Wastewater treatment can include domestic (household) wastes, commercial wastes, or industrial waste treatment. All treatments include the process of removing contaminants from sewage or wastewater. Treatments include physical, chemical, and biological processes to remove physical, chemical and biological contaminants. The most common treatments for domestic wastes (the biggest contributor to the wastes department) are anaerobic and aerobic biological treatments.  The objective is to produce an environmentally-safe treated effluent.  Effluent is end result cleaned water produced by a treatment plant. Effluent, if effectively treated, can be used as a renewable resource such as irrigation of golf courses, green areas or lawns.  In many cases, effluent is disposed of via spray fields, percolation ponds or introduced into nearby streams, or other water ways. Using advanced technology it is now possible to re-use sewage effluent for drinking water, although Singapore is the only country to implement such technology on a production scale.

Wastewater treatment plants also produce a solid waste (or treated sludge). After sludge is stabilized (by eliminating any unhealthy bacteria), it can be suitable for disposal or reuse often as fertilizer. Due to high disposal costs, many facilities are adapting their systems to include further sludge treatment so the sludge can be sold as fertilizers.  

 

There is a multitude of treatment process, each having a cost therefore all are not required or recommended for each treatment plant.  Which treatment processes are utilized depends on many factors mainly including the make-up of the collected sewage, or influent.  The harser the make-up of the influent, the more treatment processes that may be required to meet local codes and state regulations.

Treatment process can start in the collection system itself. Collection system treatment can include chemical treatments, communating (grinding up solids such as towels, rags, and other solid materials that wastewater treatment systems cannot biologically treat), odor control, grease or FOG control, and more. For more information, see lift stations discussed separately on this website.

Lift stations send sewage or influent to the treatment plant for further processing.  Influent is screened to remove solids that are not biological for collection and disposal at landfills.  After screening, the biological processes normally begin starting with aerating the influent to create an aerobic condition = oxygen is added to the water.  A positive dissolved oxygen level produces a variety of bacterium that eat contaminates in the wastewater stream.  The end result after a few days or weeks is a much cleaner wastewater stream or effluent.  This process may occur in a variety of tanks (primary aeration, secondary aeration, etc), as much as needed for the biological processes to produce clean(er) effluent.

Additional treatments or components to a wastewater treatment plant may include;

 

ESI offers training for system owners and operators.  Call to set up a time to meet and discuss your individual needs.