Much of the land mass of Australia is quite arid, meaning that the surface water flow is on the lower side of the scale. The industrial age has, however, seen the ever continuing growth of vast metropolitan areas like Melbourne that have encroached on natural water catchment areas that have numerous advantages both in waste treatment and agriculture.
Waste treatment and agriculture intersect in various ways. The livestock and crops grown as part of agricultural practice need clean water so as to flourish and be profitable to the farmers, as well as provide healthy food to the populace of Australia. Natural wetlands have the ability to clean waste water by removing heavy metals and other minerals.
In the absence of these natural wetlands, man has constructed artificial ones that mimic the role of these natural wetlands. These constructed wetlands can thus be manipulated in various ways to offer various combinations of functions.
Types of constructed wetlands
Subsurface flow wetlands are those whereby the water or effluent is directed beneath the ground of the basin that has been designated as the constructed wetland. Beneath the ground, the effluent makes contact with the substrate, which can be different forms of clay soil and gravel, as well as the roots of the plants that are growing in the basin. This enables the waste water to be filtered gradually as it goes through the various zones of soil.
Surface flow wetlands, on the other hand, are more simplistic in that the water is let to flow on the surface of the ground in the wetland basin. The water is allowed to flow on top and is exposed to the top soil as well as the sunlight, which has its various advantages as well.
Role of the constructed wetlands
Constructed wetlands play a vital role in cleaning up waste water. Agriculture nowadays involves the use of fertilizers as well as other chemicals that cause the water run-off from the farms to be thick with nutrients and heavy metals which in time will mess up the surrounding and destination ecosystems.
Basins of wetlands are therefore constructed near the farms so as to be a catchment of the water that emanates from the farm with the aim of treating it using natural means that have been placed there by man. Subsurface wetlands for example are used as a second line treatment phase after the effluent has gone through primary treatment so as to remove the solids. In the constructed treatment, the processes are mainly natural filtration methods that effectively clean up the water.
Surface flow wetlands are third in line to filter the agricultural waste water. Here, lingering pathogens decay off whereas the exposure to the ultraviolet rays in sunlight also kills them off. Sedimentation removes finer particles in the water to give out a product that is clean and can be used for other purposes like irrigation.
For these constructed wetlands to be effective, the time of exposure of the water to the soil and plant roots has to be long enough. Designers must therefore ensure that the rate of flow is very fast through the basin.