Sanitary wastewater systems, like the Arcata system, are designed to collect water from toilets, sinks, showers, and any other location with a drain. These systems are not designed to collect storm water run-off. However, like much of the nation's aging infrastructure, sewers are deteriorating. Leaks in sewers during storm events can lead to a five-fold increase in flows at wastewater treatment facilities.
Wastewater contains many constituents that are harmful to human health and the environment that need to be removed prior to discharge to the natural environment. These constituents are wide ranging:
- Pathogens - Can lead to infections and death in humans who contact the water
- Nutrients (Nitrogen and Phosphorus) - Can cause algal blooms in receiving waters, killing fish and other wildlife
- Biochemical Oxygen Demand - The degradation of organic mater by microbes consumes oxygen. This consumption can deplete aqueous oxygen concentrations enough that fish and other wildlife may die.
- Suspended Solids - Sunlight can heat water with high suspended solids faster. Higher temperatures deplete oxygen concentrations in water resulting in possible fish kills.
- Pharmaceutical and Other Chemicals - Caffeine, estrogen, and pharmaceutical chemicals are all present in wastewater. Current treatment methods do not remove these chemicals. The human health and environmental impacts of discharges with these chemicals present in the effluent are unknown.
Figure 1: Arcata's Clarifier
This page will be expanded by Fall 2008 semester Engineering 115 students.