Joseph Walters, Gregg Oelker and Valentina Lazarova
2.2 TECHNICAL CHALLENGES OF WATER QUALITY CONTROL
Secondary treated wastewater effluent produced at Los Angeles’Hyperion Treatment Plant (HTP) is normally discharged to the Pacific Ocean through a five-mile outfall pipeline. The HTP is the city’s oldest and largest wastewater treatment facility and has been operating since 1894. Hyperion treats sewage from 4 million residents, two-thirds of the city of Los Angeles. The plant has been expanded and improved numerous times over the last 100 years. The HTP uses a pure oxygen system and full secondary treatment, biosolids handling, biogas generation. Today, leading edge technological innovations capitalize upon the opportunity to recover wastewater bio-resources that are used for energy generation and agricultural applications. The daily volume of biogas production is 212,400 m3(7.5 million cubic feet) which are turned into energy, and 500 tons of biosolids per day are used as fertilizer and soil amendment. A 1.5 m (60-inch) Force Main from Hyperion was constructed from 1992 to 1995 along with a pump station to deliver 15% of the wastewater to the recycling facility.
The ECLWRF produces five types of“designer” water at the main Plant and Satellite Facilities. The average flow is 132,500 m3/d (35 MGD) with a maximum capacity of 170,300 m3/d (45 MGD). For comparison, the daily production is enough water conserved to meet the need of 60,000 households for a year.
Recycling facilities and treatment trains
The ECLWRF is the largest water recycling facility of its kind in the world, and was recognized by the National Water Treatment Technologies in 2002 as one of only six National Centers for Water Treatment Technologies. The ECLWRF (Figure 2.1) and the three satellite plants produce five different qualities of“designer”recycled water. The five types include:
Tertiary Recycled Water(Title 22 Product Water) is used for a wide variety of industrial and landscape irrigation uses and has a capacity of 151,400 m3/d (40 MGD). The process includes conventional tertiary treatment–coagulation/ flocculation/filtration/disinfection. Ferric chloride and cationic polymer are used for coagulation, and sodium hypochlorite is used for disinfection. A final minimum chlorine residual of 4.1 mg/L is required to meet the disinfection requirement of a CT of 450 mg-min/L.
Barrier Product Water, or stabilized Reverse Osmosis Water: the process consists of microfiltration (MF), followed by Reverse Osmosis (RO) and Advanced Oxidation Process (AOP–hydrogen peroxide/UV) (Figure 2.2). MF removes suspended solid material, turbidity, and some microbes. RO removes a large percentage of dissolved minerals and
Producingdesignerrecycledwater39
organic material, and most of the remaining microbes. The AOP process provides disinfection, and reduction of Nitrosodimethylamine (NDMA) to below the California Notification Level (NL), 10 ng/L (ppt). The water is stabilized using decarbonation to remove carbon dioxide, and addition of saturated lime solution to add back alkalinity and calcium. The water is used for ground water recharge and the current design capacity is 47,320 m3/d (12.5 MGD).
Pure Reverse Osmosis Water (MF/RO) is used at refineries for low pressure boilers. Design capacity is 6435 m3/d (1.7 MGD) at the ECLWRF for use at the Chevron refinery, 18,930 m3/d (5 MGD) at the Exxon-Mobil satellite facility, and 18,930 m3/d (5 MGD) at the Carson Regional Plant for use at the BP refinery. This water is very similar to Barrier Product Water, but is not treated with AOP and not stabilized prior to industrial use.
Ultra-pure Reverse Osmosis Water(MF/RO/RO) is produced at the ECLWRF, and used at the Chevron refinery in their high-pressure boilers. The capacity is 9840 m3/d (2.6 MGD). This water is close to distilled water quality.
Figure 2.1 Schematics of Edward C. Little Water Recycling Facility.
Figure 2.2 View of reverse osmosis and the advanced oxidation by UV/H2O2.
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Nitrified wateris used for industrial tower cooling towers at three refineries. Ammonia in the Title 22 recycled water is converted to nitrate through a biological fixed film process. Ammonia is problematic for the materials used in the cooling towers, and the conversion to nitrate is necessary. Design capacity at the Chevron satellite plant is 18,930 m3/d (5 MGD), at Exxon-Mobil is 18,930 m3/d (5 MGD) and at the Carson Regional Plant is 3785 m3/d (1 MGD).
The recycling facilities have been constructed in 4 phases as shown in Table 2.1.
Satellite treatment plants
The three Satellite Plants are as follows:
Chevron Nitrification Facility (CNF) further treats Title 22 recycled water received from the ECLWRF through a biological nitrification process to remove ammonia for cooling water tower application.
ExxonMobil Water Recycling Facility (XOM) further treats Title 22 recycled water from the ECLWRF through a biological nitrification and MF/RO processes for use at the ExxonMobil Refinery in Torrance. The water produced is used for cooling tower and boiler feed applications.
Carson Regional Water Recycling Facility (CRWRF) further treats Title 22 recycled water received from ECLWRF. Water processed through MF/RO and biological nitrification, then blended and sent to the BP Refinery in Carson for industrial use.
Seawater intrusion barrier
The West Coast Seawater Intrusion Barrier consists of 153 injection wells strategically located to prevent seawater intrusion into the West Coast Groundwater Basin. A total of 66,250 m3/d (17.5 MGD) of water is injected into the Barrier. The recycled water for the Barrier is blended with potable water at the blend station, located in the city of El Segundo. The ECLWRF is permitted for 75% recycled water contribution, or 47,320 m3/d (12.5 MGD) of the water injected into the Barrier.
Currently 34,070 m3/d (9 MGD) of recycled water, or about 50% of the injected water is recycled water. The permit allows expansion of the facility, and 100% recycled water injection into the Barrier if certain conditions are met. Most have been met, and West Basin is working to meet the last few conditions remaining. Phase V construction has begun to expand the Barrier Product Water production to the full capacity of 66,250 m3/d (17.5 MGD).
Recycled water distribution system
The Title 22 Distribution system of 160 km (100 miles) conveys tertiary recycled water from the ECLWRF to the Title 22 customers (Figure 2.3), as well as three satellite treatment facilities: Carson Regional Water Recycling Facility (CRWRF), ExxonMobil satellite plant (XOM) and Chevron Nitrification Facility (CNF).
Table 2.1 Treatment capacity of recycled water produced by Edward C. Little Water Recycling Facility.
Plant Year
Design flow
m3/d (MGD) Application
ECLWRF–Phase 1 1995 56,780 (15.0) Title 22
18,930 (5.0) Barrier Water: Lime Clarification-GMF/RO
ECLWRF–Phase 2 1999 56,780 (15.0) Title 22
9460 (2.5) Barrier Water: MF/RO
ECLWRF–Phase 3 2003 6430 (1.7) Industrial water: MF/RO
9840 (2.6) Industrial water: MF/RO/RO
ECLWRF–Phase 4 2006 37,850 (10) Title 22
18,930 (5.0) Barrier Water: MF/RO
Chevron 1995 18,930 (5.0) Industrial water: Nitrified
1999 16,280 (4.3)
ExxonMobil 1998 18,930 (5.0) Industrial water: MF/RO
12,110 (3.2) Industrial water: Nitrified
Carson 2000 18,930 (5.0) Industrial water: MF/RO
3785 (1.0) Industrial water: Nitrified
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There are two chlorine booster stations in the system to meet the needs of customers on the furthest ends of the system. This water is also used for irrigation at parks, golf courses, office buildings, and refineries, for toilet flushing and cooling towers, and for other industrial uses.
The Chevron El Segundo Refinery, located adjacent to ECLWRF, receives four high quality waters which include T-22 water for irrigation, nitrified water for cooling towers, single-pass RO water used in low-pressure boilers, and double-pass RO water used in high-pressure boilers. These four recycled water products are conveyed in four separate distribution system from ECLWRF and the Chevron Nitrification Facility to the refinery. Water use at the Chevron Refinery is more than 95% recycled water.
Recycled water quality Title-22 product water
The Title-22 Product Water is not drinking water though it meets all drinking water standards but should not be consumed. This recycled water has high levels of ammonia and Total Organic Carbon (TOC). The conventional tertiary process is not designed to remove ammonia, so the product water has the same ammonia level as the source water (35–45 mg/L as N). The TOC is typically 8–12 mg/L. Nutrients (potassium, nitrogen and phosphorus) are beneficial to irrigation customers and fertilizer use can often be reduced (Haeringet al.2009).
Figure 2.3 Schematics of the distribution system.
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The source water has a very high chlorine demand, due to the chemistry of wastewater, especially ammonia. To achieve the required 450 mg-min/L CT for disinfection, a much higher dose of chlorine is needed. Currently, chlorine is dosed at over 15 mg/L to meet the demand and maintain the required residual for disinfection. Studies performed at the plant have shown that chlorine decays to zero residual within 3–4 days. Customers at the far reaches of the Title 22 distribution system may see water that is older than 4 days, particularly in the winter when irrigation uses are lower and the water in the system is flowing slower. Sulfate in the water can convert to sulfide when the chlorine is gone, and this can cause the water to have an odour of“rotten eggs”. For this reasons, chlorine booster stations have been strategically placed in the distribution system to help alleviate this problem.
Barrier product water
Barrier Product Water is also not drinking water even though it is of equal to or better quality than tap water. Though it could be used for drinking (direct potable reuse), public perception and political roadblocks have stopped this from moving forward in the United States (Tchobanoglouset al. 2011). The Barrier water is injected into the ground where it is further treated in the soil. This more accepted practice, indirect potable reuse, is allowed by current regulations. Groundwater models show the injected water has a 20-year residence time in the ground prior to being pumped out in groundwater wells and used as a potable source. The water that was injected into the ground upon plant startup still is in the aquifer.
The membrane processes (MF and RO) are excellent barriers to microbial, organic, inorganic and other contaminants. AOP treatment to reduce NDMA with a UV dose of.115 mJ/cm2provides many times the dose required for disinfection. The addition of peroxide in the AOP process is an additional barrier to any unknown compound. Soil-aquifer treatment provides an additional treatment barrier.
Though the Barrier Permit was written earlier, it basically follows the requirements in the Groundwater Recharge Reuse Draft Regulations (CDPH, 2008). Barrier Product water has TOC in the 0.2–0.3 mg/L range, very low in comparison with most drinking waters, and below the permit limit of 0.5 mg/L. Total nitrogen (ammonia+nitrate+nitrite+organic nitrogen) is about 3 mg/L (as N) in the Barrier water, less than the permit limit of 5 mg/L. Coliform results are consistently not detected (daily total and fecal coliforms, and weekly E. coli). Trace metals and organics are mostly not detected. Testing of pharmaceuticals and personal care products (PPCP) has been done for many R&D projects and is required in the Barrier Permit. Though many of these compounds are detected in the source water, the only compound detected consistently in Barrier Product Water is caffeine at 10–20 ng/L, or parts per trillion (Snyderet al. 2007, 2008; Dreweset al. 2008).
Compliance record
The ECLWRF has four main permits for Plant Operation. The Barrier Permit includes required monitoring of the Influent, Barrier Product Water, Barrier Blend (Barrier Product mixed with Potable) and Groundwater Monitoring Wells in the vicinity of the injection system. The Title 22 Permit is focused on monitoring of the Title 22 Product Water as it leaves the ECLWRF and enters the Title 22 Distribution System. The Plant has two NPDES Permits for monitoring of Brine from the RO processes at the ECLWRF and CRWRF. These flows are comingled with secondary effluent discharges to the Pacific Ocean at the Hyperion Plant and LA County Joint Plant respectively (WBMWD, 2002, 2006, 2007).
The ECLWRF has an analytical laboratory (Figure 2.4), the West Basin Water Quality Lab that is certified by the State of California’s Environmental Laboratory Accreditation Program (ELAP, 2012). The laboratory is certified to test inorganic and microbiological parameters, TOC, and trace metals in both wastewater and drinking water. The lab utilizes two EPA methods (USEPA, 1993; USEPA, 1994) and all other methods from Standard Methods (SM, 1992, 1995, 1998) for testing. The lab has 6 full time staff, and produces about 2500 analytical results per month. Additional testing of organics, oil & grease, surfactants, asbestos, radioactivity, hexavalent chromium, phenol and pharmaceuticals/EDCs required by the Plant’s permits are subcontracted to an outside laboratory. Approximately 70% of all lab testing is done for process control and in support of R&D projects.
In total, the WBMWD reports approximately 40,000 values on compliance reports to the California Regional Water Quality Control Board every year. Over 25,000 of these values come from on-line process meters monitoring flow, pH, chlorine residual, turbidity, conductivity, UV absorbance, and UV intensity. About 15,000 values are reported from lab testing, performed in both the in-house and subcontract labs. In the past fiscal year (July 2010 to June 2011), the ECLWRF has an excellent record of 99.82% compliance (WBMWD, 2010, 2011).
Table 2.2 presents the average annual data for the influent and the final effluent water quality for Title 22 and Barrier treatment trains. The data clearly show the differences in water quality. The low TDS, TOC and turbidity values of the Barrier Water are indicative of the high treatment efficiency of the RO advanced treatment train.
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The quality of the Title 22 recycled wastewater has been fairly homogenous during the 15 years of operation, without any significant daily or monthly variations, despite high variations in the quality of the source water. The annual average concentrations of the most relevant water quality parameters are ,2.2 total coliforms/100 mL, ,2 NTU turbidity, and ,20 mg/L TOC. The residual chlorine was maintained at a minimum of 4.1 mg/L in order to maintain the required CT of 450 mg-min/L, and even higher to guarantee water quality in distribution systems. The main customers for the Title 22 recycled water are golf courses, parks, schools, cemeteries, commercial centers and private homes for toilet flushing.
Barrier Product Water has also seen homogeneous water quality since plant startup. The membrane processes are excellent barriers to maintain stable, high-quality water. The original plant design included disinfection by sodium hypochlorite and required CT of 450 mg-min/L. The Phase IV plant expansion added the UV/AOP process to destroy Nitrosodimethylamine (NDMA) that had been found in the Product Water. A California Notification Level (NL) of 10 ng/L for NDMA is in place, though exceedance of the limit is not enforceable. UV treatment was nonetheless added to lower the NDMA concentration below the NL. The UV and peroxide addition also ensures an extra‘barrier’to any other compound not known at this time, but could be detected in the future (WBMWD R4-2006-0069).
Table 2.3 presents the annual concentrations for those trace organic compounds that were quantified. It is interesting to note that the compounds that are detected by the conventional base neutral analysis protocol (EPA Methods 525/625) and volatile organic analysis (EPA Method 524.2) are primarily, disinfection byproducts, such as chloroform and bromoform. Other organics are not seen in the Barrier Water.
Industrial water quality
Because it has been treated using flocculation and gravity filtration, many constituents remain in the Title 22 water such as ammonia and salts. The ammonia can be corrosive to cooling towers, so that when it is used for this purpose, the ammonia must be either removed or mitigated using other treatment such as chemicals. For the refineries which use large volumes of recycled water, it is most effective and cost efficient to remove the ammonia by biological process.
Table 2.2 Monthly average water quality data of the Edward C. Little Water Recycling Facility (2009 to 2011).
Parameter Units
Influent Title 22 Water Barrier Water
Permit Measured Permit Measured Permit Measured
Turbidity NTU – 4–30 2 (2.5) 1–2.4 0.5 0.05–0.6 (average 0.092)
pH pH units – 6.8–7.2 6.5–8.5 6.5–7.3 6.5–8.5 7.7–8.0
TOC mg/L 20 8.3–66 20 8.1–14 2 0.14–0.27 (average 0.19)
TSS mg/L 30 12–43 20 1–17 – ,1
BOD mg/L 30 5–40 20 ,3–5 – ,3
TDS mg/L – – 800 730–1100 300 31–132 (average 83)
Figure 2.4 Process and water quality control.
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High quality ammonia free effluent for cooling water supply is produced by complementary advanced biological nitrification process in aerated bio-filters. Biofor® satellite treatment facilities are installed and produce water at the Chevron, Exxon/Mobil and BP oil refineries. These compact bioreactors are operated at high ammonia loading rates of up to 0.75 kg/d.m3and water velocity of 4–5 m/h, which represents a common value for the operation of aerated bio-filters during tertiary nitrification. The nitrification performance of the aerated bio-filters has been excellent until recently. For an average influent ammonia concentration of 40 mgN/L, the residual ammonia concentrations were consistently below the detection limit of 0.1 mgN/L.
Boiler feed water at the refineries requires a much higher level of purity (Table 2.4) and is therefore treated by using reverse osmosis filters with microfiltration as a pre-treatment. This process greatly reduces the mineral content. As an example, TDS is reduced from 800–900 ppm to about 50 ppm. Where even greater purity is required, a second stage of reverse osmosis treatment is performed. This reduces the TDS to below 5 ppm. Special pipes must be used for this mineral free water (comparable to distilled water) to avoid corrosion of the pipes from the water pulling out minerals during distribution.
Major challenges for operation
The major challenge for the plant operation is the deterioration of inlet water quality over time. Ammonia has increased from 20–25 mg/L (as N) in 1995 to over 40 mg/L in recent years. Chloride has increased from 130 to over 200 mg/L due to changes in water supply in Southern California and conservation of potable water. Allocations of northern California water have been reduced, and Colorado River water is higher in dissolved minerals. TDS has increased from 850 mg/L to sometimes being
Table 2.4 Industrial water quality specifications for satellite facilities.
Chevron Low
Table 2.3 Quarterly average concentrations in µg/L for specific organic compounds.
Constituent
Total Trihalomethanes 0.127 80 6.0–12 80 ND-0.9
Methylene chloride 524.2 0.03 5 0.97–2.5 5 ND-1.0
1,4–Dichlorobenzene 524.2 0.019 5 ND-0.21 5 ND
Tetrachloroethylene 524.2 0.032 5 ND 5 ND
Acid & Base/Neutral Extractable (µg/L) Bis (2–Ethylhexyl)
phthalate
525.1 0.47 4 ND-1.9 4 ND-0.58
Phenol 625 0.3 – ND – ND
Source: Adapted from West Basin Municipal Water District Annual Report, 2009, 2010.
ND–not detected above the detection limit, MCL–maximum contaminant level.
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above 1100 mg/L, also due to potable water supply changes. Processes were designed, and permits were written for water quality of the early 1990s, which was very different. Higher ammonia has posed challenges for operation of the nitrification processes which were designed to convert a lower ammonia concentration. Title 22 Product TDS and chloride limits (800 and 250 mg/L respectively) are routinely exceeded. The addition of ferric chloride as a coagulant in the Title 22 process boosts the chloride above the limit.
In addition to the long-term water quality changes described above, source water quality has been highly variable.
Turbidity can vary from 3 to 15 NTU, and has been recorded as high as 130 NTU. There are abnormal organics that sometimes are found in the inlet water. Studies have shown them to be high molecular weight polysaccharides and proteins. These have at times caused microfiltration units to foul rapidly and not recover from standard chemical cleanings. The capacity of the microfiltration units has been reduced over time. Research into processes to stabilize water quality and improve membrane performance has been performed, including ferric addition and diverting side stream flows at the source, ozonation and Dissolved Air Flotation (DAF) addition at the ECLWRF.
The source water is not disinfected, so contains high levels of microbes (bacteria, viruses, protozoa, etc.). Over time, growth of microbial colonies is thought to have caused some nitrification in the influent Force Main. A conversion of some of the ammonia to nitrite and nitrate in transport from the source is noted. A test was performed to inject chemicals at the source pump station to reduce the nitrification, but it was unsuccessful. To resolve this problem, chlorination of the Force Main has been considered.
The high chlorine demand in Title 22 Product water also causes the residual chlorine to dissipate within 3–4 days in the recycled water distribution network. Moreover, sulfide can form from sulfate, and solids can reform under reduced conditions, especially in the far reaches of the system where the water is “older”. Consequently, recycled water used for toilet flushing can have suspended solids and rotten egg odour that can cause customer complaints. Irrigation customers sometimes also complain about odour of the water. A flushing permit was used in the early years of plant operation. Water could be flushed from the distribution system and sent to the storm drains nearby. That permit could not be renewed, so chlorine booster stations were placed in strategic locations to increase the chlorine residual in the distribution system and
The high chlorine demand in Title 22 Product water also causes the residual chlorine to dissipate within 3–4 days in the recycled water distribution network. Moreover, sulfide can form from sulfate, and solids can reform under reduced conditions, especially in the far reaches of the system where the water is “older”. Consequently, recycled water used for toilet flushing can have suspended solids and rotten egg odour that can cause customer complaints. Irrigation customers sometimes also complain about odour of the water. A flushing permit was used in the early years of plant operation. Water could be flushed from the distribution system and sent to the storm drains nearby. That permit could not be renewed, so chlorine booster stations were placed in strategic locations to increase the chlorine residual in the distribution system and