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(O-3) 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/cm(2) or with exceedingly high PAA dosage (400 PPM); the related WHO microbial guideline (1,000 CFU/100 mi of Fecal Coliforms) was easily met with all three disinfectants (UV, PAA, O-3); maximum log-inactivation values were greater than or equal to 5 for UV and PAA and less than or equal to 4 for O-3. Laboratory results with tertiary effluents demonstrated that Ag+ was able to inactivate target bacteria (E. coli-B, E. coli-KI 2), while H2O2 was more effective than Ag+ against MS-2 phages. Copper (250 mu g/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.