Closing Water Loops
Membrane technologies support water reclamation and reuse
As water scarcity becomes a farther-reaching issue, more public and private entities are turning to membranes as a water reclamation and reuse solution. In an interview with Water & Wastes Digest Managing Editor Caitlin Cunningham, Separation Processes Inc.’s Kevin Alexander discusses related applications, technology considerations and success stories.
Caitlin Cunningham: How does membrane technology help close water loops?
Kevin Alexander: Membrane technology is being used in a significant number of applications to speed up the natural process of purification. For instance, microfiltration (MF) and ultrafiltration (UF) are used extensively in producing potable water from surface water sources and sources of groundwater under direct influence of surface water. These filtration applications improve water quality and allow agencies to meet the requirements of the surface water treatment rules.
These same filtration processes are used to reclaim wastewater for reuse applications. Reuse applications include providing tertiary filtration to achieve lower phosphorus levels for meeting more stringent total maximum daily load limits, providing tertiary filtration for better irrigation water quality and aquifer augmentation, and providing pretreatment for reverse osmosis (RO). Additional applications include treatment of produced waters and fracture waters for oil and natural gas production.
Membranes are used in difficultapplications—such as membrane bioreactors, which allow for reduced footprint of wastewater treatment facilities while at the same time allowing for better control of the effluent water quality. This application allows the membranes to replace the secondary clarifiers and filters in a tertiary application. The technology uses hollow-fiber MF and UF membranes to achieve low phosphorus levels, low turbidity and low silt density index (SDI).
Other membrane technologies such as nanofiltration (NF) and RO remove smaller constituents such as hardness, total dissolved solids (TDS), pharmaceuticals and compounds of emerging concern. These technologies allow for reclamation of wastewater for many applications, including reducing TDS for irrigation; reducing TDS concentrations for meeting basin salinity management plans; reclaiming acid wastes neutralization solutions and brine from ultrapure applications in chip manufacturing facilities; and reducing TDS for low- and high-pressure boiler feed applications.
Cunningham: Why are water reclamation and reuse processes important? Who can benefit from adopting them, and how?
Alexander: Water reclamation and reuse processes are important because they allow for more sustainable use of water in arid regions. My first experience with reclamation was working with Intel and the city of Chandler, Ariz. Intel and the city of Chandler partnered to allow Intel to fund the design and construction of a water treatment facility to reclaim over 80% of its water for aquifer storage and recovery. The facility began operating in 1996 and is continuing to operate. This facility experience exemplifies water reuse and how reuse allows for industry to be located in arid environments. It has continued to expand and is sustainable due to the ability to reclaim the water.
There are other examples, such as the Orange County Water District Groundwater Replenishment System (GWRS), which is the most famous water reclamation facility in the country. The GWRS allows for reclamation of 70 million gal per day of wastewater for aquifer storage and recovery as well as seawater intrusion barrier. Another facility with as much notoriety is the West Basin (Calif.) Municipal Water District facilities.
Lastly, the city of Scottsdale (Ariz.) Water Campus exemplifies the benefits of water reclamation. The facility treats wastewater for aquifer storage and recovery. The facility also improves the water quality of the wastewater by reducing TDS for use on the golf courses and assures long-term water supply for the city.
Cunningham: What membrane performance issues are important to consider with these projects?
Alexander: For MF systems in reclamation applications, the size of the system, which is determined by instantaneous membrane flux, is the most important parameter to consider. Membrane flux is the key to the most efficient operating system and to the most cost-effective membrane system.
For NF and RO, the key performance indicators for successful operation are low total organic carbon and low SDI, with an indication of a low fouling potential.