Environmental Protection

What's Driving Reuse

Growing demand and deteriorating water quality is pushing the advancement of reuse technologies

Benjamin Franklin is frequently quoted as having said: "We will never know the true value of water until the well runs dry." Although conservation was the first attempt at preserving and maintaining limited fresh water supplies, the idea of "reclaim, recycle, and reuse" was the next push for managing them. Reuse is one of the hottest and most talked about issues in the water industry today. But it is nothing new; major reuse projects have been operational for over a decade.

For many years, the world enjoyed an abundance of high-quality fresh water that was inexpensive to obtain, treat, and transport. Now, many communities and industries face water shortages, deteriorating water quality, and greater demands because of population growth, tourism, recreational use, drought, seawater intrusion, and industrial expansion. The well, so to speak, is beginning to run dry. Many water and wastewater treatment plants are struggling to keep up with higher demands or achieve the quality standards set forth by regulatory agencies. And as fresh water becomes harder to obtain and demand rises, so too does the cost to individual consumers and industrial users.

In addition to examining the past and present drivers for reuse, this article will highlight some of the technological advancements that have made water reuse an economical approach for creating sustainable water supplies that benefit communities and industries alike.

Water Shortages
The most widely publicized and innovative reuse projects are in California and Arizona. In California, the seriousness of water shortages more than a decade ago led to the development of large reuse projects aimed at supplying water for irrigation. The state reacted quickly to this new approach and developed a regulation commonly known as "Title 22" that addressed the quality of reclaimed wastewater. Not only does this regulation pertain to the water's quality, but it also regulates and approves the treatment equipment used to produce compliant water.

The next phase in California's water management program called for preventing seawater intrusion into the aquifers by treating wastewater and injecting it into deep wells. This created a hydraulic barrier to prevent the seawater from contaminating the aquifers and to protect the quality of fresh water. This approach helped increase available fresh water in the aquifers to meet the growing demands of the surrounding communities.
Potable water has traditionally been used for non-potable uses, such as irrigating golf courses, parks, and sports facilities. Reclaimed wastewater offers an alternative that can easily be used to irrigate these recreational facilities, lessening the demand on potable water sources. Municipal and industrial wastewaters have to be treated to meet discharge requirements established by the local authorities. This water can often be treated and reused directly rather than discharged into a receiving body of water, only to be recollected and retreated downstream.

The West Basin Water Recycling Facility in El Segundo, Calif., is the innovation leader in the reclaim, recycle, and reuse movement. The facility receives wastewater from the Hyperion Wastewater Treatment Plant that serves the Los Angeles area. Using low-pressure membrane filtration and reverse osmosis (RO), West Basin is able to provide five different "designer" grades of water for injection, irrigation, cooling towers, and even high-pressure boiler feedwater. Other states and countries have studied West Basin's success and have begun implementing similar projects to solve their water management problems and to build a sustainable water supply for decades to come.

Stricter Regulations
In other parts of the world, water reuse is becoming law. In Europe, for example, the European Water Framework Directive places limits on the extraction of groundwater for industrial uses, with full implementation by the year 2015. About 70 percent of the groundwater in Europe is used for industry; the remaining 30 percent is used for irrigation and drinking.

Similarly in China, Chapter 5 of the 2002 Water Law required all industries to extensively reuse water and increase water recovery, especially during new construction or plant upgrades. For the iron and steel industry, the regulations specify water intake lower than 16 m3/ton (metric tons) of product and water reuse ratio higher than 90 percent. In January 2005 the Chinese government imposed a new water consumption ratio on seven different industries. These industries can now be charged a fee for any consumption of water over the allocated amount. If the situation is not rectified within a specified timeframe, the offending enterprises will lose access to the water supplies.

Both of these laws affect new construction and set standards for existing plants as well. Industrial plants are the hardest hit and need to find alternate water sources, including reclaimed municipal wastewater, reclaiming self-generated wastewater, and seawater.

Dwindling Capacity
Communities are also being pushed to reclaim, recycle, and reuse wastewater because of their limited capacity to deliver potable water and/or treat the increased volume of municipal wastewater. Rapid population growth, tourism, and industrial expansion have placed heavy loads on these treatment facilities.

For instance, one Australian community was faced with upgrading its wastewater treatment facility due to all the reasons stated above. The upgrade was to include constructing a new pipeline to the ocean for discharge. In the early 1990s before reuse was a standard vocabulary term, a visionary engineer realized that the wastewater treatment plant could be upgraded with new separation technology, and the water could be sold to the nearby electric power plant. Low-pressure membrane filtration was installed at the treatment plant, increasing the capacity and producing a higher quality effluent with minimal investment. And a new pipeline did not have to be laid. The power plant installed an RO system to convert the high-quality reclaimed wastewater to boiler feedwater and realized significant cost savings in its water supply. This project has freed up as much as 500,000 gallons per day of fresh water for the rapidly growing community. By 2010, additional capacity will be added that will free up nearly 1 million gallons per day (mgd) of potable water for the community.
Similarly, Honolulu, Hawaii, faced upgrading its wastewater treatment facility to meet growing capacity demands and tightening ocean discharge regulations. Instead of blindly going forward with an upgrade to the treatment plant that would just discharge the water, the city entered into a public-private partnership to construct an advanced treatment facility that would produce water suitable for irrigation and industrial uses. Once again, both the city and industries enjoyed a substantial savings and freed up more 2.0 million gallons per day (mgd) of fresh water for potable use.

Increased Drought
Limited natural surface water and decreasing groundwater supplies, coupled with frequent drought conditions and large fluctuations in population, drove the city of Scottsdale, Ariz., to adopt a reuse strategy. The city has two sources of potable water: the Colorado River and groundwater aquifers. During the winter months, the population increases dramatically, which requires more potable water and generates more wastewater. The city can only withdraw a fixed volume of groundwater as dictated by the regulatory agencies, so when demand is high, it must tap into the expensive Colorado River source. The question became what to do with all the extra wastewater and how to obtain cost-effective potable water.

Although reclaiming wastewater for irrigation purposes was already common in Scottsdale, the high influx of seasonal residents created a greater volume of wastewater than could meet irrigation demands. To solve this problem, the Scottsdale Water Campus treats municipal wastewater and injects it deep into the ground to replenish the aquifers. This gives the city withdrawal "credits" to use during peak demand seasons and reduces demand on the Colorado River.

Reclaim Technology Advancements
Multibarrier filtration systems are the original technologies used in reclaim systems. Historically, these systems consisted of individual processes that required a substantial amount of land space and operator attention. Today, several unit operations such as high-rate tube settling and clarification followed by fine granular media filtration and even ultraviolet (UV) are packed into a single treatment step that removes residual biomass, turbidity, and micro-organisms. Such systems are much smaller and easier to operate than their predecessors.
Low-pressure membrane filtration is now used extensively in reuse projects around the world. These hollow-fiber membranes have a pore size of 0.04 microns that will remove bacteria, pathogens, and turbidity. (In comparison, a human hair is about 75 microns in diameter.) These membranes are routinely used downstream of either a secondary or tertiary waste treatment step to provide an extremely high-quality effluent by removing residual biomass, turbidity, and micro-organisms. Typically, some type of disinfection step such as chlorine or UV light follows the membranes before the water is used for irrigation or injection.

Membrane bioreactors (MBRs) are also being widely used in reuse projects. MBRs combine the activated sludge and clarification steps in the wastewater treatment plant into a single-unit operation. Like high-rate multibarrier filtration systems, MBRs are compact and easy to operate. And as the technology uses the same type of low-pressure membranes, its effluent is suitable for irrigation or injection, following a disinfection step.

RO systems are routinely used to improve the reclaimed water quality by reducing the dissolved solids content by 95 percent or more. Nanofiltration (NF) systems are very similar to RO systems but do not remove as much of the dissolved solids and, consequently, operate at lower pressures. RO and NF systems are employed downstream of the technologies listed above. However, most are preceded by low-pressure membranes due to their ability to provide exceptional feedwater quality to the RO and NF membranes.

Rapid sand filtration systems are another reuse solution. These systems have a shallow, 10-inch bed and contain 0.45-millimter (mm) fine-grain sand that effectively captures solid particles down to 2 to 3 microns (a process known as "surface straining"). This forms a positive barrier against solids and turbidity. The filtered effluent meets California's tough Title 22 standard for < 2 NTU (nephlometric turbidity units) turbidity that, after UV disinfection, can be used for subsurface recharge. The treated effluent can also be used for spray irrigation in citrus groves, on golf courses, on green belts, and as RO pre-treatment.

In addition to the water treatment technologies, significant advances have been made in reducing and transforming the residual biosolids. A biosolids reduction process significantly reduces the generation of biological solids through a system of interchanging solids between aerobic and non-aerobic conditions. The process is designed to tackle two main components of solids present in the mixed liquor of any conventional activated sludge plant: biological solids and non-readily degradable trash, grit, and other inert materials. The biological solids production is reduced by reconfiguring the biological treatment process. Biosolids that would normally be wasted from a conventional plant are instead sent to the side-stream interchange bioreactor where the unique conditioning environment of the process is created.

Biosolids composting systems transform wastewater treatment facility sludge into a stabilized, nutrient-rich, marketable end-product. This end-product, which can be used for landscaping, horticulture, agriculture and land reclamation, meets EPA Part 503 regulatory requirements for Process to Further Reduce Pathogens (PFRP) and Vector Attraction Reduction (VAR).

Management of our global water resources is key to creating sustainable water supplies for potable, agricultural, recreational, and industrial use. Reuse has become an accepted water conservation and environmental preservation technique. Many, if not all reuse facilities have proven to be an economical venture, even when the original drivers were not solely economic in nature. Water shortages, deteriorating water quality, and greater demands due to population growth, tourism, recreational use, drought, seawater intrusion, and industrial expansion have helped drive reuse in the past and will continue to do so in the future.

Several technological advancements for water reuse include multibarrier filtration systems, low-pressure membrane filtration, MBRs, RO, and rapid sand filtration. Biosolids-reduction processes and biosolids-composting systems treat solids produced during the wastewater treatment process to create a marketable end-product for land application.

This article originally appeared in the 09/01/2006 issue of Environmental Protection.

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