Series No. 7
Approach in Environmental Management
of Environmental Applications of Phytotechnology >
D. Floating Macrophytes
and Root Zone Plants for Improving Water Quality
Improving water quality through the use of floating macrophyte species is
another phytotechnology application. For example, different types of duck weed
and water hyacinths have been used as an alternative to waste stabilization
ponds. The inorganic nitrogen and phosphorus contained in wastewater and decompos
ed from organic pollutants by microorganisms are absorbed by the water hyacinths.
The water hyacinths with microorganisms and organic materials attached or coagulated
on root surfaces can then be harvested as feed for fish culture ponds and animal
farms. However, use of water hyacinths requires strict control, as they can
easily spread becoming a nuisance and also because they tend to incorporate
and store heavy metals.
Root zone plants can also be effectively used for the treatment of small
volumes of municipal wastewater, particularly where construction of a sewage
collection system to an adjacent wastewater treatment facility would be prohibitively
expensive. The decomposition of organic matter and denitrification usually
do not cause any problem, provided that the plant is 5 to 10 square meters
per person equivalent (depending on climatic conditions). The efficiency of
phosphorus removal is usually no more than 10 to 20% for a root zone plant.
However, this efficiency can be increased to 80% or more wit h the addition
of iron chloride which allows the precipitation of iron phosphate. The application
of this method appears to be attractive for recreational areas, where the density
of population is low, but where wastewater loadings can have a significant
E. Combined Waste Stabilisation
Ponds and Wetlands
Combining the use of artificial wetlands with waste stabilization ponds and
root zone plants is an attractive wastewater treatment method for developing
countries, recreational areas adjacent to lake ecosystems, and areas with low
population density. The reasons for this are:
||Wetlands can provide, through the use of filter media (i.e.,
sand, gravel or peat), a significant reduction of suspended matter from
maturation pond effluent.
||Wetlands can buffer the pH value of the effluent from a waste
||Effluents from waste stabilization ponds most often need a post treatment
polishing step and the use of wetlands offers an excellent cost-effective
solution to this problem.
||The use of waste stabilization ponds and wetlands, in combination,
offers a higher level of certainty as an effective pollution abatement
and aquatic ecosystems management strategy.
F. Use of Plantations
for Wastewater Treatment
Specialized, fast-growing plantations that require water and nutrients offer
an efficient, inexpensive way to recycle wastewater. Trees absorb water for
transpiration and metabolize the chemical constituents through timber biomass production. This has many advantages for some communities relative to other
conventional methods of wastewater treatment. Tree plantations operate outside
of the food chain, require little energy and have relatively low operating
costs. However, additional health and safety measures are required for these
open environment systems.
A plantation recycling system is composed of a forest plantation, a storage
lagoon and a distribution network (i.e., pumps, pipes and sprinklers). It can
be located at low cost on marginal agricultural land. To prevent groundwater
contamination, this type of effluent recycling should be practised only during
dry spells. When conditions are favourable, such as in sunny and/or windy weather,
the recycling system should be loaded to its full capacity.
The process that determines the effectiveness of fast growing plantations
for wastewater treatment is evapo-transpiration, which is largely dependent
on weather. In temperate zones where this phytotechnology has been applied,
hybrid poplars have been used because they quickly develop large foliage that
stays on trees throughout the growing season. Due to advection, greatly enhanced
by air circulation in a well-spaced plantation, this type of recycling system
can achieve very high evapo-transpiration performance. Practical operational
experience in applying this phytotechnology has enabled researchers to combine
an innovative, environmentally sound effluent recycling system with intensive
silviculture. This approach has considerable potential for recycling wastewater
in crowded and growing cities in developing countries.
G. Use of Floodlands for Water Quality Improvement and Eutrophication Control
The application of ecohydrological principles for eutrophication and phosphorous
control starts from the top of the catchment. The first stage involves the
enhancement of nutrient retention within the catchment by reforestation, the
creation of ecotone buffering zones, such as artificial flood lands, and the
optimisation of agricultural practices. The buffering zones at the land water
interface reduce the rate of groundwater flux due to evapotranspiration along
the river valley gradient. Nutrient transformation into plant biomass in ecotone
zones may further reduce the supply of nutrients into the river. The wetlands
in the river valley buffering zone reduce the mineral sediments, organic matter
and nutrient load transported by the river during floods periods through sedimentation.
Also nitrogen load can be reduced significantly by regulation the water level
to stimulate denitrification through anaerobic processes. The properties of
large scale systems are difficult to predict and therefore should be assessed
continuously at every stage of implementation and adjusted to maximise potential