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Chemical-physical water treatments: Filtration and Flocculation
The White Paper discusses the use of filtration techniques as the central step for removing particles from water ranging in size from 1 μm to 100 μm. While larger particles are removed by screening, sedimentation or flotation, smaller particles are separated by membrane processes and filtration.
The paper reviews the main filtration options and explains why volume filtration is normally preferred as the primary means of removing relatively high quantities of particles from the water, as in industrial or waste water treatment, with ‘sieving’ surface filtration used where particle content is low and safety requirements are high.
The paper discusses principal volume filter formats and tabulates the parameters required to calculate volume filter dimensioning. Principally determined by filter velocity, (volume flow divided by filter cross section) filter dimensions are also determined by whether water is to be filtered directly without pretreatment, or whether flocculation filtration is also to be applied.
The author also reviews strategies to mitigate filter clogging, including backflushing (applying reverse flow water/air pressure) and continuously operated volume filters that can be cleaned during running filtration. The paper also discusses the impact of differing filter velocities on overall filter efficiency, which can be enhanced via flocculation (using chemical clarifying agents to precipitate a process of contact and adhesion whereby particles in dispersion form larger-size clusters or ‘flocs’).
The paper summarizes the flocculation process, discusses principal primary flocculants including acid salts of trivalent aluminum or iron, and tabulates recommended dosages.
In summary, the paper explains why volume filters provide the method of choice to for separating suspended particles and turbidities from surface waters and process liquids. It provides valuable insights on how volume filtration can be optimised through careful consideration of filter design, backflushing regimes and flocculation steps. The rewards include enhanced filtrate quality and lower energy costs.
The paper is authored by Prof. Dr. Gerd Braun, who teaches and lectures at the TH Köln (University of Applied Sciences) in the fields of water treatment and membrane processes. Prof. Braun’s research approach is based on almost 20 years of industrial experience in plant engineering.