Full Description

The objective of this study was to determine the optimum backwashing strategy for two-step granular activated carbon (GAC) filtration. Special focus was put on the relationships between operational conditions and the detachment of particles during the filter-ripening sequence. This full-scale study was conducted at Helsinki Water's Vanhakaupunki Water Treatment Plant. In the plant, the GAC filtration takes place after the chemical coagulation, sedimentation, sand filtration and ozonation. The GAC filtration is followed by ultraviolet disinfection, pH adjustment and chloramination in order to ensure the microbiological quality of the drinking water and for corrosion control in the distribution system. GAC filtration was launched five months before the start of the study. After four months of operation the flow was inverted in the studied filter pair. Under normal operating conditions the regeneration frequency was estimated to be three years, i.e. the inversion of flow will take place after one and a half years. The GAC filtration consists of 10 filter pairs; the depth of the carbon bed in a single filter step is 2.8 m. The GAC filtration was designed for a flow of 5000 m3/h, and in the studied filter pair it varied between 350 m3/h and 620 m3/h. The average velocity in the filter was 9.5 m/h. Includes 14 references, tables, figures.

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Edition: Vol. - No. Published: 01/01/1999File Size: 1 file , 420 KB