Alteração dos atributos do solo e da produtividade da grama esmeralda (Zoysia japonica) fertirrigada com efluente da ETE-UFLA submetido a diferentes níveis de tratamentos

Abstract

Although there is great water availability in Brazil, scarcity and supply rationing have affected the country, highlighting the need for better management of national water resources. Irrigation is the activity of higher consumption of potable water and the alternative of combining irrigation with treatment/final disposal of wastewater is attractive, as it promotes the reuse of water and reduces environmental impacts. The objective of the present study was to evaluate the productivity of the emerald grass (Zoysia japonica), cultivated in fertirrigation with the wastewater from the Wastewater Treatment Plant of the Federal University of Lavras (UFLA-WWTP), submitted to different levels of treatment, and the change in physical and chemical characteristics of the soil. The experiment was conducted in the WWTP area, in Lavras, MG, in which a randomized block design was performed(1m2 each), with five treatments – T0: control (treated water); T1: effluent after preliminary treatment; T2: effluent after UASB reactor; T3: effluent after FBAS; T4: effluent after chlorination – and three replications. Fertigation slides were determined by the water balance method. Meteorological data were obtained from the Conventional Meteorological Station of the National Institute of Meteorology (INMET – UFLA Campus). In effluent samples – P1: after preliminary treatment; P2: after anaerobic secondary treatment; P3: after aerobic secondary treatment; P4: after tertiary treatment – hydrogen ionic potential (pH), electrical conductivity (EC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids (ST), total suspended solids (TST), phosphorus (P), Kjeldahl total nitrogen (NTK), total coliforms (TC) and thermotolerant total coliforms (CTer) were evaluated. In the 0-20cm layer of the soil, were evaluated the hydrogenation potential (pH), organic matter (OM), nitrogen, phosphorus, potassium, calcium, magnesium and sodium levels, the effective and potential cation exchange capacity (CTCef e CTCpot) and potential soil acidity, before the beginning of the experiment, for chemical characterization, and after 140 days running. Grass cuttings were carried out at 75 and 140 days after the beginning of the experiment, in which dry matter production was evaluated. The decay of coliforms in the grass was evaluated after the application of the effluents frompreliminary treatment, chlorination system and UV tank (treated effluent). Data were submitted to Kruskal-Wallis test for groupings, at a 5% significance level. Fertirrigation with effluent from different treatment stages did not resulted in significant differences in soil attributes or in grass yield, which is justified by the proximity and slope of the blocks, with one influencing the other. Thermotolerant coliformswere detected (at the detection limit of the method) on days 0 and 7 and no longer on day 14, afterfertirrigation ceased. It was concluded that raw sanitary sewage can be safely used for fertirrigation, with the interruption of application in 14 days before grass cutting or using the area, combining nutrient supply and increased productivity, with lower health risk. It is recommended to perform the experiment in a flat area or potted, in order to better control the conditions and to observe the effect of the treatments.