Young non-clitellated E. fetida were obtained from a stock culture reared in the vermicomposting unit of the Department of Botanical and Environmental Sciences, Guru Nanak Dev University, Amritsar, Punjab, India. MPIS was obtained from Haryana Dairy Development Cooperative Federation Ltd., Vita Milk Plant, Sirsa, Haryana. The sludge was collected at primary sedimentation stage. The collected sample was air dried for moisture removal. Cattle Dung (CD) was collected from a local dairy farm.

In the present work, MPIS was mixed with CD at different ratios on dry weigh basis in two sets with earthworms (ME) and without earthworms (MW) (Table 1). Plastic trays of volume 3,834 cc were filled with mixtures containing different percentages of MPIS/CD with and without earthworms in triplicates. The total weight of each tray was kept at 1 kg and according to the above mentioned proportions in Table 1, mixing of waste and cattle dung was done. The trays were covered with jute mat and were kept in a shade located in the Botanical Garden of Guru Nanak Dev University, Amritsar. The mixtures were turned over manually every 24 h for 14 days in order to eliminate the toxic gases. After 14 days, 20 young non-clitellated E. fetida with average weight were released in trays. The moisture content was maintained to 60-70% throughout the study period by sprinkling of water. In ME sets earthworms, cocoons and hatchlings were counted manually at the interval of 15 days. At the end of the experiment (90 days), worms, cocoons and hatchlings were removed. The final product produced from all the concentrations were sieved, air dried and physico-chemical parameters were analyzed. The initial physicochemical parameters of MPIS and CD were also done (Table 2).

Table 1
Preparations of milk processing industry sludge mixed with cattle dung.

Table 2
Initial physicochemical properties of milk processing industry sludge and cattle dung.

Physico-chemical analysis was done to determine the availability of total nutrient content in final MPIS feed mixtures ’ with and without earthworms. pH and electrical conductivity (EC) were determined in a double distilled water suspension of each concentration in the ratio of 1:10 (W/V). Total Organic Carbon (TOC) was measured after igniting the 0.5 g of sample in a muffle furnace at 550°c for 60 minutes as described by Nelson and Sommers [17D.W. Nelson, and L.E. Sommers, "Total carbon and organic carbon and organic matter", Method of Soil Analysis, American Society of Agronomy, Madison: Wilcosin, pp. 539-579.A.L. Page, R.H. Miller, and D.R. Keeney, ]. Micro-Kjeldhal method of AOAC [18AOAC, "Official Methods of Analysis of AOAC International", W. Horwitz Ed. 17^th ed. Gaitheresburg, Maryland, .] was used for measuring total Kjeldhal nitrogen (TKN) after digestion. The method described by John [19M.K. Johh, "Colorimetric determination of phosphorus in soil and plant material with ascorbic acid", Soil Sci., vol. 109, pp. 214-220.
[http://dx.doi.org/10.1097/00010694-197004000-00002] ] was used for measuring Total Available Phosphorus (TAP), Total Potassium (TK) and Total Sodium (TNa) after digesting the samples in diacid mixture (HClO₄:HNO₃ in 4:1 ratio). Heavy metals (Copper, Lead, Manganese and Chromium) were measured by Agilent 240 FS AA model Atomic Absorption Spectrophotometer in the digested samples.

The data was presented as mean ± SE of triplicate experiment. One-way ANOVA was used to calculate the differences among treatments. Student’s paired t-test was used to evaluate differences between initial and final values of various physico-chemical parameters. Statistical data analysis was done with the help of Statistical Package for the Social Sciences (SPSS) software.

The number of earthworms increased significantly (p≤0.05) in different waste mixtures (Fig. 1). The number of earthworms increased till 90 days in all waste mixture (ME₀, ME₂₅, ME₅₀ and ME₇₅) except ME₁₀₀ concentration. The maximum number of earthworms (41.5) was observed in waste mixture ME₂₅ on 90^th day of experiment followed by (39.0) in ME₀, ME₅₀ (37.5), ME₇₅ (34) and (28.5) in ME₁₀₀ waste mixtures. The development of clitellum was found between 30^th to 45^th days of the experiment in all the waste mixtures of MPIS. Few earlier studies also observed the slow growth rate in mixtures with higher proportion of milk processing industry waste [1S. Suthar, "Vermistabilization of wastewater sludge from milk processing industry", Ecol. Eng., vol. 47, pp. 115-119.
[http://dx.doi.org/10.1016/j.ecoleng.2012.06.005] , 2S. Suthar, P.K. Mutiyar, and S. Singh, "Vermicomposting of milk processing industry sludge spiked with plant wastes", Bioresour. Technol., vol. 116, pp. 214-219.
[http://dx.doi.org/10.1016/j.biortech.2012.03.101] [PMID: 22609678] ]. No mortality of E. fetida was observed in any concentration, the reason could be probably the non toxicity of MPIS.

The number of cocoons also showed a significant difference (p≤0.05) in different proportions of MPIS (Fig. 2). The formation of cocoon was noticed on 45^th day of the experiment in all the waste mixtures. The maximum number of cocoons was observed in ME₂₅ (49.5) on 90^th day of the experiment. Cocoon production was relatively less in higher proportions of waste like ME₁₀₀ and ME₇₅ when compared with the lower proportion ME₅₀ and ME_25. Initially, cocoon formation rate was lower, and with time, it was enhanced. It is clear from the present study that cocoon formation in different waste proportions was directly related to the feedstock quality. The results of cocoon formation are corroborated by the findings of other researchers who have analyzed waste quality dependent cocoon formation patterns in earthworms during the process of vermicomposting [7S.A. Bhat, J. Singh, and A.P. Vig, "Recycling of sugar industrial wastes through earthworm technology’", Intr. Lett. Nat. Sci., vol. 55, pp. 35-43. c
[http://dx.doi.org/10.18052/www.scipress.com/ILNS.55.35] , 20M. Xing, JianYang, Y. Wang, J. Liu, and F. Yu, "A comparative study of synchronous treatment of sewage and sludge by two vermifiltrations using an epigeic earthworm Eisenia fetida", J. Hazard. Mater., vol. 185, no. 2-3, pp. 881-888.
[http://dx.doi.org/10.1016/j.jhazmat.2010.09.103] [PMID: 21041027] ].

The number of hatchlings was also significantly different (p≤0.05) in different proportions of MPIS (Fig. 3). The first hatchlings were observed on 60^th day of experiment in ME₀, ME₂₅, ME₅₀, ME₇₅ and ME₁₀₀. The maximum number of hatchlings were observed on 90^th day of experiment in ME₂₅ (37.5) followed by ME₀ (33.0), ME₅₀ (28.5), ME₇₅ and ME₁₀₀ (20.5). Similar results have been reported by Vig et al. [21A.P. Vig, J. Singh, S.H. Wani, and S. S. Dhaliwal, "Vermicomposting of tannery sludge mixed with cattle dung into valuable manure using earthworm Eisenia fetida (Savigny)", Bioresour. Technol., vol. 102, no. 17, pp. 7941-7945.
[http://dx.doi.org/10.1016/j.biortech.2011.05.056] [PMID: 21676611] ] during vermicomposting of tannery sludge mixed with cattle dung.

Fig. (1) Number of earthworms in different waste mixtures of milk processing industry sludge and cattle dung.

Fig. (2) Number of cocoons in different waste mixtures of milk processing industry sludge and cattle dung.

Fig. (3) Number of hatchlings in different waste mixtures of milk processing industry sludge and cattle dung.

The physicochemical parameters of different proportions of MPIS and CD with and without earthworms are given in Table 3. There was a significant reduction in pH of final vermicompost as compared to initial feed mixtures with earthworms. The maximum decrease in pH was in ME₂₅ (7.6%) waste mixture and minimum in ME₅₀ (6.2%) feed mixture. The percent decrease in pH was in order of ME₂₅ > ME₀ > ME₁₀₀ > ME₇₅ > ME₅₀. The reduction in pH of final vermicompost has also been confirmed by other authors [10S.A. Bhat, J. Singh, and A.P. Vig, "Potential utilization of bagasse as feed material for earthworm Eisenia fetida and production of vermicompost", Springerplus, vol. 4, p. 11.
[http://dx.doi.org/10.1186/s40064-014-0780-y] [PMID: 25625035] , 22V.K. Garg, Y.K. Yadav, A. Sheoran, S. Chand, and P. Kaushik, "Livestock excreta management through vermicomposting using an epigeic earthworm Eisenia foetida", Environmentalist, vol. 26, pp. 269-276.
[http://dx.doi.org/10.1007/s10669-006-8641-z] , 23S. Suthar, and S. Singh, "Feasibility of vermicomposting in biostabilization of sludge from a distillery industry", Sci. Total Environ., vol. 394, no. 2-3, pp. 237-243.
[http://dx.doi.org/10.1016/j.scitotenv.2008.02.005] [PMID: 18313726] ]. The pH decrease could be due to the production of metabolic compounds of aerobic digestions (CO₂, ammonia, NO₃^- and organic acids) during vermicomposting process [24D. L. Hernandez, M.P. Garcia-Guadilla, F. Torres, P. Chacon, and M.G. Paoletti, "Identification, characterization, and preliminary evaluation of Venezuelan Amazon production systems in Puerto Ayacucho Savanna- forest ecotone", Interciencia, vol. 22, pp. 307-314.]. Suthar et al. [2S. Suthar, P.K. Mutiyar, and S. Singh, "Vermicomposting of milk processing industry sludge spiked with plant wastes", Bioresour. Technol., vol. 116, pp. 214-219.
[http://dx.doi.org/10.1016/j.biortech.2012.03.101] [PMID: 22609678] ] also confirmed a significant reduction in pH during vermicomposting of milk processing plant sludge. Das et al. [25D. Das, P. Bhattacharyya, B.C. Ghosh, and P. Banika, "Bioconversion and biodynamics of Eisenia foetida in different organic wastes through microbially enriched vermiconversion technologies", Ecol. Eng., vol. 86, pp. 154-161.
[http://dx.doi.org/10.1016/j.ecoleng.2015.11.012] ] also observed that the alkaline pH of organic waste is shifted towards the neutral pH during vermiremediation of organic wastes. This might be due to the combined action of microbial metabolism and release of organic acids during vermistabilization. The pH reduction was again related to the quality of the initial sludge mixture as it was approaching towards a neutral pH from an alkaline state.

Electrical Conductivity (EC) declined significantly (<0.05) over initial in the end product of vermicompost. The maximum decrease in EC was in also ME₂₅ (37.2%) waste mixture and minimum 24.6% in ME₇₅ feed mixture. The percent decrease in EC was in order of ME₂₅ > ME₀> ME₁₀₀> ME₅₀> ME₇₅. Waste mixtures without earthworms also showed some decline in the EC, the maximum decrease in EC was in MW₂₅ (8.1%) and minimum in MW₁₀₀ (1.9%). Singh et al. [26J. Singh, A. Kaur, A.P. Vig, and P.J. Rup, "Role of Eisenia fetida in rapid recycling of nutrients from bio sludge of beverage industry", Ecotoxicol. Environ. Saf., vol. 73, no. 3, pp. 430-435.
[http://dx.doi.org/10.1016/j.ecoenv.2009.08.019] [PMID: 19945748] ] also observed that the reduction in EC may be due to the production of soluble metabolites during vermicomposting. Varma et al. [27V.S. Varma, J. Yadav, S. Das, and A.S. Kalamdhad, "Potential of waste carbide sludge addition on earthworm growth and organic matter degradation during vermicomposting of agricultural wastes", Ecol. Eng., vol. 83, pp. 90-95.
[http://dx.doi.org/10.1016/j.ecoleng.2015.05.050] ] also reported reduction in the Electrical Conductivity (EC) during vermiconversion of waste carbide sludge and agricultural waste. The EC reduction may be due to the addition of waste carbide sludge to agricultural wastes and uptake of the minerals by earthworms. Reduction in ionic concentration will produce better compost at the end.

There was a significant decline (p < 0.05) in the Total Organic Carbon (TOC) of the end products of vermicomposting. Decline in TOC was maximum in ME₂₅ (37.9%) and minimum in ME₁₀₀ (20.1%) feed mixtures. The percentage of decrease in TOC was in order of ME₂₅ > FE₀> ME₅₀> ME₇₅> ME₁₀₀. Waste mixtures without earthworms showed slight decline in TOC. Decline in TOC was maximum in MW₅₀ (16.2%) and minimum in MW₁₀₀ (8.9%) feed mixture. TOC loss was more in which earthworm mixtures as compared to the end products of without earthworms. Suthar [1S. Suthar, "Vermistabilization of wastewater sludge from milk processing industry", Ecol. Eng., vol. 47, pp. 115-119.
[http://dx.doi.org/10.1016/j.ecoleng.2012.06.005] ] also observed a significant decrease in TOC due to combined action of earthworms and microorganisms. Similar observations have been reported by Bhat et al. [7S.A. Bhat, J. Singh, and A.P. Vig, "Recycling of sugar industrial wastes through earthworm technology’", Intr. Lett. Nat. Sci., vol. 55, pp. 35-43. c
[http://dx.doi.org/10.18052/www.scipress.com/ILNS.55.35] , 10S.A. Bhat, J. Singh, and A.P. Vig, "Potential utilization of bagasse as feed material for earthworm Eisenia fetida and production of vermicompost", Springerplus, vol. 4, p. 11.
[http://dx.doi.org/10.1186/s40064-014-0780-y] [PMID: 25625035] ] during vermicomposting of sugar mill waste. Khwairakpam and Bhargava [28M. Khwairakpam, and R. Bhargava, "Vermitechnology for sewage sludge recycling", J. Hazard. Mater., vol. 161, no. 2-3, pp. 948-954.
[http://dx.doi.org/10.1016/j.jhazmat.2008.04.088] [PMID: 18515003] ] observed that the cattle dung contains various fungal stains and other microbes like bacteria, protozoa, nematodes, fungi, actinomycetes, which play an important role in organic matter decomposition by providing extra-cellular enzymes in vermireactors. The organic carbon reduction in vermicomposting is the result of metabolic process in feed mixtures as well as assimilation of carbohydrates and other polysaccharides from the feed mixtures by earthworms. This reduction will also maintain a good C/N ratio for the end product to be used as manure.

Total Kjeldhal Nitrogen (TKN) content increased significantly with vermicomposting time in all waste mixtures in the presence of earthworms. The maximum increase in TKN was in ME₀ (46.0%) and minimum in ME₁₀₀ (23.2%). The percentage of increase in TKN was in the order of ME₀> ME₂₅> ME₅₀> ME₇₅> ME₁₀₀. Waste mixtures without earthworms also showed slight increased in TKN but not like with earthworms. The maximum increase in TKN was in MW₁₀₀ (10.8%) and minimum in MW₇₅ (7.6%). Many researchers have revealed that the earthworms add nitrogen to the final substrates in the form of mucus, nitrogenous excretory substances, growth stimulating hormones and enzymes [1S. Suthar, "Vermistabilization of wastewater sludge from milk processing industry", Ecol. Eng., vol. 47, pp. 115-119.
[http://dx.doi.org/10.1016/j.ecoleng.2012.06.005] , 29G. Tripathi, and P. Bhardwaj, "Comparative studies on biomass production, life cycles and composting efficiency of Eisenia fetida (Savigny) and Lampito mauritii (Kinberg)", Bioresour. Technol., vol. 92, no. 3, pp. 275-283.
[http://dx.doi.org/10.1016/j.biortech.2003.09.005] [PMID: 14766161] -31S. Suthar, "Recycling of agro-industrial sludge through vermitechnology", Ecol. Eng., vol. 3, pp. 1028-1036.
[http://dx.doi.org/10.1016/j.ecoleng.2010.04.015] ]. Loss in TOC might be responsible for the addition of TKN. The content of nitrogen rich substances in waste mixtures is always important for overall nitrogen enhancement of the vemicompost.

The C:N ratio decreased significantly (p < 0.05) with time in waste mixtures in the presence of earthworms. Decline in C:N ratio was maximum in ME₂₅ (57.4%) feed mixture. The percentage of decrease in C:N ratio was in order of ME₂₅ > ME₀> ME₅₀> ME₇₅> ME₁₀₀. However, waste mixtures without earthworms showed a little decrease in C:N ratio. The maximum decrease in C:N ratio was in MW₅₀ (24.3%) and minimum in MW₇₅ (16.10). Senesi et al. [32N. Senesi, "Composted materials as organic fertilizers", Sci. Total Environ., vol. 81, pp. 521-524.
[http://dx.doi.org/10.1016/0048-9697(89)90161-7] ] observed that a decline of C:N ratio to less than 20 indicates an advanced degree of organic matter stabilization and maturation. Change in C:N ratio is understandable and proportional to changes in TOC and TKN. In the present experiment, the decrease in C/N ratio in the feed mixtures with earthworms is brought about by a simultaneous decline in TOC and an increase in the TKN content. Cabrera et al. [33M.L. Cabrera, D.E. Kissel, and M.F. Vigil, "Nitrogen mineralization from organic residues: research opportunities", J. Environ. Qual., vol. 34, no. 1, pp. 75-79.
[http://dx.doi.org/10.2134/jeq2005.0075] [PMID: 15647536] ] also observed that vermicomposting resulted in faster reduction of C/N ratio as compared to traditional composting.

Total Available Phosphate (TAP) increased significantly p <0.05) with time in all the waste mixtures in the presence of earthworms. The maximum increase in TAP was recorded in ME₂₅ (47.1%) feed mixture and minimum in ME₅₀ (39.0%) feed mixture with earthworms. The percentage of increase in TAP was in order of ME₂₅> ME₁₀₀> ME₇₅> ME₀> ME₅₀. On the other hand, a little increase in TAP was also observed in waste mixtures without earthworms. The maximum increased in TAP was in MW₂₅ (17.6%) and minimum in MW₀ (11.8%) feed mixtures. Pramanik et al. [34P. Pramanik, "G.K, Ghosh, P.K. Ghosal, and P. Banik, “Changes in organic –C, N, P and K and enzyme activities in vermicompost of biodegradable organic wastes under limiting and microbial inoculants", Bioresour. Technol., vol. 98, pp. 2485-2494.
[http://dx.doi.org/10.1016/j.biortech.2006.09.017] [PMID: 17081750] ] observed that the acid production during organic matter decomposition by the micro-organisms is majorly responsible for solubilization of insoluble phosphorus, which results in TAP increase in feed mixtures with earthworms.

Total Potassium (TK) decreased significantly from initial in different waste mixtures of earthworms with time. Maximum percentage decrease in TK content of vermicompost with earthworms was in ME₀ (55.8%) and minimum in ME₇₅ (26.6%). The percentage of decrease in TK was in the order of ME₀> ME₂₅> ME₅₀> ME₁₀₀> ME_75. Slight decrease in TK was also reported in waste mixtures without earthworms. Maximum percentage decrease in TK content was in MW₀ (28.82%) and minimum in MW₁₀₀ (10.95%). Many researchers have also observed a decrease in TK after vermicomposting [7S.A. Bhat, J. Singh, and A.P. Vig, "Recycling of sugar industrial wastes through earthworm technology’", Intr. Lett. Nat. Sci., vol. 55, pp. 35-43. c
[http://dx.doi.org/10.18052/www.scipress.com/ILNS.55.35] , 35S.A. Bhat, J. Singh, and A.P. Vig, "Vermiremediation of dyeing sludge from textile mill with the help of exotic earthworm Eisenia fetida Savigny", Environ. Sci. Pollut. Res. Int., vol. 20, no. 9, pp. 5975-5982.
[http://dx.doi.org/10.1007/s11356-013-1612-2] [PMID: 23508537] , 36P. Sangwan, C.P. Kaushik, and V.K. Garg, "Feasibility of utilization of horse dung spiked filter cake in vermicomposters using exotic earthworm Eisenia foetida", Bioresour. Technol., vol. 99, no. 7, pp. 2442-2448.
[http://dx.doi.org/10.1016/j.biortech.2007.04.061] [PMID: 17574845] ]. TK concentration in the feed mixtures of MPIS with earthworms had decreased significantly as compared to without earthworm mixtures by the end of the vermicomposting, and this decrease may be due to the use of potassium by worms during their metabolic activity.

Total Sodium (TNa) decreased significantly from initial in different waste mixtures with earthworms. Maximum decline in TNa was in ME₀ (53.0%) and minimum in ME₇₅ (31.3%) waste mixture. The percentage of decrease in TNa was in order of ME₀> ME₂₅ > ME₅₀> ME₇₅> ME₁₀₀, i.e., more decrease in less waste concentration. The feed mixtures without earthworms also showed some decline in TNa. The maximum declines in TNa was in MW₀ (30.0%) waste mixture and minimum (14.5%) in MW₁₀₀ mixture, but the decrease was comparatively less than vermicomposting. Reduction in sodium concentration helps in the reduction of SAR (Sodium Adsorption Ratio) [37J.P. Mitchell, C. Shennan, M.J. Singer, D.W. Peters, R.O. Miller, T. Prichard, S.R. Grattan, J.D. Rhoades, D.M. May, and D.S. Munk, "Impacts of gypsum and winter cover crops on soil physical properties and crop productivity when irrigated with saline water", Agric. Water Manage., vol. 45, pp. 55-71.
[http://dx.doi.org/10.1016/S0378-3774(99)00070-0] ], thus affecting the efficiency of compost.

It is important to know the concentration of metals in the end product before being applied to soil due to their high risk and toxicity [38M.K. Jamali, T.G. Kazi, M.B. Arain, H.I. Afridi, N. Jalbani, G.A. Kandhro, A.Q. Shah, and J.A. Baig, "Heavy metal accumulation in different varieties of wheat (Triticum aestivum.) grown in soil amended with domestic sewage sludge", J. Hazard. Mater., vol. 164, no. 2-3, pp. 1386-1391.
[http://dx.doi.org/10.1016/j.jhazmat.2008.09.056] [PMID: 18977590] ]. The heavy metals Copper (Cu), Lead (Pb), Manganese (Mn) and Chromium (Cr) decreased significantly over initial in different waste mixtures with earthworms (Table 4). Maximum decrease in Cu was in ME₂₅ (44.6%) and minimum in ME₀ (32.7%). The percentage of decrease in Cu was in order of ME₂₅>ME₅₀>ME₇₅ME₁₀₀>ME₀. A small fraction of decrease in Cu was also observed in feed mixtures without earthworms. Maximum decrease in Cu in feed mixture was in MW₅₀ (25.5%) and minimum (12.70%) in MW₁₀₀ feed mixture. Pb content was also decreased significantly with maximum decrease in ME₅₀ (42.9%) and minimum in ME₁₀₀ (32.6%) feed mixtures with earthworms. The percentage of decrease in Pb was in order of ME₅₀>ME₂₅>ME₀>E₇₅>ME₁₀₀. Feed mixtures without earthworms also showed some decrease in Pb content. The maximum decrease in Pb was observed in ME₅₀ (25.3%) and minimum (12.8%) in ME₁₀₀. Mn decreased significantly from initial in different feed mixtures with earthworms (p<0.05). Maximum and minimum decrease in Mn was observed in ME₀ and ME₁₀₀, (36.3%) and (25.6%), respectively. The percentage of decrease in the Mn was in the order of ME₀>ME₂₅>ME₅₀>ME₇₅>ME₁₀₀. A slight decrease in Mn content was also observed in waste mixtures without earthworms. The maximum decrease in the Mn was observed in waste mixture MW₇₅ (14.17%) and minimum in feed mixture MW₁₀₀ (12.49%). Cr decreased significantly from initial in different feed mixtures with earthworms (p<0.05). Maximum decrease in Cr was in ME₂₅ (40.6%) and minimum in ME₅₀ (30.9%) waste mixture. The percentage decrease in Cr was in order of ME₂₅>ME₀>ME₇₅>ME₇₅>ME₅₀. A slight fraction of decrease in Cr was also observed in feed mixtures without earthworms. Maximum decrease in Cr was in MW₂₅ (25.3%) and minimum (17.64%) in MW₁₀₀ waste mixture. Ghyasvand et al. [39S. Ghyasvand, H. A. Alikhani, M. M. Ardalan, G. R. Savaghebi, and S. Hatami, "Effect of pre-thermocomposting on decrease of cadmium and lead pollution in vermicomposting of municipal solid waste by Eisenia fetida", Am.-Eurasian J. Agric. Environ. Sci., vol. 4, pp. 537-540.] also confirmed that the availability of heavy metals like Pb and Cd decreases due to bioaccumulation of metals by earthworms and formation of organocomplex during vermicomposting. Singh and Kalmdhad [40J. Singh, and A.S. Kalamdhad, "Reduction of bioavailability and leachability of heavy metals during vermicomposting of water hyacinth", Environ. Sci. Pollut. Res. Int., vol. 20, no. 12, pp. 8974-8985.
[http://dx.doi.org/10.1007/s11356-013-1848-x] [PMID: 23757026] ] observed reduction in water soluable heavy metals (Zn, Mn, Cu, Fe and Cr) during vermicomosting of wastes and suggested that the formation of organometallic complex compounds and bioaccumulation in earthworms reduced the final content of metals in vermicompost. Singh et al. [41"S, Singh, S.A. Bhat, J. Singh, R. Kaur, and A,P, Vig, “Vermistabilization of thermal power plant fly ash using Eisenia fetida", J. Indust. Poll. Control, vol. 32, pp. 554-561.] also observed a significant reduction in heavy metals (Cu, Pb, Mn and Cr) during the vermicomposting of thermal power plant fly ash. The present study observed that earthworms significantly reduced the bioavailability of heavy metals in the feed mixtures of MPIS as compared to feed mixtures without earthworms.

Table 3
Initial and final nutrient content (mean ± S.E.) and percent change over initial nutrient content of different proportions of milk processing industry sludge and cattle dung with and without earthworms.

Table 4
Initial and final heavy metal content (mean ± S.E.) and percent change over initial heavy metal content of different proportions of milk processing industry sludge and cattle dung with and without earthworms.