Valorização agronómica de resíduos da produção de pasta de papel

Abstract

Composting the organic waste from pulp production and its land application is an option to get an agronomic valorisation of these by products. This work aims to quantify the effects of a composted pulp waste (wood fiber and sludges from primary and secondary treatment of wastes) application to the soil. A pot trial was conducted, at controlled conditions, on a LPli soil, and with lettuce (Lactuca sativa L.) as test plant. It was applied five experimental treatments, a control and four application rates (equivalent to 25, 50, 75 and 100 t ha-1).The application of this product to the soil led to increases in lettuce yield. No phytotoxic effects were observed, even when given the highest dose (equivalent to 100 t ha-1). The composted pulp waste acted both as an organic fertilizer and a liming material, giving rise to significant responses in relation to the soil organic matter and soil pH, directly proportional to the dose applied. The product under study also contributed to the increased availability of nutrients, such as nitrogen and phosphorus, and showed to be a source of calcium for the plant. The application of the compost to the soil, even at very high doses did not result in significant increases (p> 0.05) in the levels of “total” chromium, nickel and lead in the soil. Concerning the other heavy metals analyzed (Cd, Cu, Zn and Hg) only slight changes were observed, never exceeding the permissible values in soils where it wants to apply this type of product.