Parameter foaming
Growing filamentuous microorganisms produce foam.30) They arrive in the digestion tower with the secondary sludge. There they become poorly degraded and hinder the gas discharge, so that the anaerobic sludge attains a foamy consistency and can foam over in the digestion towers. The foam- forming microorganisms develop in the denitrification zone and in the aeration basin of the water treatment plant on oxygen impact during agitation, via the recirculated sludge and over the inlet to the water treatment plant, since low winter temperatures strongly reduce the oxygen consumption, so that the quantity of dissolved oxygen increases. The filamentuous microorganisms need only a small oxygen concentration. Foam can be combated through
• mechanical foam destroyers and cutting up of the foam blisters
• addition of precipitants (e.g., two-material dosage of polymers and iron salts)
• frequent removal of the floating sludge
• decrease of the oxygen entry into the denitrification zone in the water treatment plant; e.g., by a scum on the basins, in which the denitrification runs off.
• by an air-tight housing over the denitrification zone in the water treatment plant, so that no contact with the ambient air occurs.
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