- Email: [email protected]
Vermicomposting of milk processing industry sludge spiked with plant wastes
Bioresource Technology 116 (2012) 214–219
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Vermicomposting of milk processing industry sludge spiked with plant wastes Surindra Suthar a,⇑, Pravin K. Mutiyar b, Sushma Singh c a
School of Environment & Natural Resources, Doon University, Dehradun 248001, Uttarakhand, India Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas 110 016, New Delhi, India c Department of Chemistry, N.M. Govt. (PG) College, Hanumangarh Town 335513, Rajasthan, India b
a r t i c l e
i n f o
Article history: Received 21 December 2011 Received in revised form 26 March 2012 Accepted 29 March 2012 Available online 5 April 2012 Keywords: Vermicomposting Dairy wastewater sludge C:N ratio Eisenia fetida Industrial waste
a b s t r a c t This work illustrates the vermistabilization of wastewater sludge from a milk processing industry (MPIS) unit spiked with cow dung (CD), sugarcane trash (ST) and wheat straw (WS) employing earthworms Eisenia fetida. A total of nine experimental vermibeds were established and changes in chemical parameters of waste material have been observed for 90 days. Vermistabilization caused significant reduction in pH, organic carbon and C:N ratio and substantial increase in total N, available P and exchangeable K. The waste mixture containing MPIS (60%) + CD (10%) + ST (30%) and MPIS (60%) + CD (10%) + WS (30%) had better waste mineralization rate among waste mixtures studied. The earthworm showed better biomass and cocoon numbers in all vermibeds during vermicomposting operation. Results, thus suggest the suitability of E. fetida for conversion of noxious industrial waste into value-added product for land restoration programme. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Agriculture, food processing, pulp and paper, or any agriculturebased industry produces massive quantity of liquid, gaseous or solid wastes. Such agro-industrial sludge/wastes not only spoil aesthetics sense of local habitats but at the same time also create issues of all types of environmental pollution, if proper disposal and management policy is not adopted. The dairy processing industry is the major component of food processing industry in the India. It is considered to be the largest source of food processing wastewater in many countries. Although the dairy industry is not commonly associated with sever environmental problem, it must continually consider its environmental impact – particularly as dairy pollutants are mostly of organic origin (protein, carbohydrate, lipids, suspended oils and/or grease) with high concentration of suspended solids, biochemical oxygen demand (BOD), chemical oxygen demand (COD) and nitrate contents (Britz et al., 2006). The wastewater and solids generated from dairy processing industry pose issues of safe management and disposal of treated and/or untreated wastewater solids. The traditional disposal methods such as open dumping and/or land filling practices of these materials are not only increasingly expensive, but impractical as open space becomes limited (Slater and Frederickson, 2001). Contamination of ground water, soils, as well as, food resources are some of the problems which have resulted from land filling practices of dumped waste materials (Ilgen et al., 2008). The emission of GHGs from
⇑ Corresponding author. Fax: +91 135 2533103. E-mail address: [email protected] (S. Suthar). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.03.101
waste dumping site is an issue of prime concern (IPCC, 2006; Lou and Nair, 2009). However, the stabilization of such sludge prior to use of disposal should reduce the environmental problems associated with its open dumping (Gomez-Brandon et al., 2011). In general, stabilization involves the decomposition of an organic waste into the extent of eliminating the hazards and is normally reflected by decreases in microbial activity and concentration of labile compounds (Benito et al., 2003). Composting has been appeared as important tool to stabilize the organic waste generated from different sector of the society. Composting is the most sustainable option for onsite organic waste management as it is easy to operate and can be conducted in contained space provided (Lou and Nair, 2009; Hong et al., 2010). In recent years vermicomposting has been explored extensively to recycle the nutrient stuff from organic wastes from different community sources (Suthar, 2009). Vermicomposting, utilizing earthworms, is an ecobiotechnological process that transforms energy-rich and complex organic substances into a stabilized humus-like product vermicompost (Sinha et al., 2010). According to Dominguez (2004) it is a complex process involving the joint action of earthworms and microorganisms. Although microbes are responsible for biochemical degradation of organic matter, earthworms are the important drivers of the process, conditioning the substrate and altering the biological activity. Vermistabilization is stabilization of organic material, such as sludge, involving the joint action of earthworms and microorganisms. The sludge can be stabilized effectively through vermistabilization process because of many beneficial impacts of inoculated earthworms upon aerobic decomposition process. Loehr et al. (1985) concluded that in vermicomposting system the earthworms
215
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219
maintain aerobic condition in wastes, ingest solids, convert a portion of the organics to worm biomass and respiration products and expel partially stabilized matter as discrete particles (vermicompost). The utilization of earthworm in waste stabilization practices is well documented in recently published work. There is evidence of successful utilization of earthworms for stabilizations of anthropogenic wastes generated from different industries: vinasse (Pramanik and Chung, 2011), grape mark (Gomez-Brandon et al., 2011), sago industry waste (Subramanian et al., 2010), paper mill sludge (Elvira et al., 1998), sugar factory waste (Khwairakpam and Bhargava, 2009; Suthar, 2010) and olive oil mill sludge (Moreno et al. (2000) distillery and winery industry sludge (Suthar and Singh, 2008; Gomez-Brandon et al., 2011), leather processing industry sludge (Ravindran et al., 2008) etc. After reviewing literature it is realized that dairy industry sludge can also be a candidate for vermistabilization operation. Epigeic earthworms could stabilize the sludge potentially and can accelerate the rates of destruction of sludge volatile solids in aerobic sludge greatly, which probably decreases the putrefaction; occurring because of anaerobic conditions. So, the main cause of increased rates of degradation of sludge is probably the increased aeration and turnover of wastes by the earthworms (Loehr et al., 1985). The aim of the present investigation is to stabilize the diary industry wastewater sludge spiked with plant wastes in different ratios using earthworm Eisenia fetida. The different combinations of industrial sludge and bulky materials were tested under vermistabilization operation in order to find out suitable waste mixture for optimize earthworm activity. 2. Methods 2.1. E. fetida, dairy industrial sludge and bulky agent collection To carry out the experiment specimens of earthworm species E. fetida (Savigny) were obtained from a stock culture reared in our laboratory and fed with decomposed cow dung spiked with plant litters. Freshly deposited sludge (MPIS) was collected form wastewater treatment unit of a local milk processing industry. The wet-sludge (containing 70–81% moisture) was collected in large-sized plastic containers and then brought to the laboratory for further processing. The sludge was shade dried in lab to evaporate the excess water from it. Also, regular turns were made in order to reduce the characteristics smell of putrescible substances and biotoxic compounds present in sludge; generally formed under anaerobic conditions. Partially dried sludge cake solids were then homogenized and shredded prior to use in experimental vermibeds. Three bulky materials, i.e. cow dung (CD), sugarcane trash (ST) and wheat straw (WS) were used to prepare different substrate mixture for earthworms. The substrate acts as bedding and feeding materials for inoculated earthworms. The chopped straw of wheat (WS) and fresh sugarcane trash were procured from a local agriculture farm. Fresh urine-free cow dung was procured from a local cowshed. The cow dung was partially dried in shade and homogenised manually. The main chemical characteristics of dairy processing industrial sludge cake (MPIS) and bulky agents are given in Table 1. 2.2. Experimental design The chemical characteristics especially nitrogen content and C:N ratio of waste stuff plays an important role in earthworm palatability and vermicomposting rate. The MPIS was mixed with bulky materials (CD, ST and WS) in appropriate ratio in order to balance the nutrient contents as well as bedding material size frac-
tions. Following nine feed mixtures were used for vermicomposting experimentations. T1 T2 T3 T4 T5 T6 T7 T8 T9
MPIS MPIS MPIS MPIS MPIS MPIS MPIS MPIS MPIS
(20%) + CD (80%) (40%) + CD (60%) (40%) + WS (60%) (60%) + WS (40%) (40%) + ST (60%) (60%) + ST (40%) (60%) + CD (10%) + WS (30%) (60%) + CD (10%) + ST (30%) (100%)
MPIS (100%) acts as experimental control bedding in order to compare the results of chemical and biological changes during vermicomposting in the presence of bulky agents. The chemical characteristics of initial waste mixtures (Table 2) were: 7.35–8.5 (pH), 419.18–503.65 g kg 1 (TOC), 7.96–39.73 g kg 1 (TKN), 2.32– 23.50 g kg 1 (AP), 5.67–14.46 g kg 1 (EK) and 10.60–60.52 (C:N ratio). Prior to vermistabilization the waste mixtures were pre-composted for 3 weeks for initial thermal stabilization, initiation of microbial degradation and softening of waste mixture. During this sludge mixture was turned out periodically (after 3 days) for aeration and to remove odour from decomposing wastes. The proper moisture content in composting beds was maintained. After 3-wk composting, 500 g waste mixture (dry weight basis) was separated from composting beds and filled in plastic circular containers of 2 L capacity (one for each mixture) for vermicomposting trials. Twenty earthworms (4-wk old) having individual live weights of 264– 281 mg were released into each experimental container. The experimental beddings were kept in triplicate for each treatment. The moisture content was maintained at 65–70%, throughout the study period by periodic sprinkling of adequate quantity of water. The containers were placed in a humid and shady place at an ambient temperature 27.2 °C (SD = 0.14). The earthworm mortality was observed for initial critical periods (initial 15 days of experimental starting) and data of mortality were recorded for different experimental containers. To estimate the physic-chemical changes during vermistabilization process, homogenized samples (10 g) of waste mixtures were drawn at 0, 15, 30, 45, 60, 75 and 90 days from each experimental container. The samples of substrate mixture were oven dried (48 h at 60 °C), ground in stainless steel blender and stored in sterilized plastic airtight containers. The biological productivity (biomass change, cocoon production etc.) of E. fetida was also monitored during the same interval for whole experiment duration by following method as described by Suthar (2009). 2.3. Chemical analysis The pH was measured using a digital pH meter (Systronics made) in 1:10 (w/v) aqueous solution (deionized water). Total organic carbon (TOC) was measured after igniting the sample in a Muffle furnace at 550 °C for 60 min by the method of Nelson and Sommers (1996). Total Kjeldahl nitrogen (TKN) was measured using the method described by Jackson et al. (1975). Available phosphorous (AP) was measured using the method described by Anderson and Ingram (Olsen et al., 1954). Exchangeable potassium (EK) was determined after extracting the sample using ammonium acetate (Simard, 1993). 2.4. Statistical analysis One-way ANOVA was used to analyze the differences between treatments. A Tukey’s t-test was also performed to identify the
216
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 1 Chemical characteristics (g kg
1
) of organic wastes used as amendment material (mean ± SD, n = 3).
Parameters
Industry sludge
pH Organic C Organic matter Total N Available P Exchangeable K C:N ratio a
7.05 ± 0.11 379.5 ± 5.23 657.29 ± 8.93 56.8 ± 2.34 32.9 ± 2.01 18.4 ± 0.34 5.06 ± 0.07
a
ND 491.5 ± 0.88 851.28 ± 1.5 25.2 ± 0.58 15.7 ± 0.97 6.8 ± 0.07 15.5 ± 0.7
Cow dung
ND 589.0 ± 3.0 1020.15 ± 5.3 6.03 ± 0.2 2.67 ± 0.2 12.6 ± 0.3 80.3 ± 2.8
8.5 ± 0.1 481.8 ± 0.3 834.47 ± 0.8 7.96 ± 0.2 2.32 ± 0.1 5.67 ± 0.2 14.6 ± 0.4
1
) of substrates at starts used for experimentation (mean ± SD; n = 3).
Treatmenta
pH
Corg
Ntot
Pavail
Kexch
C:N ratio
T1 T2 T3 T4 T5 T6 T7 T8 T9
7.90 ± 0.01 7.69 ± 0.01 7.60 ± 0.01 7.38 ± 0.01 7.82 ± 0.02 7.46 ± 0.01 7.35 ± 0.02 7.49 ± 0.01 8.5 ± 0.1
459.07 ± 0.47 437.16 ± 0.99 503.65 ± 0.58 460.05 ± 0.29 443.58 ± 0.38 421.11 ± 0.17 449.75 ± 1.22 419.18 ± 0.30 481.8 ± 0.3
15.94 ± 0.04 24.75 ± 0.05 23.71 ± 0.09 32.86 ± 0.05 34.03 ± 0.07 39.73 ± 0.09 30.03 ± 0.02 38.19 ± 0.04 7.96 ± 0.2
7.58 ± 0.02 13.10 ± 0.03 13.30 ± 0.11 18.73 ± 0.04 20.35 ± 0.05 23.50 ± 0.10 18.69 ± 0.06 22.21 ± 0.06 2.32 ± 0.1
7.39 ± 0.04 9.70 ± 0.04 13.44 ± 0.06 14.46 ± 0.06 10.33 ± 0.04 12.38 ± 0.04 13.85 ± 0.06 12.30 ± 0.07 5.67 ± 0.2
28.79 ± 0.06 17.66 ± 0.08 21.24 ± 0.04 14.0 ± 0.07 13.03 ± 0.01 10.60 ± 0.01 14.98 ± 0.20 10.97 ± 0.01 60.52 ± 0.4
refer to text for explanation of treatments.
homogeneous type of the data sets. SPSSÒ statistical package (Window Version 13.0) was used for data analysis. All statements reported in this study are at the p < 0.05 levels.
3. Results and discussion 3.1. Physico-chemical changes in waste mixture during vermicomposting The chemical composition of vermicomposted material was significantly different than initial waste mixtures (Table 3). There were slight changes in the pH of vermicomposted materials as compared to initial substrate materials. The pH of ready material was in the range of 7.12 ± 0.01–7.45 ± 0.05. The shifting of pH during vermicomposting process could be attributed to the production metabolic compounds of aerobic digestions of organic stuff, e.g. CO2, ammonia, NO3 and organic acids (Lopez et al., 2002). Few workers advocated the contribution of intermediate/ end products of nitrogen and phosphorous mineralization in pH shifting during vermicomposting process (Ndegwa et al., 2000). Total organic carbon decreased in all waste mixtures during vermicomposting process. TOC in vermicomposted material was in the ranges of 313.65–428.16 g kg 1. The maximum TOC reduction was in T2 (23.4%) followed by T7 (26.4%), T8 (25.2%), T4 (23.4%), T5 (23.0%), T6 (19.8%), T1 (18.9%), T3 (15.0%) and T9 (14.4%). It was Table 3 Chemical compositions (g kg Treatment T1 T2 T3 T4 T5 T6 T7 T8 T9 a
Wheat straw
ND Not determined.
Table 2 Chemical compositions (g kg
a
Sugarcane trash
a
observed that carbon mineralization rate in vermibeds was directly related to the composition of the waste feedstock. The vermibed containing plant straw and cow dung (CD) both showed the better mineralization than other waste mixtures. Recent studies suggested that cellulose rich compounds promote the carbon mineralization rate during composting/vermicomposting process probably due to colonization of cellulose decomposing fungi (Pramanik and Chung, 2011). The role of CD in waste mineralization is well documented in the literature (Suthar, 2010; Khwairakpam and Bhargava, 2009). CD contains numbers of fungal stains and greater population of other microbes, such as bacteria, protozoa, nematodes, fungi, actinomycetes, which plays an important role in organic matter decomposition by providing extra-cellular enzymes in vermibeds. The C loss in vermibeds is the results of respiration activities in substrate and digestion as well as assimilation of carbohydrates/other polysaccharides from the substrates by inoculated earthworms. A significant increase in TKN was recorded in all vermibed at the end of the process. The TKN level in vermicomposted material was in the ranges of 13.45 ± 0.45–63.59 ± 1.18 g kg 1 (Table 3). There was 1.21–1.70-fold increase in TKN in vermicomposted materials at the end of the process. The N enhancement rate in all vermibed varied significantly. In terms of N enrichment the vermibeds can be arranged in the order: T7 > T9 > T6 > T4 > T8 > T3 > T5 > T2 > T1. The nitrogen enrichment rate was slightly different among vermibeds. It could be due to the composition of waste
1
) of substrates after 90 days of experimentation (mean ± SD; n = 3).
pH
Corg
Ntot
Pavail
Kexch
C:N ratio
7.45 ± 0.05 7.44 ± 0.02 7.32 ± 0.02 7.27 ± 0.01 7.28 ± 0.02 7.24 ± 0.01 7.22 ± 0.01 7.16 ± 0.01 7.12 ± 0.01
372.5 ± 1.22 319.02 ± 1.24 428.16 ± 2.59 352.17 ± 1.94 341.75 ± 2.29 337.65 ± 2.90 331.01 ± 3.45 313.65 ± 1.15 412.5 ± 1.03
19.38 ± 0.35 31.78 ± 0.50 34.18 ± 0.94 52.31 ± 2.43 45.64 ± 7.74 63.59 ± 1.18 53.26 ± 0.14 60.06 ± 0.78 13.45 ± 0.45
8.76 ± 0.14 16.02 ± 0.38 17.48 ± 0.46 29.48 ± 0.40 27.72 ± 0.97 34.06 ± 0.93 29.55 ± 0.63 35.76 ± 0.71 6.52 ± 1.06
9.16 ± 0.09 12.86 ± 0.37 15.96 ± 0.97 17.76 ± 0.20 14.44 ± 0.29 17.55 ± 0.27 21.84 ± 0.31 19.28 ± 0.42 10.34 ± 0.98
19.22 ± 0.25 10.64 ± 0.08 12.53 ± 0.16 6.73 ± 0.16 7.49 ± 0.12 5.31 ± 0.11 6.21 ± 0.06 5.22 ± 0.04 30.65 ± 0.26
refer to 2.2 sub-section for explanation of treatments.
217
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 4 Earthworm productions during vermicomposting process (mean ± SD, n = 3). Vermibeds
Mean initial biomass of individual earthworm (mg)
Maximum individual biomass achieved (mg)
Maximum individual biomass achieved in (week)
Net biomass at the end (mg)
Maximum growth rate (mg wt worm 1 day 1)
Weigh achieved by individual earthworm (mg)
T1 T2 T3 T4 T5 T6 T7 T8 T9
273.06 ± 0.81 276.7 ± 0.26 265.0 ± 1.0 262.5 ± 0.50 271.8 ± 0.35 270.2 ± 0.72 279.5 ± 0.50 281.3 ± 1.52 267.9 ± 0.32
796.7 ± 20.8b 816.5 ± 7.69b 695.0 ± 5.0a 813.3 ± 11.6b 768.7 ± 11.9b 963.3 ± 41.5d 1022.8 ± 11.1e 988.3 ± 8.50de 870.7 ± 6.66c
75 75 60 75 75 75 75 75 75
772.0 ± 9.64b 796.0 ± 6.24b 683.7 ± 4.73a 799.7 ± 10.1b 759.0 ± 10.5b 949.7 ± 35.5d 1010.0 ± 15.6e 978.3 ± 2.08de 863.0 ± 6.56c
6.98 ± 0.27ab 7.20 ± 1.0ab 7.17 ± 0.09ab 7.34 ± 0.15b 6.62 ± 0.16a 9.24 ± 0.56d 9.90 ± 0.15d 9.43 ± 0.12d 8.03 ± 0.09c
523.6 ± 20.1bc 324.7 ± 4.51bc 308.3 ± 17.6a 302.3 ± 22.0c 354.0 ± 11.5b 301.3 ± 3.51e 353.7 ± 13.5e 451.0 ± 16.0e 345.3 ± 4.29d
Mean value followed by different letters is statistically different (ANOVA; Tukey’s t-test, P < 0.05). a refer to text for explanation of treatments.
mixture and nature of bulky agent, as used for dilution of industrial sludge. The optimum N enrichment in T4, T6, T7 and T9 should be related to the composition of feedstock. The combination of high carbon materials (crop residues) and CD acts as good energy stuff for microbial propagation in vermibeds. Also decomposer communities in fresh CD also enhance the mineralization process in vermibeds if it is supplies in appropriate proportion in worm feed. The earthworm body secretions (excreta, mucus etc.) add nitrogen in substrate if earthworms are inoculated in organic wastes for longer periods (Suthar, 2010). Also, mucus a polysaccharide is secreted by earthworm to moisten the body surface also important to enrich vermibeds with nitrogen fixers. Earthworm also alters the microclimatic conditions of vermibeds which consequently promotes microbial populations responsible for N enrichment. N fixers are important in N enrichment of vermicomposted materials. Study by Kavian and Ghatneker (1991) suggested the enhanced population of N fixers (Azotobactor and Rhizobium) in vermibeds, while working on vermicomposting of paper mill sludge. The available P content in vermicomposted material was relatively higher than initial waste mixtures, in all vermibeds (Table 3). The level of available P in worm-processed material was in the ranges of 6.52 ± 1.06–35.67 ± 0.71 g kg 1. There was about 1.16– 2.81-fold increase in available P level in vermicomposted material than initial waste mixtures. The maximum phosphorous mineralization was recorded in T9 followed by T8, T7, T4, T6, T5, T3, T2 and T1. The concentration of P in vermicomposted material may reflects the amount of organic forms of phosphorus in waste mixture, but its mineralization rate is directly affected by nature of amendment material and activities of P-mineralizing microflora in decomposing wastes. Few earlier studies indicate the highest plant available forms in vermicomposted wastes mainly due to activities of P-solubilizing bacteria and enzymatic activities of earthworm gut. The release of P in available forms is performed partly by earthworm gut phosphatases, and further release of P might be attributed to the P-solubilizing microorganisms present in worm casts. Results thus clearly suggest that phosphorous enrichment was directly related to the quality of stuff used as vermibed. There was significant increase in level of exchangeable potassium at the end of vermicomposting process in all vermibeds (Table 3). Exchangeable K in vermicomposted material was the ranges of 9.16 ± 0.09–21.84 ± 0.31 g kg 1. The level of exchangeable K in ready material was 1.19–1.82-fold high than initial level in all vermibeds. It clearly indicates that inoculation of earthworms in waste feedstock enhances the waste mineralization process. In general, when organic waste passes through the gut of worm some fraction of organic minerals is then converted into more available species of nutrients (i.e. exchangeable forms) due to the action of endogenic and/or exogenic enzymes (Suthar, 2010). Most of the
earlier reports on vermicomposting (Khwairakpam and Bhargava, 2009; Hait and Tare, 2011) have reported a higher K increase at the end. The C:N ratio is an important indicator of compost maturity as well as compost quality. In this study the C:N ratio of vermicomposted material was significantly lower than initial waste substrates. The C:N of end product was in the ranges of 5.22–30.65. According to Morais and Queda (2003) a C:N ratio below 20 is indicative of acceptable maturity while a ratio of 15 or lower is being preferred for agronomic used of composts. The vermicomposts obtained in this study showed the C:N ratio within the preferable limit as described by Morais and Queda (2003), except in T1 and T9 (Table 3). In general, the loss of carbon as carbon dioxide due to respiratory activities of earthworms and associated microflora, and simultaneously adding of nitrogen in substrate material by inoculated earthworms (through. production of mucus, enzymes and nitrogenous excrements) lowers the C:N ratio of the substrate (Suthar, 2010). 3.2. Earthworm growth and reproduction in different vermibeds The growth and cocoon production pattern in vermibed is an important indicator of waste suitability for earthworm feeds. There was statistically significant difference (ANOVA) among waste mixtures for observed parameters of earthworms: the maximum individual live weight (F = 118.95, p < 0.001), total individual biomass gain (F = 109.24, p = 0.001), the maximum individual growth rate (mg wt worm 1 day 1) (F = 80.29, p < 0.001), total cocoon numbers (F = 35.40, p < 0.001), reproduction rate (cocoon worm 1) (F = 7.32, p < 0.001) and mortality rate (F = 5.62, p = 0.001). The initial live weight of earthworm increased from 262.3–281.3 to 695.0– 1022.8 in different vermibeds during experimentations. The maximum individual weight of earthworm was recorded 1022.8 ± 11.1 mg in T7 followed 988.3 ± 8.50 mg (T8), 963.3 ± 41.5 mg (T6), 870.7 ± 6.66 mg (T9), 816.5 ± 7.69 mg (T2), 813.3 ± 11.6 mg (T4), 796.7 ± 20.8 mg (T1), 768.7 ± 11.9 mg (T5) and 695.0 ± 5.0 mg (T3). The individual biomass in E. fetida was 2.62–3.65 folds higher than initial weight in all vermibeds at the end of process (Table 4). The weight gain by individual earthworm varied significantly among different vermibeds and the maximum rate of individual biomass gain was in T1 (523.6 ± 20.1 mg) while T6 showed the minimum weigh gain (301.3 ± 3.51 mg) during experimentation. Net biomass gain in inoculated earthworms was in the order: T1 > T8 > T5 > T7 > T9 > T2 > T3 > T4 > T6. The earthworm biomass gain is directly related to the feeding rate, palatability of feedstuff and particle size of feedstock. However, chemical composition plays an important role in earthworm feeding rate and observed difference in vermibeds for earthworm biomass gain could be due to
218
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 5 Total cocoon production and reproduction patterns in E. fetida for different vermibeds (mean ± SD, n = 3). Vermibeds T1 T2 T3 T4 T5 T6 T7 T8 T9
Total cocoons obtained at the end ba
313.7 ± 13.9 324.7 ± 14.5abc 308.3 ± 17.6ab 302.3 ± 22.0a 354.0 ± 11.5c 301.3 ± 3.51a 353.7 ± 13.5c 451.0 ± 16.0d 345.3 ± 9.29ba
Reproduction rate (cocoon/worm/day) a
0.220 ± 0.021 0.224 ± 0.004a 0.233 ± 0.020a 0.247 ± 0.025a 0.267 ± 0.017b 0.233 ± 0.022a 0.249 ± 0.011a 0.311 ± 0.019b 0.234 ± 0.007a
Fecundity (Cocoons earthworm
1
)
a
16.56 ± 1.60 16.80 ± 0.33a 17.48 ± 1.52a 18.55 ± 1.92a 20.06 ± 1.33b 17.48 ± 1.70a 18.63 ± 0.84a 23.55 ± 1.45b 17.57 ± 0.54a
Mean value followed by different letters is statistically different (ANOVA; Tukey’s t-test, P < 0.05).
difference in feed compositions and its palatability (Suthar, 2008). However, there is a close relationship between feedstock quality and microbial richness of bedding substrates (Flegel and Schreder, 2000) which directly or indirectly affects the earthworm feeding rate, as microbes are the important component of earthworm diets (Gomez-Brandon et al., 2011). The growth rate was the maximum in T7 (9.90 ± 0.15 mg wt. worm 1 day 1) followed by T8 (9.43 ± 0.12 mg wt. worm 1 day 1), T6 (9.24 ± 0.56 mg wt. worm 1 day 1), T9 (8.03 ± 0.09 mg wt. worm 1 day 1), T4 (7.34 ± 0.15 mg wt. worm 1 day 1), T2 (7.20 ± 1.0 mg wt. worm 1 day 1), T3 (7.17 ± 0.09 mg wt. worm 1 day 1) T1 (6.98 ± 0.27 mg wt. worm 1 day 1) and T5 (6.62 ± 0.16 mg wt. worm 1 day 1) (Table 4). The observed difference among T1, T2 and T3 for the earthworm growth rate was not statistically significant (ANOVA/Tukey’s t-test; p = 0.132). The crop residues/plant-origin wastes have different palatability, particle size, protein and crude fiber contents that can influence the earthworm growth trends in waste mixtures during vermicomposting. The better proportion of easily metabolizable organic matter, non-assimilated carbohydrates etc. affect the normal earthworm growth in vermibeds (Kale, 1998; Khwairakpam and Bhargava, 2009). Suthar (2009) demonstrated that growth rate of earthworms in waste depends upon the microbial populations and availability of nutrient pools in vermibeds. The end biomass of earthworm was slight lower than the maximum individual biomass observed during 60–75 days of vermicomposting process. It indicates the loss in individual biomass of inoculated earthworms in different vermibeds. The individual biomass of earthworms at the end of experiment ranged between 683.7 ± 4.73 and 1010.0 ± 15.6 mg (Table 4). At the end of experiment, the individual biomass of earthworms was in the order: T7 > T8 > T6 > T9 > T4 > T2 > T1 > T5 > T3 (Table 4). It is suggested that weight loss was due to conversion of most of the used substrate to vermicompost, which further do not supports the growth in earthworms (Suthar, 2009). Few earlier studies have also demonstrated the weight loss during later period of vermicomposting process mainly due to ageing of substrate materials (Garg and Gupta, 2011). E. fetida produced cocoons in all vermibeds during experimentations. The maximum cocoon production was recorded in T8 (451.0 ± 16.0) followed by T5 (354.0 ± 11.5), T7 (353.7 ± 13.5), T9 (345.3 ± 9.29), T2 (324.7 ± 4.51), T1 (313.7 ± 13.9), T3 (308.3 ± 17.6), T4 (302.3 ± 22.0) and T6 (301.3 ± 3.51) (Table 5). Statistically, the variation among T1, T2, T3, T4, T6 and T8 treatment for total cocoon production was not significant (ANOVA/Tukeys t-test; p = 0.505). The fecundity rate (cocoons worm 1) also varied among different waste mixtures during vermicomposting process. The fecundity rate in waste-inoculated earthworms was in the ranges of 16.56 ± 1.60–23.55 ± 1.45 cocoons worm 1 in different vermibeds (Table 5). The vermibeds can be arranged in following order for fecundity rate in waste mixtures: T8 > T5 > T7 > T4 > T9 > T6 = T3 > T2 > T1 (Table 5). The cocoon produc-
Fig. 1. Earthworm mortality rate (%) in different waste mixtures during vermicomposting. The significant difference (P < 0.05) is indicated by different letters.
tion rate (cocoons worm 1 day 1) in vermibeds was observed in the ranges of 0.220 ± 0.021–0.311 ± 0.019 cocoons worm 1 day 1. The maximum cocoon production rate was recorded in T8 while T1 showed the minimum value for this parameter, i.e. 0.220 ± 0.021 (Table 5). It is clear from results that cocoon production in waste mixtures was directly related to the feedstock quality. The proportion of waste in feedstock directly affects the earthworm growth patterns in vermibeds. However microbes, which play an important role in earthworm’s diet, are directly interrelated to the quantity of the growth retarding substances in earthworm feed (Suthar, 2008). In this study, earthworm showed better reproduction performances in bedding those contained appropriate or acceptable ratio of bulking materials. In earlier studies it is suggested that greater N fractions in decomposing waste enhanced the cocoon production rate in composting earthworms (Suthar, 2010; Xing et al., 2011). The results of cocoon production rate are corroborated by the findings of other researchers who have observed waste quality dependent cocoon production patterns in earthworms during vermicomposting process (Khwairakpam and Bhargava, 2009; Xing et al., 2011). The earthworm mortality during initial stabilization period was recorded in all vermibeds during experimentation. The earthworm mortality was in the ranges of 5.0–18.3% in all vernmibeds. T4 vermibed showed the maximum earthworm mortality rate followed by T6, T3, T5, T1 = T7, T2 = T8 and T9 (Fig. 1). The observed difference among T1, T2, T7, T8 and T9 for total earthworm mortality was not statistically significant (ANOVA/ Tukeys t-test; p = 0.060). The composition and chemical quality of waste feedstock directly affects the earthworm survival in
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219
vermibeds during vermicomposting process. Probably, the production of intermediate metabolites during waste mineralization process could cause mortality in earthworms, during initial period of waste decomposition. The observed difference among different waste mixtures for earthworm mortality rate could be attributed to the quality and composition of waste composition used as substrate for earthworms. The results of this study are corroborated by the findings of other workers who have reported similar results (Gomez-Brandon et al., 2011; Hait and Tare, 2011) of earthworm mortality in vermibeds. 4. Conclusions This work provides an opportunity to utilize the potential of vermicomposting to recover nutrients from wastewater sludge from a milk processing industry. Results, thus clearly suggested that industrial sludge can be utilized effectively after mixing with bulky agents in a suitable ratio to produce valuable products. The end material (vermicomposted sludge) was rich in plant-available forms of soil nutrients and C:N ratio of it within acceptable limits (<15) except in few vermibeds. The results support the candidature of E. fetida for vermistabilization of milk processing industrial sludge. References Benito, M., Masaguer, A., Moliner, A., Arrigo, N., Palma, R.M., 2003. Chemical and microbiological parameters for the characterisation of the stability and maturity of pruning waste compost. Biol. Fertil. Soils 37, 184–189. Britz, T.J., van Schdkwyk, C., Hung, Y.T., 2006. Treatment of dairy processing waste water. In: C. Yapijakis, Y.T. Hung, H.H. Lo., L.K. Wang (Eds). Waste Treatment in the Food Processing Industry,CRC Press, New York, pp. 1–28. Dominguez, J., 2004. State-of-the-art and new perspectives on vermicomposting research. In: Edwards, C.A. (Ed.), Earthworm Ecology. CRC Press, Boca Raton, pp. 401–424. Flegel, M., Schreder, S., 2000. Importance of food quality on selected enzyme activities in earthworm casts (Dendrobaena octaedra, Lumbricidae). Soil Biol. Biochem. 32, 1191–1196. Gomez-Brandon, M., Lazcano, C., Lores, M., Dominguez, J., 2011. Short-term stabilization of grape marc through earthworms. J. Haz. Mat. 187, 291–295. Hait, S., Tare, V., 2011. Vermistabilization of primary sewage sludge. Bioresour. Technol. 102, 2812–2820. Hong, J., Xiangzhi, L., Zhaojie, C., 2010. Life cycle assessment of four municipal solid waste management scenarios in China. Waste management 30, 2362–2369. Ilgen, G., Glindemann, D., Herrmann, R., Hertel, F., Huang, J.H., 2008. Organo metals of tin, lead and mercury compounds in landfill gases and leaches from Bavaria, Germany. Waste Manag. 28, 1518–1527. IPCC (Intergovernmental Panel on Climate Change), 2006. IPCC Guidelines for National Greenhouse Gas Inventories. accessed 21.03.12. Jackson, M.L., 1975. Soil Chemical Analysis, Prentice Hall of India, New Delhi.
219
Kale, R. D., 1998. Earthworms: Nature’s gift for utilization of organic wastes. In: In: Edwards CA (ed.), Earthworm Ecology, 2nd ed., CRC Press, pp 355–373. Kavian, M.F., Ghatneker, S.D., 1991. Bio-management of dairy effluents using culture of red earthworms (Lumbricus rubellus). Indian J. Environ. Prot. 11, 680– 682. Khwairakpam, M., Bhargava, R., 2009. Vermitechnology for sewage sludge recycling. J. Haz. Mat. 161, 948–954. Loehr, R.C., Neuhauser, E.F., Malecki, M.R., 1985. Factors affecting the vermistabilization process. Water Res. 19 (10), 1311–1317. Lopez, A.M., Funamizu, N., Takakuwa, T., 2002. Characterization of feces for describing the aerobic biodegradation of feces. JSCE 720 (VII-25), 99–105. Lou, X.F., Nair, J., 2009. The impact of landfilling and composting on greenhouse gas emissions – A review. Bioresour. Technol. 100, 3792–3798. Morais, F.M.C. Queda, C.A.C., 2003. Study of storage influence on evolution of stability and maturity properties of MSW composts. In: Proceeding of the fourth International Conference of ORBIT association on Biological Processing of Organics: advances for a Sustainable Society part II Perth, Australia. Moreno, R., Benitez, E., Meglar, R., Polo, A., Gomez, M., Nogales, R., 2000. Vermicomposting as an alternative for reusing by-products from the olive oil industry. Fresenius Environ. Bull. 9, 1–8. 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., 1996. 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, pp. 539–579. Olsen, S.R., Cole, C.V., Watanabe, F.S., Dean, L.A., 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate, Circ. US Dept. Agric., 939. Pramanik, P., Chung, Y.R., 2011. Changes in fungal population of fly ash and vinasse mixture during vermicomposting by Eudrilus eugeniae and Eisenia fetida: Documentation of cellulose isozymes in vermicompost. Waste Management (doi: 10.1016/j.wasman.2010.12.017.). Ravindran, B., Dinesh, S.L., John Kennedy, L., Sekaran, G., 2008. Vermicomposting of solid waste generated from leather industries using epigeic earthworm Eisenia foetida. Appl. Biochem. Biotechnol. 151, 480–488. Simard, R.R., 1993. Ammonium acetate extractable elements. In: Martin, R., Carter, S. (Eds.), Soil Sampling and Methods of Analysis. Lewis Publisher, FL, USA, pp. 39–43. Sinha, R.K., Agarwal, S., Chauhan, K., Chandran, V., Soni, B.K., 2010. Vermiculture technology: reviving the dreams of sir charles darwin for scientific use of earthworms in sustainable development programs. Technol. Investments 3 (1), 155–172. Slater, R.A., Frederickson, J., 2001. Composting municipal waste in the UK: some lesions from Europe. Res. Conserv. Recycling 32, 359–374. Subramanian, S., Sivarajan, M., Saravanapriya, S., 2010. Chemical changes during vermicomposting of sago industry wastes. J. Haz. Mat. 179, 318–322. Suthar, S., 2008. Bioconversion of post harvest crop residues and cattle shed manure into value-added products using earthworm Eudrilus eugeniae Kinberg. Ecol. Eng. 32, 206–214. Suthar, S., 2009. Vermicomposting of vegetable market solid waste using Eisenia fetida: impact of bulking material on earthworm growth and decomposition rate. Ecol. Eng. 35, 914–920. Suthar, S., 2010. Recycling of agro-industrial sludge through vermitechnology. Ecol. Eng. 36, 1028–1036. Suthar, S., Singh, S., 2008. Feasibility of vermicomposting in biostabilization sludge from a distillery industry. Sci. Tot. Environ. 394, 237–244. Xing, M., Yang, Y., Wang, Y., Li, J., Yu, F., 2011. A comparative study of synchronous treatment of sewage and sludge by two vermifiltrations using an epigeic earthworm Eisenia fetida. J. Haz. Mat. 185, 881–888.
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Vermicomposting of milk processing industry sludge spiked with plant wastes Surindra Suthar a,⇑, Pravin K. Mutiyar b, Sushma Singh c a
School of Environment & Natural Resources, Doon University, Dehradun 248001, Uttarakhand, India Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas 110 016, New Delhi, India c Department of Chemistry, N.M. Govt. (PG) College, Hanumangarh Town 335513, Rajasthan, India b
a r t i c l e
i n f o
Article history: Received 21 December 2011 Received in revised form 26 March 2012 Accepted 29 March 2012 Available online 5 April 2012 Keywords: Vermicomposting Dairy wastewater sludge C:N ratio Eisenia fetida Industrial waste
a b s t r a c t This work illustrates the vermistabilization of wastewater sludge from a milk processing industry (MPIS) unit spiked with cow dung (CD), sugarcane trash (ST) and wheat straw (WS) employing earthworms Eisenia fetida. A total of nine experimental vermibeds were established and changes in chemical parameters of waste material have been observed for 90 days. Vermistabilization caused significant reduction in pH, organic carbon and C:N ratio and substantial increase in total N, available P and exchangeable K. The waste mixture containing MPIS (60%) + CD (10%) + ST (30%) and MPIS (60%) + CD (10%) + WS (30%) had better waste mineralization rate among waste mixtures studied. The earthworm showed better biomass and cocoon numbers in all vermibeds during vermicomposting operation. Results, thus suggest the suitability of E. fetida for conversion of noxious industrial waste into value-added product for land restoration programme. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Agriculture, food processing, pulp and paper, or any agriculturebased industry produces massive quantity of liquid, gaseous or solid wastes. Such agro-industrial sludge/wastes not only spoil aesthetics sense of local habitats but at the same time also create issues of all types of environmental pollution, if proper disposal and management policy is not adopted. The dairy processing industry is the major component of food processing industry in the India. It is considered to be the largest source of food processing wastewater in many countries. Although the dairy industry is not commonly associated with sever environmental problem, it must continually consider its environmental impact – particularly as dairy pollutants are mostly of organic origin (protein, carbohydrate, lipids, suspended oils and/or grease) with high concentration of suspended solids, biochemical oxygen demand (BOD), chemical oxygen demand (COD) and nitrate contents (Britz et al., 2006). The wastewater and solids generated from dairy processing industry pose issues of safe management and disposal of treated and/or untreated wastewater solids. The traditional disposal methods such as open dumping and/or land filling practices of these materials are not only increasingly expensive, but impractical as open space becomes limited (Slater and Frederickson, 2001). Contamination of ground water, soils, as well as, food resources are some of the problems which have resulted from land filling practices of dumped waste materials (Ilgen et al., 2008). The emission of GHGs from
⇑ Corresponding author. Fax: +91 135 2533103. E-mail address: [email protected] (S. Suthar). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.03.101
waste dumping site is an issue of prime concern (IPCC, 2006; Lou and Nair, 2009). However, the stabilization of such sludge prior to use of disposal should reduce the environmental problems associated with its open dumping (Gomez-Brandon et al., 2011). In general, stabilization involves the decomposition of an organic waste into the extent of eliminating the hazards and is normally reflected by decreases in microbial activity and concentration of labile compounds (Benito et al., 2003). Composting has been appeared as important tool to stabilize the organic waste generated from different sector of the society. Composting is the most sustainable option for onsite organic waste management as it is easy to operate and can be conducted in contained space provided (Lou and Nair, 2009; Hong et al., 2010). In recent years vermicomposting has been explored extensively to recycle the nutrient stuff from organic wastes from different community sources (Suthar, 2009). Vermicomposting, utilizing earthworms, is an ecobiotechnological process that transforms energy-rich and complex organic substances into a stabilized humus-like product vermicompost (Sinha et al., 2010). According to Dominguez (2004) it is a complex process involving the joint action of earthworms and microorganisms. Although microbes are responsible for biochemical degradation of organic matter, earthworms are the important drivers of the process, conditioning the substrate and altering the biological activity. Vermistabilization is stabilization of organic material, such as sludge, involving the joint action of earthworms and microorganisms. The sludge can be stabilized effectively through vermistabilization process because of many beneficial impacts of inoculated earthworms upon aerobic decomposition process. Loehr et al. (1985) concluded that in vermicomposting system the earthworms
215
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219
maintain aerobic condition in wastes, ingest solids, convert a portion of the organics to worm biomass and respiration products and expel partially stabilized matter as discrete particles (vermicompost). The utilization of earthworm in waste stabilization practices is well documented in recently published work. There is evidence of successful utilization of earthworms for stabilizations of anthropogenic wastes generated from different industries: vinasse (Pramanik and Chung, 2011), grape mark (Gomez-Brandon et al., 2011), sago industry waste (Subramanian et al., 2010), paper mill sludge (Elvira et al., 1998), sugar factory waste (Khwairakpam and Bhargava, 2009; Suthar, 2010) and olive oil mill sludge (Moreno et al. (2000) distillery and winery industry sludge (Suthar and Singh, 2008; Gomez-Brandon et al., 2011), leather processing industry sludge (Ravindran et al., 2008) etc. After reviewing literature it is realized that dairy industry sludge can also be a candidate for vermistabilization operation. Epigeic earthworms could stabilize the sludge potentially and can accelerate the rates of destruction of sludge volatile solids in aerobic sludge greatly, which probably decreases the putrefaction; occurring because of anaerobic conditions. So, the main cause of increased rates of degradation of sludge is probably the increased aeration and turnover of wastes by the earthworms (Loehr et al., 1985). The aim of the present investigation is to stabilize the diary industry wastewater sludge spiked with plant wastes in different ratios using earthworm Eisenia fetida. The different combinations of industrial sludge and bulky materials were tested under vermistabilization operation in order to find out suitable waste mixture for optimize earthworm activity. 2. Methods 2.1. E. fetida, dairy industrial sludge and bulky agent collection To carry out the experiment specimens of earthworm species E. fetida (Savigny) were obtained from a stock culture reared in our laboratory and fed with decomposed cow dung spiked with plant litters. Freshly deposited sludge (MPIS) was collected form wastewater treatment unit of a local milk processing industry. The wet-sludge (containing 70–81% moisture) was collected in large-sized plastic containers and then brought to the laboratory for further processing. The sludge was shade dried in lab to evaporate the excess water from it. Also, regular turns were made in order to reduce the characteristics smell of putrescible substances and biotoxic compounds present in sludge; generally formed under anaerobic conditions. Partially dried sludge cake solids were then homogenized and shredded prior to use in experimental vermibeds. Three bulky materials, i.e. cow dung (CD), sugarcane trash (ST) and wheat straw (WS) were used to prepare different substrate mixture for earthworms. The substrate acts as bedding and feeding materials for inoculated earthworms. The chopped straw of wheat (WS) and fresh sugarcane trash were procured from a local agriculture farm. Fresh urine-free cow dung was procured from a local cowshed. The cow dung was partially dried in shade and homogenised manually. The main chemical characteristics of dairy processing industrial sludge cake (MPIS) and bulky agents are given in Table 1. 2.2. Experimental design The chemical characteristics especially nitrogen content and C:N ratio of waste stuff plays an important role in earthworm palatability and vermicomposting rate. The MPIS was mixed with bulky materials (CD, ST and WS) in appropriate ratio in order to balance the nutrient contents as well as bedding material size frac-
tions. Following nine feed mixtures were used for vermicomposting experimentations. T1 T2 T3 T4 T5 T6 T7 T8 T9
MPIS MPIS MPIS MPIS MPIS MPIS MPIS MPIS MPIS
(20%) + CD (80%) (40%) + CD (60%) (40%) + WS (60%) (60%) + WS (40%) (40%) + ST (60%) (60%) + ST (40%) (60%) + CD (10%) + WS (30%) (60%) + CD (10%) + ST (30%) (100%)
MPIS (100%) acts as experimental control bedding in order to compare the results of chemical and biological changes during vermicomposting in the presence of bulky agents. The chemical characteristics of initial waste mixtures (Table 2) were: 7.35–8.5 (pH), 419.18–503.65 g kg 1 (TOC), 7.96–39.73 g kg 1 (TKN), 2.32– 23.50 g kg 1 (AP), 5.67–14.46 g kg 1 (EK) and 10.60–60.52 (C:N ratio). Prior to vermistabilization the waste mixtures were pre-composted for 3 weeks for initial thermal stabilization, initiation of microbial degradation and softening of waste mixture. During this sludge mixture was turned out periodically (after 3 days) for aeration and to remove odour from decomposing wastes. The proper moisture content in composting beds was maintained. After 3-wk composting, 500 g waste mixture (dry weight basis) was separated from composting beds and filled in plastic circular containers of 2 L capacity (one for each mixture) for vermicomposting trials. Twenty earthworms (4-wk old) having individual live weights of 264– 281 mg were released into each experimental container. The experimental beddings were kept in triplicate for each treatment. The moisture content was maintained at 65–70%, throughout the study period by periodic sprinkling of adequate quantity of water. The containers were placed in a humid and shady place at an ambient temperature 27.2 °C (SD = 0.14). The earthworm mortality was observed for initial critical periods (initial 15 days of experimental starting) and data of mortality were recorded for different experimental containers. To estimate the physic-chemical changes during vermistabilization process, homogenized samples (10 g) of waste mixtures were drawn at 0, 15, 30, 45, 60, 75 and 90 days from each experimental container. The samples of substrate mixture were oven dried (48 h at 60 °C), ground in stainless steel blender and stored in sterilized plastic airtight containers. The biological productivity (biomass change, cocoon production etc.) of E. fetida was also monitored during the same interval for whole experiment duration by following method as described by Suthar (2009). 2.3. Chemical analysis The pH was measured using a digital pH meter (Systronics made) in 1:10 (w/v) aqueous solution (deionized water). Total organic carbon (TOC) was measured after igniting the sample in a Muffle furnace at 550 °C for 60 min by the method of Nelson and Sommers (1996). Total Kjeldahl nitrogen (TKN) was measured using the method described by Jackson et al. (1975). Available phosphorous (AP) was measured using the method described by Anderson and Ingram (Olsen et al., 1954). Exchangeable potassium (EK) was determined after extracting the sample using ammonium acetate (Simard, 1993). 2.4. Statistical analysis One-way ANOVA was used to analyze the differences between treatments. A Tukey’s t-test was also performed to identify the
216
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 1 Chemical characteristics (g kg
1
) of organic wastes used as amendment material (mean ± SD, n = 3).
Parameters
Industry sludge
pH Organic C Organic matter Total N Available P Exchangeable K C:N ratio a
7.05 ± 0.11 379.5 ± 5.23 657.29 ± 8.93 56.8 ± 2.34 32.9 ± 2.01 18.4 ± 0.34 5.06 ± 0.07
a
ND 491.5 ± 0.88 851.28 ± 1.5 25.2 ± 0.58 15.7 ± 0.97 6.8 ± 0.07 15.5 ± 0.7
Cow dung
ND 589.0 ± 3.0 1020.15 ± 5.3 6.03 ± 0.2 2.67 ± 0.2 12.6 ± 0.3 80.3 ± 2.8
8.5 ± 0.1 481.8 ± 0.3 834.47 ± 0.8 7.96 ± 0.2 2.32 ± 0.1 5.67 ± 0.2 14.6 ± 0.4
1
) of substrates at starts used for experimentation (mean ± SD; n = 3).
Treatmenta
pH
Corg
Ntot
Pavail
Kexch
C:N ratio
T1 T2 T3 T4 T5 T6 T7 T8 T9
7.90 ± 0.01 7.69 ± 0.01 7.60 ± 0.01 7.38 ± 0.01 7.82 ± 0.02 7.46 ± 0.01 7.35 ± 0.02 7.49 ± 0.01 8.5 ± 0.1
459.07 ± 0.47 437.16 ± 0.99 503.65 ± 0.58 460.05 ± 0.29 443.58 ± 0.38 421.11 ± 0.17 449.75 ± 1.22 419.18 ± 0.30 481.8 ± 0.3
15.94 ± 0.04 24.75 ± 0.05 23.71 ± 0.09 32.86 ± 0.05 34.03 ± 0.07 39.73 ± 0.09 30.03 ± 0.02 38.19 ± 0.04 7.96 ± 0.2
7.58 ± 0.02 13.10 ± 0.03 13.30 ± 0.11 18.73 ± 0.04 20.35 ± 0.05 23.50 ± 0.10 18.69 ± 0.06 22.21 ± 0.06 2.32 ± 0.1
7.39 ± 0.04 9.70 ± 0.04 13.44 ± 0.06 14.46 ± 0.06 10.33 ± 0.04 12.38 ± 0.04 13.85 ± 0.06 12.30 ± 0.07 5.67 ± 0.2
28.79 ± 0.06 17.66 ± 0.08 21.24 ± 0.04 14.0 ± 0.07 13.03 ± 0.01 10.60 ± 0.01 14.98 ± 0.20 10.97 ± 0.01 60.52 ± 0.4
refer to text for explanation of treatments.
homogeneous type of the data sets. SPSSÒ statistical package (Window Version 13.0) was used for data analysis. All statements reported in this study are at the p < 0.05 levels.
3. Results and discussion 3.1. Physico-chemical changes in waste mixture during vermicomposting The chemical composition of vermicomposted material was significantly different than initial waste mixtures (Table 3). There were slight changes in the pH of vermicomposted materials as compared to initial substrate materials. The pH of ready material was in the range of 7.12 ± 0.01–7.45 ± 0.05. The shifting of pH during vermicomposting process could be attributed to the production metabolic compounds of aerobic digestions of organic stuff, e.g. CO2, ammonia, NO3 and organic acids (Lopez et al., 2002). Few workers advocated the contribution of intermediate/ end products of nitrogen and phosphorous mineralization in pH shifting during vermicomposting process (Ndegwa et al., 2000). Total organic carbon decreased in all waste mixtures during vermicomposting process. TOC in vermicomposted material was in the ranges of 313.65–428.16 g kg 1. The maximum TOC reduction was in T2 (23.4%) followed by T7 (26.4%), T8 (25.2%), T4 (23.4%), T5 (23.0%), T6 (19.8%), T1 (18.9%), T3 (15.0%) and T9 (14.4%). It was Table 3 Chemical compositions (g kg Treatment T1 T2 T3 T4 T5 T6 T7 T8 T9 a
Wheat straw
ND Not determined.
Table 2 Chemical compositions (g kg
a
Sugarcane trash
a
observed that carbon mineralization rate in vermibeds was directly related to the composition of the waste feedstock. The vermibed containing plant straw and cow dung (CD) both showed the better mineralization than other waste mixtures. Recent studies suggested that cellulose rich compounds promote the carbon mineralization rate during composting/vermicomposting process probably due to colonization of cellulose decomposing fungi (Pramanik and Chung, 2011). The role of CD in waste mineralization is well documented in the literature (Suthar, 2010; Khwairakpam and Bhargava, 2009). CD contains numbers of fungal stains and greater population of other microbes, such as bacteria, protozoa, nematodes, fungi, actinomycetes, which plays an important role in organic matter decomposition by providing extra-cellular enzymes in vermibeds. The C loss in vermibeds is the results of respiration activities in substrate and digestion as well as assimilation of carbohydrates/other polysaccharides from the substrates by inoculated earthworms. A significant increase in TKN was recorded in all vermibed at the end of the process. The TKN level in vermicomposted material was in the ranges of 13.45 ± 0.45–63.59 ± 1.18 g kg 1 (Table 3). There was 1.21–1.70-fold increase in TKN in vermicomposted materials at the end of the process. The N enhancement rate in all vermibed varied significantly. In terms of N enrichment the vermibeds can be arranged in the order: T7 > T9 > T6 > T4 > T8 > T3 > T5 > T2 > T1. The nitrogen enrichment rate was slightly different among vermibeds. It could be due to the composition of waste
1
) of substrates after 90 days of experimentation (mean ± SD; n = 3).
pH
Corg
Ntot
Pavail
Kexch
C:N ratio
7.45 ± 0.05 7.44 ± 0.02 7.32 ± 0.02 7.27 ± 0.01 7.28 ± 0.02 7.24 ± 0.01 7.22 ± 0.01 7.16 ± 0.01 7.12 ± 0.01
372.5 ± 1.22 319.02 ± 1.24 428.16 ± 2.59 352.17 ± 1.94 341.75 ± 2.29 337.65 ± 2.90 331.01 ± 3.45 313.65 ± 1.15 412.5 ± 1.03
19.38 ± 0.35 31.78 ± 0.50 34.18 ± 0.94 52.31 ± 2.43 45.64 ± 7.74 63.59 ± 1.18 53.26 ± 0.14 60.06 ± 0.78 13.45 ± 0.45
8.76 ± 0.14 16.02 ± 0.38 17.48 ± 0.46 29.48 ± 0.40 27.72 ± 0.97 34.06 ± 0.93 29.55 ± 0.63 35.76 ± 0.71 6.52 ± 1.06
9.16 ± 0.09 12.86 ± 0.37 15.96 ± 0.97 17.76 ± 0.20 14.44 ± 0.29 17.55 ± 0.27 21.84 ± 0.31 19.28 ± 0.42 10.34 ± 0.98
19.22 ± 0.25 10.64 ± 0.08 12.53 ± 0.16 6.73 ± 0.16 7.49 ± 0.12 5.31 ± 0.11 6.21 ± 0.06 5.22 ± 0.04 30.65 ± 0.26
refer to 2.2 sub-section for explanation of treatments.
217
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 4 Earthworm productions during vermicomposting process (mean ± SD, n = 3). Vermibeds
Mean initial biomass of individual earthworm (mg)
Maximum individual biomass achieved (mg)
Maximum individual biomass achieved in (week)
Net biomass at the end (mg)
Maximum growth rate (mg wt worm 1 day 1)
Weigh achieved by individual earthworm (mg)
T1 T2 T3 T4 T5 T6 T7 T8 T9
273.06 ± 0.81 276.7 ± 0.26 265.0 ± 1.0 262.5 ± 0.50 271.8 ± 0.35 270.2 ± 0.72 279.5 ± 0.50 281.3 ± 1.52 267.9 ± 0.32
796.7 ± 20.8b 816.5 ± 7.69b 695.0 ± 5.0a 813.3 ± 11.6b 768.7 ± 11.9b 963.3 ± 41.5d 1022.8 ± 11.1e 988.3 ± 8.50de 870.7 ± 6.66c
75 75 60 75 75 75 75 75 75
772.0 ± 9.64b 796.0 ± 6.24b 683.7 ± 4.73a 799.7 ± 10.1b 759.0 ± 10.5b 949.7 ± 35.5d 1010.0 ± 15.6e 978.3 ± 2.08de 863.0 ± 6.56c
6.98 ± 0.27ab 7.20 ± 1.0ab 7.17 ± 0.09ab 7.34 ± 0.15b 6.62 ± 0.16a 9.24 ± 0.56d 9.90 ± 0.15d 9.43 ± 0.12d 8.03 ± 0.09c
523.6 ± 20.1bc 324.7 ± 4.51bc 308.3 ± 17.6a 302.3 ± 22.0c 354.0 ± 11.5b 301.3 ± 3.51e 353.7 ± 13.5e 451.0 ± 16.0e 345.3 ± 4.29d
Mean value followed by different letters is statistically different (ANOVA; Tukey’s t-test, P < 0.05). a refer to text for explanation of treatments.
mixture and nature of bulky agent, as used for dilution of industrial sludge. The optimum N enrichment in T4, T6, T7 and T9 should be related to the composition of feedstock. The combination of high carbon materials (crop residues) and CD acts as good energy stuff for microbial propagation in vermibeds. Also decomposer communities in fresh CD also enhance the mineralization process in vermibeds if it is supplies in appropriate proportion in worm feed. The earthworm body secretions (excreta, mucus etc.) add nitrogen in substrate if earthworms are inoculated in organic wastes for longer periods (Suthar, 2010). Also, mucus a polysaccharide is secreted by earthworm to moisten the body surface also important to enrich vermibeds with nitrogen fixers. Earthworm also alters the microclimatic conditions of vermibeds which consequently promotes microbial populations responsible for N enrichment. N fixers are important in N enrichment of vermicomposted materials. Study by Kavian and Ghatneker (1991) suggested the enhanced population of N fixers (Azotobactor and Rhizobium) in vermibeds, while working on vermicomposting of paper mill sludge. The available P content in vermicomposted material was relatively higher than initial waste mixtures, in all vermibeds (Table 3). The level of available P in worm-processed material was in the ranges of 6.52 ± 1.06–35.67 ± 0.71 g kg 1. There was about 1.16– 2.81-fold increase in available P level in vermicomposted material than initial waste mixtures. The maximum phosphorous mineralization was recorded in T9 followed by T8, T7, T4, T6, T5, T3, T2 and T1. The concentration of P in vermicomposted material may reflects the amount of organic forms of phosphorus in waste mixture, but its mineralization rate is directly affected by nature of amendment material and activities of P-mineralizing microflora in decomposing wastes. Few earlier studies indicate the highest plant available forms in vermicomposted wastes mainly due to activities of P-solubilizing bacteria and enzymatic activities of earthworm gut. The release of P in available forms is performed partly by earthworm gut phosphatases, and further release of P might be attributed to the P-solubilizing microorganisms present in worm casts. Results thus clearly suggest that phosphorous enrichment was directly related to the quality of stuff used as vermibed. There was significant increase in level of exchangeable potassium at the end of vermicomposting process in all vermibeds (Table 3). Exchangeable K in vermicomposted material was the ranges of 9.16 ± 0.09–21.84 ± 0.31 g kg 1. The level of exchangeable K in ready material was 1.19–1.82-fold high than initial level in all vermibeds. It clearly indicates that inoculation of earthworms in waste feedstock enhances the waste mineralization process. In general, when organic waste passes through the gut of worm some fraction of organic minerals is then converted into more available species of nutrients (i.e. exchangeable forms) due to the action of endogenic and/or exogenic enzymes (Suthar, 2010). Most of the
earlier reports on vermicomposting (Khwairakpam and Bhargava, 2009; Hait and Tare, 2011) have reported a higher K increase at the end. The C:N ratio is an important indicator of compost maturity as well as compost quality. In this study the C:N ratio of vermicomposted material was significantly lower than initial waste substrates. The C:N of end product was in the ranges of 5.22–30.65. According to Morais and Queda (2003) a C:N ratio below 20 is indicative of acceptable maturity while a ratio of 15 or lower is being preferred for agronomic used of composts. The vermicomposts obtained in this study showed the C:N ratio within the preferable limit as described by Morais and Queda (2003), except in T1 and T9 (Table 3). In general, the loss of carbon as carbon dioxide due to respiratory activities of earthworms and associated microflora, and simultaneously adding of nitrogen in substrate material by inoculated earthworms (through. production of mucus, enzymes and nitrogenous excrements) lowers the C:N ratio of the substrate (Suthar, 2010). 3.2. Earthworm growth and reproduction in different vermibeds The growth and cocoon production pattern in vermibed is an important indicator of waste suitability for earthworm feeds. There was statistically significant difference (ANOVA) among waste mixtures for observed parameters of earthworms: the maximum individual live weight (F = 118.95, p < 0.001), total individual biomass gain (F = 109.24, p = 0.001), the maximum individual growth rate (mg wt worm 1 day 1) (F = 80.29, p < 0.001), total cocoon numbers (F = 35.40, p < 0.001), reproduction rate (cocoon worm 1) (F = 7.32, p < 0.001) and mortality rate (F = 5.62, p = 0.001). The initial live weight of earthworm increased from 262.3–281.3 to 695.0– 1022.8 in different vermibeds during experimentations. The maximum individual weight of earthworm was recorded 1022.8 ± 11.1 mg in T7 followed 988.3 ± 8.50 mg (T8), 963.3 ± 41.5 mg (T6), 870.7 ± 6.66 mg (T9), 816.5 ± 7.69 mg (T2), 813.3 ± 11.6 mg (T4), 796.7 ± 20.8 mg (T1), 768.7 ± 11.9 mg (T5) and 695.0 ± 5.0 mg (T3). The individual biomass in E. fetida was 2.62–3.65 folds higher than initial weight in all vermibeds at the end of process (Table 4). The weight gain by individual earthworm varied significantly among different vermibeds and the maximum rate of individual biomass gain was in T1 (523.6 ± 20.1 mg) while T6 showed the minimum weigh gain (301.3 ± 3.51 mg) during experimentation. Net biomass gain in inoculated earthworms was in the order: T1 > T8 > T5 > T7 > T9 > T2 > T3 > T4 > T6. The earthworm biomass gain is directly related to the feeding rate, palatability of feedstuff and particle size of feedstock. However, chemical composition plays an important role in earthworm feeding rate and observed difference in vermibeds for earthworm biomass gain could be due to
218
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219 Table 5 Total cocoon production and reproduction patterns in E. fetida for different vermibeds (mean ± SD, n = 3). Vermibeds T1 T2 T3 T4 T5 T6 T7 T8 T9
Total cocoons obtained at the end ba
313.7 ± 13.9 324.7 ± 14.5abc 308.3 ± 17.6ab 302.3 ± 22.0a 354.0 ± 11.5c 301.3 ± 3.51a 353.7 ± 13.5c 451.0 ± 16.0d 345.3 ± 9.29ba
Reproduction rate (cocoon/worm/day) a
0.220 ± 0.021 0.224 ± 0.004a 0.233 ± 0.020a 0.247 ± 0.025a 0.267 ± 0.017b 0.233 ± 0.022a 0.249 ± 0.011a 0.311 ± 0.019b 0.234 ± 0.007a
Fecundity (Cocoons earthworm
1
)
a
16.56 ± 1.60 16.80 ± 0.33a 17.48 ± 1.52a 18.55 ± 1.92a 20.06 ± 1.33b 17.48 ± 1.70a 18.63 ± 0.84a 23.55 ± 1.45b 17.57 ± 0.54a
Mean value followed by different letters is statistically different (ANOVA; Tukey’s t-test, P < 0.05).
difference in feed compositions and its palatability (Suthar, 2008). However, there is a close relationship between feedstock quality and microbial richness of bedding substrates (Flegel and Schreder, 2000) which directly or indirectly affects the earthworm feeding rate, as microbes are the important component of earthworm diets (Gomez-Brandon et al., 2011). The growth rate was the maximum in T7 (9.90 ± 0.15 mg wt. worm 1 day 1) followed by T8 (9.43 ± 0.12 mg wt. worm 1 day 1), T6 (9.24 ± 0.56 mg wt. worm 1 day 1), T9 (8.03 ± 0.09 mg wt. worm 1 day 1), T4 (7.34 ± 0.15 mg wt. worm 1 day 1), T2 (7.20 ± 1.0 mg wt. worm 1 day 1), T3 (7.17 ± 0.09 mg wt. worm 1 day 1) T1 (6.98 ± 0.27 mg wt. worm 1 day 1) and T5 (6.62 ± 0.16 mg wt. worm 1 day 1) (Table 4). The observed difference among T1, T2 and T3 for the earthworm growth rate was not statistically significant (ANOVA/Tukey’s t-test; p = 0.132). The crop residues/plant-origin wastes have different palatability, particle size, protein and crude fiber contents that can influence the earthworm growth trends in waste mixtures during vermicomposting. The better proportion of easily metabolizable organic matter, non-assimilated carbohydrates etc. affect the normal earthworm growth in vermibeds (Kale, 1998; Khwairakpam and Bhargava, 2009). Suthar (2009) demonstrated that growth rate of earthworms in waste depends upon the microbial populations and availability of nutrient pools in vermibeds. The end biomass of earthworm was slight lower than the maximum individual biomass observed during 60–75 days of vermicomposting process. It indicates the loss in individual biomass of inoculated earthworms in different vermibeds. The individual biomass of earthworms at the end of experiment ranged between 683.7 ± 4.73 and 1010.0 ± 15.6 mg (Table 4). At the end of experiment, the individual biomass of earthworms was in the order: T7 > T8 > T6 > T9 > T4 > T2 > T1 > T5 > T3 (Table 4). It is suggested that weight loss was due to conversion of most of the used substrate to vermicompost, which further do not supports the growth in earthworms (Suthar, 2009). Few earlier studies have also demonstrated the weight loss during later period of vermicomposting process mainly due to ageing of substrate materials (Garg and Gupta, 2011). E. fetida produced cocoons in all vermibeds during experimentations. The maximum cocoon production was recorded in T8 (451.0 ± 16.0) followed by T5 (354.0 ± 11.5), T7 (353.7 ± 13.5), T9 (345.3 ± 9.29), T2 (324.7 ± 4.51), T1 (313.7 ± 13.9), T3 (308.3 ± 17.6), T4 (302.3 ± 22.0) and T6 (301.3 ± 3.51) (Table 5). Statistically, the variation among T1, T2, T3, T4, T6 and T8 treatment for total cocoon production was not significant (ANOVA/Tukeys t-test; p = 0.505). The fecundity rate (cocoons worm 1) also varied among different waste mixtures during vermicomposting process. The fecundity rate in waste-inoculated earthworms was in the ranges of 16.56 ± 1.60–23.55 ± 1.45 cocoons worm 1 in different vermibeds (Table 5). The vermibeds can be arranged in following order for fecundity rate in waste mixtures: T8 > T5 > T7 > T4 > T9 > T6 = T3 > T2 > T1 (Table 5). The cocoon produc-
Fig. 1. Earthworm mortality rate (%) in different waste mixtures during vermicomposting. The significant difference (P < 0.05) is indicated by different letters.
tion rate (cocoons worm 1 day 1) in vermibeds was observed in the ranges of 0.220 ± 0.021–0.311 ± 0.019 cocoons worm 1 day 1. The maximum cocoon production rate was recorded in T8 while T1 showed the minimum value for this parameter, i.e. 0.220 ± 0.021 (Table 5). It is clear from results that cocoon production in waste mixtures was directly related to the feedstock quality. The proportion of waste in feedstock directly affects the earthworm growth patterns in vermibeds. However microbes, which play an important role in earthworm’s diet, are directly interrelated to the quantity of the growth retarding substances in earthworm feed (Suthar, 2008). In this study, earthworm showed better reproduction performances in bedding those contained appropriate or acceptable ratio of bulking materials. In earlier studies it is suggested that greater N fractions in decomposing waste enhanced the cocoon production rate in composting earthworms (Suthar, 2010; Xing et al., 2011). The results of cocoon production rate are corroborated by the findings of other researchers who have observed waste quality dependent cocoon production patterns in earthworms during vermicomposting process (Khwairakpam and Bhargava, 2009; Xing et al., 2011). The earthworm mortality during initial stabilization period was recorded in all vermibeds during experimentation. The earthworm mortality was in the ranges of 5.0–18.3% in all vernmibeds. T4 vermibed showed the maximum earthworm mortality rate followed by T6, T3, T5, T1 = T7, T2 = T8 and T9 (Fig. 1). The observed difference among T1, T2, T7, T8 and T9 for total earthworm mortality was not statistically significant (ANOVA/ Tukeys t-test; p = 0.060). The composition and chemical quality of waste feedstock directly affects the earthworm survival in
S. Suthar et al. / Bioresource Technology 116 (2012) 214–219
vermibeds during vermicomposting process. Probably, the production of intermediate metabolites during waste mineralization process could cause mortality in earthworms, during initial period of waste decomposition. The observed difference among different waste mixtures for earthworm mortality rate could be attributed to the quality and composition of waste composition used as substrate for earthworms. The results of this study are corroborated by the findings of other workers who have reported similar results (Gomez-Brandon et al., 2011; Hait and Tare, 2011) of earthworm mortality in vermibeds. 4. Conclusions This work provides an opportunity to utilize the potential of vermicomposting to recover nutrients from wastewater sludge from a milk processing industry. Results, thus clearly suggested that industrial sludge can be utilized effectively after mixing with bulky agents in a suitable ratio to produce valuable products. The end material (vermicomposted sludge) was rich in plant-available forms of soil nutrients and C:N ratio of it within acceptable limits (<15) except in few vermibeds. The results support the candidature of E. fetida for vermistabilization of milk processing industrial sludge. References Benito, M., Masaguer, A., Moliner, A., Arrigo, N., Palma, R.M., 2003. Chemical and microbiological parameters for the characterisation of the stability and maturity of pruning waste compost. Biol. Fertil. Soils 37, 184–189. Britz, T.J., van Schdkwyk, C., Hung, Y.T., 2006. Treatment of dairy processing waste water. In: C. Yapijakis, Y.T. Hung, H.H. Lo., L.K. Wang (Eds). Waste Treatment in the Food Processing Industry,CRC Press, New York, pp. 1–28. Dominguez, J., 2004. State-of-the-art and new perspectives on vermicomposting research. In: Edwards, C.A. (Ed.), Earthworm Ecology. CRC Press, Boca Raton, pp. 401–424. Flegel, M., Schreder, S., 2000. Importance of food quality on selected enzyme activities in earthworm casts (Dendrobaena octaedra, Lumbricidae). Soil Biol. Biochem. 32, 1191–1196. Gomez-Brandon, M., Lazcano, C., Lores, M., Dominguez, J., 2011. Short-term stabilization of grape marc through earthworms. J. Haz. Mat. 187, 291–295. Hait, S., Tare, V., 2011. Vermistabilization of primary sewage sludge. Bioresour. Technol. 102, 2812–2820. Hong, J., Xiangzhi, L., Zhaojie, C., 2010. Life cycle assessment of four municipal solid waste management scenarios in China. Waste management 30, 2362–2369. Ilgen, G., Glindemann, D., Herrmann, R., Hertel, F., Huang, J.H., 2008. Organo metals of tin, lead and mercury compounds in landfill gases and leaches from Bavaria, Germany. Waste Manag. 28, 1518–1527. IPCC (Intergovernmental Panel on Climate Change), 2006. IPCC Guidelines for National Greenhouse Gas Inventories.
219
Kale, R. D., 1998. Earthworms: Nature’s gift for utilization of organic wastes. In: In: Edwards CA (ed.), Earthworm Ecology, 2nd ed., CRC Press, pp 355–373. Kavian, M.F., Ghatneker, S.D., 1991. Bio-management of dairy effluents using culture of red earthworms (Lumbricus rubellus). Indian J. Environ. Prot. 11, 680– 682. Khwairakpam, M., Bhargava, R., 2009. Vermitechnology for sewage sludge recycling. J. Haz. Mat. 161, 948–954. Loehr, R.C., Neuhauser, E.F., Malecki, M.R., 1985. Factors affecting the vermistabilization process. Water Res. 19 (10), 1311–1317. Lopez, A.M., Funamizu, N., Takakuwa, T., 2002. Characterization of feces for describing the aerobic biodegradation of feces. JSCE 720 (VII-25), 99–105. Lou, X.F., Nair, J., 2009. The impact of landfilling and composting on greenhouse gas emissions – A review. Bioresour. Technol. 100, 3792–3798. Morais, F.M.C. Queda, C.A.C., 2003. Study of storage influence on evolution of stability and maturity properties of MSW composts. In: Proceeding of the fourth International Conference of ORBIT association on Biological Processing of Organics: advances for a Sustainable Society part II Perth, Australia. Moreno, R., Benitez, E., Meglar, R., Polo, A., Gomez, M., Nogales, R., 2000. Vermicomposting as an alternative for reusing by-products from the olive oil industry. Fresenius Environ. Bull. 9, 1–8. 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., 1996. 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, pp. 539–579. Olsen, S.R., Cole, C.V., Watanabe, F.S., Dean, L.A., 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate, Circ. US Dept. Agric., 939. Pramanik, P., Chung, Y.R., 2011. Changes in fungal population of fly ash and vinasse mixture during vermicomposting by Eudrilus eugeniae and Eisenia fetida: Documentation of cellulose isozymes in vermicompost. Waste Management (doi: 10.1016/j.wasman.2010.12.017.). Ravindran, B., Dinesh, S.L., John Kennedy, L., Sekaran, G., 2008. Vermicomposting of solid waste generated from leather industries using epigeic earthworm Eisenia foetida. Appl. Biochem. Biotechnol. 151, 480–488. Simard, R.R., 1993. Ammonium acetate extractable elements. In: Martin, R., Carter, S. (Eds.), Soil Sampling and Methods of Analysis. Lewis Publisher, FL, USA, pp. 39–43. Sinha, R.K., Agarwal, S., Chauhan, K., Chandran, V., Soni, B.K., 2010. Vermiculture technology: reviving the dreams of sir charles darwin for scientific use of earthworms in sustainable development programs. Technol. Investments 3 (1), 155–172. Slater, R.A., Frederickson, J., 2001. Composting municipal waste in the UK: some lesions from Europe. Res. Conserv. Recycling 32, 359–374. Subramanian, S., Sivarajan, M., Saravanapriya, S., 2010. Chemical changes during vermicomposting of sago industry wastes. J. Haz. Mat. 179, 318–322. Suthar, S., 2008. Bioconversion of post harvest crop residues and cattle shed manure into value-added products using earthworm Eudrilus eugeniae Kinberg. Ecol. Eng. 32, 206–214. Suthar, S., 2009. Vermicomposting of vegetable market solid waste using Eisenia fetida: impact of bulking material on earthworm growth and decomposition rate. Ecol. Eng. 35, 914–920. Suthar, S., 2010. Recycling of agro-industrial sludge through vermitechnology. Ecol. Eng. 36, 1028–1036. Suthar, S., Singh, S., 2008. Feasibility of vermicomposting in biostabilization sludge from a distillery industry. Sci. Tot. Environ. 394, 237–244. Xing, M., Yang, Y., Wang, Y., Li, J., Yu, F., 2011. A comparative study of synchronous treatment of sewage and sludge by two vermifiltrations using an epigeic earthworm Eisenia fetida. J. Haz. Mat. 185, 881–888.