Introduction

Whole Systems Approach to Ecological Design

Appropriate Technology: Water

Organic Agriculture and Local Food

Appropriate Technology: Energy

Green Building & Retrofitting

Constructed Wetlands Treatment

Constructed wetlands are built either as surface flow (SFCW) or sub-surface flow (SSFCW).  The former uses plants growing in soil over an impermeable liner.  The SFCW runs in a flooded condition.  A SSFCW has about 700 mm of gravel installed above a liner and the wastewater flows horizontally about 100 mm under the surface of the gravel – hence “sub-surface”.  Plants are grown in the gravel with their roots in the water under the gravel surface.  Typical plants used in constructed wetlands are Phragmites Australis, Typhus and Scirpus.

The building of a constructed wetland is relatively simple and is illustrated in the PowerPoint “Building a Small Constructed Wetland”, which is attached along with “Building Large Constructed Wetlands” (see aside).  The biology is quite complex, but is self-managing and self-repairing and replicating. Maintenance of the biology is only necessary every few years to weed out plants, particularly trees that have invaded the planted area.

The two primary natural wastewater treatment goals that involve biology are:

• Digestion of organic matter (measured as BOD and TSS) through anaerobic and aerobic digestion.
• Reduction of ammonia to nitrogen gas through the processes of nitrification and denitrification.

The microbial communities that will establish themselves in the treatment facility are naturally occurring in systems treating sewage.

• Biological Processes in Wastewater
• Building Constructed Wetlands

Building Small Constructed Wetlands
Click on image to download a PowerPoint presentation

Building Large Constructed Wetlands
Click on image to download a PowerPoint presentation