Real World Studies Utilizing Membrane Technology for SDWA Compliance
By. Shannon P. Murphy
The world of water regulations and regulated water contaminants continues to change rapidly. In the next few years, public water systems will be impacted by several new water regulations that they will have to comply with. These changes are based on many factors, including research on the health implications of various waterborne compounds, better detection instrumentation and lab techniques as well as water issues in general becoming more common in household conversation.
This combination equates to greater demands being placed on the water utilities’ treatment abilities. Already in a cost-reduction mode, these utilities have difficult water treatment decisions and cost structures to consider, all of which are weighed against the responsibility to provide a continuous supply of high quality water to their customers. In turn, manufacturers of water treatment products work diligently to provide cost-efficient products that can be used in various applications and under different conditions.
Arsenic and the LT2 Rule
Two regulations that are coming down the pike in the very near future are the new arsenic regulated level of 10.0 ppb (parts per billion) and the Long Term 2 Enhanced Surface Water Treatment Rule (LT2).
The allowable arsenic level is being reduced through this legislation from 50.0 ppb to 10.0 ppb effective January 2006, which affects small water systems across the United States. LT2, scheduled for completion in the fall of this year, aims to reduce disease incidence associated with Cryptosporidium and other pathogenic microorganisms in drinking water. LT2 will specifically target the addition of Cryptosporidium and other microbial protection treatment requirements to higher-risk systems while also considering the risks involved in the formation of disinfection byproducts (DBPs). These DBP requirements are important to consider as the U.S. Environmental Protection Agency (EPA) is also developing the Stage 2 Disinfection Byproducts Rule, which will contain more stringent standards for DBPs. Communities affected by the LT2 rule will need to enhance their water treatment operations to provide potentially up to 3 log (99.9 percent) reduction of Cryptosporidium. Additional information about the LT2 rule can be found on the EPA’s website (http://www.epa.gov/safewater/lt2/index.html).
Assurance in the commercial/industrial water treatment sector
For water utilities and other industrial facilities, there are many options to choose from when seeking solutions to water treatment challenges. However, selecting the one that will consistently provide quality water within specific water parameters, yet being mindful of the implications these future regulations, is not easy.
Unlike the point of entry (POE) and point of use (POU) industry where products can demonstrate the ability to remove contaminants from the water as tested under the NSF/ANSI group of water filtration standards, larger commercial and industrial units have no similar group of standards.
Based upon the need for equipment buyers, utilities and regulatory agencies to have performance data on treatment technologies, the EPA’s Office of Research and Development created the Environmental Technology Verification (ETV) program. This ETV program provides independent performance evaluations of drinking water technologies to provide confidence in products’ ability to treat water. It focuses on water treatment technologies that benefit small communities seeking compliance with the Safe Drinking Water Act.
Effectiveness of arsenic removal: an ETV project study
Watts Premier, in conjunction with MWH Consulting and NSF International, recently completed an arsenic reduction study in Thermal, Calif. The study was initiated in order to provide real-world results on Watts Premier’s M-Series of commercial and industrial RO units for removal of arsenic from drinking water. Associated ease of operation and other O&M costs were also to be evaluated as part of the objectives for the study.
Installation of the M-15000 RO system was completed within one day. As the entire system is mounted on a compact frame, the unit was able to be transported directly to the well head site via pickup truck. Once installed, the system was conditioned for one day, followed by a quick performance test, which included on-site arsenic and TDS reduction evaluation.
Through the work that Watts Premier has been conducting with small communities in the firm’s POU program for arsenic compliance, the ITS Arsenic Quick II test kit was previously verified through comparative testing as representative of actual arsenic levels in water.
Over the 31-day test, the RO unit was continuously run in order to both accelerate the testing timeframe and to provide worst-case test data for the system. Minimal pretreatment was provided to the RO unit for the duration of the test, further providing worst case testing for arsenic reduction during the life of the evaluation.
Table 1 provides a summary of the results obtained during the life of the testing. The results show that the unit was capable of reducing over 95 percent of the total arsenic in the water over the life of the ETV testing. In actuality reduction capabilities of RO to remove arsenic from water are even higher, as other field tests with significantly higher levels of influent total arsenic have produced over 98 percent reduction.
This is of significant importance for communities looking for arsenic reduction solutions as it provides a means for partial stream treatment. In short, a facility is capable of blending treated and non-treated water in order to come to a combined effluent concentration under 10 ppb. To determine the amount of treated water that needs to be processed, facility operators will need to factor in current arsenic levels, desired arsenic levels and the total system flow. Partial stream treatment can be considered in all cases. In the long run, it will save considerable time and money in operation, maintenance and replacement parts for the RO units.
Also significant in the test results was the RO system’s capability of reducing arsenite, or arsenic III. (Author’s note: I have been to numerous presentations where comments have been made regarding membrane technology capability of removing arsenate (arsenic V) but that it is not capable of reducing arsenite.) It was observed that overall the RO membranes were able to reduce 68 percent of the incoming arsenite; at one sample point specifically, a reduction of over 93 percent was achieved. Other studies conducted by EPA have shown over 75 percent reduction capabilities of arsenite by reverse osmosis.
A staged maintenance check was scheduled within the project in order to determine the time requirements for such a procedure, which consisted of replacing the prefilters on the RO unit and changing out one third of the RO membranes. This process was completed within 45 minutes from shutdown to restart.
Electrical requirements were also tracked during this test. On average, 33 kiloWatt hours (kWh) were used per day of continuous operation. In Thermal, Calif., the cost for electricity was 0.09 cents per kWh or $2.97 per day of operation. In the field, users can expect this cost to be even lower as typically these units are not in operation 24/7 as they were during the ETV test. They are more commonly used to fill either an affiliated pressure or atmosphere tank and then shut down.
This test was conducted in a condensed time frame and as such was not equipped with any pretreatment. Typically, for permanent installations there are pretreatment considerations that need to be addressed as water quality can have effects on membrane operation. One additional consideration is water temperature, as lower water temperatures will decrease the flux of the RO system. In order to compensate for this fact, it is important to size the RO unit for the coldest temperatures that will occur in use. This can easily be done through the addition of membranes.
Prevention of precipitation of organics and metals on the membrane can easily be addressed through the addition of an antiscalant prior to the RO. There are a number of antiscalants on the market today which have proven exceptional at prolonging the life of RO membranes in the field.
One product technology solving multiple needs
Membrane technology (and specifically in this article reverse osmosis) is the technology that has a proven track record at being able to provide pure water for many different applications. The simplicity of the RO process allows for convenient packaged water treatment systems that can easily be custom fitted for varying water demands and raw water quality. Packaged and customized POE and well head RO units are currently being utilized for water treatment in schools, RV parks, mobile home parks, water stores, hospitals and restaurants.
Other non-drinking water applications are benefiting from the advantages of utilizing reverse osmosis in their business. One example of this is the machining industry. Many machining facilities continuously have problems with the coolant cutting oils fouling with bacteria, excessive TDS levels and other suspended solids degrading the coolant. Through the utilization of RO technology in the processing of these cutting coolants, companies have been able to increase useable coolant life, thereby reducing both coolant replacement costs and the O&M costs associated with maintaining the tanks and the coolant.
With continued new regulations like the arsenic rule, LT2 and the upcoming tighter regulations on DBPs, membrane technology is perfectly positioned to play a major role in the growing water treatment industry. Verification testing is a means for manufacturers to show confidence in their products’ ability to reduce these contaminants from drinking water while providing reassurance to the purchasers, regulators and public water systems that a product they are purchasing will meet the performance requirement(s) they seek.
About the author
Shannon P. Murphy is vice president of Municipal Water Programs for Watts Premier Inc., a division of Watts Water Technologies, of North Andover, Mass. Murphy has a bachelor’s degree from Concordia University in Montreal, Canada, in biology and master’s degree from Wayne State University in Detroit. Murphy has also been a member of the WC&P Technical Review Committee since 2004. He can be reached at MURPHYSP@wattsind.com