Which process involves treating sludge for disposal by removing its water content?

The process that involves treating sludge for disposal by removing its water content is dewatering. Dewatering is a critical step in wastewater treatment operations, as it reduces the volume and weight of the sludge, making it easier and more economical to handle, transport, and dispose of. This process is typically accomplished through various mechanical methods, such as centrifugation, filtration, or pressing, which facilitate the extraction of water from the sludge, resulting in a more solid form that can be managed effectively.

Denitrification, on the other hand, is a biological process aimed at reducing nitrogen compounds in wastewater, primarily nitrates and nitrites, to nitrogen gas. This process does not focus on the removal of water from sludge.

Decentralization refers to the management and operation of wastewater treatment systems at a smaller scale or local level, rather than centralized facilities. This option does not relate specifically to the process of removing water from sludge for disposal.

Disinfection involves the treatment of wastewater to eliminate pathogenic microorganisms, typically using chemicals or physical methods, but it does not address the management or treatment of sludge by removing its water content.

Thus, dewatering is the appropriate process for the reduction of water in sludge, making it the correct answer in this context.