There are several benefits of membrane systems, including:
- Better removal of contaminants
- Higher efficiency
- Membrane integrity assurance
- Variable filtration ratings
- Smaller footprint
- Consistent operation
- Environment friendly
With all these benefits, the question is “has membrane water treatment become a treatment technology of choice?” Depending on the quality of the water supply, in many cases the answer is a definite, yes!
Membranes for surface water treatment
For low turbidity, high quality surface water supplies, membranes are a great option to ensure pathogens, such as Cryptosporidium and Giardia Cysts, are captured and removed. The multitude of membrane materials and pore sizes (microfiltration, ultrafiltration, nanofiltration) available have opened the possibility to use membranes on a wide variety of surface water qualities.
Membranes for groundwater treatment
Where membranes have come into their own in the past five years is in the treatment of marginal quality groundwater with high level of inorganics (iron and manganese) or low levels of natural organic materials (NOM). Permitting of a new groundwater source has become a long and arduous process in many states. Therefore, groundwater sources that may have been taken off-line because of the complexity of treatment required, are being considered for reactivation. Robust membranes, originally designed for wastewater applications, are being used in conjunction with coagulants and oxidants to remove NOM, iron and manganese.
The “Holy Grail” of water treatment —desalinating seawater
Over 50 years ago, John Kennedy said “if we could ever competitively, at a cheap rate, get fresh water from saltwater … this would be in the long range interests of humanity and would really dwarf other scientific accomplishment.” Today, membranes are being used to desalinate seawater. Although the economics of desalination are cost prohibitive for seawater in New England, several facilities do desalinate brackish water.
The challenges with membranes to date have been the need for high levels of pretreatment and the high pressures needed to drive the treatment process. Reverse Osmosis (RO) uses a semipermeable membrane to separate dissolved ions (salt) from water molecules. Feed pressures are up to 1200 psi and recovery rates for saltwater are only 30-50%.These pressures and recovery rates make RO a non-viable solution for most public water systems. A new water treatment technology called Forward Osmosis (FO) is gaining some momentum. This process is similar to the RO process with the key difference being the significantly lower feed pressures and higher recovery rates. Companies are in the process of scaling up FO for larger scale projects.
Is FO the future of desalinating? Only time will tell, but one thing is certain, membranes are here to stay and future developments will be worth following.