RESUMEN
BACKGROUND: In Denmark, large-scale waterborne outbreaks are rare. This report describes the investigation of an outbreak that occurred in the town of Køge in May 2010. METHODS: The epidemiological investigation consisted of hypothesis generating telephone interviews, followed by a cohort study among approximately 20,000 residents using an online questionnaire. Odds ratios were calculated for exposures including the number of glasses of tap water consumed. Geographical spreading was assessed using a geographical information system. The microbiological investigation included cultures of stool samples and flagellin-typing. In the environmental investigation, water samples were tested for Escherichia coli and coliform counts and for DNA of Campylobacter, Enterococcus, and Bacteroides. During the outbreak investigation a water boiling order was enforced, as tap water was considered a potential source. RESULTS: Of 45 patients with laboratory confirmed Campylobacter infection in the municipality of Køge in May, 43 lived in the area covered by the central water supply. Of 61 patients with laboratory confirmed Campylobacter jejuni by 8 June, 50 shared a common flagellin gene type--flaA type 36 (82%). The epidemic curve from the cohort study showed a wave of diarrhoea onset from 14 to 20 May (n = 176). Among these patients, the development of diarrhoea was associated with drinking tap water with a dose-response pattern (linear increase by 2 glasses: odds ratio 1.40, 95% confidence interval 1.16-1.70). No bacterial DNA was found in water samples. CONCLUSIONS: These findings indicated a point source contamination of tap water with a single clone of C. jejuni which likely occurred on 12-13 May. The water boiling order was lifted on 18 June.
Asunto(s)
Infecciones por Campylobacter/epidemiología , Campylobacter jejuni/aislamiento & purificación , Brotes de Enfermedades , Agua Potable/microbiología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Infecciones por Campylobacter/microbiología , Campylobacter jejuni/genética , Niño , Preescolar , Estudios de Cohortes , Dinamarca/epidemiología , Femenino , Flagelina/genética , Humanos , Lactante , Masculino , Persona de Mediana Edad , Análisis Multivariante , Oportunidad RelativaRESUMEN
A model for the description of the SS distribution in a full-scale recirculating activated sludge WWTP was developed. The model, based on conservation principles, uses on-line plant data as model inputs, and provides a prediction of the SS load in the inlet to the secondary clarifiers and the SS distribution in the WWTP as outputs. The calibrated model produces excellent predictions of the SS load to the secondary clarifiers, an essential variable for the operation of the aeration tank settling (ATS) process. A case study illustrated how the calibrated SS distribution model can be used to evaluate the potential benefit of ATS implementation on a full-scale recirculating WWTP. A reduction of the maximum SS peak load to the secondary clarifiers with 24.9% was obtained with ATS, whereas the cumulative SS load to the clarifiers is foreseen to be reduced with 22.5% for short rain events (4 hours duration) and with 16.6% for long rain events (24 hours duration). The SS distribution model is a useful tool for off-line studies of the potential benefits to be obtained by introducing ATS on a recirculating WWTP. Finally, the successful operation of the ATS process on the full-scale plant is illustrated with data.
Asunto(s)
Eliminación de Residuos Líquidos/métodos , Purificación del Agua/instrumentación , Purificación del Agua/métodos , Calibración , Modelos Estadísticos , Modelos Teóricos , Lluvia , Aguas del Alcantarillado , Factores de Tiempo , Movimientos del Agua , Contaminación del Agua , Tiempo (Meteorología)RESUMEN
The control of the nitrate recirculation flow in a predenitrification system is addressed. An elementary mass balance analysis on the utilisation efficiency of the influent biodegradable COD (bCOD) for nitrate removal indicates that the control problem can be broken down into two parts: maintaining the "anoxic" zone anoxic (i.e. nitrate is present throughout the anoxic zone) and maximising the usage of influent soluble bCOD for denitrification. Simulation studies using the Simulation Benchmark developed in the European COST program show that both objectives can be achieved by maintaining the nitrate concentration at the outlet of the anoxic zone at around 2 mgN/L. This setpoint appears to be robust towards variations in the influent characteristics and sludge kinetics.