Winter blooms of Microthrix parvicella at the James R. Dilorio Water Reclamation Facility caused extreme slowing of the 30-minute solids settling rate. The increase from 100 to 300 sludge volume index (SVI) led to additional wasting and more solids to dewater.The tangle of brown, matted foam formed a scum cap on the center ring of the secondary clarifiers at the plant in Pueblo, Colorado. As proteins in the bacteria degraded, they emitted an odor operators found revolting. “We tried chlorination, but it didn’t cause a die off,” says John Millard, the plant’s assistant superintendent. “That’s partly because much of the
