Faecal coliforms, faecal enterococci, &lt;i&gt;Salmonella&lt;/i&gt; Typhi and &lt;i&gt;Acanthamoeba&lt;/i&gt; spp. UV inactivation in three different biological effluents

B.E. Jiménez,N.A. Beltrán

doi:10.4314/wsa.v34i2.183647

Abstract

Efficiency of UV-light to inactivate microbial indicators, Salmonella Typhi and Acanthamoeba spp. was studied in three different biological secondary effluents. Even though effluents differed in terms of their total suspended solids content, transmittance and particle size distribution, the UV-light dose required to fulfil WHO agricultural water reuse criteria was the same (30 mW·s/cm2), because the particle content with sizes > 40 µm was similar and very small. Using this dosage, 3 log of Salmonella Typhi and faecal enterococci were also inactivated. To avoid faecal coliform and Salmonella Typhi photoreactivation, the UV dose had to be doubled and in the process 2.5 log of Acanthamoeba spp. were also inactivated. This is interesting because its presence in wastewater, pathogenicity and resistance to conventional disinfection processes has been reported in the literature. Additionally, it was found that the faecal coliforms' inactivation rate constant was the lowest one of all the bacteria studied (Salmonella Typhi and faecal enterococci), suggesting the limitation of this indicator when several kinds of pathogens are present, as is the case in developing countries.

Highlights

In 2001, water-borne diarrheic diseases represented 13% of the 15 million deaths caused by all types of infectious diseases worldwide, 74% occurring in children under the age of 5 in the developing world (Hinrichsen and Robey, 2000)
This is of particular concern for developing countries because, on the one hand, higher concentrations of a wider variety of organisms are present in wastewater compared to developed countries’ wastewater (Jiménez et al, 2001), and on the other hand, it is frequently cited in the literature that the behaviour of pathogens during disinfection is not properly modelled by common microbial indicators (Chang et al, 1985; Ashbolt et al, 2001)
WHO criteria (WHO, 2006) only set values for the faecal coliform content and suggest setting additional values for other micro-organisms depending on the local situation

Summary

Introduction

In 2001, water-borne diarrheic diseases represented 13% of the 15 million deaths caused by all types of infectious diseases worldwide, 74% occurring in children under the age of 5 in the developing world (Hinrichsen and Robey, 2000). To measure the disinfection efficiency, conventional biological indicators (faecal coliforms and enterococci) were used and two specific pathogens (Salmonella Typhi and Acan thamoeba spp.) were deemed to be of interest because they are disease agents common to developing countries and are associated with the use of wastewater for irrigation, as explained earlier.

Results

Conclusion