As the way nature works, all solutes have a tendency to move from areas of higher concentration to areas of lower concentration. This is called diffusion, which reflects nature’s preference to strive for higher randomness (entropy). When two solutions of different concentration strength are separated by a semi-permeable membrane, the diffusion will be restricted in such a way that only those having dimensions smaller than the membrane openings (pores) can go through. This restrictive passage interrupts the diffusion process and results in a concentration gradient across the membrane.
Reverse osmosis (RO), microfiltration (MF), and ultrafiltration (UF) are the most common membrane-based separation processes in use for myriad of applications. They are all based on the same principle, of a solution with solids passing through a membrane and the solids being stopped by the membrane, with the clear liquid going through. The membrane size is what varies in each of these processes.
In effect, RO is exactly what the name implies, the reverse of the natural process of osmosis, a process by which a solvent of lower concentration solution will spontaneously pass through the membrane into a more concentrated solution until the two have equal concentrations. Retentate for RO will contain salts and nonpolar solvents of sizes greater than 0.8 nm to 1.5 nm.
Nanofiltration is a recent development and is a similar pressure-driven membrane-based separation process in which particles and dissolved molecules smaller than about 2 nm are rejected.
The next level of separation is with UF, a pressure-driven membrane-based separation process in which particles and dissolved macromolecules smaller than 0.1 micrometers and larger than about 2 nm are rejected. The retentate typically includes polymers, proteins, micelles, and colloidal particulate.
Then there is MF, a pressure-driven membrane-based separation process in which particles and dissolved macromolecules larger than 0.1 micrometers are rejected. The retentate typically includes macromolecules and particulates.
Top Industry Challenges
Use of these Membranes in Technology Sensitive Processes
UF, NF, and RO membranes are often used in highly sensitive applications in industries such as microelectronics, biopharmaceutical, and food and beverage. Due to the sensitive nature of these processes, it is very important that any technology used in these applications does not fail. In many cases, end-users require their supplier to have the products validated for a particular process in order to ensure quality control. Particularly the biopharmaceutical industry is very strict on requiring validation, as the industry is prescribed to do so by the Food and Drug Administration (FDA).
Demands for Better Quality Products
With the increasing interest in using membrane filtration follows greater demands for the capabilities of existing products. The industry is facing the need for membranes resistant to heat, pH, and chemicals (solvents, chlorine) and those that consume lesser energy low energy. Another characteristic they are looking at is an increase in the recovery of product. However, fulfilling such needs does not come without a price, which can be very substantial in terms of R&D costs. In addition, end-users are increasingly demanding lower product costs, which pressures internal budgets. It is very important membrane manufacturers continue to identify specific end-user needs, as the ability to fulfill them will play a vital role in the future success of membranes
Market Scenario and Industry Trends
The competitive landscape of the US membrane elements market has had a sea change in the last few years. A number of mergers and acquisitions have changed the market segments completely and added a new dimension to it.
Amongst the most significant acquisition activities is the formation of GE Infrastructure Water and Process Technology, which took place in early 2004 when BetzBearborn, Glegg Water Conditioning and Osmonics were acquired by GE Infrastructure respectively. Other international corporations such as Siemens have also been actively adding water business on its portfolio through the acquisition of US Filter’s water processing division in the fall of 2004. The effects of these acquisitions and consolidations on the market positions of companies involved are yet to be seen.
Conversely, industry leaders in the ultrafiltration market such as Zenon Environmental Inc. choose to focus its resources on its core strength, which is to develop and manufacture ultrafiltration technology and apply it to various applicable market segments. This sense of focus enables the company to build on its strength and maintain its leadership position in the market.
A recent Frost & Sullivan study on RO, UF and MF predicts that the United States membrane elements market to be around $350 million in 2006. Market demand will continue to be particularly strong in the municipal water and wastewater treatment, as well the biopharmaceutical sectors. In recent years, intensive competitive pressure among manufacturers and the maturing of certain technology segments has impeded revenue growth of the overall market. However, as a result of rapid adoption of membrane water treatment in the municipal market and a promising future of membrane based seawater desalination, this market is projected to grow at an average rate of 7.2 percent annually till 2010. By 2010, the market is expected to reach annual revenue of $520 million.
Technology Developments
Reverse Osmosis Recovery Process Developed for Ammonium Nitrate Condensates—US
The manufacture of ammonium nitrate, used in explosives and in fertilizers, produces a condensate byproduct that has too high a concentration of free ammonia and ammonium nitrate for direct discharge into wastewater, as the EPA regulates the level of both nitrate and the ammonium ion concentration allowed in wastewater. A practical solution is to add nitric acid to convert excess ammonia in the condensate into more ammonium nitrate, and concentrate this dilute ammonium nitrate stream with an evaporator.
The cost of evaporation has increased greatly in the last two years because of the increasing cost of energy. The costs of concentrating the dilute ammonium nitrate stream can be greatly reduced with an RO process developed at Minnesota, US based GE Osmonics. The RO process removes most of the water from the condensate, and sends a much smaller concentrate stream to the evaporator, which decreases the load to the existing evaporator. Thus, more condensate capacity can be added without extra capital invested in the evaporation process.
An initial study indicated that the condensate was a very pure ammonium nitrate stream with a low RO membrane fouling tendency. With this situation, it was possible to do a detailed analysis and develop a model of the separation process from testing in the laboratory. A team of researchers at GE Osmonics analyzed the recovery process with extensive laboratory tests with a spiral-wound membrane element, to determine the separation characteristics for successful RO treatment of the condensate using test conditions that ranged from 0.2 wt% to 5.2 wt% of ammonium nitrate feed at 25 degrees C to 53 degrees C and gauge pressures up to 62 bar (900 psi). The ammonium nitrate permeability increased with increasing ammonium nitrate concentration, while the water permeability was independent of the ammonium nitrate concentration. The plant is currently in pilot testing phase and will be in commercial operation soon.
Ultrafiltration System for Processing Oily Wastewater–US
Scientists at Massachusetts-based Sanborn Technologies have designed a new UF unit titled UFV 250/500T that is very suitable for unattended operation. Its ensemble features enable the processing of oily wastewater quite effectively.
This equipment contains a mop bucket station that receives the wastewater from plant equipment such as scrubbers, washers and so on. It also consists of a process tank of a 180-gallon capacity, which has level controls and a 50 gallon cleaning tank. These capacities are among the highest in the industry today. It also comes with transfer pumps and a separator that skims the oil off the surface. This profile fits perfectly into industries manufacturing coolants, floor washings, and vibratory finishing effluents.
The membrane is made from the latest advanced polymers and the entire parts together make up for an extremely economical design of the entire system. The product comes in various discharge capacities from 50 GPD to 6000 GPD. This UF system can be used as a stand alone unit or can be used in conjunction with other filtration equipment.
Important Technology Trends
The following highlights the important trends in the R & D of membrane separation processes
- Membrane Chemistry Refinement
- Improvement in Membrane Elements Design and Configuration to Enhance Treatment Efficiency
- Reduction in Operation Energy Requirement
- NF could be a possible replacement for RO
Conclusion
The market for RO is burgeoning, and this is very visible in large desalination projects. Growth is the result of improvements in pretreatment technologies, membrane modules, and greater energy efficiency that manufacturers have provided in recent years.
Ultrafiltration is being increasingly accepted as the preferred pretreatment technology for RO desalination of brackish water and seawater, but it faces competition from older technologies such as coagulation and sand filtration. In some applications, there is competition between aerobic and anaerobic treatment of some industrial wastewater. Traditional aerobic processing was developed based on high volumes of very dilute wastewater. In the textile industry, this makes the wastewater difficult to treat in aerobic facilities because the wastewater contains dyes and has a high organic load. Anaerobic treatment can better handle high organic loads and can decolorize dyes.
For wastewater treatment, membranes figure in all the currently recommended technologies where water is to be recycled or where the effluent has to meet high standards. Wastewaters vary depending on the source. Municipal wastewater is heavy in biomaterials and membrane bioreactors (MBRs) are being recommended and used in smaller facilities and for local water reuse. Industrial wastewaters are also being treated with membrane technologies that specifically address their particular pollutants, especially where water reuse is becoming a necessity as it is used in more and more industrial settings.
For more information on the Wastewater Industry please contact Trisha Bradley, Frost & Sullivan, Corporate Communications, [email protected].