Reed beds are a not a sewage treatment system on their own, but are used in conjunction with a primary treatment such as a settling or septic tank (which will need emptying periodically). Reed beds only treat liquid effluent - solids will need to be treated elsewhere, either pumped from the septic tank and treated with the mains sewage, or composted. Reed beds are aquatic plant based systems which allow bacteria, fungi and algae to digest the sewage and clean the water. There are two basic types of reed bed - vertical flow and horizontal flow - and the best system often results from combining the two.
You would normally have two vertical flow reed beds, one operating and one resting. These operate aerobically (with oxygen) to break down pollutants, including turning toxic ammonia into nitrates. A regular maintenance procedure is to swap from one to the other, usually every few weeks. This prevents blocking and allows them to operate most efficiently. A horizontal flow bed usually follows a vertical one, and operates anaerobically (without oxygen) - turning nitrates to nitrogen gas (you may well have a consent limit on nitrate).
Vertical flow reed beds require a fall of at least 1.5 metres to provide good treatment, and about 2 square metres per person served, with the necessary size per person reducing for as the number of people increases. A horizontal flow bed requires about 1 square metre per person (but a minimum of 6 square metres). Reedbed maintenance is basic; just ensure that they are functioning effectively and keep reeds and other plants in check.
The diagram above is taken from a book we publish: Choosing Ecological Sewage Treatment (by Nick Grant, Mark Moodie & Chris Weedon), which covers all aspects of sewage treatment from reed beds to septic tanks, and helps you make the best choices for small scale-sewage treatment (up to about 50 people). It covers compost toilets, reed beds, septic tanks, cess pits, living machines, solar ponds, and how to collect and use urine and the waste water from the kitchen and bathroom. It also contains a list of further contacts. The authors have designed and installed many ecological sewage systems, pioneering their use in the UK.
If you are considering installing a reed bed system it is well worth getting expert advice to save expensive mistakes. Our Eco-Sanitation Consultant can give detailed technical advice on composting toilets, reed beds, septic tanks, leachfields, water filters, water conservation, water reuse, etc.
We also cover water and sewage treatment in some of our residential short courses.
If you have a septic tank but are having problems with it, see the publication Septic tanks: An Overview by Nick Grant.
Ecosystem services: Land use, water and waste management (5 days)
Monday, November 14, 2016