Alterações nos atributos físicos do solo pela aplicação de diferentes concentrações de esgoto sintético

Abstract

The growing demand for water required by population growth and socioeconomic development impacts the water sources around the world, amplifying the conflicts over water resources. Under those circumstances, the use of wastewater for the most different purposes has been becoming a key element in the management of water resources, helping to mitigate the harmful effects of local water deficits. Agriculture is one of the areas with the greatest potential for wastewater reuse, due to the presence of organic matter and nutrients in the effluents. Thus, the objective of this work was to assess the possible effects on the physical attributes of the superficial layer of a Oxisol after applications of synthetic domestic effluent. The experiment was conducted in a greenhouse, consisting of soil columns, segmented into rings of different dimensions, in which both treated water (TW) and synthetic effluent (SE) were applied in different proportions for a continuous 4-month period. A randomized block design was adopted, with six treatments and three replications, the treatments being: 100% WT (T0), a mixture of 20% SE and 80% TW (T1), 40% SE and 60% of TW (T2), 60% of SE and 40% of TW (T3), 80% of SE and 20% of TW (T4) and 100% of SE (T5). In the SE, the following items were checked: pH, electrical conductivity (EC), total solids (TS), suspended solids (SS), dissolved solids (DS), chemical oxygen demand (COD), oils and greases (O&G), total nitrogen Kjeldahl (NTK), Total phosphorus (P), Calcium (Ca), Magnesium (Mg) and Sodium (Na) and, in the WT, pH, EC, Ca, Mg and Na were evaluated. In the soil, before and after the application of the effluent, in the layers of from 0 to 2 cm, 2 to 5 cm, 5 to 10 cm, 10 to 15 cm and 15 to 20 cm, the specific masses of soil and particles, total porosity, macro and microporosity, water-dispersed clay (WDC) and the water retention curve were evaluated. The soil infiltration capacity curves were also evaluated, by adjusting the Kostiakov, Kostiakov-Lewis and Horton models and micrographs of the soil were obtained in order to evaluate the formation of a sealing crust. For the different attributes of the soil, the influences of the treatments was analyzed by the analysis of variance and the means were analyzed by the Tukey test at 5% of probability. An increase in the specific gravity of the soil was found with a decrease in porosity with the application of the raw effluent (T5), mainly in the most superficial layer of the soil column. The infiltration capacity of the soil was strongly impacted by the application of the effluent, the hydraulic conductivity of the saturated soil (Ks) ranged from 20.77 cm h-1 in the soil before irrigation to 6.03 cm h-1 in the soil with application of treatment T5, however in mixtures with up to 80% of synthetic effluent, the Ks was greater than 20.45 cm h-1. The model that best suited the experimental curve of the infiltration capacity was the Kostiakov-Lewis model and by means of the micrographs of the soil, it was possible to observe the formation of a crust in the soils treated with raw effluent which was responsible for the decrease of infiltration in this treatment. Therefore, the application of raw effluent in the soil presented deleterious effects, a pretreatment of wastewater being suggested in order to decrease the concentration of suspended solids before its application in the soil.