Comparison of advanced disinfecting methods for municipal wastewater reuse in agriculture

The experimental investigation carried out jointly by Italian and Israeli teams within a 3-year research project funded by the European Commission on alternative disinfection methods for reusing municipal wastewater in agriculture is described. Disinfection effectiveness of UV rays, ozone (O₃) and peracetic acid (PAA) at pilot scale and hydrogen peroxide (H₂O₂) plus silver (Ag⁺) or copper (Cu⁺²) at laboratory scale was compared for tertiary municipal effluents. Pilot plant results indicated that the well known California limit (2 CFU/100ml of Total Coliforms) was effectively met with reasonable UV doses of 100-160 mWs/cm² or with exceedingly high PAA dosage (400 PPM); the related WHO microbial guideline (1,000 CFU/100 ml of Fecal Coliforms) was easily met with all three disinfectants (UV, PAA, O₃); maximum log-inactivation values were ≥5 for UV and PAA and ≤4 for O₃. Laboratory results with tertiary effluents demonstrated that Ag⁺ was able to inactivate target bacteria (E. coli-B, E. coli-K12), while H₂O₂ was more effective than Ag⁺ against MS-2 phages. Copper (250 μg/l) had no bactericidal effect but possessed an appreciable virucidal effect. When hydrogen peroxide and copper were combined, a pronounced increase in both bactericidal and virucidal effects was obtained.