Why is lime commonly added to sludge in wastewater treatment?

Lime is commonly added to sludge in wastewater treatment primarily to raise pH levels, which helps in the reduction of pathogens. When lime is introduced to sludge, it reacts with the moisture and the components of the sludge, increasing the pH often to levels above 12. This high pH creates an environment that is hostile to many pathogens, effectively reducing their viability and helping to ensure that the treated sludge meets health and safety standards for land application or disposal.

Additionally, the increase in pH can precipitate certain heavy metals, capturing them in solid phases and further enhancing the safety of the sludge. This process is essential in wastewater treatment because the presence of pathogens can pose significant risks to public health and the environment. Thus, the application of lime is a crucial step in ensuring that the sludge can be processed safely and used beneficially.

The other options do relate to aspects of sludge treatment but are not the primary reason for the addition of lime. While lime can have effects on dewatering efficiency and may indirectly involve moisture content, its primary and most significant role in this context is the stabilization of sludge through pathogen reduction.