Canna As a Plant Filter

Cannas are practical and beautiful bio-filters

Dazzling orange cannas are a low-cost solution to wastewater filtration. Sophisticated wastewater filtration systems are too costly for many property owners and small businesses. Using a progression of simple water treatment tactics effectively eliminates contaminants from runoff systems. Cannas are a commonly available plant usable in sequential wastewater systems.

How Canna Filtration Works

Cannas take up toxins and give off water and oxygen

Cannas are used in rock/filter systems alone or as part of artificial marsh systems. Their roots quickly create a thick biological filter for sediment while their big leaves assist by giving off water into the atmosphere. Rock/filter systems depend on a substrate of gravel and rocks to promote aeration. Cannas hydroponically grown on the rock bed house microorganisms in their roots that feed on wastewater pollutants. Feeding microorganisms make compounds the cannas absorb through their roots as food. In return, cannas produce oxygen and nutrients that the microorganisms use. This symbiotic association purifies wastewater and produces oxygen for the atmosphere. Canna respiration also helps regulate greenhouse gases.

Elements Removed From Wastewater

Cannas filter out toxic metals

Canna roots can remove radioactive elements and low levels of toxic metals as well as organic wastes. The U.S. Environmental Protection Agency explains that microorganisms living symbiotically in the canna filter break down pollutants and "toxic organic compounds, such as benzene, toluene, and PCBs, into harmless elements that microorganisms and the plants can digest". When cannas have absorbed toxic wastes the leaves can be cut and disposed of safely.

Providing Effective Filtration

Cannas effectively clean nursery wastewater

An example of effective canna filtration is the El Modeno Gardens Nursery in Orange County, California. University of California researchers installed a pond and canna filter ditch to clean nursery runoff. UC Cooperative Extension Director John Kabashima noted that "after moving through the canna filter, the leftover water was clean enough to be reused on the nursery."

Who Can Benefit

Benefits include stormwater treatment

Homeowners benefit by installing canna treatment systems. The simplest type of canna filter is a long, shallow ditch holding a rock filter. Wastewater flows several inches below the surface, producing a large population of beneficial organisms. Inexpensively constructed for use with home septic systems, the canna filter trench replaces the leach field and allows septic tanks to be installed in most areas.

Cannas benefit municipalities when used in stormwater treatment. Stormwater must meet strict nitrogen and phosphorus requirements to be released. Cannas score high on removing these two contaminants. Tests conducted by Louisiana State University's Hammond Research Station found canna 'Australia' "had the greatest water consumption, total biomass production, and aboveground nitrogen and phosphorous content."

Canna Filter Cost

Building and maintenance are less costly with canna filters

Cannas are inexpensive nursery plants readily available for leach field construction. Artificial wetlands systems or rock/filter systems can be built for half the cost of conventional systems and cost two-thirds less to run. Using cannas in these systems provides a realistic low-cost alternative to conventional wastewater treatment.

References

• NASA: Aquatic Plant/Microbial Filters for Treating Septic Tank Effluent
• NASA: Aquatic Plants for Wastewater Treatment
• University of California: UC helps nurseries in Southern California stop polluting waterways
• U.S. Environmental Protection Agency: Polluted Runoff (Nonpoint Source Pollution)
• Science Daily: Canna Can - Ornamental Eliminates Pollutants from Stormwater Runoff

Resources

• Eco Tipping Points Project: Constructed Wetland
• Environment International: Treatment of wastewater by natural systems
• Water Environment Partnership in Asia (WEPA): Phytotechnology
• EcoWIN (Eco-efficient Water Infrastructure Network): Case Study on Constructed Wetlands
• Partner for Worldwide Perspectives: Draft, Constructed wetlands for greywater and domestic wastewater treatment in developing countries