What is the significance of sludge volume index

For example, if the SVI is too high, it means that the activated sludge is settling slowly and not compacting well. In these cases, the sludge usually looks fluffy. Often, this is a result of a young sludge, during the start-up of a new plant.

Excessive amount of the microorganisms will leave the activated sludge process, and lead to a higher total suspended solids concentration in the effluent. Next, for MLSS, there are actually two approaches to get the value. A conventional standard approach is by filtering the sludge, drying it and then weigh the second portion of the mixed liquid. However, this can be time consuming and a faster way is by using MLSS meter. Value of Sludge Volume Index can then be calculated from the formula given here.

Basically what the value represents is the settling characteristics that have profound effect on the return rates and also the MLSS value. The sludge volume index is one key metric you can use to check that your facility is optimized.

Sludge volume index, or SVI, is designed to provide an easy reference for wastewater treatment plant operators who want to gauge the health of their process. The index will tell you whether the mixed liquor suspended solids MLSS in the activation tank are settling at the right rate, or if they are hindering the function of your facility. You may need to make some changes to the composition of the sludge in your aeration tank based on your findings.

If your SVI is outside of this range, you may need to take steps to control the sludge levels in your system. There are various containers on the market for performing the settleability test Figure 1. Other settling containers may be used in daily plant operation. These include the 1. Refrain from using tall graduated cylinders for the settling test, as the friction created by the close walls can slow the settling, change settling velocities and give false readings. Wide-mouth containers that hold at least 1 liter are acceptable, but 2-liter containers are preferred.

Operators of sequencing batch reactor SBR facilities may take the final settleability reading in correlation to the settle time of the SBR.

For example, an SBR has a settle time of 50 minutes; the operator takes the final settleability reading at 50 minutes instead of 30 minutes. This is common, but should be noted on process control bench sheets for each SBR. This usually indicates a sludge that is dense and has rapid settling characteristics. This is most often attributed to an old, over-oxidized sludge typically seen in an extended aeration facility.

The floc particles would be dense and granular in appearance like a BB. As this type of sludge settles, it may leave a cloudy appearance in the supernate above the settled sludge blanket. This turbidity is called pinpoint floc pin-floc. The sludge usually begins settling quickly after the start of the sludge settleability test, and it does not form larger particles before settling. Most activated sludge plants seem to produce a clear, good-quality effluent with an SVI in this range.

The sludge typically settles more slowly and traps more particulate matter as it forms a uniform blanket before settling. Microscopic examination of this MLSS would show an irregularly shaped floc particle with some filaments forming a backbone for floc-forming bacteria to attach and colonize. In the settleability test, the sludge first forms a blanket and seems to flocculate together before starting to settle.