We are very excited about this! Finally, we got around to building a reed bed filtration system to deal with our greywater. Our greywater comes mainly from the kitchen, showers and laundry. We make an effort to only use natural soaps free from chemicals and microplastics. But still, it’s important to filter our wastewater so we can use it safely in the garden.
What is a reed bed?
Simply put, a reed bed is a basin filled with gravel and planted with macrophytes such as reeds and rushes. The purpose of a reed bed is to filter wastewater, either grey or black water. A reed bed filters wastewater through physical and biological interactions between the wastewater, reeds, microorganisms, gravel and atmosphere.
How does it work?
Greywater undergoes two treatment stages. First, the raw greywater flows from the house into a so-called grease trap. This is a tank where large solids, grease and oils are removed. In our case, we use a tall container equipped with two pipes. One pipe faces downwards in the container, the other pipe connects the grease trap with the reed bed tub. As the grease trap fills up with water, the grease collects on the top. Solids gather on the bottom and the liquid will be pushed through the pipes into the reed bed basin. If this doesn’t make sense, take a look at the photos further down which should illustrate how a grease trap works.
Once the greywater flows into the reed bed basin, the second filtration stage begins. This stage is really interesting as this is where the wastewater undergoes a complex natural treatment process. As the wastewater enters the reed bed, it moves through the root zones from one end to the other end of the basin. The roots of the water plants leak small amounts of oxygen which create small oxygen pockets within the anaerobic system. Fascinating, right? This mix of aerobic and anaerobic conditions create an ideal environment for the growth of microorganisms. These microorganisms sit on the surface of the gravel and plant roots where they break down organic matter and nutrients. Therefore, microorganisms are mainly responsible for removing any pollutants in the reed bed. Ideally, this process should take from five to seven days.
How to build a reed bed
Building a read bed is really easy. Once you have all the components, you should be able to assemble the system within a few hours. So what do you need?
You need a container for a grease trap. This can be a big bucket or any large container. Consider a container with a lid if you want to avoid looking at its content. You need a couple of pipes for the grease trap including an elbow so the pipe faces downwards. Then you need another pipe to connect the trap with the reed bed basin and a connector piece.
Update: After two days, we noticed that the grease trap was overflowing so we changed the design. Now we are using a straight pipe instead of a long elbow to connect the grease trap and the reed tub. In addition to that, we filled up the area around the pipe with big rocks to make it easier for the water to run through.
Next, you need two basins, one for the reed bed and another one for the water catchment. Bathtubs work or any other wide durable basin. Whatever you have at hand and works for the project. Ideally, you should be able to get everything from your local transfer station. No need to buy new. Recycle and reuse. In addition, you need more pipes to connect the reed bed basin with the catchment area.
In addition, you need more pipes to connect the reed bed basin with the catchment area. As you can see, it took us forever to drill through the tub. We even had to take turns. You might not have to do that depending on your design and if the ground is naturally sloped.
Lastly, you need gravel and water plants. Do some research on your local reeds. Obviously, it’s best to use what works for your climate. The gravel* should be between 10 – 20mm. We used a mix of both sizes.
Our reed bed system is still missing the water plants because the tub hasn’t filled up with water yet. We will add them as soon as the tub is full of water.
Update: The reeds are in! After we changed the design, the reed tub eventually filled up with water and was flowing into the catchment tub. So I planted the local reeds. I will start with 6 and see how it goes. The water in the catchment tub will be murky and brown initially because of the dirt around the reed roots and the gravel but it should eventually come out clear.
*Note: The filling material depends on your area. When I first looked up reed bed systems a lot of websites recommended scoria. However, scoria is more common in Victoria, Australia. There is no scoria in NSW and Queensland that’s why we’re using gravel. So it’s best to do some research on what’s available in your area, your local council website might be helpful here.