Problems caused by filamentous bacteria in pilot-scale nutrient-removal activated-sludge plants

Sludges from two pilot-scale nutrient-removal activated-sludge plants (a modified three-stage Bardenpho process and a Phostrip plant) were analyzed and the results examined, primarily, in relation to the formation of stable foam. The survey showed that both units produced stable foam, but this did not appear to be related either to temperature or to the more conventional operational parameters (sludge age, F:M ratio). The dominance of the sludge by Microthrix parvicella was related to the amount of uronic acids in the extracellular polymers produced by the sludge. The results also indicated that (a) the addition of fermenter elutrient, which was used to produce supplementary readily degradable COD, stimulated foam formation, and (b) the degree of phosphorus removal might also be implicated in the production of foam - and requires further scrutiny.