Constructed wetlands by haamutili

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Slide Notes

Constructed wetlands

Published on Nov 18, 2015

Permaculture and constructed wetlands

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PRESENTATION OUTLINE

Constructed wetlands

water treatment and permaculture principles

Photo by MSU IPF Facility Information Services

Pflanzenkläranlagen

Used for final treatment of water, landfill leachate or surface runoff
Can also be used for secondary treatment (our focus)
Constructed or floating wetlands, reed or willow beds, The Living Machine
Can be inexpensive, easy to construct and maintain
Productive use, decentralisation, wildlife habitat, human enjoyment

Horizontal Subsurface Flow Constructed Wetland

Vertical Flow Constructed Wetland

wastewater is categorised into "gray" and "black" waters

Water from showers and sinks, dishwashers and laundry machines is "gray"
Water from toilets, containing human waste is "black"
Constructed wetlands can be a part of treating either type, but mostly gray
If you're following the Permaculture way, you won't have "black"

Photo by JakobS

Many kinds of water treatment processes

Mechanical
Biological
Chemical
Thermal
Radiation

Mechanical: Sedimentation, filtration, reverse osmosis
Biological: Nitrification, denitrification, phytoaccumulation
Chemical: chlorination, chelation
Thermal: Boiling, distillation
Radiation: UV (breakdown of DNA and other biomolecules)

Water treatment with constructed wetlands is based on mechanical and biological treatment, with some contribution from the Sun's UV-radiation.

Photo by Janne.

Settling > Microbes > Plants

First step - or in engineering terms the "PRIMARY TREATMENT" - is some kind of settling. It can be a settling tank or a settling pool. This is where most of the nutrients and biological matter are removed. The removed solids ar called "sludge". Sludge has a very high Biological Oxygen Demand (BOD) and contains also often pathogens (especially when dealing with black water or field run-off).

Settling is a mechanical treatment process.

SECONDARY TREATMENT in large, centralized AND in contructed wetland systems is a biological treatment, that focuses on removing nitrogen, and to a smaller degree other nutrients.

Typically this is done in large, open bioreactors where the two distinct processes of NITRIFICATION and DENITRIFICATION happen. Remember these two, because we'll come back to them.

In constructed wetlands the secondary treatment is based on microbial AND plant activity. Although the microbial activity is about 90-95% of the biological treatment, the plants have several assisting functions.

plants as support

Take up nitrate (NO3) & phosphorous (P)
Create aerobic zones around roots
Roots keep soil permeable
Roots contribute to thermal stability
Dead plant matter as carbon source

The plants can use up nitrate (NO3) and also take up phosphorous.

More important than the uptake of these nutrients is the kind of environment the plants create for the mircobiota. The plants create aerobic conditions around their roots, making nitrification possible underground and enabling the the processes of nitrification and denitrification to happen in tandem. For this reason it is important to select certain kinds of plants that are adapted to survive in flooded, anaerobic soil conditions with the use of aerenchyma - air channels in the stem that bring oxygen down to the roots.

The roots also have a mechanical function in keeping the soil open for the treated water and the nutrients to flow.

In addition, the root zone is more thermally stable and can enable the mircobial processes to continue even in the winter.

The dead plant matter functions as a carbon source for the micro-organisms..... CONTINUES IN THE NEXT SLIDE

Photo by Sustainable sanitation

plants as support

Living plant matter evaporates water
Shade limits algal bloom
Give shelter to animals
Harvest (food)
Energy source

..... and the living plant matter evaporates water, in the case of systems where the water is in contact with air, the plants give shade and stop algal blooms, and lastly, offer shelter to animals such as birds.

Some of the wetland plants (helophytes), such as Myriophyllum spicatum are effective at removing heavy metals - in the case of M. spicatum at least Co, Ni, Cu and Zn.

From a permaculture point of view the plant part of constructed waterland systems is maybe the most interesting, because microbes are somewhat difficult to use as human nutrition. The treated wastewater is still likely to contain elevated levels of the important plant nutrients nitrogen, phosphorous and potassium, and as such can be used to grow useful plants. If the water is consistently low in heavy metals - these are metals or metalloids of environmental concern such as cadmium, mercury, lead and arsenic - the water could be used to grow crop-producing plants in aquaculture or as irrigation water. Another use of the water could be to grow willow, that is moisture-tolerant and fast growing, making it useful to produce wood for burning.

Photo by dhobern

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