An Analysis of Nanofiltration Treatment Applications on Recycled and Potable Water Supplies
Project ID: 400
Principal Investigator: Katherine Guerra
Research Topic: Desalination and Water Treatment
Priority Area Assignments: 2011 (Advanced Water Treatment)
Funded Fiscal Years: 2011
Recycled water can contain higher levels of salinity than may be practical for certain applications. Feed water for cooling towers and energy generation facilities are two such applications. Increased scaling and corrosion from using water with a high salt content will shorten the life and increase the maintenance of cooling towers. This is a major deterrent for certain customers to adopt the use of recycled water.
Recycled water providers, individual building owners, or energy producers have to make a decision on what level of salt removal is necessary. For some applications, reverse osmosis (RO) maybe an over-engineered solution. Nanofiltration (NF) could provide the water quality needed with less energy consumption and more water produced than RO. In addition to this, RO is currently being used on potable water to create ultra pure water for energy turbines, where as NF may be able to fill this niche.
It can be more expensive to treat water to potable standards than to recycled water standards. Therefore, wastewater utilities across the nation are developing recycled water as a new source of supply. It is in the interest of a water utility to provide recycled water using the most economical treatment process.
The main research questions to be addressed are: relative to RO, how efficient, economical, and environmentally sound is NF for treating: Recycled water for use in cooling towers? Recycled and potable water for use in energy production turbines?
This would be accomplished by evaluating the overall efficiencies of the NF vs. RO processes on recycled and potable water. Characteristics to be analyzed are: pre/post treatment requirements, water recovery, contaminant rejection, energy use, waste stream size, and disposal costs. Effectiveness would be measured by comparing how well each process meets the cooling tower and energy production turbines feed water quality standards considering life cycle costs, environmental issues, and energy reduction.
Need and Benefit
The Texas Water Development Board (TWDB) is the state agency responsible for planning, financial assistance, information and education for the conservation and development of water resources in Texas. TWDB is currently undertaking efforts to identify legal, political, regulatory, financial and technical barriers associated with advancing water reuse in Texas. These efforts will culminate in the TWDB making policy and funding recommendations on various reuse projects, both pilot/demonstration and full-scale construction, over the next 3 to 5 years. To assist in this effort, the TWDB has requested that Reclamation build upon recommendations stemming from the aforementioned effort and utilize its expertise under the R&D program to evaluate the state of technology, various applications, and economic feasibility of using NF treatment technology for water reuse. The results of this effort would assist TWDB in prioritizing educational resources, funding, and making policy decisions regarding advancement of water reuse in Texas.
The Dallas Water Utility (DWU) is a regional wholesale water provider that supplies water to the City of Dallas and 28 other municipalities in north-central Texas. Reclamation is currently collaborating with DWU on a proposed project that would convey treated reuse water for irrigation and cooling purposes. This project will help DWU postpone the development of new water supplies. A final draft appraisal report was recently completed by Reclamation. Depending on whether funds are appropriated from Congress, it is anticipated that Reclamation may start a feasibility study within the next 2 years. As part of this feasibility study, DWU would request that Reclamation investigate water quality requirements for cooling customers requiring a highly treated effluent quality (lower total dissolved solids) than that needed for irrigation uses. They also have requested that Reclamation evaluate and recommend the most appropriate and cost-effective advanced water treatment options to help DWU meet water quality needs for these uses. If Reclamation can utilize its expertise under the R&D program to evaluate and compare treatment technologies such as NF and RO for cooling applications, this would provide needed answers to questions that otherwise would have to be resolved during the feasibility study.
The San Antonio Water System (SAWS) uses groundwater from the Edwards Aquifer in south-central Texas to service approximately one million people with water and wastewater in Bexar County, Texas. City Public Service (CPS) Energy is SAWS's largest potable water customer during the summer and is the country's largest municipally owned energy utility, providing service to approximately 1 million customers in south central Texas. SAWS and CPS Energy want to explore the use of recycled water as a source for the energy process in lieu of potable water. They have requested that Reclamation evaluate and compare costs and efficiency of NF vs. RO to treat recycled water during the winter when recycled water supplies are available and demands are low. If study results show this as a feasible option, then CPS may utilize recycled water for cooling or energy production during the winter in lieu of potable water, thereby reducing CPS Energy's potable water usage. Unused potable water could then be stored in the Edwards Aquifer for use during the summer through an aquifer storage and recovery system when potable and recycled water demands are the highest.
Additionally, CPS Energy currently uses potable water and uses RO to treat the water to turn turbines for energy production. SAWS and CPS Energy have requested that Reclamation utilize its expertise under the R&D program to evaluate and compare the extent to which NF could improve the efficiency of the treatment / blowdown process. If successful, this project could illustrate how a major water stressor, powerplants, can be mitigated during summers and droughts.
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Progress report (final, PDF,
By Katherine Guerra
Research Product completed on May 29, 2014