Stratification of physical parameters in dual media filters at 10 waterworks

    Research output: Contribution to conference without a publisher/journalAbstractResearchpeer-review

    Abstract

    In Denmark, the use of dual media in rapid sand filters for drinking water treatment is widespread. In
    gravity filters with groundwater sources, the typical construction is a 50-100 cm layer of sand (granular
    quarts) overlain by a 30-50 cm layer of granular anthracite. The anthracite has a larger grain size than the
    sand, which purportedly reduces clogging and the required frequency of backwashing.
    Filter backwashing can influence the layering of filter material. According to the textbook explanation,
    backwashing removes trapped iron oxides from the pore volume and returns the grains to their original
    layered position with the anthracite on top. This study examined this explanation in detail, using filter
    media samples from 10 waterworks. The study identified potential causes of stratification or lack thereof as
    well as the variation of selected physical filter media parameters with depth.
    Large amounts of data were collected from various depths in the filters at 10 waterworks. Measured
    parameters included grain size distribution, grain coating, porosity, particle density, grain shape, bed
    expansion, iron mass balance, media age, media growth, and backwash procedures.
    Results showed that almost every physical parameter that was measured varied greatly from one
    waterworks to another. Strong correlations between certain parameters were found. The take home
    message is that a new explanation regarding the effect of backwashing of dual media rapid sand filters
    must replace the existing textbook explanation. The new narrative is closely bound to the backwash
    procedure, the age of the filter media, the density of the granular material and other parameters. This
    understanding has wide-reaching consequences for the operation of drinking water treatment plants.
    Translated title of the contributionStratificering af fysiske parametre i dual medie filtre fra 10 vandværker
    Original languageEnglish
    Publication date2019
    Number of pages28
    Publication statusPublished - 2019
    Event13th Annual Water Research Conference: Danish Water Forum - Thorvaldsensvej 40, Frederiksberg, Denmark
    Duration: 31 Jan 201931 Oct 2019
    Conference number: 13
    http://www.danishwaterforum.dk/Research/Annual_Meeting_2019/Annual_announcement2019.html

    Conference

    Conference13th Annual Water Research Conference
    Number13
    LocationThorvaldsensvej 40
    Country/TerritoryDenmark
    CityFrederiksberg
    Period31/01/1931/10/19
    Internet address

    Keywords

    • construction, environment and energy
    • drinking water
    • drinking water production
    • sand filtration

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