The aim of this work was to evaluate the effect of different mineral enrichments during composting of biodiesel production residues on chemical characteristics of the end product. The following materials were used: sugar cane bagasse, ashes of sugar cane bagasse, poultry manure, filter cake and castor oil cake. These materials were mixed and enriched with mineral nutrients NPK, serpentinite and micaxist powdered rocks and gneiss powdered rocks, to obtain eight different composts. At 0, 30, 90 and 120 days after starting composting, these materials were sampled to measure pH, electrical conductivity, C, N, ashes, and, at the last sampling, CEC and total nutrients. Only the compost enriched with NPK (with N as ammonium sulphate) comply with the legislation pertinent to compost, while the composts that received filter cake and castor oil cake, with and without, mineral addition presented pH below the accepted limit and had C and N concentrations below the minimum established in the Brazilian legislation. The addition of serpentinite and micaxist powdered rocks contributed to raise the CEC of composts.
organic residue; compost; CEC; Brazilian legislation
