Permaculture teacher Geoff Lawton scrambles through a clump of reeds perched over a some large boulders and gingerly steps over a pond choked with Duckweed and Salvinia floating on the surface. You can hear the frogs croaking in the background. Birds are singing in the trees. He peels back a clump of papyrus reeds to reveal another hidden frog pond. You may think this is a scene taken from a wilderness somewhere in a thriving jungle. We’re in a suburban Sydney backyard. A yard no bigger than most you’ll find anywhere. But its not a normal backyard. Its a Permaculture garden with its own little wetland. Building a wetland in your backyard is not something many people would ever consider – except if you’re into Permaculture. Penny Pyett’s home has a wonderful grey-water reed-bed system that looks complicated at first but is so simple to design into your garden and the benefits are many. Apart from encouraging native frogs and wetland creatures to return, its a channel for all household grey water waste.
No dumping of water back into the storm water drain and out to sea here. Penny is using her waste water for productive ends. When the water is cleaned through a series of gravel reed beds and filtered through a series of frog ponds – it gets fed to her fruit trees. Penny has got a food forest of productive trees that are also fed by the nutrient waste from ducks. Ducks in the City. You need ducks to keep eating those fat little frogs you have growing in your reed bed – right? Thats all part of the Permaculture philosophy after all. But we’re getting ahead of ourselves here so lets jump back and get back back on track. Lets take a closer look Penny’s greywater system and take a look at her design. All the greywater in the house is dumped into a header tank which is located under the house. In Penny’s case, it happens to be an old bathtub. The bathtub has a 45mm PVC pipe that runs underground to the desired spot for her three gravel reed beds. Course gravel is used to quickly soak any waste water and a series of thick reeds and boulders are used to hold the system in place should a sudden rain event or deluge occur.
Any thick gravel is suitable preferably one that doesn’t have any limestone which will alter the pH. Wetland plants are designed to grow in waterlogged soils with very low oxygen levels. Most wetland plants are adapted to “pull oxygen out of the air” and diffuse it down through the roots creating little aerobic zones. This stimulates microbial activity and bacterial growth to occur. The bacteria will break down compounds suspended in the soil and help filter the water as it runs through the various gravel beds and out to the frog ponds. Microorganisms break down about 90% of pollutants and waste breakdowns in the gravel. The plants also act as a carbon source for microbe activity when they break down and decay. Plants able to be grown in permanent water swamps Plants that are able to grow in fresh water swamps, creek and dam banks The grey water eventually drains into a small frog pond where small fish can also be added to keep the mosquito population under control.
Penny Pyett likes to recycle a lot of materials thrown out by people back into her wetland. So discarded plastic children’s play pools and sand pits are collected and recycled by Penny into her wetland garden. Buried in the garden between thick reeds, they look natural and inviting. Water is constantly in play moving through the gravel and dipping from one large pond to another and so on. Eventually the water is returned clean and back into a swale that supports a food forest system. The end result is that you end up irrigating your garden every time you take a shower or wash the dishes. Nothing is wasted as the system takes care of itself. Penny’s greywater reedbed system will be featured in The Urban Permaculture DVD out later in the year. There is some outline information below, but bear in mind that you may need to get help (such as a report) from a sanitation consultant in order to have the system passed by the Environment Agency or other relevant body. CAT offers a consultancy service, through which our sanitation consultant can give technical advice on the type of sanitation system that will best meet your needs and satisfy regulations.
For example, you could just book an hour or so with our consultant if you want to discuss the options for off mains sewerage. A vertical flow reed bed for secondary treatment should allow 2 square metres per person (but decreasing as number of people increases - so for 50 people the reed bed area could fall to 1m2 per person). The bed area is calculated on the amount of sewage each person produces, which is assumed to be around 200 litres per day in domestic settings (but less where use is daytime only). If the bed is for grey water only you would calculate the area on the basis of water produced, so for small systems that would be 1m2 for every 100 litres of sewage. Grey water reed bed areas are likely to be 30% less than for complete sewage because approximately 30% of domestic waste water goes down the toilet. A horizontal flow reed bed may be used for tertiary (third stage) treatment, but not for secondary treatment. This will need about 1 square metre per person, but with a minimum size of 6 square metres.
This bed turns nitrates into nitrogen gas, and won't be needed if you're only treating greywater - unless the effluent is flowing into a pond where a better quality is needed. The grade of pea gravel in a reed bed does not have to be too precise. 5-10mm is fine, as it's only a thin layer and is there to support the sand, and stop it washing down into the coarse gravel below (see our tipsheet for a diagram). The gravel used should ideally be washed, and graded to 20mm (but this is flexible). It will take 2-3 years for the reeds to establish, but the system can be used in that time as the reeds need the nutrients and the beds can work without reeds. Reeds aerate and provide frost protection. For controlling the discharge of effluent to a vertical reed bed, we recommend a Floating Outlet or "FLOUT" which are less prone to blocking up. You can get them from Watercourse Systems. In a vertical flow reed bed the ammonia turns into nitrates. There should be a settlement tank between vertical and horizontal flow reed beds, to take out solids that are created by the vertical flow bed (such as dead microbes).