Estudo do potencial produtivo do capim elefante sob diferentes lâminas com água residuária tratada.

Abstract

This research aimed the evaluation of productive and sanitary aspects of elephant grass (Pennisetum purpureum) submitted to different irritation depths with domestic wastewate; from the final effluent of Campina Grande city Wasterwater Treatment Plant - STP - Paraiba State - Northeast Brazil (7°13'H"S; 35052'3I"W; 550m above the sea level). The STP is formed by primary treatment (grid, degritter and Parshall flume) followed by two projected aerated ponds but now a days not in operation Elephant grass was planted in a 1.000m2 area near to the ponds, in 24 plots of 20m2 randomly distribuited and submitted to 5 different wastewater depths (Tl to T5 - STP final effuent) and control irrigated with supply water (TA). Flood irrigation was the method used and each sheet was calculated from a reference sheet (Tl), according to the local climatic conditions, soil and culture characteristics. The remaing depths (T2, T3, T4 and T5) were calculated by increasing or decreasing referende sheet values. During the experimental period (05/02 to 10/11/03) three cuting were made: 13/05 - 05/08 and 10/11/2003. Irrigation waters were analysed for pH, DO, EC, organic matter (BOD, COD and SS), ions (sodium, potassium, chlorides, calcium and magnesium), nitrogen and phosphrous and helminths eggs. Fecal contamination indicator (FC) was analysed in water, soil and culture. The variables studied in the grass were: height (m), stem diameter (cm), green matter production (kg), dry matter (% of DM), raw protein (% of PB) and NPK (%). STP final effluent presented high values of electric conductivity (1642- 1686umho/cm), showing the need of salinity control and adequate choice of irrigated cultures. On the sanitary aspect, STP final effluent did not present helminths eggs being adequate according to the WHO guidelines for fodder irrigation (category B), however with high concentrations of termotolerant coliforms (l,7-5,8xl06CFU/100mL). For grass variables significant statistical differences were not observed at the level of 5% among the different irrigation depths used. Soil contamination by termotolerant coliforms before and after the planting (10 - 107NMP/g respectively) were high. Elephant grass fecal contamination was high: 1,6x 10'MPN/g for wastewater and 8,0x1 G3 MPN/g for supply water and associated to climatic conditions such winds and rains and due to the proximity of among the experimental plots with the ponds. Even so treated wastewater must be considered as a potential source of inorganic fertilizers, as water resource in semi-arid areas but mainly as a correct environmental solution to avoid superficial water degradation particularly those used for human water supply.