A disinfection installation using the Ultraviolet technology (Trailigaz/Trojan, series UV 3000) was installed at the end of May 1994 at the new Outreau-Le Portel (Pas de Calais) municipal wastewater plant, the outflow of which flows into the sea near Le Portel beach. Such a unit is the first of this type in France. The installation is described. The disinfection guarantees are an outflow the germ concentration of which should be below 200 Escherichia coli/100 ml geometric average over 30 days, and below 2000 E. coli 100% of the time. The results obtained from 1 June to 3 October are specified.

The disinfection performance was highly satisfactory: the mean residual Escherichia coli and faecal streptococcus values were 43 and 42 germs/100 ml for kills of 3.2 and 2.8 u.log. The disinfection guarantees have never been exceeded. In particular, only 2 samples out of 58 taken showed an E. coli concentration after UV greater than 1,000 germs/100 ml. The UV transmission (T) of the effluent varied from 35 to 63% as a consequence of the station's output increase. The least satisfactory results were recorded during periods of lower % UV T. During the 4 months of the study, three acid washes were carried out of the quartz sleeves: the speed at which the UV system used at Le Portel (low pressure UV lamps in an open channel) is contaminated is thus low.

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