INDICADORES DE CONTAMINACIÓN FECAL EN BIOSÓLIDOS APLICADOS EN AGRICULTURA

Abstract

Wastewater treatment produce sludge as a by - product. Its characteristics depends of the wastewater origin and the treatment used for its depuration. Disposition of this material in agriculture, soil recuperation, reforestation and building materials are alternatives of biosolids disposal in landfilling, dumping to the sea or incineration. The application of biosolids in agriculture is conditioned not only to indicator microorganisms and pathogen concentrations, but also to the presence of toxic substances and heavy metals. The objective of this study was to determine the concentration of fecal coliforms (indicators of bacterial contamination), somatic phages and F- specific phages (indicators of viral contamination) and viable helminth eggs (indicators of parasitological contamination) in biosolids produced in a domestic wastewater treatment plant, stabilized by mesophilic anaerobic digestion. The geometric media concentrations of bacterial and viral indicators are 1,6 x 105 UFC/g dry weight for fecal coliforms, 5,0 x 103 PFP/g dry weight for somatic phages and 7,9 x 101 PFP/g dry weight for F-specific phages.The concentration of viable helminth eggs were 0.14/4g peso seco. Ascaris sp eggs presented the higher percentage of viability together with no human origin eggs (Capillaria sp, Dicrocoelium sp and Stephanarus sp… etc.). According to EPA/625/R-92/013 (1999) decree, which regulate control of pathogens and vector attraction in sewage sludge, this sludge is classified as type B due to fecal coliforms concentration (<2 x 106 UFC/g total solids). However, viable helminth eggs concentration in biosolid is less than 1 viable egg /4 g dry weight, classified as type A sludge (authorized for all uses). Although the determination and quantification of somatic phages and F-specific phages are not proposed in the EPA/625/R-92/013 (1999) decree, concentrations of this microorganisms in biosolids suppose the possible presence of enteric virus in the analyzed samples. According with this results, it can conclude that this product can be applied in agriculture with the restriction time previous to the farming to reduced the sanitary risk.