WET System - InformationThe water on our planet; the most abundant and the most abused, is yet the most accommodating of our natural resources.
We take for granted the capacity of water to be renewed and purified, largely by natural means. Water distils itself through the sun powered hydrological cycle in which it passes from rain to river, from river to the ocean, ocean to cloud, cloud to rain and rain back to the river again.
Rainfall is filtered as it passes through the soil and subsoil - on its way to wells and springs. It supports a community of animals, plants and micro-organisms which act as a biological purification system. This closely integrated community of living things, together with the physical properties of its environment, constitute an ecosystem.
This ecosystem is based upon the photosynthetic abilities of plants to absorb solar energy and the power of the microbial population to absorb chemical nutrients from soil and water redistributing them to many diverse life forms.
Wetland Ecosystem Treatment, or WET Systems, function by harnessing this innate ability to absorb and transform the organic nutrients found in wastewater, converting these into plant biomass and soil.
Within the WET System the natural productivity of wetlands is harnessed creating a purification process which uses the wastewater as a resource, converting waste into yield. As wetlands are the most productive and species diverse ecosystems to have evolved, the potential for a high biomass yield from the system is great.
Our WET Systems are not simple Reedbed Treatment Systems or conventional Facultative Pond Systems, although they do contain reeds, as well as a range of aquatic and marginal plants and a variety of willow types and wetland tree species.
The WET System comprises specially designed and constructed earth banks and ponds. As the wastewater flows through the WET System, which is densely planted with wetland trees and marginal plants, it is both purified by microbiological action and transpired by growing plants. Up to 40 different wetland species are used in and around the lagoons, ponds and reed beds. Several species of willow and many of reed, rush, sedge and other marginals are used depending on the type of wastewater to be purified.
Wastewater storage and treatment are combined in these constructed ecosystems which are designed with a large volume and holding capacity. The total hydraulic load is lowered by the evapotranspiration of the trees and the growing biomass absorbs the organic load. Coppicing the willow on the system keeps it at the peak growth rate enabling the maximum absorption of organic matter, as well as producing a useful harvest of willow each year.
The aims of a WET System design are to purify wastewater, create a rich, multi-species ecosystem and produce a useful and varied yield. The main difference between conventional Reedbed Treatment and a WET System is that unlike a conventional reedbed, no gravel is used in the construction of a WET System - soil in the root-zone is the filtration medium.
The basis of the purification process is, as with conventional treatment processes,microbiological; it relies on the biochemical transformations provided by the plethora of micro-organisms found in the soil. In WET Systems the bacteria and fungi which transform the waste are in a symbiotic, mutually beneficial, relationship with the roots of the wetland plants and trees. Within this symbiosis the plant roots provide oxygen, sugars and attachment points for the microbes, whilst the microbes mineralise the organic matter found in the wastewater making this available to the growing plants.
When coppiced the trees can be managed to produce timber or pole wood as well as willow wands which, depending on the varieties planted and the coppice cycle, can be used a source of osier whips for basketry and poles for hurdle making. Pole wood can also be produced for use in creating living willow sculptures and other structures; over a four or five year coppice cycle it can be harvested and seasoned for use as firewood.
WET Systems become more efficient at purifying the wastewater entering them the longer they are established. This is in distinct contrast to mechanical systems which over time can break down due to mechanical faults and wear on components. The 'plug-flow' kinetics of the system give a robust process which is able to cope with shock loading.
The purification processes occur in the soil/root zone and so each year, as new soil is created by the growing plants shedding their leaves and the system matures - the root zone expands and the purification potential increases.
Whilst the number of wetland habitats in the landscape has diminished, due to agricultural 'improvement', WET Systems provide a refuge for frogs, toads and newts, and shelter for birds, as well as a large variety of insects and pond life.
Depending on the type of wetland ecology which is required, and what yields are preferred, the final polishing ponds can sometimes be stocked with several species of fish which area further yield and also act as a biological indicator that the process is functioning well.
Many of our WET Systems are now also providing sought after sites for the location of beehives - as the willow catkins provide an early pollen source and the many flowering species provide nectar throughout the season - thus honey is also a potential yield from the system.
WET Systems are designed for domestic wastewater and many types of agricultural and agro-industrial effluent, including dairy farm yard and parlour washings, silage liquor runoff, cider mill wastes and pig slurry. When dealing with high strength wastewater the WET System can be preceded by an anaerobic digestion pre-treatment option. This traps the potentially damaging the greenhouse gas - methane, allowing this fuel gas to become a significant potential source of energy for the site.
In domestic applications the WET System can be designed and planted as a garden feature including an ornamental or wildlife pond and bog garden. WET Systems can be used to treat sewage from individual dwellings of any size, or for treating the wastewater from farms, villages and hamlets instead of using conventional, mechanical, treatment processes.
Biomass type willow can also be planted and used to fuel a combined heat and power boiler and so contribute to the energy needs of the farm, community or dwelling generating the wastewater which ‘feeds’ the WET System.
Constructed Wetland Ecosystems:
Integrated Wastewater Purification, Resource Production and
Resilient and Regenerative Whole Site Water Reticulation Systems Design.
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