ABSTRACT
The hygienic characteristics of the freshwater from Garda Lake used for the water supply of Sirmione were evaluated before and during the various phases of treatment. The samples were taken at the moment of entry, after ozonization, after filtration and after the addition of chlorine dioxide. The coliforms and Escherichia coli, occasionally detected in the incoming water, were reduced by ozone and eliminated by filtration. Enterococci were always absent. The overall reduction in the total bacteria count was satifactory, considering the low initial levels (96.0% and 83.0% respectively for the Heterotrophic plate count at 22 degrees and the Heterotrophic plate count at 36 degrees). The chemical and physical indicators that underwent the greatest reductions were the sulphates, iron, manganese, ammonia and the turbidity. Several species of unicellular algae belonging to Chlorophyta, Cyanophyta and Bacillariophyta were identified in the water at entry and after ozonization, but were completely eliminated during the subsequent phase of filtration. deliver of high quality services.
Subject(s)
Water Purification/methods , Chlorine Compounds , Filtration , Fresh Water , Italy , Oxides , OzoneABSTRACT
A study was carried out to compare two selective plating media commonly used to detect Listeria monocytogenes in food samples (Palcam and Oxford agar) with two more recently formulated chromogenic media (ALOA and Rapid'L.mono). A comparison was also made between the identification systems API-Listeria and Monocytogenes ID Discs. The results obtained from the analysis of 132 food samples showed that the chromogenic media allowed Listeria monocytogenes to be detected more rapidly and with higher levels of specificity and sensitivity. The efficiency of the Monocytogenes ID Discs test was confirmed, giving results comparable to those obtained with API-Listeria, but in a simpler and quicker manner.
Subject(s)
Cheese/microbiology , Chromogenic Compounds/chemistry , Food Microbiology , Listeria monocytogenes/isolation & purification , Meat/microbiology , Animals , Cattle , Poultry , SwineABSTRACT
AIMS: The aim of this study was to compare the efficiency of peracetic acid with that of chlorine dioxide in the disinfection of wastewater from a sewage treatment plant (serving about 650 000 inhabitants) that has been using peracetic acid as a disinfectant since 1998. METHODS AND RESULTS: A total of 23 samplings were made, each consisting of three samples: from secondary effluent, effluent disinfected with 2 mg l(-1) of peracetic acid and effluent disinfected with 2.2 mg l(-1) of chlorine dioxide (contact time 20 min). For each sample, measurements were made of the heterotrophic plate count at 36 degrees C, total and faecal coliforms, Escherichia coli, enterococci, pH, suspended solids and chemical oxygen demand (COD). During the first phase of the experiment the peracetic acid was seen to be less efficient than chlorine dioxide. To improve the disinfectant action a system of mechanical agitation was added which led to a greater efficiency in the inactivation of bacteria of faecal origin. CONCLUSIONS: Both products were found to be influenced by the level of microbial contamination, the amount of suspended solids and COD but not by the pH of the effluent before disinfection. The immediate mixing of the wastewater and disinfectant caused a greater reduction in enterococci. SIGNIFICANCE AND IMPACT OF THE STUDY: Since peracetic acid was seen to produce a high abatement of micro-organisms, it can be considered as a valid alternative to chlorine dioxide in the disinfection of wastewaters.
