This diagram shows an example of mechanical treatment with chemical assistance. Treatment begins with screening, flocculation and settlement prior to sand filtering to reduce total suspended solids (TSS) as a form of natural biological process post chemical dosing.
The treated water is then subjected to chemical disinfection as required to provide drinking-quality water for distribution. Increasingly membrane treatment and remineralisation processes have been added to the quality of water treatment for distribution, but nothing substitutes for nature biological treatment that occurs in healthy creeks and wetlands.
When used in the correct circumstances, constructed wetlands offer low cost surface water treatment using local resources. These natural biological systems rely on wetland plants and micro-organisms as the active agents in the treatment processes.
Wetland systems are typically tertiary treatment devices for stormwater and they are increasingly considered for broad catchment or even flood plain treatment systems. However, their use as on-line water channel devices can exceed their capability and militate against retaining any such capability.
As good a treatment system as wetlands are, it must be said that there is a significant drawback for wetlands by the quantity of contaminants being loaded from decaying organics and rubbish overlays, sediment layers and heavy metal deposits over the floor of the wetland with high turbidity levels and hydrocarbon contamination that inhibits aeration of the water body.
Thus there is a strong need to manage the intake to the wetland and be able to maintain a sustainable biological treatment process for the longer term. To optimize this tertiary treatment, additional measures at the intake of the wetland need careful design matched to the expected volumes, intake velocity and contaminate load of the catchment that the wetlands support.
Natural biological process must be maintained at a level that can be treated by the characteristics of the wetland. Organic filtration and ponding bays at the head of the intake may be used to capture sediments and reduce other contamination inhibitors for the wetland survival like hydrocarbons, algal blooms and water balance. Maintenance then is at issue as it is difficult to adequately decontaminate the wetlands and at the same time maintain the biological eco-systems to continue the treatment process.
Designs of wetlands is not widely practiced and tend to overlook the loading of contaminates and the effects on the ecology of the water body. It is prudent to implement products that optimize feed water quality prior to it entering the wetland and utilize a system of contaminate removal beyond the capability of simple GPT as a stand-alone measure of water quality improvement which often it fails to achieve.