What does the Sludge Volume Index (SVI) indicate?

The Sludge Volume Index (SVI) is primarily used to assess the settleability of sludge in wastewater treatment processes. It is calculated by measuring the volume of sludge that settles in a specified time under controlled conditions, usually expressed as milliliters per gram of suspended solids. A lower SVI indicates good settleability, meaning the sludge will compact well in the settling tanks, leading to more efficient separation of solids from liquids. Conversely, a higher SVI suggests poor settleability, which can lead to operational issues in treatment facilities, such as inefficient clarification and increased solids carryover.

In contrast, the other choices focus on different properties that are not directly related to SVI. The concentration of dissolved solids pertains to the total amount of solids that are dissolved in the water, which affects water quality but does not relate to sludge settleability. Biological oxygen demand measures the amount of oxygen consumed by microorganisms in the decomposition of organic matter, which evaluates water pollution but does not relate to the physical settling characteristics of sludge. The temperature of the sludge mixture may influence biochemical reactions but does not provide information about how well the sludge will settle, which SVI specifically addresses.