Basic Wastewater-Treatment Term: What Is the Sludge Settling Ratio (SV30)?

Because the sludge generally reaches or approaches its maximum density after 30 minutes of settling, this time is universally used as the standard measurement time for the indicator. Fifteen minutes may also be used as the standard.

The sludge settling ratio (SV30) is a very important indicator; by observing the settling ratio one can discover many problems with sludge characteristics - whether the supernatant is clear, whether it contains hard-to-settle suspended flocs, the floc particle size and compactness, and so on.

The sludge settling ratio roughly reflects the amount of sludge in the reactor and can be used to control sludge discharge; its changes can also promptly reveal abnormalities such as sludge bulking. Whether in theory or in practice, measuring the sludge settling ratio is an important method for guiding process operation, because it is simple and convenient and lets operators know at any time the concentration and quality of activated sludge in the aeration tank, so as to control the whole process parameters. By determining a stable sludge settling ratio and flexibly adjusting the load, the purpose of controlling wastewater treatment effect and ensuring effluent quality can be achieved.

The sludge settling ratio is related to the nature of the wastewater treated, the sludge concentration, the size of sludge flocs and the sludge floc characteristics, among other factors.