Avaliação ambiental da produção de briquetes de capim-elefante-roxo irrigado com efluente da ETE de Pendências- RN.

Abstract

The cultivation of purple elephant grass irrigated with treated wastewater can make a major contribution to minimize the problem such as deforestation in semi-arid regions and discharge of sewage in soil and rivers. Besides, due to its high yield potential and calorific power, it can be used as biomass for energy in the forms of briquettes. This work aimed to make an environmental assessment of briquettes production with purple elephant grass, irrigated with a final effluent of a waste stabilization pond series located in the city of Pendências–RN, northeast region of Brazil. Full scale experiments were performed from february to november 2012, in an area of 1 ha, adjacent to the waste stabilization pond series. The experimental design was randomized with plots of 12 m x 12 m with daily irrigation (T1F1 and T1F2) and three times per week irrigation (T2). The treated effluent and soil were characterized based on the monitoring of physic-chemical and bacteriological parameters, according APHA, (2005). The grass was cut in sub plots of 9m2, after 160 days of planting, to evaluate the drought mass content. Briquettes were produced by a BL-95 model briquetter, at 170°C and pressure of 100 Mpa, and then the calorific power was determined Multivariate statistical analysis was used to evaluate the best irrigation treatment and qualitative analysis of the interviews the SPSS method was performed. The WSPS final effluent presented high salinity (C3) and low risk sodification (S1), which according to the Riverside diagram the restriction for agricultural use is mild to moderate. The WSPS promoted a reduction of 7.5 log units in thermo-tolerant coliform, producing an effluent suitable for unrestricted irrigation. The productivity of grass was high (37, 39 and 43.5 t/ha of drought mass, in treatments T1 and T2) with a 7% wet basis calorific power of up to 4,170 Kcal/kg. By the end of the experiments, the soil showed saline-sodic and saline characteristics for treatments T1 and T2, respectively, however, without affecting the productivity of grass, being attributed to low rainfalls during the experimental period, which favored the evaporation of treated sewage on the ground contributing to the rise of salts in the first 0-20 cm soil layer. Soil fertility increased by up to 370% in T1 and 212.5% in T2. Regarding the substitution of firewood by briquette in the Baixo-Açu region, 85% of entrepreneurs said they were willing to do it.