If you have land space and water treatment issues, then you should be using a reed bed system instead of high cost, energy consuming water treatment systems.
WHAT IS A REED BED?
A reed bed is:
- an engineered constructed wetland designed to simulate a natural wetland for wastewater treatment.
- a biological system in which complex chemical and microbial interactions occur.
- the utilisation of sewage or effluent for growth nutrients, resulting in a clean effluent.
- physically a reed bed consists of a watertight area from 1 m2 to many hectares in which a media is placed and reeds and other aquatic plants are planted.
- an efficient and sustainable source of treatment for contaminated wastewaters.
The treatment of effluents in reed beds is best defined by the term Phytoremediation (the treatment of environmental contamination through the use of plants).
Some common applications for reed bed systems:
- Produced water – hydrocarbon contamination from oil fields
- Domestic wastewater (sewage and grey water)
- Chemical industry contaminated water
- Coke oven effluent (steelworks)
- Groundwater remediation
- Pesticides & animal waste
- Landfill leachate
- Airports—fire training grounds and PFAS
- Service stations (oil interceptors, greywater and sewage)
Reed beds use the combination of soil, microbiology and plants to remove polluting chemical species from wastewater. The most active aspect of the system is the microbiology, with the varied flora and fauna in the soil consisting of both aerobic and anaerobic organisms. The water-saturated environment can host aerobic species because the reeds promote the passage of air through their hollow stems and roots into the surrounding soil.
THE ROOT AND RHIZOME
The key environment for all phytoremediation processes is the root and rhizome as it:
- provides aerobic areas in the soil, through gaseous exchange, in order to oxygenate the root matrix;
- allows contaminants to be removed from soil and water via plant / microbial action;
- increases the conductivity of soil systems;
- excretes antibiotics from macrophyte roots;
- allows bacterial oxidation of ammonia to nitrates (nitrification) followed by denitrification to nitrogen;
- allows stabilisation (or binding) of metals, thus reducing the bioavailability of contaminating compounds; and
- provides hydraulic pathways for the flow of water through the root matrix, allowing contact with the rootzone bacteria and fungus.
We use Phragmites australis reeds within our reed beds. These reeds have a large and complex tertiary root matrix which allows for a greater treatment surface area. The soil microbes and bacteria that achieve water treatment are associated with the roots and rhizomes of the reeds, as the root structure provides them with optimum conditions. Both aerobic and anaerobic degradation mechanisms occur, as a result of the reeds transporting air down through their root structure and into the soil medium, developing pockets of oxygenated and non-oxygenated activity. As well as supplying oxygen to the bacteria, the reeds improve the soil structure, increasing the hydraulic permeability of the soil. Phragmites australis also keeps the surface of the soil porous, by wind action. As leaves shed from the plant, through senescence, they provide a layer of nutrient-rich compost on the surface of the reed bed. These reeds also provide a habitat for animals, such as wading birds, and are aesthetically pleasing.
Rhizofiltration is the use of plant roots to absorb, concentrate and precipitate heavy metals from water. It has been suggested that rhizofiltration can be used to remove target metals for mixed contaminants. The relatively low costs of these phytoremediation technologies can allow the treatment of many sites, that can not feasibly be treated by more conventional methods. Reed beds also have minimal environmental disturbance, they reduce secondary airborne and waterborne waste, and increase public acceptance.
THE SOIL BASED SYSTEM
- soils have an extremely varied and rich microflora/fauna. The number of bacteria alone in one gram of soil may range from 100,000 to several billion, depending on conditions.
- the use of soils in reed beds gives a high surface area to volume ratio, thus allowing soil based reed beds to be more compact than gravel-based systems.
- soils, and in particular their clay and humic components, facilitate adsorption, transformation and immobilisation of certain chemical species and metal ions.
- growth of plants is more vigorous in soil than other types of media, hence a much shorter maturation period is needed.
- when grown in soil, the plant’s rhizomes penetrate much more deeply, thus giving the soil-based reed bed a larger treatment surface area.
- the adsorption capacity of the soil allows the system to cope with shock loads.
ENHANCED REED-BED TECHNOLOGY (ERT)
Enhanced Reed-Bed Treatment Technology (ERT) takes all the benefits of soil-based reed beds but further enhances their treatment capabilities by a unique series of processes designed to enhance microbial activity within the growing media. Benefits of ERT Technology® include a greater treatment capacity, greater diversity of contaminants which can be degraded and reduced establishment times.
Soil-based reed bed systems differ from gravel reed beds (often known as ‘constructed wetlands’) in that the use of soil gives a much greater capacity for treatment, particularly for industrial wastewaters. The soil is naturally high in bacterial activity, meaning a wide range of contaminants can be broken down into harmless components. Soil reed beds require careful design and construction to ensure that the correct flow of water through the soil medium is achieved, but once established they are low maintenance and easy to operate. These living systems are naturally regenerative and running costs are low, especially when compared to other treatment technologies. Soil reed beds do not require periodic replacement of the growing media, as is often the case with gravel-based systems.
Properly designed, properly operated soil based reed bed systems are odourless and visually attractive. Therefore, reed beds can be incorporated into site landscaping designs to form an attractive yet functional feature.
The advantages of ERT include:
- low cost – they are often considerably cheaper than conventional technology, due to the low maintenance required in the long term;
- low maintenance – reeds are naturally regenerative;
- low energy requirements. In a study over 16 years, the typical electrical consumption was 35,000 kWh, in comparison to 40,000,000 kWh in a conventional system. Therefore, emissions from the system (47,000 kg of CO2) are also significantly lower than a conventional system (53,000,000 kg of CO2);
- sustainable: environmentally friendly and aesthetically pleasing;
- replenishment of wetland habitat which is under threat in much of the world. Seventeen countries in the Middle East will face absolute water scarcity by 2025, including Israel, Egypt, Pakistan and Southern India;
- beneficial to ecology and biodiversity;
- produces clean water which can be reused, e.g., in forestry, agriculture (irrigation of food crops, cash crops, biofuels and biomaterials), or fishery;
- provides opportunities for community development, training and education; and
- companies can demonstrate Corporate responsibility and Environmental Awareness through the use of Reed Beds.