Gauteng and NW Province

Water Reuse: Use It, Don’t Lose It

“I like to say no matter what the flavor of water is, it’s still water, and now, because of economic reasons and shortages, we’re looking at how to use any kind of water to its best advantage.” – Bob Ohlund, vice president for infrastructure and water resources for Dudek

Thursday, November 06, 2014

By Carol Brzozowski

Water scarcity now affects every continent with nearly one-fifth of the world’s population living in areas of physical scarcity and some 500 million more people approaching this situation, according to the United Nation’s Department of Economic and Social Affairs.

In the United States, in the arid Southwest, it is a particular challenge.

The UN cites “natural and human-made phenomenon” as the sources of water shortage, adding that while there is enough freshwater on the planet for seven billion people, “it is distributed unevenly and too much of it is wasted, polluted, and unsustainably managed.”

To that end, a number of entities throughout the US are engaging in water reuse efforts in an attempt to minimize the draw on potable water.

In 2012, GE released the results of a survey revealing that while most Amer­icans hesitate at the concept of “toilet to tap” recycling, more than 80% support the idea of “toilet to turf” water reuse solutions for uses that require significant amounts of nonpotable water, such as agricultural irrigation, power generation, landscaping, industrial processing and manufacturing, toilet flushing, and car washing.

The survey indicated that most Americans see an increase in safe and efficient water reuse as a competitive advantage over other countries and are looking for government leadership and industry involvement to protect water resources and advance water reuse.

Survey respondents viewed large industries, agriculture, utilities and power companies as most responsible for contributing an “extreme amount” or “quite a bit” to water scarcity. Americans also are cognizant of the energy/water nexus, with more than 8 in 10 understanding it takes energy to deliver water, and more than 7 in 10 aware that water is needed to create energy.

Those surveyed expect energy industry leaders to demonstrate water stewardship by using recycled water to produce electricity, which they believe can positively impact cost and efficiency. More than half of the respondents indicated they’d be willing to pay up to 12% more for water to ensure future generations will be less vulnerable.

New technologies are helping to increase water reuse efforts, with many occurring in California, where water conservation is of particular concern. Case in point: following two years of research and development and three years of pilot testing, American Water Chemicals (AWC) has made its first full-scale delivery of AWC A-110 antiscalant to the Ground Water Replenishing System (GWRS) of the Orange County Water District (OCWD) in California, the site of the world’s largest reverse osmosis (RO) plant.

The GWRS puts wastewater through an advanced treatment process in order to treat the water to beyond drinking water standards. It then takes the treated wastewater—that would normally be discharged to the ocean—and mingles it with the local water supply by replenishing a local groundwater aquifer.

AWC provides clients with membrane water treatment services and products such as RO antiscalants, RO cleaning chemicals, and MF/UF (microfiltration/ultrafiltration) cleaning chemicals. The products and services are designed to reduce operating costs, eliminate acid dosing and reduce the frequency of membrane cleanings.

OCWD had experienced numerous silica-scaling incidents, leading to the use of hazardous ammonium bifluoride (ABF) as a membrane cleaner. AWC used OCWD historical feedwater data for a series of research experiments. The findings are a link between phosphate scale and silica formation. These were outlined in a paper presented at the 2011 IDA (International Desalination Association) World Congress in Perth, Australia, an area all too familiar with drought. Further lab experimentation determined that variations in iron coagulant carryover had a direct impact on antiscalant demand.

A comparison of OCWD feed water and operational history confirmed a correlation between surges in ferric ion levels and silica scaling events. The AWC A-110 was developed around OCWD’s complex wastewater feed and designed for control of high phosphate and silica scales in the presence of ferric ion carryover. OCWD began piloting the AWC A-110 in August 2011 and continued testing through different temperatures and at varying pH levels. By early 2014, it was determined that AWC A-110 was effectively inhibiting scale in the pilot at a dosage of 3.5 ppm and an operating pH of 6.9.

OCWD gave AWC the green light to provide antiscalant for the full-scale 70-MGD GWRS. The operation at a higher pH level was expected to potentially result in significant operational savings for the district as a result of reduced acid consumption. The OCWD GWRS is in the process of expanding to 100-MGD production capacity.

Mo Malki, CEO of AWC, says recent R&D work had shown the product to be “extremely effective” for controlling aluminum silicate scales. The company presented its findings to that effect at the 2013 IDA World Congress in Tianjin, China.

Wotj RO being one of the primary treatment processes, GWRS “relies a lot on pre-treatment chemicals to make sure that reverse osmosis process is operating properly and can run without excessive scaling or fouling,” points out Mehul Patel, GWRS program manager. “One of the key things we try to do is add a proprietary antiscalant chemical. We recently switched over to this new American Water Chemicals product.”

Patel says any new chemical used by the GWRS is tested on a pilot scale by using a small-scale RO pilot unit. “We tested it for two years before we decided to bring it into the plant on a full scale, because it showed promise in the pilot test,” says Patel.

Patel says the GWRS previously had an antiscalant product that had worked fine in certain instances, “but it didn’t work long-term as far as inhibiting this special kind of foulant or scale, so we had to resort to using ammonium biflouride, which is kind of dangerous and can cause long-term damage to the equipment if it’s used often.”

During the pilot testing, American Water Chemicals’ AWC A-110 showed promise that it’s better at inhibiting scale from forming, “and that may prevent us from having to use the cleaning chemicals like ammonium biflouride in the future,” notes Patel.

If AWC A-110 is successful, “that can not only get us away from using a harsh chemical, but it can obviously keep our RO process running longer and more efficiently the way we’ve always envisioned it would if we had the right antiscalant product,” adds Patel. “The reverse osmosis will run at lower pressure, which allows us to be more efficient in the amount of water we make and how long we’re online. It will hopefully improve our treatment process, as well, by keeping the reverse osmosis from fouling. That is the big culprit in high-pressure membrane systems: allowing the fouling to get too out of hand to where the process is less efficient.

“It’s a good way to try to recycle or reuse this water that would normally not be used for drinking water augmentation, but it takes a lot of onsite testing and pilot testing, not only of just the equipment itself, but down to the chemicals, to know that this process will work for your particular situation,” he says.

Silicon Valley
The Santa Clara Valley Water District (SCVWD) is a water wholesaler for California’s Santa Clara County, an area also known to many as Silicon Valley, and serves 1.8 million residents and more than 200,000 commuters. Additionally, SCVWD manages both surface and groundwater systems in the county.

The district regularly forecasts future water demands and plans how to conserve available drinking water. Forecasts have predicted shortages of as much as 125,000 acre-feet (AF) by 2030, at which time the population in the county is predicted to increase by 520,000. The use of recycled water for irrigation, industrial, and agricultural uses has become a significant component in the water agency’s strategy to satisfy the county’s water needs as the county’s population grows and water demand rises.

South Bay Water Recycling—administered by the City of San Jose—currently manages the recycled water program, providing disinfected tertiary filtered secondary effluent to more than 700 customers that include golf courses, parks, school property, business parks, agricultural lands, and industrial users (for processes and cooling towers) around the South Bay.

A previous study identified that salinity was a major constituent of concern in the existing recycled water supply, and consistent water quality is critical to industrial users’ operations. It was determined that an advanced recycled water treatment facility (ARWTF) could produce a high-quality effluent which, when blended with the existing recycled water, would reduce the salinity and provide a more consistent recycled water quality.

Another study was performed to assess the feasibility of an ARWTF. The SCVWD conducted the feasibility study in consultation with stakeholder groups and other interested parties. The evaluation approach of the feasibility study combined extensive background research with public and stakeholder meetings prior to and as part of the development and evaluation of potential ARWTF projects.

The primary components of the background research effort included a thorough sampling of the county’s potable water sources and water from wastewater treatment plants, a comprehensive assessment of potential markets for recycled water use, development of a Stakeholder Involvement Plan, and an assessment of the impacts of recycled water use on groundwater and surface water supplies. The study concluded that an ARWTF would produce high-quality water capable of meeting the future water recycling goals.

After conducting background research, the project stakeholders evaluated potential projects with criteria agreed upon by all stakeholder groups. The projects included a demonstration-scale project with a capacity of 1 MGD, and five full-scale projects ranging in size from 10 MGD to 45 MGD. The team reviewed applicable regulations, developed permitting strategies, evaluated life cycle costs, and considered each alternative’s funding opportunities.

The selected alternative was an expandable 8-MGD capacity facility, which is the largest advanced water purification plant in northern California and the first of its kind in the Bay Area. The project was completed in March 2014. The facility was renamed the Silicon Valley Advanced Water Purification Center.

The primary goals of the project were to protect sensitive groundwater by reducing the total dissolved solids (TDS) of the recycled water stream from 750 mg/L (average) to about 500 mg/L 95% of the time, and demonstrate the technology for future potable reuse.

The ARWTF would use secondary effluent from the San Jose/Santa Clara Regional Wastewater Facility (SJ/SC RWF) and provide advanced treatment with MF/UF, RO and ultraviolet light (UV) disinfection to produce high-purity recycled water with a TDS concentration of 50 to 500 mg/L. The ARWTF operations would differ during dry-weather months and wet-weather months. During dry-weather months, the initial demand for recycled water would be high (~13 MGD).

To meet this high demand, product water from the ARWTF would need to be blended with tertiary effluent produced from the existing wastewater treatment plant. The targeted blended water TDS is 500 mg/L at all times. It is expected that the blended water TDS would be 400 mg/L for at least 75% of the time. To meet permit requirements, all recycled water produced at the ARWTF during dry months would be treated with MF/UF, RO, and UV disinfection.

During wet-weather months, the initial demand for recycled water would be lower (~3 MGD). At these times, it was expected that the recycled water produced in the new ARWTF would be sufficient to meet the recycled water demand, and blending would not be necessary. During wet-weather months, the MF filtrate would have two treatment paths: first, to pump through RO then disinfect with UV, and second to pump directly through UV without RO treatment.

There were some predicaments in planning the solution. “Working with multiple agencies that may have differing objectives can typically be challenging,” says Jim Clark, senior vice president and project director, Black & Veatch’s water business. The company worked with the municipalities to identify solutions.

“The cities of San Jose and Santa Clara own and operate the SJ/SC RWF, but a total of seven cities and sanitation/sanitary districts discharge to the SJ/SC RWF under a series of master agreements,” says Clark. “The City of San Jose is the administering agency, and the city council is the final decision-making body. The stated core service of the city’s environmental services department is to manage wastewater for suitable discharge into the South San Francisco Bay and for beneficial reuse to protect the environment and public health.”

South Bay Water Recycling is to develop, operate, and maintain a recycled water system that reduces effluent to the Bay and provides a reliable and high-quality alternative water supply. “SCVWD’s mission is to provide the Silicon Valley with safe, clean water for a healthy life, environment, and economy,” says Clark.

While representatives of each of the agencies agree that optimizing water recycling is important and valuable, they also need to consider the needs and financial impacts on their individual constituents, says Clark. “For example, not all of the ratepayers contributing to the SJ/SC RWF would necessarily benefit from the SCVWD ARWTF,” says Clark. “Accordingly, finding an acceptable balance among the various stakeholders required much discussion.”

Water-quality management is a critical component to most recycled water projects. By reducing the discharge of treated wastewater, the pollutant load on the receiving body is also reduced, Clark says.

“Using advanced treatment processes to further remove pollutants and other potentially harmful constituents such as salt from the recycled water improves groundwater quality and opens up additional potential uses for the recycled water, which further reduces the demand on potable water requirements,” he adds.

There is a finite amount of water on earth, and significantly less available fresh water, Clark points out. “We must reuse the water resources multiple times in order to accommodate the world’s increasing population. In most cases, it is less costly to reuse treated wastewater than to find new water supplies. It is also far less costly to provide advanced treatment to wastewater than to desalinate ocean water. It is better for our environment, more sustainable, and the best thing we can do to help preserve this precious resource.”

The project has increased the reliability of a locally controlled, drought-proof, high-quality, recycled water supply for reuse, and has also reduced reliance on more energy-intensive imported water supply options, including from the Sacramento/San Joaquin Delta, says Clark.

Water efficiency measures include:

  • implementing rain gardens and passive irrigation to capture, store, treat, and use all water that falls on the building roof,
  • landscaping with native plants using less than half the water of a typical landscape, conserving existing wildlife habitats, and promoting biodiversity,
  • monitoring computerized moisture sensors to conserve water and provide the exact amount needed for irrigation, and
  • blending rainwater with reclaimed and potable water to control saline levels necessary for proper irrigation.

Author’s Bio: Carol Brzozowski specializes in topics related to resource management and technology.

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