WASTREAT

ECOS OUVERTURE  1997-1999

External Inter-regional Co-operation Projects

Constructed Wetlands

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Experience in Greece

General

During the past decades, intensification of human activities along with limited public awareness on environmental management issues, have resulted in degradation of natural resources.

The principal objective of wastewater treatment is generally to allow municipal and/or industrial effluents to be disposed of without danger to human health or unacceptable damage and degradation to the environment. The management of municipal wastewaters through both treatment and reuse, is a prerequisite for the protection and sustainable use of water resources. If small communities are to meet wastewater treatment requirements of the future, they must have treatment systems that are not only effective and reliable, but also simple and inexpensive to construct and operate.

At the beginning of the 20th century, a few cities and industries began to recognize that the discharge of sewage directly into the streams caused except of health problems, degradation of natural water bodies and this led to the construction of sewage-treatment facilities. At about the same time, the septic tank was introduced as a mean of treating domestic sewage from individual households both in suburban and rural areas. Nevertheless, and because of sizable social and economic problems and the absence of public perception on environmental issues, during the first half of the 20th century, few municipalities and industries provided wastewater treatment.

The summary of technologies using for wastewater treatment, can be divided into two main categories:

Natural systems

Conventional or mechanical systems

Natural treatment systems are available for the treatment of organic wastewaters such as municipal, and tend to be lower in cost and less sophisticated in operation and maintenance. In contrast to conventional treatment systems, natural systems may also provide indirect benefits such as aesthetic improvement of the landscape, wildlife habitat, and recreational and educational areas. Additionally, their effluents can be reused for irrigation.

These man-made constructed systems, treat wastewaters utilizing physical, chemical and biological processes just like nature does and without any additional energy or chemical input. Although these processes are slower comparing with the high-rate processes held in conventional treatment systems, they treat wastewaters reliably and continuously if properly designed and not overloaded. Among natural systems, constructed wetlands have been used widely around the world and a considerable record of experience and design practice has been documented all over the world.

Constructed wetland for EKBY's wastewater treatment

The main advantages of constructed wetlands for wastewater treatment are in general:

Simplicity. These systems are simple to construct.

Low cost. Constructed wetlands are less expensive than other wastewater treatment systems, regarding construction and maintenance. There is no need for high-cost, electromechanical equipment, or for high consumption of electrical energy.

High efficiency. They provide effective and reliable wastewater treatment under fluctuating hydraulic and contaminant loading rates.

They can be aesthetically pleasing and they also provide habitat for wildlife and human enjoyment.

Cost-effective and environmentally friendly treatment

Reuse of treated wastewater for irrigation and/or other purposes.

Disadvantages of constructed wetlands include high land area requirements (depending on the design, they may require a relatively large land area compared to a conventional facility), the need for a preliminary treatment before the wastewaters treated by the system (normally they do not used to treat raw wastewaters), the need of higher (than a conventional system) retention time, and that they may cause problems with pests.

Nutrient-rich waters flowing into a water body, may lose some of their nutrient load when passing through wetland vegetation. Creation of vegetated wetland buffer zones along rivers has been effective for controlling non-point source pollution and restoring water quality of rivers. Wetland buffer zones can reduce the concentration of nutrients, pesticides and sediments in the surface runoff and thus prevent degradation of water quality in lakes, streams and rivers. This means that constructed wetlands may and should be integrated into management plans for conservation of both soil and water resources of a watershed, or integrated as parts of major restoration projects.

 

 

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e-mail: wastreat@ekby.gr

EKBY (Greek Biotope / Wetland Centre)