Which solids retention treatment method typically has a retention time of about 20 days?

The solids retention treatment method associated with a typical retention time of about 20 days is aerobic digestion. This process involves the microbial breakdown of organic matter in the presence of oxygen, which helps in reducing the volume of sludge produced in wastewater treatment. During aerobic digestion, microorganisms consume the organic material, leading to a reduction in pathogens and the stabilization of the sludge.

The retention time of around 20 days allows sufficient time for the microbes to effectively digest the organic solids, producing carbon dioxide, water, and stabilized organic matter. This helps in achieving a significant reduction in the amount of solid waste, facilitating easier management and disposal of the treated sludge.

Other methods, such as composting, do not specifically align with a typical retention time of 20 days and involve different processes and conditions, while filtration focuses on separating solids from liquids rather than retaining solids for breakdown. Incineration is a thermal treatment process aimed at reducing waste volume through combustion, which is fundamentally different from the biological processes involved in aerobic digestion.