Comparison of single and dual media filtration in a full-scale drinking water treatment plant

In this paper, the operation of mono and dual media filter beds was examined in a large-scale drinking watertreatment plant, located in Thessaloniki (N. Greece). The efficiency of filtration process was improved, regardingthe removal of undesirable constituents, which mainly include organic matter and suspended solids (turbidity). Acomparison was attempted between a sand filter bed (of 1 m depth) and a dual media filter bed, consisting of sand(60 cm-bottom) and anthracite (40 cm-top) layers. Two alternative treatment schemes were examined: theconventional coagulation-flocculation/sedimentation, followed by gravity filtration and the direct filtration (i.e.coagulation-flocculation and filtration, but without sedimentation). All these experiments were conducted at fullscalefilter beds, presenting an effective surface area of 40 m2 and with a volume loading rate over 375 m3 h-1 (i.e.large-scale experiments); therefore, the respective velocity was around 10 m h-1. The performance of filter bedswas assessed in terms of removal capacity, regarding mainly the turbidity, as well as the head-loss build-up. Itwas found that the dual media filter bed produced water of the same (high) quality as the single bed, but with theadvantage of operating at greater filtration cycles (around 3 times higher), which resulted to a 10% higher waterproduction.