A Case Study of Integrated Waste Water Treatment

Wastewater treatment does not have to rely purely on engineered, artificial processes — it can also combine artificial treatment with natural, ecosystem-based processes, and the town of Arcata on the northern coast of California is a well-known example of this integrated approach.

Working together with biologists from Humboldt State University, the residents of Arcata built a two-stage treatment system. In the first stage, the wastewater goes through conventional treatment: sedimentation, filtering and chlorination. Even after this, a good deal of dangerous pollutant remains — including dissolved heavy metals — which conventional treatment alone cannot remove. To deal with this residual pollution, the town's biologists designed a second, natural stage: a chain of six interconnected marshes spread across roughly 60 hectares of marshland, deliberately seeded with plants, algae, fungi and bacteria that neutralise, absorb and assimilate the remaining pollutants. As the partially treated water flows through this marsh system, it is purified further by entirely natural biological processes.

A welcome side-effect is that these marshes have become a genuine wildlife sanctuary, now home to a rich diversity of fish, birds and other animals. A local citizens' group, "Friends of the Arcata Marsh" (FOAM), takes responsibility for maintaining and protecting the site.

Rethinking sanitation itself: ecological sanitation …