Control of Microthrix parvicella in Activated Sludge Plants by Dosage of Polyaluminium Salts: Possible Mechanisms

Abstract

AbstractAn effective control of the filamentous bacterium Microthrix parvicella in activated sludge wastewater treatment plants can take place by dosage of polyaluminium chloride, PAX‐14. The mechanism how it works is largely unknown. The purpose of this study was to investigate in detail the mechanism by which PAX‐14 controls M. parvicella. After addition of PAX‐14, a reduction in substrate uptake, measured as uptake of radiolabelled oleic acid and trioleic acid under anaerobic conditions was observed by microautoradiography, indicating an effect on the physiology of M. parvicella or on the ability to transport substrate into the cell. Hydrophobic surface properties of the bacterium were not altered, but a significant reduction of exoenzyme activity was observed after PAX‐14 addition. This was measured as bulk enzyme activity as well as surface‐associated enzyme activity for esterase and lipase. New lipase production was not inhibited, indicating a need for a continuous addition of PAX‐14 for an efficient control of M. parvicella. Furthermore, since PAX‐14 is an efficient flocculating agent, it improved formation of dense flocs, so M. parvicella was embedded into floc material, making access to substrate difficult due to increased diffusional resistance. In conclusion, there seemed to be several reasons why PAX‐14 could control M. parvicella: The physiology and particularly the lipase production were partly inhibited, the accessibility of substrate was affected, and a better flocculation occurred.