Many of these filter bottom sediments and water for food. To pass out or through soil by water percolation. A harmful chemical or waste material discharged into the environment. Primary treatment uses screens and sedimentation tanks to remove most materials likely to float on the water or settle on the bottom. Secondary treatment uses a biological process to consume organic materials in the waste, and disinfects the effluent.
Tertiary treatment removes additional nutrients, suspended solids and other pollutants.
Published by the San Francisco Estuary Project in August, 1992.