Publised November 2009
Power Engineering Magazine
With the latest advances in technology application, the power industry may have more options than it did in the past for treating wastewater. It’s a great time to rethink the traditional approaches for water treatment or reuse and look at new, cost-effective alternatives.
If your current water treatment system works fine then you may be wondering why you should consider fixing something that isn’t broken. However, there can be challenges and issues with some conventional treatment options that have not yet surfaced, and if faced with a problem, could be very costly to fix. Newer treatment alternatives have begun to be applied with consideration of environmental and economic impact, thus providing a more sustainable water treatment scheme, which represents a better investment in the long run for the plant and plant neighbors.
But first, let’s take a closer look at how you define wastewater. Typically, power plant managers think of wastewater as two flows, the reject or the discharge streams of existing makeup water treatment or equipment. These could include blow downs of cooling towers, boilers and general process waste streams. However, water treatment can be much more inclusive as it relates to not just wastewater, but reuse of that water to extend the performance of equipment, reduce maintenance costs and even improve operational efficiency.
As the power industry broadens the spectrum of water treatment beyond just process water and wastewater – and to include water reuse – opportunities for cost and environmental savings multiply. New water treatment technologies offering a “total solutions” approach may help power plants to improve environmental compliance and sustainability by reducing overall their water consumption with efficient water balance plans. These advanced applications of technologies not only treat wastewater, but can even minimize waste in the first place. First let’s take a look at the common challenges, and conventional water treatment solutions commonly used to treat them.
Traditional Water Treatment Options Can Present Certain Challenges
An ever-present challenge for fossil fuel plants as well as some other power plants is the need to reduce their environmental footprint. Because the Environmental Protection Agency along with federal, state and local governments closely monitor power plants, it’s important to know and understand these regulations to determine the best wastewater treatment solution.
For example, air emissions from coal-fired plants are under increasingly tight scrutiny. Just recently, the federal government sued a Midwest company over pollution from six Chicago area coal-fired plants, giving them a decade to clean up or shut down. Environmental violations unique to the power plants extend beyond bursts of soot, but to wastewater contamination as well.
Another challenge inherent to the power industry is the existence of ash ponds (or evaporation ponds) which are open pits where wastewater collects. Problems can occur with overflowing during heavy rainfall or hazardous metals leaching out. Not only can this present a significant environmental hazard, but clean up costs can be very expensive. Also, this type of wastewater site is usually highly regulated by a local municipality that can charge substantial fines and taxes.
Traditionally, resin-based technologies, sometimes called deionizers or split stream de-alkalizers, have been popular for treating water in power plants. But this approach has its share of shortcomings. For one, its larger carbon footprint raises concern among today’s environmentally conscious power companies. That’s because plants still need to neutralize the waste that comes after regeneration, as well as neutralize the water because it may have high pH and low pH swings and has to be sent somewhere before it can be discharged.
Second, to get into the hydrogen and hydroxyl form, a company must have acid and caustic on site, which can lead to delivery and storage challenges. Local municipalities may regulate large delivery trucks with chemicals as well as storage facilities. Ultimately, the plant needs to determine the best storage facility for toxic materials and how to secure it safety to prevent worker and environmental hazards.
New Wastewater Treatment Applications: Membrane-based Technology
On the flipside, newer, safer and more environmentally friendly options for improving water treatment at power plants are emerging. These include membrane-based technologies such as reverse osmosis, ultra-filtration, micro-filtration and nano-filtration, which are now being used for waste minimization and to optimize water efficiencies at the plant level.
Membrane technologies have a smaller carbon footprint and are better for the environment. They also allow overall system recoveries to be higher than the recoveries normally experienced in the past when discussing pretreatment for makeup.
Primary Applications for Membranes
Membranes can effectively be applied to the brine application or reject streams of existing reverse osmosis (RO) systems in a plant. Thanks to today’s technological advancements, it is now possible to put brine RO on a reject stream and increase the amount of water that is sent back to the front end, instead of funneling all of it down the drain.
Membrane technologies can also be applied to the pre-treatment of challenging influent conditions, such as reuse process water that is high in Total Suspended Solids (TSS), which are solids in water that can be trapped by a filter. TSS can include a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes and sewage. High concentrations of TSS can cause many problems for stream health and aquatic life.
Ultra filtration (UF) membranes may allow operators access to difficult water supplies to address these stream health concerns. Additionally, UF or other membrane technologies can potentially reduce the carbon footprint when pre-treating an RO unit, which then could pre-treat a mixed bed deionizer. This is ideal for plants that are not able to remove the mixed bed deionizer on site, but can now reduce the amount of times it has to regenerate because the UF is feeding it better water.
For a greenfield site, a UF in front of an RO allows the plant to decrease the size of its RO. The largest impact appears to be the reduction of the operating costs. There is less water consumed, longer time between cleanings, and longer life on RO membranes. Also, the RO may be able to be smaller due to the ability to run water through at a faster rate due to the fact that the feed water from the UF to the RO unit is now ultra-filtered instead of resin-based.
In addition, membrane technologies can be applied to non-biological process streams, which may be able to be used and sent back to the plant for possible usage in cooling towers or boiler feed applications. Membranes are being applied to the effluent water going to cooling towers on slip streams, thus reducing the amount of chemicals being consumed.
Benefits of Using Newer Technologies
Less chemicals
Membrane technologies offer greener alternatives to disinfection. In the end, they allow power plants to take simple soft water, brine solution with electricity and a power supply and make a disinfectant that significantly reduces the need for chemicals. As compared to traditional disinfection options, membrane technologies help plants to minimize the amount of biocides that are needed in cooling towers. The RO water is less corrosive than standard makeup water which, in the end, saves money on equipment maintenance, repair and premature replacement.
Reuse and waste minimization
The major advantage is that membrane technologies can reuse and/or minimize waste by being able to utilize an existing stream and pump it back into other areas of a plant where they can use that water again, such as in cooling towers or boiler feed applications. This provides environmental benefits and cost efficiencies.
Tighter security
Global applications of electronics are emerging in the water treatment industry as a supplement, or even as an alternative, to traditional programmable logic controllers (PLCs). Alternative electronic controllers that are attached to softeners, carbons, multimedia, RO or the membrane lines of existing equipment can offer lower cost alternatives. It typically is a fraction of the cost of PLC technology and may offer several advantages for power companies.
For one, alternative electronic controllers can eliminate some land lines and still be able to generate the data at a lower cost as opposed to a very sophisticated PLC that might be used to just “watch” equipment work. Second, in a larger building where there is less supervision, alternative electronic controllers can essentially sit on a piece of equipment and send a signal directly to the PLC using RS-485 or cellular technology. This is an ideal solution for high security areas that need sophisticated monitoring to ensure 24/7 safety. Recent applications of the technology can detect when personnel go in and out of the control room. Thus providing additional security once not thought about in years past.
Special Considerations for Power Plants
While there are numerous benefits to these new water treatment and reuse technologies, they do present some special considerations that power plant managers must keep in mind.
To start, because the technology is new and may not have been applied before, a company may want to pilot the equipment and conduct feasibility studies before making an investment. For example, to evaluate an ash pond may require bringing in test equipment and running a six month test to validate and verify projections. While this isn’t a huge pitfall, power engineers do need to consider the amount of time it will take to conduct a thorough, technical water analysis. Only once this type of water analysis is completed can the plant identify the appropriate membrane technologies.
Another major factor that many wastewater treatment providers overlook is simply not taking a total solutions approach. However, newer technologies such as GBE have better telemetry and data gathering capabilities, so that plant managers are able to make accurate, concise decisions on whether to invest in new equipment or to enhance their existing equipment.
Based on this upfront water analysis and detailed data on the functionality of existing equipment, power plants are able to make improvements to how they’ve approached water issues in the past. Membrane technologies offer a promising solution and are becoming a preferred technology for water treatment – even for the toughest of challenges. As they grow in popularity and in range of applications, the cost for membranes will continue to go down. At the same time, more years of testing, data and experience with these membrane technologies will make their value go way up.
What Lies Ahead for Water Treatment Solutions
When it comes to water treatment technology, the future holds unlimited thinking outside the box that’s going to allow the power industry to have a more complete solution.
With new technologies such as membranes, plants can reduce the amount of chemicals used on a site and use their water more efficiently – all while saving space, costs and having less of a carbon footprint. Different varieties of membranes make it easier to treat very specific conditions. For example, ultra-filtration is an ideal option for influent wastewater treatment and reuse process water, whereas nano-filtration is a good choice for plants in geographic areas such as California and Florida that may have chloride discharge concerns. GBE is another technology advancement that enhances remote equipment monitoring, communication and security – providing valuable data that a PLC alone cannot, to ensure peak efficiency and avoid system failure.
As referenced earlier, a “total solutions” approach gives power plants only what they want and need to optimize water treatment and re-use. Following an initial analysis, power plants can benefit from a custom-engineered water treatment system that is pre-configured to match their specific requirements by combining electronic controls, RO and water softening technologies on a single global platform. By integrating all of these elements together, power companies get an end-to-end water treatment solution that allows them to mange all applications more efficiently and cost-effectively versus operating multiple pieces of equipment. The system’s flexible, containerized and mobile approach is also well suited for peaking plants in remote areas which require more robust materials and monitoring.
Even though newer technologies are being introduced every day in the marketplace, power companies still need to maintain existing technologies. But we are seeing more expertise in field service areas that did not exist 10 or 20 years ago, so such equipment can be more easily serviced, upgraded and expanded to address more advanced water treatment and reuse needs.
The options and benefits of water treatment for power plants if virtually endless. It does, however, require rethinking traditional approaches, performing more rigorous testing and a willingness to try new filtration technology and remote electronic monitoring. The upsides of environmental and cost savings, however, are well worth the shift in mindset as power companies position themselves well into the future.
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About the Author
Rod McNelly, Vice President, Commercial & Industrial, Culligan International – North America, is responsible for leading and growing the company’s industrial business which consists of large scale customized, engineered water treatment solutions. Mr. McNelly has over 20 years of industrial sales and management experience. He began his career with 3M and has worked for other major companies including Ionpure, USFilter and most recently Siemens Water Technology. Mr. McNelly has a Bachelor of Science degree in Environmental and Health Management from Indiana State University. Mr. McNelly can be reached at: rod.mcnelly@culligan.com.