Membranes are used to purify drinking water, desalinate seawater and brackish groundwater, purify proteins, enzymes and bio-molecules, concentrate fruit juices, clarify and disinfect beer, wine and spirits, treat municipal and industrial wastewaters for safe discharge or beneficial reuse, and produce high-purity water for boiler feed, power generation and high-tech manufacturing.
Membrane filtration of non-traditional waters is the key to a sustainable water future, but water treatment solutions based on conventional membrane materials and controls are ineffective, unreliable and/or too expensive.
What can membranes do?
How do membranes work?
Membranes offer a physical separation barrier with pores that range in size from micrometers through nanometers to Angstroms; hence, membranes offer the ability to separate large particles from small particles, large molecules from small molecules, metals and mineral ions from water and all of the above.
The key to success in deploying membrane technology is to select a membrane with a pore size small enough to achieve the desired separation, but as large as possible to minimize the energy demand (and operating cost) of the separation process. Also, it is important that a membrane does not encounter substances it was not designed to separate.
For example, RO membranes are the “tightest” or most selective water filtration membrane technology designed to remove salt ions from water; however, if RO membranes encounter bacteria, oil emulsions or colloidal materials they foul up very quickly, lose water production and require the system to be shutdown to enable chemical cleaning.
Frequent shutdowns and cleanings damage membranes and reduce their useful life. Therefore, if you have a challenging wastewater that ultimately requires RO treatment, UF membranes may be used in front of RO to remove the fouling substances. The increased capital expense to add the UF pre-treatment is often more than paid for by the operational efficiency gained by minimizing fouling, down-time, cleaning chemical consumption and membrane replacement.
TECHNICAL PAPERS & CASE STUDIES
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What can membranes replace?
In water and wastewater treatment, MF and UF membranes are used in place of sedimentation and granular media filtration, which require large land-areas and chemical pre-treatment (coagulation/flocculation). Since the early 1990s, MF and UF membranes gained rapid acceptance and are now considered mainstream technology for removing suspended solids including bacteria, protozoa, clay particles, viruses, proteins and macromolecules. Nano-filtration and reverse osmosis technologies have replaced chemical softening, ion exchange, activated carbon and thermal processes for desalination and advanced water purification.
In industrial process separations, NF/RO technologies have largely replaced phase separations (distillation, extraction, etc.) and MF/UF have replaced conventional media filtration technologies. In either case, membranes typically offer higher selectivity, higher yield (less waste), lower energy demand and lower total cost of separation. Membrane materials and processes have been developed to selectively separate azotropic, racemic and chiral mixtures through combinations of solute-membrane affinity and the size of membrane pores. Membranes are used for laboratory analytical separations as well as product concentration, purification and sterilization in biotech, pharmaceutical, food and beverage and dairy industries.
What are the benefits of membrane technology?
In any application, once the influent and effluent compositions are known (or defined), a membrane can be selected to meet practically any separation need. Purified or concentrated product recoveries often exceed 98%. Membrane systems are generally more automated and smaller footprint (50-70% less space) than other separation processes. Automation allows (1) less operator attention, and automated alarms when attention is required and (2) in-place testing to quickly confirm that the membrane is not breached. Membranes separations take less energy than phase separations and last much longer than conventional media filtration technologies so that the total cost of separation is reduced. Some membranes have a useful life expectancy over 10 years.
How Water Planet overcomes the traditional limitations of membrane filtration.
Membrane filtration offers an absolute barrier to contaminants, which is a step-change in water treatment performance over conventional technologies. The ‘Achilles heel’ of membrane technology is that the contaminants being removed by a filtration membrane rapidly clog or “foul” its pores. Hence, fouling is inevitable.
Fouling reduces the sustainable water flux, net water recovery and process uptime while increasing footprint, membrane area, energy-demand, cleaning frequency, process downtime, wasted water and membrane replacement. Fouling fundamentally drives the cost of membrane filtration.
Fouling limits membrane technology. What is required to combat membrane fouling?
- Robust, easy to clean membranes
- Intelligent, self-adaptive controls
- Optimized process integration
Water Planet’s proprietary PolyCera® membranes were developed to extend the range of polymeric membrane filtration to the most challenging applications.