Condições do reúso dos efluentes finais das ETE'S do Estado da Paraíba.

Abstract

The present work aimed an evaluation of reuse conditions of the final effluents of 10 Sewage Treatment Plants in the municipalities of João Pessoa (Róger and Mangabeira), Guarabira, Sapé, Campina Grande, Monteiro, Itaporanga, Patos, Sousa and Cajazeiras - PB using the World Health Organization recommended standarts. The experimental period (aug/2000 to may/2004), was divided in 4 climatic periods of drought and a single rain period. The variables studied were pH, EC, TDS, ammonia, thermotolerant coliforms, Escherichia. coli, helminths eggs; SAR (Sodium Absoption Rate) and salinity were calculated to evaluate the potential problem of infiltration and the risk of soil salinization respectively. The results were submitted to (1) box plot statistical technique; (2) variance analysis (ANOVA) single factor with 5% significance level and (3) the GT-2 graphic method to compare mean values simultaneously. The Riverside classification was applied to define the final effluents use categories for salinity and sodicity. The pH of most finals effluents ranged from 6.5 to 8.4 and were considered appropriate to irrigation. The final effluents of Sousa (drought 2) and Cajazeiras (drought 2, drought 3 and rain) did not present any use restrictions when salinity (evaluated trhought EC and TDS) was used. The salintity, evalualted through TDS, showed final effluents with medium to high degree of salinity. The infiltration potential problems using EC and S.A.R., showed that final effluents of Cajazeiras, Itaporanga, Róger, Sapé and Sousa (drought 3), Cajazeiras, Itaporanga, and Sousa (drought 4) and Cajazeiras, Guarabira, Itaporanga, Mangabeira, Monteiro Sapé and Sousa (rain) presented a degree of restriction of low to moderate while others STP did not. Using the Riverside classification, during droughts 3 and 4, most final effluents were inserted in C3 - S1 and C3 - S2 categories and in the rain period, in C2 - S1, C3 - S1 and C3 - S2. Independent of climatic period, the effluents were framed into C3 - S1 (Mangabeira and Róger), C3 - S1 and C3 - S2 (Campina Grande, Guarabira and Sapé) and C2 - S1 (Cajazeiras). For the majority of effluents, ammonia concentrations were above the recommended standart of 30mg/L. The final effluent microbiological quality did not riched the sanitary standard of W.H.O. (1989) due to the excess of thermotolerant coliforms (> 1000FC/100ml), being inappropriate for unrestricted irrigation in spite of the absende of helminths eggs. The variance analysis demonstrated significant differences among the groups for pH, E.C. T.D.S. and ammonia during drought and rain period. The final effluents were rich in ammonia and presented excess of thermotolerant coliforms contaminating rivers and receiving water bodies. The most recent standard of the World Health Organization (WHO, 2006), for unrestricted and restricted reuse contemplate several reuse options (each one with maximum concentrations of E.coli, until 10E6/100mL) with sewage treatment methods and agricultural handling (irrigation techniques and cultures to be irrigated). In this work only the final effluents of Cajazeiras (droughts 3, 4 and rain), Mangabeira (droughts 3 and 4 and rain), Itaporanga and Sousa (drought 3), Sapé and Sousa (drought 4) were inserted in some of the options suggested by WHO. The other final effluents were not inserted in any option, due to high values of E.coli above 10E6/100mL, being inappropriate for the any irrigation type, in spite helminths eggs be absent in all 10 STP final effluents.