Defining Wastewater Treatment

This report defines "wastewater" as more than just sewage from municipal sewage systems. It also includes water discharged from our homes (showers, washing machines, kitchen sinks, etc.), businesses (commercial and industrial manufacturing processes), and storm drains. Each of these sources contains various waste products and is ultimately either discharged into surface waters or infiltrates back into the ground. 

To understand the relation between wastewater management and water quality, it is important to understand the process of wastewater treatment. Wastewater treatment processes rely on different processes to remove contaminants from wastewater so that it can be returned to the environment with minimal adverse impacts.  In general, wastewater treatment at Wastewater Treatment Facilities (WWTFs) may utilize three stages of wastewater treatment: primary, secondary, and tertiary. Treatment processes usually produce sludge, which also must be treated and disposed of properly. In most urban and urbanizing areas, wastewater is generally conveyed to a central WWTF for treatment and discharged into nearby surface waters. Other treatment systems include on-site septic systems (anaerobic treatment)* and land application systems.        

Figure 1. Wastewater Treatment Plant     Source:  http://www.durhamcountync.gov

On-site septic systems are more commonly used in low density areas. This process involves low levels of treatment in an on-site underground vault, with discharge into the ground. A suitable soil treatment area is necessary for efficient operation of these systems.**   In general, wastewater treated in a septic system percolates downward to replenish the groundwater, which many communities rely on for drinking water.

On-site treatment systems  are gaining popularity. These systems utilize aerated lagoons and/or other various levels of treatment followed by spray or subsurface irrigation of the treated wastewater. These systems often provide good treatment of wastewater before it is used to irrigate golf courses, open fields or municipal landscaping. On-site treatment systems can improve water quality and quantity in the area. These systems protect water quality by not discharging into surface waters. The treated wastewater infiltrates into the ground aiding in aquifer recharge.

Septic System vs. Land Application Systems

Source: MSU	Source:  Sheaffer & Roland Technology Report (PDF)

*Operating in the absence of air (anaerobic treatment), solids settle out in the septic treatment tank and bacteria breaks down waste effluent) into simpler molecules. The wastewater produced drains into elongated, perforated pipes attached to the septic treatment tank which release the wastewater into the soil.

**Suitable soils will remove nutrients and slowly filter the water as it percolates to the subsurface aquifers.