Vermicomposting of tannery sludge mixed with cattle dung into valuable manure using earthworm Eisenia fetida (Savigny)

The present study revealed the role of earthworm in converting tannery sludge into a valuable product. Tannery sludge was toxic to earthworm, therefore it was mixed with cattle dung in different proportions viz. 0:100 (T0), 10:90 (T10), 25:75 (T25), 50:50 (T50) and 75:25 (T75) on dry weight basis. The minimum mortality and highest population buildup of worms was in T0 mixture. Nitrogen, sodium, phosphorus and pH increased from initial in the range of 7.3–66.6%, 16.90–70.58%, 8.57–44.8% and 2.8–13.65%, respectively. On the other hand potassium, organic carbon and electrical conductivity decreased in the range of 4.34–28.5%, 7.54–22.35% and 32.35–53.12%, respectively. C:N ratio decreased from 20.53% to 47.36% in the final products. Transition metals increased significantly from the initial value and within the permissible limit. The result indicated that vermicomposting with Eisenia fetida is better for changing this sludge into nutrient rich manure in a short period of time.