The WWETCO FlexFilter™ from WesTech Engineering received a huge vote of confidence this fall when the State of New Jersey released a report highly rating its performance for the satellite treatment of combined sewer overflows (CSOs).
Typically, sanitary sewer systems transport household, commercial, and industrial wastewater to a sewerage treatment plant. Storm sewers transport rainwater and melted snow discharged into a waterway. In most areas, these two types of sewer systems function separately from each other.
However, in older urban communities, the sanitary and storm sewers are combined. These systems are called combined sewer systems (CSS). During heavy rainfall or significant snowmelt, the CSS overflows causing discharges of mixed untreated sewage and stormwater into waterways, to protect the treatment plant from overflowing.
These discharges are called combined sewer overflows. They often contain untreated human waste, solids, floatable materials, oil, grease, pathogens, and other pollutants that impact water quality and affect the recreational use and enjoyment of waterways.
An increasing focus on CSO control plans
In the mid-90s, CSO control programs began to put an increased focus on discharge permits. Over time, CSOs have become a more urgent issue, requiring cities to come up with long-term control plans to protect water quality objectives.
“The bottom line is that the law says you have to deal with this problem so these discharges don’t cause exceedance of water quality standards,” says WWETCO specialist Mark Boner, of WesTech Engineering. “That’s driving the search for new solutions.”
New Jersey is one state where CSOs are a priority concern, says Stanley Cach, Manager, Director’s Office, Division of Water Quality, New Jersey Department of Environmental Protection (NJDEP). He points out that the primary goal of any CSO control program is to implement the most cost-effective controls to reduce water quality impacts from CSOs.
New Jersey’s CSO permittees completed their feasibility studies in 2007 by addressing the national CSO policy that included the elimination or reduction of CSOs to achieve the appropriate water quality objectives of the Clean Water Act. These studies, prepared by the CSO permittees, analyzed cost-effective alternatives including the elimination of CSOs by sewer separation and reduction of CSOs by the construction of storage facilities, while maximizing the flows to treatment plants.
From among all the alternatives, these studies found that eliminating the CSOs by sewer separation was the most expensive alternative; the second most expensive alternative was the storage, transport, and treatment of CSOs. Both alternatives were cost prohibitive.
Boner says: “A lot of cities are building or planning to build big basins or deep tunnels to collect and store these flows for subsequent treatment. These can be multibillion-dollar programs.”
“Not only is that one of the most expensive alternatives, but it also requires a huge amount of land area,” says Cach. “These storage tanks can be the size of football fields.”
In the 1980s, the City of Trenton had available land at their treatment facility. The city constructed a 20.3-million-gallon detention basin encompassing 6 acres to capture the combined sewer flows from the wet weather events for ultimate treatment prior to discharge.
But most of New Jersey’s CSO treatment facilities, located in urban areas, do not have the land necessary for horizontal wet weather storage tanks. Available land is limited, and costs are at a premium. One permittee is considering constructing multiple deep-shaft storage wells. All these systems require a transport network connected to the treatment facility, with a significant initial cost investment.
New Jersey’s feasibility studies indicated that the most cost-effective alternative was to treat the CSOs near their source, at the discharge locations.
However, in 2007 – when the studies were completed – treating CSOs at remote discharge locations was uncommon because the existing treatment technologies were limited. Also, the performance of these technologies was not yet fully proven; either it was not independently verified, or it was ineffective in achieving water quality objectives.
“Finding a cost-effective CSO treatment alternative was important for the State of New Jersey,” says Cach. “Our vision was to ‘Find a 21st century solution to a 20th century problem’ – CSOs.”
Assembling a team of experts
New Jersey was one of the first states to evaluate end-of-pipe treatment technologies for wet weather flows. The evaluation was conducted by way of a comprehensive, collaborative study. The Bayonne Municipal Utilities Authority (BMUA) offered to undertake the study, called The Wet Weather Flow Treatment and Disinfection Demonstration Project.
Matt MacDonald served as the project manager, with input from two teams of national experts organized for guidance, review, and recommendations: The Technical Advisory Committee (TAC) with seven professional engineers, and the Regulatory Oversight Team (ROT) with 16 members.
Both teams included representatives from NJDEP and Rutgers University, and from the U.S. Environmental Protection Agency (EPA).
Previously, Cach had called the EPA headquarters to find out if anyone was testing end-of-pipe wet weather treatment technology. “I was hopeful I could learn from their experiences and collaborate with the researchers,” he says.
Cach was told that nobody was testing end-of-pipe treatment technology. “The EPA wanted our report when our demonstration project was completed,” says Cach. “I collaborated with the EPA’s Richard Field, P.E., Leader, Wet Weather Flow Management Program for Edison, New Jersey, who endorsed our demonstration project.”
Cach summarizes the reasons behind Field’s strong support for the venture, aside from the EPA’s obvious interest in research, in general.
According to Cach, Field believed that an evaluation of new and improved high-rate disinfection technologies that would satisfy the intent of national and state CSO control policies and mandates would result not only in local municipal and state benefits, but also would make a significant and beneficial impact at the national level.
“The proposed project had the potential to save the state and nation hundreds of millions of dollars, while reducing risks to human health,” says Cach.
In addition to the TAC and ROT teams, Cach also consulted with Boner during The Wet Weather Flow Treatment and Disinfection Demonstration Project.
Boner had been recommended to Cach by Peter Moffa, a member of the TAC who worked with Boner previously on a wet weather research project with the EPA and the Water Environment Research Foundation (WERF).
A brief history of the WWETCO FlexFilter
As an independent consultant specializing in CSOs, Boner had developed a compressed media filter that had been tested alongside other technologies in a five-year national demonstration project in Columbus, Georgia.
Peer-reviewed by a team of experts under the oversight of WERF and the EPA, the pilot demonstrated the success of this system, which became known as the WWETCO FlexFilter™ when it was acquired by WesTech Engineering Inc. in 2010.
“They saw the benefit, from the pilot testing that we had done. They saw the performance, and they saw that it was simple,” Boner says.
“Most of the stuff that’s out there requires a lot of operator attention. And storms can happen anytime – at night, on weekends and holidays, when people are not at the plant. Every other system would have required them to add people to run these facilities. They saw that ours is very passive, it pretty much operates by itself.”
The WWETCO FlexFilter operates so independently, in fact, Boner says, that you don’t need to have anybody on hand to clean it.
Boner says: “There’s minimal mechanical operation, with only valves and a low-pressure blower. It’s simple to clean – as the filter removes solids, the water will rise over the media bed to a certain level, which tells the controls that it needs to be cleaned now. A blower turns on to scrub and lift the dirty water out of the filter media and flowing to the sanitary sewer interceptor. And then the filter goes right back to work. There’s no labor involved, and no chemicals.”
Two-year test period for the Wet Weather Flow Treatment and Disinfection Demonstration
It was apparent, from the feasibility studies, that satellite facilities, end-of-pipe treatment, could have lower long-term operational needs and costs, and be adaptable to multiple siting locations. In reviewing past studies, a number of questions arose:
- Could the technology performance be verified and validated in a New Jersey demonstration project?
- Could they produce an effluent that would meet water quality standards?
- Could an alternate chemical disinfectant, such a peracetic acid, be utilized with a hydraulic retention time of three to five minutes?
- Could UV treatment be employed effectively?
- Could these treatment technologies be simple operation, low cost maintenance, and competitively cost effective?
Cach says, “The primary focus of the demonstration project was to select and verify the performance of selected technologies to treat CSO discharges for solids removal and disinfection under field conditions as suitable for remote satellite locations.”
Scientifically valid performance data was developed to evaluate the effectiveness of wet weather treatment technologies and to provide engineering practitioners with an improved understanding of the potential for using satellite end-of-the-pipe wet weather CSO treatment: reliability, scalability, anticipated capital and operations and maintenance costs, etc.
The Demonstration Project verified the performance of the selected technologies and validated those technologies that are suitable for the treatment of combined sewer overflow discharges at remote satellite locations.
The Wet Weather Flow Treatment and Disinfection Demonstration Project was conducted over a two-year period, 2014 and 2015, at the BMUA’s Oak Street facilities, which receives CSOs from the City of Bayonne. The project was sponsored and funded by the BMUA, with grants and collaboration from the EPA and NJDEP.
The pilot treatment included high-rate and enhanced high-rate solids removal and disinfection. A total of six technologies were tested in 18 treatment process combinations over nine wet weather events. The technologies included two high-rate solids treatment, a vortex unit (Storm King with Swirl Cleanse), and a plate settler unit (Terre Kleen), as well as an enhanced high-rate solids treatment, which was a compressed media filter (WesTech’s WWETCO FlexFilter).
Three types of disinfection units were also included: Chemical disinfection (peracetic acid, PAA), and ultraviolet (UV) disinfection (low and medium pressure units).
The results of the project demonstrated that the vortex and plate settler units are effective as preliminary treatment for inorganic solids removal, but not sufficient for the lighter solids removal needed for UV disinfection.
The compressed media WWETCO FlexFilter is capable of high performance Total Suspended Solids (TSS) removal (90%) allowing effluent UV disinfection (medium or low pressure), as well as for PAA.
Both UV technologies are capable of achieving water quality objectives of pathogen inactivation and TSS removal, but must be preceded by compressed media filtration technology or its equivalent. Cach says, “The performance of the compressed media filter technology was impressive; it effectively reduced TSS an average of 90% for UV or chemical disinfection.”
A report summarizes the demonstration project results
The Wet Weather Flow Treatment and Disinfection Demonstration Project Report demonstrated that high-rate / high-performance satellite treatment including solids removal and disinfection is attainable and can be used in appropriate instances to protect public health and aquatic biology.
The Project Report helps advance the findings of the study in several ways, says Cach:
- Satellite facility construction and operating costs are typically achievable at significantly lower costs than regional solutions, such as transport and treatment or sewer separation, given past experiences, and the Report’s costs information.
- This Demonstration Project was conducted under the NJDEP and USEPA oversight with peer review from two teams of national experts.
- The Project Report provides the engineering practitioners with an improved understanding of wet weather treatment technologies and their potential use as satellite end-of-the-pipe wet weather CSO treatment.
- The Project Report has been recognized as an excellent guidance document. It represents a valuable addition to data from other pilot and full-scale projects, and collectively serves as the basis to select appropriate components for remote satellite treatment of combined sewer and stormwater overflow.
- The results of the Project Report provide the CSO permittees with another viable alternative to their CSO Long Term Control Plan.
- It can provide a phased approach for a community with multiple CSO discharges for a segmented implementation of their CSO controls, considering the community’s financial capability.
- Satellite facilities can be unmanned, odor free, and adaptable to multiple locations, given the small footprint of the compressed media filter treatment, and can be constructed below grade to accommodate at-grade, park-like, green ways, open space, and a community’s other multiple use considerations.
Cach says the Demonstration Project Report was a comprehensive collaborative project that incorporated a wide variety of organizations, from technology manufacturers to governmental agencies such as the BMUA, EPA, NJDEP, and Passaic Valley Sewerage Commission.
Satellite treatment has been proven as a cost-effective treatment alternative
Satellite treatment is a viable, cost-effective treatment alternative for many of New Jersey’s CSO communities, and the compressed media filter has a proven track record of success now.
Boner says: “The New Jersey report is exciting because here you have a state that has recognized that the best way to solve the CSO is at the source. They went into this trying to find out, are there technologies that can deal with this problem at the discharge location, and they concluded that there is. This is one technology that can work in a satellite operation, with no staff, no chemicals, and no residuals left over.”
With many areas experiencing more frequent and severe storm events, and with water quality regulations tightening, Boner sees plenty of future need. “There are thousands and thousands of wet weather sewer overflows throughout the country, and a lot of other communities out there who have the same problem that New Jersey has. And our technology is right there.”
While the WWETCO FlexFilter is considered a leading-edge technology, it’s not an experimental or untested one. Springfield, Ohio, used the FlexFilter in its new 100-MGD plant on the Mad River, making it the largest compressible media filter in the world. And it has met water quality standards consistently for three years, successfully protecting the Mad River from more than 40 wet weather events.
And numerous other CSO projects are under construction or in the contract stage. “I think we’re going to see it pop up in many more constructions,” Boner says.
Additional applications for the WWETCO FlexFilter
The WWETCO FlexFilter is also being used successfully to treat sanitary sewer overflows (SSOs). Also a weather-related issue, SSOs occur in sewers that carry only sanitary flow, but which have become leaky with age.
“The pipes have bad joints, so when it rains and the ground gets saturated, the pipes become a French drain,” says Boner.
The WWETCO FlexFilter can be used to upgrade an existing basin as well as in new construction.
“It makes a very good addition when retrofitted into an existing filtration system that’s too old or just not doing enough,” says Darin St. Germain, Group Leader, Concrete Filtration Systems for WesTech. “The regulations are getting tighter and tighter on what you can release, and those changes are going to continue to happen.”
The WWETCO FlexFilter’s versatility allows it to be applied as tertiary treatment during normal plant operation in between storm events. When wet weather increases flows, a portion (or all) of the tertiary filter automatically converts to a storm flow filter, then switches back to tertiary treatment when the surge subsides, St. Germain explains. “The market opportunities for this type of tertiary treatment are going to continue to grow.”
A number of other applications take advantage of the WWETCO FlexFilter’s high rates of solids removal to enhance the operation of existing facilities and open the door to emerging technologies.
For example, the FlexFilter is being studied for upfront carbon removal in biogas plants.
“The carbon is removed by the filter and then sent to anaerobic digestion, which produces more gas, meanwhile lowering the energy needs of the filter,” Boner says. “By taking the carbon out upfront, you produce more gas and reduce the energy footprint.”
The California Energy Commission recently approved a pilot study using the WWETCO FlexFilter for carbon diversion in a northern California biogas facility, to be launched in 2018.
“It’s no longer an untested product; it’s out there being used successfully in a variety of capacities,” says St. Germain. “Engineers and designers are seeing, here’s something I can do that’s cost effective and can manage the problem without a lot of labor required. As more people are learning about the WWETCO FlexFilter, more opportunities are emerging.”
“There’s significant water quality improvement and public health benefit of this 21st century treatment technology and ultimately, that’s our goal,” says Cach.