Free-floating aquatic plants cultivated in water canals above the planter boxes in the greenhouse remove final traces of nutrients and pathogens. Aquatic plants are chosen for their ability to absorb particular nutrients and to remove pathogens, metals and other contaminants from wastewater.

The extensive root systems of aquatic plants create an excellent habitat for the microbial populations necessary for water treatment (Reed et al., 1987). Aquatic plant systems have been shown to be very effective as a secondary or tertiary stage for water treatment and nutrient removal (USEPA, 1988).

Ethnobotanists are at work identifying which plants in nature are best suited to these tasks, while genetic engineers are manipulating DNA strands in order to design new plant varieties which perform these specific tasks exceptionally well. These plants are either selectively bred or genetically engineered to maximize their water reclamation potential.

Duckweed , pennywort, and water hyacinth are examples of species found in nature which are particularly suited to taking up nutrients through their roots and storing these nutrients in their leaves. These plants can then be harvested and used as natural fertilizer, thus reclaiming the valuable nutrients found in our wastewater (North Carolina State University, Septic Systems – WWW).

As aquatic plants grow, they take up simple forms of nitrogen and phosphorus, and secrete complex organic molecules back into the water. Bacteria and larval stages of many organisms then digest these organic molecules. Bacteria break down easily decomposed organic matter to form simpler substances which then become food for algae and other organisms. Algae and other aquatic plants provide shelter and substrates for many types of fish and invertebrates and assimilate large amounts of nutrients and significant amounts of trace elements, thus further purifying the water. (Patrick, R. 1976 – WWW).

Examples of Aquatic Plants Suited for Water Treatment

Water Lily has an extensive root system with rapid growth rates, but is sensitive to cold temperatures. It is an ideal plant for water treatment systems in warm climates.

Duckweed (Lemma spp.) has greater cold tolerance than water hyacinth and a good capacity for nutrient absorption.

Pennywort (Hydrocotyl spp.) is relatively cold tolerant with a very good capacity for nutrient uptake.