Longer life for water treatment reed beds A green technology that uses reed beds to treat wastewater has received a major boost thanks to an EU initiative that extends the system's working life. Climate Change and Environment © Thinkstock There are over 12 000 constructed wetlands across Europe, which are used to further treat wastewater that has already been passed through water treatment plants. The wetlands usually comprise a gravel bed planted with reeds through which the wastewater passes and is purified by biofilms of microorganisms living on the gravel's surface. Original predictions for the working life of constructed wetlands were 50-100 years. However, because the gravel becomes clogged, this figure has been drastically revised to an average lifetime of less than 10 years. Moreover, refurbishing the system is both time consuming and expensive, and disrupts the water treatment process. The ARBI (Autonomous reed bed installations) project successfully demonstrated a transportable system containing purpose built magnetic resonance sensors, which give prior warning of clogging. Water quality sensors measured dissolved oxygen, redox, pH and temperature. An industrial programmable logic controller was also produced and used to automate the system, making measurements and adjusting the bed conditions. The probes are deployed at several locations within a wetland to provide measurements of the clog state of the gravel bed at different depths, enabling the problem to be isolated and speedily dealt with. This means that the entire reed bed does not need to be removed and replanted. ARBI is a modular system that offers a step change in constructed wetland technology, supplying an off-the-shelf solution. This can be easily tailored to customers' needs with regard to treatment volume and contaminant level by simply using multiple modules. The system monitors clogging and helps maintain optimal conditions with minimal need for human intervention. It can also be applied to other water treatment systems based on subsurface flows, including slow-rate sand filters and river bank filtration. ARBI will benefit those organisations that wish to install reed beds for water treatment, but were discouraged by concerns over cost and performance. It will therefore enable environmentally friendly constructed wetland treatments to be used far more widely than previously thought possible. This will increase the potential size of the market for reed bed installers and by enabling it to reach its true potential. Keywords Reed beds, water treatment, wetlands, biofilm, ARBI, clogging, magnetic resonance sensors
