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R.o. plants biofouling an overview


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An overview about the biofouling of Reverse Osmosis desalination Plants.

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R.o. plants biofouling an overview

  1. 1. José Luis Pérez Talavera VALORIZA AGUA
  2. 2. SUBJECTS  To detect false biofouling  Is there a link between biofouling and bacterial content?  Biofouling and bacterial stress  Plant shut down risk
  3. 3. FALSE BIOFOULING  Very frequent mistake among operators ,confounding inorganic with organic fouling.  Case study nº 1: Aluminium fouling  Case study nº 2: Iron fouling
  4. 4. Case study nº1: Aluminium  City water B.W.R.O. Plant with severe fouling problems . (Weekly C.I.P.)  All chemical companies and R.O. experts diagnosed as biofouling, recommending to switch to cellulose acetate membranes.  We discovered the aluminum fouling ,produced by a ph reduction from 8.5 to 6.5 (Just the minimum solubility point of aluminium).  Problem solved once ph was further reduced to 5.5
  5. 5. Case study nº1: Aluminium
  6. 6. Case study nº 2: Iron  Open intake S.W.R.O. Plant with severe fouling .  Based on bad biological quality of feed water.  We discovered the origin of the problem : A very high iron dosage of 20 p.p.m. as Cl3Fe  They determined the dosage according jar test.  Jar tests are not suitable for R.O. Plants.  Problem solved once the dosage was decreased to 0.5 p.p.m.
  7. 7. Case study nº 2: Iron • Up to year 2005 ------- 20 p.p.m. Cl3Fe C.I.P.S. ------------- 5 per year per skid • After year 2005 ------ 0,5 p.p.m. Cl3Fe C.I.P.S. ------------- 1 per year per skid
  8. 8. FALSE TOPIC: Link between severity of biofouling and bacterial content.
  9. 9. FALSE TOPIC: Link between severity of biofouling and bacterial content. PARAMETERS OPEN SEA INSIDE LAGOON Heterotrophic 22ºC 3,500 165,000 Heterotrophic 37ºC 1000 150,000 Total Enterobacterias 250 8,750 Anaerobic 2,750 7,000 Bacillus spp 2,000 100,000 Yeasts and molds 250 18,750
  10. 10. FALSE TOPIC: Link between severity of biofouling and bacterial content.  In spite of the fact of the big difference in the bacterial content between the lagoon and the open sea, the S.W.R.O. Plant performed very well.  C.I.P. only once a year or even longer.  Trick: No attack to the bacterias.
  11. 11. EPS-TEP and Biofouling  It has being determined that Exo Polymeric Substances (EPS), mainly Polysaccharides, including natural Transparent Exopolymer Particles (TEP), are responsible for the biofouling of the membranes. (R.O. and M.F./U.F.)  Bacterias, per se, are not responsible, unless have being forced to produce EPS.  Number of bacterias is not important.
  12. 12. EPS-TEP and Biofouling  Bacteria produce EPS when they are stressed by a big change in their environment.  The biggest the attack, the more the production of EPS  Oxidants are the biggest producers of EPS.  Ph change affects in a minor degree.
  13. 13. SEA SNOW (EPS)
  14. 14. CHLORINATION-DECHLORINATION  In the early times, membrane makers forced to operators, the use of chlorine.  Plants did not perform well.  C.I.P.s were very frequent, almost once a month.
  15. 15. CHLORINATION-DECHLORINATION  The questions we made were:  Why there in not biofouling in the sand of the beaches?  Why the big formation of biofilm after the injection of SBS?  Could be the chlorination the origin of the problem?
  16. 16. CHLORINATION-DECHLORINATION  CASE STUDY Nº 3  S.W.R.O. Plant (Open intake)  Heavy biofouling, required C.I.P. every month.
  18. 18. CHLORINATION-DECHLORINATION  In the eighties, we decided to eliminate the chlorination, in order to improve the operation.  The membrane maker was against and cancelled the warranty, but we went ahead.  The decision we took, was a success
  19. 19. CHLORINATION-DECHLORINATION • With (C-D) C.I.P.s ------------- 13 per year per skid • Without (C-D) C.I.P.s------------- 1 per year per skid
  20. 20. CHLORINATION-DECHLORINATION  CASE STUDY Nº 4  B.W.R.O. Plant fed with city water  Feed water is chlorinated
  21. 21. CHLORINATION-DECHLORINATION  Ultra pure water plant  Pre-treatment based on U.F. membranes.  Heavy biofouling film after the SBS injection point.  No way of solving the problem.
  22. 22. CHLORINATION-DECHLORINATION  The inspection of the pipe in the area of the SBS injection, showed a bright and clean surface before the injection point and a thick film of biofouling after it.  Plant continues changing membranes every 6 months.
  24. 24. PH CHANGE  Case study nº 5  SWRO Plant with acid addition to ph 7  CIP frequency was once every 10 – 11 months  After removing the acid, got a little improvement , switching to 11-12 months.
  25. 25. OPERATION RULES  If you do not bother the bacterias, they don’t hurt you  The less chemicals you add, the better operation you get.  All the Plants I have operated, have no chemicals addition or only anti scalants.
  26. 26. ANTI SCALANTS  Anti scalants are another source of fouling.  Blend of organic and biofouling obtained.  Phosphonates are the best, but not all the brands.  It’s necessary to perform pilots in order to choose the best one.  There are big differences among brands.  Acrilates and Maleates not recommended. 
  27. 27. SHUT DOWN CONSERVATION  Plant shutdown is a dangerous period.  Many ways of conservation are used  SBS solution as preserving method, is the most popular.  I found terrible effects sometimes, due to the formation of heavy film of anaerobic bacteria.
  28. 28. SHUT DOWN CONSERVATION Another method use a safe biocide as thiazoline. The method I use with a great result, is keeping a small flow of feed water running constantly or with short breaks.  Avoiding the stagnant water, no biofouling is formed.
  29. 29. SHUT DOWN CONSERVATION  This method has a lot of other benefits:  Fouling: avoiding its formation in sand and cartridge filters, as well as pipes.  Mechanical: keep high pressure pumps running. (No need of turning shaft by hand regularly).