Which method is NOT commonly used for sludge disposal?

Incineration is not commonly used for sludge disposal in wastewater treatment processes for several reasons. While it is a method that can reduce the volume of sludge significantly by converting it to ash, the practice is subject to strict environmental regulations and high operational costs. Additionally, incineration can potentially release harmful emissions if not properly managed, making it less favorable compared to other methods.

In contrast, land application, discharge into sanitary sewers, and disposal into lagoons are widely accepted methods. Land application allows the nutrients in sludge to be utilized for agricultural purposes, while discharge into sanitary sewers is a common practice for treating sludge alongside other waste. Disposal into lagoons involves creating a controlled environment for thickening and stabilizing sludge, which is also a frequently utilized disposal technique. Thus, while incineration is indeed a method of sludge management, it is not as widely implemented as the other options presented.