Vermicomposting of different types of tanning sludge (liming and primary) mixed with cattle dung

Abstract The complexity of the generation of solid residues is a present issue, because of the polluting potential of many materials produced. Therefore, the objective of this study is to assess vermicomposting of different types of tanning sludge (liming and primary), aiming at reuse in agriculture. Thus, the types of tanning sludge known as liming and primary (tannery industry from, Pires do Rio, Goias, Brazil) were mixed to cattle dung in different proportions (10, 20, 30, 40 and 50%, dry basis) and then earthworms of the species Eisenia foetida were introduced. After 120 days, the composts were chemically analyzed. Our results demonstrate that the vermicomposting of different types mixtures of the of tannery sludge with cattle dung (10–50% concentrations) is capable of increasing concentrations of N, K, Ca, Mg and Na. Primary sludge mixtures with cattle dung, at higher concentrations (20–50%) reduce the concentration of the Cu, while liming sludge mixtures with cattle dung (20–50% concentrations) increase the concentration of the element. On the other hand, mixtures containing primary sludge reduces the concentration of Fe and increase the concentration of Zn. Finally, independent of the sludge mixed and the concentrations of the cattle dung used in this study, these substrates reduce the TOC concentration and C/N, which are one of the most traditional indicators of the maturation of a compost.