Mobility and distribution of whey solutions in soil columns

Abstract

In Brazil’s food industry, dairy production is one of the most important sectors, whose most relevant byproduct is whey. Due to the difficulties of reuse and environmental impacts caused when discarded as effluent in water bodies, an alternative for its final destination would be the application of this residue in the soil. The purpose of this study was to determine chemical changes and mobility and distribution of solutes in the soil after applications of whey rates, as well as to analyze the leachate collected after each application. The test was carried out in a laboratory, in PVC columns filled with soil. The treatments consisted of 2 x 2 samples of a typical dystrophic Red-Yellow Oxisol   (Oxisol) and a typical dystrophic fluvic Inceptisol (Inceptisol), sampled in the layers 0- 20 and 20-40 cm. Each experimental unit consisted of 11 PVC rings (diameter of 6.6 cm, height of 7 cm). The columns were arranged in a randomized complete block design with five replications. Four whey rates were applied, corresponding to a soil pore volume of 0.2, at intervals of six days. The leachate was collected 24 and 120 hours after each application to measure pH, electrical conductivity (EC), chemical oxygen demand (COD), contents of total N, N-NH₄⁺, N-NO₃^-, Na, K, Ca, and Mg. Six days after the last whey application, the columns were opened and the soil of each ring was analyzed for pH, EC, total N, N-NH₄⁺, N-NO₃^-, Na, K, Ca, and Mg. The high electrolyte concentrations of whey resulted in a general increase in soil EC. The increase of N-NH₄⁺ and N-NO₃^- in the soil was high due to mineralization. High concentrations of K, Na and Ca caused displacement of Mg from the exchange complex. It was concluded that from an environmental standpoint, whey soil application is a viable alternative, given that problems of salinization and leaching of undesirable elements are avoided by an adequate management.