments are in the range 1.15, 1.13, 1.13, 1.17, 1.16, 1.24, 1.17 and 1.12-folds for the monocultures, polycultures and control, respectively. The highest increment was observed in the reactor with polyculture reactor R6. There was no significant variation for Ca on all the sampling days. Interactions between earthworms and microorganisms are of major importance in degradation of organic matter and release of microbial nutrients (Aira et al., 2002). 3.9. Trace elements (Mn, Zn, Pb, Cd, Cr, Cu and Fe) Trace elements in small amounts may be essential for plant growth; however, in higher concentrations they are likely to have detrimental effects upon plant growth (Whittle and Dyson, 2002). So, prior to vermicompost application to the soils, there is a need to determine the trace element concentrations in the final vermicompost. In the experiments trace element concentrations (Cd, Cr, Pb, Fe and Cu) were lower than in the initial feed mixtures except for Mn and Zn. The decrease in the metal concentration is due to the accumulation of metals in the earthworm body as there is no leaching of the cations by extra water drainage or otherwise, the decrease in trace element level is due to weight loss in the course of composting followed by organic matter decomposition, release of CO2 and water and mineralization processes (Amir et al., 2005). The total metal content of final compost in all the reactors was very low which according to the standards ensure safe application of compost laid down in municipal waste (management and handling rules) notified by the Ministry of Environment and Forest, Government of India (CPHEEO, 2000) and are considered as soil fertilizer with good quality. All the heavy metal contents showed

3.10. Coliforms Coliforms are the indicators of the presence of pathogens. Use of such an indicator, as opposed to the actual disease-causing organisms, is advantageous as the indicators generally occur at higher frequencies than the pathogens and are simpler and safe to detect. The average number of TC was reduced to 99.9–99.94%, 97–99.94% and 99.65% for reactors with the monocultures, polycultures and control, respectively (Table 5). FS are commonly considered to be the best indicator of fecal population. They are more resistant to different environmental factors than the coliforms. The result for FS was observed as 99.99% reduction for the reactors with monocultures as well as polycultures and 99.8% reduction for R8. The reduction in FC was observed to be 98–99.9%, 95–99% and 93% for the reactors with the monocultures, polycultures and control, respectively. The reduction was presumably because of the elimination of the coliforms as they enter the food chain of the earthworm. The coliforms varied significantly for all the reactors (P < 0.05) on all sampling days. 3.11. Oxygen uptake rate (OUR) OUR is the most accepted method for the determination of biological activity of a material (Gomez et al., 2006). It measures compost stability by evaluating the amount of readily biodegradable organic matter still present in the sample through its carbonaceous oxygen demand. OUR reduction was observed to be 64.88%, 58.24% and 59.74% for reactors with monoculture while the reduction was observed to be 61.88%, 68.52%, 64.23% and 68.95% for the reactors with polycultures. The lowest percentage reduction was observed to be 33.19% in control reactor as shown in Fig. 2. A sharp decrease

Fig. 2. CO2 evolution during the vermicomposting of filter mud.

Table 5 Variation in FS and FC during vermicomposting of filter mud. Reactors

R1 R2 R3 R4 R5 R6 R7 R8

FS (MPN/g wet weight)

FC (MPN/g wet weight)

15 days

30 days

45 days

15 days

30 days

45 days

4.3  103 ± 400a 2.3  103 ± 300be 930 ± 90fgh 2.3  103 ± 200e 2.3  105 ± 600c 80 ± 10g 90 ± 15hg 9.3  104 ± 600d

300 ± 70a 300 ± 65a 230 ± 20a 280 ± 30a 9.3  103 ± 450c 40 ± 4a 80 ± 6a 2.3  104 ± 400d

30 ± 4a 23 ± 2a 23 ± 3a 23 ± 2a 30 ± 5a 23 ± 3a 23 ± 2a 9.3  103 ± 200b

2.3  104 ± 680a 2.3  104 ± 690a 4.3  104 ± 700c 2.3  105 ± 800d 1.5  105 ± 790e 1.5  105 ± 700fe 4.3  104 ± 500gc 2.3  105 ± 600bd

4.3  103 ± 300a 9.3  103 ± 500b 2.3  104 ± 710ch 4.3  104 ± 780de 4.3  104 ± 650e 9.3  104 ± 770f 1.5  104 ± 650g 2.3  104 ± 670h

230 ± 80ac 1.5  103 ± 160b 1.5  103 ± 150b 1.5  103 ± 140b 230 ± 70c 2300 ± 200d 9.3  103 ± 270e 1.5  104 ± 530f

Values followed by the same letter within each column are not significantly different.

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(30–43%) observed in the reactors R1, R4, R5, R6 and R7 after the initial 1 week could be due to a considerable drop in temperature and moisture content (Liang et al., 2003). OUR varied significantly for all the reactors (P < 0.05) on all sampling days. 3.12. CO2 evolution Carbon dioxide evolution is the most direct technique of compost stability because it measures carbon derived directly from the compost being tested. Thus CO2 evolution directly correlates to aerobic respiration, the truest measure of respiration and hence aerobic biological activity. Percentage reduction in CO2 evolution was observed to be 66.35%, 58.11% and 61.17% for reactors with monoculture while the reduction was observed to be 62.58%, 69.88%, 73.17%, and 75.52% for the reactors with polycultures (Fig. 3). The CO2 evolution varied significantly for all the reactors (P < 0.05) on all sampling days. The highest decrease in rate of respiration activity occurred during the initial 15–30 days for the reactor R1 with 48% while the highest decrease in rate of respiration occurred during 30–45 days in R7 with 52.63%. The decrease in CO2 evolution was very low after 45 days of composting in all worm worked reactors, indicating the stability of finished compost. 3.13. Growth and reproduction of earthworms The vermicompost was dark brown (towards blackish) in color and homogeneous after 45 days of earthworm’s activity. The changes in worm biomass for all pure as well as mixed cultures over the experimentation period are illustrated in Table 6. At the end of the 45 days, the earthworm biomass had increased slowly in all the reactors. The increase in weight of earthworm biomass during the composting period varied between 35 and 40 g. The increase in weight of earthworm biomass during the composting period varied between 35 and 40 g which amounts to 70–80% in-

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crease in biomass. The increases in biomass are in the range 60– 70% and 70–80% for the monoculture reactors and polyculture reactors, respectively. In general, the maximum increase was recorded in the case of R5 (80%) and minimum in R4 (10%). The maximum mean number of cocoons/worm/day observed for R4 (0.68) was the highest of all the cultures while R5 (0.33), R6 (0.28) and R7 (0.26) showed more or less similar value. Overall, the mean cocoon production of the reactors R4, R5, R6, R7 were very good when compared to monoculture reactors which clearly indicates that polycultures using local worms can also be utilized for the bioconversion of filter mud. In context of the number of juveniles hatched the monoculture reactors showed very poor performance as compared to the polycultures reactors. 4. Conclusions The use of filter mud as raw material in the vermicomposting systems can potentially help to convert this waste into valueadded products, i.e., vermicompost. The vermicomposts obtained in this study were rich in nitrogen, phosphorus, and potassium, and also hygienically safe as pathogens were absent confirmed by coliform results. The vermicompost obtained from monoculture and polyculture reactors were matured and stable as confirmed by the OUR results. Although, both the cultures worked equally well, the best results could be obtained from the polyculture reactors and also the increase in earthworm biomass and juveniles were much higher indicating preference of polycultures over monocultures. Acknowledgements The authors are very thankful to Uttarakhand State Council for Science and Technology (UCOST) for the financial support. References

Fig. 3. OUR variation during the vermicomposting of filter mud.

Table 6 Live biomass production (earthworms) in different reactors. Reactors

Mean weight of earthworms (g) Initial

Final

R1 R2 R3 R4 R5 R6 R7

50 50 50 50 50 50 50

85 85 80 55 90 80 60

Live biomass (% change)

No. of cocoons (worms/day)

No. of juveniles hatched/100 g of vermicompost

41.17 41.17 37.5 9.09 44.44 37.5 16.66

0.31 0.35 0.35 0.68 0.33 0.28 0.26

1 1 0 0 8 11 9

All data represent average of triplicates.

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