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Vermiconversion of wastewater sludge from textile mill mixed with anaerobically digested biogas plant slurry employing Eisenia foetida
ARTICLE IN PRESS
Ecotoxicology and Environmental Safety 65 (2006) 412–419 www.elsevier.com/locate/ecoenv
Vermiconversion of wastewater sludge from textile mill mixed with anaerobically digested biogas plant slurry employing Eisenia foetida V.K. Garga,, Priya Kaushika, Neeraj Dilbaghib a
Department of Environmental Science and Engineering, Guru Jambheshwar University, Hisar 125001, India b Department of Biotechnology, Guru Jambheshwar University, Hisar 125001, India Received 24 May 2004; received in revised form 2 March 2005 Available online 25 April 2005
Abstract Vermicomposting is commonly used for the management of organic wastes. We have investigated the potential of an epigeic earthworm, Eisenia foetida, to transform solid textile mill sludge (STMS) spiked with anaerobically digested biogas plant slurry (BPS) into vermicompost to evaluate the feasibility of vermicomposting in industries for waste management. The growth and reproduction of E. foetida was monitored in a range of different feed mixtures for 15 weeks in laboratory under controlled experimental conditions. E. foetida did not survive in fresh STMS. But worms grew and reproduced in STMS spiked with BPS feed mixtures. A greater percentage of STMS in feed mixture affected biomass gain and cocoon production by earthworms. The maximum growth was recorded in 100% BPS. The net weight gain by E. foetida in 100% BPS was two–four-fold higher than STMScontaining feed mixtures. After 15 weeks, maximum cocoons (78) were counted in 100% BPS and minimum (26) in 60% BPS+40% STMS feed. Vermicomposting resulted in pH shift toward acidic, significant reduction in C:N ratio, and increase in nitrogen, phosphorus, and potassium contents. Microbial activity measured as dehydrogenase activity increased with time up to day 75 but decreased on day 90, indicating the exhaustion of feed and decrease in microbial activity. These experiments demonstrate that vermicomposting can be an alternate technology for the recycling and environmentally safe disposal/management of textile mill sludge using an epigeic earthworm, E. foetida, if mixed with anaerobically digested BPS in appropriate ratios. r 2005 Elsevier Inc. All rights reserved. Keywords: Eisenia foetida; Vermicomposting; Solid textile mill sludge; Anaerobically digested biogas plant slurry; Biomass growth; Cocoon production; C:N ratio; Dehydrogenase activity
1. Introduction The commercially and ecologically sustainable management of industrial sludges is a great challenge worldwide. Industrial sludge disposal technologies adopted around the world include land filling, land spreading, incineration, thermal drying, lime stabilization, and composting. The authors have observed that, due to the prohibitive cost of sludge management, most of the textile mills in India dispose wastewater sludge in agricultural fields, open dumps, fellow land, and poorly managed sanitary landfills, and along railway tracks Corresponding author. Fax: +91 1662 276240.
E-mail address: [email protected] (V.K. Garg). 0147-6513/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2005.03.002
which can pollute surface or subsurface water, causing public health hazards. Meanwhile limited landfill space, more stringent national waste disposal regulations, and public consciousness have made land filling and land spreading increasingly expensive and impractical. Therefore, industries and municipalities are in search of sustainable sludge management technologies. The situation of sludge management in other developing countries is no different and may perhaps exist elsewhere also (Abbasi and Ramasamy, 2001). Use of earthworms for waste management, organic matter stabilization, soil detoxification, and vermicompost production has been reported. The transformation of industrial sludge into vermicompost is of double interest: on one hand, waste is converted into a
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value-added product and, on the other; it controls waste that is a consequence of increasing industrialization. Considerable work has been carried out on the use of earthworms in composting various organic wastes such as cattle dung (Gunadi et al., 2002); plant litter (Frederickson et al., 1997); municipal sludge (Dominguez et al., 2000); sericulture waste (Gunathilagraj and Ravignanam, 1996); paper waste (Gajalakshmi et al., 2002); horse waste (Edwards et al., 1998; Hartenstein et al., 1979); weeds (Gajalakshmi et al., 2001); pig waste (Chan and Griffiths, 1988; Reeh, 1992); agricultural residues (Bansal and Kapoor, 2000); domestic kitchen waste (Sinha et al., 2002), etc. In the past decade, many large-scale vermicomposting facilities have been developed all over the world with varying success. The largest vermicomposting facility in the United States is operated by American Resource Recovery in Westley, California. Currently 250,000 kg of earthworms process 75,000 t of waste annually. The wastes include paper–pulp waste generated from recycled cardboard, tomato residues, and green waste (Sherman-Huntoon, 2000). The Sydney Waters in New South Wales set up a vermicomposting plant of 40 million worms to degrade up to 200 t of urban waste per week (Sinha et al., 2002). Kale (1991) reported that Japan had imported 3000 t of earthworms from the United States in 1985–1987 for cellulose waste vermicomposting. But there are only a few studies on the vermicomposting of industrial sludges. Kaushik et al. (2003) and Garg et al. (2005) reported that textile mill sludge can be potentially useful as a raw substrate in vermicomposting if mixed up to 30% with cow dung (CD) or poultry droppings. Butt (1993) showed that paper-mill sludge was a suitable feed for Lumbricus terrestris under laboratory conditions. By the addition of spent yeast from the brewing industry, the C:N ratio of this sludge could be adjusted according to the requirements. Elvira et al. (1996) studied the efficiency of Eisenia andrei (Bouche) in bioconverting paper–pulp mill sludge mixed with primary sewage sludge. The presence of earthworms accelerated mineralization of organic matter, favored breakdown of structural polysaccharides, and increased humification rate. Solid paper-mill sludge mixed with sewage sludge in a 3:2 ratio resulted in the highest growth rate and the lowest mortality of E. andrei, whereas paper-mill sludge mixed with pig slurry exhibited a high mortality (Elvira et al., 1996). High mortality was attributed to changes in the environmental characteristics. Eisenia foetida is an epigeic earthworm species which lives in organic wastes and requires high moisture content, adequate amounts of suitable organic material, and dark conditions for proper growth and development (Chaudhari and Bhattacharjee, 2002; Gunadi and Edwards, 2003; Gunadi et al., 2002). In order to utilize this species successfully in vermicomposting, its survival,
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growth, and fecundity in different wastes should be known. In our laboratory, work is in progress to demonstrate that the raw material base for vermicomposting can be enlarged and some solid waste disposal problems can be solved (Garg et al., 2005; Kaushik et al., 2003, 2004). The laboratory-based experiments described in this paper aim to investigate the effects of solid textile mill sludge (STMS) spiked with biogas plant slurry (BPS) on growth and fecundity of an epigeic earthworm, E. foetida, as well to assess the physicochemical changes affected in different feed mixtures. It was hypothesized that different percentages of STMS in feed mixtures would affect the vermicompost quality and growth and reproduction of E. foetida. 2. Materials and methods 2.1. Cow dung Fresh CD was procured from the Devi Bhawan cow farm, Hisar, India. The main characteristics of CD were pH (1:10 ratio) 7.90, total organic carbon (TOC) 497 g kg 1, total Kjeldhal nitrogen (TKN) 7.1 g kg 1, total available phosphorus (TAP) 5.30 g kg 1, and C:N ratio 69.2. 2.2. Biogas plant slurry Anaerobically digested BPS was procured from postmethanation storage tank of an on-farm biogas plant. The raw material used in the biogas plant was the CD collected from an intensively livestocked cow farm at the village Agroha, Hisar, India. The main characteristics of BPS were pH (1:10 ratio) 8.30, TOC 416 g kg 1, TKN 5.2 g kg 1, TAP 5.3 g kg 1, and C:N ratio 80.0. 2.3. Solid textile mill sludge Fresh STMS was obtained from the wastewater treatment plant of a textile factory (H.P. Cotton Mill Ltd.) located near Hisar, India. The main characteristics of STMS were total solids 197 g kg 1, pH (1:10 ratio) 8.3, TOC 142 g kg 1, TKN 0.74 g kg 1, and C:N ratio 199. The sludge was dried in shade prior to use for vermicomposting. 2.4. Eisenia foetida Nonclitellated hatchlings of the earthworm E. foetida were randomly picked for use in the experiments from several stock cultures containing 500–2000 earthworms in each, maintained in the laboratory with CD as culturing material. Each hatchling weighed between 0.100 and 0.250 g. 2.5. Stoichiometry All the waste quantities were used on a dry weight basis that was obtained by oven drying known quantities of material at 110 1C in a hot air oven to constant mass.
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2.6. Experimental design Six feed mixtures having different ratios of BPS and STMS, including one with CD only, were established. One-liter cylindrical plastic containers were filled with 150 g of each feed mixture (on a dry weight basis) (Table 1). All containers were kept in darkness at room temperature (22–26 1C). The moisture content of the feed in each container was maintained at 60–80% throughout the study period by sprinkling adequate quantities of water. These mixtures were turned over manually every day for 15 days in order to eliminate volatile toxic substances. After 15 days, five nonclitellated hatchlings of E. foetida were introduced in each container. There were three replicates for each feed mixture. No additional food was added at any stage during the study period. Another set of feed mixtures without earthworms was established as control to compare the results. 2.7. Growth and fecundity study Biomass gain, clitellum development, and cocoon production by the earthworms in each feed mixture were recorded weekly for 3 months. The feed in the container was turned out, and earthworms and cocoons were separated from the feed by hand sorting, after which they were counted and weighed after washing them with water and drying them by paper towels. The worms were weighed with full guts. Then all earthworms and the feed (but not cocoons) were returned to their respective containers. At the end of the vermicomposting period, the earthworms and cocoons were separated and the final compost from each container was air-dried at room temperature. Homogenized samples of final compost were ground in a stainless steel blender and stored in airtight plastic vials for further chemical analysis. 2.8. Chemical analyses Homogenized samples (about 3 g on a dry weight basis) of the feed materials were drawn at 0, 30, 45, 60, 75, and 90 days from each container to monitor the changes in C:N ratio and dehydrogenase activity with time. Samples were drawn at day 90 only from the control feeds for physicochemical analysis. All the chemicals used were analytical reagent grade supplied by S.D. Fine Chemicals, Mumbai, India. Alkaliresistant borosilicate glass apparatus and double glass-distilled Table 1 Content (percentage) of different wastes in initial feed mixture Feed mixture no.
Biogas plant STMSa (g) slurry (BPS) (g)
Cow dung (CD) (g)
1 2 3 4 5 6
0 150 (100)b 135 (90)b 120 (80)b 105 (70)b 90 (60)b
150 (100)b 0 0 0 0 0
a
0 0 15 30 45 60
(10)b (20)b (30)b (40)b
Solid textile mill sludge. The figures in parentheses indicate the percentage content in the initial feed mixture. b
water were used throughout the study for analytical work. The samples were used for chemical analysis on a dry weight basis obtained by oven-drying the known quantities of material at 110 1C. All the samples were analyzed in triplicate and results were averaged. The results were reproducible within 3–7% error limits. The pH was determined using a double-distilled water suspension of each mixture in the ratio of 1:10 (w/v) that had been agitated mechanically for 30 min and filtered through Whatman No. 1 filter paper. TOC was measured using the method of Nelson and Sommers (1982). TKN was determined after digesting the sample with concentrated H2SO4 and concentrated HClO4 (9:1, v/v) by the Bremner and Mulvaney (1982) procedure. Total phosphorus was analyzed using the colorimetric method with molybdenum in sulfuric acid. Total potassium was determined after digesting the sample in a diacid mixture (concentrated HNO3:concentrated HClO4, 4:1, v/v), by a flame photometer (Elico, CL 22 D, Hydrabad, India). Dehydrogenase enzyme activity was measured using the method of Casida et al. (1964). One gram of each feed mixture was mixed with 1.0 mL of 2,3,5-triphenyltetrazolium chloride (3%) in 2.5 mL double-distilled water and incubated at 30 1C for 24 h. The accumulation of the end product triphenylformazan (TPF) was determined in methanol extract (10 mL) using a spectrophotometer (Elico, SL 150, Hyderabad, India) at 485 nm.
3. Results 3.1. Characteristics of initial feed mixtures The percentages of BPS and STMS in different feed mixtures given to E. foetida during the experimental period are given in Table 1. Considering the difference in characteristics of BPS and STMS, all the feed mixtures were analyzed for different physicochemical quality parameters. The pH values of initial feed mixtures (IM) were in the alkaline range (8.3–7.2). The TOC content of BPS was more than that of STMS. The TKN content ranged from 2.5 g kg 1 (in 60% BPS+40% STMS) to 7.1 g kg 1 (in 100% BPS). The TKN content decreased with increase in STMS ratio in different feed mixtures (Table 2). We also observed differences in C:N ratio and other mineral constituents in different feed mixtures. Earlier studies have reported that STMS alone (Kaushik et al., 2003) cannot be used as a raw material for vermicomposting and some additive was required in the feed mixture. 3.2. Survival and growth of Eisenia foetida in different feeds The growth curves of E. foetida in the studied feed mixtures over the observation period are given in Fig. 1. The highest worm biomass was observed in the 100% BPS (1180 mg earthworm 1) and the lowest in the 60% BPS+40% STMS feed mixture (510 mg earthworm 1). The maximum worm biomass attained in 100% CD (1120 mg earthworm 1) was slightly lower than that in 100% BPS. Increasing percentage of STMS in the feed
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Table 2 Nutrient content (g kg 1) in the initial feed mixture (IM) and the final product (FP) Feed no.
1 2 3 4 5 6 a
TOCa
pH
TKNa
TAPa
TKa
IM
FP
IM
FP
IM
FP
IM
FP
IM
FP
7.9 8.3 8.0 7.9 7.4 7.2
6.7 7.1 6.6 6.8 6.5 6.3
497 416 402 369 346 323
355 301 298 276 256 207
7.1 5.2 5.0 4.1 2.7 2.5
13.6 8.3 8.1 6.9 6.3 5.4
5.3 5.3 5.2 5.0 4.1 3.9
5.6 6.8 6.8 6.4 4.5 4.2
10.7 11.2 7.3 7.3 6.1 4.9
18.5 13.7 9.2 10.0 8.1 6.4
See text. 1400
Mean individual biomass (mg)
1200 1000 800 600 400 200 0 0
14
28
42 56 Time (days)
70
84
100%CD
100%BPS
90%BPS+10%STMS
80%BPS+20%STMS
70%BPS+30%STMS
60%BPS+40%STMS
98
Clitellum development in worms was started during the fourth or fifth week in all the feed mixtures. Cocoon production was started during the seventh week in 100% BPS, the eighth week in 90% BPS+10% STMS feed mixture, and the ninth week in the remaining feed mixtures. After 15 weeks maximum cocoons (78) were counted in 100% BPS and minimum (26) in 60% BPS+40% STMS feed. The mean number of cocoons produced was between 15.6 (in 100% BPS) and 5.2 (in 60% BPS+40% STMS) cocoons earthworm 1 for different feed mixtures tested (Table 4). The mean number of cocoons produced per worm per day of 0.29 in both 100% BPS and 100% CD was 242% greater than 0.12 cocoons produced per day in 60% BPS+40% STMS feed. 3.3. Changes in the fertilizer quality of the feed wastes
Fig. 1. Growth curves of Eisenia foetida in different feed mixtures.
mixtures promoted a decrease in biomass of E. foetida. The maximum worm biomass was attained in the 10th or 11th week in all the feed mixtures except the 60% BPS+40% STMS feed mixture (eighth week). The net weight gain by E. foetida in 100% BPS was two–fourfold higher than that in STMS-containing feed mixtures. The growth rate (mg weight gained day 1 earthworm 1) has been considered a good comparative index to compare the growth of earthworms in different feeds (Edwards et al., 1998). The highest growth rate was observed in 100% BPS (12.99 mg earthworm 1 day 1), whereas the 60% BPS+40% STMS feed mixture supported the least growth (4.61 mg earthworm 1 day 1). The net weight gain by E. foetida (wet weight) per g dry weight of food source (dry weight basis) was highest in 100% BPS (33.33 mg g 1) and lowest in 60% BPS+40% STMS feed mixture (8.6 mg g 1) (Table 3). The growth rate data and worm weight gain per unit food source data further indicated that 100% BPS is a better option as feed for E. foetida than 100% CD. Table 4 summarizes sexual development and cocoon production by E. foetida in different feed mixtures.
Changes in fertilizer value of the vermicompost produced using different feed mixtures are given in Table 2. There were slight changes in the pH values in all the feed mixtures (Table 2). In general, there was a shift toward acidic/neutral pH (6.3–7.1) from the initial alkaline pH (8.3–7.2). Most other reports on vermicomposting (Gunadi and Edwards, 2003; Mitchell, 1997) have also reported similar results. However, our results are in contradiction to the observations of Datar et al. (1997). They have reported an increase in pH with time during vermicomposting. From 25% to 28% of TOC was lost in different feed mixtures by the end of the vermicomposting period except in the 60% BPS+40% STMS feed mixture, in which TOC reduction was 35.9%, whereas TOC decrease in control feeds was in the range of 13–22% (Fig. 2a). Our results are supported by other co-workers (Elvira et al., 1998; Kaushik et al., 2003), who have reported, 20–45% loss of TOC as CO2 during vermicomposting of different industrial sludges. Tripathi and Bhardwaj (2004) have also reported a lesser decrease in TOC in control beds than in worminoculated feed beds. TKN content increased by between 2.8 and 6.5 g kg 1 in different feed mixtures, probably because of mineralization of organic matter (Table 2). TKN increase in 100% CD was two-fold
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Table 3 Growth of Eisenia foetida in different feed mixtures Feed no.
1 2 3 4 5 6
Mean initial weight Maximum weight earthworm 1 (mg) achieved earthworm 1 (mg)
Maximum weight achieved in
Net weight gain earthworm 1 (mg)
Growth rate worm 1 day (mg)
228 180 202 252 202 252
11th week 11th week 11th week 10th week 10th week 8th week
892 1000 518 446 452 258
11.58 12.99 6.73 6.37 6.46 4.61
1120 1180 720 698 654 510
1
Worm weight gained per unit dry feed mixture (mg g 1) 29.73 33.33 17.27 14.87 15.07 8.6
Table 4 Cocoon production by Eisenia foetida in different feed mixtures Feed no.
Clitellum development started after
Cocoon production started in
Total no. of cocoons produced after 15 weeks
No. of cocoons produced earthworm 1
1 2 3 4 5 6
4th 4th 4th 4th 5th 5th
9th 7th 8th 9th 9th 9th
62 78 62 49 38 26
12.4 15.6 12.4 9.8 7.6 5.2
week week week week week week
800
Initial TOC Without worm With worms
600 TOC (g/kg)
week week week week week week
400 200 0
(a)
1
2
3
4
16 TKN (g/kg)
5
6
Feed No.
Initial TKN Without worm With worms
12 8 4 0
1
2
3
(b)
5
6
4
5
6
Initial C: N Without worm With worms
160 C: N ratio
4 Feed No.
120 80 40 0
(c)
1
2
3 Feed No.
Fig 2. Comparison of TOC change (a), TKN change (b), and C:N ratio (c).
greater than in all other tested feed mixtures. Increase in TKN was in the range 0.6–2.2 g kg 1 in control feeds (Fig. 2b). The C:N ratio, one of the most widely used indices for maturity of organic wastes, decreased with time for all the animal wastes (Table 5). Initial C:N ratio was in the range 69.2–129.2. Exceptionally high C:N ratios in STMS-containing feed mixtures can be attributed to initially lower content of nitrogen in these feeds. Final C:N ratios were in the range 26.1–40.6, whereas the final C:N ratio of the control feed was higher (in the range 43.2–83.4) than worm-inoculated feeds (Fig. 2c). Dehydrogenase activity is a useful indicator of microbial activity in soil and other biological ecosystems (Garcia et al., 1997), since it is an intracellular enzyme related to the oxidative phosphorylation process (Trevors, 1984). It has also been regarded as an indicator of the advancement of the composting process (Diaz-Burgos et al., 1992). Dehydrogenase activity decreased with increasing percentage of STMS in the feed mixtures on day zero. Increase in dehydrogenase activity in all the studied wastes after 30 days indicated increased microbial activity (Table 6). Maximum dehydrogenase activity was recorded on day 75 which lowered on day 90 in all the feeds. Maximum dehydrogenase activity was recorded in 100% BPS and 100% CD (20007100 mg TPF g 1 h 1) and minimum in 60% BPS+40% STMS (500 mg TPF g 1 h 1) on day 75.
ARTICLE IN PRESS V.K. Garg et al. / Ecotoxicology and Environmental Safety 65 (2006) 412–419 Table 5 Changes in C:N ratio of different feed mixtures during vermicomposting Feed no.
1 2 3 4 5 6
Time (days) 0
30
45
60
75
90
69.2 80.0 80.4 90.0 128.2 129.2
49.6 67.1 63.7 76.4 103.8 100.7
41.8 56.2 54.9 66.2 85.3 83.5
34.9 49.3 48.6 58.7 68.6 64.9
29.7 41.5 40.6 48.9 51.5 46.8
26.1 36.8 36.8 40.0 40.6 38.3
Table 6 Changes in dehydrogenase activity (mg TPF g mixtures during vermicomposting Feed no.
1 2 3 4 5 6
1
h 1) of different feed
Time (days) 0
30
60
75
90
490 449 212 249 208 185
842 1600 510 476 455 425
1460 1885 605 505 498 486
1875 1980 845 710 545 530
1490 1360 770 355 311 379
Phosphorus content (TP) was higher in the final composts than in the IM (Table 2). Total potassium (TK) content was also higher in the final product than in the IM. In contrast, a decrease in TK has been reported for the vermicomposting of paper–pulp mill sludge (Elvira et al., 1998). They have attributed this decrease to leaching of the soluble elements by excess water that drained through mass. Benitez et al. (1999) have found that the leachates collected during vermicomposting process had higher K concentrations. These studies support our results, as water was sprinkled in such quantities in this study that there was no excess water which avoided the leaching of minerals with run off water.
4. Discussion No mortality was observed in any feed mixture during the study period. Gunadi and Edwards (2003) have reported the death of E. foetida after 2 weeks in fresh cattle solids, although physicochemical properties were suitable for the growth of the earthworms. They attributed the deaths of earthworms to the anaerobic conditions which developed after 2 weeks in fresh cattle solids. In our experiments, all the wastes were precomposted for 2 weeks and during this period all the toxic gases produced might have been eliminated. It is established that precomposting is essential to avoid the
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deaths of the worms. After the initial biomass gain, stabilization and, later, weight loss by earthworms were observed in all the feed mixtures tested. The loss in worm biomass can be attributed to the exhaustion of food. When E. foetida received food below a maintenance level, it lost weight at a rate which depended upon the quantity and nature of its ingestible substrates (Neuhauser et al., 1980). However, Dominguez et al. (2000) reported a decrease in worm biomass even when additional food was added to the experiment every week. The difference between rates of cocoon production in different feed mixtures could be related to the biochemical quality of the feed mixtures, which is one of the important factors in determining onset of cocoon production (Edwards et al., 1998; Flack and Hartenstein, 1984). The feeds that provide earthworms with a sufficient amount of easily metabolizable organic matter and nonassimilated carbohydrates favor the growth and reproduction of the earthworms (Edwards, 1988). The greater percentage of STMS in the feed mixture significantly affected cocoon production. Kaushik et al. (2003, 2004) have reported that addition of at least 30% CD in STMS was essential for the survival of E. foetida. Elvira et al. (1997) showed that E. andrei was unable to survive in paper–pulp mill sludge. However, feed mixtures of paper-mill sludge with pig and poultry slurry were suitable materials for vermicomposting. They attributed this mortality to degradation processes that result in changes in environmental characteristics. The vermicompost produced was darker in color and had been processed into a homogeneous mixture after 15 weeks of worm activity, whereas the feed mixtures maintained without earthworms remained as compact mass. The pH shift towards acidic conditions could be attributed to mineralization of the nitrogen and phosphorus into nitrites/nitrates and orthophosphates; bioconversion of the organic material led to intermediate species of organic acids (Ndegwa et al., 2000). They have also reported that different substrates result in the production of different intermediate species and hence different wastes show a different behavior in pH shift. The final TKN content in vermicompost is dependent on the initial nitrogen present in the feed material and the degree of decomposition (Crawford, 1983). According to Viel et al. (1987), losses in organic carbon might be responsible for nitrogen addition. Addition of nitrogen in the form of mucus, nitrogenous excretory substances, growth-stimulating hormones and enzymes from earthworms have also been reported (Tripathi and Bhardwaj, 2004). According to them, these nitrogen-rich substances were not originally present in the feed material and hence might have contributed to the additional nitrogen content. Decrease in pH may be another important factor in nitrogen retention as this element is lost as volatile ammonia at higher pH values
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(Hartenstein and Hartenstein, 1981). Earthworms also have a great impact on nitrogen transformations in manure, by enhancing nitrogen mineralization, so that mineral nitrogen was retained in the nitrate form (Atiyeh et al., 2000). According to Senapati et al. (1980), loss of carbon as carbon dioxide in the process of respiration and production of mucus and nitrogenous excrements enhances the level of nitrogen, which lowers the C:N ratio in the feeds during vermicomposting. Our results are supported by the observations that TKN in different vermicomposts was two–five-fold higher than control feeds (Fig. 2b). Similarly, decrease in the TOC and C:N ratio was greater in worm-inoculated feed mixtures than in the respective controls (Fig. 2a and c). This indicates that less time is required for waste stabilization in the presence of worms. Levi-Minzi et al. (1986) reported that the C:N ratio of farmyard manure decreased after storing for a period of 3 months. But in our experiments, decrease in the C:N ratio was observed even after 30 days from the start of the experiment, demonstrating much more rapid decomposition and higher rates of mineralization of the organic matter (Table 5). Dehydrogenase activity is dependent on the substrate availability (Moore and Russel, 1972), so the decrease of the activity means that most of the easily available organic matter had been decomposed/exhausted before day 90 of the vermicomposting process under the given conditions. Increase in TP during vermicomposting is probably due to mineralization and mobilization of phosphorus due to bacterial and faecal phosphatase activity of earthworms (Edwards and Lofty, 1972). Satchell and Martin (1984) found an increase of 25% in TP of paper waste sludge, after worm activity. They contributed this increase in TP to direct action of worm gut enzymes and indirectly by stimulation of the microflora.
5. Conclusion The information presented in this paper provides a basis for the utilization of STMS spiked with BPS in small as well as large-scale vermicomposting facilities. The growth and reproduction of the E. foetida was best when allowed to feed on 100% BPS or 100% CD. Addition of STMS in BPS retarded the biomass gain and reproduction by the worms. The growth rate and cocoon production by the earthworms was having an inverse relationship with the percentage of STMS in the feed mixture. The net weight gain by the earthworms was significantly lower in feed mixtures having 40% STMS. Our results, also reported in literature, establish a direct relationship between the worm biomass growth and the quality of the food (Butt, 1993; Elvira et al., 1998; Kaushik et al., 2004). It appears that the initial few weeks after introduction of earthworms to feed mixtures
are the most critical. During this period, most of the decomposition and stabilization of feed mixtures by the earthworms occurs. The pH of final product was lower than that of initial feeds, which may be attributed to evolution of CO2 and accumulation of organic acids. The vermicomposting process not only decreased the organic carbon content but also substantially increased the nitrogen content. The final product was more stabilized, as demonstrated by a significant decrease in C:N ratio. The decrease in dehydrogenase activity at 90 days sampling indicates the exhaustion of easily metabolizable components of the feed. This study demonstrates the usefulness of vermicomposting technology for the management of STMS. However, further studies are needed on the use of STMS-containing vermicompost in fields.
References Abbasi, S.A., Ramasamy, E.V., 2001. Solid Waste Management with Earthworms. Discovery Publishing House, New Delhi, p. 78. Atiyeh, R.M., Dominguez, J., Subler, S., Edwards, C.A., 2000. Changes in biochemical properties of cow manure during processing by earthworms (Eisenia andrei Bouche) and the effects on seedling growth. Pedobiologia 44, 709–724. Bansal, S., Kapoor, K.K., 2000. Vermicomposting of crop residues and cattle dung with Eisenia foetida. Bioresour. Technol. 73, 95–98. Benitez, E., Nogales, R., Elvira, C., Masciandaro, G., Ceccanti, B., 1999. Enzyme activities as indicators of the stabilization of sewage sludge composting with Eisenia foetida. Bioresour. Technol. 67, 297–303. Bremner, J.M., Mulvaney, R.G., 1982. Nitrogen total. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Method of Soil Analysis. American Society of Agronomy, Madison, WI, pp. 575–624. Butt, K.R., 1993. Utilization of solid paper mill sludge and spent brewery yeast as a feed for soil-dwelling earthworms. Bioresour. Technol. 44, 105–107. Casida Jr., L.E., Klevin, D.A., Santoro, T., 1964. Soil dehydrogenase activity. Soil Sci. 93, 371–376. Chan, L.P.S., Griffiths, D.A., 1988. The vermicomposting of pretreated pig manure. Biol. Wastes 24, 57–69. Chaudhari, P.S., Bhattacharjee, G., 2002. Capacity of various experimental diets to support biomass and reproduction of Perionyx excavatus. Bioresour. Technol. 82, 147–150. Crawford, J.H., 1983. Review of composting. Process Biochem. 18, 14–15. Datar, M.T., Rao, M.N., Reddy, S., 1997. Vermicomposting—a technological option for solid waste management. J. Solid Waste Technol. Manage. 24 (2), 89–93. Diaz-Burgos, M.A., Ceccanti, B., Polo, A., 1992. Monitoring biochemical activity during sewage sludge composting. Biol. Fertil. Soil 16, 145–150. Dominguez, J., Edwards, C.A., Webster, M., 2000. Vermicomposting of sewage sludge: effects of bulking materials on the growth and reproduction of the earthworm Eisenia andrei. Pedobiologia 44, 24–32. Edwards, C.A., 1988. Breakdown of animal, vegetable and industrial organic wastes by earthworms. In: Edwards, C.A., Neuhauser, E.F. (Eds.), Earthworms in Waste and Environmental Management. SPB Academic Publishing, The Hague, pp. 21–31. Edwards, C.A., Lofty, J.R., 1972. Biology of Earthworms. Chapman & Hall, London.
ARTICLE IN PRESS V.K. Garg et al. / Ecotoxicology and Environmental Safety 65 (2006) 412–419 Edwards, C.A., Dominguez, J., Neuhauser, E.F., 1998. Growth and reproduction of Parionyx excavatus (Perr.) (Megascolecidae) as factors in organic waste management. Biol. Fertil. Soils 27, 155–161. Elvira, C., Goicoechea, M., Sampdro, L., Mato, S., Nogales, R., 1996. Bioconversion of solid paper–pulp mill sludge by earthworms. Bioresour. Technol. 75, 173–177. Elvira, C., Sampedro, L., Dominguez, J., Mato, S., 1997. Vermicomposting of wastewater sludge from paper–pulp industry with nitrogen rich materials. Soil Biol. Biochem. 29, 759–762. Elvira, C., Sampedro, L., Benitez, E., Nogales, R., 1998. Vermicomposting of sludges from paper mill and dairy industries with Eisenia andrei: a pilot scale study. Bioresour. Technol. 63, 205–211. Flack, F.M., Hartenstein, R., 1984. Growth of the earthworm Eisenia foetida on microorganisms and cellulose. Soil Biol. Biochem. 16, 491–495. Frederickson, J., Butt, K.R., Morris, R.M., Daniel, C., 1997. Combining vermiculture with traditional green waste composting system. Soil Biol. Biochem. 29, 725–730. Gajalakshmi, S., Ramasamy, E.V., Abbasi, S.A., 2001. Assessment of sustainable vermiconversion of water hyacinth at different reactor efficiencies employing Eudrilus engeniae Kingburg. Bioresour. Technol. 80, 131–135. Gajalakshmi, S., Ramasamy, E.V., Abbasi, S.A., 2002. Vermicomposting of paper waste with the anecic earthworm Lampito mauritii Kingburg. Indian J. Chem. Technol. 9, 306–311. Garcia, C., Hernandez, T., Costa, F., 1997. Potential use of dehydrogenase activity as an index of microbial activity in degraded soils. Commun. Soil Sci. Plant An. 28, 123–134. Garg, V.K., Kaushik, Priya, 2005. Vermistabilization of textile mill sludge spiked with poultry droppings by an epigeic earthworm Eisenia foetida. Bioresour. Technol. 96, 1189–1193. Gunadi, B., Blount, C., Edward, C.A., 2002. The growth and fecundity of Eisenia foetida (Savigny) in cattle solids pre-composted for different periods. Pedobiologia 46, 15–23. Gunadi, B., Edwards, C.A., 2003. The effect of multiple applications of different organic wastes on the growth, fecundity and survival of Eisenia foetida ( Savigny) (Lumbricidae). Pedobiologia 47 (4), 321–330. Gunathilagraj, K., Ravignanam, T., 1996. Vermicomposting of sericulture wastes. Madras Agric. J., 455–457. Hartenstein, R., Hartenstein, F., 1981. Physico-chemical changes affected in activated sludge by the earthworm Eisenia foetida. J. Environ. Qual. 10, 377–382. Hartenstein, R., Neuhauser, E.F., Kaplan, D.L., 1979. Reproductive potential of the earthworm Eisenia foetida. Oecologia 43, 329–340. Kale, R., 1991. Vermiculture: Scope for New Biotechnology. Zoological Survey of India, Calcutta. Kaushik, Priya, Garg, V.K., 2003. Vermicomposting of mixed solid textile mill sludge and cow dung with the epigeic earthworm Eisenia foetida. Bioresour. Technol. 90, 311–316.
419
Kaushik, Priya, Garg, V.K., 2004. Dynamics of biological and chemical parameters during vermicomposting of solid textile mill sludge mixed with dung and agricultural residues. Bioresour. Technol. 94 (2), 203–209. Levi-Minzi, R., Riffaldi, R., Saviozzi, A., 1986. Organic matter and nutrients in fresh and mature farmyard manure. Agric. Wastes 16, 225–236. Mitchell, A., 1997. Production of Eisenia foetida and vermicompost from feed lot cattle manure. Soil Biol. Biochem. 29, 763–766. Moore, A.W., Russel, J.S., 1972. Factors affecting dehydro genase activity as an index of soil fertility. Plant Soil 37, 675–682. Ndegwa, P.M., Thompson, S.A., Das, K.C., 2000. Effects of stocking density and feeding rate on vermicomposting of biosolids. Bioresour. Technol. 71, 5–12. Nelson, D.W., Sommers, L.E., 1982. Total carbon and organic carbon and organic matter. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Method of Soil Analysis. American Society of Agronomy, Madison, WI, pp. 539–579. Neuhauser, E.F., Hartenstein, R., Kaplan, D.L., 1980. Growth of the earthworm Eisenia foetida in relation to population density and food rationing. OIKOS 35, 93–98. Reeh, U., 1992. Influence of population densities on growth and reproduction of the earthworm Eisenia andrei on pig manure. Soil Biol. Biochem. 24, 1327–1331. Satchell, J.E., Martin, K., 1984. Phosphate activity in earthworm faeces. Soil Biol. Biochem. 16, 191–194. Senapati, B.K., Dash, M.C., Rane, A.K., Panda, B.K., 1980. Observation on the effect of earthworms in the decomposition process in soil under laboratory conditions. Comp. Physiol. Ecol. 5, 140–142. Sherman-Huntoon, R., 2000. Latest developments in mid-to-largescale vermicomposting. Biocycle 41 (11), 51–54. Sinha, R.K., Heart, S., Agarwal, S., Asadi, R., Carretero, E., 2002. Vermiculture and waste management: study of action of earthworms Eisenia foetida, Eudrilus euginae and Parionyx excavatus on biodegradation of some community wastes in India and Australia. Environmentalist 22, 261–268. Trevors, J.T., 1984. Dehydrogenase activity in soil. A comparison between the INT and TTC assay. Soil Biol. Biochem. 16, 673–674. Tripathi, G., Bhardwaj, P., 2004. Comparative studies on biomass production, life cycles and composting efficiency of Eisenia foetida (Savigny) and Lampito mauritii (Kinberg). Bioresour. Technol. 95, 77–83. Viel, M., Sayag, D., Andre, L., 1987. Optimization of agricultural, industrial waste management through in-vessel composting. In: de Bertoldi, M. (Ed.), Compost: Production, Quality and Use. Elseiver Applied Science, Essex, pp. 230–237.
Ecotoxicology and Environmental Safety 65 (2006) 412–419 www.elsevier.com/locate/ecoenv
Vermiconversion of wastewater sludge from textile mill mixed with anaerobically digested biogas plant slurry employing Eisenia foetida V.K. Garga,, Priya Kaushika, Neeraj Dilbaghib a
Department of Environmental Science and Engineering, Guru Jambheshwar University, Hisar 125001, India b Department of Biotechnology, Guru Jambheshwar University, Hisar 125001, India Received 24 May 2004; received in revised form 2 March 2005 Available online 25 April 2005
Abstract Vermicomposting is commonly used for the management of organic wastes. We have investigated the potential of an epigeic earthworm, Eisenia foetida, to transform solid textile mill sludge (STMS) spiked with anaerobically digested biogas plant slurry (BPS) into vermicompost to evaluate the feasibility of vermicomposting in industries for waste management. The growth and reproduction of E. foetida was monitored in a range of different feed mixtures for 15 weeks in laboratory under controlled experimental conditions. E. foetida did not survive in fresh STMS. But worms grew and reproduced in STMS spiked with BPS feed mixtures. A greater percentage of STMS in feed mixture affected biomass gain and cocoon production by earthworms. The maximum growth was recorded in 100% BPS. The net weight gain by E. foetida in 100% BPS was two–four-fold higher than STMScontaining feed mixtures. After 15 weeks, maximum cocoons (78) were counted in 100% BPS and minimum (26) in 60% BPS+40% STMS feed. Vermicomposting resulted in pH shift toward acidic, significant reduction in C:N ratio, and increase in nitrogen, phosphorus, and potassium contents. Microbial activity measured as dehydrogenase activity increased with time up to day 75 but decreased on day 90, indicating the exhaustion of feed and decrease in microbial activity. These experiments demonstrate that vermicomposting can be an alternate technology for the recycling and environmentally safe disposal/management of textile mill sludge using an epigeic earthworm, E. foetida, if mixed with anaerobically digested BPS in appropriate ratios. r 2005 Elsevier Inc. All rights reserved. Keywords: Eisenia foetida; Vermicomposting; Solid textile mill sludge; Anaerobically digested biogas plant slurry; Biomass growth; Cocoon production; C:N ratio; Dehydrogenase activity
1. Introduction The commercially and ecologically sustainable management of industrial sludges is a great challenge worldwide. Industrial sludge disposal technologies adopted around the world include land filling, land spreading, incineration, thermal drying, lime stabilization, and composting. The authors have observed that, due to the prohibitive cost of sludge management, most of the textile mills in India dispose wastewater sludge in agricultural fields, open dumps, fellow land, and poorly managed sanitary landfills, and along railway tracks Corresponding author. Fax: +91 1662 276240.
E-mail address: [email protected] (V.K. Garg). 0147-6513/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2005.03.002
which can pollute surface or subsurface water, causing public health hazards. Meanwhile limited landfill space, more stringent national waste disposal regulations, and public consciousness have made land filling and land spreading increasingly expensive and impractical. Therefore, industries and municipalities are in search of sustainable sludge management technologies. The situation of sludge management in other developing countries is no different and may perhaps exist elsewhere also (Abbasi and Ramasamy, 2001). Use of earthworms for waste management, organic matter stabilization, soil detoxification, and vermicompost production has been reported. The transformation of industrial sludge into vermicompost is of double interest: on one hand, waste is converted into a
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value-added product and, on the other; it controls waste that is a consequence of increasing industrialization. Considerable work has been carried out on the use of earthworms in composting various organic wastes such as cattle dung (Gunadi et al., 2002); plant litter (Frederickson et al., 1997); municipal sludge (Dominguez et al., 2000); sericulture waste (Gunathilagraj and Ravignanam, 1996); paper waste (Gajalakshmi et al., 2002); horse waste (Edwards et al., 1998; Hartenstein et al., 1979); weeds (Gajalakshmi et al., 2001); pig waste (Chan and Griffiths, 1988; Reeh, 1992); agricultural residues (Bansal and Kapoor, 2000); domestic kitchen waste (Sinha et al., 2002), etc. In the past decade, many large-scale vermicomposting facilities have been developed all over the world with varying success. The largest vermicomposting facility in the United States is operated by American Resource Recovery in Westley, California. Currently 250,000 kg of earthworms process 75,000 t of waste annually. The wastes include paper–pulp waste generated from recycled cardboard, tomato residues, and green waste (Sherman-Huntoon, 2000). The Sydney Waters in New South Wales set up a vermicomposting plant of 40 million worms to degrade up to 200 t of urban waste per week (Sinha et al., 2002). Kale (1991) reported that Japan had imported 3000 t of earthworms from the United States in 1985–1987 for cellulose waste vermicomposting. But there are only a few studies on the vermicomposting of industrial sludges. Kaushik et al. (2003) and Garg et al. (2005) reported that textile mill sludge can be potentially useful as a raw substrate in vermicomposting if mixed up to 30% with cow dung (CD) or poultry droppings. Butt (1993) showed that paper-mill sludge was a suitable feed for Lumbricus terrestris under laboratory conditions. By the addition of spent yeast from the brewing industry, the C:N ratio of this sludge could be adjusted according to the requirements. Elvira et al. (1996) studied the efficiency of Eisenia andrei (Bouche) in bioconverting paper–pulp mill sludge mixed with primary sewage sludge. The presence of earthworms accelerated mineralization of organic matter, favored breakdown of structural polysaccharides, and increased humification rate. Solid paper-mill sludge mixed with sewage sludge in a 3:2 ratio resulted in the highest growth rate and the lowest mortality of E. andrei, whereas paper-mill sludge mixed with pig slurry exhibited a high mortality (Elvira et al., 1996). High mortality was attributed to changes in the environmental characteristics. Eisenia foetida is an epigeic earthworm species which lives in organic wastes and requires high moisture content, adequate amounts of suitable organic material, and dark conditions for proper growth and development (Chaudhari and Bhattacharjee, 2002; Gunadi and Edwards, 2003; Gunadi et al., 2002). In order to utilize this species successfully in vermicomposting, its survival,
413
growth, and fecundity in different wastes should be known. In our laboratory, work is in progress to demonstrate that the raw material base for vermicomposting can be enlarged and some solid waste disposal problems can be solved (Garg et al., 2005; Kaushik et al., 2003, 2004). The laboratory-based experiments described in this paper aim to investigate the effects of solid textile mill sludge (STMS) spiked with biogas plant slurry (BPS) on growth and fecundity of an epigeic earthworm, E. foetida, as well to assess the physicochemical changes affected in different feed mixtures. It was hypothesized that different percentages of STMS in feed mixtures would affect the vermicompost quality and growth and reproduction of E. foetida. 2. Materials and methods 2.1. Cow dung Fresh CD was procured from the Devi Bhawan cow farm, Hisar, India. The main characteristics of CD were pH (1:10 ratio) 7.90, total organic carbon (TOC) 497 g kg 1, total Kjeldhal nitrogen (TKN) 7.1 g kg 1, total available phosphorus (TAP) 5.30 g kg 1, and C:N ratio 69.2. 2.2. Biogas plant slurry Anaerobically digested BPS was procured from postmethanation storage tank of an on-farm biogas plant. The raw material used in the biogas plant was the CD collected from an intensively livestocked cow farm at the village Agroha, Hisar, India. The main characteristics of BPS were pH (1:10 ratio) 8.30, TOC 416 g kg 1, TKN 5.2 g kg 1, TAP 5.3 g kg 1, and C:N ratio 80.0. 2.3. Solid textile mill sludge Fresh STMS was obtained from the wastewater treatment plant of a textile factory (H.P. Cotton Mill Ltd.) located near Hisar, India. The main characteristics of STMS were total solids 197 g kg 1, pH (1:10 ratio) 8.3, TOC 142 g kg 1, TKN 0.74 g kg 1, and C:N ratio 199. The sludge was dried in shade prior to use for vermicomposting. 2.4. Eisenia foetida Nonclitellated hatchlings of the earthworm E. foetida were randomly picked for use in the experiments from several stock cultures containing 500–2000 earthworms in each, maintained in the laboratory with CD as culturing material. Each hatchling weighed between 0.100 and 0.250 g. 2.5. Stoichiometry All the waste quantities were used on a dry weight basis that was obtained by oven drying known quantities of material at 110 1C in a hot air oven to constant mass.
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2.6. Experimental design Six feed mixtures having different ratios of BPS and STMS, including one with CD only, were established. One-liter cylindrical plastic containers were filled with 150 g of each feed mixture (on a dry weight basis) (Table 1). All containers were kept in darkness at room temperature (22–26 1C). The moisture content of the feed in each container was maintained at 60–80% throughout the study period by sprinkling adequate quantities of water. These mixtures were turned over manually every day for 15 days in order to eliminate volatile toxic substances. After 15 days, five nonclitellated hatchlings of E. foetida were introduced in each container. There were three replicates for each feed mixture. No additional food was added at any stage during the study period. Another set of feed mixtures without earthworms was established as control to compare the results. 2.7. Growth and fecundity study Biomass gain, clitellum development, and cocoon production by the earthworms in each feed mixture were recorded weekly for 3 months. The feed in the container was turned out, and earthworms and cocoons were separated from the feed by hand sorting, after which they were counted and weighed after washing them with water and drying them by paper towels. The worms were weighed with full guts. Then all earthworms and the feed (but not cocoons) were returned to their respective containers. At the end of the vermicomposting period, the earthworms and cocoons were separated and the final compost from each container was air-dried at room temperature. Homogenized samples of final compost were ground in a stainless steel blender and stored in airtight plastic vials for further chemical analysis. 2.8. Chemical analyses Homogenized samples (about 3 g on a dry weight basis) of the feed materials were drawn at 0, 30, 45, 60, 75, and 90 days from each container to monitor the changes in C:N ratio and dehydrogenase activity with time. Samples were drawn at day 90 only from the control feeds for physicochemical analysis. All the chemicals used were analytical reagent grade supplied by S.D. Fine Chemicals, Mumbai, India. Alkaliresistant borosilicate glass apparatus and double glass-distilled Table 1 Content (percentage) of different wastes in initial feed mixture Feed mixture no.
Biogas plant STMSa (g) slurry (BPS) (g)
Cow dung (CD) (g)
1 2 3 4 5 6
0 150 (100)b 135 (90)b 120 (80)b 105 (70)b 90 (60)b
150 (100)b 0 0 0 0 0
a
0 0 15 30 45 60
(10)b (20)b (30)b (40)b
Solid textile mill sludge. The figures in parentheses indicate the percentage content in the initial feed mixture. b
water were used throughout the study for analytical work. The samples were used for chemical analysis on a dry weight basis obtained by oven-drying the known quantities of material at 110 1C. All the samples were analyzed in triplicate and results were averaged. The results were reproducible within 3–7% error limits. The pH was determined using a double-distilled water suspension of each mixture in the ratio of 1:10 (w/v) that had been agitated mechanically for 30 min and filtered through Whatman No. 1 filter paper. TOC was measured using the method of Nelson and Sommers (1982). TKN was determined after digesting the sample with concentrated H2SO4 and concentrated HClO4 (9:1, v/v) by the Bremner and Mulvaney (1982) procedure. Total phosphorus was analyzed using the colorimetric method with molybdenum in sulfuric acid. Total potassium was determined after digesting the sample in a diacid mixture (concentrated HNO3:concentrated HClO4, 4:1, v/v), by a flame photometer (Elico, CL 22 D, Hydrabad, India). Dehydrogenase enzyme activity was measured using the method of Casida et al. (1964). One gram of each feed mixture was mixed with 1.0 mL of 2,3,5-triphenyltetrazolium chloride (3%) in 2.5 mL double-distilled water and incubated at 30 1C for 24 h. The accumulation of the end product triphenylformazan (TPF) was determined in methanol extract (10 mL) using a spectrophotometer (Elico, SL 150, Hyderabad, India) at 485 nm.
3. Results 3.1. Characteristics of initial feed mixtures The percentages of BPS and STMS in different feed mixtures given to E. foetida during the experimental period are given in Table 1. Considering the difference in characteristics of BPS and STMS, all the feed mixtures were analyzed for different physicochemical quality parameters. The pH values of initial feed mixtures (IM) were in the alkaline range (8.3–7.2). The TOC content of BPS was more than that of STMS. The TKN content ranged from 2.5 g kg 1 (in 60% BPS+40% STMS) to 7.1 g kg 1 (in 100% BPS). The TKN content decreased with increase in STMS ratio in different feed mixtures (Table 2). We also observed differences in C:N ratio and other mineral constituents in different feed mixtures. Earlier studies have reported that STMS alone (Kaushik et al., 2003) cannot be used as a raw material for vermicomposting and some additive was required in the feed mixture. 3.2. Survival and growth of Eisenia foetida in different feeds The growth curves of E. foetida in the studied feed mixtures over the observation period are given in Fig. 1. The highest worm biomass was observed in the 100% BPS (1180 mg earthworm 1) and the lowest in the 60% BPS+40% STMS feed mixture (510 mg earthworm 1). The maximum worm biomass attained in 100% CD (1120 mg earthworm 1) was slightly lower than that in 100% BPS. Increasing percentage of STMS in the feed
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Table 2 Nutrient content (g kg 1) in the initial feed mixture (IM) and the final product (FP) Feed no.
1 2 3 4 5 6 a
TOCa
pH
TKNa
TAPa
TKa
IM
FP
IM
FP
IM
FP
IM
FP
IM
FP
7.9 8.3 8.0 7.9 7.4 7.2
6.7 7.1 6.6 6.8 6.5 6.3
497 416 402 369 346 323
355 301 298 276 256 207
7.1 5.2 5.0 4.1 2.7 2.5
13.6 8.3 8.1 6.9 6.3 5.4
5.3 5.3 5.2 5.0 4.1 3.9
5.6 6.8 6.8 6.4 4.5 4.2
10.7 11.2 7.3 7.3 6.1 4.9
18.5 13.7 9.2 10.0 8.1 6.4
See text. 1400
Mean individual biomass (mg)
1200 1000 800 600 400 200 0 0
14
28
42 56 Time (days)
70
84
100%CD
100%BPS
90%BPS+10%STMS
80%BPS+20%STMS
70%BPS+30%STMS
60%BPS+40%STMS
98
Clitellum development in worms was started during the fourth or fifth week in all the feed mixtures. Cocoon production was started during the seventh week in 100% BPS, the eighth week in 90% BPS+10% STMS feed mixture, and the ninth week in the remaining feed mixtures. After 15 weeks maximum cocoons (78) were counted in 100% BPS and minimum (26) in 60% BPS+40% STMS feed. The mean number of cocoons produced was between 15.6 (in 100% BPS) and 5.2 (in 60% BPS+40% STMS) cocoons earthworm 1 for different feed mixtures tested (Table 4). The mean number of cocoons produced per worm per day of 0.29 in both 100% BPS and 100% CD was 242% greater than 0.12 cocoons produced per day in 60% BPS+40% STMS feed. 3.3. Changes in the fertilizer quality of the feed wastes
Fig. 1. Growth curves of Eisenia foetida in different feed mixtures.
mixtures promoted a decrease in biomass of E. foetida. The maximum worm biomass was attained in the 10th or 11th week in all the feed mixtures except the 60% BPS+40% STMS feed mixture (eighth week). The net weight gain by E. foetida in 100% BPS was two–fourfold higher than that in STMS-containing feed mixtures. The growth rate (mg weight gained day 1 earthworm 1) has been considered a good comparative index to compare the growth of earthworms in different feeds (Edwards et al., 1998). The highest growth rate was observed in 100% BPS (12.99 mg earthworm 1 day 1), whereas the 60% BPS+40% STMS feed mixture supported the least growth (4.61 mg earthworm 1 day 1). The net weight gain by E. foetida (wet weight) per g dry weight of food source (dry weight basis) was highest in 100% BPS (33.33 mg g 1) and lowest in 60% BPS+40% STMS feed mixture (8.6 mg g 1) (Table 3). The growth rate data and worm weight gain per unit food source data further indicated that 100% BPS is a better option as feed for E. foetida than 100% CD. Table 4 summarizes sexual development and cocoon production by E. foetida in different feed mixtures.
Changes in fertilizer value of the vermicompost produced using different feed mixtures are given in Table 2. There were slight changes in the pH values in all the feed mixtures (Table 2). In general, there was a shift toward acidic/neutral pH (6.3–7.1) from the initial alkaline pH (8.3–7.2). Most other reports on vermicomposting (Gunadi and Edwards, 2003; Mitchell, 1997) have also reported similar results. However, our results are in contradiction to the observations of Datar et al. (1997). They have reported an increase in pH with time during vermicomposting. From 25% to 28% of TOC was lost in different feed mixtures by the end of the vermicomposting period except in the 60% BPS+40% STMS feed mixture, in which TOC reduction was 35.9%, whereas TOC decrease in control feeds was in the range of 13–22% (Fig. 2a). Our results are supported by other co-workers (Elvira et al., 1998; Kaushik et al., 2003), who have reported, 20–45% loss of TOC as CO2 during vermicomposting of different industrial sludges. Tripathi and Bhardwaj (2004) have also reported a lesser decrease in TOC in control beds than in worminoculated feed beds. TKN content increased by between 2.8 and 6.5 g kg 1 in different feed mixtures, probably because of mineralization of organic matter (Table 2). TKN increase in 100% CD was two-fold
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Table 3 Growth of Eisenia foetida in different feed mixtures Feed no.
1 2 3 4 5 6
Mean initial weight Maximum weight earthworm 1 (mg) achieved earthworm 1 (mg)
Maximum weight achieved in
Net weight gain earthworm 1 (mg)
Growth rate worm 1 day (mg)
228 180 202 252 202 252
11th week 11th week 11th week 10th week 10th week 8th week
892 1000 518 446 452 258
11.58 12.99 6.73 6.37 6.46 4.61
1120 1180 720 698 654 510
1
Worm weight gained per unit dry feed mixture (mg g 1) 29.73 33.33 17.27 14.87 15.07 8.6
Table 4 Cocoon production by Eisenia foetida in different feed mixtures Feed no.
Clitellum development started after
Cocoon production started in
Total no. of cocoons produced after 15 weeks
No. of cocoons produced earthworm 1
1 2 3 4 5 6
4th 4th 4th 4th 5th 5th
9th 7th 8th 9th 9th 9th
62 78 62 49 38 26
12.4 15.6 12.4 9.8 7.6 5.2
week week week week week week
800
Initial TOC Without worm With worms
600 TOC (g/kg)
week week week week week week
400 200 0
(a)
1
2
3
4
16 TKN (g/kg)
5
6
Feed No.
Initial TKN Without worm With worms
12 8 4 0
1
2
3
(b)
5
6
4
5
6
Initial C: N Without worm With worms
160 C: N ratio
4 Feed No.
120 80 40 0
(c)
1
2
3 Feed No.
Fig 2. Comparison of TOC change (a), TKN change (b), and C:N ratio (c).
greater than in all other tested feed mixtures. Increase in TKN was in the range 0.6–2.2 g kg 1 in control feeds (Fig. 2b). The C:N ratio, one of the most widely used indices for maturity of organic wastes, decreased with time for all the animal wastes (Table 5). Initial C:N ratio was in the range 69.2–129.2. Exceptionally high C:N ratios in STMS-containing feed mixtures can be attributed to initially lower content of nitrogen in these feeds. Final C:N ratios were in the range 26.1–40.6, whereas the final C:N ratio of the control feed was higher (in the range 43.2–83.4) than worm-inoculated feeds (Fig. 2c). Dehydrogenase activity is a useful indicator of microbial activity in soil and other biological ecosystems (Garcia et al., 1997), since it is an intracellular enzyme related to the oxidative phosphorylation process (Trevors, 1984). It has also been regarded as an indicator of the advancement of the composting process (Diaz-Burgos et al., 1992). Dehydrogenase activity decreased with increasing percentage of STMS in the feed mixtures on day zero. Increase in dehydrogenase activity in all the studied wastes after 30 days indicated increased microbial activity (Table 6). Maximum dehydrogenase activity was recorded on day 75 which lowered on day 90 in all the feeds. Maximum dehydrogenase activity was recorded in 100% BPS and 100% CD (20007100 mg TPF g 1 h 1) and minimum in 60% BPS+40% STMS (500 mg TPF g 1 h 1) on day 75.
ARTICLE IN PRESS V.K. Garg et al. / Ecotoxicology and Environmental Safety 65 (2006) 412–419 Table 5 Changes in C:N ratio of different feed mixtures during vermicomposting Feed no.
1 2 3 4 5 6
Time (days) 0
30
45
60
75
90
69.2 80.0 80.4 90.0 128.2 129.2
49.6 67.1 63.7 76.4 103.8 100.7
41.8 56.2 54.9 66.2 85.3 83.5
34.9 49.3 48.6 58.7 68.6 64.9
29.7 41.5 40.6 48.9 51.5 46.8
26.1 36.8 36.8 40.0 40.6 38.3
Table 6 Changes in dehydrogenase activity (mg TPF g mixtures during vermicomposting Feed no.
1 2 3 4 5 6
1
h 1) of different feed
Time (days) 0
30
60
75
90
490 449 212 249 208 185
842 1600 510 476 455 425
1460 1885 605 505 498 486
1875 1980 845 710 545 530
1490 1360 770 355 311 379
Phosphorus content (TP) was higher in the final composts than in the IM (Table 2). Total potassium (TK) content was also higher in the final product than in the IM. In contrast, a decrease in TK has been reported for the vermicomposting of paper–pulp mill sludge (Elvira et al., 1998). They have attributed this decrease to leaching of the soluble elements by excess water that drained through mass. Benitez et al. (1999) have found that the leachates collected during vermicomposting process had higher K concentrations. These studies support our results, as water was sprinkled in such quantities in this study that there was no excess water which avoided the leaching of minerals with run off water.
4. Discussion No mortality was observed in any feed mixture during the study period. Gunadi and Edwards (2003) have reported the death of E. foetida after 2 weeks in fresh cattle solids, although physicochemical properties were suitable for the growth of the earthworms. They attributed the deaths of earthworms to the anaerobic conditions which developed after 2 weeks in fresh cattle solids. In our experiments, all the wastes were precomposted for 2 weeks and during this period all the toxic gases produced might have been eliminated. It is established that precomposting is essential to avoid the
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deaths of the worms. After the initial biomass gain, stabilization and, later, weight loss by earthworms were observed in all the feed mixtures tested. The loss in worm biomass can be attributed to the exhaustion of food. When E. foetida received food below a maintenance level, it lost weight at a rate which depended upon the quantity and nature of its ingestible substrates (Neuhauser et al., 1980). However, Dominguez et al. (2000) reported a decrease in worm biomass even when additional food was added to the experiment every week. The difference between rates of cocoon production in different feed mixtures could be related to the biochemical quality of the feed mixtures, which is one of the important factors in determining onset of cocoon production (Edwards et al., 1998; Flack and Hartenstein, 1984). The feeds that provide earthworms with a sufficient amount of easily metabolizable organic matter and nonassimilated carbohydrates favor the growth and reproduction of the earthworms (Edwards, 1988). The greater percentage of STMS in the feed mixture significantly affected cocoon production. Kaushik et al. (2003, 2004) have reported that addition of at least 30% CD in STMS was essential for the survival of E. foetida. Elvira et al. (1997) showed that E. andrei was unable to survive in paper–pulp mill sludge. However, feed mixtures of paper-mill sludge with pig and poultry slurry were suitable materials for vermicomposting. They attributed this mortality to degradation processes that result in changes in environmental characteristics. The vermicompost produced was darker in color and had been processed into a homogeneous mixture after 15 weeks of worm activity, whereas the feed mixtures maintained without earthworms remained as compact mass. The pH shift towards acidic conditions could be attributed to mineralization of the nitrogen and phosphorus into nitrites/nitrates and orthophosphates; bioconversion of the organic material led to intermediate species of organic acids (Ndegwa et al., 2000). They have also reported that different substrates result in the production of different intermediate species and hence different wastes show a different behavior in pH shift. The final TKN content in vermicompost is dependent on the initial nitrogen present in the feed material and the degree of decomposition (Crawford, 1983). According to Viel et al. (1987), losses in organic carbon might be responsible for nitrogen addition. Addition of nitrogen in the form of mucus, nitrogenous excretory substances, growth-stimulating hormones and enzymes from earthworms have also been reported (Tripathi and Bhardwaj, 2004). According to them, these nitrogen-rich substances were not originally present in the feed material and hence might have contributed to the additional nitrogen content. Decrease in pH may be another important factor in nitrogen retention as this element is lost as volatile ammonia at higher pH values
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(Hartenstein and Hartenstein, 1981). Earthworms also have a great impact on nitrogen transformations in manure, by enhancing nitrogen mineralization, so that mineral nitrogen was retained in the nitrate form (Atiyeh et al., 2000). According to Senapati et al. (1980), loss of carbon as carbon dioxide in the process of respiration and production of mucus and nitrogenous excrements enhances the level of nitrogen, which lowers the C:N ratio in the feeds during vermicomposting. Our results are supported by the observations that TKN in different vermicomposts was two–five-fold higher than control feeds (Fig. 2b). Similarly, decrease in the TOC and C:N ratio was greater in worm-inoculated feed mixtures than in the respective controls (Fig. 2a and c). This indicates that less time is required for waste stabilization in the presence of worms. Levi-Minzi et al. (1986) reported that the C:N ratio of farmyard manure decreased after storing for a period of 3 months. But in our experiments, decrease in the C:N ratio was observed even after 30 days from the start of the experiment, demonstrating much more rapid decomposition and higher rates of mineralization of the organic matter (Table 5). Dehydrogenase activity is dependent on the substrate availability (Moore and Russel, 1972), so the decrease of the activity means that most of the easily available organic matter had been decomposed/exhausted before day 90 of the vermicomposting process under the given conditions. Increase in TP during vermicomposting is probably due to mineralization and mobilization of phosphorus due to bacterial and faecal phosphatase activity of earthworms (Edwards and Lofty, 1972). Satchell and Martin (1984) found an increase of 25% in TP of paper waste sludge, after worm activity. They contributed this increase in TP to direct action of worm gut enzymes and indirectly by stimulation of the microflora.
5. Conclusion The information presented in this paper provides a basis for the utilization of STMS spiked with BPS in small as well as large-scale vermicomposting facilities. The growth and reproduction of the E. foetida was best when allowed to feed on 100% BPS or 100% CD. Addition of STMS in BPS retarded the biomass gain and reproduction by the worms. The growth rate and cocoon production by the earthworms was having an inverse relationship with the percentage of STMS in the feed mixture. The net weight gain by the earthworms was significantly lower in feed mixtures having 40% STMS. Our results, also reported in literature, establish a direct relationship between the worm biomass growth and the quality of the food (Butt, 1993; Elvira et al., 1998; Kaushik et al., 2004). It appears that the initial few weeks after introduction of earthworms to feed mixtures
are the most critical. During this period, most of the decomposition and stabilization of feed mixtures by the earthworms occurs. The pH of final product was lower than that of initial feeds, which may be attributed to evolution of CO2 and accumulation of organic acids. The vermicomposting process not only decreased the organic carbon content but also substantially increased the nitrogen content. The final product was more stabilized, as demonstrated by a significant decrease in C:N ratio. The decrease in dehydrogenase activity at 90 days sampling indicates the exhaustion of easily metabolizable components of the feed. This study demonstrates the usefulness of vermicomposting technology for the management of STMS. However, further studies are needed on the use of STMS-containing vermicompost in fields.
References Abbasi, S.A., Ramasamy, E.V., 2001. Solid Waste Management with Earthworms. Discovery Publishing House, New Delhi, p. 78. Atiyeh, R.M., Dominguez, J., Subler, S., Edwards, C.A., 2000. Changes in biochemical properties of cow manure during processing by earthworms (Eisenia andrei Bouche) and the effects on seedling growth. Pedobiologia 44, 709–724. Bansal, S., Kapoor, K.K., 2000. Vermicomposting of crop residues and cattle dung with Eisenia foetida. Bioresour. Technol. 73, 95–98. Benitez, E., Nogales, R., Elvira, C., Masciandaro, G., Ceccanti, B., 1999. Enzyme activities as indicators of the stabilization of sewage sludge composting with Eisenia foetida. Bioresour. Technol. 67, 297–303. Bremner, J.M., Mulvaney, R.G., 1982. Nitrogen total. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Method of Soil Analysis. American Society of Agronomy, Madison, WI, pp. 575–624. Butt, K.R., 1993. Utilization of solid paper mill sludge and spent brewery yeast as a feed for soil-dwelling earthworms. Bioresour. Technol. 44, 105–107. Casida Jr., L.E., Klevin, D.A., Santoro, T., 1964. Soil dehydrogenase activity. Soil Sci. 93, 371–376. Chan, L.P.S., Griffiths, D.A., 1988. The vermicomposting of pretreated pig manure. Biol. Wastes 24, 57–69. Chaudhari, P.S., Bhattacharjee, G., 2002. Capacity of various experimental diets to support biomass and reproduction of Perionyx excavatus. Bioresour. Technol. 82, 147–150. Crawford, J.H., 1983. Review of composting. Process Biochem. 18, 14–15. Datar, M.T., Rao, M.N., Reddy, S., 1997. Vermicomposting—a technological option for solid waste management. J. Solid Waste Technol. Manage. 24 (2), 89–93. Diaz-Burgos, M.A., Ceccanti, B., Polo, A., 1992. Monitoring biochemical activity during sewage sludge composting. Biol. Fertil. Soil 16, 145–150. Dominguez, J., Edwards, C.A., Webster, M., 2000. Vermicomposting of sewage sludge: effects of bulking materials on the growth and reproduction of the earthworm Eisenia andrei. Pedobiologia 44, 24–32. Edwards, C.A., 1988. Breakdown of animal, vegetable and industrial organic wastes by earthworms. In: Edwards, C.A., Neuhauser, E.F. (Eds.), Earthworms in Waste and Environmental Management. SPB Academic Publishing, The Hague, pp. 21–31. Edwards, C.A., Lofty, J.R., 1972. Biology of Earthworms. Chapman & Hall, London.
ARTICLE IN PRESS V.K. Garg et al. / Ecotoxicology and Environmental Safety 65 (2006) 412–419 Edwards, C.A., Dominguez, J., Neuhauser, E.F., 1998. Growth and reproduction of Parionyx excavatus (Perr.) (Megascolecidae) as factors in organic waste management. Biol. Fertil. Soils 27, 155–161. Elvira, C., Goicoechea, M., Sampdro, L., Mato, S., Nogales, R., 1996. Bioconversion of solid paper–pulp mill sludge by earthworms. Bioresour. Technol. 75, 173–177. Elvira, C., Sampedro, L., Dominguez, J., Mato, S., 1997. Vermicomposting of wastewater sludge from paper–pulp industry with nitrogen rich materials. Soil Biol. Biochem. 29, 759–762. Elvira, C., Sampedro, L., Benitez, E., Nogales, R., 1998. Vermicomposting of sludges from paper mill and dairy industries with Eisenia andrei: a pilot scale study. Bioresour. Technol. 63, 205–211. Flack, F.M., Hartenstein, R., 1984. Growth of the earthworm Eisenia foetida on microorganisms and cellulose. Soil Biol. Biochem. 16, 491–495. Frederickson, J., Butt, K.R., Morris, R.M., Daniel, C., 1997. Combining vermiculture with traditional green waste composting system. Soil Biol. Biochem. 29, 725–730. Gajalakshmi, S., Ramasamy, E.V., Abbasi, S.A., 2001. Assessment of sustainable vermiconversion of water hyacinth at different reactor efficiencies employing Eudrilus engeniae Kingburg. Bioresour. Technol. 80, 131–135. Gajalakshmi, S., Ramasamy, E.V., Abbasi, S.A., 2002. Vermicomposting of paper waste with the anecic earthworm Lampito mauritii Kingburg. Indian J. Chem. Technol. 9, 306–311. Garcia, C., Hernandez, T., Costa, F., 1997. Potential use of dehydrogenase activity as an index of microbial activity in degraded soils. Commun. Soil Sci. Plant An. 28, 123–134. Garg, V.K., Kaushik, Priya, 2005. Vermistabilization of textile mill sludge spiked with poultry droppings by an epigeic earthworm Eisenia foetida. Bioresour. Technol. 96, 1189–1193. Gunadi, B., Blount, C., Edward, C.A., 2002. The growth and fecundity of Eisenia foetida (Savigny) in cattle solids pre-composted for different periods. Pedobiologia 46, 15–23. Gunadi, B., Edwards, C.A., 2003. The effect of multiple applications of different organic wastes on the growth, fecundity and survival of Eisenia foetida ( Savigny) (Lumbricidae). Pedobiologia 47 (4), 321–330. Gunathilagraj, K., Ravignanam, T., 1996. Vermicomposting of sericulture wastes. Madras Agric. J., 455–457. Hartenstein, R., Hartenstein, F., 1981. Physico-chemical changes affected in activated sludge by the earthworm Eisenia foetida. J. Environ. Qual. 10, 377–382. Hartenstein, R., Neuhauser, E.F., Kaplan, D.L., 1979. Reproductive potential of the earthworm Eisenia foetida. Oecologia 43, 329–340. Kale, R., 1991. Vermiculture: Scope for New Biotechnology. Zoological Survey of India, Calcutta. Kaushik, Priya, Garg, V.K., 2003. Vermicomposting of mixed solid textile mill sludge and cow dung with the epigeic earthworm Eisenia foetida. Bioresour. Technol. 90, 311–316.
419
Kaushik, Priya, Garg, V.K., 2004. Dynamics of biological and chemical parameters during vermicomposting of solid textile mill sludge mixed with dung and agricultural residues. Bioresour. Technol. 94 (2), 203–209. Levi-Minzi, R., Riffaldi, R., Saviozzi, A., 1986. Organic matter and nutrients in fresh and mature farmyard manure. Agric. Wastes 16, 225–236. Mitchell, A., 1997. Production of Eisenia foetida and vermicompost from feed lot cattle manure. Soil Biol. Biochem. 29, 763–766. Moore, A.W., Russel, J.S., 1972. Factors affecting dehydro genase activity as an index of soil fertility. Plant Soil 37, 675–682. Ndegwa, P.M., Thompson, S.A., Das, K.C., 2000. Effects of stocking density and feeding rate on vermicomposting of biosolids. Bioresour. Technol. 71, 5–12. Nelson, D.W., Sommers, L.E., 1982. Total carbon and organic carbon and organic matter. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Method of Soil Analysis. American Society of Agronomy, Madison, WI, pp. 539–579. Neuhauser, E.F., Hartenstein, R., Kaplan, D.L., 1980. Growth of the earthworm Eisenia foetida in relation to population density and food rationing. OIKOS 35, 93–98. Reeh, U., 1992. Influence of population densities on growth and reproduction of the earthworm Eisenia andrei on pig manure. Soil Biol. Biochem. 24, 1327–1331. Satchell, J.E., Martin, K., 1984. Phosphate activity in earthworm faeces. Soil Biol. Biochem. 16, 191–194. Senapati, B.K., Dash, M.C., Rane, A.K., Panda, B.K., 1980. Observation on the effect of earthworms in the decomposition process in soil under laboratory conditions. Comp. Physiol. Ecol. 5, 140–142. Sherman-Huntoon, R., 2000. Latest developments in mid-to-largescale vermicomposting. Biocycle 41 (11), 51–54. Sinha, R.K., Heart, S., Agarwal, S., Asadi, R., Carretero, E., 2002. Vermiculture and waste management: study of action of earthworms Eisenia foetida, Eudrilus euginae and Parionyx excavatus on biodegradation of some community wastes in India and Australia. Environmentalist 22, 261–268. Trevors, J.T., 1984. Dehydrogenase activity in soil. A comparison between the INT and TTC assay. Soil Biol. Biochem. 16, 673–674. Tripathi, G., Bhardwaj, P., 2004. Comparative studies on biomass production, life cycles and composting efficiency of Eisenia foetida (Savigny) and Lampito mauritii (Kinberg). Bioresour. Technol. 95, 77–83. Viel, M., Sayag, D., Andre, L., 1987. Optimization of agricultural, industrial waste management through in-vessel composting. In: de Bertoldi, M. (Ed.), Compost: Production, Quality and Use. Elseiver Applied Science, Essex, pp. 230–237.