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Reverse Osmosis System Cleaning Ⅰ

After a stage of operation, RO membranes will be polluted with calcium, calcium sulfate, barium sulfate, strontium sulfate, metal oxide matter (Fe, Mn, Cu, Ni, Al, etc.), silicon deposition, inorganic and organic mixture, NOM natural organic matter, compound organic (e.g. antiscalant, dispersion medicine, cation compound electrolyte), and microbiology (algae, mold, fungi).

Fouling includes various deposition covering membranes and in water. These fouling will cause performance of system weak, reducing water-output volume and salt-escape.

  Type and speed of fouling are created by various factors and slowly, but membranes elements will be destroyed fast, so early control is important and necessary. When stopping operation for a long time or in daily repairing, it is need to clean membranes.

1, Composition and reason of fouling and confirm method

   1, Composition of fouling

  Deposition:CaCO4, CASO4, BaSO4

  Bacteria and mucus of and Bacteria

  Wreckage of organic

  Colloid: Slime and colloid silicon

  Hydroxide of metal

  Chemical deposition

  2, Reason of fouling

  2.1 Convection deposition

Concentrated water of various polluted particle is through RO membranes surface, the procedure of membranes absorbing particle is named ” Convection deposition”, which is main reason of pollution.

  2.2 Concentration polarization

Concentration polarization will cause membranes fouling. Appearance of concentration polarization will raise concentration of neighboring membranes surface fast, raising block at edge flow and mass impetus down, fouling will create.

2.3 Residue block

Residue cause membranes fouling fast. The plastics net in liquid channel between spiral membranes and flat membranes is supporting membranes but blocking flow, fouling will deposit here.

3, Confirm method for fouling

To option the best cleaner and method against to various pollution on membranes accordance with next steps:

3.1 Analysis system performance data

3.2 Analysis fouling possibility and raw water quality

3.3 Check and comparison front clean result

3.4Analysis SDI value measured left fouling on microhole filter membranes.

3.5 Analysis deposition on safe filter core

3.6 Check inner surface of water-input and section of water-in and out of membranes element, red/ brown means polluted by iron, as mud or colloid means organic and microbiology.

2, Chemical clean of anti-infiltration membranes

After anti-infiltration membranes operating for a certain period, with depositing on membranes surface, membranes performance will down and may be cleaned. Anti-infiltration membranes cleaning method consists physics(paper pressure clean and position clean), chemical clean and physics-chemical compound clean, in them chemical clean is widely used. Under chemical reaction condition of water-solution, resolution and dispersion, scaling and fouling may be cleaned surface of anti-infiltration membranes.

1, Cleaning condition of anti-infiltration membranes

To option following method:

1.1Under nominal water-input, water-output volume will reduce in 10~15%.

1.2For keeping nominal water-output volume, after temperature correcting water-output volume raises in 10~15%

1.3Water-output quality down in 10~15% and salt-escape volume raises10~15%.

1.4Pressure difference between all stages raise clearly.

    The above-mentioned condition may be referent to performance of anti-infiltration membranes after system operation for 48 hours. But notification that: if water-input temperature down, water-output volume of membranes will down meanwhile. When find problem, membranes element maybe not need to be cleaned. Nominal clean frequency is once in per 3~12 months. If more times are carried , anti-infiltration pre-treatment system must be adjusted and redesigned. If once is carried in per three-month, equipment may be retransformed. For membranes element performance reducing in 30~50% of nominal value, the element must be replaced.

2, Analysis fouling on RO membranes

   Various fouling must be cleaned with various method, or the problem is serious. Next method may be used:

2.1 Analysis anti-infiltration membranes operation record

2.2 Analysis water quality of raw water2.3 Check old clean record

2.4 Analysis SDI value measured left fouling on microhole filter membranes.

2.5 Analysis deposition on safe filter core

2.6 Check inner surface of water-input and section of water-in and out of membranes element, red/ brown means polluted by iron, as mud or colloid means organic and microbiology.

3, Option for chemical clean medicine on anti-infiltration membranes

   Suitable chemical clean medicine and method is relative with many factors. For the best effect, it may be cleaned with various combined medicine. LD-811 is used to clean inorganic salt deposition on anti-infiltration membranes. LDR-812 is used to clean organic matter and colloid pollution. Main procedure: firstly cleaning with acid method and then alkaline medicine. Detergent is commonly filled into clean medicine to help to remove serious bio and organic dirt. To fill ammonia in acid clean medicine may overcome difficult solution ferrous citrate in simple acid clean medicine. Filling EDTA into alkaline clean medicine to except colloid and, organic, microbiology and sulfate.

4, Effect to clean result from PH value, temperature and clean period

   When cleaning RO membranes with acid medicine, PH value may be kept in a low range, but in a high range based on cleaning RO membranes with alkaline medicine. Meanwhile, raising temperature in a proper level (above 15) and delaying clean period. At cleaning, the PH value, temperature and period of clean medicine will be control in a certain range. (attached Table 1)

 
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