B. Bio-Fouling Prevention


 Treatment Purpose:

In rare occasion dissolved matter may precipitate on the screen surface and the automatic backwash cleaning is unable to remove the precipitations, or bio-film growth. In these cases, chemical cleaning is required.

 The purpose of chemical acid treatment is to dissolve precipitates of Calcium Carbonate, Magnesium Carbonate compounds, Iron Oxides and Manganese Oxides.

 General Cleaning:

 A highly efficient screen cleaning practice is washing the screens with pressured steam or clean water. Forms of Acids: Most of the freely available mineral acids are suitable for treatment (as long as they do not contain gypsum). The common ones are we use are listed below:

 - Hydrochloric acid (HCL) is the most corrosive acid to most
   metal piping material.
- Sulfuric acid (H2SO4)
- Phosphoric acid (H2P04)
- Nitric acid (HN03)
- Oxalic acid (H2C2O4)
- Citric acid (C6H8O7) 


- Hydrochloric acid is very effective for calcium carbonate scaling
- Phosphoric & Oxalic acids are effective for iron deposits
- Citric acid is effective for manganese oxide deposited
- Phosphoric & Nitric acids to remove organic compounds

Acid Concentration:

 It is recommended to dilute the acid to a concentration of about 1-2% where the acid is still effective (It is more cost effective and less dangerous)

 COP Instructions: 
1. Before inserting the screen into the diluted solution, make sure that all plastic parts, seals, rubber etc. are removed & disconnected from the screen and that the screen is cleaned from waste (Nylon is sensitive to acids).

 2. Prepare a suitable solution in tank (make sure that the tank material are compatible with this chemical)

 3. Soak the screen in the solution for 10 – 20 minutes (depending on the amount and kind of precipitates).

 4. Rinse the screen with a large amount of fresh water.

 5. Inspect the screen visually - if the screen is not cleaned continue with the process for an additional 10 – 20 minutes.

 6. Rinse the screen with a large amount of fresh water.

 Organic and Biofilm Removal:

 Implement the same procedure (COP instructions)

 Organic Compounds and Biofilm can be clean with Hypochlorite solution (NaOCl or CaOCl) at 0.1-0.5%, for about 5-15 minutes. If the screen is not cleaned, rinse with water and then continue with cleaning as above.

 It is possible also to use Phosphoric or Nitric acid.


 Acids and Hydrochloride are harmful to people and animals. Read and follow manufacturers and authorities recommended safety instructions carefully. USE ALL precautions and wear protective gear when working with acids to prevent contact with skin, eyes & mouth. (Acid may cause burns, blindness & death if swallowed).

B. Bio-Fouling Prevention

Sigma filters screen in 2ndry Treated Effluents of Municipal Wastewater.

Chlorination Options:

 Chlorine dosing during operation:  A dose of 5 –10 ppm chlorine for about half an hour per day or every few days (according to the filtration grade) is required. To make sure that the chlorine concentration and duration of dosing are sufficient, check for residual chlorine at the filter outlet (after 15 – 20 minutes). The system requires dosing equipment.

There are other ways to prevent biofouling on the filters, if none of
the above is found appropriate for your application.

Please contact your professional support contact person for further information.

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