ANS:A - settlable solids

The Imhoff cone is a simple yet effective device used in wastewater treatment to determine the settleable solids present in a water sample. These settleable solids are typically particles or substances that are heavy enough to settle to the bottom of a container under the influence of gravity within a specific time period. Here's how the Imhoff cone works:

1. Collection of Sample: A representative sample of wastewater is collected from the treatment process or the source being monitored.
2. Filling the Cone: The Imhoff cone is filled with the water sample up to a marked level. The cone typically has a specific volume capacity, often 1 liter.
3. Allowing Settling: The filled cone is left undisturbed for a specified settling period, usually 1 hour. During this time, the settleable solids in the water sample gradually settle to the bottom of the cone under the influence of gravity.
4. Observation and Measurement: After the settling period, the volume of settled solids, indicated by the sediment layer at the bottom of the cone, is measured. This volume represents the settleable solids present in the water sample.
5. Calculation: The settleable solids are typically expressed in terms of milliliters per liter (ml/L) or in grams per liter (g/L) of the water sample.

The Imhoff cone provides a quick and relatively simple method for estimating the settleable solids content in wastewater, which is important for assessing the efficiency of treatment processes and determining the potential for sedimentation in treatment facilities. It is particularly useful in facilities where more sophisticated instruments for measuring solids content may not be available or practical.