Effectiveness of the use of Ag, Cu and PAA to disinfect municipal wastewater

Abstract

The WHO defines Category A wastewater as one which does not contain more than 1000 FCU100 ml⁻¹ of faecal coliforms (FC) and less than 1 helminth egg (HE) per litre. The objectives of this work were to determine: 1) the disinfectant capacity of different concentrations of silver (Ag), silver‐copper (Ag‐Cu) and silver‐copper‐peracetic acid (Ag‐Cu‐PAA) when added to samples of raw wastewater (RW), with a contact time of 60 minutes; 2) the optimal concentration and contact time required by the better performing disinfectant, determined from the previous stage, to obtain Category A RW; 3) the effect of the selected disinfectant when applied to RW, the effluent of activated sludge (ASE) and the effluent of sand filters (FE) for 10, 30 and 60 min duration. The Ag:Cu:PAA ratio of 0.6:6.0:100.0 mg l⁻¹, showed the best disinfectant capability to produce Category A wastewater. The ratio of 0.1:1.0:20.0 mg l⁻¹ of Ag:Cu:PAA and a contact time of 10 minutes are the optimal values to produce Category A wastewater in RW. For RW and ASE, the optimal ratios and times for Ag:Cu:PAA were: 1.2:12.0:90.0 mg l⁻¹ at 60 min and 0.1:1.0:20.0 for 10 min, respectively. The FE samples showed concentrations of FC and HE below the standards of the WHO; therefore, their disinfection is not necessary.

Keywords:

• wastewater disinfection
• silver
• copper
• peracetic acid
• pathogen microorganisms

Acknowledgements

The authors acknowledge Servicios Peñoles S.A. de C.V. for their economic support for the study, as well as Catalina Maya and Paulina Aguilar for carrying out the detection analysis of helminth eggs. A patent application is pending, series number NL/a/2006/000029.