Which of the following describes primary treatment in sewage processes?

Primary treatment in sewage processes primarily involves the separation of solids from liquids through sedimentation. This stage focuses on the physical removal of large solids and particulates from wastewater. During this process, sewage is held in a large tank where denser solids settle to the bottom, forming what is known as primary sludge, while the lighter materials and liquids rise to the top, forming a scum layer. This process significantly reduces the organic load and suspended solids in the sewage before it moves on to secondary treatment, where biological processes further break down remaining nutrients and pollutants.

The other choices represent different stages or processes within wastewater treatment. Biological degradation of organic matter is a characteristic of secondary treatment, not primary. Filtration and disinfection occur during tertiary treatment, which focuses on improving the quality of treated water before release back into the environment. Recycling of nutrients is not a specific function of primary treatment but rather part of a broader ecological approach to wastewater management, often seen in advanced treatment systems. Thus, the emphasis in primary treatment is specifically on settling and separation, making the description of separation of solids from liquids through sedimentation the accurate choice.