MODELACION DEL TIEMPO DE CONSERVACION DE MUESTRAS BIOLOGICAS DE AGUA

According to standard analytical methodologies, in order preserve water samples for microbial determination, they must be maintained under 10 degree C for a maximum period of 6 hours for non-drinking water and 30 hours for drinking water. Although there is not an explicit reference to the water organic content, the difference between recommended preservation times could be related with it. Therefore, water samples with low organic content can be preserved for longer periods than those with a higher content. Several samples of water with different organic content (domestic wastewaters, from slaughterhouses and poultry farms, and from shallow wells) were analyzed. Models were developed in order to determine indicator organisms in CFU/100 mL (total and faecal coliforms, and enterococcus) as a function of BOD sub(5). The assessment was carried out 6 to 48 hours after sampling. It was found that high BOD sub(5) concentration in water is not a decisive factor when indicator organisms in CFU/100 mL are to be estimated (there is not a significant difference between total or faecal coliforms, neither between enterococcus between 0 and 48 hours). Nevertheless, there is a significant difference between total coliforms in CFU/100 mL when determined at 0 and 6 hours. This contradicts the established in several analytical methods. Samples for faecal coliforms determination can be preserved up to 6 hours, but at 18 hours there is a significant difference for results obtained in CFU/100 mL. For enterococcus, there is no significant difference in preservation between 0 and 48 hours.Original Abstract: Segun los metodos analiticos convencionales, se debe mantener la temperatura por debajo de 10 degree C para la preservacion de muestras de aguapara analisis microbiologicos por un periodo maximo de 6 horas para aguas no potables y 30 horas para aguas de consumo. Aunque explicitamente no se hace referenda de la carga organica, la diferencia del tiempo de preservacion puede estar relacionada. Es decir, muestras con cargas organicas menores pueden preservarse por mas tiempo que aquellas con cargas organicas mayores. Se analizaron muestras de agua con diferentes cargas organicas; el analisis de los datos permitio desarrollar modelos para determinar las UFC/100 mL de organismos indicadores (coliformes totales, coliformes fecales y enterococos) en muestras de agua, en funcion de la DBO sub(5). Las determinaciones se hicieron entre 6 y 48 horas despues de la toma de muestras. El tiem