Aplicação de efluente de estação de tratamento de esgoto em solo cultivado com grama Esmeralda (Zoysia japonica)

Abstract

The population increase, associated with socioeconomic development, established new levels of water demand and use, increasing the pressure on water resources. Whenever quality water required for a particular use becomes a scarce resource, alternatives to supplementation or reduction of consumption are sought in order to restore a balance between supply and demand. In these circumstances, the use of treated wastewater can help mitigate the damaging effects of local water deficits. The objective of the prese nt work was to evaluate the effect of different rates of effluent from the Sewage Treatment Plant of the Federal University of Lavras (ETE-UFLA) on soil chemical characteristics, productivity and chemical composition of Zoysia japonica, as well as to evaluate the potential use of the effluent in the irrigation of areas cultivated with Zoysia japonica. The experiment was conducted in a grassy area located next to ETE-UFLA, in Lavras/MG. In the experimental area, 20 plots of 1.0 m 2 were delimited spaced 1.0 m apart. The effluent used came from ETE-UFLA, after secondary treatment. The application of the effluent began on 07/18/2016, ending on 11/18/2016. The applied slides were determined by the water balance method, taking into account the evapotranspiration occurred in the intervals between the irrigations. From the values of the slides applied and the average BOD of the effluent, the effluent application rates were calculated, corresponding to 0; 0.131; 0.262; 0.393 and 0.524 kg ha -1 day -1 BOD. A randomized complete block design was used, with five treatments and four replications. In the effluent, pH, electrical conductivity (EC), turbidity, total solids, suspended solids, biochemical Oxygen demand (BOD), chemical Oxygen demand (COD), total Kjeldahl Nitrogen (TKN), total Phosphorus (P), total coliforms, thermotolerant coliforms, Calcium (Ca), Magnesium (Mg), Potassium (K) and Sodium (Na). In the soil, before and after the application of the effluent, in the layers of 0 to 0.20 m and 0.20 to 0.40 m, pH, EC, organic matter (MO), NTK, P, Ca, Mg, K and Na. On the grass, the dry matter yield and l eaf contents of N, P, K, Ca, Mg and Na were evaluated. The results were submitted to statistical analysis, using the F test, and the means were compared by the Tuke y test, both at 5% probability. The effluent showed to contain high concentration of pathogenic microorganisms, evidencing the need for polishing before its use. The application of the effluent provided significant changes in the pH, K, Ca+Mg, and Na value s of the soil, as well as increased dry matter yield and N, P, K and Na concentrations. Rates of up to 0.524 kg ha -1 day -1 BOD of the ETE-UFLA effluent can be applied to areas cultivated with Zoysia japonica. It is recommended that the effluent application be evaluated by monitoring periods higher than the one carried out in this study, since it is important to observe the climatic variations, the soil conditions and the effect of the effluent application in the long term.