NOTES FROM DIFFERENT SOURCES AND PERSONAL
Performance of some FILMTEC membranes | SW30HR | BW30 | XLE | NF270 |
Feed pressure (psi) | 370 | 150 | 70 | 50 |
Feed pressure (bar) | 25 | 10 | 5 | 3.5 |
Rejection (%) | ||||
Sodium chloride NaCl | 99.7 | 99.4 | 98.6 | 80 |
Calcium chloride CaCl2 | 99.8 | 99.4 | 98.8 | 50 |
Magnesium sulfate MgSO4 | 99.9 | 99.7 | 99.2 | 99.3 |
At 18 GFD (30 l/m2h), 2,000 mg/l solute concentration, 25°C, pH 7-8, 10% recovery per 40-inch element.
- Performance des membranes:
- As a general rule, membranes with a high water permeability (low feed pressure) also havea higher salt permeability compared to membranes with lower water permeability. The permeability of solutes decreases (the rejection increases) with an increase in the:
- degree of dissociation: weak acids, for example lactic acid, are rejected much better at higher pH when the dissociation is high
- ionic charge: e.g. divalent ions are better rejected than monovalent ions
- molecular weight: higher molecular weight species are better rejected
- nonpolarity: less polar substances are rejected better
- degree of hydration:highly hydrated species, e.g. chloride, are better rejected than less hydrated ones, e.g. nitratedegree of molecular branching: e.g. iso-propanol is better rejected than n-propanol. ( )
Salt concentration — raw concentration (expected in permeate) - BW ——5000 (50)
- SW ——3000 – 15000 (150)
- SWHR -10000 – 50000 (500)
- TW—— 5000 (50)
- NF —— 1000 (500)
- TDS que les membranes de Filmtec peuvent supporter:
Molecular weight cut-off ( from Filmtec)
The RO membrane acts as a barrier to all dissolved salts and inorganic molecules, as well as organic molecules with a molecular weight greater than approximately 100. Rejection of dissolved salts is typically 95% to greater than 99%.
Nanofiltration (NF) : Organic molecules with molecular weights greater than 200-400 are rejected. Also, dissolved salts are rejected in the range of 20-98%. Salts which have monovalent anions (e.g. sodium chloride or calcium chloride) have rejections of 20-80%, whereas salts with divalent anions (e.g. magnesium sulfate) have higher rejections of 90-98%.
We don’t have specific MWCO information for our different NF products, but perhaps the following will give you some guidance:
FILMTEC NF90 Elements: Removal of TOC, nitrates, pesticides, herbicides, hardness, iron, salts.
>97% MgSO4 rejection 85 – 95% NaCl rejection
FILMTEC NF270 Elements: Removal of color, TOC, medium to low calcium passage, high salt passage.
>97% MgSO4 rejection 40-60% CaCl2 rejection
FILMTEC NF200 Elements: Removal of TOC, atrazine, medium calcium passage, medium to high salt passage.
97% MgSO4 rejection 35 – 50% CaCl2 rejection
Membrane systems arrays are designed with 0.5 MGal or more increments. The full size of an array is limited to 2,5 MGal
Membrane systems are designed in 1, 2 or 3 stages maximum.
In each stage a vessel contains currently 4 to 6 until 8 maximum membranes
Recovery rates are following (when no concentrate recycled) :
1 stage: 50%
2 stages: 50% – 75%
3 stages: 75%
Recycling concentrate allows to increase recovery.
These values are not effective when there is just 1 membrane. The recovery of 1 membrane is between 15 to 20%.
In one stage, recovery increases when number of membranes are increased.
- Membranes cleaning
Formulations for MF membrane cleaning (surface water treatment)
Acid cleaning
- 1) 2% acide citrique
- 2) 0,05% HCl + 0,15% EDTA
- 3) 0,05% H2SO4 + 0,15% EDTA
The 3rd formulation was more effective
Base
- 1) 2% NaOH + 1% Surfactant
- 2) 2% NaOH + 0,5% H2O2 + 0,15% EDTA
The 2nd formulation was more effective
Have a look on Elimelech papers on NF270 and NF90 cleaning .
Membrane fouling Elimelech
- Formulation: 1 nM EDTA / 1% SDS (ou 10 mM/L et plus / pH 11. seems more effective than EDTA + NaOH for DOC .
- pH 11 is reached by adding NaOH. SDS activity is not related to pH, but EDTA need acidic condition. EDTA in totally unprotonated just arount pH 11. That situation is necessary for reaction with divalent cations that create bonds between membrane and organic material.
- pH EDTA solution: around 4.8.
- pH SDS solution: around 9.
- SDS: Sodium dodecyl sulfate (SDS or NaDS) (CH3(CH2)11OSO3Na) (FW 288.38), also known as sodium lauryl sulfate (SLS), is an ionic surfactant
- RO membranes cleaning formulations:
- 0.15% (w) Na percarbonate
- 0.12–0.13% (w) NaDBS
- pH 11.7–11.9(w/NaOH)
- Sodium dodecylbenzenesulfonate (NaDBS),
- Sodium Percarbonate: 2Na2CO3
- 3H2O2
- Molecular formula : 2Na2CO3 3H2O2
- Molecular Weight: 314
- Appearance : White granule, odorless
- Bulk Density : 0.92~1.08(g/ml)
- Active Oxygen(AO) : 12% or more
- PH(1% solution) PH(1% aq.soln.) : 10~11
- Solubility(g/100g water) : 12 (5oC); 14 (20oC); 18.5 (40oC)
- Other formulations
-
Cleaning solution Foulants Metal Inorganic Biological Organics Silica Results at sparsely soluble inorganic salts oxides colloids(silt) matter Dhekelia D.P. 2.5% (w) citric acid pH 4.0 (w/NH4OH) Effective Effective Effective Not effective 0.5–0.75% (w) P3Ultrasil 53 Effective Not effective pH 10.8-11.0(w/NaOH) 0.2–0.25% Na2S2O4 Effective Preferred Some effect on RO1–4 NaOCl, 140 g/m³ active Cl2 Effective Effective Not effective PH 11.5–12.0 (w/NaOH) 1.0% (W) NaHMP Effective Effective Effective Not effective 0.15% (w) Na percarbonate Preferred Effective Effective Effective Very effective 0.12–0.13% (w) NaDBS pH 11.7–11.9(w/NaOH) 0.5–1.0% (w) Permaclean 67 Effective Effective Not effective pH 10.5–11.0 (w/NaOH) Sodium carbonate Not effective High pH–NaOH PH 11.7 Prefitted Very little effect
NF270 90 pore size, Elimelech Retention of Emerging Water and Wastewater, imstec054.pdf
- D. Nghiem1,2,a#, A. I. Schäfer2,b, M. Elimelech1,c
http://www.membrane.unsw.edu.au/imstec03/content/papers/NHIA/imstec054.pdf
Theretical membrane pore size :
NF270: 0,34 nm/ 0,42 nm
NF90: 0,29 nm/ 0,34 nm
Removal NF270 / NF90
Na 44% / 88%
Ca: 53% / 99%
NaCl (3g/L):40% / 85%
pH of polyetersulfone membrane isoelectric point: 2.9
isoelectric pH of the clean membrane which is around pH 2.9
NF270 and NF90 membranes are negatively charged at pH superior to 3.