| Tertiary Treatment | |||
|---|---|---|---|
| Overview | Nitrogen Removal | Phosphorus Removal | |
| Land Treatment | Membrane Filtration | References | |
Land Treatment
There are numerous methods of utilizing land for the purposes of tertiary treatment. These methods of land treatment utilize the microorganisms within the soil to breakdown nutrients. These technologies are usually limited to smaller communities and private applications (Tchobanoglous 1985). When using treated wastewater on land applications there are pathogen regulations that must be adhered to depending on what the water is being reused for. The United Nations Food and Agriculture Organization summarize California regulations on pathogens.
There are several types of land treatment:
- Types of land treatment
- slow rate (irrigating water tolerant crop)
- rapid infiltration (for highly permeable sandy soils)
- overland flow (irrigation over water tolerant grasses)
- wetland application
- septic tank-leach fields
Given the Arcata Wastewater treatment plant includes wetlands this document is only going to discuss wetland applications:
Wetlands
Wetland applications through use of constructed ponds and marshes is a tertiary treatment alternative when available land is not an issue. In addition to plant roots utilizing nutrients in the water, wetlands produce tertiary treatment due to the aerobic, anaerobic zones of the water body that breakdown nitrogen. The aerobic level is near the surface and anaerobic level is near the bottom (Figure 4). For relatively low cost, wetlands are capable of producing total nitrogen concentrations as low as 1 mg/L (Tchobanoglous 1985). The results vary with season because many plants in the winter die and decay, releasing some nutrients back into the water lowering the treatment capability.
Figure 4-1 Stratisfied layers in a wetland application.
The EPA has highlighted several case studies of wetlands and the wildlife habitats used to treat wastewater.