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Sanitary evaluation of wastewater from stabilization ponds for agricultural irrigation at Säo Paulo state

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Maria Tereza Pepe Razzolini
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Faculdade de Saúde Pública (FSP/CIR)
Defense date:
Examining board members:
Wanda Maria Risso Günther; Glavur Rogerio Matte; José Luiz Negrão Mucci; Petra Sanchez Sanchez; Maria Inês Zanoli Sato
Advisor: Wanda Maria Risso Günther

Due the water scarcity and the necessity to improve of hydric systems management the reuse appears as an altemative to agricultural irrigation and other activities. However, wastewater reuse demands special attention because there are many diseases transmitted by contaminated waters. This concern shows the importance of the satisfactory sanitary quality to protect public health. Objective. Studying the viability of treated wastewater by stabilization ponds located in Lins (SP) to reuse in agricultural in relation to WHO recommendations (1989), presence of E.coli O157 through out sorological reaction and polymerase chain reaction (PCR), Salmonella detection, presence and viability of helminthes eggs, quantification of coliphages and efficiency of disinfection using sodium hypochlorite and ozone. Methods. The enumeration of total coliform and E. coli, Salmonella isolation, coliphages density and helminthes eggs determination were carried out according to Cetesb guidelines and Standard Methods for the Examination of Water and Wastewater (20th ed., 2000). The viability of helminthes eggs was determined according Yanko(1988). Results. E. coli concentration in treated wastewater samples revealed values higher than WHO guidelines (1989) to irrestricted (category A) and restricted (category B) irrigation, Ascaris eggs were detected as well as Salmonella . The coliphages density, 6,0x102 to 8,5x104 UFP/100mL , was not high in the analyzed samples. There was variation in the concentration of total coliform and E. coli in treated wastewater disinfected with sodium hypochlorite depending of dosis and contact time employed. The best results were observed in the range between 8,6 - 15 mg/L of sodium hypochlorite at 30 minutes of contact time. When the ozone was used the results obtained did not reveal satisfactory efficiency in total coliform and E. coli reduction. In relation to helminthes eggs elimination the disinfectant agents used were not efficient. The coliphages reduction using sodium hypochlorite was between O - 2 logs units depending of dosis and contact time employed, after ozone disinfection the reduction of these microorganisms was low. Conclusions. The treated wastewater did not present satisfactory microbiological and parasitological quality to irrestricted (category A) and restricted (category B) irrigation according to WHO (1989) guidelines. Under the conditions of this investigation, the disinfectants agents used were not effective in the elimination of fecal indicators to reach WHO ( 1989) recommendations. Salmonella was detected in treated wastewater samples studied and coliphages concentration was compatible with literatura data, between 1 03 to 104 UFP/1 OOmL. E. coli O157 was not detected in treated wastewater sample analyzed. Even though, due the acquired results the final effluent from stabilization ponds system in Lins (SP) should not be used in irrestricted and restricted irrigation second WHO (1989) recommendations as public health protect measure to exposed groups to this kind of waters. (AU)