Reúso controlado de água na irrigação de alface (Lactuca sativa L.).

Abstract

Treated wastewater has been used all over the world as an alternative water source for several uses, mainly those less stringent in quality. The practice of reuse is sanitary and envirionmental safe when does not increase the risk of disease transmission in farmers and final consumers. Therefore the World Health Organization (1989) recommends as microbiological and parasitological guidelines values up to lOOOFC/100 mL and less than 1 helminth egg/liter in the effluent used in irrestricted irrigation. The present work reports an experience o f direct controlled reuse o f domestic wastewater treated in stabilization ponds in lettuce (Lactuca sativa L.) cultivation and its influence over the vegetable microbiological and parasitological quality. The physical and chemical modifications occured in the soil with wastewater and addition o f organic manuring were also investigated. The experiment was conduted in the Campina Grande Sewage Treatment Plant - Paraiba State - Brazil, in a randomized experimentent with four repetitions, being the factors two types of irrigation water (supply and wastewater treated by stabilization ponds) and presence or abscence bovine manure. Two cycles o f lettuce cultivation were carried out and statistically analyzed: the first j u ly to august/2003 and the second October to november/2003. Irrigation water were analysed for physico-chemical and microbiological variables; parasitological analyses was performed only in wastewater irrigation water. Soil was sampled at the end o f each cultivation cycle and analyzed for chemical (fertility, salinity, micronutrients, and heavy metals) and physical variables. Macro and micronutrients and heavy metals analyses were accomplished in lettuce root and leaves as well as non-destructive measurements and productivity. Results showed that lettuce irrigated with pond effluent presented lower microbiological quality to that established by ANVISA Resolution 12/2001. In other hand higher productivities and values of non-destructive variables were found in lettuces produced under wasterwater irrigation together with organic manure. Addition o f matter organic via bovine manure promoted larger alterations in soil and lettuce chemical and physics characteristics. Wastewater reuse in agricultural activities becomes safer when chemical, physics and microbiological aspects o f "water - soil - plant" system are attended particularly for cultures to be ingested raw.