Sludge Volume Index (SVI) - Microbial Discovery Group



What is SVI?-12700065786000Sludge Volume Index (SVI)Sludge volume index is a common measurement that we use to determine sludge quality. In wastewater treatment processes, a good quality sludge will generally produce a good quality effluent. SVI takes into consideration the mixed liquor suspended solids concentration (MLSS) and the volume that a certain amount of sludge takes up. Generally, a good quality sludge has an SVI in the range of 50-150 mL/gram. SVI Test ProcedureThe SVI test is very simple. It requires a 1000 mL graduated cylinder. Collect a gallon of sludge, mix gently, and pour into the cylinder. After 30 minutes, record the volume to which the sludge settles.SVI CalculationInterpreting ResultsThe higher the SVI, the slower the sludge settles. If the sludge is settling too slow, this can result in loss of suspended solids over the clarifier weirs. If the SVI settles too quickly, and the SVI is <50 this can be due to pin floc, which is commonly (but not always) caused by old sludge. It is recommended to perform the SVI test every day. It is beneficial to determine the SVI for 30 minute as well as occasionally for 60 minute settling. The majority of the settling should occur within the first 30 minutes. If there is a change in your SVI, it is recommended to perform a microscopic evaluation to determine the cause. It is also useful to leave the settled sludge in the container and observe if there is a rise time, in which the sludge floats. This indicates denitrification. If the rise time is <2 hours, there is risk of floating sludge in the clarifier and steps need to be taken to reduce nitrate, BOD, and increase oxygen going into the clarifier. ................
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