The present study demonstrates the vermistabilization of paper mill wastewater sludge (PMS) spiked with cow dung (CD) employing indigenous epigeic earthworm Perionyx excavatus Perrier. A total of six treatments were prepared along with a positive control (PC) and negative control (NC). Twenty earthworms were released into each treatment including PC and NC without earthworms. The different proportions viz., T1 (CD - 100%), T2 (PMS:CD - 1:3), T3 (PMS:CD - 1:2), T4 (PMS:CD - 1:1), T5 (PMS:CD - 3:1), T6 (PMS:CD - 2:1), PC (PMS - 100%) and NC (PMS - 100%) and changes in chemical parameters and microbial properties were recorded during the course of 60 days. Vermistabilization caused a significant decrease in the level of heavy metals: Cd (2.9-27.8%), Cu (0.22-42.3%), Pb (1.3-56.3%) and Cr (0.8-46.2%). The bioconcentration factor (BCFs) was also calculated and great amount of heavy metals accumulated in their body (mg kg(-1)) that ranged from 0.31 +/- 0.003-0.45 +/- 0.007 for Cd, 0.12 +/- 0.005-0.24 +/- 0.003 for Cu, 0.15 +/- 0.005-0.31 +/- 0.006 for Pb and 0.29 +/- 0.007-0.56 +/- 0.001 mg kg(-1) for Cr, accumulation of heavy metals are in the order: Cr > Cd > Pb > Cu. The physicochemical parameters of earthworm treated substrate such as electrical conductivity, total nitrogen, total phosphorus and total potassium were significantly increased; whereas, pH, total organic carbon, C:N ratio (carbon: nitrogen) and C:P ratio (carbon: phosphorus) were reduced after 60 days of vermistabilization. The vermistabilized materials also had a higher population of bacteria (98.90 +/- 0.30 CFU x 10(6) g(-1)), fungi (43.75 +/- 0.55 CFU x 10(3) g(-1)) and actinomycetes (67.65 +/- 0.45 CFU x 10(5) g(-1)) than initial mixtures. Moreover, several histopathological changes were observed in earthworm tissues viz., disintegration of cells, irregular surface of epidermis, cellular debris, irregular cellular compartmentation, and oval-shaped nucleus. Higher level of histopathological abnormalities was recorded in PC (PMS-100%) while none were detected in lower concentrations of PMS. Furthermore, the study concludes that the paper mill sludge in a mixture of cow dung (1:1 ratio) can be a useful proposition for utilizing this hazardous waste through the adoption of vermitechnology.
