OVERVIEW

Constructed Wetlands

Constructed wetlands for wastewater treatment emulate the natural self-cleaning processes found in soils by trickling polluted water down onto a filter-bed substrate.
In contrast with conventional water purification processes, the system is semi-extensive, not intensive.

Nature is left to complete its purification work in its own time, which offers key advantages:

  1. High pollutant removal performances that stay dependably constant over time
  2. Maximal protection of the receiving environment as the filters double up as a physical barrier (zero risk of sludge entrainment with treated effluent)
  3. Slow mineralization of the filter deposit layer and conversion of sludge to compost that can be re-used as organic amendment after a decade of in-service operation (‘intensive’ processes produce liquid sludges that come with daily management constraints)
  4. Seamless integration into the landscape
  5. Easier operational input comparable to community-scale feature landscaping work

How It Works

What the filter-bed substrate does:

  1. It mechanically captures and traps the suspended solids (pollution called fine-to-colloidal particles) carried in the influent wastewater
  2. It serves as a substrate for water-purifying organisms (breakdown of dissolved contaminants)
  3. It drains the water and aerates the system

What the top-layer reed bed does:

  1. It declogs the filter-bed surface through the action of new roots and shoots and rhizomes that constantly create free spaces and they grow through
  2. It transfers oxygen from the plant down to its root system to fuel the microbial activity of the filter
  3. It increases the number of microorganism attachment sites

A Little Historical Perspective

The first constructed wetlands were developed in Germany the 1960s in the wake of pioneering investigations led by scientists Dr Reinhold KICKUTH and Dr Kathe SEIDEL focused on establishing wastewater treatment systems engineered to mimic the functional ecosystem at marshland borders.
After several years of tests and trials, the technique was introduced to France in the late 1980s. The commune of Pannessières (in the Jura) was one of the first communes in France to adopt this kind of wastewater treatment system.
Research led at the IRSTEA (in its days as ‘Cemagref’) then lent the treatment process scientific credibility.

Appropriately geared to rural-community needs, this process technology has since attracted increasing interest from local-government authorities as it offers efficient performance and environmentally-conscious landscape feature integration at little operation and maintenance cost.

Today, France counts over 250 constructed wetlands for wastewater treatment and over 400 constructed wetlands for sludge treatment.

Segmentation of wastewater treatment processes designed to < 2000 PE nominal capacity (from Golla et al. 2010). “Fate of phosphorus in constructed wetland reedbeds“, Kim B. 2014.

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