Other Fate Processes
Volatilization and Sorption
Volatilization is basically the process of evaporation from the wastewater. Sorption is the process in which a chemical sticks to a solid surface such as a clay or soil particle, bacteria or some other particle in the wastewater.
Sorption to Sludge
The other major process that occurs during wastewater treatment is sorption to sludge. Sludge is composed of live and dead bacteria that grow in wastewater treatment plants. Many ingredients will stick, or adsorb, onto sludge. During wastewater treatment, sludge and the ingredients stuck on it are removed.
Sludge can be disposed of in a number of ways, including landfill, incineration and application to farm fields. Application to farm fields helps to reduce the need to landfill or incinerate this waste and provides a service to the farmer, since sludge is an excellent fertilizer.
Dilution occurs as soon as the product is used and disposed of down the drain. Dilution occurs during transport to the wastewater treatment plant and when the effluent or sludge reaches the environment. The most important aspect of dilution is the fact that it changes dramatically from site to site and with the season.
Clearly, on average, small wastewater treatment plants on large rivers have a much larger dilution factor than large wastewater treatment plants on small rivers. But what happens as river flow is reduced during a drought or just during the dry part of the year? Rainfall has a huge impact on river flow that can dramatically influence the dilution factor. Hence, the simple process of understanding dilution becomes very complex.