MICROBIOLOGICAL PERFORMANCE AND SALMONELLA DYNAMICS IN A WASTE-WATER DEPURATION POND SYSTEM OF SOUTHEASTERN SPAIN

The Salmonella presence and the microbiological quality indicators,tot al and fecal coliforms and coliphages of E. coli C, have been studied in a overloaded wastewater lagoon system treating urban wastewatrers o f the village of Guardamar del Segura (Alicante, Spain). Classical mic robiological technology to detect salmonellae was used, including pree nrichment, enrichment, selective media plating and biochemical and ser ological confirmation. Water was physicochemically characterized accor ding to GOD, SS, temperature, pH and dissolved oxygen. The selective m igration step through Rappaport-Vassiliadis semisolid agar medium was essential for the consistent detection of Salmonella in the different lagoon effluents. Total and fecal coliform levels of up to 10(5)-10(6) MPN/100 ml were detected in the final effluent. High coliphage concen trations of 10(3)-10(4) pfu/ml were also found in the effluent waters. Salmonella was always detected in 100 ml samples and eventually reach ed an order of value of 10(3) MPN/100 ml. Total coliform reduction was higher in the anaerobic ponds whereas fecal coliforms were more effic iently eliminated in the facultative (mostly ''anoxic'') lagoons. Coli phage reduction was higher in the facultative lagoons when compared to the anaerobic ponds. On many occasions, no reduction or eventual incr ement of the concentration of salmonellae was detected in the effluent s from the anaerobic ponds compared to concentrations of the patohogen in the influent raw wastewaters. The possibility exists for a capacit y of Salmonella to multiply in the anoxic phase of the wastewater trea tment, but the presence of microorganisms in raw sewage waters which c ould mask Salmonella detection with the enrichment methodology employe d cannot be ruled out.