Microbiological quality assessment of irrigation water by means of particle size.

Abstract

The Word Health Organization (2006) recommends limiting helminth ova (HO) and faecal coliform (FC) content in water to be reused by agriculture in order to avoid unnecessary health risks. The techniques currently used to determine the microbial content in raw and treated wastewater are costly, complex, and time-consuming. However, it has not been acknowledged that microorganisms are particles with different sizes that could be measured using a particle size counter (PSC). In this research, the relationship between HO content and the volume of particles having a size of 20-80 ¼m was determined using a PSC, both in raw wastewater and effluent produced by a physicochemical Advanced Primary Treatment process. Using the same method, faecal coliforms and Salmonella spp. content was also related to the number of particles, with sizes between 0.7-1.5 ¼m and 1.5-4.0 ¼m respectively. However, since the range of concentrations found in both untreated and treated water was very similar (from 5 to 8 log units) the equation generated for these relations do not have a practical application. In contrast, a very good and useful relationship was found for helminth ova, allowing their measurement in 5 minutes and at $3 USD per sample, a cost 7.5 times lower than the current commercial rate.