Desinfección de agua: acción comparativa del ozono y cloro sobre un amplio espectro bacteriano / [Water disinfection: comparative activities of ozone and chlorine on a wide spectrum of bacteria]

Ozone and chlorine are agents that disinfect by destroying, neutralizing or inhibiting the growth of pathogenic microorganisms. The treatment of drinking water with ozone has shown to be more efficient against spores of Bacillus subtilis. It was observed that the ozone already in dose of 0.35 mg/l produced the reduction of at least 5 log in populations of approximately 1 x 10(6) cells/ml of Escherichia coli, Vibrio cholerae, Salmonella typhi, Yersinia enterocolitica, Pseudomonas aeruginosa, Aeromonas hydrophila, Listeria monocytogenes and Staphylococcus aureus. With a dose of 0.50 mg/l of chlorine, the reduction was much smaller for the tested microorganisms (except Vibrio cholerae), while the effect of 2 mg/l of chlorine was similar to the ozone treatment. For spores of Bacillus subtilis, the reduction observed with ozone concentrations of 0.35 and 0.70 mg/l was of almost 3 log, while no considerable effect was obtained with chlorine in the tested conditions. Our results have shown that both disinfectans were consumed during the treatment period, probably because of the own water demand and the added bacterial mass.

Modificación del método de Pack para la microdeterminación de diacetilo en cultivos mixtos / [Modification of the Pack method for the microdetermination of diacetyl in mixed cultures]

Prill and Hammer’s method (4) for microdetermination of diacetyl was modified by several authors (1-3, 7), but retaining the same principle: diacetyl is converted into dimethylglyoxime by reaction with hydroxylamine; the oxime is subsequently converted into a pink ammonoferrous glyoximate and its colour is measured by absorbance at 530 nm. In the present communication a procedure based on the method of Pack et al. (3) is proposed with the following modifications: 1. Omission of carboy and suction flask; 2. Elongation of the connecting tubing between sample and trap tubes and relocation of the trap tubes to a higher level. 3. Replacement of rubber tubing by pvc connection and of rubber stoppers by neoprene ones. 4. A more accurate regulation of the nitrogen flow. 5. Protection of the Fe SO4 against oxidation. 6. Omission of the rinse of the trap tips with K2 HPO4 solution. 7. Use of diacetyl as a standard instead of dimethylglyoxime.