R.O Biofouling Control: Case Histories Describing successful Transitioning from Oxidising to NonOxidising MicrobicidesP.J. Allison, A.Maartens, E.Rava, S.Steenekamp:Buckman Laboratories M.P.Augustyn, P.G.Boshoff :- Sasol Synfuels P.J.Scurr:- Columbus Stainless
Introduction Biofouling due to microbial growth in
R.O. Systems can be linked to 56 to 74% of typical costs of membrane operation (Kelle Zieher and Phillip,2000) Traditionally chlorine-based biocides have been used to control microbial fouling in the approach flow areas.
Susceptibility of R.O.Membranes to Chlorine attack Cellulose acetate membranes are
resistant to chlorine whereas Thin Film Composite (TFC) Polyamide membranes are highly sensitive to oxidative degradation De-chlorination using a reductive chemical such as sodium bisulphite is required prior to PA membranes.
Advantages of Chlorination Chlorine is relatively cheap, kills
microbes rapidly, and has a broad spectrum of control It can be applied in the form of gaseous chlorine or liquid sodium hypochlorite solutions
Disadvantages of Chlorination Some resistant genera of bacteria such
as Brevundimonas and Pseudomonas are difficult to kill with low concentrations of chlorine Exposure of microorganisms to sublethal dosages of chlorine induces production of excessive amounts of extracellular polymeric substances (EPS) as a defense mechanism - leading to severe slime formation.
Disadvantages of Chlorine Corrosivity of chlorine to metals. Humic acids are broken down into smaller
organic fragments ,which serve as a nutrient source in downstream chlorine - free areas of the feedwater stream. Over-dosage of bisulphite can aggravate deposition .
Refinery Case Study A large R.O. facility at a refinery in SA was
experiencing major problems with biofouling in the T.R.O. plant that provides permeate as feedwater to a downstream polyamide spiral wound (S.R.O.) facility producing high quality boiler feedwater. Chlorination ,followed by de-chlorination was
being practised to control TRO feedwater microbiological contaminants.
Refinery Case Study Problems experienced Microbiological growth (including algae,
bacteria and fungi) was prevalent in the de-chlorinated feedwater to the R.O. plant R.O.membrane life was significantly lower than expected. CIP costs were elevated Operational stability was impaired due to bisulphite deposition and biofouling.
Refinery R.O. Facility Process Flow DiagramCAE Ponds
Ash Production Ash Dams
640 m3/h
920 m3/h 524 m3/h
365 m3/h
TRO 1
TRO 2
Falling Film Evaporators
275 m3/h
SRO 345 m3/h
387 m3/h
310 m3/h
Boiler Feed Water
Raw Water Reservoir
Feedwater to T.R.O. Plants
Clear ash effluent Salty aqueous solution Not hazardous in calcium, sulphate, sodium
Tubular Reverse Osmosis (T.R.O) Plant 1
Tubular Reverse Osmosis 1 Commissioned in 1995 Capacity of plant = 14 Ml/d Design recovery = 45 %
11 modular units 960 TRO modules HP pumps, feed flow control, flow reversal system,
recovery control system and chemical cleaning change over system
T.R.O. Plant 2
Commissioned in 2002 Capacity of plant = 22 Ml/d Design recovery = 43 % 2 process lines 8 modular units 480 TRO modules HP pumps, feed flow control, flow reversal system, recovery control system and chemical cleaning change over system
Filter section:
Self cleaning filters Filter flushing Antiscalant addition Biocide shock facilities Intermediate buffering Heating of water
Tubular Reverse Osmosis Plant 2
SRO Plant
S.R.O. Plant Commissioned in 1997 Capacity of plant = 7.4 Ml/d product
Design recovery = 90 % 3 SRO trains with polyamide membranes 3 Stages of concentration 10:5:3 configuration Single permeate stream
Final brine = concentrate from the last stage
Microbiological Monitoring Conducted Heterotrophic Plate Counts ( HPCs) Spore Former Counts
Bacterial species identifications Microscopic analysis of biofilm and
deposits Biocide kill studies Minimum Inhibitory Concentration Tests
log cfu/ml 7.00 6.50 6.00 5.50 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00
Heterotrophic / Total Viable Plate Count
Train 1 Train 2 Date Train 3 67 Permeate
Unit 68 SRO Feed to first stage Total Viable Count
01-Dec-02 08-Dec-02 15-Dec-02 22-Dec-02 29-Dec-02 05-Jan-03 12-Jan-03 19-Jan-03 26-Jan-03 02-Feb-03 09-Feb-03 16-Feb-03 23-Feb-03 02-Mar-03 09-Mar-03 16-Mar-03 23-Mar-03 30-Mar-03 06-Apr-03 13-Apr-03 20-Apr-03 27-Apr-03 04-May-03 11-May-03 18-May-03 25-May-03 01-Jun-03 08-Jun-03 15-Jun-03 22-Jun-03 29-Jun-03 06-Jul-03 13-Jul-03 7.00 6.50 6.00 5.50 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 log cfu/ml
log cfu/ml 0.00 01-Dec-02 08-Dec-02 15-Dec-02 22-Dec-02 29-Dec-02 05-Jan-03 12-Jan-03 19-Jan-03 26-Jan-03 02-Feb-03 09-Feb-03 16-Feb-03 23-Feb-03 02-Mar-03 09-Mar-03 16-Mar-03 Date 23-Mar-03 30-Mar-03 06-Apr-03 13-Apr-03 20-Apr-03 27-Apr-03 04-May-03 11-May-03 18-May-03 25-May-03 01-Jun-03 08-Jun-03 15-Jun-03 22-Jun-03 29-Jun-03 06-Jul-03 13-Jul-03 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 67 Permeate Train 3 Train 2 Train 1 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00
Unit 68 SRO
Pseudomonas Plate CountsFeed to first stagePseudomonas
log cfu/ml
ATP MeasurementAdenosine Triphosphate = Microbial energy storing compound indicates viable organisms
Sample Point
ATP R.L.U.
HPC CFU/ml R2A Agar 3,0 x 103
U68 0.014 permeate U69 0.016 permeate
2,0 x104
Microbiological Population Study
AnalysisAerobes Pseudomonas Aeromonas Moulds Slime-formers H2S producers Anaerobes Spore formers E. coli Coliforms Acid producers
Culture mediumR2A Pseudomonas agar Aeromonas agar Malt extract agar Sabouraud dextrose agar Kligler Iron agar Plate count agar Plate count agar + heat Petrifilm Petrifilm Dextrose Tryptone agar
Result (cfu/g)5 x 103 2 x 102 None detected 1 x 101 5 x 102 None detected None detected 1 x 101 None detected None detected None detected
Bacterial Identifications Pseudomonas
Widespread in the environment ,most predominant encapsulated bacterium in many industrial water systems and in medical biofilmsSpore-forming, slime-forming bacteria that produce large quantities of EPS(extracellular polymeric substances) Gram negative bacterium that produces capsular material
Bacillus
Aeromonas
Microscopy of slime deposits
Fungal hyphae
Scanning Electron Micrograph showing bacterial slime (12,000X mag)
Slime AnalysisSRO SLIME: TRAIN 2 PHASE 1 SUMMARY The dominant species were: Slime-forming bacteria : Burkholderia cepacia, Pseudomonas putida, Spore-forming ,slime former Bacillus spp Mould : Verticillium spp.
R.O. Reference for use of NonOxidising Biocides(Motorola ,Austin Texas, USA) Plant manufacturing semi-conductor
devices ,requiring high purity water Make up water was filtered ,treated and purified municipal water + recycled second pass R.O. reject water injected with hypochlorite ,followed by bisulphite Five double pass R.O. units each having a 7-3-1 cellulose acetate array, followed by a 4 -2 thin film composite array
High Costs associated with Biofouling CIP Cleaning every 3 weeks High Consumables (filters) expenditure
Shock treatments of hypo Membrane replacement before expected High labour costs for R.O. cleans
Introduction of Non Oxidising Biocide at Motorola Added at a concentration of 15 mg/l into
R.O feed stream ,with chlorine present , followed by dechlor step . Biocide gave protection in de-chlorinated areas. TOC analyses confirmed that the biocide molecule was excluded and did not carry through in the TFC permeate
International References Motorola, Austin Texas Temple Inland Corporation Amoco Refinery Texas Utilities
Introduction of Non Oxidising Biocides to S.A Refinery Two alternating non oxidising biocides
(with membrane compatibility approval) were recommended to ensure broad spectrum control, and prevent bacterial resistance. Laboratory Biocide Kill studies were conducted on R.O. feedwater to assess efficacy of each biocide against indigent microflora
Results of Kill studyMinimum Inhibitory Concentration 110 100 90 80% KILL
70 60 50 40 30 20 10 Control 5 ppm 10 ppm 15 ppm 20 ppm 25 ppm Dosages 35 ppm 50 ppm 100 ppm
BL 6057 BL 6042 BL 1421 (New)
Implementation of Biocide Treatment Programme 50 mg/l of Biocide A dosed five days per
week Supplemented with 35 mg/l of Biocide B dosed two days per week Subsequently, dosage was optimised to
25 mg/l and 40 mg/l respectively
Results at Refinery R.O. Facility Improved cleanliness in feedwater
stream Reduction in biofouling ,therefore reduced need for CIP Maintained R.O. Pressures No negative impact on salt passage Extended membrane life before replacement
South African Steel Plant Case History Chlorination was used to control algal and
bacterial growth in the feedwater to a TRO facility that was used to treat effluent water from a stainless steel production facility Excessive blinding of the pre-filtration system and poor operational stability prompted a request for a plant microbiological audit and recommendation for a non oxidising biocide
Visit to Refinery Plant personnel from the Steel plant made a
visit to the refinery to inspect the R.O. application described in the preceding Case Study . Non oxidising biocide dosage was initiated in the R.O. feedwater using an automated dosing pump. Algae contamination in the dams was treated by application of an algaecide A Coagulant was added to precipitate suspended solids and reduce the SDI.
Recommendation for Non Oxidisng Programme Automated dosing station
Bunded areas for spill containment Bulk storage tanks with offloading facilities Timer controlled Automated flow and valve control Computerised dosing control Frequency of dosing
2 hours every 24 hours Biocide Non oxidising
Process Flow DiagramBiocide Flocculant Sandfilters Cartridge Filters (5 and 1 micron)
R.O. 1
Dam
Dam
R.O. 2
Onsite Monitoring Microbiological Tests
Total chlorophyll a ( Algae) Heterotrophic Plate Counts ATP Adenosine Tri-phosphate (in R.L.U.- Relative Light Units)pH Feedwater turbidity (NTU) ; SDI ; suspended solids PO4 NO3 Cr
Chemical Tests
Microbiological Monitoring ResultsSample HPC cfu/ml 4 X 104 Pseudomonas cfu/ml 6 X 103 ATP ( R.L.U.)
Pond 2
5.049
Pond 2B
5 X 103
3 x 101
1.877
Pond 3B Dam 3C RO 2 SF RO 2 CF
1 X 103 2 X 103 1 X 103 2 X 104
1 x 101 2 x 101 < 10