BACTERIOLOGICAL CHANGES ASSOCIATED WITH GRANULAR ACTIVATED CARBON IN A PILOT WATER-TREATMENT PLANT

Bacteriological analysis were performed on collected water samples fro m a conventional water treatment pilot plant in Cincinnati, Ohio in wh ich granular activated carbon (GAC) has been used as the final process to assess the impact of GAC on the bacteriological quality and incide nce of antibiotic resistant bacteria in water produced. Heterotrophic bacterial counts (HPC) at 20 degrees C was stabilized at 10(2) to 19(4 ) cfu mL(-1) and did not markedly differ at different water treatment processes. On the other hand, slight reduction in HPC was observed for the effluent produced from sand filter and GAC contactors. Effluents produced from both the sand filter and GAC contactors showed 2 log red uction in coliforms count. Fecal coliform showed the same rate of redu ction as a result of sand filtration, while it reached undetectable nu mbers in the effluent of GAC contactors. Subculturing the isolated str ains in tryptic soy broth revealed that 61.3, 61.5, 12.6 and 8.5% of H PC at 28 degrees C, total coliforms and fecal coliform, respectively w ere non-culturable. In this case, R2A or R3A broth was used as subcult uring media. The incidence of coliform resistant strains among isolate s varied significantly according to the source of water samples. Multi ple antibiotic resistance (MAR) was not always high in the same sample s in which the overall resistance was high. The species composition va ried considerably in different water samples. Selection for bacteria e xhibiting resistance to antibiotic or antibiotics was observed under s ome experimental conditions using different doses of chlorine. The ant ibiotic resistance character was mostly transferable. As a conclusion, the use of GAC has no observable adverse effect on the bacteriologica l quality of the water produced from the pilot plant under investigati on.