Effect of chlorine in controlling the filamentous bulking in dairy activated sludge and its settling characteristics

Filamentous bulking is one of the major problems in activated sludge operation that hinders the settling of sludge. Filamentous bulking occurs only when the filamentous bacteria grow in larger amount as compared to the floc forming bacteria. There are several short-term and long-term methods for controlling the filamentous bulking and addition of chlorine is one of the short-term methods to control the filamentous growth, which is considered to be the universal success. Batch settling tests were conducted with the dairy waste in a batch reactor and settling studies were carried out before and after chlorination by varying initial MLSS from 2 g/L to 8 g/L with a MCRT of 5 days. Zone settling velocity was found to increase appreciably. The microbial growth was observed and the filamentous bacteria were identified as Sphaerotilus natans and Nostocoida limicola. It is found out that the nutrient deficiency was the main cause for the filamentous growth and settling velocity improved on the addition of chlorine. There has been a considerable decrease in the sludge volume index after chlorination.