Wastewater is water that has been used and must be treated before it is released into another body of water, so that it does not cause further pollution of water sources. Wastewater comes from a variety of sources.
Everything that you flush down your toilet or rinse down the drain is wastewater. Rainwater and runoff, along with various pollutants, go down street gutters and eventually end up at a wastewater treatment facility.
Wastewater can also come from agricultural and industrial sources. Some waste waters are more difficult to treat than others; for example, industrial wastewater can be difficult to treat, whereas domestic wastewater is relatively easy to treat. Different region has the different standards for the wastewater treatment. I am posting here a link with a basic information which we used in our work. Your requirement may vary depending upon the type of contaminated wastewater you have but this post will give you a general idea. http://www.eolss.net/Sample-Chapters/C09/E4-11-03-04.pdf