DESIGN AND CONSTRUCTION
Designing a reedbed
system is not simple
Being a natural treatment, reedbeds do not fall within the framework
of the exact sciences and the various equations include factors of uncertainty
that the designer must carefully evaluate. For this reason it is important
to contact a company with great experience.
not very deep.
Since the roots of the plants used do not reach depths greater than
80 cm, reedbeds have a maximum depth of about 80-100 m. Reedbeds with
higher depths are unnecessary and counterproductive as part of the waste
water escapes the action of the plants.
One of the
limits of reedbeds and constructed wetlands is the need for dedicated
Constructed wetlands needs more usable area than conventional systems,
not always available to those who would like to apply it.
reedbed is easy
The lack of advanced technology suggests that it is relatively easy
to build a reedbed, but in reality there are several technical solutions
to follow, unknown to most people, which makes it necessary to rely
on a tried and tested product.
are filled with soil
Soil must never be used for filling reedbeds. It damages the plant impairing
its functionality since it causes the growth of weeds and probably the
clogging of the entire system. Aquatic plants have to live only on what
they find in the wastewater and they don't have to draw nourishment
from chemical and biological elements of the soil.
divided into two categories: horizontal subsurface flow and vertical
The most common of all are the horizontal subsurface flow reedbeds (maximum
depth 0.8 m), easier to realize and easier to manage. The vertical flow
ones (maximum depth 1.1 m) need smaller surface but require a discontinuous
supply of wastewater only possible with equalization tanks and pump
station that increase operating costs.
The plants suitable
for reedbeds belong to a few selected species
For reedbeds can be used Phragmites Australis, several varieties of
Typha, Juncus, Carex, Scirpus and Iris Pseudacorus.
USE AND OPERATION
not suitable for seasonal use
Nothing could be more false! Reedbeds are precisely the most suitable
system to treat wastewater from seasonal users, such as farms, campings,
hotels, country houses, etc.. Unlike conventional activated sludge systems,
reedbeds do not suffer variations in organic load being able to have
much higher hydraulic residence times. This makes them particularly
effective in the treatment of wastewater of seasonal activities such
constructed wetlands are suitable for re-use of wastewater
Constructed wetlands, if well sized, allow reuse for irrigation of wastewater,
with obvious advantages of energy saving and re-use of the resource.
allows the high reduction of the bacterial load
It has been proved that reedbeds reduce 99% of the bacteria present
in the wastewater, with peaks of 99.9%. In fact, the alternation of
aerobic and anaerobic conditions in the aggregates that fill the system
does not allow the survival of the vast majority of bacteria in the
generate odors and allows the proliferation of annoying insects such
In subsurface flow systems the level of the wastewater is maintained
at a minimum depth of 10-15 cm from the surface: the surface of the
reedbed is then dry. This prevents bad odors and the deposit of insect
larvae (problems may occur in systems with surface flow, pond type,
not dealt with here).
After a few years
the acquatic plants need to be replaced
In reedbeds, if properly dimensioned, you do not need to replace the
periodic emptying of septic tanks
As with the other treatment systems, for the proper functioning through
time of a reed bed, septic tanks must be emptied periodically (the frequency
depends on the volume of the septic tank).
Some plants can
be cut in the winter period
In cold weather the plants used in the majority of cases (Typha and
Phragmites Australis) acquire that "dry" aspect of that some
may not like. These plants can be cut even up to a few centimeters in
height. This does not reduce the exchange of oxygen in the rhizosphere
(roots-substrate) which allows the treatment of the wastewater.
The costs of
management and maintenance of reedbeds are almost zero or insignificant
Except for the periodic emptying of the pre-treatment, however required
for all treatment systems, constructed wetlands and reedbeds does not
have significant management costs, as devoid of electromechanical parts
(and therefore it is not even necessary skilled labor). Only for vertical
subsurface flow reedbeds, for which it is necessary a discontinuous
flow of the wastewater, there are costs associated with the use of pumps.
For this reason, if possible, for small plants it is recommended the
use of horizontal subsurface flow systems, in which there is no need
for electricity and complex technologies.
wetlands are made to last
A constructed wetland, if well designed and well managed, can last more
than 25 years.
If poorly managed
a reedbed can become clogged
If the pre-treatments are not emptied periodically, the plant slowly
becomes clogged, thus invalidating the operation of a plant also well
built. Nevertheless, in most cases, appropriate measures taken during
construction can make simple the possible intervention of maintenance
needed for resetting the system.