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Urban Water CycleWater Treatment
Where We Treat Your Water The Philadelphia Water Department has three drinking water treatment plants.
The Baxter Water Treatment Plant treats an average of 200 million gallons a day--enough water to fill almost one-third of the Spectrum. When the Baxter Plant was opened in 1909 it was called the Torresdale Plant. It was renamed in 1982 for Samuel S. Baxter, the first Philadelphia Water Commissioner. The Baxter Plant treats water from the Delaware River. Baxter provides water to almost 60% of the City's population. It also serves some parts of Lower Bucks County.
The Belmont Water Treatment Plant treats an average of 40 million gallons a day. At that rate, treated water from the Belmont Plant would fill the Spectrum in ten days. The plant uses water from the Schuylkill, which has a higher mineral content and is slightly harder than water from the Delaware River. The Belmont Plant was opened in 1904 on the site where a pumping station had once stood in the late 1860s.
The Queen Lane Water Treatment Plant treats an average of 70 million gallons a day. Water treated by Queen Lane would fill the Spectrum in six and one-half days. This plant also uses water from the Schuylkill River.
The Belmont and Queen Lane Plants provide about 40% of the City's population with water.
The treatment of drinking water is an extracting process and Philadelphia's treatment plants take a number of precautions to make sure it is done right. Each plant has its own system of testing. All three of our drinking water treatment plants operate 24 hours a day. Every three hours, they test the water at each stage of treatment at each plant. These tests allow the plant operators, on staff 24 hours a day, to adjust their treatment to varying conditions (weather and upstream treatment can affect the quality of the water before we get it). Chemists at our water treatment plants perform more than 350,000 tests annually to ensure process control. If there is a chemical spill upstream, the intake pipe can be closed until the spill passes. Some testing may also be performed by digital analyzers working continuously. All three plants have about a day's storage capacity without pumping from the rivers. Plant supervisors are on call 24 hours a day to deal with any kind of problem that may arise.
Why We Chlorinate Your Drinking Water? Throughout history there have been epidemics of disease brought on by contaminated drinking water. Cholera, typhoid, and dysentery--all water-borne diseases--have been the cause of massive death. It was not until the 19th century that scientists proved that by cleaning up our drinking water we could put an end to these killers.
By the beginning of the 20th century, water in both the Schuylkill and Delaware Rivers was so contaminated that many Philadelphians died of typhoid fever and cholera every year. To combat water-borne diseases, Philadelphia began building its first water treatment plants in 1902. Treatment at the time consisted of filtering the water through beds of sand and allowing it to settle. When the plants were put into service, typhoid deaths dropped to one-fourth of what they had been. When chlorine was added to the water in 1913, typhoid and cholera were wiped out.
Disinfection of all public water supplies is required by state and federal law. The EPA and other health agencies recognize that using chlorine is the most effective way to protect public health from disease-causing organisms that can be found in rivers and streams. Because chlorine used by itself can react with natural materials in rivers to chemically form disinfection byproducts such as Trihalomethanes (THMs), we have been adjusting our chlorine process for some time to reduce this chemical reaction. But we also ensure that the treated water that is distributed through the City's water mains to your homes has a "chlorine residual," which continues to protect your water against bacteria and other organisms on its journey to your home tap.
Water Storage & Distribution Our water distribution system has the distinction of being one of the firsts in the country. When the Fairmount Water Works began operating in 1815, approximately 63 homes were connected by wooden mains to its reservoir, which was located on the hilltop now occupied by the Philadelphia Museum of Art.
Today's water distribution system serves an approximately 130 square mile area. Our three water treatment plants draw water from the Schuylkill and Delaware Rivers, process the river water to make it safe and drinkable, and then distribute the water to approximately 1.5 million Philadelphia residents through almost 3,300 miles of water mains.
These mains range in size from 6 to 93 inches in diameter, with an average age of 76 years. Water mains 16 inches in diameter and larger have much greater structural strength due to thicker walls. Less than two percent of the main breaks in Philadelphia occur on mains 16 inches or larger in diameter. Under favorable conditions, a water main is expected to function well for 100 to 120 years.
Eighty-seven percent of the City's mains are cast iron, the water industry's material of choice until the mid-1960s. At that time, the introduction of ductile iron pipes revolutionized the industry because this material is stronger and more flexible than cast iron. In addition to the water mains, there are approximately 27,700 standard pressure fire hydrants and about 83,800 valves. Our distribution crews are responsible for repairing and maintaining the city's water main distribution system.
Load Control At our Load Control Center, our water transport operators use a state-of-the-art, computerized system, to monitor and regulate flow and pressure of the water supply throughout Philadelphia and most parts of lower Bucks County. Through this high-speed intelligence system, data is picked up by electronic sensors and relayed via microwaves to the Center. Center technicians can control 17 pumping stations, 18 reservoirs, and five water storage tanks. They also monitor water pressure at 40 locations throughout the city, and the city's high-pressure system, which is used to fight fires.
Wastewater & Stormwater Collection At the Philadelphia Water Department, our goal is not only to maintain the city's water quality but also to improve the condition of our environment. The first step in controlling pollution is lowering the amount of pollutants released into our watersheds.
To get rid of waste, we use a system of combined sewers in half of our neighborhoods. This system is designed to collect a mixture of sanitary waste and stormwater and send it to a water pollution control plant. The other half of Philadelphia's neighborhoods use a separate sewer system. This system collects and transports sanitary waste to a water pollution control plant in a sanitary sewer. Stormwater is transported to a stream via a storm sewer.
Whether we have separate sewers for stormwater and sanitary waste, or a combined sewer for both, it's critical to keep foreign matter out. It is possible for wastewater to flow directly into creeks and rivers -- causing treatment costs to rise.
Recently, we faced a strategic choice when deciding how to deal with treating stormwater that overflows from our combined sewer system. These overflows occur after heavy rainfalls called storm events. When the rainfall in Philadelphia is average for this region, we get enough rain for 66 storm events per year. Our combined sewers are currently designed so that during heavy storm events, stormwater overflows are diverted to our local streams and rivers. Combined sewers transport a combination of stormwater and sanitary waste. When overflows occur, the water is diverted to waterways instead of going to one of our water pollution control plants where we would normally treat it to remove pollutants and debris.
To help contain and control these stormwater overflows, the Philadelphia Water Department has begun work on the Long Term Control Plan for Combined Sewer Overflows. We have invested $50 million in immediate capital improvements to the sewer system, while at the same time developing a comprehensive watershed plan. The goal of the city's Long Term Control Plan is to minimize the stormwater overflows and to nurture healthy, beautiful watersheds.
Industrial Waste--Our Commitment To Business The Greater Philadelphia region is home to many businesses and industries -- from major chemical plants to the corner dry cleaner. And all businesses and industries use water. For those who produce potentially hazardous wastewater as a by-product, the Philadelphia Water Department (PWD) has established a set of Wastewater Control Regulations, set up to protect our rivers, streams, and sewer systems.
We have divided industrial waste pollutants into two types: those which can be treated at our wastewater treatment plants, and those which cannot. Some pollutants would cause air pollution if permitted into the plants, so these substances are also prohibited. PWD sets a fee for treating polluted wastewater in our plants, based on how concentrated the pollution is in the wastewater. We have developed a list of substances which are prohibited from discharge into wastewater and our treatment plants. PWD issues permits for Wastewater Discharge, and issues permits to clean up polluted groundwater so that nearby streams and rivers are not affected.
PWD uses inspectors and investigators to assure that these regulations are being enforced at the industrial plant levels, and many industries must now use an aggressive pre-treatment program to reduce the levels of pollutants in their wastewater even before it reaches the PWD plants.
Where Philadelphia's Wastewater is Treated? The Northeast Wastewater Treatment Plant cleans 190 million gallons of wastewater per day and is the oldest water pollution control plant in Philadelphia. The plant was built in 1923 with secondary treatment facilities first installed in 1952, twenty years before such treatment at wastewater plants was required by an act of Congress across the United States. The plant was rebuilt most recently from 1979 to 1990.
The Southwest Wastewater Treatment Plant cleans 194 million gallons per day and was built as part of the City's massive stream clean up in the early 1950s. Its expansion and renovation began in 1975 and continued through 1983 to meet more strict federal water pollution control laws.
The Southeast Wastewater Treatment Plant, the City's smallest and newest water pollution control facility, cleans 91 million gallons of water per day and was also built during Philadelphia's stream clean up in the 1950s.
How Philadelphia's Wastewater is Treated Our Philadelphia sewer system has nearly 3,000 miles of sewers, that's slightly more than the width of the United States. Wastewater travels along some part of that system to one of three water pollution control plants, where a combined average of 471 million gallons per day (MGD) is cleaned and discharged into the Delaware River.
Under natural conditions, sewage discharged into a relatively clean river will decompose over time. Solids settle to the bottom where bacteria and other microbes break them down. Eventually, rivers would renew themselves except that people create so much sewage that, without treatment, all our waterways would be dead. Wastewater treatment mimics natural physical and biological processes to clean the water, but does so at a faster, controlled pace.
Why Wastewater is Treated? The earliest accounts of the Delaware River describe its vitality. Towards the end of the 17th century, William Penn complained that there were so many sturgeons in the River, that they leapt into the air and endangered small boats. As late as 1896, the Delaware was said to be one of the best shad rivers on the East Coast.
By the middle of the 20th century, however, this beautiful river had become a black, smelly, open sewer. In the 1940s, 85% of Philadelphia's sewage was discharged directly into a river already fouled by the residential and industrial waste of upstream communities.
Hydrogen sulfide gas, which smells like rotten eggs, ate away at the metal on ships and nearby buildings. Longshoremen were reported sick from working in such an unhealthy environment and floating debris clogged ships' engines. A newspaper editor complained that you could smell the Delaware as far away as Broad and Chestnut streets.
The Schuylkill was in no better shape. It was polluted by discharges from mining and raw sewage. In the 1880s, interceptor sewers were built to route Philadelphia's sewage downstream of the city's water intakes, but upstream discharges continued to foul the water supply.
In order for fish to breathe, there has to be a certain amount of oxygen dissolved in the water. A clean river generally has 6-7 parts per million (ppm) of dissolved oxygen, or 6-7 grams of oxygen dissolved in 1 million grams of water (one part per million is equivalent to one penny in $10,000). Fish have a hard time breathing in water with less than 4 ppm of dissolved oxygen. By late 1946, the twenty-mile stretch of the Delaware River from the Ben Franklin Bridge to Bridgeport, Delaware contained no dissolved oxygen. The river was dead.
Philadelphia began treating its wastewater in 1923. Three water pollution control plants were operating by 1953. By the 1960s, as treatment began to show some effect on the river, shad returned in large numbers.
In the early 1970s, Philadelphia committed itself to achieving water quality above the national standards and today, 43 species of fish are now living in the Philadelphia stretch of the River. Many parts of the Delaware and Schuylkill have now been declared swimmable and fishable.
The fish are not the only ones to benefit from the vastly improved water -- the cleaner River also attracts more businesses to our ports. The tremendous commercial, recreational and residential development taking place around Penn's Landing is all possible because of improved water quality.
If the Philadelphia Water Department had not cleaned up our portion of the Delaware there would be no restaurants overlooking the water; no riverside parks, festivals, and apartments; no marinas; no hotels; no tall ships; no riverboat excursions; no aquarium in Camden; no Fairmount Water Works restoration; and no plans for more development.
Wastewater Treatment Process Steps One to Three: Preliminary Treatment. Wastewater flows through several sets of bar racks and screens where debris is removed. The trash is collected from the bar racks and screens and is hauled to a landfill off-site. Approximately, 75% of the wastewater must then be pumped where it meets with the "gravity flow." It then flows through basins at a speed that allows only the heaviest suspended particles, called grit, to settle. Grit is composed of inorganic materials such as sand and gravel that enter the plant through storm sewers. Grit is removed from the basins and sent to a landfill off-site.
Step Four: Primary Treatment. Primary treatment physically removes 45-50% of the solids suspended in the wastewater. The wastewater flows slowly through primary sedimentation tanks. The solids that are heavier than water sink to the bottom, while scum and grease float to the top. The solids on the bottom are scraped out and pumped to digesters, while the scum and grease are pumped to concentration tanks and then landfilled off-site.
Steps Five to Six: Secondary Treatment. Secondary treatment uses biological processes to remove organic materials -- materials from living organisms -- still dissolved or suspended in the wastewater after primary treatment. The wastewater is combined with activated sludge, material containing the same microorganisms, or "microbes," that decompose sewage in nature. The wastewater and activated sludge are aerated with air and mixed together in aeration tanks.
This creates an ideal environment for the microorganisms to "eat" the organics. The wastewater from the aeration tanks then flows to the final sedimentation tanks. Wastewater slowly flows through these tanks, allowing the solids to settle. The settled solids, secondary sludge, are pumped to another process where they are thickened to 4% to 5% and then pumped to the digesters. Just before reaching the river, the water is mixed with enough chlorine to kill any remaining disease-causing organisms. The EPA requires 85% removal of suspended solids from wastewater. The treated water that leaves the plant -- called effluent -- is even cleaner than that.
The digested sludge from the Northeast Plant is barged 12 miles down the Delaware River and up the Schuylkill to the Biosolids Recycling Center where it is thickened, or dewatered, to 25% to 30% solids. After dewatering, the biosolids may be composted, land applied or landfilled off-site.
Our employees also operate a 73-acre biosolids recycling facility -- the largest of its type in the United States. This facility processes the biosolids resulting from wastewater treatment for a variety of environmentally beneficial uses including compost for gardening and horticulture, revegtation of strip mines, fertilizer for farmlands, and restoration of City parks and play fields.
In past decades, many communities -- including Philadelphia -- dumped sewage sludge offshore in the ocean. Since 1988, however, we have been safely treating and processing biosolids from Southeastern Pennsylvania, recycling most biosolids into environmentally beneficial products used for strip mine reclamation, agricultural application, and community gardening. |
Sanitary sewers in streets begin at 10" in diameter and mount upward until they reach giant collector size box sewers about 14 feet by 13 feet. Storm sewers are from 18 inches to 20 feet diameter tunnels.  |
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