What are the advantages of using a reed-bed system?

They are environmentally friendly using only natural sustainable ecological processes.  Gravity driven systems don’t require any energy input.  Maintenance requirements are low but as with most systems cannot be ignored.  Operational and maintenance costs are low and can be carried out by anyone with a modicum of gardening skills and common sense.
They are highly effective when properly designed and can be used in combination with ponds and wetlands to produce near river quality water. Vertical flow reed-beds are more effective at nitrifying effluents, converting ammonia into nitrates and nitrites, than most package sewage treatment plants.