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Pros Report Advances in Biological Engineering

The pond industry continues to refine its techniques for enabling efficient and effective biofiltration.

By Lori Luechtefeld

As ponds and water gardens are designed to mimic nature, so are the water quality maintenance processes. In nature, microscopic organisms, or beneficial bacteria, help remove waste from the water and drive the natural nitrogen cycle. Pond professionals report looking to replicate this vital process in their projects. Their preferred means of doing so vary widely.

Mechanical filtration - the physical act of removing debris from the water - proves fairly straightforward, according to Andy Schoenberger, outdoor living product manager or Franklin Electric in Oklahoma City. The subsequent biological filtration process, however, allows for more creative license, he said. "As long as there is an appropriately sized place for the beneficial bacteria to grow and multiply - whether a bog, waterfall filter or pressurized filter - we achieve the purpose," Schoenberger said.

The main goal of biological filtration is to support a thriving colony of beneficial bacteria, which will feed on pond waste and organic matter and convert deadly ammonia into nitrates that pond plants can take up. To support biological filtration, Rick Bartel, administrator and primary instructor at the Savio Water Feature Institute in Chattanooga, Tenn., said two elements prove vital: surfaces that nitrifying bacteria can adhere to and enough of those surfaces to support the level of beneficial bacteria required to keep up with the pond's waste levels.

"One of the biggest mistakes contractors make with biological filtration is that they don't put enough filtration on water features," Bartel said. "Waterfalls are getting bigger, and people are cramming more water through the same filters."

John Russell, CEO of Russell Watergardens & Koi in Redmond, Wash., said myriad devices designed to house colonies of beneficial bacteria exist - from waterfall and bead filters to pressurized and gravity filters. No matter the type of biofilter, ease of cleaning remains a key consideration. “If it’s easy to clean, owners will clean [the filter] more often and it will run at peak efficiency,” he said. “When it’s hard to clean, they don't clean it."

Many biological filtration systems also provide mechanical filtration by catching debris, said Bob Gordon, owner of Pond Systems in Santa Rosa, Calif. For such systems to work properly, he said the mechanical and biological filtration functions must remain somewhat separate, because if too much debris becomes trapped in a filter, it can snuff out the beneficial bacteria harbored there. "In the long run, the ability to safely and thoroughly clean a biofilter is what makes the difference between one biofilter and another," Gordon said.

Certain multi-chambered systems act as mechanical and biological filters due to the nature of the media used, said Ryan Kilmartin, biologist and system designer for Waterlife Design Group, a sister company to Aquatic EcoSystems Inc. in Apopka, Fla.

"The media captures solids and is constructed of a material that is conducive to the colonization of waste-removing bacteria," Kilmartin said. "When biomedia is clogged with solids, however, heterotrophic bacteria start to form, which compete with the good microorganisms for space and resources and can drain oxygen from the water."

When it comes to waterfall filters, Russell said the only way to clean many models is to take out the media and hose them off - something many homeowners do not relish doing. To enable routine, easy cleaning, Russell said his company introduced the Hydro Vortex back­flushable waterfall feature.

Backwashable biological filters are the new standard, according to Demi Fortuna, Proline product manager for Danner Mfg. Inc. in Islandia, N.Y. True biological filters need two to four weeks to get the bacterial colonies growing, he said. After that, the sticky biofilm that develops on the media surface starts to trap even fine debris.

"In contrast to the pad-type filters, the more clogged it gets, the better it works," Fortuna said. "The discrete pieces of media also drop their accumulated debris very easily, as the pieces swirl around, or fluidize, during the backwash cycle."

For example, Fortuna said the Proline low-pressure filter system uses a manually operated agitator to fluidize the media bed. "Low-pressure, high-efficiency pumps can be coupled to the filter to maximize flow per watt without losing the ability to backwash," he said.

Along these lines, Les Wilson, director of equipment at TetraPond in Blacksbury, Va., said recent improvements to the product category include design upgrades to internal media, switching from foam to bio-activators and enhancements in back-flushing performance.

While bead filters are used widely for biological filtration, Kilmartin said the broader filtration system must be designed in a way that enables them to operate efficiently. "The beads provide a high level of surface area," he said, "but if you are using the system as a mechanical filter as well, you will have to backwash to remove waste, losing beneficial bacteria during the process." Kilmartin reported a growing popularity of low-space bioreactors. "These systems use Kaldnes media, which offers maximum surface area for the good bacteria to colonize," he said. "It is neutrally buoyant, which allows continuous tumbling, preventing the buildup of solids and dead bacteria." This type of setup can prove cost prohibitive and difficult to hide, Kilmartin said, because they usually are tall and water must return by gravity to the pond.

Beyond waterfall and bead filters, Scott Cohen, a garden artisan with The Green Scene in Canoga Park, Calif., said plant importance cannot be understated when discussing biofiltration. "We talk a lot about types of filters and skimmers, but I think plants are of paramount importance," he said. Not only do plants aerate ponds and filter out toxins, he said, but they also add beauty.

Schoenberger reported that using nature for biological filtration is seeing a resurgence in popularity. For example, bog filtration uses plants and gravel to keep the pond clean, he said, mimicking nature on a smaller scale.

Some manufactured filtration products reflect this trend toward more-natural filtration. For example, Little Giant waterfall filter boxes become bog filters when owners add plant baskets to the unit, Schoenberger said. "The plant baskets are filled with gravel, planted and placed on top of the biological media for a third layer of filtration," he said.

Dave Jones, owner of the Pond Professional in Woodstock, Ga., said that though he has been building bog filters for more than 20 years, the popularization of this pond filtration style happened only within the past five to six years. He reported a preference for upflow bog systems, which periodically can be flushed.

"In a properly designed bog filter, you're getting a settling chamber, mechanical filtration, biological remediation and nutrient uptake all together," Jones said. "Bog filtration also is fun, as it allows plant enthusiasts to explore more options."

For a bog filter to provide appropriate biofiltration, however, space is required, Jones said. The surface area on the bog's gravel does not offer the same amount of surface area as specially designed filter media, he said.

Using nature as a means of biofiltration serves a practical purpose as well as an aesthetic one, said Jay Archer, a landscape artist with John Jay Landscape Development in Katonah, N.Y. Plants and natural wetlands constructions continue to filter 24/7, without electricity, he said. Should the power fail, shutting off waterfalls and other manufactured filtration systems, natural biofiltration will continue to occur while owners get the system up and running again.

Archer said floating treatment wetlands represent one of the latest trends in biofiltration. These floating wetlands that can serve as a home to nitrate-absorbing plants, prove particularly useful in pond setups where space does not permit a land-based wetland filtration system, he said. Regardless, whether owners use a floating island, a bog filter or a pressurized beat filter, Archer said the ultimate goal of biofiltration remains the same. “The idea is to have an ecologically balanced system,” he said. “For that, you need beneficial bacteria.”

Lori Luechtefeld regularly contributes to Water Garden News. Her previous article, “Mechanical Filtration Grows More Sophisticated,” appeared in the July 2010 issue.