Introduction
San Jose-Santa Clara Regional Wastewater Facility (RWF) and Silicon Valley Advanced Water Purification Center (WPC) are part of a complex water infrastructure owned and operated by Santa Clara Valley Water District (SCVWD). Founded in 1929, SCVWD mobilized to provide safe, clean water; flood protection and stewardship of streams. The District manages 10 reservoirs and operates three water treatments plants that clean and disinfect 220 million gallons a day of drinking water from imported water and four local reservoirs. The RWF plant accounts for 110 million gallons a day serving 1.4 million residents and 17,000 business-related sewer connections in the cities of San Jose, Santa Clara, Milpitas, Cupertino, Campbell, Los Gatos, Monte Sereno, and Saratoga. Santa Clara Valley Water District’s water infrastructure includes a $54 million dollar investment in the innovative Silicon Valley Advanced Water Purification Center (WPC). Due to current drought conditions, SCVWD looks to expedite usage of its WPC, with goals to expand recycled water to make up for 10% of the county’s water demand by 2025.
Advancements at the Silicon Valley Advanced Water Purification Center would make our local community less dependent on snow melt from the Sierra Nevada that makes its way to the Sacramento – San Joaquin Delta before being imported to Santa Clara County treatment plants or aquifers – accounting for half our water supply. The federal government determines how much Sierra Nevada water we receive annually. The additional benefits of investing in the Silicon Valley Advanced Water Purification Center vision would be to replenish our aquifers with purified water for drinking and to alleviate any infrastructure damage caused by land subsidence.
WPC feels confident that technology advancements and careful monitoring will allow it to provide potable water to residents of the local area in the very near future.
According to WPC, it hopes not only to hybridize recycled water with purified water for more diverse use but more importantly it wants to add an additional cleansing process to meet and exceed drinking water standards. In this paper we’ll look at the processes the water is put through at the San Jose-Santa Clara Regional Wastewater Facility in addition to the Silicon Valley Advanced Water Purification Center. We’ll also review future plans, sustainability and adverse or beneficial environmental impacts.
History and background
Water quality in Santa Clara County before wastewater treatment plants was unsanitary. Before “advanced purification centers” people would discard their sewage on streets and into local waterways. It wasn’t until the 1880‘s that the City of San Jose built a meager sewage system to deliver untreated wastewater to the Bay. In the 1940’s indoor plumbing became more popular which generated more wastewater leading to the passing of the federal Water Pollution Control Act of 1948. By 1950 Santa Clara County implemented two water systems for stormwater and wastewater to reduce the amount of water requiring treatment. In 1964 the RWF incorporated a secondary treatment to meet state regulations and accommodate a growing population. The Clean Water Act enacted in 1972, aimed at limiting and regulating pollution, forced the RWF to expand again and it began to include tertiary treatment to meet CWA standards. Motivated by population growth and the need to conserve water, the South Bay Water Recycling facility was constructed in 1998 leading the way to a brighter sustainable future. (San José-Santa Clara Regional Wastewater Facility History. 2015)
Pollutants
The pollutants that are directed to the San Jose-Santa Clara Regional Wastewater Facility are byproduct of human activity. Ideally only feces, urine and toilet paper are supposed to be thrown in the toilet but other foreign objects and chemicals such as baby wipes, cigarette butts, dental floss, Viagra, birth control, and pharmaceuticals make it into the toilets and sent to the RWF where it is removed, but trace elements of pharmaceuticals are left behind and released into the Bay. Also, cooking grease, oils and fats are supposed to be thrown in the trash but instead many people dispose of it down their kitchen sink. This can clog pipes and cause sewer overflows. The amount of tons hauled of grit, grease and screenings in 2014 was 447 tons of grit, 501 tons of grease, and 607 tons of screenings. (Ervin, J. 2014)
In addition to serving public residents of the county the RWF also has 17,000 main connections to businesses in the surrounding area serving industries such as: food service, automotive, metal finishing, photo processing, and manufacturing.
The RWF is responsible for processing conventional pollutants and adhering to their 2014 NPDES Permit; established effluent limitations for Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), BOD & TSS Percent Removal, Oil & Grease, pH, Total Chlorine Residual, Turbidity, Total Ammonia, and Enterococcus bacteria. Receiving water’s dissolved oxygen level cannot fall below 5.0 mg/L due to effluent discharges. (Ervin, J. 2014)
The RWF monitors six priority pollutants: copper, nickel, cyanide, dioxin, indeno (1,2,3-cd) pyrene, and mercury. Additionally, six priority pollutant metals: arsenic, cadmium, chromium, selenium, silver, zinc, lead and non-priority metals such as: antimony, beryllium, and thallium and much more.
One of the goals is to protect the health, environment, and economy of the South Bay by cleaning wastewater to near-drinking water standards before discharging it into the Bay.
The San Jose-Santa Clara Regional Wastewater Facility and Silicon Valley Advanced Water Purification Center have a mutualistic relationship so it’s beneficial to know how each facility operates.
San Jose-Santa Clara Regional Wastewater Facility (RWF)
Let’s begin with the San Jose-Santa Clara Regional Wastewater Facility since it would be the first recipient of wastewater in the treatment cycle. The City of San Jose built the original wastewater facility in 1956 and has since operated it 24 hours a day 7 days a week. In 1959, the City of Santa Clara helped fund upgrades, gaining approximately 20% ownership. Operating on an $80 million annual budget overseen by San Jose and Santa Clara city councils, RWF employs 200 employees and is regulated by both the Regional Water Quality Control Board and the Bay Area Air Quality Management District. Buffered by RWF managed bay lands, the 175-acre operations site has about 4 miles of tunnels that hold various valves, engines, and infrastructure. The plants has the capacity to take in and process 167 million gallons of water a day but on average processes 110 million gallons of water a day. The RWF boast a 12,000 square-foot award-winning laboratory that employs 20 technicians, chemists, and microbiologists and conducts 5,000 tests monthly to ensure proper treatment and compliance for both RWF and for industrial dischargers. The RWF is funded by rate revenue from contracting agencies, which in turn set rates that include their respective sanitary sewer system costs. (San Jose-Santa Clara Regional Wastewater Facility. 2014)
Treatment Process
After wastewater enters the San José-Santa Clara Regional Wastewater Facility it undergoes a three-step treatment process to remove solids, pollutants, and pathogenic bacteria. Machinery and gravity separate solids from the wastewater. Added bacteria clean the water pollutants before the flow enters the advanced filter process. The treatment process produces water that is 99% purified and is subsequently discharged into the Bay.
Headworks (Pretreatment) - Entrance point of wastewater (influent) where heavy-duty rotating bars pull out large debris. The new headworks structure is in its final testing phase. The system was built to avoid accidental sewage spills due to mechanical malfunction, earthquakes or other unexpected events. The original structure system has never been taken out of service for maintenance. If this system failed, it could result in a raw sewage spill onto facility grounds. Berms and other protections surround the system to prevent sewage from entering the Bay.
Primary tanks - This 24-hour physical process removes about 50 percent of wastewater contaminants. In large tanks, the flow is slowed to allow gravity to separate large particles. This process mimics the natural processes of creeks and rivers, where sediments settle to the bottom. Fiberglass bars, or flights, move across the tank surface to skim off fats, oils, and grease. Flights gradually rotate from the top to the bottom and the settled solid particles are moved into the digesters.
Digesters - The pollutants and solid material removed during the three treatment steps are separated from the liquid flows in digester tanks. It takes 25 to 30 days for anaerobic bacteria to stabilize unwanted material and reduce the pathogens and other disease-causing organisms in the solids. Anaerobic bacteria operate best without oxygen and at about 98 degrees. Digesters produce methane gas, which meets 35% of the WPC's energy needs.
Secondary Treatment
Aeration
Aeration is a biological process that produces 95% clean water by pumping air into the flow. The oxygen-rich (aerobic) environment nurtures the growth of naturally-occurring aerobic bacteria that “eat” solids.
Clarifiers
After aeration, secondary wastewater is slowed in a set of 1-million gallon clarifier tanks to allow aerobic bacteria to settle at the bottom; wastewater becomes 95% clean. Treated water remains in the clarifiers for one to three hours. Mechanical arms move slowly around the tank to collect scum and bacteria for the digesters. Some bacteria are then sent back to the aeration tanks to repeat the process.
Tertiary Treatment
Clarified wastewater is filtered and chlorinated in a process called tertiary filtration, becoming 99% clean; the chlorine is neutralized before water is discharged to prevent harm to aquatic life.
Outfall Channel
After tertiary treatment, about 90% of the treated water is piped to the outfall channel. From here, it flows to Artesian Slough, through Coyote Creek, and eventually into the wetlands of the 30,000-acre Don Edwards-San Francisco Bay National Wildlife Refuge. Because of the outfall channels proximity many birds and fish such as: striped bass, large-mouthed bass and Chinook salmon are found here.
Of the 110 million gallons a day (mgd) treated at the facility 13% of the treated water is sent to South Bay Water Recycling and used to irrigate food crops, parks, schools, golf courses, street medians, and business park landscaping for an annual average of 14 million gallons a day (mgd) of recycled water reuse. (Secondary & Tertiary Treatment. 2015)
The byproduct of RWF’s water treatment process is sludge. This sludge collected during the treatment process is pumped to 11 anaerobic 1-million gallon digester tanks. Methane is produced in these tanks, and captured to help meet about 35% of RWF energy needs. After about 30 days, the sludge is transferred to open lagoons to dry and become biosolids. An average of 45,000 tons of biosolids are produced annually and used as alternative daily cover for landfills, helping reduce vermin and wind-blown litter.
Silicon Valley Advanced Water Purification Center (WPC)
Next let’s assess the Silicon Valley Advanced Water Purification Center’s water treatment process, current usage, technology, and future usages. After taking a tour at this facility I was very impressed with how clean it was and the state-of-the-art technology. Santa Clara Valley Water District partnered with the City of San Jose and Santa Clara to meet the demand of Santa Clara County residents. The facility cost $72 million to build and is currently being used to make highly purified water that can be blended with recycled water from RWF increasing its quality for more diverse usage. The plant can produce 8 million gallons a day of highly purified water.
The Process
The purification center uses a three step process (microfiltration, reverse osmosis and ultraviolet light) that mimics the process of how Mother Nature cleans water naturally.
First, microfiltration is the process where treated wastewater is pushed through filtration membranes made of thousands of very fine pores 1/300th the width of a human hair. Bacteria, protozoa, solids and some viruses are filtered out.
Second, the reverse osmosis process forces water using very high pressure through holes so small only H20 molecules can fit through. This removes salts, viruses and most but not all contaminants such as pharmaceuticals, personal care products and pesticides.
Third, now that the water is clean ultraviolet light is used as an additional safety procedure to inactive any viruses and any trace organic elements. There are 6 UV trains each having two vessels, each vessel holds 40 high-intensity UV bulbs for a total of 480 high-intensity UV bulbs.
How does the engineered facility work?
Four 200 horsepower intake pumps deliver 8 million gallons of water a day that has gone through two levels of treatment at the RWF. The water is then forced through fine pores 1/300th the width of a human hair during microfiltration, before being transferred to a 225,000-gallon stainless steel tank. The water then flows to the reverse osmosis transfer pumps where it is pumped through cartridge filters as pre-treatment before going to the RO pumps. Three 500 horsepower pumps boost the pressure of the water before two chemicals are added to eliminate scaling, mineral build up and to protect the reverse osmosis membranes. The reverse osmosis process involves forcing water, using high pressure (50-190 psi), through thin membranes with pores so small only H20 molecules can fit through. Water produces excessive CO2 so a decarbonization process is incorporate to reduce corrosion. Ultraviolet light is used for sterilization before the water is sent to a 2.25 million gallon stainless steel storage tank. From here the water is sent to the Transmission Pump Station for blending with tertiary-treated recycled water from RWF. The improved water is then sent to the South Bay Water Recycling distribution system that serves over 600 customers.
Conclusion
According to a WPC engineer, the infrastructure to transport water from the WPC to the Campbell percolation ponds along highway 17 would take 7 years to build and cost $72 million. As well as require constant energy to function, this is because the water would need to be pumped against gravity. I believe it’s a great investment especially since the WPC plans to introduce an advanced oxidation process to increase effectiveness in producing water that meets and exceed State Water Board regulations. This would be a game changer for our water future since recycled water could be used for more diverse agricultural crops and industry, groundwater recharge and eventually drinking.
In addition it’s less expensive and more sustainable than tapping into the ocean because of the high loads of energy needed to pressurize salt during the reverse osmosis process. I think it’s very important to continue to monitor and limit water releases into the bay as much as possible because of fragile anadromous fish and migratory birds and other aquatic species.
As far as I can tell the RWF and WPC have been doing a great job in managing our waste water while producing productive innovative engineering that efficiently supports over 1 million people. I applaud these facilities for their foresight and investment in the use of recycled water for a more sustainable future.
References
Environmental Services - Water Pollution Control Plant Annual Reports. (n.d.). Retrieved November 10, 2015, from http://www.sanjoseca.gov/Archive.aspx?AMID=161&Type=&ADID
Ervin, J. (Ed.). (n.d.). 2014 Annual Self Monitoring Report. Retrieved November 2, 2015, from http://www.sanjoseca.gov/ArchiveCenter/ViewFile/Item/2535
Frequently asked questions about advanced water purification. (n.d.). Purifying Water for a Sustainable Tomorrow.
Purifying Water for a Sustainable Tomorrow. (n.d.). An Introduction to Advanced Water Purification.
San José-Santa Clara Regional Wastewater Facility. (2014, September 3). Retrieved November 2, 2015, from https://www.sanjoseca.gov/DocumentCenter/View/34681
San José-Santa Clara Regional Wastewater Facility History. (n.d.). Retrieved November 13, 2015, from https://www.sanjoseca.gov/index.aspx?NID=1666
Secondary & Tertiary Treatment. (n.d.). Retrieved October 27, 2015, from https://www.sanjoseca.gov/index.aspx?NID=2365
Silicon Valley Advanced Water Purification Center. (n.d.). Retrieved from http://purewatersv.org/advanced-water-treatment-facility
Tour of Silicon Valley Purification Center
Talk with Silicon Valley Purification Center staff
Written by Richard Tejeda