Constructed Wetlands and Reed Beds
The constructed wetlands and reed beds water treatment methods are part of the scientific field of phytoremediation. This field deals with water and land purification using plants and the microorganisms related to them. Constructed Wetlands mainly purify water and in some cases, sludge.
Constructed wetland is a general name for many methods and approaches. What they all have in common is the use of aquatic plants in the purification process. Aquatic plants have a unique characteristic, a system of transferring gasses. The plant transfers oxygen from the air to the roots that are in a saturated bed, naturally lacking oxygen. At the same time, the plant releases gasses into the air in the purification process, specifically nitrogen. Besides oxygen, the plant releases additional substances to the roots that create an ideal soil for microorganisms which dissolve the pollutants in the wastewater. Different plants have different microorganism environments and passing water through these different environments (a process called consortium), allows even for molecules that are hard to degrade, to gradually decompose and revert to mineral form.
The unique ability of aquatic plants to create saturated oxygen rich areas in proximity to anaerobic areas enables efficient processes of nitrification and denitrification in the same system, while releasing inert nitrogen in gas form.
The use of many different types of plants (different types of emergent lilies, Cyperus, sedge, reeds, phragmites, cattail, bulrush, Juncus, pennywort, scotch grass, Spartina, submerged plants e.g. Sagittarius, centella and many others), not only enables the consortium, it also enables the precise use of plants with different "expertise" and treating a large variety of pollutants. This variety gives the system the ability to withstand natural disasters and man-made damage, since different plants have different levels of sensitivity, and it is almost impossible for the entire system to be compromised by an unusual pollutant.
Reed beds were developed in Europe in the 1960s by engineers. The ecological-biological side of it was perceived to be less important, and the working assumption was that the type of plant is of no importance. In most of the systems what is planted is Phragmites australis and in some – Typha (cattail), mostly since these plants are widely accessible in Europe and are able to withstand the European winter. Newer more holistic approaches consider the invasiveness, water use efficiency and phytotransformation potential of species.
Research in the past decades attempts to characterize plants, types of soil, hydrological flow and their combined ability to purify different kinds of pollutants in the water. We now know that every plant excretes different substances to the rhizosphere, creating an environment that is fit for a different variety of microorganisms. A different structure of the roots and the absorption and vaporization ability lead to different "specialization" of plants towards different pollutants.
Furthermore, there is currently great emphasis on the co-metabolism effect according to which molecules that are hard to degrade begin the decomposition process around one plant (which may be e.g. reducing its toxicity) and continue to degrade around another. This collaboration effect in dissolving hard pollutants does not exist in monoculture reed beds.
Another extremely important element is the soil structure. The primary function of the soil matrix is to meet the hydraulic requirements aligned with the type and volume of the treated water but the biological and chemical structure also has significant impact on the final outcome, a fact which is the subject of many research studies focusing on a variety of pollutants ranging from nutrients to salinity.
In order to bridge the gap between science and engineering in this field, the Water Revive engineering company relies on the accumulated knowledge of its parent company Ofra Aqua Plants which has invested more than two decades of research in phytoremediation and is currently the custodian of hundreds of aquatic plant species, many of which are extinct in the natural habitats.
In all ecological systems, especially in water systems, it is not possible and not wise to try and force the reality. What works in a certain environment, will not necessarily work in the same manner in a different environment. Ofra Aqua Plants possesses and spends significant resources in order to acclimatize, diagnose and develop the methods and plants that fit best to the Israeli water and climate, and expanded to further climates including the European with freezing winters.
Since its establishment, Water Revive has taken upon itself to continue the research and development in the field of drinking water. The constructed wetland system of Water Revive is a unique Israeli developed system. This is a tailor-made system adapted to the conditions and environment it is built in.
Ofra Aqua Plants studies matters that are crucial to the Israeli environment that were historically of lesser interest in Europe and other more water-rich countries, and therefore were never researched: such as what is the extent of water loss of different plants? Ironically, reeds including phragmites and Arundo donax (another common plant used in reed beds) are the largest consumers of water amongst the plants tested. What is the ability of different plants and flow methods to extract boron and chlorides, which are rising in Israeli irrigation waters due to increased desalination and wastewater recycling ? A study conducted by Ofra Aqua Plants regarding the ability of different plants to extract boron shows that the leading plants in Europe are amongst the worst purifiers. What is the salt composition preferred by different plants? Is there a correlation between domineering and purification skills? (there actually is none). What is the composition of microbes in the subsurface of particularly effective systems and how can this consortium be encouraged? What is the best carbon source and its optimal concentration for enhanced denitrification to produce zero-nitrate levels in drinking water? The unique, long-term accumulation of knowledge and experience by Ofra Aqua Plants is the primary reason for the stability and high level of function of the beautiful, practical systems that are the company’s hallmark.