Nocardia effects in waste activated sludge

Two effects of Nocardia in waste activated sludge (WAS) were investigated: (i) the influence of WAS in the solids treatment recycle streams on Nocardia persistence in the activated sludge, and (ii) the effect of Nocardia in WAS on anaerobic digester foaming. About 4% of the Nocardia present in the mixed liquor was due to seeding from the WAS solids in the dissolved air flotation thickener recycle stream recycle. Nocardia filaments in WAS at levels of between 10⁴ to 10⁶ intersections/g VSS resulted in Nocardia levels of approximately 10⁴ to 10⁵ intersections/g VSS in anaerobic digesters that treated both WAS and primary sludge. The effect of disinfecting these Nocardia filaments in the WAS with Cl₂ was investigated at Cl₂ dose ranges of 20-60 mg Cl₂/l WAS and 100-200 mg Cl₂/l WAS on a lab scale using batch foaming tests to assess success. Chlorination with 20 - 60 mg Cl₂/l WAS approximately doubled both sludge foaming potential and foam stability. At Cl₂ doses of 100-200 mg Cl₂/l WAS, foaming potential was increased almost 10-fold, and foam stability was increased by 2.5 times. These results indicate that chlorination of WAS feed to an anaerobic digester for inactivation of Nocardia should not be practiced.