AQUAPHOR APRO 1000 LPH, Руководство пользователя

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3. Scaling
Scaling is a water chemistry problem originating from the precipitation and deposition of sparingly soluble salts.
The typical scenario is a brackish water system operated at high recovery without proper pretreatment. Scaling
usually starts in the last stage and then moves gradually to the upstream stages. Waters containing high concen-
trations of calcium, bicarbonate and/or sulfate can scale a membrane system within hours. Scaling with barium
or with fluoride is typically very slow because of the low concentrations involved.
The corrective measures are:
▪
Cleaning with acid and/or an alkaline EDTA solution.
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An analysis of the spent solution may help to verify the cleaning effect.
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Optimize cleaning depending on scaling salts present.
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Carbonate scaling: lower pH, adjust antiscalant dosage.
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Sulfate scaling: lower recovery, adjust antiscalant dosage and type.
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Fluoride scaling: lower recovery, adjust antiscalant dosage or type.
10.5.3 LOW FLOW AND LOW SOLUTE PASSAGE
1. Compaction and Intrusion
Membrane compaction and intrusion are typically associated with low permeate flow and improved salt rejec-
tion. Compaction is the result of applied pressure and temperature compressing the membrane which may result
in a decline in flux and salt passage. Intrusion is the plastic deformation of the membrane when pressed against
the permeate channel spacer under excessive forces and/or temperatures. The pattern of the permeate spacer is
visibly imprinted on the membrane. Intrusion is typically associated with low flow. In practice, compaction and
intrusion may occur simultaneously and are difficult to distinguish from each other. Although the membrane
shows little compaction and intrusion when operated properly, significant compaction and intrusion might occur
under the following conditions:
▪
High feed pressure.
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High temperature.
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Water hammer.
The corrective measures are:
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Damaged elements must be replaced, or new elements must be added to the system to compensate for the
flux loss.
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New elements should be distributed evenly into parallel positions. It should be avoided to have vessels
loaded exclusively used elements.
2. Organic Fouling
The adsorption of organic matter present in the feedwater on the membrane surface causes flux loss, especially
in the first stage. In many cases, the adsorption layer acts as an additional barrier for dissolved salts, or plugs
pinholes of the membrane, resulting in a lower salt passage. Organics with a high molecular mass and with hy-
drophobic or cationic groups can produce such an effect. Examples are oil traces or cationic polyelectrolytes,
which are sometimes used in the pretreatment. Organics are very difficult to remove from the membrane surface.
To identify organic fouling:
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Analyze deposits from filter cartridges and identify organic powder.
▪
Analyze the incoming water for oil and grease, as well as for organic contaminants in general.
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Check pretreatment coagulants and filter aids, especially cationic polyelectrolytes.
▪
Check cleaning detergents and surfactants.