Filtralite Mono-Multi Fine as an Alternative to Anthracite/Sand Used in the Molde Process
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The objective of this Master thesis was to find out if a new filter combination called Filtralite Mono-Multi Fine (FMMF) could be used as an alternative to the conventional media combination anthracite and sand. The FMMF combination is made of crushed expanded clay aggregate, with a high density bottom layer and a normal density top layer. The media are used in a coagulation contact filtration process, as a part of a 3-media filter with a bottom alkalinity layer, which is in Norway referred to as the Molde process. Pilot testing of the coagulation contact filtration process, was conducted with one filter containing the FMMF and a bottom alkalinity layer, and a second reference filter containing anthracite, sand and a bottom alkalinity layer. The water was first coagulated using an iron chloride sulphate with 15\% acid and then filtered through both filters. Effluent water was sampled and analysed using the lab at the waterworks. Both filters where set-up with pressure out-takes several places along the filter depth. In these out-takes pressure was measured continuously and used to calculate the filters head loss development and head loss distribution along the filter depth. From the results it was found that using an iron dose of 2.6 mg Fe/l, provided good coagulation of the raw water. The water quality from the FMMF filter was almost as good as the reference filter for the two measured filter runs of 9.4 and 13.5 hours. The ripening of the FMMF filter was shown to be 20-75 min longer then the reference filter. Initial head loss in the FMMF media was found to be 41-73\% lower than the reference filter. However, the FMMF media showed low utilization of filter depth capacity because the solids where retained only in the top section of the filter, causing high rates of head loss development. From FMMF product information, a problem with overlapping settling velocities between the FMMF fraction was recognized, meaning the FMMF fraction will completely mix after backwashing. In addition, was it found that one of the FMMF fractions contained a large amount of finer grains. Based on the finding it was concluded that FMMF does not work as a dual filter media, and it could therefore not be recommended as an alternative to anthracite and sand used in the Molde process.