It is often possible and advisable for an industry to discharge its waste directly at a municipal treatment plant, where a certain portion of the pollution can be removed. A municipal sewage-treatment plant, if designed and operated properly can handle a major part of the industrial waste, with the exception of toxic substances like cyanides and heavy metals. Discharge of untreated industrial waste directly into a nearby stream should be permitted only after a detailed survey, by competent and certified sanitary engineers.

Levels of treatment:

Treatment levels are often divided into primary, secondary and tertiary.

1. Primary treatment:

It involves separating a portion of the suspended solids from the wastewater. Screening and sedimentation usually accomplish this separation process. The effluent from primary treatment will contain a considerable amount of organic material.

1. Secondary treatment:

The effluent got after primary treatment is further treated. Biological processes in this state remove the organic matter and the residual suspended solids. Refractory or biologically resistant materials still remain in the effluents. 

1. Tertiary treatment:

Tertiary treatment is also known as advanced treatment. The effluent here goes through various processes to make sure the water to be sent to stream is free from all the harmful agents. These processes include: coagulation, filtration, activated carbon adsorption, electro dialysis, reverse osmosis, ozonation, and advanced oxidation.