Brasilia's urban growth has caused the increase of domestic sewage sludge, production generating a large volume of biosolid - a final product of sludge treatment - deposited at the Companhia de Saneamento de Brasilia (CAESB) sewage treatment plants. Although there is still a lack of technical data on health, environmental safety and economic viability, it has been used as a soil amendment and fertilizer by farmers in the neighbouring areas. The biosolid produced at one of the sewage treatment plants of CAESB, with a water content of 90 dag kg-1 (10 dag kg-1 dry matter), was tested as a fertilizer for corn production in an Oxisol at rates of 54, 108 and 216 t ha-1. Results showed that, after three years, a sole application of 54 t ha-1 of biosolid maintained an average corn yield of 4,700 kg ha-1. The regression model, adjusted by a quadratic polynomial equation, Y = 2349.3** + 41.579**x - 0.1097**x², R² = 0.9824**, where Y is the corn grain productivity (kg ha-1) and x, the rate of applied biosolid (t ha-1), showed that maximum yield would be obtained at the rate of 189.51 t ha-1. Using the phosphorus (P2O5) content as a reference to plant requirement, the biosolid was more efficient than chemical fertilization with triple superphosphate, giving an average fertilizer value of 125 % during the three year-period of cultivation. At the rate of 54 t ha-1, the biosolid added to the soil 240 kg of P2O5, 320 kg of N, 160 kg of Ca and 13 kg of K2O. Heavy metal (Cd, Pb e Hg) concentration in this biosolid is much lower than the critical concentration limit established for its use, and the application of 54 t ha-1 of wet biosolid adds very small amounts of those metals, which suggests that soil contamination by those pollutants will not be a problem unless industrial residues contaminate the urban sludge.
urban residues; sewage sludge; biosolid; heavy metals