FOAMING IN ANAEROBIC DIGESTERS CAUSED BY MICROTHRIX-PARVICELLA

Three large wastewater treatment plants in the greater Stockholm area have experienced serious anaerobic digester foaming. Microscopic studi es of the sludge from the foam phase showed a network of the filamento us organism Microthrix parvicella. The morphology of the long, coiled filament appeared to be affected by the anaerobic conditions where it became broken up into to shorter end thicker filaments. The operating strategy to prevent foam in the anaerobic digesters at these plants is to control the growth of M. parvicella in the activated sludge tanks by increasing the sludge load. Top installed stirrers and the addition of poly-aluminium salt have also been used to prevent foam formation. (C) 1998 IAWQ. Published by Elsevier Science Ltd.