Membrane Testing

Cleaning & Pretreatment Studies

Cleaning fouling deposits from membranes is often difficult to achieve, highly labour intensive and expensive. Cleaning trials at a lab scale are very useful and a cost effective way of evaluating cleaning chemicals, which have potential for use at full scale. Membrane Futures has the ability to test membrane cleaning techniques.

Ineffective pretreatment can lead to membrane failure. The addition of antiscalants, biocides and changes to the chemistry of feedwater are generally used to mitigate failure of membrane systems. Laboratory tests can be used to evaluate modified pretreatment options.

Bench Scale Cleaning

Bench scale cleaning trials are a quick and inexpensive way of screening commodity and/or proprietary chemical cleaners for both RO and MF processes. Generally jar test cleaning trials involve soaking and analysis of spent cleaning solutions and the membrane surface. The effectiveness of these basic cleaning trials is assessed by techniques such as ICP-AES, TOC and SEM-EDS analysis.

Full Module Cleaning Evaluation

Coupon cleaning tests can be used to assess the change in permeability of RO, UF and MF membranes before and after cleaning. Salt rejection of RO membranes is also assessed. Cleaning can be performed on full scale modules. This is a cost effective way to test new cleaning regimes and to trial proprietary chemical cleaners. These are generally used once cleaning has been optimised via coupon testing.

Antiscalant Studies

Membrane scale potential can be investigate on a laboratory scale. Feed water from a plant can be concentrated up using a small flat sheet RO/NF process. Once at the required concentration the system can be operated at elevated concentration for an extended period. During this time, changes in flux and permeate quality can be monitored with and without the use of antiscalant.

Membrane Selection and Evaluation Trials

Feedwater from a plant can be concentrated using flat sheet RO and NF processes. The system characteristics can be monitored throughout the concentration process to determine when there is a decline in membrane performance. An autopsy can then be performed on the membrane sample to assess the fouling produced. This is useful in providing proof of an indicative limit of recovery that may be expected by a plant and can be used to compare different types of membranes.

Integrity Testing

Both hollow fiber and flat sheet membranes are susceptible to failure associated with integrity problems. This failure can be a result of manufacturing defects or damaged caused as a result of operation. There are a variety of techniques that Membrane Futures can perform to measure integrity and assess the cause of integrity issues.

Visual Inspections

Visual inspection is useful for flat sheet, hollow fiber and cartridge filter membrane. It quickly identifies failed RO glue lines, RO delamination, damaged membrane surfaces, MF fiber damage and MF pot damage. Visual inspection is also useful in determine the distribution of fouling throughout a membrane module or filter material.

Bubble Test, PDT, Vacuum Testing and Dye Testing

In many cases, damaged membranes are not clearly visible. Techniques are available to quickly find non-visible damage. Bubble testing and dye testing is used to isolate the exact location(s) of integrity failure in hollow fiber and reverse osmosis modules. Pressure decay tests (PDT) quantify the extent of hollow fiber membrane damage. Vacuum testing is used to compare used and unused spiral wound modules to determine if modules have suffered damage or membrane degradation.

Microscopic Examination

Microscopy is useful to closely examine damaged membranes. Assessment of the type of surface damage (i.e. puncture, abrasion, cutting, degradation) can provide clues on the cause of the damage. More advanced microscopy such as scanning electron microscopy (SEM) when combined with energy dispersive spectroscopy (EDS) can be used to assess debris around the failed region and potentially link this to a cause of failure. EDS can also be used to assess if compounds have precipitated within the pores of membrane fiber(s).

Permeability Testing

Often membrane integrity is not related to physical rupture or damage that has occurred at a surface. Permeability testing is used on a laboratory scale to compare the performance of used and new membranes. In the case of hollow fiber membranes flux is measured at a constant feed pressure and changes in the flux provides an indication of damage at the fiber surface. For RO membranes, coupon testing is performed to determine specific flux and salt rejection.

Tensile and Bubble Point Testing - hollow fiber membranes

If membrane failure has occurred, tensile testing and bubble point testing can be used to assess the physical property of the membrane material. Chemical damage can change the strength of hollow fiber membrane material causing them to break. Also, precipitation of compounds in membrane fibers can cause the membrane properties to change.