Installed at the outlets of septic tanks, effluent filters provide an economical way to trap suspended solids or particles reintroduced from scum or sludge layers before they discharge to drainfields. Clogged filters cause poor performance of the septic tank, but they create a problem far easier and less expensive to solve than restoring or replacing a soil absorption system.
“A clogged filter is a good thing,” says Peter Gavin, president of Polylok Inc. in Wallingford, Conn. “Homeowners are protecting the most expensive portion of their on-site systems. What ultimately makes leachfields fail is solids plugging the pores of the soil, preventing water from percolating down. Toilets gurgling and sinks draining more slowly are passive warnings to homeowners that their septic tanks need servicing.”
When designing his company’s first effluent filter, Ted Meyers, president of Tuf-Tite Inc. in Lake Zurich, Ill., aimed to keep people interested in their septic tanks. “The original purpose of effluent filters was to trap large, inorganic objects such as cigarette butts, prophylactics, and feminine hygiene products, as it’s difficult to remove them once they enter the drainfield,” he says.
Over the years, filters have morphed to trapping smaller solids and hair and lint particles bigger than 1/16 inch. “Some people want to make openings smaller than that, but they will clog faster in normal septic tanks,” Meyers observes.
Matt Byers, on-site wastewater manager for Zoeller Pump Co. in Louisville, Ky., believes filters are great because they protect pumping systems and signal potential homeowner abuse. “If a 4-inch filter plugs up in less than three months, something is going on at that house,” he says.
Design basics
In an effluent filter, wastewater flows by gravity through slot-configured orifices. Manufacturers agree that effluent filters have more similarities than differences. Their designs work like draining pasta in a colander, except that the screen and mesh openings aren’t round, they’re linear. To determine linear inches of filtration, manufacturers multiply the number of slots by their length, usually 1 1/2 inches.
For example, Polylok’s most popular filter, the PL-122, handles residential and commercial flows of 1,500 gpd. Its screen filter has 122 feet of 1/16-inch filtration (the industry’s standard width). The PL-525 residential-commercial filter has 525 feet of filtration and handles 10,000 gpd.
Zoeller’s WW residential series has deep-pleated slots with 132 feet of filtration and a flow rate of 1,000 gpd. The deluxe residential-commercial filter has 528 feet of filtration and handles 4,000 gpd. Both filters are polypropylene.
Tuf-Tite’s 4-inch-diameter EF-4 residential series has 86 feet of 1/16-inch filtration area and handles 800 gpd. The 6-inch-diameter EF-6 commercial series has 244 feet of filtration and handles 1,500 gpd. Both have high-speed, injection-molded sanitary tee housings with solids deflectors.
How high is the water?
Several manufacturers, including Zoeller, recommend not cleaning the filter if the water level in the tank is above the invert of the outlet. Even if a pump truck were on site, however, many consider the labor-intensive task unworthy of 50 or 100 gallons. In most cases, the filter is simply pulled, allowing material on it to rush out the tank with the excess water.
Polylok’s solution to that problem is a built-in, automatic shut-off ball. When the filter is removed, the water level in the tank pushes up a 4 1/2-inch ball that allows only 1/16-inch filtration. “One of the first things we did after buying Zabel’s line of effluent filters was to incorporate the ball into the 12- by 20-inch A100, A300, and A600 series commercial filters as an option,” Gavin says.
Zoeller developed the bypass system for its filters — a slotted, 4-inch PVC secondary screen that remains in the sanitary tee to catch chunks when the filter is removed. Maintainers merely rinse the material back down the tee and into the tank.
Polylok’s Zabel A100, A300, and A600 residential series uses disc dam technology. According to Gavin, solids collect on horizontal discs as water flows up the filter to the outlet of the cartridge. In front of the outlet is a vertical disc or dam, and above it are 1/16-. 1/32-, or 1/64-inch vertical slots of various lengths. “Solids slough off the dam and fall back into the tank, while effluent flows through the slots,” Gavin says.
Manufacturers also use components to set their filters apart. For example, Polylok has a dedicated filter cartridge and polypropylene housing that prevents the cartridge from being installed incorrectly. The PL-122 has a bushing that accepts 3- or 4-inch Schedule 40 or SDR 35 pipe. The PL-125 accepts 4- and 6-inch Schedule 40 pipe.
“We also can retrofit Zabel and Polylok filters with an optional high level alarm that alerts homeowners to service the tank because solids have built up in the filter,” Gavin says. The alarm paid big dividends for a woman who, during the bitter Connecticut winter, was recycling her newspapers in the garbage disposal.
Meyers says that Tuf-Tite’s filters differ in that the slots are on the horizontal plane to create more surface area in a given space. Byers says that Zoeller’s deep-pleated, slotted design retains big chunks.
Pressure filters
According to Gary Koteskey, president of Sim/Tech Filters Inc. in Boyne City, Mich., pressure systems that cycle or time dose to evenly distribute the effluent must be protected with pressure filters, because gravity filters are designed for septic tanks. “Many in the industry still make this mistake,” he says. “Inappropriate use of gravity filters allows debris in the dosing tank to reach the dispersal bed, and just a small handful can plug the entire system.”
The most common scenario, Koteskey says, is maintenance contractors removing plugged effluent filters, thereby permitting water above the invert of the outlet to escape. An influx of 25 gallons per inch churns up everything in the dosing tank including electrical tape, butyl ribbon, tie straps, and organic material. When the pump cycles, the debris enters the distribution system.
“When 5 or 10 percent of the orifices are plugged, the biology doesn’t have enough time to treat the concentrated wastewater coming out the remaining holes,” Koteskey says. “Systems may function like that for years, sending untreated effluent into the groundwater and creating environmental hazards.”
Properly functioning systems discharge evenly through all the orifices, dispersing an average of one gallon per square foot per day. “Drip systems require filtration because the emitters are so small, but many states don’t specify filtration for mound and sand filter systems because their manuals were written years before pressure filters were available,” Koteskey says.
The small disc or spin-clean filters used in drip and spray irrigation systems are inappropriate for high-volume systems because they create head pressure, necessitating an increase in pump size to push the effluent through the filter. “Because of that, filters plug quickly,” Koteskey says. “To achieve low head pressure, our 85 gpm A2 residential series has 70 square inches or 41 percent open area, producing two-tenths-of-a-pound head loss.” The 3-inch-diameter by 18-inch-long stainless steel filter has more than 22,000 round holes 1/16 inch in diameter.
The filter’s one-piece, injection-molded PVC housing screws to the discharge port of the pump, and connects to the force main with a Schedule 80 PVC union. The scrubbing action caused by the pump prevents the filter from plugging easily.
Koteskey encourages installing gravity effluent filters in septic tanks, as they increase the long-evity of pressure filters. “It’s a win-win combination for the on-site system,” he says. To eliminate residual toilet tissue, lint, and hair reaching the drainfield, he recommends adding a filter sock inside the pressure filter screen. Socks also are necessary in situations that dump large volumes of water into the septic tank and roil up the settled solids. Socks have 600 micron (0.024 inch), 150 micron (0.005 inch), or 100 micron (0.004 inch) filtration.
On the horizon
Manufacturers agree that maintenance is a huge issue. “Maintenance contracts are a sound idea, but whoever inspects and maintains those systems should be licensed,” Meyers says. “Some regulators expect effluent filters to be a cure-all or substitute for advanced treatment units. Expecting filters to do things they were never designed to is a problem in education.”
Given the complex nature of today’s waste stream, Byers believes it is essential for the majority of on-site systems to have filters, annual inspections, and the documentation. “A paper trail would be a boon to consumers and Realtors,” he says.
Byers wants manufacturers to establish effluent filter guidelines that present what few facts are known, then let health departments use them to educate homeowners. “We have no published scientific studies on effluent filters,” he says. “We need funded definitive research on septic tank and effluent filter systems, then use that information to develop the next generation of filters.”
