TUESDAY, JAN 17, 2023: NOTE TO FILE

Module 2-9

Lagoon and tank based treatment

THESE TWO NATURAL SYSTEMS are both idea of ecovillage communities. Both rely on the biology outlined in the section Constructed Wetlands. The first is a lagoon-based cascade system with floating ecologies. The second is a more highly engineered and compact system using tanks: the Food Chain Reactor (FBR).

Lagoon-based natural treatment system with floating ecologies

THIS SYSTEM WORKS on similar aquatic biological principles to constructed wetlands. However, it uses energy to supply aeration and mixing, is more highly engineered and has a smaller physical footprint. It has five components:

▪ Floating Structure, that supports the active systems

▪ Aeration, either fine bubble or submersible venturi

▪ Floating planted areas, with roots in the water

▪ Geotextile media for enhanced attached growth treatment

▪ Bioaugmentation, as necessary

This lagoon system has a smaller physical footprint than a constructed wetland with the same loading. Operating costs are higher because aeration is used. Aeration can be designed to use renewable energy (solar and small-scale wind turbines) on site.

The systems can be designed to minimize the buildup of sludge, where sufficient hydraulic retention time is available. In general, larger retention time results in the need for a larger lagoon. The sludge is digested as part of the lagoon ecology. Sludge removal every ten years is achievable. Floatation is normally provided by High Density Polyethylene pipes (HDPE). Long lengths of pipe are welded on site.

How does a lagoon system compare with “conventional” technology such as activated sludge?

▪ Lower capital cost

▪ Robust and simpler systems to operate

▪ Lower energy required for operations

▪ Substantially less sludge

▪ Combination of the above means lower operating costs, and

▪ Lower life cycle costs

▪ Uses more land

▪ Beautiful systems that are natural.

For an example, see the website of the ecological engineering company Biomatrix Water, located at the Findhorn ecovillage in Scotland.