Dear EcoNews: Arcata Marsh

Dear EcoNews,

I have always enjoyed taking a nice stroll at the Arcata Marsh and Wildlife Sanctuary, as it is such a peaceful and unique place. I know that the Marsh also serves as a wastewater treatment facility, but I don’t understand how it functions or why the birds are able to live safely amidst the treatment water. 

How exactly does this process work and could this be implemented in other coastal locations?

    -Puzzled Pedestrian


Dear Puzzled Pedestrian,

The 307-acre Arcata Marsh is indeed a jewel among Humboldt Bay’s constructed wetlands. It combines beautiful trails with habitat for native plants and animals, and is an inviting place for over 300 species of migratory and resident birds. It is also a key component in a hard-won, environmentally sound wastewater treatment system. The innovative engineering is used in other communities along both coasts, on the Great Lakes, and in other countries.

Here, wastewater treatment occurs in four general stages: conventional processing, oxidation ponds, treatment wetlands, and enhancement wetlands. 

Arcata’s sewers deliver wastewater to the plant on south G Street, where it goes into the headworks, like other conventional systems. It is first screened to remove sand, sticks and other debris. Next, liquids (effluent) are separated from solids (sludge). Sludge is digested, dried and composted.

 Subsequent steps are where the wastewater plant’s innovation occurs. Now clarified, the liquid (primary-treated water) is pumped into a series of oxidation ponds, where algae creates oxygen which bacteria and other microorganisms use to break down the organic compounds found in human waste. At the bottoms of these ponds anaerobic bacteria break down whatever harmful components remain. The water is not toxic. Plants, aquatic insect larvae, and other food can be plentiful in the ponds. It’s an inviting buffet for birds.

Now organisms that oxidized the water must be removed. The secondary-treated water is pumped into treatment wetlands. The plants in the six treatment marshes–including the ubiquitous cattails–shade these ponds so that algae can’t grow. The bacteria that live among the marsh plants feed on the dying organisms, cleaning this water.

In order to kill any remaining pathogens, harmful bacteria, or viruses, the water is returned to the plant for chlorine treatments, followed by sulfur dioxide treatments to remove chlorine. A new ultraviolet light disinfection system will replace the chlorine system in the next few years, thereby ridding the system of any chemical agents.

Now the water moves to the enhancement wetlands, where nutrients and suspended solids sink to the bottom. Currently this water travels back to the plant for one more round of chlorine and sulfur dioxide treatment before it is released into the bay. But once the ultraviolet system is operating, water will go directly into the bay from the enhancement marsh — one less step.

Please drop by the Arcata Marsh Interpretive Center to interact with the hands-on displays that explain the wastewater system. And keep enjoying all the peace and beauty of the marsh trails.

– Lynn Jones, Friends of the Arcata Marsh 

Board Member