Feasibility of vermicomposting in biostabilization of sludge from a distillery industry

The feasibility of vermicomposting technology to stabilize the distillery industry sludge mixed with a bulking agent (cow dung) in different proportions viz. 20% (T1), 40% (T2), 60% (T3) and 80% (T4), was tested using composting earthworm Perionyx excavatus for 90 days. The vermitreated sludge was evaluated for different physico-chemical parameters and all vermibeds expressed a significant decrease in pH (10.5-19.5%) organic C contents (12.8-27.2%), and an increase in total N (128.8-151.9%), available P (19.5-78.3%) as well as exchangeable K (95.4-182.5%), Ca (45.9-115.6%), and Mg contents (13.2-58.6%). Data suggested that inoculated earthworms could maximize the decomposition and mineralization rate, if sludge is used with appropriate bulking material for earthworm feed. Vermicomposting also caused significant reduction in total concentration of metals: Zn (15.1-39.6%), Fe (5.2-29.8%), Mn (2.6-36.5%) and Cu (8.6-39.6%) in sludge. Bioconcentration factors (BCFs) for metals in different treatments were also calculated and the greater values of BCFs indicate the capability of earthworms to accumulate a considerable amount of metals in their tissues from substrate. The reproduction biology of P. excavatus in different treatments was also monitoring during experimentation and they showed the maximum rate of biomass gain, growth (mg weight worm(-1) week(-1)) and cocoon production rate in T2, while least values of these parameters were in T4 treatment. The feasibility of earthworms to mitigate the metal toxicity and to enhance the nutrient profile in sludge might be useful in sustainable land restoration practices at low-input basis.