Control of Sludge Volume Index in Activated Sludge Process

Sludge volume index (SVI) is a measure of the settling ability of activated sludge. It is the volume in milliliters occupied by 1 gram of suspended solids when allowed to settle for 30 minutes. A high SVI indicates poor settling and can lead to operational problems such as loss of biomass, poor effluent quality, and high energy consumption. Here are the ways to control SVI in an activated sludge process:

Reducing Recycling Ratio

The recycling ratio is the ratio of the return sludge flow rate to the influent flow rate. By reducing the recycling ratio, the solids retention time (SRT) in the aeration tank is increased, which promotes the growth of dense and compact flocs. Dense flocs settle faster and result in a lower SVI. However, reducing the recycling ratio too much can lead to a decrease in effluent quality.

Aeration

Aeration is an important factor in the activated sludge process as it provides the oxygen necessary for the growth of microorganisms. Adequate aeration promotes the formation of dense and compact flocs, which settle faster and result in a lower SVI. However, excessive aeration can lead to the breakage of flocs and the release of suspended solids, which can increase the SVI.

Adding Chlorine

Chlorine is an oxidizing agent that can help to break down organic matter in the activated sludge. This can lead to the formation of smaller and more compact flocs, which settle faster and result in a lower SVI. However, excessive use of chlorine can also lead to the destruction of the biomass and decrease in the treatment efficiency.

Increase the Depth of Aeration Tank

Increasing the depth of the aeration tank can provide more space for the flocs to settle and compact. This can lead to a lower SVI. However, increasing the depth of the aeration tank can also increase the energy consumption and capital costs of the treatment plant.

Conclusion

In conclusion, reducing the recycling ratio is the most effective way to control SVI in an activated sludge process. However, it is important to note that all the above factors are interrelated and should be considered together to optimize the treatment efficiency and cost-effectiveness of the process.