Constructed
wetland systems are based upon the symbiotic relationships found in natural
marsh ecosystems at the soil / water interface. These relationships, between
bacteria and other microorganisms, animals and algae are responsible for most
of the world's naturally pure water which we adapt for specific needs, using
a wide variety of plants.
Our objective
is to employ complex ecological relationships to create a 'food web' which
enables waste product to be broken down and assimilated in plant and animal
biomass. This distinguishes our approach from conventional waste treatment
methods.
Each wetland
plant has a particular speciality in the purification of organic and inorganic
waste and is planted in a specially designed filter bed. The system maintains
an aerobic environment, in the filter bed, using both vertical and horizontal
flows, accelerating natural biological processes.
Once bacteria
and microorganisms are established on aquatic plant roots and rhizomes, they
form a symbiotic relationship with the plants, resulting in increased breakdown
and removal of effluent from the wastewater surrounding the root system. Plants
release exudates which protect bacteria and microbial populations from competition.
These exudates are also efficient at the removal of harmful bacteria and microorganisms
found in sewage as well as balancing pH.
During microbial
degradation of the organics, metabolites are produced which the plants and
microorganisms utilise as a food source along with nitrogen, phosphorus and
minerals, each using the others' waste products. The electrical charges on
aquatic plant root hairs also react with opposite charges on colloidal particles
and suspended solids, causing them to adhere to the roots, thus removing suspended
solids from the wastewater stream.
Digestion and
assimilation of these organic particles is accomplished by the plants and
microorganisms. Oxygen is translocated from the upper leaf areas to the root
area, producing an aerobic zone around the roots and rhizomes which facilitates
breakdown of domestic and farm sewage, silage and sludge. The anaerobic pockets
accelerate denitrification processes.
Aquatic plants
are able to absorb certain organic molecules intact, which are translocated
and eventually metabolized by plant enzymes - as is seen in the use of systemic
insecticides, which enter the plant via roots and shoots and pass through
the tissues. The biological reactions which take place between plants, microorganisms,
bacteria, algae and environmental pollutants are numerous and complex, and
demonstrate that aquatic plants have a broader function than simply supplying
a large surface area for microorganisms.
The results
have been so striking that the USA Environmental Protection Agency, (EPA)
has given its approval for systems based upon these principles to be used
in treatment of sewage and sludge, (primary through tertiary) and for use
in removal of heavy metals and toxicants from wastewater and land.
Ponds
and wetlands are used for the treatment of sewage for communities, agricultural
waste, landfill leachate and contaminated surface water. The diverse ecology
produces an excellent effluent while also enhancing the environment.
The complex
food web of a pond ecology combined with long retention times enables difficult
or high strength wastes to be degraded. Screened primary sewage or agricultural
waste can be degraded anaerobically at the bottom of the pond while maintaining
an aerobic surface layer. One advantage is that no sludge is produced as all
the nutrients are consumed by the flora and fauna within the pond and wetlands.
There are excellent
technical arguments for using ponds in conjunction with wetlands. Ponds contain
large numbers of organisms with generation times in the order of days and
not years as in wetlands. They contain principally algae, which grow using
sunlight (photosynthesis) and evolve oxygen, and bacteria grow in their vicinity
and absorb the oxygen and consume both ammonia and organics in the waste stream,
releasing carbon dioxide which the algae absorb.
A pond uses a
closed carbon cycle where the algae and bacteria recycle the carbon dioxide,
unlike conventional waste treatment methods such as activated sludge where
the cycle is open and oxygen has to be continuously supplied, and carbon dioxide
removed. The closed cycle operation of a pond reduces (but does not eliminate)
the need for mixing or aeration, since the algae and bacteria are self supporting.
There are other
benefits. The growth of algae produces a strong pH shift towards alkaline
conditions and this favours both ammonia evaporation and nitrification. The
high pH shift also causes phosphate mineralisation. We would expect the ponds
to have aeration for back-up purposes.
The greatest
benefit of the pond system is its rapid response to shock loading events.
As bacteria and algae have short generation times they are able to adjust
their population levels according to the loading received. In addition they
can recover from shock loads reasonably quickly. This has the added benefit
of protecting the associated wetlands from the effects of raw shock loading,
partly by dilution within the residence time of the pond and partly through
the biochemical activities of the organisms within the pond.
Wetlands that
occur at pond outlets serve to trap the algae and bacteria, allowing grazing
organisms to shelter within the wetland plants and consume algae and bacterial
floc. This is the first step of the food chain that occurs in a mature wetland.
The basic properties
of wetland treatment systems are that of combined microbial filter and root
zone mineralisation. The optimal design for a pond outfall wetland bed in
a treatment system is one which changes from horizontal flow to vertical flow
at the end.
The horizontal
flow section allows filter feeding organisms to trap the algal and bacterial
loading and the vertical section traps and metabolises residual nutrients.
The tail end section of each bed must have a humus trap to catch any residual
floc to prevent sludge from getting into the following pond. The humus is
discharged onto trees that the surround the treatment system, acting as a
shelter-belt, which utilise the nutrients contained within the humus for growth.
Ponds naturally
evolve in nature into bogs which are colonised by trees. If a pond is required
to absorb nutrients then it will consequentially become eutrophic, (nutrient
rich). Nutrients in ponds are not only assimilated, they are also produced
by the continuous recycling of nutrients. This contrasts with activated sludge,
where the organisms are rapidly assimilating nutrients and organics, and are
in an exponential growth phase.
Ponds have organisms
of all ages and the average nutrient levels reflect the steady state turnover
of these nutrients. Ponds must be correctly designed, otherwise the average
nutrient levels in the outflow will progressively rise, year after year. In
the case of phosphate this is critical, because accumulation of phosphates
can eventually lead to the development of toxic blooms of blue green algae.
Algae remove
phosphate and nutrients from the wastestream which is a necessary part of
wastewater treatment. The build-up of phosphate and nutrients, (and potentially
blooms of blue-green algae) in our proposed system is controlled through filtering
out the algae, which contain the phosphate and nutrients, on a daily basis.
The algae are
filtered through wetland beds, which consume and mineralise the nutrients
and algae, removing the problem. The humus generated from the wetlands are
discharged onto trees where it helps build-up the soil and supports the growth
of trees and other land plants.
The sizing of
ponds and associated wetlands must reflect the effects of annual temperature
variations, otherwise microbial washout at low growth rates in winter can
result in the whole system becoming ineffective. This is the natural progression
seen in natural pond and wetland systems. The wetlands naturally grow densest
where the loadings are highest, and their filtering and assimilative actions
are adapted to these conditions. Any pond and wetland system must be designed
to allow the system to self evolve.
Lake Aid
Systems (LAS), floating wind powered aerators, add processing capability
to a pond - based system. LAS also addresses the majority of lagoon
related problems including odours, short-circuiting, sludge accumulations,
shock loading, septic influents, stratification, algae problems, winter ice
cover and overall processing inconsistency, all with zero-to-low energy and
virtually no increase in on-going maintenance or manpower.