The second shift
Commercial and agricultural uses for reclaimed water are gaining popularity in municipalities and businesses across the country. Previously forced to pay top dollar for fully treated water, the public and private sectors are realizing major benefits from reclaimed water usage. When the indirect benefits to the environment are also taken into consideration, it is apparent that water reuse is no longer merely an attractive theory, but an environmental and economic necessity.
Many commercial and agricultural water users in Florida's West Orange and Southeast Lake counties are seeing dramatic benefits since the inception of their water reclamation system 13 years ago. The project, Water Conserv II, is a cooperative venture between the city of Orlando, Orange County, and the agricultural community. Encompassing 4,000 acres of citrus groves and several public and commercial sites, it is the largest water reuse project of its kind in the world, and the first in Florida to irrigate crops produced for human consumption. Examining this success can provide insight and direction for other water management officials and engineers when it comes time to institute reclamation projects in their areas.
The history of reclaimed water
Wastewater reclamation has progressed greatly since the beginning of the 20th century, achieving a multitude of objectives along the way. These include: water pollution control to reduce pathogen problems and to keep underprocessed water out of circulation; augmenting water supplies through replenishment of underground or surface water reservoirs to prevent overdrafting of aquifers; and providing an alternative water resource for applications that may not need high-quality water.
According to Takashi Asano, PhD, PE, editor of the book Wastewater Reclamation and Reuse, the planned reuse of wastewater in the United States became popular in the early part of this century through the pioneering efforts of California farmers and legislators. In 1912, the central California farming town of Bakersfield used reclaimed wastewater to irrigate corn, barley, alfalfa, cotton and grazing pastures. In 1918, California state water officials promulgated the first water reuse regulations, adopting the first rules addressing the use of treated gray water for irrigation.
In the 1940s, chlorinated wastewater effluent was used for steel processing. Later, in the 1960s, urban water reuse systems were developed in several states, including Florida. The federal government passed the Federal Water Pollution Control Act in 1972 to restore and maintain the biological integrity of the nation's waters, with the ultimate goal of zero discharge of pollutants into them.
Due to a gigantic increase in its population base in the 1970s, Florida more aggressively pursued wastewater reclamation as a viable alternative for agricultural and commercial uses, wrote David York, PhD, PE, and Elsa Potts, PE, in a scientific paper titled The Evolution of Florida's Reuse Program. Reuse programs in Tallahassee in 1961 and St. Petersburg in the late 1970s charted the way for reuse across the state.
Classifications of reclaimed water
The guidelines for the utilization and classification of reclaimed water are currently under the jurisdiction of state governments. Florida, in particular, has a comprehensive plan that details certain criteria that must be met before reclaimed water can be used for certain purposes.
The reclaimed water cycle begins by taking the wastewater from domestic uses of what was originally "potable" water. Typically this does not include wastewater from industrial sources, but can encompass commercial users such as hotels, restaurants and business offices.
This wastewater is sent to a treatment facility where it is treated and disinfected to a level that renders the water safe enough to be put to beneficial use. However, the scope of "use" is stratified by the degree of treatment, which is generally divided into three levels.
Primary treatment involves the physical handling of wastewater. Typically, screens and sedimentation basins are used to remove large insoluble items.
Secondary treatment enlists biological processes to further cleanse the water. Activated sludge, trickling filters and disinfection come into play. At this point, the fecal coliform bacterial count is reduced below 200 per 100 milliliters (mL).
The above two processes only constitute the minimum level of basic treatment in the state of Florida. The water is only deemed safe enough for "restricted access" - i.e., it can only be used in areas where public access is restricted. It may be used for the irrigation of crops, but only if they are not consumed by humans.
One example exists in Tallahassee, where 2,000 acres of feed crops for animal consumption are irrigated with basic level, reclaimed water.
To be considered safe for public access, an advanced level of treatment is required - sometimes referred to as the tertiary level. This involves further filtration to decrease turbidity and to remove single-celled organisms such as giardia. Furthermore, a higher level of disinfection is employed. Typically, chlorine is added to lower coliform levels below detection.
While water which has undergone tertiary treatment cannot be classified as potable, it is fully qualified to be "public-access" reclaimed water. This opens up a large pool of potential uses, including the irrigation of golf courses, parks, schoolyards, freeway and landfill berms, some crops consumed by humans, and even residential lawns. If supply exceeds demand, any excess amounts of public-access reclaimed water may be directly discharged into rapid infiltration basins to recharge the aquifers. No further treatment is normally required.
Water Conserv II
The Water Conserv II system - a jointly owned cooperative between the city of Orlando and Orange County, Fla. - is the largest reclamation project of its kind in the United States. The project's cycle of breathing new life into "old" water begins with transferring municipal wastewater from homes and businesses to two secondary water treatment facilities: the city of Orlando's McLeod Road Water Reclamation Facility and Orange County's South Regional Water Reclamation Facility.
At these two plants, water is brought up to "public-access" grade reclaimed water through tertiary treatment. An average volume of 30 million gallons per day (mgd) is then piped through 21 miles of transmission lines to the main distribution center in West Orange County.
The distribution center is a centralized, computer-controlled system of transmission lines ranging in size from 6 inches to 54 inches, carrying water at a normal line pressure of between 80 psi and 120 psi. Thanks to a 43-mile distribution network, the center feeds the reclaimed water to approximately 70 agricultural users, six major commercial customers and four rapid infiltration basin (RIB) sites covering 1,700 acres. Since the purpose of these basins - typically surrounded by a man-made berm - is to speed the process of getting water into the Floridian aquifer, the sites were specifically selected based upon their percolation ability. Sixty percent of the volume is sent to agricultural and commercial customers, while the remaining 40 percent goes into the water table via the RIBs.
Customers receive their portion of reclaimed water through 74 turnouts - connection points to the main water distribution lines. A pressure valve and a propeller flow meter is installed on each turnout, to allow every user to regulate, record, and monitor their own flowrates. Additionally, a supervisory control and data acquisition (SCADA) system monitors each flow meter and electronically sends the data back to the distribution center for tracking and billing purposes.
Most of the turnouts serve the agricultural needs of individual growers and the Mid-Florida Citrus Foundation. As an incentive to enlist these agricultural customers, users receive the reclaimed water at no cost for a period of 20 years. Additionally, distribution pipes are extended to the growers' property line. More than 4,000 acres of citrus trees, eight outdoor foliage and landscape nurseries, two ferneries and one tree farm are currently irrigated with reclaimed water.
The other turnouts provide water to commercial and public users such as the Orange County National Golf Center, an animal shelter, two landfills and a soil-cement production facility - all of which also receive the reclaimed water for free.
Finally, some of the water is diverted to the RIB sites. This provides alternative disposal capacity for excess flows, specifically the amount that agricultural and commercial customers do not utilize.
Woodard & Curran Inc., Winter Garden, Fla., is the contract operator of Water Conserv II. Operating personnel quickly realized that this valuable stream of water was only as reliable as the infrastructure that delivered it. Nowhere was this more evident than in the flow monitoring system. With 145 flow meters spread throughout the entire project, any failures would jeopardize the data's credibility in determining user allotments and distribution measurements.
"We actually have flow meters from two different companies in operation," said Phil Cross, project manager for Water Conserv II, "but some of them would not hold up under the high flow conditions for very long. Over time, the readings from these meters would start to drift because their internal circuit boards would malfunction. We'd have to shut down that transmission line to repair the meters whenever these accuracy problems arose.
Cross decided to switch to flow meters manufactured by Water Specialties Corp., Porterville, Calif. "Their meters have proven to be rugged and reliable - we've had 25 percent less down-time issues since installing them," he said.
Reaping the benefits of using reclaimed water
Once the operators of Water Conserv II installed the new meters into the transmission flowlines, an improvement in the measurement reliability was evident. The results include better data collection, lower meter repair costs and reduced downtime. Given the new stability of their monitoring system, the operators were able to concentrate on what they do best: providing a valuable resource to their many customers.
For example, the Mid-Florida Citrus Foundation has worked in conjunction with the cooperative reuse project for many years to study the effects of reclaimed water on citrus fruit and other crops.
"Research results from the Citrus Foundation conclude that citrus trees grow faster, gain more canopy volume, yield and pounds of juice per acre as more reclaimed water is applied," Cross said. "So as highly treated potable water continues to face tougher and tighter restrictions by water management districts, reclaimed water becomes a very attractive alternative for irrigation."
Woodard & Curran's own research calculated that by providing agricultural users with reclaimed water at suitable pressures for irrigation, growers have realized increased crop yields of 10 percent to 30 percent and tree growth of up to 400 percent. The increases are not due to the reclaimed water itself, but the abundant availability of this water. Since the water is currently free, growers maintain higher soil moisture levels.
While the economic benefits of using reclaimed water are more immediate, the environmental pluses are many and significant. Because used water has traditionally been considered a liability instead of an asset, the success of this project counters many myths about reclaimed water.
For example, reuse eliminates the discharge of minimally treated water into surface waters such as lakes, streams and rivers; it reduces dependence on underground aquifers by reducing well water usage; and it actually replenishes the aquifer through the discharge of surplus water into rapid infiltration basins. As an added benefit, the excess water helps establish preserves for endangered and threatened plants and animals.
"There is a large influx of people moving to Florida, so we're beginning to face a water shortage here," Cross said. "We've already started to suffer from the consequences of overdrafting the aquifers in the central areas of the state, and in the coastal areas we're seeing an intrusion of seawater into our freshwater aquifers. Reclaimed water presents a very viable alternative to reduce dependence on water from those sources."
Water Conserv II has proven that the application of reclaimed water for commercial and agricultural uses is a win-win situation. Ultimately, it is the public who benefits from the recycling of this valuable natural resource.
This article originally appeared in the 07/01/1999 issue of Environmental Protection.