The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
In the next 10 years, the expected swell in global population will undoubtedly lead to greater water needs and a rise in the production of wastewater. Already, as communities approach the limits of available water supplies in their efforts to meet the needs of potable, agricultural, industrial and commercial consumers, water reclamation and reuse are becoming necessary to conserve and expand the dwindling supply. Additionally, the global water reuse market is driven by environmental and socioeconomic factors that include increasingly stringent regulations to protect public health, economic incentives for implementing reuse systems and the development of a competitive alternative to advanced water treatment.
Major reuse applications include urban, industrial, agricultural, environmental and recreational uses, groundwater recharge and augmentation of potable supplies. In the U.S., an estimated 1.7 billion gal per day is reused and reclaimed. In fact, on a volume basis, reclaimed water use is growing at an estimated 15% per year. According to a recently released technical market research report, “Water Recycling and Reuse: Technologies and Materials” (RGB-331), from BCC Research, the total value of the U.S. water recycling and reuse industry was about $2.2 billion in 2005. By 2010, total market revenue will reach approximately $3.3 billion, at an average annual growth rate (AAGR) of 8.8%.
The benefits of reuse, in both water-deficient regions and highly populated but temperate regions, include savings from not having to develop new water sources, reduced treatment requirements and the economic value of reclaimed water.
Reuse at Every Scale
Urban reuse systems provide reclaimed water for non-potable purposes such as irrigation, commercial uses, ornamental landscaping, fire protection and more. But, despite significant progress in recent years, urban reuse systems have not yet been widely implemented across the U.S. Therefore, to remain “green” and reduce the strain on limited potable water supplies and limit their contribution to increasing wastewater quantities, commercial and industrial users are left to seek out and implement solutions to reuse their process water.
Water treatment professionals involved in the sale and installation of membrane filtration systems will continue to play an important role in the growing reuse market. These technologies are attractive treatment options for commercial and industrial users interested in reusing their process water because membrane filtration systems operate under a continuous process that is easily automated. Typically, membrane systems are configured in a modular design that offers easy adaptation to varying flow rates.
Of the commonly accepted categories of membrane filtration systems including reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF), RO removes the smallest-sized particles. While MF does not remove dissolved materials, it is used to remove submicron suspended materials in the size range of 0.01 to 1 micron. Biological and some organic matter are typically removed using UF because the pore sizes are usually less than 0.01 micron. Dissolved ionic contaminants are rejected with NF, but to a lesser degree than is achievable with RO, which can reject more than 99% of all ionic solids.
Osmosis is the natural process for movement of water in different concentrations of dissolved solids through a semi-permeable membrane, equalizing the strength of the solution on both sides of a membrane. Osmotic pressure is the responsible force causing flow of water through the membrane from the dilute side to the concentrated side until both sides reach equilibrium. Applying pressure to the concentrated solution, the flow of water through the membrane is reversed, resulting in a very dilute solution and a more concentrated solution. This process is RO. As pressure is applied to the solution, usually by a pump, water passes through micropores in the membrane, and dissolved salts and larger organic molecules (greater than 200 grams per mole) are retained by the membrane.
Most RO technology uses a cross flow process to allow the membrane to continually clean itself. As some of the fluid passes through the membrane, the rest continues downstream, sweeping the rejected species away from the membrane.
Membrane treatment technologies are successful processes for water reuse applications—whether in full-scale urban reuse systems or on an individual commercial or industrial user level. As the global trend in water reuse continues to grow, and prices for membrane systems continue to become more competitive, the reuse market can expect to see a greater influx of these technologies employed in applications.