Removal of indicator bacteria, human enteric viruses, Giardia cysts, and Cryptosporidium oocysts at a large wastewater primary treatment facility

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Abstract:

Pathogens and fecal indicator bacteria occurrence and removal were studied for a period of 6 months at the Montreal Urban Community wastewater treatment facility. With a capacity of about 7.6 million cubic metres per day (two billion U.S. gallons per day), it is the largest primary physico-chemical treatment plant in America. The plant discharges a nondisinfected effluent containing about 20 mg/L of suspended matter and 0.5 mg/L of total phosphorus on the basis of average annual concentrations. BDO5 (annual mean) is 75 mg/L before treatment and 32 mg/L after treatment. Samples were collected for a period of 6 months, and they demonstrated that the plant was not efficient at removing indicator bacteria and the pathogens tested. Fecal coliforms were the most numerous of the indicator bacteria and their removal averaged 25%. Fecal streptococci removal was 29%, while Escherichia coli removal was 12%. In untreated sewage, fecal coliforms, E. coli, and human enteric viruses were more numerous in summer and early autumn. Fecal streptococci counts remained relatively similar throughout the period. Clostridium perfringens removal averaged 51%. Giardia cysts levels were not markedly different throughout the study period, and 76% of the cysts were removed by treatment. Cryptosporidium oocyst counts were erratic, probably due to the methods, and removal was 27%. Human enteric viruses were detected in all samples of raw and treated wastewater with no removal observed (0%). Overall, the plant did not perform well for the removal of fecal indicator bacteria, human enteric viruses, or parasite cysts. Supplementary treatment and disinfection were recommended to protect public health. Various alternatives are being evaluated.

Nous avons étudié pendant 6 mois, la présence et l'enlèvement de microorganismes pathogènes et de bactéries indicatrices fécales à la station d'épuration de la Communauté Urbaine de Montréal. Cette station, avec une capacité de 7.6 millions de mètres cubes par jour est la plus vaste en Amérique. La station rejette un effluent non désinfecté contenant en moyenne annuelle 20 mg/L de matières en suspension et 0.5 mg/L de phosphore total. La DBO5 (moyenne annuelle) est de 75 mg/L avant traitement et de 32 mg/L après traitement. Des échantillons recueillis pendant 6 mois ont montré que la station n'était pas efficace pour l'enlèvement des bactéries indicatrices et les microorganismes pathogènes. Les coliformes fécaux étaient les plus fréquents parmi les indicateurs bactériens de pollution fécale et leur enlèvement ne dépasse pas 25%. L'enlèvement des streptocoques fécaux était de 29% alors que celui de Escherichia coli ne dépassait pas 12%. Dans l'affluent, les coliformes fécaux, E. coli et les virus entériques humains étaient plus nombreux pendant l'été au début de l'automne. Les dénombrements de streptocoques fécaux étaient quant à eux plus stables au cours de la période d'observation. L'enlèvement de Clostridium perfringens était de 51%, celui des kystes de Giardia de 76% avec des niveaux semblables pendant toute la période, et l'enlèvement des oocystes Cryptosporidium de 27 %, mais les dénombrements étaient moins stables. Les virus entériques humains étaient présents en tout temps et le traitement n'avait aucun effet sur eux. Comme on le craignait, la station d'épuration élimine peu les microorganismes pathogènes et les germes indicateurs. Des traitements supplémentaires ont été recommandés pour protéger la santé publique.

Document Type: Research Article

Publication date: March 1, 2001

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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