Water repurification via reverse osmosis

DESALINATION ELSEVIER

Desalination 117 (1998) 73-78

Water repurification via reverse osmosis P a u l G a g l i a r d o a*, S a m e r A d h a m b, R h o d e s T r u s s e l l c, A d a m O l i v i e r i d aCity of San Diego, MWWD, 600 B Street, San Diego, CA 92101, Tel.: +619-533-4222, Fax: +619-533-4267, E-mail. [email protected]; bMontgomery Watson, 555 East Walnut Street, Pasadena, CA 91101, Tel.: +626-568-6751, Fax: +626-568-6323; CMontgomery Watson, 300 N. Lake, Suite 1200, Pasadena, CA 91101, Tel.: +626-568-6651, Fax: +626-568-6619; and dpublic Health Institute, 1410 Jackson, Suite B, Oakland, CA 94612, USA, Tel.: +510-832-2852, Fax: +510-832-2856

Received 7 July 1998; accepted 12 July 1998

Abstract The City of San Diego in California, United States, (City) is developing new water sources to serve its arid region. Water repurification, in which reclaimed water receives additional advanced water treatment (AWT) prior to its discharge to a potable water supply reservoir, is one of the encouraging alternatives being implemented by the City to reduce the region's reliance on less dependable imported water. The City adopted the reverse osmosis (RO) process as the foundation for the AWT because RO has been shown to accomplish the best overall removal of organics, trace metals and total dissolved solids. In addition, RO has the potential for removal of all classes of pathogens. The California Department of Health Services (DHS) issued a conditional approval of the San Diego Water Repurification project in August, 1994. Several of the comments in the DHS conditional approval letter addressed the disinfection strategy and the reliability of the membrane processes in the AWT train. In response to the DHS comments, the City of San Diego initiated a major pilot testing program to evaluate the performance of various prequalified pretreatment and RO membranes. This program was initiated in 1995 and is still ongoing. Pursuant to the work performed at the Aqua2000 Research Center the DHS issued a letter on March 4, 1998, approving the Water Repurification System. The results of these studies demonstrated RO is a very effective and reliable process for water repurification. Minimal membrane fouling was observed for all of the polyamide RO membranes employed in the study. Significant contaminant rejection was achieved by all RO membrane purifying the reclaimed water to meet and exceed drinking water standards. Wide range of virus rejection was observed for the RO membranes which was dependent on the RO membrane type/manufacturer. The system consistently produces a product water that exceeds all drinking water standards. Keywords:

Reverse osmosis, drinking water, wastewater, public health, repurification

W a t e r is the u l t i m a t e r e c y c l e d resource, The total a m o u n t o f water on earth remains essentially constant although its distribution

changes. The recycling m e c h a n i s m is natural: the hydrologic cycle. W a t e r evaporates from surface reservoirs and enters the atmosphere

*Corresponding author. Presented at the Conference on Membranes in Drinking and Industrial Water Production, Amsterdam, September 21-24, 1998, International Water Services Association, European Desalination Society and American Water Works Association 0011-9164/98/$ - See front matter © 1998 Elsevier Science B.V. All fights reserved. PII SO011-9164(98)00069-1

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as water vapor. It returns to earth as precipitation. San Diego receives approximately nine inches of rainfall per year. The City must import 90 percent of our water from hundreds of miles away. This puts the City in a precarious position. Visionary strategic thinking and p l a n n i n g have allowed d e v e l o p m e n t in southern California to proceed and thrive. But as the latest drought (1987-93) once again reminded us, water supply reliability is difficult to achieve. By focusing our future planning on a mix of resources, we may be able to lessen the impact of supply fluctuations. Demand management, agricultural transfers, seawater or brackish water desalination and water reclamation or repurification are all options that must be analyzed for regional costs and benefits. The hydrologic cycle is efficient at recycling water but is it relatively slow and its impacts uncertain. Precipitation does not always fall when or where it is needed. A logical conclusion is to then try and control and manage a systemic hydrologic cycle. A resource of under-utilized water and a recycling system are all that is necessary. Sea water is plentiful in San Diego, but the cost of reducing the salinity from 36,000 ppm TDS to 500 ppm is relatively high. San Diego generates approximately 190 million gallons of wastewater per day. This flow is treated and discharged into the ocean. Recycling this commodity would significantly add to the water resources available for consumption. San Diego County was able to rely solely on local water supplies due to its relatively large reservoirs compared to its population in the 1940's. When the U.S. entered World War II, the situation changed dramatically because San Diego became a key location for the Navy. The population quickly doubled and, under pressure from the federal government and county leaders, the San Diego County Water Authority (CWA) was organized to import water to San Diego. By 1950 imported water accounted for 50 percent of

the region's total supply. The Metropolitan Water District of Southern California (MWD) supplies all the water for the CWA aqueduct system, most of the flow coming from the Colorado River. CWA is currently MWD's largest customer using approximately 26 percent of the District's total water supply. The MWD is using an Integrated Resources Planning (IRP) process to determine the best way to satisfy the region's future water needs in an era of interdependency. The IRP process gathers input from all affected stakeholders; m e m b e r agencies, general public, business, industry, agriculture and environmental groups, in order to develop a consensus. Stakeholders also assist MWD in developing the proper mix of resources necessary to achieve its reliability objective. In 1994, basic capital improvement projects necessary to produce the needed water were adopted. The CWA, in 1997, prepared a Water Resources Plan that was an outgrowth of MWD's interdependency policy. In this water resources plan local water resource development opportunities were identified and projected. The mix of resources included demand management, reclamation, groundwater d e v e l o p m e n t and seawater desalination. It is clear that we must develop a reliable as well as adequate supply of water to allow San Diego to continue to successfully grow. Local b i o - t e c h n o l o g y c o m p a n i e s when queried about the m o s t i m p o r t a n t determination for a plant location answered that uninterrupted availability of water was the most critical issue. New water resource projects can take the form of water transfers from agricultural land, or finding other new imported water sources. This assumes one can deliver it to San Diego when it is needed, otherwise, local or regional storage projects must be developed in conjunction with water conveyance projects. Two major storage projects are currently underway in the region. The MWD is constructing the Eastside Reservoir in

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Southern Riverside County. This 800,000 AF reservoir will provide additional reliability for Southern California. This reservoir doubles the aboveground storage capacity in the Southland and will guarantee water delivery to MWD's customers for five months in case of a cataclysmic seismic event. This project, which was first envisioned in 1984, is an example of how an integrated, comprehensive planning process can lead to the successful implementation of a generational project. On another front, the CWA just approved the Emergency Storage Project (ESP). This project proposes to add 90,000 AF of additional water storage in the San Diego region; enough to last the area for two months in case of a major earthquake on the Elsinore fault. Notwithstanding these projects, it remains extremely difficult to build new dams anywhere in California. In addition, San Diego has a dearth of useable groundwater basins. Thus, water conservation and water reclamation rise to the forefront as critical water supply options. It is estimated the regional population will grow to 3.3 million in 2010. Current regional population is 2.4 million persons. Based on these growth estimates regional water demand is expected to be 902,000 of AFY in 2010. Of that total, 70,000 AF may be made up by demand management activities. That leaves a supply that must be provided of 832,000 AF. The most severe cutback imposed on CWA by MWD occurred in 1991 when a 31 percent shortage was imposed. If 2010 is a drought year and supplies are reduced this m a x i m u m amount, CWA's total available supply would be approximately 524,000 AF. This includes 50,000 AF of reclamation; 15,000 AF of groundwater; 20,000 AF of desalination; 75,000 AF of water transfers, and 54,000 AF of dependable local supplies. A total of 738,000 AF of water, or 88 percent of the expected demand would be available. In an effort to broaden the potential application of reclaimed water to include indirect potable applications as well as c o n v e n t i o n a l n o n p o t a b l e uses such as

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landscape irrigation and industrial process water, the City, since the early 1980s, has c o n d u c t e d research into the advanced treatment and ultimate use of reclaimed water as a supplement to potable water supplies. This research, including health effects studies, has c o n c l u d e d that a d v a n c e d treated reclaimed water can be safely and reliably used to augment drinking water supplies. The North City Water Reclamation Plant (NCWRP), located in the North University City community of San Diego, is a 30 mgd tertiary treatment facility completed in 1997 that can produce 30,000 AFY of reclaimed water. In order to make more efficient and cost effective use of this resource, the City has investigated the advanced treatment of a portion of NCWRP's reclaimed water and the conveyance of this highly treated reclaimed water to the San Vicente Reservoir, one of the City's primary raw water supply reservoirs. In the reservoir, advanced treated reclaimed water would be blended with other raw water supplies (local runoff and imported water) prior to c o n v e n t i o n a l filtration and disinfection at the Alvarado Filtration Plant and ultimate distribution to the retail customer. This indirect potable reuse concept has been termed "repurification", with the advanced treated reclaimed water known as "repurified water". The Water Repurification Feasibility Study completed in June, 1994, provided a detailed project proposal for review by the California Department of Health Services (DHS) and a blue ribbon panel of independent experts in public health and water treatment. The study documented the extensive research conducted in the field of indirect potable reuse, including comprehensive water quality and health effects studies conducted in Denver, Colorado; Tampa, Florida; and Los Angeles County, California, in additional to nearly fifteen years of research conducted locally by the City. On August 31, 1994, DHS granted conceptual conditional approval for the Water Repurification Project. One of the key guidelines that DHS established was that

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Table 1 Comparison of repurified water (Aqua2000 Pilot Plant) to California State Drinking Water Standards

Table 1 Continuation Parameter

Parameter

State MCL

Clarity (NTU) Turbidity

0.5

0.05 (508)

Microbiological (P/A) Coliform bacteria Fecal coliform bacteria

5% 0

0% (98) 0 (98)

Volatile organic chemicals (mg/1) Benzene Carbon tetrachloride (CCL4) 1,2-Dichlorobenzene 1,4-Dichlorobenzene 1,1-Dichloroethane (1,1-DCA) 1,2-Dichloroethane (1,2-DCA) 1,1-Dichlorecethylene (1,1-DCE) cis- 1,2-Dichloroethylene trans- 1,2-Dichloroethylene Dichloromethane

0.001 0.0005 0.6 0.005 0.005 0.0005 0.006 0.006 0.01 0.005 1,2-Dichloropropane 0.005 1,3-Dichloropropane 0.0005 Ethylbenzene 0.7 Monochlorobenzene 0.07 Styrene 0.1 1,1,2,2-Tetrachloroethane 0.001 Tetrachloroethylene (PCE) 0.005 Toluene 0.15 1,2,4-Trichlorobenzene 0.07 1,1,1-Trichloroethane (1,1,1-TCA) 0.2 1,1,2-Trichloroethane (1,1,1-TCA) 0.005 Trichloroethylene (TCE) 0.005 Trichlorofluoromethane (Freon 11) 0.15 Trichloro-trifluoroethane (Freon 113) 1.2 Vinyl chloride (VC) 0.0005 Xylenes (single isomer 1.75 and sum of isomers) Total trihalomethanes (THMs) 0.1 Non-volatile synthetic organic (rag/l) Alachlor Atrazine Bentezon Benzo(a)pyrene Carbofuran (Furanda) Chlordane 2,4-D Dalapon Dibromochloropropane DBCP Di(2-ethylexyl)adipate Di(2-ethylexyl)phthalate

<0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 N/A <0.0001 <0.0001 <0.0005 (14)

chemicals (SOCs) 0.002 0.003 0.018 0.0002 0.018 0.0001 0.07 0.2 0.0002 0.4 0.004

State MCL

Repurified water*

<0.00005 <0.00005 <0.0005 <0.00002 <0.0009 <0.00005 <0.0001 <0.001 <0.00001 <0.0006 <0.0006

Dinoseb 0.007 Diquat 0.02 Endothal 0.1 Endrin 0.002 Ethylene dibromide (EDB) 0.00005 Glyphosate 0.7 Heptachlor 0.00001 Heptachlor epoxide 0.00001 Hexachlorobenzene 0.001 Hexachlorocyclopentadiene 0.05 Lindane 0.0002 Methoxychlor 0.04 Molinate 0.02 Oxamyl 0.2 Pentachlorophenol 0.001 Picloram 0.5 Polychlorinated biphenyls (PCBs) 0.0005 Simazine (Poncep) 0.004h Thiobencarb 0.07 Toxaphene 0.003 2,3,7,8-TCDD (Dioxin) 3.00E-08 2,4,5-TP (Suvex) 0.05 Inorganic chemicals (mg/1) Aluminum Antimony Arsenic Asbestos Barium Beryllium Cadmium Chromium

1 0.006 0.05 7 MFL 1 0.004 0.005 0.05

Copper Cyanide Fluoride Lead Mercury Nickel Nitrate as NO3 Nitrate + nitrite as nitrogen Nitrate as nitrogen Selenium Thallium

1.3 0.2 1.4-2.4 0.015 0.002 0.1 45 10 1 0.05 0.002~

Radionuclides (pCi/1) Gross Alpha (excl. radon & uranium) 15 Gross Beta 50 Uranium 20 Radium 226 & 228 5 Strontium-90 8 Tritium 20,000

Repufified water NA <0.0004 <0.005 <0.00001 <0.00001 <0.006 <0.00001 <0.00001 <0.00005 <0.00005 <0.0000! <0.00005 <0.0002 <0.002 <0.0001 <0.0001 NA <0.0001 <0.0002 <0.0005 NA <0.0002 <0.002 <0.0005 <0.001 NA <0.0033 <0.0002 <0.0005 <0.0001 (10) <0.001 NA <0.03 <0.0005 <0.0005 <0.0002 <0.85 (56) NA <0.07 (36) <0.002 <0.0002 <0.3 <0.4 <0.3 <0.3 <0.4 NA

P. Gagliardo et al. / Desalination 117 (1998) 73-78 Table 1 Continuation Parameter

State MCL

Repufified water

Secondary standards - Aesthetic standards (mg/1) Aluminum 0.2 <0.0002 Color 15 <1 Copper 1 <0.001 Corrosivity Non-corrosive -1.4 LI Foaming agents (MBAS) 0.5 <0.05 Iron 0.3 <0.05 (19) Manganese 0.05 <0.001

(15) Odor threshold Silver Thiobencarb Chloride Sulfate Zinc Secondary standards short term) (mg/l) TDS Spec. conduct. (~tmhos) Chloride Sulfate

3 0.1 0.001 250 250 5~

NA <0.0005 <0 .0002 1.3 (20) 0.4 (20) <0.0002

Ranges (Recommended, upper, 500, 900, 250, 250,

1000, 1500 1600, 2200 500, 600 500, 600

<12 (24) 12 (518) 1.3 (20) 0.4 (20)

Additional parameters (mg/1) pH Hardness (as CaCO3) Sodium Calcium Potassium Magnesium

6.5-8.5 -

6.2 (25) <5 (22) <5 (10) <1 (10) <0.5 <3 (10)

Future regulated parameters (mg/l) HAA5 0.06 Bromate

-

Radon Chlorite

-

<0.0006 (13) <0.005

(15) <50 <0.02

*Number in parentheses indicates total number of results. NA = not available from lab as of 6/9/98.

reverse osmosis (RO) treatment must be provided for the entire flow. In a March 4, 1998 letter the DHS approved specific components of the advance water treatment process. The approved system for treating the reclaimed water for indirect

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potable purposes consists of low pressure membrane RO pretreatment (either MF or UF), RO, ion exchange and ozonation. Public health and safety is the City's primary consideration in water repurification. Water repurification already safely takes place in major metropolitan areas around the country. Northern Virginia, for example, has repurified up to 20 million gallons of water per day since 1978 without any reported health problems. Like the San Diego proposal, the repurified water is blended with water already in a reservoir before it is treated and delivered to customers. California has successfully been recharging underground drinking water aquifers with reclaimed water for more than three decades with no adverse health effects being reported. The basic repurified water treatment process proposed for San Diego is similar to other water repurification systems which have been investigated within the past 15 years. Each of these repurified water investigations concluded that repurified water represented a supply as safe as the existing water supply. Table 1 lists the State of California drinking water standards and the Repurified Water Quality. As can be seen from a side-by-side comparison, the repurified water exceeds all drinking water standards. The repurification process is considered safe because the fundamental principle of the system is the "multiple barrier" concept. The water industry uses multiple barriers combined with strict water quality targets to determine if the water supply system can respond to the challenges of potential contaminants. In this approach, several treatment processes or c o m p o n e n t s are included in the water supply system so that, should one process or component not meet expectations, other components will provide the protection necessary to maintain a safe supply. In standard drinking water treatment, the initial defense is watershed protection at the water source. Other safeguards include protection of the raw water transmission facilities, physical removal and disinfection at the t r e a t m e n t plant, and c o n t i n u o u s

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disinfection in the distribution system that delivers water to the customer. The proposed water repurification program relies heavily on this multiple barrier concept. As an example, barriers to water-borne pathogens (enteric viruses, bacteria and protozoan cysts such as Giardia and Cryptosporidium) are provided in the wastewater treatment process, in the advanced water repurification treatment process, in the pipeline to the reservoir, at the receiving water reservoir, at the final water treatment plant, and in the distribution pipeline to the customer. Equally, multiple processes with the capacity to remove heavy metals and trace organics are included at several points in the system. In fact, the first barrier is an aggressive source control program that prohibits discharge of many of these substances to the wastewater collection system. A six-point Reliability Assurance Plan to ensure the safety of the region's water supply

has been adopted. The plan's components include: source control to restrict the introduction of c o n t a m i n a n t s into the w a s t e w a t e r c o l l e c t i o n s y s t e m , close monitoring and control of water reclamation facilities, state-of-the-art treatment technology providing multiple opportunities for removal of impurities, instantaneous diversion of repurified water if it does not meet regulatory driven standards, blending with local and imported sources, and comprehensive monitoring and response. RO is the foundation of the water repurification treatment technology. RO is proven, state-of-the-art technology already in use in drinking water production throughout the world. To c o m p l e m e n t RO, water repurification treatment adds a disinfection step using ozone to provide additional safeguards against microorganisms. An additional benefit of the use of ozone is that is produces better tasting water.