Biological mechanisms involved in bioflocculation disturbances caused by phenol

Abstract

The research focused on the clarification of the biological mechanisms involved in bioflocculation disturbances caused by the exposure of suspended biomass to phenol shock loading. Contact experiments were performed by exposing activated sludge biomass under non-growth and under growth conditions to various concentrations of phenol. Severe damage to the settling of biosolids could be observed, especially under growth conditions. The following mechanisms were found to be relevant to these disturbances: (1) cellular lysis resulted in the creation of a fraction of small particles (<0.45 μm) which could be considered as mostly cellular debris, due to their sizes and especially to their lack of oxygen uptake; (2) lower hydrophobicity of biosolids surfaces, could be a result of the amphiphatic properties exerted by the phenol molecule, as well as by the cellular components released to the aqueous phase by lysis and by membranal damage; (3) the exposure to phenol caused the unbinding of exocellular biopolymers from biosolids surfaces to the aqueous solution, creating conditions of poor settleability resulting from: (a) bioflocs characterized by low density; (b) dispersion of small biofloc fragments; (c) dispersion of single cells; (4) phenol loading was found able to lower the cellular ATP concentrations and this inhibition of the cellular bioenergetics could also be a factor impairing the boflocculation process.