Even Hurricanes Can't Dampen Performance of Alabama Stormwater Direct Filtration Facility
Hurricanes that have hammered the United States' Gulf Coast in recent years caused millions of dollars in damages in cites and towns in Texas, Louisiana, Mississippi, and Alabama. While cities lying hundreds of miles inland escaped serious damage, these storms still have created local challenges, particularly for municipal water and wastewater treatment facilities.
he city of Birmingham, AL, is located 250 miles north of the Gulf of Mexico. In 2003, a $300 million peak-flow treatment facility was installed just a few miles from the city’s downtown area, dramatically improving wastewater quality in the surrounding community. But the Village Creek Wastewater Treatment Plant faced stern tests in the last two years as Hurricane Ivan in 2004 and Hurricanes Katrina and Rita in 2005 dumped a total of about a foot-and-a-half of rain on the city in a short time span. The facility passed the test thanks to deep bed filter technology and innovative new methods for ensuring consistent water flow.
For many years, heavy rainfalls in Alabama’s largest city caused flow at the Village Creek plant to increase from a normal 30 million gallons per day to more than 360 million gallons per day. Any flow beyond approximately 80 million gallons per day had to be bypassed to the Village Creek waterway, which feeds Bayview Lake.
To address the problem, a pilot filtration study was commissioned by the Environmental Services Department of Jefferson County, AL, and by consulting engineers Gary L. Owen & Associates of Birmingham. A pilot filter plant containing two 10-square-foot filters, each housing a 5-foot depth of large, rounded sand filter media, was supplied by Severn Trent Services.
Pilot testing of the deep-bed sand filtration took place in the summer of 2000. The pilot program lasted more than two months while a variety of flows, solids loadings, and operating techniques were investigated. Operations focused on loading the pilot filters with about 100 milligrams per liter total suspended solids (TSS) wastewater at 10 gallons per minute per square foot of filtration rate. This represented applied loading rates that were two to four times higher than previous experience and required developing new ways to maintain filter flow.
During testing, monthly average effluent limits were 30 milligrams per liter TSS and 25 milligrams per liter carbonaceous biochemical oxygen demand. The pilot plant consistently met these limits during repetitive testing. The best effluent and longest filter runs were achieved with no chemical addition.
Conventionally operated filters quickly would have plugged with such high influent flow and solids loadings. So, during the pilot study, new methods of operating and backwashing were developed to keep the water moving. These methods now are patented.
One proprietary Severn Trent operating method used is called SpeedBump. This method employs a “bump” operation to remove or purge accumulated gases such as nitrogen and carbon dioxide that can potentially build up in the interstitial media voids. The SpeedBump process applies backwash water to the bottom of the filter, releasing entrapped gas into the atmosphere and reducing head loss. Suspended solids are retained within the media and are backwashed out of the filter by a simultaneous injection of air and water and returned to the upstream biological treatment units at the end of each cycle. By operating down flow, excellent levels of solids removal are achieved, eliminating the need for clarifiers and additional effluent polishing filters.
At Village Creek, the SpeedBump process involved stopping effluent flow from the first filter, reversing the flow using the backwash pumps for a short period (about one minute), then proceeding immediately to the next filter while flow was restored to the first filter, and so on. Closing influent valves during this process is optional, depending on the initial water level in the filter.
This continuous process provided a surprisingly effective reduction in the backup wastewater. According to Dave Slack, general manager of Severn Trent Services’ office in Tampa, FL, “Originally, our customer at Village Creek wasn’t convinced the SpeedBump process would be an important part of the operation. But after seeing the system in operation, he recognized its significance. It allowed water levels in the filters to drop below the overflow point for a period of 20 minutes to as much as two hours. The technique was key to achieving reasonable filter runtimes when handling high wastewater flows and heavy solids loadings.”
Further testing was done to simulate the “first flush” of the collection system in the first few hours of a major rain event. This led to the development of new backwashing methods to allow for continuous application of 200 to 500 milligrams per liter TSS undiluted raw wastewater to the filters at about 5 gallons per minute per square foot. With this very high loading, filter runtime was cut to about an hour, even with 20-minute-interval speed bumping.
A short air-water backwash of only a few minutes was enough to expel most of the solids causing the backup and get the flow going again. This proprietary method, called SpeedWash, has been automated in the large filter plant to proceed continuously, seamlessly, and quickly from one filter to the next, completing the circuit in sufficient time to operate at elevated solids loading conditions.
The first flush treatment tests produced effluent quality of about 40 milligrams per liter TSS, below the projected weekly permit average of 45 milligrams per liter.
 |
| 360 MGD Village Creek Wastewater Treatment Plant |
The new plant was put into operation in July 2003. With deep-bed sand filters, the new system is capable of handling the base flow plus flow from a second new bio plant, which became operational in October 2004. The system also includes a 340-million-gallon-per-day pump station; 20 surge basins with a total capacity of 90 million gallons that can handle up to six hours of peak flow; a second new biological treatment plant; and ultraviolet (UV) disinfection.
The plant includes 22 deep-bed filters, each with 1,160-square-foot filtration surface area. The filters are laid out in two trains with room for expansion. The new control methods and innovative piping designs (a technology package referred to as StormMaster) allow continuous, rolling execution of up to two simultaneous air-water backwashes and four water-only backwashes at the same time, divided among the two filter trains to control head loss and expel excess solids during wet-weather events. These events peak at up to 360 million gallons per day for four hours, with elevated flows persisting for as much as 24 hours. However, between storms the plant is successfully polishing 60 million gallons per day of final effluent for discharge to Village Creek. A portion of the peak flow continues to be handled by the existing biological treatment plant. Dirty backwash water is sent to thickeners in the biological treatment plants.
The full-scale, heavy-duty filter design has been successful in large, new high-flow plants in other locations and in heavy industrial and steel mill services all over the world. In addition to handling wet-weather flows, the filters serve a valuable role of effluent polishing for many municipalities.
Deep-bed filters also are used to achieve high-level disinfection and reuse-quality effluent in many areas of the United States during drought conditions, such as the state of Florida during winter months. Currently, the state uses more than 9 billion gallons of water per day, with agricultural use comprising two-thirds of the total. The Florida Department of Environmental Protection now is requiring that most wastewater treatment plants employ treatment technologies that will provide reuse-quality effluent of less than 5 parts per million (ppm) TSS to save potable water. In response, the state now has reuse plants totaling a nominal capacity of 1.1 billion gallons per day. More than 35% of this total is being treated by Severn Trent’s deep-bed filter technology. Several of these plants also are advanced wastewater treatment plants (large AWTP), which also have the ability to remove nutrients to stop eutrophication of receiving waters when the reuse storage tanks are full in wet weather and discharge is necessary.
One key feature of the Village Creek filters is the 6-foot-deep bed of large, rounded sand, which allows for high flow rates, large storage capacity for heavy solids loadings, and long runtimes. Self-flocculating mechanisms for solids lodged within the filter media reduce the need for chemical addition.
 |
| 22 TETRA DeepBed filters, each with 1,160-ft2 filtration surface area |
A second key feature is the filter underdrain. Rows of arched concrete blocks rest on the filter floor, leaving large passages for water to flow under and between rows. This design, called a T-block system, is extremely resistant to biological fouling, making it ideally suited for wastewater applications. The blocks also protect the backwash air-distribution system.
A third key feature is a system of stainless steel backwash air laterals under alternate rows of T-blocks. The system precisely meters air under the entire bottom of the filter, allowing for even, effective backwashing. The design stands up well to heavy-duty conditions and provides zero maldistribution. Many plants have used this system for more than 20 years with no major maintenance or loss of media.
“Simultaneous air-water backwashing provides far superior cleaning capability and much lower water consumption than separate air scouring and high-rate water washing,” says Slack. “This is important in a large, heavily loaded filter plant. Backwash water consumption during rare peak flow operation is calculated to be about 10% of forward flow, but only 1% to 2% for normal operation. A field survey found that other filter types were averaging 11% of forward flow for backwash, even for normal operations. As a result, the Village Creek plant is benefiting from reduced recycle flows and treatment costs.”
Adjacent to the new filter plant are 24 surge basins that hold the first flush of undiluted wastewater with the highest concentration of pollutants for later processing. This water may be applied directly to the filters at the operator’s discretion.
The new biological treatment plant also takes in some of the surge flow directly. All wastewater treated by the new facility also passes through the new filters.
Final effluent is treated by UV disinfection before discharge to Village Creek. UV disinfection is greatly enhanced when supplied with filtered water, resulting in improved kill effectiveness, reduced power draw, and greatly lowered tube maintenance.
On September 16, 2004, the plant received its first significant test when Hurricane Ivan roared through the state. Ivan lost some of its power as it made its way from the Gulf Coast toward northern portions of the state, but it was still a tropical storm as it passed through Birmingham and Jefferson County during the late afternoon and early evening. While peak wind gusts were significantly reduced by then to just 45 to 55 miles per hour, the storm dumped nearly 10 inches of rain on the area.
The new facility handled the torrential rainfall as it was designed to. Rain infiltration into the collection system caused flows to rise rapidly. A 182-million-gallon-per-dayflow was applied to the filters, which they handled without difficulty. The SpeedBump cycle was utilized, reducing head loss in the filters as planned.
Later in November the plant experienced three consecutive days of high flow, with flow measured at 187 million gallons per day on November 24; 164 million gallons per day on November 25; and 137 million gallons per day on November 26.
“The effluent TSS in each instance—during Hurricane Ivan and during the three consecutive days in November—ranged from one to no more than 12 ppm TSS,” says Slack. “In some cases, the use of the patented SpeedBump feature lowered the cell level from 89% to 55%, establishing its criticality.”
Hurricanes Katrina and Rita, which wreaked havoc and record-setting damage along the Gulf Coast in 2005, were little more than rain events in Birmingham when compared to Hurricane Ivan. The storms combined to drop more than 6 additional inches of rain on the area during just a few hours. Again, the Village Creek facility handled the increased flow without any difficulties.
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More moderate rainfalls have, of course, been the norm for the facility since its installation. On May 5, 8, and 15, 2006, the facility tested the filters under normal conditions using just six of the 22 deep-bed filters. The average flow applied to the filters was 14.7 million gallons per day; plant influent averaged 51 ppm TSS; secondary clarifier effluent averaged 4.4 ppm TSS; filter effluent averaged a little over 0.2 ppm TSS. The secondary effluent was backwashed less than every other day per filter during the testing. TSS removal efficiency across the six filters averaged greater than 94%.
According to David Lee, plant manager at Village Creek, the system has provided multiple benefits. “The deep-bed filters have worked exactly as intended,” Lee says. “Our tests in May demonstrated very efficient TSS removal to less than 1 ppm—and a removal efficiency of greater than 90% is outstanding. The system has proven its ability to handle significant water flow, so the bypass feature has never been required. All in all, the deep-bed filter technology not only has helped the Village Creek plant improve wastewater quality but has benefited the Village Creek waterway and Bayview Lake—despite three recent hurricanes.”
September-October 2006
Even Hurricanes Can't Dampen Performance of Alabama Stormwater Direct Filtration Facility
Hurricanes that have hammered the United States' Gulf Coast in recent years caused millions of dollars in damages in cites and towns in Texas, Louisiana, Mississippi, and Alabama. While cities lying hundreds of miles inland escaped serious damage, these storms still have created local challenges, particularly for municipal water and wastewater treatment facilities.
he city of Birmingham, AL, is located 250 miles north of the Gulf of Mexico. In 2003, a $300 million peak-flow treatment facility was installed just a few miles from the city’s downtown area, dramatically improving wastewater quality in the surrounding community. But the Village Creek Wastewater Treatment Plant faced stern tests in the last two years as Hurricane Ivan in 2004 and Hurricanes Katrina and Rita in 2005 dumped a total of about a foot-and-a-half of rain on the city in a short time span. The facility passed the test thanks to deep bed filter technology and innovative new methods for ensuring consistent water flow.
For many years, heavy rainfalls in Alabama’s largest city caused flow at the Village Creek plant to increase from a normal 30 million gallons per day to more than 360 million gallons per day. Any flow beyond approximately 80 million gallons per day had to be bypassed to the Village Creek waterway, which feeds Bayview Lake.
To address the problem, a pilot filtration study was commissioned by the Environmental Services Department of Jefferson County, AL, and by consulting engineers Gary L. Owen & Associates of Birmingham. A pilot filter plant containing two 10-square-foot filters, each housing a 5-foot depth of large, rounded sand filter media, was supplied by Severn Trent Services.
Pilot testing of the deep-bed sand filtration took place in the summer of 2000. The pilot program lasted more than two months while a variety of flows, solids loadings, and operating techniques were investigated. Operations focused on loading the pilot filters with about 100 milligrams per liter total suspended solids (TSS) wastewater at 10 gallons per minute per square foot of filtration rate. This represented applied loading rates that were two to four times higher than previous experience and required developing new ways to maintain filter flow.
During testing, monthly average effluent limits were 30 milligrams per liter TSS and 25 milligrams per liter carbonaceous biochemical oxygen demand. The pilot plant consistently met these limits during repetitive testing. The best effluent and longest filter runs were achieved with no chemical addition.
Conventionally operated filters quickly would have plugged with such high influent flow and solids loadings. So, during the pilot study, new methods of operating and backwashing were developed to keep the water moving. These methods now are patented.
One proprietary Severn Trent operating method used is called SpeedBump. This method employs a “bump” operation to remove or purge accumulated gases such as nitrogen and carbon dioxide that can potentially build up in the interstitial media voids. The SpeedBump process applies backwash water to the bottom of the filter, releasing entrapped gas into the atmosphere and reducing head loss. Suspended solids are retained within the media and are backwashed out of the filter by a simultaneous injection of air and water and returned to the upstream biological treatment units at the end of each cycle. By operating down flow, excellent levels of solids removal are achieved, eliminating the need for clarifiers and additional effluent polishing filters.
At Village Creek, the SpeedBump process involved stopping effluent flow from the first filter, reversing the flow using the backwash pumps for a short period (about one minute), then proceeding immediately to the next filter while flow was restored to the first filter, and so on. Closing influent valves during this process is optional, depending on the initial water level in the filter.
This continuous process provided a surprisingly effective reduction in the backup wastewater. According to Dave Slack, general manager of Severn Trent Services’ office in Tampa, FL, “Originally, our customer at Village Creek wasn’t convinced the SpeedBump process would be an important part of the operation. But after seeing the system in operation, he recognized its significance. It allowed water levels in the filters to drop below the overflow point for a period of 20 minutes to as much as two hours. The technique was key to achieving reasonable filter runtimes when handling high wastewater flows and heavy solids loadings.”
Further testing was done to simulate the “first flush” of the collection system in the first few hours of a major rain event. This led to the development of new backwashing methods to allow for continuous application of 200 to 500 milligrams per liter TSS undiluted raw wastewater to the filters at about 5 gallons per minute per square foot. With this very high loading, filter runtime was cut to about an hour, even with 20-minute-interval speed bumping.
A short air-water backwash of only a few minutes was enough to expel most of the solids causing the backup and get the flow going again. This proprietary method, called SpeedWash, has been automated in the large filter plant to proceed continuously, seamlessly, and quickly from one filter to the next, completing the circuit in sufficient time to operate at elevated solids loading conditions.
The first flush treatment tests produced effluent quality of about 40 milligrams per liter TSS, below the projected weekly permit average of 45 milligrams per liter.
|
| 360 MGD Village Creek Wastewater Treatment Plant |
The new plant was put into operation in July 2003. With deep-bed sand filters, the new system is capable of handling the base flow plus flow from a second new bio plant, which became operational in October 2004. The system also includes a 340-million-gallon-per-day pump station; 20 surge basins with a total capacity of 90 million gallons that can handle up to six hours of peak flow; a second new biological treatment plant; and ultraviolet (UV) disinfection.
The plant includes 22 deep-bed filters, each with 1,160-square-foot filtration surface area. The filters are laid out in two trains with room for expansion. The new control methods and innovative piping designs (a technology package referred to as StormMaster) allow continuous, rolling execution of up to two simultaneous air-water backwashes and four water-only backwashes at the same time, divided among the two filter trains to control head loss and expel excess solids during wet-weather events. These events peak at up to 360 million gallons per day for four hours, with elevated flows persisting for as much as 24 hours. However, between storms the plant is successfully polishing 60 million gallons per day of final effluent for discharge to Village Creek. A portion of the peak flow continues to be handled by the existing biological treatment plant. Dirty backwash water is sent to thickeners in the biological treatment plants.
The full-scale, heavy-duty filter design has been successful in large, new high-flow plants in other locations and in heavy industrial and steel mill services all over the world. In addition to handling wet-weather flows, the filters serve a valuable role of effluent polishing for many municipalities.
Deep-bed filters also are used to achieve high-level disinfection and reuse-quality effluent in many areas of the United States during drought conditions, such as the state of Florida during winter months. Currently, the state uses more than 9 billion gallons of water per day, with agricultural use comprising two-thirds of the total. The Florida Department of Environmental Protection now is requiring that most wastewater treatment plants employ treatment technologies that will provide reuse-quality effluent of less than 5 parts per million (ppm) TSS to save potable water. In response, the state now has reuse plants totaling a nominal capacity of 1.1 billion gallons per day. More than 35% of this total is being treated by Severn Trent’s deep-bed filter technology. Several of these plants also are advanced wastewater treatment plants (large AWTP), which also have the ability to remove nutrients to stop eutrophication of receiving waters when the reuse storage tanks are full in wet weather and discharge is necessary.
One key feature of the Village Creek filters is the 6-foot-deep bed of large, rounded sand, which allows for high flow rates, large storage capacity for heavy solids loadings, and long runtimes. Self-flocculating mechanisms for solids lodged within the filter media reduce the need for chemical addition.
|
| 22 TETRA DeepBed filters, each with 1,160-ft2 filtration surface area |
A second key feature is the filter underdrain. Rows of arched concrete blocks rest on the filter floor, leaving large passages for water to flow under and between rows. This design, called a T-block system, is extremely resistant to biological fouling, making it ideally suited for wastewater applications. The blocks also protect the backwash air-distribution system.
A third key feature is a system of stainless steel backwash air laterals under alternate rows of T-blocks. The system precisely meters air under the entire bottom of the filter, allowing for even, effective backwashing. The design stands up well to heavy-duty conditions and provides zero maldistribution. Many plants have used this system for more than 20 years with no major maintenance or loss of media.
“Simultaneous air-water backwashing provides far superior cleaning capability and much lower water consumption than separate air scouring and high-rate water washing,” says Slack. “This is important in a large, heavily loaded filter plant. Backwash water consumption during rare peak flow operation is calculated to be about 10% of forward flow, but only 1% to 2% for normal operation. A field survey found that other filter types were averaging 11% of forward flow for backwash, even for normal operations. As a result, the Village Creek plant is benefiting from reduced recycle flows and treatment costs.”
Adjacent to the new filter plant are 24 surge basins that hold the first flush of undiluted wastewater with the highest concentration of pollutants for later processing. This water may be applied directly to the filters at the operator’s discretion.
The new biological treatment plant also takes in some of the surge flow directly. All wastewater treated by the new facility also passes through the new filters.
Final effluent is treated by UV disinfection before discharge to Village Creek. UV disinfection is greatly enhanced when supplied with filtered water, resulting in improved kill effectiveness, reduced power draw, and greatly lowered tube maintenance.
On September 16, 2004, the plant received its first significant test when Hurricane Ivan roared through the state. Ivan lost some of its power as it made its way from the Gulf Coast toward northern portions of the state, but it was still a tropical storm as it passed through Birmingham and Jefferson County during the late afternoon and early evening. While peak wind gusts were significantly reduced by then to just 45 to 55 miles per hour, the storm dumped nearly 10 inches of rain on the area.
The new facility handled the torrential rainfall as it was designed to. Rain infiltration into the collection system caused flows to rise rapidly. A 182-million-gallon-per-dayflow was applied to the filters, which they handled without difficulty. The SpeedBump cycle was utilized, reducing head loss in the filters as planned.
Later in November the plant experienced three consecutive days of high flow, with flow measured at 187 million gallons per day on November 24; 164 million gallons per day on November 25; and 137 million gallons per day on November 26.
“The effluent TSS in each instance—during Hurricane Ivan and during the three consecutive days in November—ranged from one to no more than 12 ppm TSS,” says Slack. “In some cases, the use of the patented SpeedBump feature lowered the cell level from 89% to 55%, establishing its criticality.”
Hurricanes Katrina and Rita, which wreaked havoc and record-setting damage along the Gulf Coast in 2005, were little more than rain events in Birmingham when compared to Hurricane Ivan. The storms combined to drop more than 6 additional inches of rain on the area during just a few hours. Again, the Village Creek facility handled the increased flow without any difficulties.
More moderate rainfalls have, of course, been the norm for the facility since its installation. On May 5, 8, and 15, 2006, the facility tested the filters under normal conditions using just six of the 22 deep-bed filters. The average flow applied to the filters was 14.7 million gallons per day; plant influent averaged 51 ppm TSS; secondary clarifier effluent averaged 4.4 ppm TSS; filter effluent averaged a little over 0.2 ppm TSS. The secondary effluent was backwashed less than every other day per filter during the testing. TSS removal efficiency across the six filters averaged greater than 94%.
According to David Lee, plant manager at Village Creek, the system has provided multiple benefits. “The deep-bed filters have worked exactly as intended,” Lee says. “Our tests in May demonstrated very efficient TSS removal to less than 1 ppm—and a removal efficiency of greater than 90% is outstanding. The system has proven its ability to handle significant water flow, so the bypass feature has never been required. All in all, the deep-bed filter technology not only has helped the Village Creek plant improve wastewater quality but has benefited the Village Creek waterway and Bayview Lake—despite three recent hurricanes.”