Better water quality? It is possible
Water is the new gold. Despite the wet spring and the rain that continued to fall during the summer months, we still live in a region with significant water scarcity. It may be hard to believe, but Flanders is one of the regions with the greatest water stress in the world. The strategic water reserves deep in the ground are shrinking, just as in many other European countries. This is partly because we live in a densely populated and built-up area, where we allow our precious blue liquid to drain to the sea too quickly through streams, canals and rivers, and we quite simply need a lot of water: at home, in intensive agriculture and in industry. Climate change also plays a role.
The power of natural water purification with wetland plants
But don’t despair. There is good news as well. Today, there are many restoration programs and Blue Deal projects where we are restoring biodiversity, rehabilitating the landscape, structurally raising the groundwater level, and restoring the sponge effect of peatlands. Moreover, there are countless ways to use water more wisely and efficiently. To begin with, we can avoid wasting a single drop of drinking water, by collecting rainwater, and purifying and reusing our wastewater. This can be done through water purification with wetland plants.
Towards a cleaner future: the battle for pure water
Water purification is crucial to ensure the availability of clean water and combat environmental pollution. A major challenge is the improvement of our water quality. One example is the nitrate concentrations in our groundwater, which are too high (more than 50 mg per litre) due to eutrophication. Persistent nitrate pollution is already making drinking water extraction difficult, which highlights the importance of our water quality. There are also excessive concentrations of phosphate and several heavy metals. This is why the European Water Framework Directive 2000/60/EC (WFD) came into force in 2000. The European Union (EU) member states agreed to have clean and ecologically healthy ground and surface water by 2027. Although water quality is slowly improving, 64% of Flemish water bodies still score poorly or inadequately, according to figures from the Flanders Environment Agency (VMM), which is responsible for monitoring water quality. Some say that water quality will become the new nitrogen, leading to legal battles, permit stops, and fines. The question arises whether the 2027 deadline is realistic and whether the European rules are too strict. After all, other member states are also struggling to meet the goals. What is certain is that significant measures are still needed to achieve the objectives of the Water Framework Directive.
Within Sweco, our hydraulic engineering team is taking a multidisciplinary approach to comprehensively study our water system and restore the water balance in Flanders. For example, we are involved in the preparation of master plans, the execution of green-blue infrastructure, the construction of wadis, the re-meandering of rivers, the redevelopment of floodplains and valleys, the restoration of water buffering capacity and wetlands. With support from Europe and in collaboration with universities, we are also implementing innovative water projects, such as the installation of helophyte filters: a natural method of water purification using wetland plants.
Natural purification with wetland plants
Traditional water purification methods are usually energy-intensive and require chemicals and advanced technologies. However, we can also purify water in a natural and sustainable way using reeds and wetland plants, also known as reed bed filters or, technically, helophyte filters. Sand, plants, and bacteria do the work. Where we want to use clean water for irrigation and non-potable purposes, natural purification with wetland plants is a promising alternative to conventional water purification methods.
The power of nature: how a helophyte filter works
A helophyte filter is based on various physical, chemical, and biological processes. Its relative simplicity is its strength: nature does almost all the work. Specifically, it involves an excavated basin where wetland plants (helophytes) such as reeds, cattails, and sweet flag grow. These plants create an ideal habitat for bacteria. The plants act like a pump: they transport oxygen through their roots to and below the water surface. Aerobic bacteria live around the roots, thriving on the waste materials in the dirty water, converting it into nutrients, and finally consuming it. In this way, they help to purify the water.
Different filters for different challenges
There are different types of helophyte filters, depending on the quantity and pollution level of the water. The most common are the flow field, the horizontal flow filter, and the vertical flow filter.
- The simplest filter is a flow field. A flow field is a shallow, wide water passage where the dirty water flows through. It is used to purify large quantities of lightly polluted water.
- In a horizontal flow filter, the wastewater is collected in a pre-settling tank where an initial breakdown process takes place. Solid particles and greasy substances are separated, which prevents the filter from clogging. Water is then introduced at the side of the basin after which it flows horizontally and through a free fall through the sand bed and past the plant roots.
- With a vertical flow filter, the wastewater is also pre-treated (anaerobic pre-treatment) to dissolve all dirt particles. The water is then pumped over the reed bed, where the dirty water trickles down through the plant roots and a basin of sand and gravel for an extended period. The wastewater generally remains in the system longer. With controllable systems, the retention time of the water can be adjusted using sluices at the inlet and outlet.
More than just purification: the many benefits of reed bed filters
In addition to being a natural and environmentally friendly purification method, the reed bed filter provides three additional advantages. Firstly, the operational costs are lower than those of conventional water purification systems. Secondly, the aesthetic value is greater, as wetland plants create a natural and varied landscape. They also serve as a habitat for various species, including ducks, fish, birds, frogs, and dragonflies. Finally, cattails can be used as bio-based building material. To build more climate-friendly, bio-based, and circular, we need innovative materials. The initial test results with cattails and other plants are promising. Cattails are very light and airy, which makes them excellent insulators. They are therefore a high-quality, sustainable alternative to glass wool or polyurethane foam.
By embracing natural water purification methods, we contribute to a sustainable future. We work towards better water quality and a healthier living environment for both people and nature thanks to innovative, environmentally-friendly solutions.
