The agronomic use of biosolid is considered an adequate alternative to its disposal and, although a technical knowledge about its fertilizing properties is already available, information on its qualitative, economical and practical aspects for its use on the field is also needed. The biosolid produced by the "Companhia de Saneamento de Brasília" (CAESB) showed an appreciable variability in nutrient concentration among each monthly sampling from August, 1995 to July, 1996 and among the sludge treatment plants (ETEs) where the biosolid is generated. The variability, which is higher for macronutrients (Ca, N, P, K, Mg and S) and lower for micronutrients and heavy metals, requires a dosage adjustment at each application. The biosolid is available to users free of charge but there is a transportation fee, which, due to the biosolid's high water content, is viable only up to certain distance; within the conditions of this study, the maximum distance was 122 kilometers. By simulation, a reduction of the water content from 90 dag kg-1 to 70 dag kg-1 increased the distance of transportation from 112 to 365 kilometers, expanding the potential area of utilization. The field application of 54 t ha-1 of biosolid (90 dag kg-1 of water) showed the highest benefit/cost ratio (R$ 1.12 of return for each R$ 1.00 invested) when compared to the other biosolid and mineral fertilizer applications (all of them with returns below R$ 1.00 for each R$ 1.00 invested; the highest dose of biosolid showed a negative return). Besides its best comparative performance, which can qualify it as a preliminary dose for recommendation, the application of 54 t ha-1 of biosolid (90 dag kg-1 of water) requires transportation and manipulation of a large volume of material, which can be a limiting factor to its use.
sewage sludge; biosolid; nutrients; transportation; economic aspects