“The wastewater treatment plant handles all sewage for the City of Arcata. Raw sewage enters the headworks, where the sludge is separated from the effluent. The sludge is digested, dried, and composted for use on city grounds. The clarified wastewater is sent to the 49 acres of oxidation ponds where time, aquatic plants, and microorganisms purify it. Arcata’s wastewater then circulates through a six-marsh system, filled with plants and animals that feed on the nutrients that are left. The water that is finally discharged into Humboldt Bay has gone through “enhanced” secondary treatment, thanks to the marsh system, and is completely potable.”

http://www.humboldt.edu/arcatamarsh/treatmenthome.html

If done correctly it should be possible to get biogas from the initial decomposition and then fertilizer from the leftover solids. (Assuming you can keep heavy metals out of the system.)

The marsh pond system creates an amazing wildlife area. One would never know that it was part of a municipal waste treatment system.

The water that exits the ponds is extremely clean. It goes into Humboldt Bay and close by are major oyster farms which closely monitor the condition of the water. There has never been a water quality issue.

Quite possibly by isolating parts of the existing lake and establishing plant growth the water in the lake could be cleaned to a much better condition than it now is in.

If you’re interested in this idea get in touch with the people who run the web site. I think you’ll find them extremely helpful.